HTTP Extensions for Web Distributed Authoring and Versioning (WebDAV)
RFC 4918

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Network Working Group                                  L. Dusseault, Ed.
Request for Comments: 4918                                   CommerceNet
Obsoletes: 2518                                                June 2007
Category: Standards Track

 HTTP Extensions for Web Distributed Authoring and Versioning (WebDAV)

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   Web Distributed Authoring and Versioning (WebDAV) consists of a set
   of methods, headers, and content-types ancillary to HTTP/1.1 for the
   management of resource properties, creation and management of
   resource collections, URL namespace manipulation, and resource
   locking (collision avoidance).

   RFC 2518 was published in February 1999, and this specification
   obsoletes RFC 2518 with minor revisions mostly due to
   interoperability experience.

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Table of Contents

   1. Introduction ....................................................7
   2. Notational Conventions ..........................................8
   3. Terminology .....................................................8
   4. Data Model for Resource Properties .............................10
      4.1. The Resource Property Model ...............................10
      4.2. Properties and HTTP Headers ...............................10
      4.3. Property Values ...........................................10
           4.3.1. Example - Property with Mixed Content ..............12
      4.4. Property Names ............................................14
      4.5. Source Resources and Output Resources .....................14
   5. Collections of Web Resources ...................................14
      5.1. HTTP URL Namespace Model ..................................15
      5.2. Collection Resources ......................................15
   6. Locking ........................................................17
      6.1. Lock Model ................................................18
      6.2. Exclusive vs. Shared Locks ................................19
      6.3. Required Support ..........................................20
      6.4. Lock Creator and Privileges ...............................20
      6.5. Lock Tokens ...............................................21
      6.6. Lock Timeout ..............................................21
      6.7. Lock Capability Discovery .................................22
      6.8. Active Lock Discovery .....................................22
   7. Write Lock .....................................................23
      7.1. Write Locks and Properties ................................24
      7.2. Avoiding Lost Updates .....................................24
      7.3. Write Locks and Unmapped URLs .............................25
      7.4. Write Locks and Collections ...............................26
      7.5. Write Locks and the If Request Header .....................28
           7.5.1. Example - Write Lock and COPY ......................28
           7.5.2. Example - Deleting a Member of a Locked
                  Collection .........................................29
      7.6. Write Locks and COPY/MOVE .................................30
      7.7. Refreshing Write Locks ....................................30
   8. General Request and Response Handling ..........................31
      8.1. Precedence in Error Handling ..............................31
      8.2. Use of XML ................................................31
      8.3. URL Handling ..............................................32
           8.3.1. Example - Correct URL Handling .....................32
      8.4. Required Bodies in Requests ...............................33
      8.5. HTTP Headers for Use in WebDAV ............................33
      8.6. ETag ......................................................33
      8.7. Including Error Response Bodies ...........................34
      8.8. Impact of Namespace Operations on Cache Validators ........34
   9. HTTP Methods for Distributed Authoring .........................35
      9.1. PROPFIND Method ...........................................35
           9.1.1. PROPFIND Status Codes ..............................37

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           9.1.2. Status Codes for Use in 'propstat' Element .........37
           9.1.3. Example - Retrieving Named Properties ..............38
           9.1.4. Example - Using 'propname' to Retrieve All
                  Property Names .....................................39
           9.1.5. Example - Using So-called 'allprop' ................41
           9.1.6. Example - Using 'allprop' with 'include' ...........43
      9.2. PROPPATCH Method ..........................................44
           9.2.1. Status Codes for Use in 'propstat' Element .........44
           9.2.2. Example - PROPPATCH ................................45
      9.3. MKCOL Method ..............................................46
           9.3.1. MKCOL Status Codes .................................47
           9.3.2. Example - MKCOL ....................................47
      9.4. GET, HEAD for Collections .................................48
      9.5. POST for Collections ......................................48
      9.6. DELETE Requirements .......................................48
           9.6.1. DELETE for Collections .............................49
           9.6.2. Example - DELETE ...................................49
      9.7. PUT Requirements ..........................................50
           9.7.1. PUT for Non-Collection Resources ...................50
           9.7.2. PUT for Collections ................................51
      9.8. COPY Method ...............................................51
           9.8.1. COPY for Non-collection Resources ..................51
           9.8.2. COPY for Properties ................................52
           9.8.3. COPY for Collections ...............................52
           9.8.4. COPY and Overwriting Destination Resources .........53
           9.8.5. Status Codes .......................................54
           9.8.6. Example - COPY with Overwrite ......................55
           9.8.7. Example - COPY with No Overwrite ...................55
           9.8.8. Example - COPY of a Collection .....................56
      9.9. MOVE Method ...............................................56
           9.9.1. MOVE for Properties ................................57
           9.9.2. MOVE for Collections ...............................57
           9.9.3. MOVE and the Overwrite Header ......................58
           9.9.4. Status Codes .......................................59
           9.9.5. Example - MOVE of a Non-Collection .................60
           9.9.6. Example - MOVE of a Collection .....................60
      9.10. LOCK Method ..............................................61
           9.10.1. Creating a Lock on an Existing Resource ...........61
           9.10.2. Refreshing Locks ..................................62
           9.10.3. Depth and Locking .................................62
           9.10.4. Locking Unmapped URLs .............................63
           9.10.5. Lock Compatibility Table ..........................63
           9.10.6. LOCK Responses ....................................63
           9.10.7. Example - Simple Lock Request .....................64
           9.10.8. Example - Refreshing a Write Lock .................65
           9.10.9. Example - Multi-Resource Lock Request .............66
      9.11. UNLOCK Method ............................................68
           9.11.1. Status Codes ......................................68

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           9.11.2. Example - UNLOCK ..................................69
   10. HTTP Headers for Distributed Authoring ........................69
      10.1. DAV Header ...............................................69
      10.2. Depth Header .............................................70
      10.3. Destination Header .......................................71
      10.4. If Header ................................................72
           10.4.1. Purpose ...........................................72
           10.4.2. Syntax ............................................72
           10.4.3. List Evaluation ...................................73
           10.4.4. Matching State Tokens and ETags ...................74
           10.4.5. If Header and Non-DAV-Aware Proxies ...............74
           10.4.6. Example - No-tag Production .......................75
           10.4.7. Example - Using "Not" with No-tag Production ......75
           10.4.8. Example - Causing a Condition to Always
                   Evaluate to True ..................................75
           10.4.9. Example - Tagged List If Header in COPY ...........76
           10.4.10. Example - Matching Lock Tokens with
                    Collection Locks .................................76
           10.4.11. Example - Matching ETags on Unmapped URLs ........76
      10.5. Lock-Token Header ........................................77
      10.6. Overwrite Header .........................................77
      10.7. Timeout Request Header ...................................78
   11. Status Code Extensions to HTTP/1.1 ............................78
      11.1. 207 Multi-Status .........................................78
      11.2. 422 Unprocessable Entity .................................78
      11.3. 423 Locked ...............................................78
      11.4. 424 Failed Dependency ....................................79
      11.5. 507 Insufficient Storage .................................79
   12. Use of HTTP Status Codes ......................................79
      12.1. 412 Precondition Failed ..................................79
      12.2. 414 Request-URI Too Long .................................79
   13. Multi-Status Response .........................................80
      13.1. Response Headers .........................................80
      13.2. Handling Redirected Child Resources ......................81
      13.3. Internal Status Codes ....................................81
   14. XML Element Definitions .......................................81
      14.1. activelock XML Element ...................................81
      14.2. allprop XML Element ......................................82
      14.3. collection XML Element ...................................82
      14.4. depth XML Element ........................................82
      14.5. error XML Element ........................................82
      14.6. exclusive XML Element ....................................83
      14.7. href XML Element .........................................83
      14.8. include XML Element ......................................83
      14.9. location XML Element .....................................83
      14.10. lockentry XML Element ...................................84
      14.11. lockinfo XML Element ....................................84
      14.12. lockroot XML Element ....................................84

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      14.13. lockscope XML Element ...................................84
      14.14. locktoken XML Element ...................................85
      14.15. locktype XML Element ....................................85
      14.16. multistatus XML Element .................................85
      14.17. owner XML Element .......................................85
      14.18. prop XML Element ........................................86
      14.19. propertyupdate XML Element ..............................86
      14.20. propfind XML Element ....................................86
      14.21. propname XML Element ....................................87
      14.22. propstat XML Element ....................................87
      14.23. remove XML Element ......................................87
      14.24. response XML Element ....................................88
      14.25. responsedescription XML Element .........................88
      14.26. set XML Element .........................................88
      14.27. shared XML Element ......................................89
      14.28. status XML Element ......................................89
      14.29. timeout XML Element .....................................89
      14.30. write XML Element .......................................89
   15. DAV Properties ................................................90
   16. Precondition/Postcondition XML Elements .......................98
   17. XML Extensibility in DAV .....................................101
   18. DAV Compliance Classes .......................................103
      18.1. Class 1 .................................................103
      18.2. Class 2 .................................................103
      18.3. Class 3 .................................................103
   19. Internationalization Considerations ..........................104
   20. Security Considerations ......................................105
      20.1. Authentication of Clients ...............................105
      20.2. Denial of Service .......................................106
      20.3. Security through Obscurity ..............................106
      20.4. Privacy Issues Connected to Locks .......................106
      20.5. Privacy Issues Connected to Properties ..................107
      20.6. Implications of XML Entities ............................107
      20.7. Risks Connected with Lock Tokens ........................108
      20.8. Hosting Malicious Content ...............................108
   21. IANA Considerations ..........................................109
      21.1. New URI Schemes .........................................109
      21.2. XML Namespaces ..........................................109
      21.3. Message Header Fields ...................................109
           21.3.1. DAV ..............................................109
           21.3.2. Depth ............................................110
           21.3.3. Destination ......................................110
           21.3.4. If ...............................................110
           21.3.5. Lock-Token .......................................110
           21.3.6. Overwrite ........................................111
           21.3.7. Timeout ..........................................111
      21.4. HTTP Status Codes .......................................111
   22. Acknowledgements .............................................112

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   23. Contributors to This Specification ...........................113
   24. Authors of RFC 2518 ..........................................113
   25. References ...................................................114
      25.1. Normative References.....................................114
      25.2. Informative References ..................................115
   Appendix A.  Notes on Processing XML Elements ....................117
      A.1. Notes on Empty XML Elements ..............................117
      A.2. Notes on Illegal XML Processing ..........................117
      A.3. Example - XML Syntax Error ...............................117
      A.4. Example - Unexpected XML Element .........................118
   Appendix B. Notes on HTTP Client Compatibility ...................119
   Appendix C. The 'opaquelocktoken' Scheme and URIs ................120
   Appendix D. Lock-null Resources ..................................120
      D.1. Guidance for Clients Using LOCK to Create Resources ......121
   Appendix E. Guidance for Clients Desiring to Authenticate ........121
   Appendix F. Summary of Changes from RFC 2518 .....................123
      F.1. Changes for Both Client and Server Implementations .......123
      F.2. Changes for Server Implementations .......................125
      F.3. Other Changes ............................................126

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1.  Introduction

   This document describes an extension to the HTTP/1.1 protocol that
   allows clients to perform remote Web content authoring operations.
   This extension provides a coherent set of methods, headers, request
   entity body formats, and response entity body formats that provide
   operations for:

   Properties: The ability to create, remove, and query information
   about Web pages, such as their authors, creation dates, etc.

   Collections: The ability to create sets of documents and to retrieve
   a hierarchical membership listing (like a directory listing in a file
   system).

   Locking: The ability to keep more than one person from working on a
   document at the same time.  This prevents the "lost update problem",
   in which modifications are lost as first one author, then another,
   writes changes without merging the other author's changes.

   Namespace Operations: The ability to instruct the server to copy and
   move Web resources, operations that change the mapping from URLs to
   resources.

   Requirements and rationale for these operations are described in a
   companion document, "Requirements for a Distributed Authoring and
   Versioning Protocol for the World Wide Web" [RFC2291].

   This document does not specify the versioning operations suggested by
   [RFC2291].  That work was done in a separate document, "Versioning
   Extensions to WebDAV" [RFC3253].

   The sections below provide a detailed introduction to various WebDAV
   abstractions: resource properties (Section 4), collections of
   resources (Section 5), locks (Section 6) in general, and write locks
   (Section 7) specifically.

   These abstractions are manipulated by the WebDAV-specific HTTP
   methods (Section 9) and the extra HTTP headers (Section 10) used with
   WebDAV methods.  General considerations for handling HTTP requests
   and responses in WebDAV are found in Section 8.

   While the status codes provided by HTTP/1.1 are sufficient to
   describe most error conditions encountered by WebDAV methods, there
   are some errors that do not fall neatly into the existing categories.
   This specification defines extra status codes developed for WebDAV
   methods (Section 11) and describes existing HTTP status codes
   (Section 12) as used in WebDAV.  Since some WebDAV methods may

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   operate over many resources, the Multi-Status response (Section 13)
   has been introduced to return status information for multiple
   resources.  Finally, this version of WebDAV introduces precondition
   and postcondition (Section 16) XML elements in error response bodies.

   WebDAV uses XML ([REC-XML]) for property names and some values, and
   also uses XML to marshal complicated requests and responses.  This
   specification contains DTD and text definitions of all properties
   (Section 15) and all other XML elements (Section 14) used in
   marshalling.  WebDAV includes a few special rules on extending WebDAV
   XML marshalling in backwards-compatible ways (Section 17).

   Finishing off the specification are sections on what it means for a
   resource to be compliant with this specification (Section 18), on
   internationalization support (Section 19), and on security
   (Section 20).

2.  Notational Conventions

   Since this document describes a set of extensions to the HTTP/1.1
   protocol, the augmented BNF used herein to describe protocol elements
   is exactly the same as described in Section 2.1 of [RFC2616],
   including the rules about implied linear whitespace.  Since this
   augmented BNF uses the basic production rules provided in Section 2.2
   of [RFC2616], these rules apply to this document as well.  Note this
   is not the standard BNF syntax used in other RFCs.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   Note that in natural language, a property like the "creationdate"
   property in the "DAV:" XML namespace is sometimes referred to as
   "DAV:creationdate" for brevity.

3.  Terminology

   URI/URL - A Uniform Resource Identifier and Uniform Resource Locator,
   respectively.  These terms (and the distinction between them) are
   defined in [RFC3986].

   URI/URL Mapping - A relation between an absolute URI and a resource.
   Since a resource can represent items that are not network
   retrievable, as well as those that are, it is possible for a resource
   to have zero, one, or many URI mappings.  Mapping a resource to an
   "http" scheme URI makes it possible to submit HTTP protocol requests
   to the resource using the URI.

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   Path Segment - Informally, the characters found between slashes ("/")
   in a URI.  Formally, as defined in Section 3.3 of [RFC3986].

   Collection - Informally, a resource that also acts as a container of
   references to child resources.  Formally, a resource that contains a
   set of mappings between path segments and resources and meets the
   requirements defined in Section 5.

   Internal Member (of a Collection) - Informally, a child resource of a
   collection.  Formally, a resource referenced by a path segment
   mapping contained in the collection.

   Internal Member URL (of a Collection) - A URL of an internal member,
   consisting of the URL of the collection (including trailing slash)
   plus the path segment identifying the internal member.

   Member (of a Collection) - Informally, a "descendant" of a
   collection.  Formally, an internal member of the collection, or,
   recursively, a member of an internal member.

   Member URL (of a Collection) - A URL that is either an internal
   member URL of the collection itself, or is an internal member URL of
   a member of that collection.

   Property - A name/value pair that contains descriptive information
   about a resource.

   Live Property - A property whose semantics and syntax are enforced by
   the server.  For example, the live property DAV:getcontentlength has
   its value, the length of the entity returned by a GET request,
   automatically calculated by the server.

   Dead Property - A property whose semantics and syntax are not
   enforced by the server.  The server only records the value of a dead
   property; the client is responsible for maintaining the consistency
   of the syntax and semantics of a dead property.

   Principal - A distinct human or computational actor that initiates
   access to network resources.

   State Token - A URI that represents a state of a resource.  Lock
   tokens are the only state tokens defined in this specification.

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4.  Data Model for Resource Properties

4.1.  The Resource Property Model

   Properties are pieces of data that describe the state of a resource.
   Properties are data about data.

   Properties are used in distributed authoring environments to provide
   for efficient discovery and management of resources.  For example, a
   'subject' property might allow for the indexing of all resources by
   their subject, and an 'author' property might allow for the discovery
   of what authors have written which documents.

   The DAV property model consists of name/value pairs.  The name of a
   property identifies the property's syntax and semantics, and provides
   an address by which to refer to its syntax and semantics.

   There are two categories of properties: "live" and "dead".  A live
   property has its syntax and semantics enforced by the server.  Live
   properties include cases where a) the value of a property is
   protected and maintained by the server, and b) the value of the
   property is maintained by the client, but the server performs syntax
   checking on submitted values.  All instances of a given live property
   MUST comply with the definition associated with that property name.
   A dead property has its syntax and semantics enforced by the client;
   the server merely records the value of the property verbatim.

4.2.  Properties and HTTP Headers

   Properties already exist, in a limited sense, in HTTP message
   headers.  However, in distributed authoring environments, a
   relatively large number of properties are needed to describe the
   state of a resource, and setting/returning them all through HTTP
   headers is inefficient.  Thus, a mechanism is needed that allows a
   principal to identify a set of properties in which the principal is
   interested and to set or retrieve just those properties.

4.3.  Property Values

   The value of a property is always a (well-formed) XML fragment.

   XML has been chosen because it is a flexible, self-describing,
   structured data format that supports rich schema definitions, and
   because of its support for multiple character sets.  XML's self-
   describing nature allows any property's value to be extended by
   adding elements.  Clients will not break when they encounter
   extensions because they will still have the data specified in the
   original schema and MUST ignore elements they do not understand.

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   XML's support for multiple character sets allows any human-readable
   property to be encoded and read in a character set familiar to the
   user.  XML's support for multiple human languages, using the "xml:
   lang" attribute, handles cases where the same character set is
   employed by multiple human languages.  Note that xml:lang scope is
   recursive, so an xml:lang attribute on any element containing a
   property name element applies to the property value unless it has
   been overridden by a more locally scoped attribute.  Note that a
   property only has one value, in one language (or language MAY be left
   undefined); a property does not have multiple values in different
   languages or a single value in multiple languages.

   A property is always represented with an XML element consisting of
   the property name, called the "property name element".  The simplest
   example is an empty property, which is different from a property that
   does not exist:

      <R:title xmlns:R="http://www.example.com/ns/"></R:title>

   The value of the property appears inside the property name element.
   The value may be any kind of well-formed XML content, including both
   text-only and mixed content.  Servers MUST preserve the following XML
   Information Items (using the terminology from [REC-XML-INFOSET]) in
   storage and transmission of dead properties:

   For the property name Element Information Item itself:

      [namespace name]

      [local name]

      [attributes] named "xml:lang" or any such attribute in scope

      [children] of type element or character

   On all Element Information Items in the property value:

      [namespace name]

      [local name]

      [attributes]

      [children] of type element or character

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   On Attribute Information Items in the property value:

      [namespace name]

      [local name]

      [normalized value]

   On Character Information Items in the property value:

      [character code]

   Since prefixes are used in some XML vocabularies (XPath and XML
   Schema, for example), servers SHOULD preserve, for any Information
   Item in the value:

      [prefix]

   XML Infoset attributes not listed above MAY be preserved by the
   server, but clients MUST NOT rely on them being preserved.  The above
   rules would also apply by default to live properties, unless defined
   otherwise.

   Servers MUST ignore the XML attribute xml:space if present and never
   use it to change whitespace handling.  Whitespace in property values
   is significant.

4.3.1.  Example - Property with Mixed Content

   Consider a dead property 'author' created by the client as follows:

     <D:prop xml:lang="en" xmlns:D="DAV:">
       <x:author xmlns:x='http://example.com/ns'>
         <x:name>Jane Doe</x:name>
         <!-- Jane's contact info -->
         <x:uri type='email'
                added='2005-11-26'>mailto:jane.doe@example.com</x:uri>
         <x:uri type='web'
                added='2005-11-27'>http://www.example.com</x:uri>
         <x:notes xmlns:h='http://www.w3.org/1999/xhtml'>
           Jane has been working way <h:em>too</h:em> long on the
           long-awaited revision of <![CDATA[<RFC2518>]]>.
         </x:notes>
       </x:author>
     </D:prop>

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   When this property is requested, a server might return:

     <D:prop xmlns:D='DAV:'><author
             xml:lang='en'
             xmlns:x='http://example.com/ns'
             xmlns='http://example.com/ns'
             xmlns:h='http://www.w3.org/1999/xhtml'>
         <x:name>Jane Doe</x:name>
         <x:uri   added="2005-11-26" type="email"
           >mailto:jane.doe@example.com</x:uri>
         <x:uri   added="2005-11-27" type="web"
           >http://www.example.com</x:uri>
         <x:notes>
           Jane has been working way <h:em>too</h:em> long on the
           long-awaited revision of &lt;RFC2518&gt;.
         </x:notes>
       </author>
     </D:prop>

   Note in this example:

   o  The [prefix] for the property name itself was not preserved, being
      non-significant, whereas all other [prefix] values have been
      preserved,

   o  attribute values have been rewritten with double quotes instead of
      single quotes (quoting style is not significant), and attribute
      order has not been preserved,

   o  the xml:lang attribute has been returned on the property name
      element itself (it was in scope when the property was set, but the
      exact position in the response is not considered significant as
      long as it is in scope),

   o  whitespace between tags has been preserved everywhere (whitespace
      between attributes not so),

   o  CDATA encapsulation was replaced with character escaping (the
      reverse would also be legal),

   o  the comment item was stripped (as would have been a processing
      instruction item).

   Implementation note: there are cases such as editing scenarios where
   clients may require that XML content is preserved character by
   character (such as attribute ordering or quoting style).  In this
   case, clients should consider using a text-only property value by
   escaping all characters that have a special meaning in XML parsing.

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4.4.  Property Names

   A property name is a universally unique identifier that is associated
   with a schema that provides information about the syntax and
   semantics of the property.

   Because a property's name is universally unique, clients can depend
   upon consistent behavior for a particular property across multiple
   resources, on the same and across different servers, so long as that
   property is "live" on the resources in question, and the
   implementation of the live property is faithful to its definition.

   The XML namespace mechanism, which is based on URIs ([RFC3986]), is
   used to name properties because it prevents namespace collisions and
   provides for varying degrees of administrative control.

   The property namespace is flat; that is, no hierarchy of properties
   is explicitly recognized.  Thus, if a property A and a property A/B
   exist on a resource, there is no recognition of any relationship
   between the two properties.  It is expected that a separate
   specification will eventually be produced that will address issues
   relating to hierarchical properties.

   Finally, it is not possible to define the same property twice on a
   single resource, as this would cause a collision in the resource's
   property namespace.

4.5.  Source Resources and Output Resources

   Some HTTP resources are dynamically generated by the server.  For
   these resources, there presumably exists source code somewhere
   governing how that resource is generated.  The relationship of source
   files to output HTTP resources may be one to one, one to many, many
   to one, or many to many.  There is no mechanism in HTTP to determine
   whether a resource is even dynamic, let alone where its source files
   exist or how to author them.  Although this problem would usefully be
   solved, interoperable WebDAV implementations have been widely
   deployed without actually solving this problem, by dealing only with
   static resources.  Thus, the source vs. output problem is not solved
   in this specification and has been deferred to a separate document.

5.  Collections of Web Resources

   This section provides a description of a type of Web resource, the
   collection, and discusses its interactions with the HTTP URL
   namespace and with HTTP methods.  The purpose of a collection
   resource is to model collection-like objects (e.g., file system
   directories) within a server's namespace.

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   All DAV-compliant resources MUST support the HTTP URL namespace model
   specified herein.

5.1.  HTTP URL Namespace Model

   The HTTP URL namespace is a hierarchical namespace where the
   hierarchy is delimited with the "/" character.

   An HTTP URL namespace is said to be consistent if it meets the
   following conditions: for every URL in the HTTP hierarchy there
   exists a collection that contains that URL as an internal member URL.
   The root, or top-level collection of the namespace under
   consideration, is exempt from the previous rule.  The top-level
   collection of the namespace under consideration is not necessarily
   the collection identified by the absolute path '/' -- it may be
   identified by one or more path segments (e.g., /servlets/webdav/...)

   Neither HTTP/1.1 nor WebDAV requires that the entire HTTP URL
   namespace be consistent -- a WebDAV-compatible resource may not have
   a parent collection.  However, certain WebDAV methods are prohibited
   from producing results that cause namespace inconsistencies.

   As is implicit in [RFC2616] and [RFC3986], any resource, including
   collection resources, MAY be identified by more than one URI.  For
   example, a resource could be identified by multiple HTTP URLs.

5.2.  Collection Resources

   Collection resources differ from other resources in that they also
   act as containers.  Some HTTP methods apply only to a collection, but
   some apply to some or all of the resources inside the container
   defined by the collection.  When the scope of a method is not clear,
   the client can specify what depth to apply.  Depth can be either zero
   levels (only the collection), one level (the collection and directly
   contained resources), or infinite levels (the collection and all
   contained resources recursively).

   A collection's state consists of at least a set of mappings between
   path segments and resources, and a set of properties on the
   collection itself.  In this document, a resource B will be said to be
   contained in the collection resource A if there is a path segment
   mapping that maps to B and that is contained in A.  A collection MUST
   contain at most one mapping for a given path segment, i.e., it is
   illegal to have the same path segment mapped to more than one
   resource.

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   Properties defined on collections behave exactly as do properties on
   non-collection resources.  A collection MAY have additional state
   such as entity bodies returned by GET.

   For all WebDAV-compliant resources A and B, identified by URLs "U"
   and "V", respectively, such that "V" is equal to "U/SEGMENT", A MUST
   be a collection that contains a mapping from "SEGMENT" to B.  So, if
   resource B with URL "http://example.com/bar/blah" is WebDAV compliant
   and if resource A with URL "http://example.com/bar/" is WebDAV
   compliant, then resource A must be a collection and must contain
   exactly one mapping from "blah" to B.

   Although commonly a mapping consists of a single segment and a
   resource, in general, a mapping consists of a set of segments and a
   resource.  This allows a server to treat a set of segments as
   equivalent (i.e., either all of the segments are mapped to the same
   resource, or none of the segments are mapped to a resource).  For
   example, a server that performs case-folding on segments will treat
   the segments "ab", "Ab", "aB", and "AB" as equivalent.  A client can
   then use any of these segments to identify the resource.  Note that a
   PROPFIND result will select one of these equivalent segments to
   identify the mapping, so there will be one PROPFIND response element
   per mapping, not one per segment in the mapping.

   Collection resources MAY have mappings to non-WebDAV-compliant
   resources in the HTTP URL namespace hierarchy but are not required to
   do so.  For example, if resource X with URL
   "http://example.com/bar/blah" is not WebDAV compliant and resource A
   with "URL http://example.com/bar/" identifies a WebDAV collection,
   then A may or may not have a mapping from "blah" to X.

   If a WebDAV-compliant resource has no WebDAV-compliant internal
   members in the HTTP URL namespace hierarchy, then the WebDAV-
   compliant resource is not required to be a collection.

   There is a standing convention that when a collection is referred to
   by its name without a trailing slash, the server MAY handle the
   request as if the trailing slash were present.  In this case, it
   SHOULD return a Content-Location header in the response, pointing to
   the URL ending with the "/".  For example, if a client invokes a
   method on http://example.com/blah (no trailing slash), the server may
   respond as if the operation were invoked on http://example.com/blah/
   (trailing slash), and should return a Content-Location header with
   the value http://example.com/blah/.  Wherever a server produces a URL
   referring to a collection, the server SHOULD include the trailing
   slash.  In general, clients SHOULD use the trailing slash form of
   collection names.  If clients do not use the trailing slash form the
   client needs to be prepared to see a redirect response.  Clients will

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   find the DAV:resourcetype property more reliable than the URL to find
   out if a resource is a collection.

   Clients MUST be able to support the case where WebDAV resources are
   contained inside non-WebDAV resources.  For example, if an OPTIONS
   response from "http://example.com/servlet/dav/collection" indicates
   WebDAV support, the client cannot assume that
   "http://example.com/servlet/dav/" or its parent necessarily are
   WebDAV collections.

   A typical scenario in which mapped URLs do not appear as members of
   their parent collection is the case where a server allows links or
   redirects to non-WebDAV resources.  For instance, "/col/link" might
   not appear as a member of "/col/", although the server would respond
   with a 302 status to a GET request to "/col/link"; thus, the URL
   "/col/link" would indeed be mapped.  Similarly, a dynamically-
   generated page might have a URL mapping from "/col/index.html", thus
   this resource might respond with a 200 OK to a GET request yet not
   appear as a member of "/col/".

   Some mappings to even WebDAV-compliant resources might not appear in
   the parent collection.  An example for this case are servers that
   support multiple alias URLs for each WebDAV-compliant resource.  A
   server may implement case-insensitive URLs, thus "/col/a" and
   "/col/A" identify the same resource, yet only either "a" or "A" is
   reported upon listing the members of "/col".  In cases where a server
   treats a set of segments as equivalent, the server MUST expose only
   one preferred segment per mapping, consistently chosen, in PROPFIND
   responses.

6.  Locking

   The ability to lock a resource provides a mechanism for serializing
   access to that resource.  Using a lock, an authoring client can
   provide a reasonable guarantee that another principal will not modify
   a resource while it is being edited.  In this way, a client can
   prevent the "lost update" problem.

   This specification allows locks to vary over two client-specified
   parameters, the number of principals involved (exclusive vs. shared)
   and the type of access to be granted.  This document defines locking
   for only one access type, write.  However, the syntax is extensible,
   and permits the eventual specification of locking for other access
   types.

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6.1.  Lock Model

   This section provides a concise model for how locking behaves.  Later
   sections will provide more detail on some of the concepts and refer
   back to these model statements.  Normative statements related to LOCK
   and UNLOCK method handling can be found in the sections on those
   methods, whereas normative statements that cover any method are
   gathered here.

   1.  A lock either directly or indirectly locks a resource.

   2.  A resource becomes directly locked when a LOCK request to a URL
       of that resource creates a new lock.  The "lock-root" of the new
       lock is that URL.  If at the time of the request, the URL is not
       mapped to a resource, a new empty resource is created and
       directly locked.

   3.  An exclusive lock (Section 6.2) conflicts with any other kind of
       lock on the same resource, whether either lock is direct or
       indirect.  A server MUST NOT create conflicting locks on a
       resource.

   4.  For a collection that is locked with a depth-infinity lock L, all
       member resources are indirectly locked.  Changes in membership of
       such a collection affect the set of indirectly locked resources:

       *  If a member resource is added to the collection, the new
          member resource MUST NOT already have a conflicting lock,
          because the new resource MUST become indirectly locked by L.

       *  If a member resource stops being a member of the collection,
          then the resource MUST no longer be indirectly locked by L.

   5.  Each lock is identified by a single globally unique lock token
       (Section 6.5).

   6.  An UNLOCK request deletes the lock with the specified lock token.
       After a lock is deleted, no resource is locked by that lock.

   7.  A lock token is "submitted" in a request when it appears in an
       "If" header (Section 7, "Write Lock", discusses when token
       submission is required for write locks).

   8.  If a request causes the lock-root of any lock to become an
       unmapped URL, then the lock MUST also be deleted by that request.

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6.2.  Exclusive vs. Shared Locks

   The most basic form of lock is an exclusive lock.  Exclusive locks
   avoid having to deal with content change conflicts, without requiring
   any coordination other than the methods described in this
   specification.

   However, there are times when the goal of a lock is not to exclude
   others from exercising an access right but rather to provide a
   mechanism for principals to indicate that they intend to exercise
   their access rights.  Shared locks are provided for this case.  A
   shared lock allows multiple principals to receive a lock.  Hence any
   principal that has both access privileges and a valid lock can use
   the locked resource.

   With shared locks, there are two trust sets that affect a resource.
   The first trust set is created by access permissions.  Principals who
   are trusted, for example, may have permission to write to the
   resource.  Among those who have access permission to write to the
   resource, the set of principals who have taken out a shared lock also
   must trust each other, creating a (typically) smaller trust set
   within the access permission write set.

   Starting with every possible principal on the Internet, in most
   situations the vast majority of these principals will not have write
   access to a given resource.  Of the small number who do have write
   access, some principals may decide to guarantee their edits are free
   from overwrite conflicts by using exclusive write locks.  Others may
   decide they trust their collaborators will not overwrite their work
   (the potential set of collaborators being the set of principals who
   have write permission) and use a shared lock, which informs their
   collaborators that a principal may be working on the resource.

   The WebDAV extensions to HTTP do not need to provide all of the
   communications paths necessary for principals to coordinate their
   activities.  When using shared locks, principals may use any out-of-
   band communication channel to coordinate their work (e.g., face-to-
   face interaction, written notes, post-it notes on the screen,
   telephone conversation, email, etc.)  The intent of a shared lock is
   to let collaborators know who else may be working on a resource.

   Shared locks are included because experience from Web-distributed
   authoring systems has indicated that exclusive locks are often too
   rigid.  An exclusive lock is used to enforce a particular editing
   process: take out an exclusive lock, read the resource, perform
   edits, write the resource, release the lock.  This editing process
   has the problem that locks are not always properly released, for
   example, when a program crashes or when a lock creator leaves without

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   unlocking a resource.  While both timeouts (Section 6.6) and
   administrative action can be used to remove an offending lock,
   neither mechanism may be available when needed; the timeout may be
   long or the administrator may not be available.

   A successful request for a new shared lock MUST result in the
   generation of a unique lock associated with the requesting principal.
   Thus, if five principals have taken out shared write locks on the
   same resource, there will be five locks and five lock tokens, one for
   each principal.

6.3.  Required Support

   A WebDAV-compliant resource is not required to support locking in any
   form.  If the resource does support locking, it may choose to support
   any combination of exclusive and shared locks for any access types.

   The reason for this flexibility is that locking policy strikes to the
   very heart of the resource management and versioning systems employed
   by various storage repositories.  These repositories require control
   over what sort of locking will be made available.  For example, some
   repositories only support shared write locks, while others only
   provide support for exclusive write locks, while yet others use no
   locking at all.  As each system is sufficiently different to merit
   exclusion of certain locking features, this specification leaves
   locking as the sole axis of negotiation within WebDAV.

6.4.  Lock Creator and Privileges

   The creator of a lock has special privileges to use the lock to
   modify the resource.  When a locked resource is modified, a server
   MUST check that the authenticated principal matches the lock creator
   (in addition to checking for valid lock token submission).

   The server MAY allow privileged users other than the lock creator to
   destroy a lock (for example, the resource owner or an administrator).
   The 'unlock' privilege in [RFC3744] was defined to provide that
   permission.

   There is no requirement for servers to accept LOCK requests from all
   users or from anonymous users.

   Note that having a lock does not confer full privilege to modify the
   locked resource.  Write access and other privileges MUST be enforced
   through normal privilege or authentication mechanisms, not based on
   the possible obscurity of lock token values.

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6.5.  Lock Tokens

   A lock token is a type of state token that identifies a particular
   lock.  Each lock has exactly one unique lock token generated by the
   server.  Clients MUST NOT attempt to interpret lock tokens in any
   way.

   Lock token URIs MUST be unique across all resources for all time.
   This uniqueness constraint allows lock tokens to be submitted across
   resources and servers without fear of confusion.  Since lock tokens
   are unique, a client MAY submit a lock token in an If header on a
   resource other than the one that returned it.

   When a LOCK operation creates a new lock, the new lock token is
   returned in the Lock-Token response header defined in Section 10.5,
   and also in the body of the response.

   Servers MAY make lock tokens publicly readable (e.g., in the DAV:
   lockdiscovery property).  One use case for making lock tokens
   readable is so that a long-lived lock can be removed by the resource
   owner (the client that obtained the lock might have crashed or
   disconnected before cleaning up the lock).  Except for the case of
   using UNLOCK under user guidance, a client SHOULD NOT use a lock
   token created by another client instance.

   This specification encourages servers to create Universally Unique
   Identifiers (UUIDs) for lock tokens, and to use the URI form defined
   by "A Universally Unique Identifier (UUID) URN Namespace"
   ([RFC4122]).  However, servers are free to use any URI (e.g., from
   another scheme) so long as it meets the uniqueness requirements.  For
   example, a valid lock token might be constructed using the
   "opaquelocktoken" scheme defined in Appendix C.

   Example: "urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6"

6.6.  Lock Timeout

   A lock MAY have a limited lifetime.  The lifetime is suggested by the
   client when creating or refreshing the lock, but the server
   ultimately chooses the timeout value.  Timeout is measured in seconds
   remaining until lock expiration.

   The timeout counter MUST be restarted if a refresh lock request is
   successful (see Section 9.10.2).  The timeout counter SHOULD NOT be
   restarted at any other time.

   If the timeout expires, then the lock SHOULD be removed.  In this
   case the server SHOULD act as if an UNLOCK method was executed by the

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   server on the resource using the lock token of the timed-out lock,
   performed with its override authority.

   Servers are advised to pay close attention to the values submitted by
   clients, as they will be indicative of the type of activity the
   client intends to perform.  For example, an applet running in a
   browser may need to lock a resource, but because of the instability
   of the environment within which the applet is running, the applet may
   be turned off without warning.  As a result, the applet is likely to
   ask for a relatively small timeout value so that if the applet dies,
   the lock can be quickly harvested.  However, a document management
   system is likely to ask for an extremely long timeout because its
   user may be planning on going offline.

   A client MUST NOT assume that just because the timeout has expired,
   the lock has immediately been removed.

   Likewise, a client MUST NOT assume that just because the timeout has
   not expired, the lock still exists.  Clients MUST assume that locks
   can arbitrarily disappear at any time, regardless of the value given
   in the Timeout header.  The Timeout header only indicates the
   behavior of the server if extraordinary circumstances do not occur.
   For example, a sufficiently privileged user may remove a lock at any
   time, or the system may crash in such a way that it loses the record
   of the lock's existence.

6.7.  Lock Capability Discovery

   Since server lock support is optional, a client trying to lock a
   resource on a server can either try the lock and hope for the best,
   or perform some form of discovery to determine what lock capabilities
   the server supports.  This is known as lock capability discovery.  A
   client can determine what lock types the server supports by
   retrieving the DAV:supportedlock property.

   Any DAV-compliant resource that supports the LOCK method MUST support
   the DAV:supportedlock property.

6.8.  Active Lock Discovery

   If another principal locks a resource that a principal wishes to
   access, it is useful for the second principal to be able to find out
   who the first principal is.  For this purpose the DAV:lockdiscovery
   property is provided.  This property lists all outstanding locks,
   describes their type, and MAY even provide the lock tokens.

   Any DAV-compliant resource that supports the LOCK method MUST support
   the DAV:lockdiscovery property.

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7.  Write Lock

   This section describes the semantics specific to the write lock type.
   The write lock is a specific instance of a lock type, and is the only
   lock type described in this specification.

   An exclusive write lock protects a resource: it prevents changes by
   any principal other than the lock creator and in any case where the
   lock token is not submitted (e.g., by a client process other than the
   one holding the lock).

   Clients MUST submit a lock-token they are authorized to use in any
   request that modifies a write-locked resource.  The list of
   modifications covered by a write-lock include:

   1.  A change to any of the following aspects of any write-locked
       resource:

       *  any variant,

       *  any dead property,

       *  any live property that is lockable (a live property is
          lockable unless otherwise defined.)

   2.  For collections, any modification of an internal member URI.  An
       internal member URI of a collection is considered to be modified
       if it is added, removed, or identifies a different resource.
       More discussion on write locks and collections is found in
       Section 7.4.

   3.  A modification of the mapping of the root of the write lock,
       either to another resource or to no resource (e.g., DELETE).

   Of the methods defined in HTTP and WebDAV, PUT, POST, PROPPATCH,
   LOCK, UNLOCK, MOVE, COPY (for the destination resource), DELETE, and
   MKCOL are affected by write locks.  All other HTTP/WebDAV methods
   defined so far -- GET in particular -- function independently of a
   write lock.

   The next few sections describe in more specific terms how write locks
   interact with various operations.

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7.1.  Write Locks and Properties

   While those without a write lock may not alter a property on a
   resource it is still possible for the values of live properties to
   change, even while locked, due to the requirements of their schemas.
   Only dead properties and live properties defined as lockable are
   guaranteed not to change while write locked.

7.2.  Avoiding Lost Updates

   Although the write locks provide some help in preventing lost
   updates, they cannot guarantee that updates will never be lost.
   Consider the following scenario:

   Two clients A and B are interested in editing the resource
   'index.html'.  Client A is an HTTP client rather than a WebDAV
   client, and so does not know how to perform locking.

   Client A doesn't lock the document, but does a GET, and begins
   editing.

   Client B does LOCK, performs a GET and begins editing.

   Client B finishes editing, performs a PUT, then an UNLOCK.

   Client A performs a PUT, overwriting and losing all of B's changes.

   There are several reasons why the WebDAV protocol itself cannot
   prevent this situation.  First, it cannot force all clients to use
   locking because it must be compatible with HTTP clients that do not
   comprehend locking.  Second, it cannot require servers to support
   locking because of the variety of repository implementations, some of
   which rely on reservations and merging rather than on locking.
   Finally, being stateless, it cannot enforce a sequence of operations
   like LOCK / GET / PUT / UNLOCK.

   WebDAV servers that support locking can reduce the likelihood that
   clients will accidentally overwrite each other's changes by requiring
   clients to lock resources before modifying them.  Such servers would
   effectively prevent HTTP 1.0 and HTTP 1.1 clients from modifying
   resources.

   WebDAV clients can be good citizens by using a lock / retrieve /
   write /unlock sequence of operations (at least by default) whenever
   they interact with a WebDAV server that supports locking.

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   HTTP 1.1 clients can be good citizens, avoiding overwriting other
   clients' changes, by using entity tags in If-Match headers with any
   requests that would modify resources.

   Information managers may attempt to prevent overwrites by
   implementing client-side procedures requiring locking before
   modifying WebDAV resources.

7.3.  Write Locks and Unmapped URLs

   WebDAV provides the ability to send a LOCK request to an unmapped URL
   in order to reserve the name for use.  This is a simple way to avoid
   the lost-update problem on the creation of a new resource (another
   way is to use If-None-Match header specified in Section 14.26 of
   [RFC2616]).  It has the side benefit of locking the new resource
   immediately for use of the creator.

   Note that the lost-update problem is not an issue for collections
   because MKCOL can only be used to create a collection, not to
   overwrite an existing collection.  When trying to lock a collection
   upon creation, clients can attempt to increase the likelihood of
   getting the lock by pipelining the MKCOL and LOCK requests together
   (but because this doesn't convert two separate operations into one
   atomic operation, there's no guarantee this will work).

   A successful lock request to an unmapped URL MUST result in the
   creation of a locked (non-collection) resource with empty content.
   Subsequently, a successful PUT request (with the correct lock token)
   provides the content for the resource.  Note that the LOCK request
   has no mechanism for the client to provide Content-Type or Content-
   Language, thus the server will use defaults or empty values and rely
   on the subsequent PUT request for correct values.

   A resource created with a LOCK is empty but otherwise behaves in
   every way as a normal resource.  It behaves the same way as a
   resource created by a PUT request with an empty body (and where a
   Content-Type and Content-Language was not specified), followed by a
   LOCK request to the same resource.  Following from this model, a
   locked empty resource:

   o  Can be read, deleted, moved, and copied, and in all ways behaves
      as a regular non-collection resource.

   o  Appears as a member of its parent collection.

   o  SHOULD NOT disappear when its lock goes away (clients must
      therefore be responsible for cleaning up their own mess, as with
      any other operation or any non-empty resource).

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   o  MAY NOT have values for properties like DAV:getcontentlanguage
      that haven't been specified yet by the client.

   o  Can be updated (have content added) with a PUT request.

   o  MUST NOT be converted into a collection.  The server MUST fail a
      MKCOL request (as it would with a MKCOL request to any existing
      non-collection resource).

   o  MUST have defined values for DAV:lockdiscovery and DAV:
      supportedlock properties.

   o  The response MUST indicate that a resource was created, by use of
      the "201 Created" response code (a LOCK request to an existing
      resource instead will result in 200 OK).  The body must still
      include the DAV:lockdiscovery property, as with a LOCK request to
      an existing resource.

   The client is expected to update the locked empty resource shortly
   after locking it, using PUT and possibly PROPPATCH.

   Alternatively and for backwards compatibility to [RFC2518], servers
   MAY implement Lock-Null Resources (LNRs) instead (see definition in
   Appendix D).  Clients can easily interoperate both with servers that
   support the old model LNRs and the recommended model of "locked empty
   resources" by only attempting PUT after a LOCK to an unmapped URL,
   not MKCOL or GET, and by not relying on specific properties of LNRs.

7.4.  Write Locks and Collections

   There are two kinds of collection write locks.  A depth-0 write lock
   on a collection protects the collection properties plus the internal
   member URLs of that one collection, while not protecting the content
   or properties of member resources (if the collection itself has any
   entity bodies, those are also protected).  A depth-infinity write
   lock on a collection provides the same protection on that collection
   and also provides write lock protection on every member resource.

   Expressed otherwise, a write lock of either kind protects any request
   that would create a new resource in a write locked collection, any
   request that would remove an internal member URL of a write locked
   collection, and any request that would change the segment name of any
   internal member.

   Thus, a collection write lock protects all the following actions:

   o  DELETE a collection's direct internal member,

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   o  MOVE an internal member out of the collection,

   o  MOVE an internal member into the collection,

   o  MOVE to rename an internal member within a collection,

   o  COPY an internal member into a collection, and

   o  PUT or MKCOL request that would create a new internal member.

   The collection's lock token is required in addition to the lock token
   on the internal member itself, if it is locked separately.

   In addition, a depth-infinity lock affects all write operations to
   all members of the locked collection.  With a depth-infinity lock,
   the resource identified by the root of the lock is directly locked,
   and all its members are indirectly locked.

   o  Any new resource added as a descendant of a depth-infinity locked
      collection becomes indirectly locked.

   o  Any indirectly locked resource moved out of the locked collection
      into an unlocked collection is thereafter unlocked.

   o  Any indirectly locked resource moved out of a locked source
      collection into a depth-infinity locked target collection remains
      indirectly locked but is now protected by the lock on the target
      collection (the target collection's lock token will thereafter be
      required to make further changes).

   If a depth-infinity write LOCK request is issued to a collection
   containing member URLs identifying resources that are currently
   locked in a manner that conflicts with the new lock (see Section 6.1,
   point 3), the request MUST fail with a 423 (Locked) status code, and
   the response SHOULD contain the 'no-conflicting-lock' precondition.

   If a lock request causes the URL of a resource to be added as an
   internal member URL of a depth-infinity locked collection, then the
   new resource MUST be automatically protected by the lock.  For
   example, if the collection /a/b/ is write locked and the resource /c
   is moved to /a/b/c, then resource /a/b/c will be added to the write
   lock.

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7.5.  Write Locks and the If Request Header

   A user agent has to demonstrate knowledge of a lock when requesting
   an operation on a locked resource.  Otherwise, the following scenario
   might occur.  In the scenario, program A, run by User A, takes out a
   write lock on a resource.  Program B, also run by User A, has no
   knowledge of the lock taken out by program A, yet performs a PUT to
   the locked resource.  In this scenario, the PUT succeeds because
   locks are associated with a principal, not a program, and thus
   program B, because it is acting with principal A's credential, is
   allowed to perform the PUT.  However, had program B known about the
   lock, it would not have overwritten the resource, preferring instead
   to present a dialog box describing the conflict to the user.  Due to
   this scenario, a mechanism is needed to prevent different programs
   from accidentally ignoring locks taken out by other programs with the
   same authorization.

   In order to prevent these collisions, a lock token MUST be submitted
   by an authorized principal for all locked resources that a method may
   change or the method MUST fail.  A lock token is submitted when it
   appears in an If header.  For example, if a resource is to be moved
   and both the source and destination are locked, then two lock tokens
   must be submitted in the If header, one for the source and the other
   for the destination.

7.5.1.  Example - Write Lock and COPY

   >>Request

     COPY /~fielding/index.html HTTP/1.1
     Host: www.example.com
     Destination: http://www.example.com/users/f/fielding/index.html
     If: <http://www.example.com/users/f/fielding/index.html>
         (<urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6>)

   >>Response

     HTTP/1.1 204 No Content

   In this example, even though both the source and destination are
   locked, only one lock token must be submitted (the one for the lock
   on the destination).  This is because the source resource is not
   modified by a COPY, and hence unaffected by the write lock.  In this
   example, user agent authentication has previously occurred via a
   mechanism outside the scope of the HTTP protocol, in the underlying
   transport layer.

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7.5.2.  Example - Deleting a Member of a Locked Collection

   Consider a collection "/locked" with an exclusive, depth-infinity
   write lock, and an attempt to delete an internal member "/locked/
   member":

   >>Request

     DELETE /locked/member HTTP/1.1
     Host: example.com

   >>Response

     HTTP/1.1 423 Locked
     Content-Type: application/xml; charset="utf-8"
     Content-Length: xxxx

     <?xml version="1.0" encoding="utf-8" ?>
     <D:error xmlns:D="DAV:">
       <D:lock-token-submitted>
         <D:href>/locked/</D:href>
       </D:lock-token-submitted>
     </D:error>

   Thus, the client would need to submit the lock token with the request
   to make it succeed.  To do that, various forms of the If header (see
   Section 10.4) could be used.

   "No-Tag-List" format:

     If: (<urn:uuid:150852e2-3847-42d5-8cbe-0f4f296f26cf>)

   "Tagged-List" format, for "http://example.com/locked/":

     If: <http://example.com/locked/>
         (<urn:uuid:150852e2-3847-42d5-8cbe-0f4f296f26cf>)

   "Tagged-List" format, for "http://example.com/locked/member":

     If: <http://example.com/locked/member>
         (<urn:uuid:150852e2-3847-42d5-8cbe-0f4f296f26cf>)

   Note that, for the purpose of submitting the lock token, the actual
   form doesn't matter; what's relevant is that the lock token appears
   in the If header, and that the If header itself evaluates to true.

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7.6.  Write Locks and COPY/MOVE

   A COPY method invocation MUST NOT duplicate any write locks active on
   the source.  However, as previously noted, if the COPY copies the
   resource into a collection that is locked with a depth-infinity lock,
   then the resource will be added to the lock.

   A successful MOVE request on a write locked resource MUST NOT move
   the write lock with the resource.  However, if there is an existing
   lock at the destination, the server MUST add the moved resource to
   the destination lock scope.  For example, if the MOVE makes the
   resource a child of a collection that has a depth-infinity lock, then
   the resource will be added to that collection's lock.  Additionally,
   if a resource with a depth-infinity lock is moved to a destination
   that is within the scope of the same lock (e.g., within the URL
   namespace tree covered by the lock), the moved resource will again be
   added to the lock.  In both these examples, as specified in
   Section 7.5, an If header must be submitted containing a lock token
   for both the source and destination.

7.7.  Refreshing Write Locks

   A client MUST NOT submit the same write lock request twice.  Note
   that a client is always aware it is resubmitting the same lock
   request because it must include the lock token in the If header in
   order to make the request for a resource that is already locked.

   However, a client may submit a LOCK request with an If header but
   without a body.  A server receiving a LOCK request with no body MUST
   NOT create a new lock -- this form of the LOCK request is only to be
   used to "refresh" an existing lock (meaning, at minimum, that any
   timers associated with the lock MUST be reset).

   Clients may submit Timeout headers of arbitrary value with their lock
   refresh requests.  Servers, as always, may ignore Timeout headers
   submitted by the client, and a server MAY refresh a lock with a
   timeout period that is different than the previous timeout period
   used for the lock, provided it advertises the new value in the LOCK
   refresh response.

   If an error is received in response to a refresh LOCK request, the
   client MUST NOT assume that the lock was refreshed.

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8.  General Request and Response Handling

8.1.  Precedence in Error Handling

   Servers MUST return authorization errors in preference to other
   errors.  This avoids leaking information about protected resources
   (e.g., a client that finds that a hidden resource exists by seeing a
   423 Locked response to an anonymous request to the resource).

8.2.  Use of XML

   In HTTP/1.1, method parameter information was exclusively encoded in
   HTTP headers.  Unlike HTTP/1.1, WebDAV encodes method parameter
   information either in an XML ([REC-XML]) request entity body, or in
   an HTTP header.  The use of XML to encode method parameters was
   motivated by the ability to add extra XML elements to existing
   structures, providing extensibility; and by XML's ability to encode
   information in ISO 10646 character sets, providing
   internationalization support.

   In addition to encoding method parameters, XML is used in WebDAV to
   encode the responses from methods, providing the extensibility and
   internationalization advantages of XML for method output, as well as
   input.

   When XML is used for a request or response body, the Content-Type
   type SHOULD be application/xml.  Implementations MUST accept both
   text/xml and application/xml in request and response bodies.  Use of
   text/xml is deprecated.

   All DAV-compliant clients and resources MUST use XML parsers that are
   compliant with [REC-XML] and [REC-XML-NAMES].  All XML used in either
   requests or responses MUST be, at minimum, well formed and use
   namespaces correctly.  If a server receives XML that is not well-
   formed, then the server MUST reject the entire request with a 400
   (Bad Request).  If a client receives XML that is not well-formed in a
   response, then the client MUST NOT assume anything about the outcome
   of the executed method and SHOULD treat the server as malfunctioning.

   Note that processing XML submitted by an untrusted source may cause
   risks connected to privacy, security, and service quality (see
   Section 20).  Servers MAY reject questionable requests (even though
   they consist of well-formed XML), for instance, with a 400 (Bad
   Request) status code and an optional response body explaining the
   problem.

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8.3.  URL Handling

   URLs appear in many places in requests and responses.
   Interoperability experience with [RFC2518] showed that many clients
   parsing Multi-Status responses did not fully implement the full
   Reference Resolution defined in Section 5 of [RFC3986].  Thus,
   servers in particular need to be careful in handling URLs in
   responses, to ensure that clients have enough context to be able to
   interpret all the URLs.  The rules in this section apply not only to
   resource URLs in the 'href' element in Multi-Status responses, but
   also to the Destination and If header resource URLs.

   The sender has a choice between two approaches: using a relative
   reference, which is resolved against the Request-URI, or a full URI.
   A server MUST ensure that every 'href' value within a Multi-Status
   response uses the same format.

   WebDAV only uses one form of relative reference in its extensions,
   the absolute path.

      Simple-ref = absolute-URI | ( path-absolute [ "?" query ] )

   The absolute-URI, path-absolute and query productions are defined in
   Sections 4.3, 3.3, and 3.4 of [RFC3986].

   Within Simple-ref productions, senders MUST NOT:

   o  use dot-segments ("." or ".."), or

   o  have prefixes that do not match the Request-URI (using the
      comparison rules defined in Section 3.2.3 of [RFC2616]).

   Identifiers for collections SHOULD end in a '/' character.

8.3.1.  Example - Correct URL Handling

   Consider the collection http://example.com/sample/ with the internal
   member URL http://example.com/sample/a%20test and the PROPFIND
   request below:

   >>Request:

     PROPFIND /sample/ HTTP/1.1
     Host: example.com
     Depth: 1

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   In this case, the server should return two 'href' elements containing
   either

   o  'http://example.com/sample/' and
      'http://example.com/sample/a%20test', or

   o  '/sample/' and '/sample/a%20test'

   Note that even though the server may be storing the member resource
   internally as 'a test', it has to be percent-encoded when used inside
   a URI reference (see Section 2.1 of [RFC3986]).  Also note that a
   legal URI may still contain characters that need to be escaped within
   XML character data, such as the ampersand character.

8.4.  Required Bodies in Requests

   Some of these new methods do not define bodies.  Servers MUST examine
   all requests for a body, even when a body was not expected.  In cases
   where a request body is present but would be ignored by a server, the
   server MUST reject the request with 415 (Unsupported Media Type).
   This informs the client (which may have been attempting to use an
   extension) that the body could not be processed as the client
   intended.

8.5.  HTTP Headers for Use in WebDAV

   HTTP defines many headers that can be used in WebDAV requests and
   responses.  Not all of these are appropriate in all situations and
   some interactions may be undefined.  Note that HTTP 1.1 requires the
   Date header in all responses if possible (see Section 14.18,
   [RFC2616]).

   The server MUST do authorization checks before checking any HTTP
   conditional header.

8.6.  ETag

   HTTP 1.1 recommends the use of ETags rather than modification dates,
   for cache control, and there are even stronger reasons to prefer
   ETags for authoring.  Correct use of ETags is even more important in
   a distributed authoring environment, because ETags are necessary
   along with locks to avoid the lost-update problem.  A client might
   fail to renew a lock, for example, when the lock times out and the
   client is accidentally offline or in the middle of a long upload.
   When a client fails to renew the lock, it's quite possible the
   resource can still be relocked and the user can go on editing, as
   long as no changes were made in the meantime.  ETags are required for
   the client to be able to distinguish this case.  Otherwise, the

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   client is forced to ask the user whether to overwrite the resource on
   the server without even being able to tell the user if it has
   changed.  Timestamps do not solve this problem nearly as well as
   ETags.

   Strong ETags are much more useful for authoring use cases than weak
   ETags (see Section 13.3.3 of [RFC2616]).  Semantic equivalence can be
   a useful concept but that depends on the document type and the
   application type, and interoperability might require some agreement
   or standard outside the scope of this specification and HTTP.  Note
   also that weak ETags have certain restrictions in HTTP, e.g., these
   cannot be used in If-Match headers.

   Note that the meaning of an ETag in a PUT response is not clearly
   defined either in this document or in RFC 2616 (i.e., whether the
   ETag means that the resource is octet-for-octet equivalent to the
   body of the PUT request, or whether the server could have made minor
   changes in the formatting or content of the document upon storage).
   This is an HTTP issue, not purely a WebDAV issue.

   Because clients may be forced to prompt users or throw away changed
   content if the ETag changes, a WebDAV server SHOULD NOT change the
   ETag (or the Last-Modified time) for a resource that has an unchanged
   body and location.  The ETag represents the state of the body or
   contents of the resource.  There is no similar way to tell if
   properties have changed.

8.7.  Including Error Response Bodies

   HTTP and WebDAV did not use the bodies of most error responses for
   machine-parsable information until the specification for Versioning
   Extensions to WebDAV introduced a mechanism to include more specific
   information in the body of an error response (Section 1.6 of
   [RFC3253]).  The error body mechanism is appropriate to use with any
   error response that may take a body but does not already have a body
   defined.  The mechanism is particularly appropriate when a status
   code can mean many things (for example, 400 Bad Request can mean
   required headers are missing, headers are incorrectly formatted, or
   much more).  This error body mechanism is covered in Section 16.

8.8.  Impact of Namespace Operations on Cache Validators

   Note that the HTTP response headers "Etag" and "Last-Modified" (see
   [RFC2616], Sections 14.19 and 14.29) are defined per URL (not per
   resource), and are used by clients for caching.  Therefore servers
   must ensure that executing any operation that affects the URL
   namespace (such as COPY, MOVE, DELETE, PUT, or MKCOL) does preserve
   their semantics, in particular:

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   o  For any given URL, the "Last-Modified" value MUST increment every
      time the representation returned upon GET changes (within the
      limits of timestamp resolution).

   o  For any given URL, an "ETag" value MUST NOT be reused for
      different representations returned by GET.

   In practice this means that servers

   o  might have to increment "Last-Modified" timestamps for every
      resource inside the destination namespace of a namespace operation
      unless it can do so more selectively, and

   o  similarly, might have to re-assign "ETag" values for these
      resources (unless the server allocates entity tags in a way so
      that they are unique across the whole URL namespace managed by the
      server).

   Note that these considerations also apply to specific use cases, such
   as using PUT to create a new resource at a URL that has been mapped
   before, but has been deleted since then.

   Finally, WebDAV properties (such as DAV:getetag and DAV:
   getlastmodified) that inherit their semantics from HTTP headers must
   behave accordingly.

9.  HTTP Methods for Distributed Authoring

9.1.  PROPFIND Method

   The PROPFIND method retrieves properties defined on the resource
   identified by the Request-URI, if the resource does not have any
   internal members, or on the resource identified by the Request-URI
   and potentially its member resources, if the resource is a collection
   that has internal member URLs.  All DAV-compliant resources MUST
   support the PROPFIND method and the propfind XML element
   (Section 14.20) along with all XML elements defined for use with that
   element.

   A client MUST submit a Depth header with a value of "0", "1", or
   "infinity" with a PROPFIND request.  Servers MUST support "0" and "1"
   depth requests on WebDAV-compliant resources and SHOULD support
   "infinity" requests.  In practice, support for infinite-depth
   requests MAY be disabled, due to the performance and security
   concerns associated with this behavior.  Servers SHOULD treat a
   request without a Depth header as if a "Depth: infinity" header was
   included.

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   A client may submit a 'propfind' XML element in the body of the
   request method describing what information is being requested.  It is
   possible to:

   o  Request particular property values, by naming the properties
      desired within the 'prop' element (the ordering of properties in
      here MAY be ignored by the server),

   o  Request property values for those properties defined in this
      specification (at a minimum) plus dead properties, by using the
      'allprop' element (the 'include' element can be used with
      'allprop' to instruct the server to also include additional live
      properties that may not have been returned otherwise),

   o  Request a list of names of all the properties defined on the
      resource, by using the 'propname' element.

   A client may choose not to submit a request body.  An empty PROPFIND
   request body MUST be treated as if it were an 'allprop' request.

   Note that 'allprop' does not return values for all live properties.
   WebDAV servers increasingly have expensively-calculated or lengthy
   properties (see [RFC3253] and [RFC3744]) and do not return all
   properties already.  Instead, WebDAV clients can use propname
   requests to discover what live properties exist, and request named
   properties when retrieving values.  For a live property defined
   elsewhere, that definition can specify whether or not that live
   property would be returned in 'allprop' requests.

   All servers MUST support returning a response of content type text/
   xml or application/xml that contains a multistatus XML element that
   describes the results of the attempts to retrieve the various
   properties.

   If there is an error retrieving a property, then a proper error
   result MUST be included in the response.  A request to retrieve the
   value of a property that does not exist is an error and MUST be noted
   with a 'response' XML element that contains a 404 (Not Found) status
   value.

   Consequently, the 'multistatus' XML element for a collection resource
   MUST include a 'response' XML element for each member URL of the
   collection, to whatever depth was requested.  It SHOULD NOT include
   any 'response' elements for resources that are not WebDAV-compliant.
   Each 'response' element MUST contain an 'href' element that contains
   the URL of the resource on which the properties in the prop XML
   element are defined.  Results for a PROPFIND on a collection resource
   are returned as a flat list whose order of entries is not

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   significant.  Note that a resource may have only one value for a
   property of a given name, so the property may only show up once in
   PROPFIND responses.

   Properties may be subject to access control.  In the case of
   'allprop' and 'propname' requests, if a principal does not have the
   right to know whether a particular property exists, then the property
   MAY be silently excluded from the response.

   Some PROPFIND results MAY be cached, with care, as there is no cache
   validation mechanism for most properties.  This method is both safe
   and idempotent (see Section 9.1 of [RFC2616]).

9.1.1.  PROPFIND Status Codes

   This section, as with similar sections for other methods, provides
   some guidance on error codes and preconditions or postconditions
   (defined in Section 16) that might be particularly useful with
   PROPFIND.

   403 Forbidden - A server MAY reject PROPFIND requests on collections
   with depth header of "Infinity", in which case it SHOULD use this
   error with the precondition code 'propfind-finite-depth' inside the
   error body.

9.1.2.  Status Codes for Use in 'propstat' Element

   In PROPFIND responses, information about individual properties is
   returned inside 'propstat' elements (see Section 14.22), each
   containing an individual 'status' element containing information
   about the properties appearing in it.  The list below summarizes the
   most common status codes used inside 'propstat'; however, clients
   should be prepared to handle other 2/3/4/5xx series status codes as
   well.

   200 OK - A property exists and/or its value is successfully returned.

   401 Unauthorized - The property cannot be viewed without appropriate
   authorization.

   403 Forbidden - The property cannot be viewed regardless of
   authentication.

   404 Not Found - The property does not exist.

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9.1.3.  Example - Retrieving Named Properties

   >>Request

     PROPFIND /file HTTP/1.1
     Host: www.example.com
     Content-type: application/xml; charset="utf-8"
     Content-Length: xxxx

     <?xml version="1.0" encoding="utf-8" ?>
     <D:propfind xmlns:D="DAV:">
       <D:prop xmlns:R="http://ns.example.com/boxschema/">
         <R:bigbox/>
         <R:author/>
         <R:DingALing/>
         <R:Random/>
       </D:prop>
     </D:propfind>

   >>Response

     HTTP/1.1 207 Multi-Status
     Content-Type: application/xml; charset="utf-8"
     Content-Length: xxxx

     <?xml version="1.0" encoding="utf-8" ?>
     <D:multistatus xmlns:D="DAV:">
       <D:response xmlns:R="http://ns.example.com/boxschema/">
         <D:href>http://www.example.com/file</D:href>
         <D:propstat>
           <D:prop>
             <R:bigbox>
               <R:BoxType>Box type A</R:BoxType>
             </R:bigbox>
             <R:author>
               <R:Name>J.J. Johnson</R:Name>
             </R:author>
           </D:prop>
           <D:status>HTTP/1.1 200 OK</D:status>
         </D:propstat>
         <D:propstat>
           <D:prop><R:DingALing/><R:Random/></D:prop>
           <D:status>HTTP/1.1 403 Forbidden</D:status>
           <D:responsedescription> The user does not have access to the
      DingALing property.
           </D:responsedescription>
         </D:propstat>

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       </D:response>
       <D:responsedescription> There has been an access violation error.
       </D:responsedescription>
     </D:multistatus>

   In this example, PROPFIND is executed on a non-collection resource
   http://www.example.com/file.  The propfind XML element specifies the
   name of four properties whose values are being requested.  In this
   case, only two properties were returned, since the principal issuing
   the request did not have sufficient access rights to see the third
   and fourth properties.

9.1.4.  Example - Using 'propname' to Retrieve All Property Names

   >>Request

     PROPFIND /container/ HTTP/1.1
     Host: www.example.com
     Content-Type: application/xml; charset="utf-8"
     Content-Length: xxxx

     <?xml version="1.0" encoding="utf-8" ?>
     <propfind xmlns="DAV:">
       <propname/>
     </propfind>

   >>Response

     HTTP/1.1 207 Multi-Status
     Content-Type: application/xml; charset="utf-8"
     Content-Length: xxxx

     <?xml version="1.0" encoding="utf-8" ?>
     <multistatus xmlns="DAV:">
       <response>
         <href>http://www.example.com/container/</href>
         <propstat>
           <prop xmlns:R="http://ns.example.com/boxschema/">
             <R:bigbox/>
             <R:author/>
             <creationdate/>
             <displayname/>
             <resourcetype/>
             <supportedlock/>
           </prop>
           <status>HTTP/1.1 200 OK</status>

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         </propstat>
       </response>
       <response>
         <href>http://www.example.com/container/front.html</href>
         <propstat>
           <prop xmlns:R="http://ns.example.com/boxschema/">
             <R:bigbox/>
             <creationdate/>
             <displayname/>
             <getcontentlength/>
             <getcontenttype/>
             <getetag/>
             <getlastmodified/>
             <resourcetype/>
             <supportedlock/>
           </prop>
           <status>HTTP/1.1 200 OK</status>
         </propstat>
       </response>
     </multistatus>

   In this example, PROPFIND is invoked on the collection resource
   http://www.example.com/container/, with a propfind XML element
   containing the propname XML element, meaning the name of all
   properties should be returned.  Since no Depth header is present, it
   assumes its default value of "infinity", meaning the name of the
   properties on the collection and all its descendants should be
   returned.

   Consistent with the previous example, resource
   http://www.example.com/container/ has six properties defined on it:
   bigbox and author in the "http://ns.example.com/boxschema/"
   namespace, and creationdate, displayname, resourcetype, and
   supportedlock in the "DAV:" namespace.

   The resource http://www.example.com/container/index.html, a member of
   the "container" collection, has nine properties defined on it, bigbox
   in the "http://ns.example.com/boxschema/" namespace and creationdate,
   displayname, getcontentlength, getcontenttype, getetag,
   getlastmodified, resourcetype, and supportedlock in the "DAV:"
   namespace.

   This example also demonstrates the use of XML namespace scoping and
   the default namespace.  Since the "xmlns" attribute does not contain
   a prefix, the namespace applies by default to all enclosed elements.
   Hence, all elements that do not explicitly state the namespace to
   which they belong are members of the "DAV:" namespace.

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9.1.5.  Example - Using So-called 'allprop'

   Note that 'allprop', despite its name, which remains for backward-
   compatibility, does not return every property, but only dead
   properties and the live properties defined in this specification.

   >>Request

     PROPFIND /container/ HTTP/1.1
     Host: www.example.com
     Depth: 1
     Content-Type: application/xml; charset="utf-8"
     Content-Length: xxxx

     <?xml version="1.0" encoding="utf-8" ?>
     <D:propfind xmlns:D="DAV:">
       <D:allprop/>
     </D:propfind>

   >>Response

     HTTP/1.1 207 Multi-Status
     Content-Type: application/xml; charset="utf-8"
     Content-Length: xxxx

     <?xml version="1.0" encoding="utf-8" ?>
     <D:multistatus xmlns:D="DAV:">
       <D:response>
         <D:href>/container/</D:href>
         <D:propstat>
           <D:prop xmlns:R="http://ns.example.com/boxschema/">
             <R:bigbox><R:BoxType>Box type A</R:BoxType></R:bigbox>
             <R:author><R:Name>Hadrian</R:Name></R:author>
             <D:creationdate>1997-12-01T17:42:21-08:00</D:creationdate>
             <D:displayname>Example collection</D:displayname>
             <D:resourcetype><D:collection/></D:resourcetype>
             <D:supportedlock>
               <D:lockentry>
                 <D:lockscope><D:exclusive/></D:lockscope>
                 <D:locktype><D:write/></D:locktype>
               </D:lockentry>
               <D:lockentry>
                 <D:lockscope><D:shared/></D:lockscope>
                 <D:locktype><D:write/></D:locktype>
               </D:lockentry>
             </D:supportedlock>
           </D:prop>

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           <D:status>HTTP/1.1 200 OK</D:status>
         </D:propstat>
       </D:response>
       <D:response>
         <D:href>/container/front.html</D:href>
         <D:propstat>
           <D:prop xmlns:R="http://ns.example.com/boxschema/">
             <R:bigbox><R:BoxType>Box type B</R:BoxType>
             </R:bigbox>
             <D:creationdate>1997-12-01T18:27:21-08:00</D:creationdate>
             <D:displayname>Example HTML resource</D:displayname>
             <D:getcontentlength>4525</D:getcontentlength>
             <D:getcontenttype>text/html</D:getcontenttype>
             <D:getetag>"zzyzx"</D:getetag>
             <D:getlastmodified
               >Mon, 12 Jan 1998 09:25:56 GMT</D:getlastmodified>
             <D:resourcetype/>
             <D:supportedlock>
               <D:lockentry>
                 <D:lockscope><D:exclusive/></D:lockscope>
                 <D:locktype><D:write/></D:locktype>
               </D:lockentry>
               <D:lockentry>
                 <D:lockscope><D:shared/></D:lockscope>
                 <D:locktype><D:write/></D:locktype>
               </D:lockentry>
             </D:supportedlock>
           </D:prop>
           <D:status>HTTP/1.1 200 OK</D:status>
         </D:propstat>
       </D:response>
     </D:multistatus>

   In this example, PROPFIND was invoked on the resource
   http://www.example.com/container/ with a Depth header of 1, meaning
   the request applies to the resource and its children, and a propfind
   XML element containing the allprop XML element, meaning the request
   should return the name and value of all the dead properties defined
   on the resources, plus the name and value of all the properties
   defined in this specification.  This example illustrates the use of
   relative references in the 'href' elements of the response.

   The resource http://www.example.com/container/ has six properties
   defined on it: 'bigbox' and 'author in the
   "http://ns.example.com/boxschema/" namespace, DAV:creationdate, DAV:
   displayname, DAV:resourcetype, and DAV:supportedlock.

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   The last four properties are WebDAV-specific, defined in Section 15.
   Since GET is not supported on this resource, the get* properties
   (e.g., DAV:getcontentlength) are not defined on this resource.  The
   WebDAV-specific properties assert that "container" was created on
   December 1, 1997, at 5:42:21PM, in a time zone 8 hours west of GMT
   (DAV:creationdate), has a name of "Example collection" (DAV:
   displayname), a collection resource type (DAV:resourcetype), and
   supports exclusive write and shared write locks (DAV:supportedlock).

   The resource http://www.example.com/container/front.html has nine
   properties defined on it:

   'bigbox' in the "http://ns.example.com/boxschema/" namespace (another
   instance of the "bigbox" property type), DAV:creationdate, DAV:
   displayname, DAV:getcontentlength, DAV:getcontenttype, DAV:getetag,
   DAV:getlastmodified, DAV:resourcetype, and DAV:supportedlock.

   The DAV-specific properties assert that "front.html" was created on
   December 1, 1997, at 6:27:21PM, in a time zone 8 hours west of GMT
   (DAV:creationdate), has a name of "Example HTML resource" (DAV:
   displayname), a content length of 4525 bytes (DAV:getcontentlength),
   a MIME type of "text/html" (DAV:getcontenttype), an entity tag of
   "zzyzx" (DAV:getetag), was last modified on Monday, January 12, 1998,
   at 09:25:56 GMT (DAV:getlastmodified), has an empty resource type,
   meaning that it is not a collection (DAV:resourcetype), and supports
   both exclusive write and shared write locks (DAV:supportedlock).

9.1.6.  Example - Using 'allprop' with 'include'

   >>Request

     PROPFIND /mycol/ HTTP/1.1
     Host: www.example.com
     Depth: 1
     Content-Type: application/xml; charset="utf-8"
     Content-Length: xxxx

     <?xml version="1.0" encoding="utf-8" ?>
     <D:propfind xmlns:D="DAV:">
       <D:allprop/>
       <D:include>
         <D:supported-live-property-set/>
         <D:supported-report-set/>
       </D:include>
     </D:propfind>

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   In this example, PROPFIND is executed on the resource
   http://www.example.com/mycol/ and its internal member resources.  The
   client requests the values of all live properties defined in this
   specification, plus all dead properties, plus two more live
   properties defined in [RFC3253].  The response is not shown.

9.2.  PROPPATCH Method

   The PROPPATCH method processes instructions specified in the request
   body to set and/or remove properties defined on the resource
   identified by the Request-URI.

   All DAV-compliant resources MUST support the PROPPATCH method and
   MUST process instructions that are specified using the
   propertyupdate, set, and remove XML elements.  Execution of the
   directives in this method is, of course, subject to access control
   constraints.  DAV-compliant resources SHOULD support the setting of
   arbitrary dead properties.

   The request message body of a PROPPATCH method MUST contain the
   propertyupdate XML element.

   Servers MUST process PROPPATCH instructions in document order (an
   exception to the normal rule that ordering is irrelevant).
   Instructions MUST either all be executed or none executed.  Thus, if
   any error occurs during processing, all executed instructions MUST be
   undone and a proper error result returned.  Instruction processing
   details can be found in the definition of the set and remove
   instructions in Sections 14.23 and 14.26.

   If a server attempts to make any of the property changes in a
   PROPPATCH request (i.e., the request is not rejected for high-level
   errors before processing the body), the response MUST be a Multi-
   Status response as described in Section 9.2.1.

   This method is idempotent, but not safe (see Section 9.1 of
   [RFC2616]).  Responses to this method MUST NOT be cached.

9.2.1.  Status Codes for Use in 'propstat' Element

   In PROPPATCH responses, information about individual properties is
   returned inside 'propstat' elements (see Section 14.22), each
   containing an individual 'status' element containing information
   about the properties appearing in it.  The list below summarizes the
   most common status codes used inside 'propstat'; however, clients
   should be prepared to handle other 2/3/4/5xx series status codes as
   well.

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   200 (OK) - The property set or change succeeded.  Note that if this
   appears for one property, it appears for every property in the
   response, due to the atomicity of PROPPATCH.

   403 (Forbidden) - The client, for reasons the server chooses not to
   specify, cannot alter one of the properties.

   403 (Forbidden): The client has attempted to set a protected
   property, such as DAV:getetag.  If returning this error, the server
   SHOULD use the precondition code 'cannot-modify-protected-property'
   inside the response body.

   409 (Conflict) - The client has provided a value whose semantics are
   not appropriate for the property.

   424 (Failed Dependency) - The property change could not be made
   because of another property change that failed.

   507 (Insufficient Storage) - The server did not have sufficient space
   to record the property.

9.2.2.  Example - PROPPATCH

   >>Request

     PROPPATCH /bar.html HTTP/1.1
     Host: www.example.com
     Content-Type: application/xml; charset="utf-8"
     Content-Length: xxxx

     <?xml version="1.0" encoding="utf-8" ?>
     <D:propertyupdate xmlns:D="DAV:"
             xmlns:Z="http://ns.example.com/standards/z39.50/">
       <D:set>
         <D:prop>
           <Z:Authors>
             <Z:Author>Jim Whitehead</Z:Author>
             <Z:Author>Roy Fielding</Z:Author>
           </Z:Authors>
         </D:prop>
       </D:set>
       <D:remove>
         <D:prop><Z:Copyright-Owner/></D:prop>
       </D:remove>
     </D:propertyupdate>

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   >>Response

     HTTP/1.1 207 Multi-Status
     Content-Type: application/xml; charset="utf-8"
     Content-Length: xxxx

     <?xml version="1.0" encoding="utf-8" ?>
     <D:multistatus xmlns:D="DAV:"
             xmlns:Z="http://ns.example.com/standards/z39.50/">
       <D:response>
         <D:href>http://www.example.com/bar.html</D:href>
         <D:propstat>
           <D:prop><Z:Authors/></D:prop>
           <D:status>HTTP/1.1 424 Failed Dependency</D:status>
         </D:propstat>
         <D:propstat>
           <D:prop><Z:Copyright-Owner/></D:prop>
           <D:status>HTTP/1.1 409 Conflict</D:status>
         </D:propstat>
         <D:responsedescription> Copyright Owner cannot be deleted or
           altered.</D:responsedescription>
       </D:response>
     </D:multistatus>

   In this example, the client requests the server to set the value of
   the "Authors" property in the
   "http://ns.example.com/standards/z39.50/" namespace, and to remove
   the property "Copyright-Owner" in the same namespace.  Since the
   Copyright-Owner property could not be removed, no property
   modifications occur.  The 424 (Failed Dependency) status code for the
   Authors property indicates this action would have succeeded if it
   were not for the conflict with removing the Copyright-Owner property.

9.3.  MKCOL Method

   MKCOL creates a new collection resource at the location specified by
   the Request-URI.  If the Request-URI is already mapped to a resource,
   then the MKCOL MUST fail.  During MKCOL processing, a server MUST
   make the Request-URI an internal member of its parent collection,
   unless the Request-URI is "/".  If no such ancestor exists, the
   method MUST fail.  When the MKCOL operation creates a new collection
   resource, all ancestors MUST already exist, or the method MUST fail
   with a 409 (Conflict) status code.  For example, if a request to
   create collection /a/b/c/d/ is made, and /a/b/c/ does not exist, the
   request must fail.

   When MKCOL is invoked without a request body, the newly created
   collection SHOULD have no members.

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   A MKCOL request message may contain a message body.  The precise
   behavior of a MKCOL request when the body is present is undefined,
   but limited to creating collections, members of a collection, bodies
   of members, and properties on the collections or members.  If the
   server receives a MKCOL request entity type it does not support or
   understand, it MUST respond with a 415 (Unsupported Media Type)
   status code.  If the server decides to reject the request based on
   the presence of an entity or the type of an entity, it should use the
   415 (Unsupported Media Type) status code.

   This method is idempotent, but not safe (see Section 9.1 of
   [RFC2616]).  Responses to this method MUST NOT be cached.

9.3.1.  MKCOL Status Codes

   In addition to the general status codes possible, the following
   status codes have specific applicability to MKCOL:

   201 (Created) - The collection was created.

   403 (Forbidden) - This indicates at least one of two conditions: 1)
   the server does not allow the creation of collections at the given
   location in its URL namespace, or 2) the parent collection of the
   Request-URI exists but cannot accept members.

   405 (Method Not Allowed) - MKCOL can only be executed on an unmapped
   URL.

   409 (Conflict) - A collection cannot be made at the Request-URI until
   one or more intermediate collections have been created.  The server
   MUST NOT create those intermediate collections automatically.

   415 (Unsupported Media Type) - The server does not support the
   request body type (although bodies are legal on MKCOL requests, since
   this specification doesn't define any, the server is likely not to
   support any given body type).

   507 (Insufficient Storage) - The resource does not have sufficient
   space to record the state of the resource after the execution of this
   method.

9.3.2.  Example - MKCOL

   This example creates a collection called /webdisc/xfiles/ on the
   server www.example.com.

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   >>Request

     MKCOL /webdisc/xfiles/ HTTP/1.1
     Host: www.example.com

   >>Response

     HTTP/1.1 201 Created

9.4.  GET, HEAD for Collections

   The semantics of GET are unchanged when applied to a collection,
   since GET is defined as, "retrieve whatever information (in the form
   of an entity) is identified by the Request-URI" [RFC2616].  GET, when
   applied to a collection, may return the contents of an "index.html"
   resource, a human-readable view of the contents of the collection, or
   something else altogether.  Hence, it is possible that the result of
   a GET on a collection will bear no correlation to the membership of
   the collection.

   Similarly, since the definition of HEAD is a GET without a response
   message body, the semantics of HEAD are unmodified when applied to
   collection resources.

9.5.  POST for Collections

   Since by definition the actual function performed by POST is
   determined by the server and often depends on the particular
   resource, the behavior of POST when applied to collections cannot be
   meaningfully modified because it is largely undefined.  Thus, the
   semantics of POST are unmodified when applied to a collection.

9.6.  DELETE Requirements

   DELETE is defined in [RFC2616], Section 9.7, to "delete the resource
   identified by the Request-URI".  However, WebDAV changes some DELETE
   handling requirements.

   A server processing a successful DELETE request:

      MUST destroy locks rooted on the deleted resource

      MUST remove the mapping from the Request-URI to any resource.

   Thus, after a successful DELETE operation (and in the absence of
   other actions), a subsequent GET/HEAD/PROPFIND request to the target
   Request-URI MUST return 404 (Not Found).

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9.6.1.  DELETE for Collections

   The DELETE method on a collection MUST act as if a "Depth: infinity"
   header was used on it.  A client MUST NOT submit a Depth header with
   a DELETE on a collection with any value but infinity.

   DELETE instructs that the collection specified in the Request-URI and
   all resources identified by its internal member URLs are to be
   deleted.

   If any resource identified by a member URL cannot be deleted, then
   all of the member's ancestors MUST NOT be deleted, so as to maintain
   URL namespace consistency.

   Any headers included with DELETE MUST be applied in processing every
   resource to be deleted.

   When the DELETE method has completed processing, it MUST result in a
   consistent URL namespace.

   If an error occurs deleting a member resource (a resource other than
   the resource identified in the Request-URI), then the response can be
   a 207 (Multi-Status).  Multi-Status is used here to indicate which
   internal resources could NOT be deleted, including an error code,
   which should help the client understand which resources caused the
   failure.  For example, the Multi-Status body could include a response
   with status 423 (Locked) if an internal resource was locked.

   The server MAY return a 4xx status response, rather than a 207, if
   the request failed completely.

   424 (Failed Dependency) status codes SHOULD NOT be in the 207 (Multi-
   Status) response for DELETE.  They can be safely left out because the
   client will know that the ancestors of a resource could not be
   deleted when the client receives an error for the ancestor's progeny.
   Additionally, 204 (No Content) errors SHOULD NOT be returned in the
   207 (Multi-Status).  The reason for this prohibition is that 204 (No
   Content) is the default success code.

9.6.2.  Example - DELETE

   >>Request

     DELETE  /container/ HTTP/1.1
     Host: www.example.com

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   >>Response

     HTTP/1.1 207 Multi-Status
     Content-Type: application/xml; charset="utf-8"
     Content-Length: xxxx

     <?xml version="1.0" encoding="utf-8" ?>
     <d:multistatus xmlns:d="DAV:">
       <d:response>
         <d:href>http://www.example.com/container/resource3</d:href>
         <d:status>HTTP/1.1 423 Locked</d:status>
         <d:error><d:lock-token-submitted/></d:error>
       </d:response>
     </d:multistatus>

   In this example, the attempt to delete
   http://www.example.com/container/resource3 failed because it is
   locked, and no lock token was submitted with the request.
   Consequently, the attempt to delete http://www.example.com/container/
   also failed.  Thus, the client knows that the attempt to delete
   http://www.example.com/container/ must have also failed since the
   parent cannot be deleted unless its child has also been deleted.
   Even though a Depth header has not been included, a depth of infinity
   is assumed because the method is on a collection.

9.7.  PUT Requirements

9.7.1.  PUT for Non-Collection Resources

   A PUT performed on an existing resource replaces the GET response
   entity of the resource.  Properties defined on the resource may be
   recomputed during PUT processing but are not otherwise affected.  For
   example, if a server recognizes the content type of the request body,
   it may be able to automatically extract information that could be
   profitably exposed as properties.

   A PUT that would result in the creation of a resource without an
   appropriately scoped parent collection MUST fail with a 409
   (Conflict).

   A PUT request allows a client to indicate what media type an entity
   body has, and whether it should change if overwritten.  Thus, a
   client SHOULD provide a Content-Type for a new resource if any is
   known.  If the client does not provide a Content-Type for a new
   resource, the server MAY create a resource with no Content-Type
   assigned, or it MAY attempt to assign a Content-Type.

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   Note that although a recipient ought generally to treat metadata
   supplied with an HTTP request as authoritative, in practice there's
   no guarantee that a server will accept client-supplied metadata
   (e.g., any request header beginning with "Content-").  Many servers
   do not allow configuring the Content-Type on a per-resource basis in
   the first place.  Thus, clients can't always rely on the ability to
   directly influence the content type by including a Content-Type
   request header.

9.7.2.  PUT for Collections

   This specification does not define the behavior of the PUT method for
   existing collections.  A PUT request to an existing collection MAY be
   treated as an error (405 Method Not Allowed).

   The MKCOL method is defined to create collections.

9.8.  COPY Method

   The COPY method creates a duplicate of the source resource identified
   by the Request-URI, in the destination resource identified by the URI
   in the Destination header.  The Destination header MUST be present.
   The exact behavior of the COPY method depends on the type of the
   source resource.

   All WebDAV-compliant resources MUST support the COPY method.
   However, support for the COPY method does not guarantee the ability
   to copy a resource.  For example, separate programs may control
   resources on the same server.  As a result, it may not be possible to
   copy a resource to a location that appears to be on the same server.

   This method is idempotent, but not safe (see Section 9.1 of
   [RFC2616]).  Responses to this method MUST NOT be cached.

9.8.1.  COPY for Non-collection Resources

   When the source resource is not a collection, the result of the COPY
   method is the creation of a new resource at the destination whose
   state and behavior match that of the source resource as closely as
   possible.  Since the environment at the destination may be different
   than at the source due to factors outside the scope of control of the
   server, such as the absence of resources required for correct
   operation, it may not be possible to completely duplicate the
   behavior of the resource at the destination.  Subsequent alterations
   to the destination resource will not modify the source resource.
   Subsequent alterations to the source resource will not modify the
   destination resource.

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9.8.2.  COPY for Properties

   After a successful COPY invocation, all dead properties on the source
   resource SHOULD be duplicated on the destination resource.  Live
   properties described in this document SHOULD be duplicated as
   identically behaving live properties at the destination resource, but
   not necessarily with the same values.  Servers SHOULD NOT convert
   live properties into dead properties on the destination resource,
   because clients may then draw incorrect conclusions about the state
   or functionality of a resource.  Note that some live properties are
   defined such that the absence of the property has a specific meaning
   (e.g., a flag with one meaning if present, and the opposite if
   absent), and in these cases, a successful COPY might result in the
   property being reported as "Not Found" in subsequent requests.

   When the destination is an unmapped URL, a COPY operation creates a
   new resource much like a PUT operation does.  Live properties that
   are related to resource creation (such as DAV:creationdate) should
   have their values set accordingly.

9.8.3.  COPY for Collections

   The COPY method on a collection without a Depth header MUST act as if
   a Depth header with value "infinity" was included.  A client may
   submit a Depth header on a COPY on a collection with a value of "0"
   or "infinity".  Servers MUST support the "0" and "infinity" Depth
   header behaviors on WebDAV-compliant resources.

   An infinite-depth COPY instructs that the collection resource
   identified by the Request-URI is to be copied to the location
   identified by the URI in the Destination header, and all its internal
   member resources are to be copied to a location relative to it,
   recursively through all levels of the collection hierarchy.  Note
   that an infinite-depth COPY of /A/ into /A/B/ could lead to infinite
   recursion if not handled correctly.

   A COPY of "Depth: 0" only instructs that the collection and its
   properties, but not resources identified by its internal member URLs,
   are to be copied.

   Any headers included with a COPY MUST be applied in processing every
   resource to be copied with the exception of the Destination header.

   The Destination header only specifies the destination URI for the
   Request-URI.  When applied to members of the collection identified by
   the Request-URI, the value of Destination is to be modified to
   reflect the current location in the hierarchy.  So, if the Request-
   URI is /a/ with Host header value http://example.com/ and the

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   Destination is http://example.com/b/, then when
   http://example.com/a/c/d is processed, it must use a Destination of
   http://example.com/b/c/d.

   When the COPY method has completed processing, it MUST have created a
   consistent URL namespace at the destination (see Section 5.1 for the
   definition of namespace consistency).  However, if an error occurs
   while copying an internal collection, the server MUST NOT copy any
   resources identified by members of this collection (i.e., the server
   must skip this subtree), as this would create an inconsistent
   namespace.  After detecting an error, the COPY operation SHOULD try
   to finish as much of the original copy operation as possible (i.e.,
   the server should still attempt to copy other subtrees and their
   members that are not descendants of an error-causing collection).

   So, for example, if an infinite-depth copy operation is performed on
   collection /a/, which contains collections /a/b/ and /a/c/, and an
   error occurs copying /a/b/, an attempt should still be made to copy
   /a/c/.  Similarly, after encountering an error copying a non-
   collection resource as part of an infinite-depth copy, the server
   SHOULD try to finish as much of the original copy operation as
   possible.

   If an error in executing the COPY method occurs with a resource other
   than the resource identified in the Request-URI, then the response
   MUST be a 207 (Multi-Status), and the URL of the resource causing the
   failure MUST appear with the specific error.

   The 424 (Failed Dependency) status code SHOULD NOT be returned in the
   207 (Multi-Status) response from a COPY method.  These responses can
   be safely omitted because the client will know that the progeny of a
   resource could not be copied when the client receives an error for
   the parent.  Additionally, 201 (Created)/204 (No Content) status
   codes SHOULD NOT be returned as values in 207 (Multi-Status)
   responses from COPY methods.  They, too, can be safely omitted
   because they are the default success codes.

9.8.4.  COPY and Overwriting Destination Resources

   If a COPY request has an Overwrite header with a value of "F", and a
   resource exists at the Destination URL, the server MUST fail the
   request.

   When a server executes a COPY request and overwrites a destination
   resource, the exact behavior MAY depend on many factors, including
   WebDAV extension capabilities (see particularly [RFC3253]).  For

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   example, when an ordinary resource is overwritten, the server could
   delete the target resource before doing the copy, or could do an in-
   place overwrite to preserve live properties.

   When a collection is overwritten, the membership of the destination
   collection after the successful COPY request MUST be the same
   membership as the source collection immediately before the COPY.
   Thus, merging the membership of the source and destination
   collections together in the destination is not a compliant behavior.

   In general, if clients require the state of the destination URL to be
   wiped out prior to a COPY (e.g., to force live properties to be
   reset), then the client could send a DELETE to the destination before
   the COPY request to ensure this reset.

9.8.5.  Status Codes

   In addition to the general status codes possible, the following
   status codes have specific applicability to COPY:

   201 (Created) - The source resource was successfully copied.  The
   COPY operation resulted in the creation of a new resource.

   204 (No Content) - The source resource was successfully copied to a
   preexisting destination resource.

   207 (Multi-Status) - Multiple resources were to be affected by the
   COPY, but errors on some of them prevented the operation from taking
   place.  Specific error messages, together with the most appropriate
   of the source and destination URLs, appear in the body of the multi-
   status response.  For example, if a destination resource was locked
   and could not be overwritten, then the destination resource URL
   appears with the 423 (Locked) status.

   403 (Forbidden) - The operation is forbidden.  A special case for
   COPY could be that the source and destination resources are the same
   resource.

   409 (Conflict) - A resource cannot be created at the destination
   until one or more intermediate collections have been created.  The
   server MUST NOT create those intermediate collections automatically.

   412 (Precondition Failed) - A precondition header check failed, e.g.,
   the Overwrite header is "F" and the destination URL is already mapped
   to a resource.

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   423 (Locked) - The destination resource, or resource within the
   destination collection, was locked.  This response SHOULD contain the
   'lock-token-submitted' precondition element.

   502 (Bad Gateway) - This may occur when the destination is on another
   server, repository, or URL namespace.  Either the source namespace
   does not support copying to the destination namespace, or the
   destination namespace refuses to accept the resource.  The client may
   wish to try GET/PUT and PROPFIND/PROPPATCH instead.

   507 (Insufficient Storage) - The destination resource does not have
   sufficient space to record the state of the resource after the
   execution of this method.

9.8.6.  Example - COPY with Overwrite

   This example shows resource
   http://www.example.com/~fielding/index.html being copied to the
   location http://www.example.com/users/f/fielding/index.html.  The 204
   (No Content) status code indicates that the existing resource at the
   destination was overwritten.

   >>Request

     COPY /~fielding/index.html HTTP/1.1
     Host: www.example.com
     Destination: http://www.example.com/users/f/fielding/index.html

   >>Response

     HTTP/1.1 204 No Content

9.8.7.  Example - COPY with No Overwrite

   The following example shows the same copy operation being performed,
   but with the Overwrite header set to "F." A response of 412
   (Precondition Failed) is returned because the destination URL is
   already mapped to a resource.

   >>Request

     COPY /~fielding/index.html HTTP/1.1
     Host: www.example.com
     Destination: http://www.example.com/users/f/fielding/index.html
     Overwrite: F

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   >>Response

     HTTP/1.1 412 Precondition Failed

9.8.8.  Example - COPY of a Collection

   >>Request

     COPY /container/ HTTP/1.1
     Host: www.example.com
     Destination: http://www.example.com/othercontainer/
     Depth: infinity

   >>Response

     HTTP/1.1 207 Multi-Status
     Content-Type: application/xml; charset="utf-8"
     Content-Length: xxxx

     <?xml version="1.0" encoding="utf-8" ?>

     <d:multistatus xmlns:d="DAV:">
       <d:response>
         <d:href>http://www.example.com/othercontainer/R2/</d:href>
         <d:status>HTTP/1.1 423 Locked</d:status>
         <d:error><d:lock-token-submitted/></d:error>
       </d:response>
     </d:multistatus>

   The Depth header is unnecessary as the default behavior of COPY on a
   collection is to act as if a "Depth: infinity" header had been
   submitted.  In this example, most of the resources, along with the
   collection, were copied successfully.  However, the collection R2
   failed because the destination R2 is locked.  Because there was an
   error copying R2, none of R2's members were copied.  However, no
   errors were listed for those members due to the error minimization
   rules.

9.9.  MOVE Method

   The MOVE operation on a non-collection resource is the logical
   equivalent of a copy (COPY), followed by consistency maintenance
   processing, followed by a delete of the source, where all three
   actions are performed in a single operation.  The consistency
   maintenance step allows the server to perform updates caused by the
   move, such as updating all URLs, other than the Request-URI that
   identifies the source resource, to point to the new destination
   resource.

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   The Destination header MUST be present on all MOVE methods and MUST
   follow all COPY requirements for the COPY part of the MOVE method.
   All WebDAV-compliant resources MUST support the MOVE method.

   Support for the MOVE method does not guarantee the ability to move a
   resource to a particular destination.  For example, separate programs
   may actually control different sets of resources on the same server.
   Therefore, it may not be possible to move a resource within a
   namespace that appears to belong to the same server.

   If a resource exists at the destination, the destination resource
   will be deleted as a side-effect of the MOVE operation, subject to
   the restrictions of the Overwrite header.

   This method is idempotent, but not safe (see Section 9.1 of
   [RFC2616]).  Responses to this method MUST NOT be cached.

9.9.1.  MOVE for Properties

   Live properties described in this document SHOULD be moved along with
   the resource, such that the resource has identically behaving live
   properties at the destination resource, but not necessarily with the
   same values.  Note that some live properties are defined such that
   the absence of the property has a specific meaning (e.g., a flag with
   one meaning if present, and the opposite if absent), and in these
   cases, a successful MOVE might result in the property being reported
   as "Not Found" in subsequent requests.  If the live properties will
   not work the same way at the destination, the server MAY fail the
   request.

   MOVE is frequently used by clients to rename a file without changing
   its parent collection, so it's not appropriate to reset all live
   properties that are set at resource creation.  For example, the DAV:
   creationdate property value SHOULD remain the same after a MOVE.

   Dead properties MUST be moved along with the resource.

9.9.2.  MOVE for Collections

   A MOVE with "Depth: infinity" instructs that the collection
   identified by the Request-URI be moved to the address specified in
   the Destination header, and all resources identified by its internal
   member URLs are to be moved to locations relative to it, recursively
   through all levels of the collection hierarchy.

   The MOVE method on a collection MUST act as if a "Depth: infinity"
   header was used on it.  A client MUST NOT submit a Depth header on a
   MOVE on a collection with any value but "infinity".

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   Any headers included with MOVE MUST be applied in processing every
   resource to be moved with the exception of the Destination header.
   The behavior of the Destination header is the same as given for COPY
   on collections.

   When the MOVE method has completed processing, it MUST have created a
   consistent URL namespace at both the source and destination (see
   Section 5.1 for the definition of namespace consistency).  However,
   if an error occurs while moving an internal collection, the server
   MUST NOT move any resources identified by members of the failed
   collection (i.e., the server must skip the error-causing subtree), as
   this would create an inconsistent namespace.  In this case, after
   detecting the error, the move operation SHOULD try to finish as much
   of the original move as possible (i.e., the server should still
   attempt to move other subtrees and the resources identified by their
   members that are not descendants of an error-causing collection).
   So, for example, if an infinite-depth move is performed on collection
   /a/, which contains collections /a/b/ and /a/c/, and an error occurs
   moving /a/b/, an attempt should still be made to try moving /a/c/.
   Similarly, after encountering an error moving a non-collection
   resource as part of an infinite-depth move, the server SHOULD try to
   finish as much of the original move operation as possible.

   If an error occurs with a resource other than the resource identified
   in the Request-URI, then the response MUST be a 207 (Multi-Status),
   and the errored resource's URL MUST appear with the specific error.

   The 424 (Failed Dependency) status code SHOULD NOT be returned in the
   207 (Multi-Status) response from a MOVE method.  These errors can be
   safely omitted because the client will know that the progeny of a
   resource could not be moved when the client receives an error for the
   parent.  Additionally, 201 (Created)/204 (No Content) responses
   SHOULD NOT be returned as values in 207 (Multi-Status) responses from
   a MOVE.  These responses can be safely omitted because they are the
   default success codes.

9.9.3.  MOVE and the Overwrite Header

   If a resource exists at the destination and the Overwrite header is
   "T", then prior to performing the move, the server MUST perform a
   DELETE with "Depth: infinity" on the destination resource.  If the
   Overwrite header is set to "F", then the operation will fail.

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9.9.4.  Status Codes

   In addition to the general status codes possible, the following
   status codes have specific applicability to MOVE:

   201 (Created) - The source resource was successfully moved, and a new
   URL mapping was created at the destination.

   204 (No Content) - The source resource was successfully moved to a
   URL that was already mapped.

   207 (Multi-Status) - Multiple resources were to be affected by the
   MOVE, but errors on some of them prevented the operation from taking
   place.  Specific error messages, together with the most appropriate
   of the source and destination URLs, appear in the body of the multi-
   status response.  For example, if a source resource was locked and
   could not be moved, then the source resource URL appears with the 423
   (Locked) status.

   403 (Forbidden) - Among many possible reasons for forbidding a MOVE
   operation, this status code is recommended for use when the source
   and destination resources are the same.

   409 (Conflict) - A resource cannot be created at the destination
   until one or more intermediate collections have been created.  The
   server MUST NOT create those intermediate collections automatically.
   Or, the server was unable to preserve the behavior of the live
   properties and still move the resource to the destination (see
   'preserved-live-properties' postcondition).

   412 (Precondition Failed) - A condition header failed.  Specific to
   MOVE, this could mean that the Overwrite header is "F" and the
   destination URL is already mapped to a resource.

   423 (Locked) - The source or the destination resource, the source or
   destination resource parent, or some resource within the source or
   destination collection, was locked.  This response SHOULD contain the
   'lock-token-submitted' precondition element.

   502 (Bad Gateway) - This may occur when the destination is on another
   server and the destination server refuses to accept the resource.
   This could also occur when the destination is on another sub-section
   of the same server namespace.

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9.9.5.  Example - MOVE of a Non-Collection

   This example shows resource
   http://www.example.com/~fielding/index.html being moved to the
   location http://www.example.com/users/f/fielding/index.html.  The
   contents of the destination resource would have been overwritten if
   the destination URL was already mapped to a resource.  In this case,
   since there was nothing at the destination resource, the response
   code is 201 (Created).

   >>Request

     MOVE /~fielding/index.html HTTP/1.1
     Host: www.example.com
     Destination: http://www.example/users/f/fielding/index.html

   >>Response

     HTTP/1.1 201 Created
     Location: http://www.example.com/users/f/fielding/index.html

9.9.6.  Example - MOVE of a Collection

   >>Request

     MOVE /container/ HTTP/1.1
     Host: www.example.com
     Destination: http://www.example.com/othercontainer/
     Overwrite: F
     If: (<urn:uuid:fe184f2e-6eec-41d0-c765-01adc56e6bb4>)
        (<urn:uuid:e454f3f3-acdc-452a-56c7-00a5c91e4b77>)

   >>Response

     HTTP/1.1 207 Multi-Status
     Content-Type: application/xml; charset="utf-8"
     Content-Length: xxxx

     <?xml version="1.0" encoding="utf-8" ?>
     <d:multistatus xmlns:d='DAV:'>
       <d:response>
         <d:href>http://www.example.com/othercontainer/C2/</d:href>
         <d:status>HTTP/1.1 423 Locked</d:status>
         <d:error><d:lock-token-submitted/></d:error>
       </d:response>
     </d:multistatus>

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   In this example, the client has submitted a number of lock tokens
   with the request.  A lock token will need to be submitted for every
   resource, both source and destination, anywhere in the scope of the
   method, that is locked.  In this case, the proper lock token was not
   submitted for the destination
   http://www.example.com/othercontainer/C2/.  This means that the
   resource /container/C2/ could not be moved.  Because there was an
   error moving /container/C2/, none of /container/C2's members were
   moved.  However, no errors were listed for those members due to the
   error minimization rules.  User agent authentication has previously
   occurred via a mechanism outside the scope of the HTTP protocol, in
   an underlying transport layer.

9.10.  LOCK Method

   The following sections describe the LOCK method, which is used to
   take out a lock of any access type and to refresh an existing lock.
   These sections on the LOCK method describe only those semantics that
   are specific to the LOCK method and are independent of the access
   type of the lock being requested.

   Any resource that supports the LOCK method MUST, at minimum, support
   the XML request and response formats defined herein.

   This method is neither idempotent nor safe (see Section 9.1 of
   [RFC2616]).  Responses to this method MUST NOT be cached.

9.10.1.  Creating a Lock on an Existing Resource

   A LOCK request to an existing resource will create a lock on the
   resource identified by the Request-URI, provided the resource is not
   already locked with a conflicting lock.  The resource identified in
   the Request-URI becomes the root of the lock.  LOCK method requests
   to create a new lock MUST have an XML request body.  The server MUST
   preserve the information provided by the client in the 'owner'
   element in the LOCK request.  The LOCK request MAY have a Timeout
   header.

   When a new lock is created, the LOCK response:

   o  MUST contain a body with the value of the DAV:lockdiscovery
      property in a prop XML element.  This MUST contain the full
      information about the lock just granted, while information about
      other (shared) locks is OPTIONAL.

   o  MUST include the Lock-Token response header with the token
      associated with the new lock.

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9.10.2.  Refreshing Locks

   A lock is refreshed by sending a LOCK request to the URL of a
   resource within the scope of the lock.  This request MUST NOT have a
   body and it MUST specify which lock to refresh by using the 'If'
   header with a single lock token (only one lock may be refreshed at a
   time).  The request MAY contain a Timeout header, which a server MAY
   accept to change the duration remaining on the lock to the new value.
   A server MUST ignore the Depth header on a LOCK refresh.

   If the resource has other (shared) locks, those locks are unaffected
   by a lock refresh.  Additionally, those locks do not prevent the
   named lock from being refreshed.

   The Lock-Token header is not returned in the response for a
   successful refresh LOCK request, but the LOCK response body MUST
   contain the new value for the DAV:lockdiscovery property.

9.10.3.  Depth and Locking

   The Depth header may be used with the LOCK method.  Values other than
   0 or infinity MUST NOT be used with the Depth header on a LOCK
   method.  All resources that support the LOCK method MUST support the
   Depth header.

   A Depth header of value 0 means to just lock the resource specified
   by the Request-URI.

   If the Depth header is set to infinity, then the resource specified
   in the Request-URI along with all its members, all the way down the
   hierarchy, are to be locked.  A successful result MUST return a
   single lock token.  Similarly, if an UNLOCK is successfully executed
   on this token, all associated resources are unlocked.  Hence, partial
   success is not an option for LOCK or UNLOCK.  Either the entire
   hierarchy is locked or no resources are locked.

   If the lock cannot be granted to all resources, the server MUST
   return a Multi-Status response with a 'response' element for at least
   one resource that prevented the lock from being granted, along with a
   suitable status code for that failure (e.g., 403 (Forbidden) or 423
   (Locked)).  Additionally, if the resource causing the failure was not
   the resource requested, then the server SHOULD include a 'response'
   element for the Request-URI as well, with a 'status' element
   containing 424 Failed Dependency.

   If no Depth header is submitted on a LOCK request, then the request
   MUST act as if a "Depth:infinity" had been submitted.

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9.10.4.  Locking Unmapped URLs

   A successful LOCK method MUST result in the creation of an empty
   resource that is locked (and that is not a collection) when a
   resource did not previously exist at that URL.  Later on, the lock
   may go away but the empty resource remains.  Empty resources MUST
   then appear in PROPFIND responses including that URL in the response
   scope.  A server MUST respond successfully to a GET request to an
   empty resource, either by using a 204 No Content response, or by
   using 200 OK with a Content-Length header indicating zero length

9.10.5.  Lock Compatibility Table

   The table below describes the behavior that occurs when a lock
   request is made on a resource.

     +--------------------------+----------------+-------------------+
     | Current State            | Shared Lock OK | Exclusive Lock OK |
     +--------------------------+----------------+-------------------+
     | None                     | True           | True              |
     | Shared Lock              | True           | False             |
     | Exclusive Lock           | False          | False*            |
     +--------------------------+----------------+-------------------+

   Legend: True = lock may be granted.  False = lock MUST NOT be
   granted. *=It is illegal for a principal to request the same lock
   twice.

   The current lock state of a resource is given in the leftmost column,
   and lock requests are listed in the first row.  The intersection of a
   row and column gives the result of a lock request.  For example, if a
   shared lock is held on a resource, and an exclusive lock is
   requested, the table entry is "false", indicating that the lock must
   not be granted.

9.10.6.  LOCK Responses

   In addition to the general status codes possible, the following
   status codes have specific applicability to LOCK:

   200 (OK) - The LOCK request succeeded and the value of the DAV:
   lockdiscovery property is included in the response body.

   201 (Created) - The LOCK request was to an unmapped URL, the request
   succeeded and resulted in the creation of a new resource, and the
   value of the DAV:lockdiscovery property is included in the response
   body.

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   409 (Conflict) - A resource cannot be created at the destination
   until one or more intermediate collections have been created.  The
   server MUST NOT create those intermediate collections automatically.

   423 (Locked), potentially with 'no-conflicting-lock' precondition
   code - There is already a lock on the resource that is not compatible
   with the requested lock (see lock compatibility table above).

   412 (Precondition Failed), with 'lock-token-matches-request-uri'
   precondition code - The LOCK request was made with an If header,
   indicating that the client wishes to refresh the given lock.
   However, the Request-URI did not fall within the scope of the lock
   identified by the token.  The lock may have a scope that does not
   include the Request-URI, or the lock could have disappeared, or the
   token may be invalid.

9.10.7.  Example - Simple Lock Request

   >>Request

     LOCK /workspace/webdav/proposal.doc HTTP/1.1
     Host: example.com
     Timeout: Infinite, Second-4100000000
     Content-Type: application/xml; charset="utf-8"
     Content-Length: xxxx
     Authorization: Digest username="ejw",
       realm="ejw@example.com", nonce="...",
       uri="/workspace/webdav/proposal.doc",
       response="...", opaque="..."

     <?xml version="1.0" encoding="utf-8" ?>
     <D:lockinfo xmlns:D='DAV:'>
       <D:lockscope><D:exclusive/></D:lockscope>
       <D:locktype><D:write/></D:locktype>
       <D:owner>
         <D:href>http://example.org/~ejw/contact.html</D:href>
       </D:owner>
     </D:lockinfo>

   >>Response

     HTTP/1.1 200 OK
     Lock-Token: <urn:uuid:e71d4fae-5dec-22d6-fea5-00a0c91e6be4>
     Content-Type: application/xml; charset="utf-8"
     Content-Length: xxxx

     <?xml version="1.0" encoding="utf-8" ?>
     <D:prop xmlns:D="DAV:">

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       <D:lockdiscovery>
         <D:activelock>
           <D:locktype><D:write/></D:locktype>
           <D:lockscope><D:exclusive/></D:lockscope>
           <D:depth>infinity</D:depth>
           <D:owner>
             <D:href>http://example.org/~ejw/contact.html</D:href>
           </D:owner>
           <D:timeout>Second-604800</D:timeout>
           <D:locktoken>
             <D:href
             >urn:uuid:e71d4fae-5dec-22d6-fea5-00a0c91e6be4</D:href>
           </D:locktoken>
           <D:lockroot>
             <D:href
             >http://example.com/workspace/webdav/proposal.doc</D:href>
           </D:lockroot>
         </D:activelock>
       </D:lockdiscovery>
     </D:prop>

   This example shows the successful creation of an exclusive write lock
   on resource http://example.com/workspace/webdav/proposal.doc.  The
   resource http://example.org/~ejw/contact.html contains contact
   information for the creator of the lock.  The server has an activity-
   based timeout policy in place on this resource, which causes the lock
   to automatically be removed after 1 week (604800 seconds).  Note that
   the nonce, response, and opaque fields have not been calculated in
   the Authorization request header.

9.10.8.  Example - Refreshing a Write Lock

   >>Request

     LOCK /workspace/webdav/proposal.doc HTTP/1.1
     Host: example.com
     Timeout: Infinite, Second-4100000000
     If: (<urn:uuid:e71d4fae-5dec-22d6-fea5-00a0c91e6be4>)
     Authorization: Digest username="ejw",
       realm="ejw@example.com", nonce="...",
       uri="/workspace/webdav/proposal.doc",
       response="...", opaque="..."

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   >>Response

     HTTP/1.1 200 OK
     Content-Type: application/xml; charset="utf-8"
     Content-Length: xxxx

     <?xml version="1.0" encoding="utf-8" ?>
     <D:prop xmlns:D="DAV:">
       <D:lockdiscovery>
         <D:activelock>
           <D:locktype><D:write/></D:locktype>
           <D:lockscope><D:exclusive/></D:lockscope>
           <D:depth>infinity</D:depth>
           <D:owner>
             <D:href>http://example.org/~ejw/contact.html</D:href>
           </D:owner>
           <D:timeout>Second-604800</D:timeout>
           <D:locktoken>
             <D:href
             >urn:uuid:e71d4fae-5dec-22d6-fea5-00a0c91e6be4</D:href>
           </D:locktoken>
           <D:lockroot>
             <D:href
             >http://example.com/workspace/webdav/proposal.doc</D:href>
           </D:lockroot>
         </D:activelock>
       </D:lockdiscovery>
     </D:prop>

   This request would refresh the lock, attempting to reset the timeout
   to the new value specified in the timeout header.  Notice that the
   client asked for an infinite time out but the server choose to ignore
   the request.  In this example, the nonce, response, and opaque fields
   have not been calculated in the Authorization request header.

9.10.9.  Example - Multi-Resource Lock Request

   >>Request

     LOCK /webdav/ HTTP/1.1
     Host: example.com
     Timeout: Infinite, Second-4100000000
     Depth: infinity
     Content-Type: application/xml; charset="utf-8"
     Content-Length: xxxx
     Authorization: Digest username="ejw",
       realm="ejw@example.com", nonce="...",

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       uri="/workspace/webdav/proposal.doc",
       response="...", opaque="..."

     <?xml version="1.0" encoding="utf-8" ?>
     <D:lockinfo xmlns:D="DAV:">
       <D:locktype><D:write/></D:locktype>
       <D:lockscope><D:exclusive/></D:lockscope>
       <D:owner>
         <D:href>http://example.org/~ejw/contact.html</D:href>
       </D:owner>
     </D:lockinfo>

   >>Response

     HTTP/1.1 207 Multi-Status
     Content-Type: application/xml; charset="utf-8"
     Content-Length: xxxx

     <?xml version="1.0" encoding="utf-8" ?>
     <D:multistatus xmlns:D="DAV:">
       <D:response>
         <D:href>http://example.com/webdav/secret</D:href>
         <D:status>HTTP/1.1 403 Forbidden</D:status>
       </D:response>
       <D:response>
         <D:href>http://example.com/webdav/</D:href>
         <D:status>HTTP/1.1 424 Failed Dependency</D:status>
       </D:response>
     </D:multistatus>

   This example shows a request for an exclusive write lock on a
   collection and all its children.  In this request, the client has
   specified that it desires an infinite-length lock, if available,
   otherwise a timeout of 4.1 billion seconds, if available.  The
   request entity body contains the contact information for the
   principal taking out the lock -- in this case, a Web page URL.

   The error is a 403 (Forbidden) response on the resource
   http://example.com/webdav/secret.  Because this resource could not be
   locked, none of the resources were locked.  Note also that the a
   'response' element for the Request-URI itself has been included as
   required.

   In this example, the nonce, response, and opaque fields have not been
   calculated in the Authorization request header.

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9.11.  UNLOCK Method

   The UNLOCK method removes the lock identified by the lock token in
   the Lock-Token request header.  The Request-URI MUST identify a
   resource within the scope of the lock.

   Note that use of the Lock-Token header to provide the lock token is
   not consistent with other state-changing methods, which all require
   an If header with the lock token.  Thus, the If header is not needed
   to provide the lock token.  Naturally, when the If header is present,
   it has its normal meaning as a conditional header.

   For a successful response to this method, the server MUST delete the
   lock entirely.

   If all resources that have been locked under the submitted lock token
   cannot be unlocked, then the UNLOCK request MUST fail.

   A successful response to an UNLOCK method does not mean that the
   resource is necessarily unlocked.  It means that the specific lock
   corresponding to the specified token no longer exists.

   Any DAV-compliant resource that supports the LOCK method MUST support
   the UNLOCK method.

   This method is idempotent, but not safe (see Section 9.1 of
   [RFC2616]).  Responses to this method MUST NOT be cached.

9.11.1.  Status Codes

   In addition to the general status codes possible, the following
   status codes have specific applicability to UNLOCK:

   204 (No Content) - Normal success response (rather than 200 OK, since
   200 OK would imply a response body, and an UNLOCK success response
   does not normally contain a body).

   400 (Bad Request) - No lock token was provided.

   403 (Forbidden) - The currently authenticated principal does not have
   permission to remove the lock.

   409 (Conflict), with 'lock-token-matches-request-uri' precondition -
   The resource was not locked, or the request was made to a Request-URI
   that was not within the scope of the lock.

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9.11.2.  Example - UNLOCK

   >>Request

     UNLOCK /workspace/webdav/info.doc HTTP/1.1
     Host: example.com
     Lock-Token: <urn:uuid:a515cfa4-5da4-22e1-f5b5-00a0451e6bf7>
     Authorization: Digest username="ejw"
       realm="ejw@example.com", nonce="...",
       uri="/workspace/webdav/proposal.doc",
       response="...", opaque="..."

   >>Response

     HTTP/1.1 204 No Content

   In this example, the lock identified by the lock token
   "urn:uuid:a515cfa4-5da4-22e1-f5b5-00a0451e6bf7" is successfully
   removed from the resource
   http://example.com/workspace/webdav/info.doc.  If this lock included
   more than just one resource, the lock is removed from all resources
   included in the lock.

   In this example, the nonce, response, and opaque fields have not been
   calculated in the Authorization request header.

10.  HTTP Headers for Distributed Authoring

   All DAV headers follow the same basic formatting rules as HTTP
   headers.  This includes rules like line continuation and how to
   combine (or separate) multiple instances of the same header using
   commas.

   WebDAV adds two new conditional headers to the set defined in HTTP:
   the If and Overwrite headers.

10.1.  DAV Header

    DAV              = "DAV" ":" #( compliance-class )
    compliance-class = ( "1" | "2" | "3" | extend )
    extend           = Coded-URL | token
                       ; token is defined in RFC 2616, Section 2.2
    Coded-URL        = "<" absolute-URI ">"
                       ; No linear whitespace (LWS) allowed in Coded-URL
                       ; absolute-URI defined in RFC 3986, Section 4.3

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   This general-header appearing in the response indicates that the
   resource supports the DAV schema and protocol as specified.  All DAV-
   compliant resources MUST return the DAV header with compliance-class
   "1" on all OPTIONS responses.  In cases where WebDAV is only
   supported in part of the server namespace, an OPTIONS request to non-
   WebDAV resources (including "/") SHOULD NOT advertise WebDAV support.

   The value is a comma-separated list of all compliance class
   identifiers that the resource supports.  Class identifiers may be
   Coded-URLs or tokens (as defined by [RFC2616]).  Identifiers can
   appear in any order.  Identifiers that are standardized through the
   IETF RFC process are tokens, but other identifiers SHOULD be Coded-
   URLs to encourage uniqueness.

   A resource must show class 1 compliance if it shows class 2 or 3
   compliance.  In general, support for one compliance class does not
   entail support for any other, and in particular, support for
   compliance class 3 does not require support for compliance class 2.
   Please refer to Section 18 for more details on compliance classes
   defined in this specification.

   Note that many WebDAV servers do not advertise WebDAV support in
   response to "OPTIONS *".

   As a request header, this header allows the client to advertise
   compliance with named features when the server needs that
   information.  Clients SHOULD NOT send this header unless a standards
   track specification requires it.  Any extension that makes use of
   this as a request header will need to carefully consider caching
   implications.

10.2.  Depth Header

      Depth = "Depth" ":" ("0" | "1" | "infinity")

   The Depth request header is used with methods executed on resources
   that could potentially have internal members to indicate whether the
   method is to be applied only to the resource ("Depth: 0"), to the
   resource and its internal members only ("Depth: 1"), or the resource
   and all its members ("Depth: infinity").

   The Depth header is only supported if a method's definition
   explicitly provides for such support.

   The following rules are the default behavior for any method that
   supports the Depth header.  A method may override these defaults by
   defining different behavior in its definition.

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   Methods that support the Depth header may choose not to support all
   of the header's values and may define, on a case-by-case basis, the
   behavior of the method if a Depth header is not present.  For
   example, the MOVE method only supports "Depth: infinity", and if a
   Depth header is not present, it will act as if a "Depth: infinity"
   header had been applied.

   Clients MUST NOT rely upon methods executing on members of their
   hierarchies in any particular order or on the execution being atomic
   unless the particular method explicitly provides such guarantees.

   Upon execution, a method with a Depth header will perform as much of
   its assigned task as possible and then return a response specifying
   what it was able to accomplish and what it failed to do.

   So, for example, an attempt to COPY a hierarchy may result in some of
   the members being copied and some not.

   By default, the Depth header does not interact with other headers.
   That is, each header on a request with a Depth header MUST be applied
   only to the Request-URI if it applies to any resource, unless
   specific Depth behavior is defined for that header.

   If a source or destination resource within the scope of the Depth
   header is locked in such a way as to prevent the successful execution
   of the method, then the lock token for that resource MUST be
   submitted with the request in the If request header.

   The Depth header only specifies the behavior of the method with
   regards to internal members.  If a resource does not have internal
   members, then the Depth header MUST be ignored.

10.3.  Destination Header

   The Destination request header specifies the URI that identifies a
   destination resource for methods such as COPY and MOVE, which take
   two URIs as parameters.

      Destination = "Destination" ":" Simple-ref

   If the Destination value is an absolute-URI (Section 4.3 of
   [RFC3986]), it may name a different server (or different port or
   scheme).  If the source server cannot attempt a copy to the remote
   server, it MUST fail the request.  Note that copying and moving
   resources to remote servers is not fully defined in this
   specification (e.g., specific error conditions).

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   If the Destination value is too long or otherwise unacceptable, the
   server SHOULD return 400 (Bad Request), ideally with helpful
   information in an error body.

10.4.  If Header

   The If request header is intended to have similar functionality to
   the If-Match header defined in Section 14.24 of [RFC2616].  However,
   the If header handles any state token as well as ETags.  A typical
   example of a state token is a lock token, and lock tokens are the
   only state tokens defined in this specification.

10.4.1.  Purpose

   The If header has two distinct purposes:

   o  The first purpose is to make a request conditional by supplying a
      series of state lists with conditions that match tokens and ETags
      to a specific resource.  If this header is evaluated and all state
      lists fail, then the request MUST fail with a 412 (Precondition
      Failed) status.  On the other hand, the request can succeed only
      if one of the described state lists succeeds.  The success
      criteria for state lists and matching functions are defined in
      Sections 10.4.3 and 10.4.4.

   o  Additionally, the mere fact that a state token appears in an If
      header means that it has been "submitted" with the request.  In
      general, this is used to indicate that the client has knowledge of
      that state token.  The semantics for submitting a state token
      depend on its type (for lock tokens, please refer to Section 6).

   Note that these two purposes need to be treated distinctly: a state
   token counts as being submitted independently of whether the server
   actually has evaluated the state list it appears in, and also
   independently of whether or not the condition it expressed was found
   to be true.

10.4.2.  Syntax

     If = "If" ":" ( 1*No-tag-list | 1*Tagged-list )

     No-tag-list = List
     Tagged-list = Resource-Tag 1*List

     List = "(" 1*Condition ")"
     Condition = ["Not"] (State-token | "[" entity-tag "]")
     ; entity-tag: see Section 3.11 of [RFC2616]
     ; No LWS allowed between "[", entity-tag and "]"

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     State-token = Coded-URL

     Resource-Tag = "<" Simple-ref ">"
     ; Simple-ref: see Section 8.3
     ; No LWS allowed in Resource-Tag

   The syntax distinguishes between untagged lists ("No-tag-list") and
   tagged lists ("Tagged-list").  Untagged lists apply to the resource
   identified by the Request-URI, while tagged lists apply to the
   resource identified by the preceding Resource-Tag.

   A Resource-Tag applies to all subsequent Lists, up to the next
   Resource-Tag.

   Note that the two list types cannot be mixed within an If header.
   This is not a functional restriction because the No-tag-list syntax
   is just a shorthand notation for a Tagged-list production with a
   Resource-Tag referring to the Request-URI.

   Each List consists of one or more Conditions.  Each Condition is
   defined in terms of an entity-tag or state-token, potentially negated
   by the prefix "Not".

   Note that the If header syntax does not allow multiple instances of
   If headers in a single request.  However, the HTTP header syntax
   allows extending single header values across multiple lines, by
   inserting a line break followed by whitespace (see [RFC2616], Section
   4.2).

10.4.3.  List Evaluation

   A Condition that consists of a single entity-tag or state-token
   evaluates to true if the resource matches the described state (where
   the individual matching functions are defined below in
   Section 10.4.4).  Prefixing it with "Not" reverses the result of the
   evaluation (thus, the "Not" applies only to the subsequent entity-tag
   or state-token).

   Each List production describes a series of conditions.  The whole
   list evaluates to true if and only if each condition evaluates to
   true (that is, the list represents a logical conjunction of
   Conditions).

   Each No-tag-list and Tagged-list production may contain one or more
   Lists.  They evaluate to true if and only if any of the contained
   lists evaluates to true (that is, if there's more than one List, that
   List sequence represents a logical disjunction of the Lists).

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   Finally, the whole If header evaluates to true if and only if at
   least one of the No-tag-list or Tagged-list productions evaluates to
   true.  If the header evaluates to false, the server MUST reject the
   request with a 412 (Precondition Failed) status.  Otherwise,
   execution of the request can proceed as if the header wasn't present.

10.4.4.  Matching State Tokens and ETags

   When performing If header processing, the definition of a matching
   state token or entity tag is as follows:

   Identifying a resource: The resource is identified by the URI along
   with the token, in tagged list production, or by the Request-URI in
   untagged list production.

   Matching entity tag: Where the entity tag matches an entity tag
   associated with the identified resource.  Servers MUST use either the
   weak or the strong comparison function defined in Section 13.3.3 of
   [RFC2616].

   Matching state token: Where there is an exact match between the state
   token in the If header and any state token on the identified
   resource.  A lock state token is considered to match if the resource
   is anywhere in the scope of the lock.

   Handling unmapped URLs: For both ETags and state tokens, treat as if
   the URL identified a resource that exists but does not have the
   specified state.

10.4.5.  If Header and Non-DAV-Aware Proxies

   Non-DAV-aware proxies will not honor the If header, since they will
   not understand the If header, and HTTP requires non-understood
   headers to be ignored.  When communicating with HTTP/1.1 proxies, the
   client MUST use the "Cache-Control: no-cache" request header so as to
   prevent the proxy from improperly trying to service the request from
   its cache.  When dealing with HTTP/1.0 proxies, the "Pragma: no-
   cache" request header MUST be used for the same reason.

   Because in general clients may not be able to reliably detect non-
   DAV-aware intermediates, they are advised to always prevent caching
   using the request directives mentioned above.

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10.4.6.  Example - No-tag Production

     If: (<urn:uuid:181d4fae-7d8c-11d0-a765-00a0c91e6bf2>
       ["I am an ETag"])
       (["I am another ETag"])

   The previous header would require that the resource identified in the
   Request-URI be locked with the specified lock token and be in the
   state identified by the "I am an ETag" ETag or in the state
   identified by the second ETag "I am another ETag".

   To put the matter more plainly one can think of the previous If
   header as expressing the condition below:

     (
       is-locked-with(urn:uuid:181d4fae-7d8c-11d0-a765-00a0c91e6bf2) AND
       matches-etag("I am an ETag")
     )
     OR
     (
       matches-etag("I am another ETag")
     )

10.4.7.  Example - Using "Not" with No-tag Production

     If: (Not <urn:uuid:181d4fae-7d8c-11d0-a765-00a0c91e6bf2>
     <urn:uuid:58f202ac-22cf-11d1-b12d-002035b29092>)

   This If header requires that the resource must not be locked with a
   lock having the lock token
   urn:uuid:181d4fae-7d8c-11d0-a765-00a0c91e6bf2 and must be locked by a
   lock with the lock token
   urn:uuid:58f202ac-22cf-11d1-b12d-002035b29092.

10.4.8.  Example - Causing a Condition to Always Evaluate to True

   There may be cases where a client wishes to submit state tokens, but
   doesn't want the request to fail just because the state token isn't
   current anymore.  One simple way to do this is to include a Condition
   that is known to always evaluate to true, such as in:

     If: (<urn:uuid:181d4fae-7d8c-11d0-a765-00a0c91e6bf2>)
       (Not <DAV:no-lock>)

   "DAV:no-lock" is known to never represent a current lock token.  Lock
   tokens are assigned by the server, following the uniqueness
   requirements described in Section 6.5, therefore cannot use the
   "DAV:" scheme.  Thus, by applying "Not" to a state token that is

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   known not to be current, the Condition always evaluates to true.
   Consequently, the whole If header will always evaluate to true, and
   the lock token urn:uuid:181d4fae-7d8c-11d0-a765-00a0c91e6bf2 will be
   submitted in any case.

10.4.9.  Example - Tagged List If Header in COPY

   >>Request

     COPY /resource1 HTTP/1.1
     Host: www.example.com
     Destination: /resource2
     If: </resource1>
       (<urn:uuid:181d4fae-7d8c-11d0-a765-00a0c91e6bf2>
       [W/"A weak ETag"]) (["strong ETag"])

   In this example, http://www.example.com/resource1 is being copied to
   http://www.example.com/resource2.  When the method is first applied
   to http://www.example.com/resource1, resource1 must be in the state
   specified by "(<urn:uuid:181d4fae-7d8c-11d0-a765-00a0c91e6bf2> [W/"A
   weak ETag"]) (["strong ETag"])".  That is, either it must be locked
   with a lock token of "urn:uuid:181d4fae-7d8c-11d0-a765-00a0c91e6bf2"
   and have a weak entity tag W/"A weak ETag" or it must have a strong
   entity tag "strong ETag".

10.4.10.  Example - Matching Lock Tokens with Collection Locks

     DELETE /specs/rfc2518.txt HTTP/1.1
     Host: www.example.com
     If: <http://www.example.com/specs/>
       (<urn:uuid:181d4fae-7d8c-11d0-a765-00a0c91e6bf2>)

   For this example, the lock token must be compared to the identified
   resource, which is the 'specs' collection identified by the URL in
   the tagged list production.  If the 'specs' collection is not locked
   by a lock with the specified lock token, the request MUST fail.
   Otherwise, this request could succeed, because the If header
   evaluates to true, and because the lock token for the lock affecting
   the affected resource has been submitted.

10.4.11.  Example - Matching ETags on Unmapped URLs

   Consider a collection "/specs" that does not contain the member
   "/specs/rfc2518.doc".  In this case, the If header

     If: </specs/rfc2518.doc> (["4217"])

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   will evaluate to false (the URI isn't mapped, thus the resource
   identified by the URI doesn't have an entity matching the ETag
   "4217").

   On the other hand, an If header of

     If: </specs/rfc2518.doc> (Not ["4217"])

   will consequently evaluate to true.

   Note that, as defined above in Section 10.4.4, the same
   considerations apply to matching state tokens.

10.5.  Lock-Token Header

      Lock-Token = "Lock-Token" ":" Coded-URL

   The Lock-Token request header is used with the UNLOCK method to
   identify the lock to be removed.  The lock token in the Lock-Token
   request header MUST identify a lock that contains the resource
   identified by Request-URI as a member.

   The Lock-Token response header is used with the LOCK method to
   indicate the lock token created as a result of a successful LOCK
   request to create a new lock.

10.6.  Overwrite Header

      Overwrite = "Overwrite" ":" ("T" | "F")

   The Overwrite request header specifies whether the server should
   overwrite a resource mapped to the destination URL during a COPY or
   MOVE.  A value of "F" states that the server must not perform the
   COPY or MOVE operation if the destination URL does map to a resource.
   If the overwrite header is not included in a COPY or MOVE request,
   then the resource MUST treat the request as if it has an overwrite
   header of value "T".  While the Overwrite header appears to duplicate
   the functionality of using an "If-Match: *" header (see [RFC2616]),
   If-Match applies only to the Request-URI, and not to the Destination
   of a COPY or MOVE.

   If a COPY or MOVE is not performed due to the value of the Overwrite
   header, the method MUST fail with a 412 (Precondition Failed) status
   code.  The server MUST do authorization checks before checking this
   or any conditional header.

   All DAV-compliant resources MUST support the Overwrite header.

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10.7.  Timeout Request Header

      TimeOut = "Timeout" ":" 1#TimeType
      TimeType = ("Second-" DAVTimeOutVal | "Infinite")
                 ; No LWS allowed within TimeType
      DAVTimeOutVal = 1*DIGIT

   Clients MAY include Timeout request headers in their LOCK requests.
   However, the server is not required to honor or even consider these
   requests.  Clients MUST NOT submit a Timeout request header with any
   method other than a LOCK method.

   The "Second" TimeType specifies the number of seconds that will
   elapse between granting of the lock at the server, and the automatic
   removal of the lock.  The timeout value for TimeType "Second" MUST
   NOT be greater than 2^32-1.

   See Section 6.6 for a description of lock timeout behavior.

11.  Status Code Extensions to HTTP/1.1

   The following status codes are added to those defined in HTTP/1.1
   [RFC2616].

11.1.  207 Multi-Status

   The 207 (Multi-Status) status code provides status for multiple
   independent operations (see Section 13 for more information).

11.2.  422 Unprocessable Entity

   The 422 (Unprocessable Entity) status code means the server
   understands the content type of the request entity (hence a
   415(Unsupported Media Type) status code is inappropriate), and the
   syntax of the request entity is correct (thus a 400 (Bad Request)
   status code is inappropriate) but was unable to process the contained
   instructions.  For example, this error condition may occur if an XML
   request body contains well-formed (i.e., syntactically correct), but
   semantically erroneous, XML instructions.

11.3.  423 Locked

   The 423 (Locked) status code means the source or destination resource
   of a method is locked.  This response SHOULD contain an appropriate
   precondition or postcondition code, such as 'lock-token-submitted' or
   'no-conflicting-lock'.

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11.4.  424 Failed Dependency

   The 424 (Failed Dependency) status code means that the method could
   not be performed on the resource because the requested action
   depended on another action and that action failed.  For example, if a
   command in a PROPPATCH method fails, then, at minimum, the rest of
   the commands will also fail with 424 (Failed Dependency).

11.5.  507 Insufficient Storage

   The 507 (Insufficient Storage) status code means the method could not
   be performed on the resource because the server is unable to store
   the representation needed to successfully complete the request.  This
   condition is considered to be temporary.  If the request that
   received this status code was the result of a user action, the
   request MUST NOT be repeated until it is requested by a separate user
   action.

12.  Use of HTTP Status Codes

   These HTTP codes are not redefined, but their use is somewhat
   extended by WebDAV methods and requirements.  In general, many HTTP
   status codes can be used in response to any request, not just in
   cases described in this document.  Note also that WebDAV servers are
   known to use 300-level redirect responses (and early interoperability
   tests found clients unprepared to see those responses).  A 300-level
   response MUST NOT be used when the server has created a new resource
   in response to the request.

12.1.  412 Precondition Failed

   Any request can contain a conditional header defined in HTTP (If-
   Match, If-Modified-Since, etc.) or the "If" or "Overwrite"
   conditional headers defined in this specification.  If the server
   evaluates a conditional header, and if that condition fails to hold,
   then this error code MUST be returned.  On the other hand, if the
   client did not include a conditional header in the request, then the
   server MUST NOT use this status code.

12.2.  414 Request-URI Too Long

   This status code is used in HTTP 1.1 only for Request-URIs, not URIs
   in other locations.

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13.  Multi-Status Response

   A Multi-Status response conveys information about multiple resources
   in situations where multiple status codes might be appropriate.  The
   default Multi-Status response body is a text/xml or application/xml
   HTTP entity with a 'multistatus' root element.  Further elements
   contain 200, 300, 400, and 500 series status codes generated during
   the method invocation. 100 series status codes SHOULD NOT be recorded
   in a 'response' XML element.

   Although '207' is used as the overall response status code, the
   recipient needs to consult the contents of the multistatus response
   body for further information about the success or failure of the
   method execution.  The response MAY be used in success, partial
   success and also in failure situations.

   The 'multistatus' root element holds zero or more 'response' elements
   in any order, each with information about an individual resource.
   Each 'response' element MUST have an 'href' element to identify the
   resource.

   A Multi-Status response uses one out of two distinct formats for
   representing the status:

   1.  A 'status' element as child of the 'response' element indicates
       the status of the message execution for the identified resource
       as a whole (for instance, see Section 9.6.2).  Some method
       definitions provide information about specific status codes
       clients should be prepared to see in a response.  However,
       clients MUST be able to handle other status codes, using the
       generic rules defined in Section 10 of [RFC2616].

   2.  For PROPFIND and PROPPATCH, the format has been extended using
       the 'propstat' element instead of 'status', providing information
       about individual properties of a resource.  This format is
       specific to PROPFIND and PROPPATCH, and is described in detail in
       Sections 9.1 and 9.2.

13.1.  Response Headers

   HTTP defines the Location header to indicate a preferred URL for the
   resource that was addressed in the Request-URI (e.g., in response to
   successful PUT requests or in redirect responses).  However, use of
   this header creates ambiguity when there are URLs in the body of the
   response, as with Multi-Status.  Thus, use of the Location header
   with the Multi-Status response is intentionally undefined.

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13.2.  Handling Redirected Child Resources

   Redirect responses (300-303, 305, and 307) defined in HTTP 1.1
   normally take a Location header to indicate the new URI for the
   single resource redirected from the Request-URI.  Multi-Status
   responses contain many resource addresses, but the original
   definition in [RFC2518] did not have any place for the server to
   provide the new URI for redirected resources.  This specification
   does define a 'location' element for this information (see
   Section 14.9).  Servers MUST use this new element with redirect
   responses in Multi-Status.

   Clients encountering redirected resources in Multi-Status MUST NOT
   rely on the 'location' element being present with a new URI.  If the
   element is not present, the client MAY reissue the request to the
   individual redirected resource, because the response to that request
   can be redirected with a Location header containing the new URI.

13.3.  Internal Status Codes

   Sections 9.2.1, 9.1.2, 9.6.1, 9.8.3, and 9.9.2 define various status
   codes used in Multi-Status responses.  This specification does not
   define the meaning of other status codes that could appear in these
   responses.

14.  XML Element Definitions

   In this section, the final line of each section gives the element
   type declaration using the format defined in [REC-XML].  The "Value"
   field, where present, specifies further restrictions on the allowable
   contents of the XML element using BNF (i.e., to further restrict the
   values of a PCDATA element).  Note that all of the elements defined
   here may be extended according to the rules defined in Section 17.
   All elements defined here are in the "DAV:" namespace.

14.1.  activelock XML Element

   Name:   activelock

   Purpose:   Describes a lock on a resource.

   <!ELEMENT activelock (lockscope, locktype, depth, owner?, timeout?,
             locktoken?, lockroot)>

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14.2.  allprop XML Element

   Name:   allprop

   Purpose:   Specifies that all names and values of dead properties and
      the live properties defined by this document existing on the
      resource are to be returned.

   <!ELEMENT allprop EMPTY >

14.3.  collection XML Element

   Name:   collection

   Purpose:   Identifies the associated resource as a collection.  The
      DAV:resourcetype property of a collection resource MUST contain
      this element.  It is normally empty but extensions may add sub-
      elements.

   <!ELEMENT collection EMPTY >

14.4.  depth XML Element

   Name:   depth

   Purpose:   Used for representing depth values in XML content (e.g.,
      in lock information).

   Value:   "0" | "1" | "infinity"

   <!ELEMENT depth (#PCDATA) >

14.5.  error XML Element

   Name:   error

   Purpose:   Error responses, particularly 403 Forbidden and 409
      Conflict, sometimes need more information to indicate what went
      wrong.  In these cases, servers MAY return an XML response body
      with a document element of 'error', containing child elements
      identifying particular condition codes.

   Description:   Contains at least one XML element, and MUST NOT
      contain text or mixed content.  Any element that is a child of the
      'error' element is considered to be a precondition or
      postcondition code.  Unrecognized elements MUST be ignored.

   <!ELEMENT error ANY >

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14.6.  exclusive XML Element

   Name:   exclusive

   Purpose:   Specifies an exclusive lock.

   <!ELEMENT exclusive EMPTY >

14.7.  href XML Element

   Name:   href

   Purpose:   MUST contain a URI or a relative reference.

   Description:   There may be limits on the value of 'href' depending
      on the context of its use.  Refer to the specification text where
      'href' is used to see what limitations apply in each case.

   Value:   Simple-ref

   <!ELEMENT href (#PCDATA)>

14.8.  include XML Element

   Name:   include

   Purpose:   Any child element represents the name of a property to be
      included in the PROPFIND response.  All elements inside an
      'include' XML element MUST define properties related to the
      resource, although possible property names are in no way limited
      to those property names defined in this document or other
      standards.  This element MUST NOT contain text or mixed content.

   <!ELEMENT include ANY >

14.9.  location XML Element

   Name:   location

   Purpose:   HTTP defines the "Location" header (see [RFC2616], Section
      14.30) for use with some status codes (such as 201 and the 300
      series codes).  When these codes are used inside a 'multistatus'
      element, the 'location' element can be used to provide the
      accompanying Location header value.

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   Description:   Contains a single href element with the same value
      that would be used in a Location header.

   <!ELEMENT location (href)>

14.10.  lockentry XML Element

   Name:   lockentry

   Purpose:   Defines the types of locks that can be used with the
      resource.

   <!ELEMENT lockentry (lockscope, locktype) >

14.11.  lockinfo XML Element

   Name:   lockinfo

   Purpose:   The 'lockinfo' XML element is used with a LOCK method to
      specify the type of lock the client wishes to have created.

   <!ELEMENT lockinfo (lockscope, locktype, owner?)  >

14.12.  lockroot XML Element

   Name:   lockroot

   Purpose:   Contains the root URL of the lock, which is the URL
      through which the resource was addressed in the LOCK request.

   Description:   The href element contains the root of the lock.  The
      server SHOULD include this in all DAV:lockdiscovery property
      values and the response to LOCK requests.

   <!ELEMENT lockroot (href) >

14.13.  lockscope XML Element

   Name:   lockscope

   Purpose:   Specifies whether a lock is an exclusive lock, or a shared
      lock.

     <!ELEMENT lockscope (exclusive | shared) >

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14.14.  locktoken XML Element

   Name:   locktoken

   Purpose:   The lock token associated with a lock.

   Description:   The href contains a single lock token URI, which
      refers to the lock.

   <!ELEMENT locktoken (href) >

14.15.  locktype XML Element

   Name:   locktype

   Purpose:   Specifies the access type of a lock.  At present, this
      specification only defines one lock type, the write lock.

   <!ELEMENT locktype (write) >

14.16.  multistatus XML Element

   Name:   multistatus

   Purpose:   Contains multiple response messages.

   Description:   The 'responsedescription' element at the top level is
      used to provide a general message describing the overarching
      nature of the response.  If this value is available, an
      application may use it instead of presenting the individual
      response descriptions contained within the responses.

   <!ELEMENT multistatus (response*, responsedescription?)  >

14.17.  owner XML Element

   Name:   owner

   Purpose:   Holds client-supplied information about the creator of a
      lock.

   Description:   Allows a client to provide information sufficient for
      either directly contacting a principal (such as a telephone number
      or Email URI), or for discovering the principal (such as the URL

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      of a homepage) who created a lock.  The value provided MUST be
      treated as a dead property in terms of XML Information Item
      preservation.  The server MUST NOT alter the value unless the
      owner value provided by the client is empty.  For a certain amount
      of interoperability between different client implementations, if
      clients have URI-formatted contact information for the lock
      creator suitable for user display, then clients SHOULD put those
      URIs in 'href' child elements of the 'owner' element.

   Extensibility:   MAY be extended with child elements, mixed content,
      text content or attributes.

   <!ELEMENT owner ANY >

14.18.  prop XML Element

   Name:   prop

   Purpose:   Contains properties related to a resource.

   Description:   A generic container for properties defined on
      resources.  All elements inside a 'prop' XML element MUST define
      properties related to the resource, although possible property
      names are in no way limited to those property names defined in
      this document or other standards.  This element MUST NOT contain
      text or mixed content.

   <!ELEMENT prop ANY >

14.19.  propertyupdate XML Element

   Name:   propertyupdate

   Purpose:   Contains a request to alter the properties on a resource.

   Description:   This XML element is a container for the information
      required to modify the properties on the resource.

   <!ELEMENT propertyupdate (remove | set)+ >

14.20.  propfind XML Element

   Name:   propfind

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   Purpose:   Specifies the properties to be returned from a PROPFIND
      method.  Four special elements are specified for use with
      'propfind': 'prop', 'allprop', 'include', and 'propname'.  If
      'prop' is used inside 'propfind', it MUST NOT contain property
      values.

   <!ELEMENT propfind ( propname | (allprop, include?) | prop ) >

14.21.  propname XML Element

   Name:   propname

   Purpose:   Specifies that only a list of property names on the
      resource is to be returned.

   <!ELEMENT propname EMPTY >

14.22.  propstat XML Element

   Name:   propstat

   Purpose:   Groups together a prop and status element that is
      associated with a particular 'href' element.

   Description:   The propstat XML element MUST contain one prop XML
      element and one status XML element.  The contents of the prop XML
      element MUST only list the names of properties to which the result
      in the status element applies.  The optional precondition/
      postcondition element and 'responsedescription' text also apply to
      the properties named in 'prop'.

   <!ELEMENT propstat (prop, status, error?, responsedescription?) >

14.23.  remove XML Element

   Name:   remove

   Purpose:   Lists the properties to be removed from a resource.

   Description:   Remove instructs that the properties specified in prop
      should be removed.  Specifying the removal of a property that does
      not exist is not an error.  All the XML elements in a 'prop' XML
      element inside of a 'remove' XML element MUST be empty, as only
      the names of properties to be removed are required.

   <!ELEMENT remove (prop) >

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14.24.  response XML Element

   Name:   response

   Purpose:   Holds a single response describing the effect of a method
      on resource and/or its properties.

   Description:   The 'href' element contains an HTTP URL pointing to a
      WebDAV resource when used in the 'response' container.  A
      particular 'href' value MUST NOT appear more than once as the
      child of a 'response' XML element under a 'multistatus' XML
      element.  This requirement is necessary in order to keep
      processing costs for a response to linear time.  Essentially, this
      prevents having to search in order to group together all the
      responses by 'href'.  There are, however, no requirements
      regarding ordering based on 'href' values.  The optional
      precondition/postcondition element and 'responsedescription' text
      can provide additional information about this resource relative to
      the request or result.

   <!ELEMENT response (href, ((href*, status)|(propstat+)),
                       error?, responsedescription? , location?) >

14.25.  responsedescription XML Element

   Name:   responsedescription

   Purpose:   Contains information about a status response within a
      Multi-Status.

   Description:   Provides information suitable to be presented to a
      user.

   <!ELEMENT responsedescription (#PCDATA) >

14.26.  set XML Element

   Name:   set

   Purpose:   Lists the property values to be set for a resource.

   Description:   The 'set' element MUST contain only a 'prop' element.
      The elements contained by the 'prop' element inside the 'set'
      element MUST specify the name and value of properties that are set
      on the resource identified by Request-URI.  If a property already
      exists, then its value is replaced.  Language tagging information
      appearing in the scope of the 'prop' element (in the "xml:lang"

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      attribute, if present) MUST be persistently stored along with the
      property, and MUST be subsequently retrievable using PROPFIND.

   <!ELEMENT set (prop) >

14.27.  shared XML Element

   Name:   shared

   Purpose:   Specifies a shared lock.

   <!ELEMENT shared EMPTY >

14.28.  status XML Element

   Name:   status

   Purpose:   Holds a single HTTP status-line.

   Value:   status-line (defined in Section 6.1 of [RFC2616])

   <!ELEMENT status (#PCDATA) >

14.29.  timeout XML Element

   Name:   timeout

   Purpose:   The number of seconds remaining before a lock expires.

   Value:   TimeType (defined in Section 10.7)

      <!ELEMENT timeout (#PCDATA) >

14.30.  write XML Element

   Name:   write

   Purpose:   Specifies a write lock.

   <!ELEMENT write EMPTY >

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15.  DAV Properties

   For DAV properties, the name of the property is also the same as the
   name of the XML element that contains its value.  In the section
   below, the final line of each section gives the element type
   declaration using the format defined in [REC-XML].  The "Value"
   field, where present, specifies further restrictions on the allowable
   contents of the XML element using BNF (i.e., to further restrict the
   values of a PCDATA element).

   A protected property is one that cannot be changed with a PROPPATCH
   request.  There may be other requests that would result in a change
   to a protected property (as when a LOCK request affects the value of
   DAV:lockdiscovery).  Note that a given property could be protected on
   one type of resource, but not protected on another type of resource.

   A computed property is one with a value defined in terms of a
   computation (based on the content and other properties of that
   resource, or even of some other resource).  A computed property is
   always a protected property.

   COPY and MOVE behavior refers to local COPY and MOVE operations.

   For properties defined based on HTTP GET response headers (DAV:get*),
   the header value could include LWS as defined in [RFC2616], Section
   4.2.  Server implementors SHOULD strip LWS from these values before
   using as WebDAV property values.

15.1.  creationdate Property

   Name:   creationdate

   Purpose:   Records the time and date the resource was created.

   Value:   date-time (defined in [RFC3339], see the ABNF in Section
      5.6.)

   Protected:   MAY be protected.  Some servers allow DAV:creationdate
      to be changed to reflect the time the document was created if that
      is more meaningful to the user (rather than the time it was
      uploaded).  Thus, clients SHOULD NOT use this property in
      synchronization logic (use DAV:getetag instead).

   COPY/MOVE behavior:   This property value SHOULD be kept during a
      MOVE operation, but is normally re-initialized when a resource is
      created with a COPY.  It should not be set in a COPY.

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   Description:   The DAV:creationdate property SHOULD be defined on all
      DAV compliant resources.  If present, it contains a timestamp of
      the moment when the resource was created.  Servers that are
      incapable of persistently recording the creation date SHOULD
      instead leave it undefined (i.e. report "Not Found").

   <!ELEMENT creationdate (#PCDATA) >

15.2.  displayname Property

   Name:   displayname

   Purpose:   Provides a name for the resource that is suitable for
      presentation to a user.

   Value:   Any text.

   Protected:   SHOULD NOT be protected.  Note that servers implementing
      [RFC2518] might have made this a protected property as this is a
      new requirement.

   COPY/MOVE behavior:   This property value SHOULD be preserved in COPY
      and MOVE operations.

   Description:   Contains a description of the resource that is
      suitable for presentation to a user.  This property is defined on
      the resource, and hence SHOULD have the same value independent of
      the Request-URI used to retrieve it (thus, computing this property
      based on the Request-URI is deprecated).  While generic clients
      might display the property value to end users, client UI designers
      must understand that the method for identifying resources is still
      the URL.  Changes to DAV:displayname do not issue moves or copies
      to the server, but simply change a piece of meta-data on the
      individual resource.  Two resources can have the same DAV:
      displayname value even within the same collection.

   <!ELEMENT displayname (#PCDATA) >

15.3.  getcontentlanguage Property

   Name:   getcontentlanguage

   Purpose:   Contains the Content-Language header value (from Section
      14.12 of [RFC2616]) as it would be returned by a GET without
      accept headers.

   Value:   language-tag (language-tag is defined in Section 3.10 of
      [RFC2616])

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   Protected:   SHOULD NOT be protected, so that clients can reset the
      language.  Note that servers implementing [RFC2518] might have
      made this a protected property as this is a new requirement.

   COPY/MOVE behavior:   This property value SHOULD be preserved in COPY
      and MOVE operations.

   Description:   The DAV:getcontentlanguage property MUST be defined on
      any DAV-compliant resource that returns the Content-Language
      header on a GET.

   <!ELEMENT getcontentlanguage (#PCDATA) >

15.4.  getcontentlength Property

   Name:   getcontentlength

   Purpose:   Contains the Content-Length header returned by a GET
      without accept headers.

   Value:   See Section 14.13 of [RFC2616].

   Protected:   This property is computed, therefore protected.

   Description:   The DAV:getcontentlength property MUST be defined on
      any DAV-compliant resource that returns the Content-Length header
      in response to a GET.

   COPY/MOVE behavior:   This property value is dependent on the size of
      the destination resource, not the value of the property on the
      source resource.

   <!ELEMENT getcontentlength (#PCDATA) >

15.5.  getcontenttype Property

   Name:   getcontenttype

   Purpose:   Contains the Content-Type header value (from Section 14.17
      of [RFC2616]) as it would be returned by a GET without accept
      headers.

   Value:   media-type (defined in Section 3.7 of [RFC2616])

   Protected:   Potentially protected if the server prefers to assign
      content types on its own (see also discussion in Section 9.7.1).

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   COPY/MOVE behavior:   This property value SHOULD be preserved in COPY
      and MOVE operations.

   Description:   This property MUST be defined on any DAV-compliant
      resource that returns the Content-Type header in response to a
      GET.

   <!ELEMENT getcontenttype (#PCDATA) >

15.6.  getetag Property

   Name:   getetag

   Purpose:   Contains the ETag header value (from Section 14.19 of
      [RFC2616]) as it would be returned by a GET without accept
      headers.

   Value:   entity-tag (defined in Section 3.11 of [RFC2616])

   Protected:  MUST be protected because this value is created and
      controlled by the server.

   COPY/MOVE behavior:   This property value is dependent on the final
      state of the destination resource, not the value of the property
      on the source resource.  Also note the considerations in
      Section 8.8.

   Description:   The getetag property MUST be defined on any DAV-
      compliant resource that returns the Etag header.  Refer to Section
      3.11 of RFC 2616 for a complete definition of the semantics of an
      ETag, and to Section 8.6 for a discussion of ETags in WebDAV.

   <!ELEMENT getetag (#PCDATA) >

15.7.  getlastmodified Property

   Name:   getlastmodified

   Purpose:   Contains the Last-Modified header value (from Section
      14.29 of [RFC2616]) as it would be returned by a GET method
      without accept headers.

   Value:   rfc1123-date (defined in Section 3.3.1 of [RFC2616])

   Protected:   SHOULD be protected because some clients may rely on the
      value for appropriate caching behavior, or on the value of the
      Last-Modified header to which this property is linked.

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   COPY/MOVE behavior:   This property value is dependent on the last
      modified date of the destination resource, not the value of the
      property on the source resource.  Note that some server
      implementations use the file system date modified value for the
      DAV:getlastmodified value, and this can be preserved in a MOVE
      even when the HTTP Last-Modified value SHOULD change.  Note that
      since [RFC2616] requires clients to use ETags where provided, a
      server implementing ETags can count on clients using a much better
      mechanism than modification dates for offline synchronization or
      cache control.  Also note the considerations in Section 8.8.

   Description:   The last-modified date on a resource SHOULD only
      reflect changes in the body (the GET responses) of the resource.
      A change in a property only SHOULD NOT cause the last-modified
      date to change, because clients MAY rely on the last-modified date
      to know when to overwrite the existing body.  The DAV:
      getlastmodified property MUST be defined on any DAV-compliant
      resource that returns the Last-Modified header in response to a
      GET.

   <!ELEMENT getlastmodified (#PCDATA) >

15.8.  lockdiscovery Property

   Name:   lockdiscovery

   Purpose:   Describes the active locks on a resource

   Protected:   MUST be protected.  Clients change the list of locks
      through LOCK and UNLOCK, not through PROPPATCH.

   COPY/MOVE behavior:   The value of this property depends on the lock
      state of the destination, not on the locks of the source resource.
      Recall that locks are not moved in a MOVE operation.

   Description:   Returns a listing of who has a lock, what type of lock
      he has, the timeout type and the time remaining on the timeout,
      and the associated lock token.  Owner information MAY be omitted
      if it is considered sensitive.  If there are no locks, but the
      server supports locks, the property will be present but contain
      zero 'activelock' elements.  If there are one or more locks, an
      'activelock' element appears for each lock on the resource.  This
      property is NOT lockable with respect to write locks (Section 7).

   <!ELEMENT lockdiscovery (activelock)* >

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15.8.1.  Example - Retrieving DAV:lockdiscovery

   >>Request

     PROPFIND /container/ HTTP/1.1
     Host: www.example.com
     Content-Length: xxxx
     Content-Type: application/xml; charset="utf-8"

     <?xml version="1.0" encoding="utf-8" ?>
     <D:propfind xmlns:D='DAV:'>
       <D:prop><D:lockdiscovery/></D:prop>
     </D:propfind>

   >>Response

     HTTP/1.1 207 Multi-Status
     Content-Type: application/xml; charset="utf-8"
     Content-Length: xxxx

     <?xml version="1.0" encoding="utf-8" ?>
     <D:multistatus xmlns:D='DAV:'>
       <D:response>
         <D:href>http://www.example.com/container/</D:href>
         <D:propstat>
           <D:prop>
             <D:lockdiscovery>
              <D:activelock>
               <D:locktype><D:write/></D:locktype>
               <D:lockscope><D:exclusive/></D:lockscope>
               <D:depth>0</D:depth>
               <D:owner>Jane Smith</D:owner>
               <D:timeout>Infinite</D:timeout>
               <D:locktoken>
                 <D:href
             >urn:uuid:f81de2ad-7f3d-a1b2-4f3c-00a0c91a9d76</D:href>
               </D:locktoken>
               <D:lockroot>
                 <D:href>http://www.example.com/container/</D:href>
               </D:lockroot>
              </D:activelock>
             </D:lockdiscovery>
           </D:prop>
           <D:status>HTTP/1.1 200 OK</D:status>
         </D:propstat>
       </D:response>
     </D:multistatus>

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   This resource has a single exclusive write lock on it, with an
   infinite timeout.

15.9.  resourcetype Property

   Name:   resourcetype

   Purpose:   Specifies the nature of the resource.

   Protected:   SHOULD be protected.  Resource type is generally decided
      through the operation creating the resource (MKCOL vs PUT), not by
      PROPPATCH.

   COPY/MOVE behavior:   Generally a COPY/MOVE of a resource results in
      the same type of resource at the destination.

   Description:   MUST be defined on all DAV-compliant resources.  Each
      child element identifies a specific type the resource belongs to,
      such as 'collection', which is the only resource type defined by
      this specification (see Section 14.3).  If the element contains
      the 'collection' child element plus additional unrecognized
      elements, it should generally be treated as a collection.  If the
      element contains no recognized child elements, it should be
      treated as a non-collection resource.  The default value is empty.
      This element MUST NOT contain text or mixed content.  Any custom
      child element is considered to be an identifier for a resource
      type.

   Example: (fictional example to show extensibility)

       <x:resourcetype xmlns:x="DAV:">
           <x:collection/>
           <f:search-results xmlns:f="http://www.example.com/ns"/>
       </x:resourcetype>

15.10.  supportedlock Property

   Name:   supportedlock

   Purpose:   To provide a listing of the lock capabilities supported by
      the resource.

   Protected:   MUST be protected.  Servers, not clients, determine what
      lock mechanisms are supported.

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   COPY/MOVE behavior:   This property value is dependent on the kind of
      locks supported at the destination, not on the value of the
      property at the source resource.  Servers attempting to COPY to a
      destination should not attempt to set this property at the
      destination.

   Description:   Returns a listing of the combinations of scope and
      access types that may be specified in a lock request on the
      resource.  Note that the actual contents are themselves controlled
      by access controls, so a server is not required to provide
      information the client is not authorized to see.  This property is
      NOT lockable with respect to write locks (Section 7).

   <!ELEMENT supportedlock (lockentry)* >

15.10.1.  Example - Retrieving DAV:supportedlock

   >>Request

     PROPFIND /container/ HTTP/1.1
     Host: www.example.com
     Content-Length: xxxx
     Content-Type: application/xml; charset="utf-8"

     <?xml version="1.0" encoding="utf-8" ?>
     <D:propfind xmlns:D="DAV:">
       <D:prop><D:supportedlock/></D:prop>
     </D:propfind>

   >>Response

     HTTP/1.1 207 Multi-Status
     Content-Type: application/xml; charset="utf-8"
     Content-Length: xxxx

     <?xml version="1.0" encoding="utf-8" ?>
     <D:multistatus xmlns:D="DAV:">
       <D:response>
         <D:href>http://www.example.com/container/</D:href>
         <D:propstat>
           <D:prop>
             <D:supportedlock>
               <D:lockentry>
                 <D:lockscope><D:exclusive/></D:lockscope>
                 <D:locktype><D:write/></D:locktype>
               </D:lockentry>
               <D:lockentry>
                 <D:lockscope><D:shared/></D:lockscope>

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                 <D:locktype><D:write/></D:locktype>
               </D:lockentry>
             </D:supportedlock>
           </D:prop>
           <D:status>HTTP/1.1 200 OK</D:status>
         </D:propstat>
       </D:response>
     </D:multistatus>

16.  Precondition/Postcondition XML Elements

   As introduced in Section 8.7, extra information on error conditions
   can be included in the body of many status responses.  This section
   makes requirements on the use of the error body mechanism and
   introduces a number of precondition and postcondition codes.

   A "precondition" of a method describes the state of the server that
   must be true for that method to be performed.  A "postcondition" of a
   method describes the state of the server that must be true after that
   method has been completed.

   Each precondition and postcondition has a unique XML element
   associated with it.  In a 207 Multi-Status response, the XML element
   MUST appear inside an 'error' element in the appropriate 'propstat or
   'response' element depending on whether the condition applies to one
   or more properties or to the resource as a whole.  In all other error
   responses where this specification's 'error' body is used, the
   precondition/postcondition XML element MUST be returned as the child
   of a top-level 'error' element in the response body, unless otherwise
   negotiated by the request, along with an appropriate response status.
   The most common response status codes are 403 (Forbidden) if the
   request should not be repeated because it will always fail, and 409
   (Conflict) if it is expected that the user might be able to resolve
   the conflict and resubmit the request.  The 'error' element MAY
   contain child elements with specific error information and MAY be
   extended with any custom child elements.

   This mechanism does not take the place of using a correct numeric
   status code as defined here or in HTTP, because the client must
   always be able to take a reasonable course of action based only on
   the numeric code.  However, it does remove the need to define new
   numeric codes.  The new machine-readable codes used for this purpose
   are XML elements classified as preconditions and postconditions, so
   naturally, any group defining a new condition code can use their own
   namespace.  As always, the "DAV:" namespace is reserved for use by
   IETF-chartered WebDAV working groups.

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   A server supporting this specification SHOULD use the XML error
   whenever a precondition or postcondition defined in this document is
   violated.  For error conditions not specified in this document, the
   server MAY simply choose an appropriate numeric status and leave the
   response body blank.  However, a server MAY instead use a custom
   condition code and other supporting text, because even when clients
   do not automatically recognize condition codes, they can be quite
   useful in interoperability testing and debugging.

   Example - Response with precondition code

   >>Response

      HTTP/1.1 423 Locked
      Content-Type: application/xml; charset="utf-8"
      Content-Length: xxxx

      <?xml version="1.0" encoding="utf-8" ?>
      <D:error xmlns:D="DAV:">
        <D:lock-token-submitted>
          <D:href>/workspace/webdav/</D:href>
        </D:lock-token-submitted>
      </D:error>

   In this example, a client unaware of a depth-infinity lock on the
   parent collection "/workspace/webdav/" attempted to modify the
   collection member "/workspace/webdav/proposal.doc".

   Some other useful preconditions and postconditions have been defined
   in other specifications extending WebDAV, such as [RFC3744] (see
   particularly Section 7.1.1), [RFC3253], and [RFC3648].

   All these elements are in the "DAV:" namespace.  If not specified
   otherwise, the content for each condition's XML element is defined to
   be empty.

   Name:  lock-token-matches-request-uri

   Use with:  409 Conflict

   Purpose:  (precondition) -- A request may include a Lock-Token header
      to identify a lock for the UNLOCK method.  However, if the
      Request-URI does not fall within the scope of the lock identified
      by the token, the server SHOULD use this error.  The lock may have
      a scope that does not include the Request-URI, or the lock could
      have disappeared, or the token may be invalid.

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   Name:  lock-token-submitted (precondition)

   Use with:  423 Locked

   Purpose:  The request could not succeed because a lock token should
      have been submitted.  This element, if present, MUST contain at
      least one URL of a locked resource that prevented the request.  In
      cases of MOVE, COPY, and DELETE where collection locks are
      involved, it can be difficult for the client to find out which
      locked resource made the request fail -- but the server is only
      responsible for returning one such locked resource.  The server
      MAY return every locked resource that prevented the request from
      succeeding if it knows them all.

   <!ELEMENT lock-token-submitted (href+) >

   Name:  no-conflicting-lock (precondition)

   Use with:  Typically 423 Locked

   Purpose:  A LOCK request failed due the presence of an already
      existing conflicting lock.  Note that a lock can be in conflict
      although the resource to which the request was directed is only
      indirectly locked.  In this case, the precondition code can be
      used to inform the client about the resource that is the root of
      the conflicting lock, avoiding a separate lookup of the
      "lockdiscovery" property.

   <!ELEMENT no-conflicting-lock (href)* >

   Name:  no-external-entities

   Use with:  403 Forbidden

   Purpose:  (precondition) -- If the server rejects a client request
      because the request body contains an external entity, the server
      SHOULD use this error.

   Name:  preserved-live-properties

   Use with:  409 Conflict

   Purpose:  (postcondition) -- The server received an otherwise-valid
      MOVE or COPY request, but cannot maintain the live properties with
      the same behavior at the destination.  It may be that the server

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      only supports some live properties in some parts of the
      repository, or simply has an internal error.

   Name:  propfind-finite-depth

   Use with:  403 Forbidden

   Purpose:  (precondition) -- This server does not allow infinite-depth
      PROPFIND requests on collections.

   Name:  cannot-modify-protected-property

   Use with:  403 Forbidden

   Purpose:  (precondition) -- The client attempted to set a protected
      property in a PROPPATCH (such as DAV:getetag).  See also
      [RFC3253], Section 3.12.

17.  XML Extensibility in DAV

   The XML namespace extension ([REC-XML-NAMES]) is used in this
   specification in order to allow for new XML elements to be added
   without fear of colliding with other element names.  Although WebDAV
   request and response bodies can be extended by arbitrary XML
   elements, which can be ignored by the message recipient, an XML
   element in the "DAV:" namespace SHOULD NOT be used in the request or
   response body unless that XML element is explicitly defined in an
   IETF RFC reviewed by a WebDAV working group.

   For WebDAV to be both extensible and backwards-compatible, both
   clients and servers need to know how to behave when unexpected or
   unrecognized command extensions are received.  For XML processing,
   this means that clients and servers MUST process received XML
   documents as if unexpected elements and attributes (and all children
   of unrecognized elements) were not there.  An unexpected element or
   attribute includes one that may be used in another context but is not
   expected here.  Ignoring such items for purposes of processing can of
   course be consistent with logging all information or presenting for
   debugging.

   This restriction also applies to the processing, by clients, of DAV
   property values where unexpected XML elements SHOULD be ignored
   unless the property's schema declares otherwise.

   This restriction does not apply to setting dead DAV properties on the
   server where the server MUST record all XML elements.

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   Additionally, this restriction does not apply to the use of XML where
   XML happens to be the content type of the entity body, for example,
   when used as the body of a PUT.

   Processing instructions in XML SHOULD be ignored by recipients.
   Thus, specifications extending WebDAV SHOULD NOT use processing
   instructions to define normative behavior.

   XML DTD fragments are included for all the XML elements defined in
   this specification.  However, correct XML will not be valid according
   to any DTD due to namespace usage and extension rules.  In
   particular:

   o  Elements (from this specification) are in the "DAV:" namespace,

   o  Element ordering is irrelevant unless otherwise stated,

   o  Extension attributes MAY be added,

   o  For element type definitions of "ANY", the normative text
      definition for that element defines what can be in it and what
      that means.

   o  For element type definitions of "#PCDATA", extension elements MUST
      NOT be added.

   o  For other element type definitions, including "EMPTY", extension
      elements MAY be added.

   Note that this means that elements containing elements cannot be
   extended to contain text, and vice versa.

   With DTD validation relaxed by the rules above, the constraints
   described by the DTD fragments are normative (see for example
   Appendix A).  A recipient of a WebDAV message with an XML body MUST
   NOT validate the XML document according to any hard-coded or
   dynamically-declared DTD.

   Note that this section describes backwards-compatible extensibility
   rules.  There might also be times when an extension is designed not
   to be backwards-compatible, for example, defining an extension that
   reuses an XML element defined in this document but omitting one of
   the child elements required by the DTDs in this specification.

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18.  DAV Compliance Classes

   A DAV-compliant resource can advertise several classes of compliance.
   A client can discover the compliance classes of a resource by
   executing OPTIONS on the resource and examining the "DAV" header
   which is returned.  Note particularly that resources, rather than
   servers, are spoken of as being compliant.  That is because
   theoretically some resources on a server could support different
   feature sets.  For example, a server could have a sub-repository
   where an advanced feature like versioning was supported, even if that
   feature was not supported on all sub-repositories.

   Since this document describes extensions to the HTTP/1.1 protocol,
   minimally all DAV-compliant resources, clients, and proxies MUST be
   compliant with [RFC2616].

   A resource that is class 2 or class 3 compliant must also be class 1
   compliant.

18.1.  Class 1

   A class 1 compliant resource MUST meet all "MUST" requirements in all
   sections of this document.

   Class 1 compliant resources MUST return, at minimum, the value "1" in
   the DAV header on all responses to the OPTIONS method.

18.2.  Class 2

   A class 2 compliant resource MUST meet all class 1 requirements and
   support the LOCK method, the DAV:supportedlock property, the DAV:
   lockdiscovery property, the Time-Out response header and the Lock-
   Token request header.  A class 2 compliant resource SHOULD also
   support the Timeout request header and the 'owner' XML element.

   Class 2 compliant resources MUST return, at minimum, the values "1"
   and "2" in the DAV header on all responses to the OPTIONS method.

18.3.  Class 3

   A resource can explicitly advertise its support for the revisions to
   [RFC2518] made in this document.  Class 1 MUST be supported as well.
   Class 2 MAY be supported.  Advertising class 3 support in addition to
   class 1 and 2 means that the server supports all the requirements in
   this specification.  Advertising class 3 and class 1 support, but not
   class 2, means that the server supports all the requirements in this
   specification except possibly those that involve locking support.

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   Example:

            DAV: 1, 3

19.  Internationalization Considerations

   In the realm of internationalization, this specification complies
   with the IETF Character Set Policy [RFC2277].  In this specification,
   human-readable fields can be found either in the value of a property,
   or in an error message returned in a response entity body.  In both
   cases, the human-readable content is encoded using XML, which has
   explicit provisions for character set tagging and encoding, and
   requires that XML processors read XML elements encoded, at minimum,
   using the UTF-8 [RFC3629] and UTF-16 [RFC2781] encodings of the ISO
   10646 multilingual plane.  XML examples in this specification
   demonstrate use of the charset parameter of the Content-Type header
   (defined in [RFC3023]), as well as XML charset declarations.

   XML also provides a language tagging capability for specifying the
   language of the contents of a particular XML element.  The "xml:lang"
   attribute appears on an XML element to identify the language of its
   content and attributes.  See [REC-XML] for definitions of values and
   scoping.

   WebDAV applications MUST support the character set tagging, character
   set encoding, and the language tagging functionality of the XML
   specification.  Implementors of WebDAV applications are strongly
   encouraged to read "XML Media Types" [RFC3023] for instruction on
   which MIME media type to use for XML transport, and on use of the
   charset parameter of the Content-Type header.

   Names used within this specification fall into four categories: names
   of protocol elements such as methods and headers, names of XML
   elements, names of properties, and names of conditions.  Naming of
   protocol elements follows the precedent of HTTP, using English names
   encoded in US-ASCII for methods and headers.  Since these protocol
   elements are not visible to users, and are simply long token
   identifiers, they do not need to support multiple languages.
   Similarly, the names of XML elements used in this specification are
   not visible to the user and hence do not need to support multiple
   languages.

   WebDAV property names are qualified XML names (pairs of XML namespace
   name and local name).  Although some applications (e.g., a generic
   property viewer) will display property names directly to their users,
   it is expected that the typical application will use a fixed set of
   properties, and will provide a mapping from the property name and
   namespace to a human-readable field when displaying the property name

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   to a user.  It is only in the case where the set of properties is not
   known ahead of time that an application need display a property name
   to a user.  We recommend that applications provide human-readable
   property names wherever feasible.

   For error reporting, we follow the convention of HTTP/1.1 status
   codes, including with each status code a short, English description
   of the code (e.g., 423 (Locked)).  While the possibility exists that
   a poorly crafted user agent would display this message to a user,
   internationalized applications will ignore this message, and display
   an appropriate message in the user's language and character set.

   Since interoperation of clients and servers does not require locale
   information, this specification does not specify any mechanism for
   transmission of this information.

20.  Security Considerations

   This section is provided to detail issues concerning security
   implications of which WebDAV applications need to be aware.

   All of the security considerations of HTTP/1.1 (discussed in
   [RFC2616]) and XML (discussed in [RFC3023]) also apply to WebDAV.  In
   addition, the security risks inherent in remote authoring require
   stronger authentication technology, introduce several new privacy
   concerns, and may increase the hazards from poor server design.
   These issues are detailed below.

20.1.  Authentication of Clients

   Due to their emphasis on authoring, WebDAV servers need to use
   authentication technology to protect not just access to a network
   resource, but the integrity of the resource as well.  Furthermore,
   the introduction of locking functionality requires support for
   authentication.

   A password sent in the clear over an insecure channel is an
   inadequate means for protecting the accessibility and integrity of a
   resource as the password may be intercepted.  Since Basic
   authentication for HTTP/1.1 performs essentially clear text
   transmission of a password, Basic authentication MUST NOT be used to
   authenticate a WebDAV client to a server unless the connection is
   secure.  Furthermore, a WebDAV server MUST NOT send a Basic
   authentication challenge in a WWW-Authenticate header unless the
   connection is secure.  An example of a secure connection would be a
   Transport Layer Security (TLS) connection employing a strong cipher
   suite and server authentication.

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   WebDAV applications MUST support the Digest authentication scheme
   [RFC2617].  Since Digest authentication verifies that both parties to
   a communication know a shared secret, a password, without having to
   send that secret in the clear, Digest authentication avoids the
   security problems inherent in Basic authentication while providing a
   level of authentication that is useful in a wide range of scenarios.

20.2.  Denial of Service

   Denial-of-service attacks are of special concern to WebDAV servers.
   WebDAV plus HTTP enables denial-of-service attacks on every part of a
   system's resources.

   o  The underlying storage can be attacked by PUTting extremely large
      files.

   o  Asking for recursive operations on large collections can attack
      processing time.

   o  Making multiple pipelined requests on multiple connections can
      attack network connections.

   WebDAV servers need to be aware of the possibility of a denial-of-
   service attack at all levels.  The proper response to such an attack
   MAY be to simply drop the connection.  Or, if the server is able to
   make a response, the server MAY use a 400-level status request such
   as 400 (Bad Request) and indicate why the request was refused (a 500-
   level status response would indicate that the problem is with the
   server, whereas unintentional DoS attacks are something the client is
   capable of remedying).

20.3.  Security through Obscurity

   WebDAV provides, through the PROPFIND method, a mechanism for listing
   the member resources of a collection.  This greatly diminishes the
   effectiveness of security or privacy techniques that rely only on the
   difficulty of discovering the names of network resources.  Users of
   WebDAV servers are encouraged to use access control techniques to
   prevent unwanted access to resources, rather than depending on the
   relative obscurity of their resource names.

20.4.  Privacy Issues Connected to Locks

   When submitting a lock request, a user agent may also submit an
   'owner' XML field giving contact information for the person taking
   out the lock (for those cases where a person, rather than a robot, is
   taking out the lock).  This contact information is stored in a DAV:
   lockdiscovery property on the resource, and can be used by other

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   collaborators to begin negotiation over access to the resource.
   However, in many cases, this contact information can be very private,
   and should not be widely disseminated.  Servers SHOULD limit read
   access to the DAV:lockdiscovery property as appropriate.
   Furthermore, user agents SHOULD provide control over whether contact
   information is sent at all, and if contact information is sent,
   control over exactly what information is sent.

20.5.  Privacy Issues Connected to Properties

   Since property values are typically used to hold information such as
   the author of a document, there is the possibility that privacy
   concerns could arise stemming from widespread access to a resource's
   property data.  To reduce the risk of inadvertent release of private
   information via properties, servers are encouraged to develop access
   control mechanisms that separate read access to the resource body and
   read access to the resource's properties.  This allows a user to
   control the dissemination of their property data without overly
   restricting access to the resource's contents.

20.6.  Implications of XML Entities

   XML supports a facility known as "external entities", defined in
   Section 4.2.2 of [REC-XML], which instructs an XML processor to
   retrieve and include additional XML.  An external XML entity can be
   used to append or modify the document type declaration (DTD)
   associated with an XML document.  An external XML entity can also be
   used to include XML within the content of an XML document.  For non-
   validating XML, such as the XML used in this specification, including
   an external XML entity is not required by XML.  However, XML does
   state that an XML processor may, at its discretion, include the
   external XML entity.

   External XML entities have no inherent trustworthiness and are
   subject to all the attacks that are endemic to any HTTP GET request.
   Furthermore, it is possible for an external XML entity to modify the
   DTD, and hence affect the final form of an XML document, in the worst
   case, significantly modifying its semantics or exposing the XML
   processor to the security risks discussed in [RFC3023].  Therefore,
   implementers must be aware that external XML entities should be
   treated as untrustworthy.  If a server chooses not to handle external
   XML entities, it SHOULD respond to requests containing external
   entities with the 'no-external-entities' condition code.

   There is also the scalability risk that would accompany a widely
   deployed application that made use of external XML entities.  In this
   situation, it is possible that there would be significant numbers of
   requests for one external XML entity, potentially overloading any

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   server that fields requests for the resource containing the external
   XML entity.

   Furthermore, there's also a risk based on the evaluation of "internal
   entities" as defined in Section 4.2.2 of [REC-XML].  A small,
   carefully crafted request using nested internal entities may require
   enormous amounts of memory and/or processing time to process.  Server
   implementers should be aware of this risk and configure their XML
   parsers so that requests like these can be detected and rejected as
   early as possible.

20.7.  Risks Connected with Lock Tokens

   This specification encourages the use of "A Universally Unique
   Identifier (UUID) URN Namespace" ([RFC4122]) for lock tokens
   (Section 6.5), in order to guarantee their uniqueness across space
   and time.  Version 1 UUIDs (defined in Section 4) MAY contain a
   "node" field that "consists of an IEEE 802 MAC address, usually the
   host address.  For systems with multiple IEEE addresses, any
   available one can be used".  Since a WebDAV server will issue many
   locks over its lifetime, the implication is that it may also be
   publicly exposing its IEEE 802 address.

   There are several risks associated with exposure of IEEE 802
   addresses.  Using the IEEE 802 address:

   o  It is possible to track the movement of hardware from subnet to
      subnet.

   o  It may be possible to identify the manufacturer of the hardware
      running a WebDAV server.

   o  It may be possible to determine the number of each type of
      computer running WebDAV.

   This risk only applies to host-address-based UUID versions.  Section
   4 of [RFC4122] describes several other mechanisms for generating
   UUIDs that do not involve the host address and therefore do not
   suffer from this risk.

20.8.  Hosting Malicious Content

   HTTP has the ability to host programs that are executed on client
   machines.  These programs can take many forms including Web scripts,
   executables, plug-in modules, and macros in documents.  WebDAV does
   not change any of the security concerns around these programs, yet
   often WebDAV is used in contexts where a wide range of users can
   publish documents on a server.  The server might not have a close

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   trust relationship with the author that is publishing the document.
   Servers that allow clients to publish arbitrary content can usefully
   implement precautions to check that content published to the server
   is not harmful to other clients.  Servers could do this by techniques
   such as restricting the types of content that is allowed to be
   published and running virus and malware detection software on
   published content.  Servers can also mitigate the risk by having
   appropriate access restriction and authentication of users that are
   allowed to publish content to the server.

21.  IANA Considerations

21.1.  New URI Schemes

   This specification defines two URI schemes:

   1.  the "opaquelocktoken" scheme defined in Appendix C, and

   2.  the "DAV" URI scheme, which historically was used in [RFC2518] to
       disambiguate WebDAV property and XML element names and which
       continues to be used for that purpose in this specification and
       others extending WebDAV.  Creation of identifiers in the "DAV:"
       namespace is controlled by the IETF.

   Note that defining new URI schemes for XML namespaces is now
   discouraged.  "DAV:" was defined before standard best practices
   emerged.

21.2.  XML Namespaces

   XML namespaces disambiguate WebDAV property names and XML elements.
   Any WebDAV user or application can define a new namespace in order to
   create custom properties or extend WebDAV XML syntax.  IANA does not
   need to manage such namespaces, property names, or element names.

21.3.  Message Header Fields

   The message header fields below should be added to the permanent
   registry (see [RFC3864]).

21.3.1.  DAV

   Header field name: DAV

   Applicable protocol: http

   Status: standard

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   Author/Change controller: IETF

   Specification document: this specification (Section 10.1)

21.3.2.  Depth

   Header field name: Depth

   Applicable protocol: http

   Status: standard

   Author/Change controller: IETF

   Specification document: this specification (Section 10.2)

21.3.3.  Destination

   Header field name: Destination

   Applicable protocol: http

   Status: standard

   Author/Change controller: IETF

   Specification document: this specification (Section 10.3)

21.3.4.  If

   Header field name: If

   Applicable protocol: http

   Status: standard

   Author/Change controller: IETF

   Specification document: this specification (Section 10.4)

21.3.5.  Lock-Token

   Header field name: Lock-Token

   Applicable protocol: http

   Status: standard

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   Author/Change controller: IETF

   Specification document: this specification (Section 10.5)

21.3.6.  Overwrite

   Header field name: Overwrite

   Applicable protocol: http

   Status: standard

   Author/Change controller: IETF

   Specification document: this specification (Section 10.6)

21.3.7.  Timeout

   Header field name: Timeout

   Applicable protocol: http

   Status: standard

   Author/Change controller: IETF

   Specification document: this specification (Section 10.7)

21.4.  HTTP Status Codes

   This specification defines the HTTP status codes

   o  207 Multi-Status (Section 11.1)

   o  422 Unprocessable Entity (Section 11.2),

   o  423 Locked (Section 11.3),

   o  424 Failed Dependency (Section 11.4) and

   o  507 Insufficient Storage (Section 11.5),

   to be updated in the registry at
   <http://www.iana.org/assignments/http-status-codes>.

   Note: the HTTP status code 102 (Processing) has been removed in this
   specification; its IANA registration should continue to reference RFC
   2518.

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22.  Acknowledgements

   A specification such as this thrives on piercing critical review and
   withers from apathetic neglect.  The authors gratefully acknowledge
   the contributions of the following people, whose insights were so
   valuable at every stage of our work.

   Contributors to RFC 2518

   Terry Allen, Harald Alvestrand, Jim Amsden, Becky Anderson, Alan
   Babich, Sanford Barr, Dylan Barrell, Bernard Chester, Tim Berners-
   Lee, Dan Connolly, Jim Cunningham, Ron Daniel, Jr., Jim Davis, Keith
   Dawson, Mark Day, Brian Deen, Martin Duerst, David Durand, Lee
   Farrell, Chuck Fay, Wesley Felter, Roy Fielding, Mark Fisher, Alan
   Freier, George Florentine, Jim Gettys, Phill Hallam-Baker, Dennis
   Hamilton, Steve Henning, Mead Himelstein, Alex Hopmann, Andre van der
   Hoek, Ben Laurie, Paul Leach, Ora Lassila, Karen MacArthur, Steven
   Martin, Larry Masinter, Michael Mealling, Keith Moore, Thomas Narten,
   Henrik Nielsen, Kenji Ota, Bob Parker, Glenn Peterson, Jon Radoff,
   Saveen Reddy, Henry Sanders, Christopher Seiwald, Judith Slein, Mike
   Spreitzer, Einar Stefferud, Greg Stein, Ralph Swick, Kenji Takahashi,
   Richard N. Taylor, Robert Thau, John Turner, Sankar Virdhagriswaran,
   Fabio Vitali, Gregory Woodhouse, and Lauren Wood.

   Two from this list deserve special mention.  The contributions by
   Larry Masinter have been invaluable; he both helped the formation of
   the working group and patiently coached the authors along the way.
   In so many ways he has set high standards that we have toiled to
   meet.  The contributions of Judith Slein were also invaluable; by
   clarifying the requirements and in patiently reviewing version after
   version, she both improved this specification and expanded our minds
   on document management.

   We would also like to thank John Turner for developing the XML DTD.

   The authors of RFC 2518 were Yaron Goland, Jim Whitehead, A. Faizi,
   Steve Carter, and D. Jensen.  Although their names had to be removed
   due to IETF author count restrictions, they can take credit for the
   majority of the design of WebDAV.

   Additional Acknowledgements for This Specification

   Significant contributors of text for this specification are listed as
   contributors in the section below.  We must also gratefully
   acknowledge Geoff Clemm, Joel Soderberg, and Dan Brotsky for hashing
   out specific text on the list or in meetings.  Joe Hildebrand and
   Cullen Jennings helped close many issues.  Barry Lind described an
   additional security consideration and Cullen Jennings provided text

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   for that consideration.  Jason Crawford tracked issue status for this
   document for a period of years, followed by Elias Sinderson.

23.  Contributors to This Specification

   Julian Reschke
   <green/>bytes GmbH
   Hafenweg 16, 48155 Muenster, Germany
   EMail: julian.reschke@greenbytes.de

   Elias Sinderson
   University of California, Santa Cruz
   1156 High Street, Santa Cruz, CA 95064
   EMail: elias@cse.ucsc.edu

   Jim Whitehead
   University of California, Santa Cruz
   1156 High Street, Santa Cruz, CA 95064
   EMail: ejw@soe.ucsc.edu

24.  Authors of RFC 2518

   Y. Y. Goland
   Microsoft Corporation
   One Microsoft Way
   Redmond, WA 98052-6399
   EMail: yarong@microsoft.com

   E. J. Whitehead, Jr.
   Dept. Of Information and Computer Science
   University of California, Irvine
   Irvine, CA 92697-3425
   EMail: ejw@ics.uci.edu

   A. Faizi
   Netscape
   685 East Middlefield Road
   Mountain View, CA 94043
   EMail: asad@netscape.com

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   S. R. Carter
   Novell
   1555 N. Technology Way
   M/S ORM F111
   Orem, UT 84097-2399
   EMail: srcarter@novell.com

   D. Jensen
   Novell
   1555 N. Technology Way
   M/S ORM F111
   Orem, UT 84097-2399
   EMail: dcjensen@novell.com

25.  References

25.1.  Normative References

   [REC-XML]          Bray, T., Paoli, J., Sperberg-McQueen, C., Maler,
                      E., and F. Yergeau, "Extensible Markup Language
                      (XML) 1.0 (Fourth Edition)", W3C REC-xml-20060816,
                      August 2006,
                      <http://www.w3.org/TR/2006/REC-xml-20060816/>.

   [REC-XML-INFOSET]  Cowan, J. and R. Tobin, "XML Information Set
                      (Second Edition)", W3C REC-xml-infoset-20040204,
                      February 2004, <http://www.w3.org/TR/2004/
                      REC-xml-infoset-20040204/>.

   [REC-XML-NAMES]    Bray, T., Hollander, D., Layman, A., and R. Tobin,
                      "Namespaces in XML 1.0 (Second Edition)", W3C REC-
                      xml-names-20060816, August 2006, <http://
                      www.w3.org/TR/2006/REC-xml-names-20060816/>.

   [RFC2119]          Bradner, S., "Key words for use in RFCs to
                      Indicate Requirement Levels", BCP 14, RFC 2119,
                      March 1997.

   [RFC2277]          Alvestrand, H., "IETF Policy on Character Sets and
                      Languages", BCP 18, RFC 2277, January 1998.

   [RFC2616]          Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
                      Masinter, L., Leach, P., and T. Berners-Lee,
                      "Hypertext Transfer Protocol -- HTTP/1.1",
                      RFC 2616, June 1999.

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   [RFC2617]          Franks, J., Hallam-Baker, P., Hostetler, J.,
                      Lawrence, S., Leach, P., Luotonen, A., and L.
                      Stewart, "HTTP Authentication: Basic and Digest
                      Access Authentication", RFC 2617, June 1999.

   [RFC3339]          Klyne, G., Ed. and C. Newman, "Date and Time on
                      the Internet: Timestamps", RFC 3339, July 2002.

   [RFC3629]          Yergeau, F., "UTF-8, a transformation format of
                      ISO 10646", STD 63, RFC 3629, November 2003.

   [RFC3986]          Berners-Lee, T., Fielding, R., and L. Masinter,
                      "Uniform Resource Identifier (URI): Generic
                      Syntax", STD 66, RFC 3986, January 2005.

   [RFC4122]          Leach, P., Mealling, M., and R. Salz, "A
                      Universally Unique IDentifier (UUID) URN
                      Namespace", RFC 4122, July 2005.

25.2.  Informative References

   [RFC2291]          Slein, J., Vitali, F., Whitehead, E., and D.
                      Durand, "Requirements for a Distributed Authoring
                      and Versioning Protocol for the World Wide Web",
                      RFC 2291, February 1998.

   [RFC2518]          Goland, Y., Whitehead, E., Faizi, A., Carter, S.,
                      and D. Jensen, "HTTP Extensions for Distributed
                      Authoring -- WEBDAV", RFC 2518, February 1999.

   [RFC2781]          Hoffman, P. and F. Yergeau, "UTF-16, an encoding
                      of ISO 10646", RFC 2781, February 2000.

   [RFC3023]          Murata, M., St. Laurent, S., and D. Kohn, "XML
                      Media Types", RFC 3023, January 2001.

   [RFC3253]          Clemm, G., Amsden, J., Ellison, T., Kaler, C., and
                      J. Whitehead, "Versioning Extensions to WebDAV
                      (Web Distributed Authoring and Versioning)",
                      RFC 3253, March 2002.

   [RFC3648]          Whitehead, J. and J. Reschke, Ed., "Web
                      Distributed Authoring and Versioning (WebDAV)
                      Ordered Collections Protocol", RFC 3648,
                      December 2003.

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   [RFC3744]          Clemm, G., Reschke, J., Sedlar, E., and J.
                      Whitehead, "Web Distributed Authoring and
                      Versioning (WebDAV) Access Control Protocol",
                      RFC 3744, May 2004.

   [RFC3864]          Klyne, G., Nottingham, M., and J. Mogul,
                      "Registration Procedures for Message Header
                      Fields", BCP 90, RFC 3864, September 2004.

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Appendix A.  Notes on Processing XML Elements

A.1.  Notes on Empty XML Elements

   XML supports two mechanisms for indicating that an XML element does
   not have any content.  The first is to declare an XML element of the
   form <A></A>.  The second is to declare an XML element of the form
   <A/>.  The two XML elements are semantically identical.

A.2.  Notes on Illegal XML Processing

   XML is a flexible data format that makes it easy to submit data that
   appears legal but in fact is not.  The philosophy of "Be flexible in
   what you accept and strict in what you send" still applies, but it
   must not be applied inappropriately.  XML is extremely flexible in
   dealing with issues of whitespace, element ordering, inserting new
   elements, etc.  This flexibility does not require extension,
   especially not in the area of the meaning of elements.

   There is no kindness in accepting illegal combinations of XML
   elements.  At best, it will cause an unwanted result and at worst it
   can cause real damage.

A.3.  Example - XML Syntax Error

   The following request body for a PROPFIND method is illegal.

      <?xml version="1.0" encoding="utf-8" ?>
      <D:propfind xmlns:D="DAV:">
       <D:allprop/>
       <D:propname/>
      </D:propfind>

   The definition of the propfind element only allows for the allprop or
   the propname element, not both.  Thus, the above is an error and must
   be responded to with a 400 (Bad Request).

   Imagine, however, that a server wanted to be "kind" and decided to
   pick the allprop element as the true element and respond to it.  A
   client running over a bandwidth limited line who intended to execute
   a propname would be in for a big surprise if the server treated the
   command as an allprop.

   Additionally, if a server were lenient and decided to reply to this
   request, the results would vary randomly from server to server, with
   some servers executing the allprop directive, and others executing
   the propname directive.  This reduces interoperability rather than
   increasing it.

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A.4.  Example - Unexpected XML Element

   The previous example was illegal because it contained two elements
   that were explicitly banned from appearing together in the propfind
   element.  However, XML is an extensible language, so one can imagine
   new elements being defined for use with propfind.  Below is the
   request body of a PROPFIND and, like the previous example, must be
   rejected with a 400 (Bad Request) by a server that does not
   understand the expired-props element.

      <?xml version="1.0" encoding="utf-8" ?>
      <D:propfind xmlns:D="DAV:"
      xmlns:E="http://www.example.com/standards/props/">
       <E:expired-props/>
      </D:propfind>

   To understand why a 400 (Bad Request) is returned, let us look at the
   request body as the server unfamiliar with expired-props sees it.

      <?xml version="1.0" encoding="utf-8" ?>
      <D:propfind xmlns:D="DAV:"
                  xmlns:E="http://www.example.com/standards/props/">
      </D:propfind>

   As the server does not understand the 'expired-props' element,
   according to the WebDAV-specific XML processing rules specified in
   Section 17, it must process the request as if the element were not
   there.  Thus, the server sees an empty propfind, which by the
   definition of the propfind element is illegal.

   Please note that had the extension been additive, it would not
   necessarily have resulted in a 400 (Bad Request).  For example,
   imagine the following request body for a PROPFIND:

      <?xml version="1.0" encoding="utf-8" ?>
      <D:propfind xmlns:D="DAV:"
                  xmlns:E="http://www.example.com/standards/props/">
       <D:propname/>
       <E:leave-out>*boss*</E:leave-out>
      </D:propfind>

   The previous example contains the fictitious element leave-out.  Its
   purpose is to prevent the return of any property whose name matches
   the submitted pattern.  If the previous example were submitted to a
   server unfamiliar with 'leave-out', the only result would be that the
   'leave-out' element would be ignored and a propname would be
   executed.

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Appendix B.  Notes on HTTP Client Compatibility

   WebDAV was designed to be, and has been found to be, backward-
   compatible with HTTP 1.1.  The PUT and DELETE methods are defined in
   HTTP and thus may be used by HTTP clients as well as WebDAV-aware
   clients, but the responses to PUT and DELETE have been extended in
   this specification in ways that only a WebDAV client would be
   entirely prepared for.  Some theoretical concerns were raised about
   whether those responses would cause interoperability problems with
   HTTP-only clients, and this section addresses those concerns.

   Since any HTTP client ought to handle unrecognized 400-level and 500-
   level status codes as errors, the following new status codes should
   not present any issues: 422, 423, and 507 (424 is also a new status
   code but it appears only in the body of a Multistatus response.)  So,
   for example, if an HTTP client attempted to PUT or DELETE a locked
   resource, the 423 Locked response ought to result in a generic error
   presented to the user.

   The 207 Multistatus response is interesting because an HTTP client
   issuing a DELETE request to a collection might interpret a 207
   response as a success, even though it does not realize the resource
   is a collection and cannot understand that the DELETE operation might
   have been a complete or partial failure.  That interpretation isn't
   entirely justified, because a 200-level response indicates that the
   server "received, understood, and accepted" the request, not that the
   request resulted in complete success.

   One option is that a server could treat a DELETE of a collection as
   an atomic operation, and use either 204 No Content in case of
   success, or some appropriate error response (400 or 500 level) for an
   error.  This approach would indeed maximize backward compatibility.
   However, since interoperability tests and working group discussions
   have not turned up any instances of HTTP clients issuing a DELETE
   request against a WebDAV collection, this concern is more theoretical
   than practical.  Thus, servers are likely to be completely successful
   at interoperating with HTTP clients even if they treat any collection
   DELETE request as a WebDAV request and send a 207 Multi-Status
   response.

   In general, server implementations are encouraged to use the detailed
   responses and other mechanisms defined in this document rather than
   make changes for theoretical interoperability concerns.

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Appendix C.  The 'opaquelocktoken' Scheme and URIs

   The 'opaquelocktoken' URI scheme was defined in [RFC2518] (and
   registered by IANA) in order to create syntactically correct and
   easy-to-generate URIs out of UUIDs, intended to be used as lock
   tokens and to be unique across all resources for all time.

   An opaquelocktoken URI is constructed by concatenating the
   'opaquelocktoken' scheme with a UUID, along with an optional
   extension.  Servers can create new UUIDs for each new lock token.  If
   a server wishes to reuse UUIDs, the server MUST add an extension, and
   the algorithm generating the extension MUST guarantee that the same
   extension will never be used twice with the associated UUID.

     OpaqueLockToken-URI = "opaquelocktoken:" UUID [Extension]
       ; UUID is defined in Section 3 of [RFC4122].  Note that LWS
       ; is not allowed between elements of
       ; this production.

     Extension = path
       ; path is defined in Section 3.3 of [RFC3986]

Appendix D.  Lock-null Resources

   The original WebDAV model for locking unmapped URLs created "lock-
   null resources".  This model was over-complicated and some
   interoperability and implementation problems were discovered.  The
   new WebDAV model for locking unmapped URLs (see Section 7.3) creates
   "locked empty resources".  Lock-null resources are deprecated.  This
   section discusses the original model briefly because clients MUST be
   able to handle either model.

   In the original "lock-null resource" model, which is no longer
   recommended for implementation:

   o  A lock-null resource sometimes appeared as "Not Found".  The
      server responds with a 404 or 405 to any method except for PUT,
      MKCOL, OPTIONS, PROPFIND, LOCK, UNLOCK.

   o  A lock-null resource does however show up as a member of its
      parent collection.

   o  The server removes the lock-null resource entirely (its URI
      becomes unmapped) if its lock goes away before it is converted to
      a regular resource.  Recall that locks go away not only when they
      expire or are unlocked, but are also removed if a resource is
      renamed or moved, or if any parent collection is renamed or moved.

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   o  The server converts the lock-null resource into a regular resource
      if a PUT request to the URL is successful.

   o  The server converts the lock-null resource into a collection if a
      MKCOL request to the URL is successful (though interoperability
      experience showed that not all servers followed this requirement).

   o  Property values were defined for DAV:lockdiscovery and DAV:
      supportedlock properties but not necessarily for other properties
      like DAV:getcontenttype.

   Clients can easily interoperate both with servers that support the
   old model "lock-null resources" and the recommended model of "locked
   empty resources" by only attempting PUT after a LOCK to an unmapped
   URL, not MKCOL or GET.

D.1.  Guidance for Clients Using LOCK to Create Resources

   A WebDAV client implemented to this specification might find servers
   that create lock-null resources (implemented before this
   specification using [RFC2518]) as well as servers that create locked
   empty resources.  The response to the LOCK request will not indicate
   what kind of resource was created.  There are a few techniques that
   help the client deal with either type.

      If the client wishes to avoid accidentally creating either lock-
      null or empty locked resources, an "If-Match: *" header can be
      included with LOCK requests to prevent the server from creating a
      new resource.

      If a LOCK request creates a resource and the client subsequently
      wants to overwrite that resource using a COPY or MOVE request, the
      client should include an "Overwrite: T" header.

      If a LOCK request creates a resource and the client then decides
      to get rid of that resource, a DELETE request is supposed to fail
      on a lock-null resource and UNLOCK should be used instead.  But
      with a locked empty resource, UNLOCK doesn't make the resource
      disappear.  Therefore, the client might have to try both requests
      and ignore an error in one of the two requests.

Appendix E.  Guidance for Clients Desiring to Authenticate

   Many WebDAV clients that have already been implemented have account
   settings (similar to the way email clients store IMAP account
   settings).  Thus, the WebDAV client would be able to authenticate
   with its first couple requests to the server, provided it had a way
   to get the authentication challenge from the server with realm name,

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   nonce, and other challenge information.  Note that the results of
   some requests might vary according to whether or not the client is
   authenticated -- a PROPFIND might return more visible resources if
   the client is authenticated, yet not fail if the client is anonymous.

   There are a number of ways the client might be able to trigger the
   server to provide an authentication challenge.  This appendix
   describes a couple approaches that seem particularly likely to work.

   The first approach is to perform a request that ought to require
   authentication.  However, it's possible that a server might handle
   any request even without authentication, so to be entirely safe, the
   client could add a conditional header to ensure that even if the
   request passes permissions checks, it's not actually handled by the
   server.  An example of following this approach would be to use a PUT
   request with an "If-Match" header with a made-up ETag value.  This
   approach might fail to result in an authentication challenge if the
   server does not test authorization before testing conditionals as is
   required (see Section 8.5), or if the server does not need to test
   authorization.

   Example - forcing auth challenge with write request

   >>Request

     PUT /forceauth.txt HTTP/1.1
     Host: www.example.com
     If-Match: "xxx"
     Content-Type: text/plain
     Content-Length: 0

   The second approach is to use an Authorization header (defined in
   [RFC2617]), which is likely to be rejected by the server but which
   will then prompt a proper authentication challenge.  For example, the
   client could start with a PROPFIND request containing an
   Authorization header containing a made-up Basic userid:password
   string or with actual plausible credentials.  This approach relies on
   the server responding with a "401 Unauthorized" along with a
   challenge if it receives an Authorization header with an unrecognized
   username, invalid password, or if it doesn't even handle Basic
   authentication.  This seems likely to work because of the
   requirements of RFC 2617:

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   "If the origin server does not wish to accept the credentials sent
   with a request, it SHOULD return a 401 (Unauthorized) response.  The
   response MUST include a WWW-Authenticate header field containing at
   least one (possibly new) challenge applicable to the requested
   resource."

   There's a slight problem with implementing that recommendation in
   some cases, because some servers do not even have challenge
   information for certain resources.  Thus, when there's no way to
   authenticate to a resource or the resource is entirely publicly
   available over all accepted methods, the server MAY ignore the
   Authorization header, and the client will presumably try again later.

   Example - forcing auth challenge with Authorization header

   >>Request

     PROPFIND /docs/ HTTP/1.1
     Host: www.example.com
     Authorization: Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ==
     Content-type: application/xml; charset="utf-8"
     Content-Length: xxxx

     [body omitted]

Appendix F.  Summary of Changes from RFC 2518

   This section lists major changes between this document and RFC 2518,
   starting with those that are likely to result in implementation
   changes.  Servers will advertise support for all changes in this
   specification by returning the compliance class "3" in the DAV
   response header (see Sections 10.1 and 18.3).

F.1.  Changes for Both Client and Server Implementations

   Collections and Namespace Operations

   o  The semantics of PROPFIND 'allprop' (Section 9.1) have been
      relaxed so that servers return results including, at a minimum,
      the live properties defined in this specification, but not
      necessarily return other live properties.  The 'allprop' directive
      therefore means something more like "return all properties that
      are supposed to be returned when 'allprop' is requested" -- a set
      of properties that may include custom properties and properties
      defined in other specifications if those other specifications so
      require.  Related to this, 'allprop' requests can now be extended
      with the 'include' syntax to include specific named properties,

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      thereby avoiding additional requests due to changed 'allprop'
      semantics.

   o  Servers are now allowed to reject PROPFIND requests with Depth:
      Infinity.  Clients that used this will need to be able to do a
      series of Depth:1 requests instead.

   o  Multi-Status response bodies now can transport the value of HTTP's
      Location response header in the new 'location' element.  Clients
      may use this to avoid additional roundtrips to the server when
      there is a 'response' element with a 3xx status (see
      Section 14.24).

   o  The definition of COPY has been relaxed so that it doesn't require
      servers to first delete the target resources anymore (this was a
      known incompatibility with [RFC3253]).  See Section 9.8.

   Headers and Marshalling

   o  The Destination and If request headers now allow absolute paths in
      addition to full URIs (see Section 8.3).  This may be useful for
      clients operating through a reverse proxy that does rewrite the
      Host request header, but not WebDAV-specific headers.

   o  This specification adopts the error marshalling extensions and the
      "precondition/postcondition" terminology defined in [RFC3253] (see
      Section 16).  Related to that, it adds the "error" XML element
      inside multistatus response bodies (see Section 14.5, however note
      that it uses a format different from the one recommended in RFC
      3253).

   o  Senders and recipients are now required to support the UTF-16
      character encoding in XML message bodies (see Section 19).

   o  Clients are now required to send the Depth header on PROPFIND
      requests, although servers are still encouraged to support clients
      that don't.

   Locking

   o  RFC 2518's concept of "lock-null resources" (LNRs) has been
      replaced by a simplified approach, the "locked empty resources"
      (see Section 7.3).  There are some aspects of lock-null resources
      clients cannot rely on anymore, namely, the ability to use them to
      create a locked collection or the fact that they disappear upon
      UNLOCK when no PUT or MKCOL request was issued.  Note that servers
      are still allowed to implement LNRs as per RFC 2518.

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   o  There is no implicit refresh of locks anymore.  Locks are only
      refreshed upon explicit request (see Section 9.10.2).

   o  Clarified that the DAV:owner value supplied in the LOCK request
      must be preserved by the server just like a dead property
      (Section 14.17).  Also added the DAV:lockroot element
      (Section 14.12), which allows clients to discover the root of
      lock.

F.2.  Changes for Server Implementations

   Collections and Namespace Operations

   o  Due to interoperability problems, allowable formats for contents
      of 'href' elements in multistatus responses have been limited (see
      Section 8.3).

   o  Due to lack of implementation, support for the 'propertybehavior'
      request body for COPY and MOVE has been removed.  Instead,
      requirements for property preservation have been clarified (see
      Sections 9.8 and 9.9).

   Properties

   o  Strengthened server requirements for storage of property values,
      in particular persistence of language information (xml:lang),
      whitespace, and XML namespace information (see Section 4.3).

   o  Clarified requirements on which properties should be writable by
      the client; in particular, setting "DAV:displayname" should be
      supported by servers (see Section 15).

   o  Only 'rfc1123-date' productions are legal as values for DAV:
      getlastmodified (see Section 15.7).

   Headers and Marshalling

   o  Servers are now required to do authorization checks before
      processing conditional headers (see Section 8.5).

   Locking

   o  Strengthened requirement to check identity of lock creator when
      accessing locked resources (see Section 6.4).  Clients should be
      aware that lock tokens returned to other principals can only be
      used to break a lock, if at all.

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   o  Section 8.10.4 of [RFC2518] incorrectly required servers to return
      a 409 status where a 207 status was really appropriate.  This has
      been corrected (Section 9.10).

F.3.  Other Changes

   The definition of collection state has been fixed so it doesn't vary
   anymore depending on the Request-URI (see Section 5.2).

   The DAV:source property introduced in Section 4.6 of [RFC2518] was
   removed due to lack of implementation experience.

   The DAV header now allows non-IETF extensions through URIs in
   addition to compliance class tokens.  It also can now be used in
   requests, although this specification does not define any associated
   semantics for the compliance classes defined in here (see
   Section 10.1).

   In RFC 2518, the definition of the Depth header (Section 9.2)
   required that, by default, request headers would be applied to each
   resource in scope.  Based on implementation experience, the default
   has now been reversed (see Section 10.2).

   The definitions of HTTP status code 102 ([RFC2518], Section 10.1) and
   the Status-URI response header (Section 9.7) have been removed due to
   lack of implementation.

   The TimeType format used in the Timeout request header and the
   "timeout" XML element used to be extensible.  Now, only the two
   formats defined by this specification are allowed (see Section 10.7).

Author's Address

   Lisa Dusseault (editor)
   CommerceNet
   2064 Edgewood Dr.
   Palo Alto, CA  94303
   US

   EMail: ldusseault@commerce.net

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Full Copyright Statement

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Acknowledgement

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   Internet Society.

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