draft-ietf-webdav-rfc2518bis-01

Y. Goland, Microsoft
Internet Draft E. Whitehead, UCSC
Document: draft-ietf-webdav-rfc2518bis-01.txt A. Faizi, Netscape
Expires: Dec 2002 S. Carter, Novell
D. Jensen, Novell
L. Dusseault, Xythos

HTTP Extensions for Distributed Authoring - WebDAV RFC2518 bis

Status of this Memo

This document is an Internet-Draft and is in full conformance
with all provisions of Section 10 of RFC2026.

Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six
months and may be updated, replaced, or obsoleted by other documents
at any time. It is inappropriate to use Internet-Drafts as
reference material or to cite them other than as "work in progress."

The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt

The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.

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 RFC 2119
[RFC2119].

Abstract

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, namespace
manipulation, and resource locking (collision avoidance).

RFC2518 was published in February 1998, and this draft makes only
minor revisions mostly due to interoperability experience.

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Table of Contents

1 Introduction...................................................6
2 Notational Conventions.........................................7
3 Terminology....................................................8
4 Data Model for Resource Properties.............................8
4.1 The Resource Property Model..................................8
4.2 Existing Metadata Proposals..................................9
4.3 Properties and HTTP Headers..................................9
4.4 Property Values.............................................10
4.5 Property Names..............................................10
4.6 Media Independent Links.....................................11
5 Collections of Web Resources..................................11
5.1 HTTP URL Namespace Model....................................11
5.2 Collection Resources........................................12
5.3 Source Resources and Output Resources.......................13
6 Locking.......................................................14
6.1 Exclusive Vs. Shared Locks..................................14
6.2 Required Support............................................15
6.3 Lock Tokens.................................................16
6.4 opaquelocktoken Lock Token URI Scheme.......................16
6.5 Lock Capability Discovery...................................17
6.6 Active Lock Discovery.......................................17
6.7 Usage Considerations........................................17
7 Write Lock....................................................18
7.1 Methods Restricted by Write Locks...........................18
7.2 Write Locks and Lock Tokens.................................18
7.3 Write Locks and Properties..................................19
7.4 Write Locks and Unmapped URLs...............................19
7.5 Write Locks and Collections.................................20
7.6 Write Locks and the If Request Header.......................20
7.6.1 Example - Write Lock........................................21
7.7 Write Locks and COPY/MOVE...................................21
7.8 Refreshing Write Locks......................................22
8 HTTP Methods for Distributed Authoring........................22
8.1 PROPFIND....................................................23
8.1.1 Example - Retrieving Named Properties.......................24
8.1.2 Example - Using propname to Retrieve all Property Names.....25
8.2 PROPPATCH...................................................27
8.2.1 Status Codes for use with 207 (Multi-Status)................27
8.2.2 Example - PROPPATCH.........................................28
8.3 MKCOL Method................................................29
8.3.1 Request.....................................................29
8.3.2 Status Codes................................................29
8.3.3 Example - MKCOL.............................................30
8.4 GET, HEAD for Collections...................................30
8.5 POST for Collections........................................31

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8.6 DELETE......................................................31
8.6.1 DELETE for Non-Collection Resources.........................31
8.6.2 DELETE for Collections......................................31
8.7 PUT.........................................................32
8.7.1 PUT for Non-Collection Resources............................32
8.7.2 PUT for Collections.........................................33
8.8 COPY Method.................................................33
8.8.1 COPY for HTTP/1.1 resources.................................33
8.8.2 COPY for Properties.........................................33
8.8.3 COPY for Collections........................................34
8.8.4 COPY and the Overwrite Header...............................35
8.8.5 Status Codes................................................35
8.8.6 Example - COPY with Overwrite...............................36
8.8.7 Example - COPY with No Overwrite............................36
8.8.8 Example - COPY of a Collection..............................36
8.9 MOVE Method.................................................37
8.9.1 MOVE for Properties.........................................38
8.9.2 MOVE for Collections........................................38
8.9.3 MOVE and the Overwrite Header...............................39
8.9.4 Status Codes................................................39
8.9.5 Example - MOVE of a Non-Collection..........................39
8.9.6 Example - MOVE of a Collection..............................40
8.10 LOCK Method................................................41
8.10.1 Operation..................................................41
8.10.2 The Effect of Locks on Properties and Collections..........41
8.10.3 Locking Replicated Resources...............................42
8.10.4 Depth and Locking..........................................42
8.10.5 Interaction with other Methods.............................42
8.10.6 Lock Compatibility Table...................................42
8.10.7 Status Codes...............................................43
8.10.8 Example - Simple Lock Request..............................43
8.10.9 Example - Refreshing a Write Lock..........................44
8.10.10 Example - Multi-Resource Lock Request.....................45
8.11 UNLOCK Method..............................................47
8.11.1 Example - UNLOCK...........................................47
9 HTTP Headers for Distributed Authoring........................47
9.1 DAV Header..................................................48
9.2 Depth Header................................................48
9.3 Destination Header..........................................49
9.4 If Header...................................................49
9.4.1 No-tag-list Production......................................50
9.4.2 Tagged-list Production......................................50
9.4.3 not Production..............................................51
9.4.4 Matching Function...........................................51
9.4.5 If Header and Non-DAV Compliant Proxies.....................52
9.5 Lock-Token Header...........................................52
9.6 Overwrite Header............................................52

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9.7 Status-URI Response Header..................................53
9.8 Timeout Request Header......................................53
10 Status Code Extensions to HTTP/1.1............................54
10.1 102 Processing.............................................54
10.2 207 Multi-Status...........................................54
10.3 422 Unprocessable Entity...................................55
10.4 423 Locked.................................................55
10.5 424 Failed Dependency......................................55
10.6 507 Insufficient Storage...................................55
11 Multi-Status Response.........................................55
12 XML Element Definitions.......................................56
12.1 activelock XML Element.....................................56
12.1.1 depth XML Element..........................................56
12.1.2 locktoken XML Element......................................56
12.1.3 timeout XML Element........................................56
12.2 collection XML Element.....................................57
12.3 href XML Element...........................................57
12.4 link XML Element...........................................57
12.4.1 dst XML Element............................................57
12.4.2 src XML Element............................................58
12.5 lockentry XML Element......................................58
12.6 lockinfo XML Element.......................................58
12.7 lockscope XML Element......................................58
12.7.1 exclusive XML Element......................................59
12.7.2 shared XML Element.........................................59
12.8 locktype XML Element.......................................59
12.8.1 write XML Element..........................................59
12.9 multistatus XML Element....................................59
12.9.1 response XML Element.......................................60
12.9.2 responsedescription XML Element............................60
12.10 owner XML Element..........................................61
12.11 prop XML element...........................................61
12.12 propertyupdate XML element.................................61
12.12.1 remove XML element........................................62
12.12.2 set XML element...........................................62
12.13 propfind XML Element.......................................62
12.13.1 allprop XML Element.......................................62
12.13.2 propname XML Element......................................63
13 DAV Properties................................................64
13.1 creationdate Property......................................64
13.2 displayname Property.......................................64
13.3 getcontentlanguage Property................................64
13.4 getcontentlength Property..................................65
13.5 getcontenttype Property....................................65
13.6 getetag Property...........................................65
13.7 getlastmodified Property...................................66
13.8 lockdiscovery Property.....................................66

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13.8.1 Example - Retrieving the lockdiscovery Property............66
13.9 resourcetype Property......................................67
13.10 source Property............................................68
13.10.1 Example - A source Property...............................68
13.11 supportedlock Property.....................................69
13.11.1 Example - Retrieving the supportedlock Property...........69
14 Instructions for Processing XML in DAV........................70
15 DAV Compliance Classes........................................71
15.1 Class 1....................................................71
15.2 Class 2....................................................71
16 Internationalization Considerations...........................71
17 Security Considerations.......................................73
17.1 Authentication of Clients..................................73
17.2 Denial of Service..........................................73
17.3 Security through Obscurity.................................74
17.4 Privacy Issues Connected to Locks..........................74
17.5 Privacy Issues Connected to Properties.....................74
17.6 Reduction of Security due to Source Link...................75
17.7 Implications of XML External Entities......................75
17.8 Risks Connected with Lock Tokens...........................75
18 IANA Considerations...........................................76
19 Intellectual Property.........................................77
20 Acknowledgements..............................................77
21 References....................................................79
21.1 Normative References.......................................79
21.2 Informational References...................................80
22 Authors' Addresses............................................82
23 Appendices....................................................83
23.1 Appendix 1 - WebDAV Document Type Definition...............83
23.2 Appendix 2 - ISO 8601 Date and Time Profile................84
23.3 Appendix 3 - Notes on Processing XML Elements..............85
23.3.1 Notes on Empty XML Elements................................85
23.3.2 Notes on Illegal XML Processing............................85
23.4 Appendix 4: Node Field Generation Without the IEEE 802 Address
87
24 Full Copyright Statement......................................88

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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. Also,
the ability to link pages of any media type to related pages.

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.

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 standard 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 resource
properties (section 4), collections of resources (section 5), and
locking operations (section 6). These sections introduce the
abstractions manipulated by the WebDAV-specific HTTP methods
described in section 8, "HTTP Methods for Distributed Authoring".

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 Extensible Markup Language (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. As a rule of thumb,
parameters are encoded in XML entity bodies when they have unbounded
length, or when they may be shown to a human user and hence require
encoding in an ISO 10646 character set. Otherwise, parameters are
encoded within HTTP headers. Section 9 describes the new HTTP
headers used with WebDAV methods.

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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.

XML elements used in this specification are defined in section 12. A
DTD is provided in Appendix 1. However, legal XML may not be valid
according to this DTD, because unknown XML elements may appear in
WebDAV syntax without making the syntax illegal.

The XML namespace extension is also 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 of a
versioning method unless that XML element is explicitly defined in
an IETF RFC.

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. New status codes developed for the WebDAV methods are
defined in section 10. Since some WebDAV methods may operate over
many resources, the Multi-Status response has been introduced to
return status information for multiple resources. The Multi-Status
response is described in section 11.

WebDAV employs the property mechanism to store information about the
current state of the resource. For example, when a lock is taken
out on a resource, a lock information property describes the current
state of the lock. Section 13 defines the properties used within the
WebDAV specification.

Finishing off the specification are sections on what it means to be
compliant with this specification (section 15), on
internationalization support (section 16), and on security (section
17).

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
[RFC2068]. Since this augmented BNF uses the basic production rules
provided in section 2.2 of [RFC2068], these rules apply to this
document as well.

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3 Terminology

URI/URL - A Uniform Resource Identifier and Uniform Resource
Locator, respectively. These terms (and the distinction between
them) are defined in [RFC2396].

Collection - A resource that contains a set of URIs, termed member
URIs, which identify member resources and meets the requirements in
section 5 of this specification.

Member URI - A URI which is a member of the set of URIs contained by
a collection.

Internal Member URI - A Member URI that is immediately relative to
the URI of the collection (the definition of immediately relative is
given in section 5.2).

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 "getcontentlength" property
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.

Null Resource - A resource which responds with a 404 (Not Found) to
any HTTP/1.1 or DAV method except for PUT, MKCOL, OPTIONS and LOCK.
A NULL resource MUST NOT appear as a member of its parent
collection.

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.

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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 read-
only, 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 Existing Metadata Proposals

Properties have long played an essential role in the maintenance of
large document repositories, and many current proposals contain some
notion of a property, or discuss web metadata more generally. These
include PICS [REC-PICS], PICS-NG, XML, Web Collections, and several
proposals on representing relationships within HTML. Work on PICS-NG
and Web Collections has been subsumed by the Resource Description
Framework (RDF) metadata activity of the World Wide Web Consortium.
RDF consists of a network-based data model and an XML representation
of that model.

Some proposals come from a digital library perspective. These
include the Dublin Core [RFC2413] metadata set and the Warwick
Framework [WF], a container architecture for different metadata
schemas. The literature includes many examples of metadata,
including MARC [USMARC], a bibliographic metadata format, and a
technical report bibliographic format employed by the Dienst system
[RFC1807]. Additionally, the proceedings from the first IEEE
Metadata conference describe many community-specific metadata sets.

Participants of the 1996 Metadata II Workshop in Warwick, UK [WF],
noted that "new metadata sets will develop as the networked
infrastructure matures" and "different communities will propose,
design, and be responsible for different types of metadata." These
observations can be corroborated by noting that many community-
specific sets of metadata already exist, and there is significant
motivation for the development of new forms of metadata as many
communities increasingly make their data available in digital form,
requiring a metadata format to assist data location and cataloging.

4.3 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

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headers is inefficient. Thus a mechanism is needed which allows a
principal to identify a set of properties in which the principal is
interested and to set or retrieve just those properties.

4.4 Property Values

The value of a property when expressed in XML MUST be well formed.

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 new elements. Older clients will not break when they
encounter extensions because they will still have the data specified
in the original schema and will ignore elements they do not
understand. 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 (in the case of WebDAV properties,
this attribute is placed on the æpropÆ element), handles cases where
the same character set is employed by multiple human languages.

Other XML attributes in property values are significant. The server
MUST persistently store the XML attribute information stored on XML
elements contained by the XML element whose name is the name of the
property. Attributes on the property name element SHOULD be
persistently stored and restored in PROPFIND responses (other than
the "xml:lang" and namespace attributes which MUST be stored). The
XML attribute xml:space MUST not be used to change white space
handling.

White space in property values is significant.

4.5 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 [RFC2396], 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

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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 which 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.

4.6 Media Independent Links

Although HTML resources support links to other resources, the Web
needs more general support for links between resources of any media
type (media types are also known as MIME types, or content types).
WebDAV provides such links. A WebDAV link is a special type of
property value, formally defined in section Error! Reference source
not found., that allows typed connections to be established between
resources of any media type. The property value consists of source
and destination Uniform Resource Identifiers (URIs); the property
name identifies the link type.

5 Collections of Web Resources

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

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.
The root, or top-level collection of the namespace under
consideration is exempt from the previous rule.

Neither HTTP/1.1 nor WebDAV require that the entire HTTP URL
namespace be consistent. However, certain WebDAV methods are
prohibited from producing results that cause namespace
inconsistencies.

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Although implicit in [RFC2068] and [RFC2396], 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

A collection is a resource whose state consists of at least a list
of internal member URIs and a set of properties, but which may have
additional state such as entity bodies returned by GET. An internal
member URI MUST be immediately relative to a base URI of the
collection. That is, the internal member URI is equal to a
containing collection's URI plus an additional segment for non-
collection resources, or additional segment plus trailing slash "/"
for collection resources, where segment is defined in section 3.3 of
[RFC2396].

Any given internal member URI MUST only belong to the collection
once, i.e., it is illegal to have multiple instances of the same URI
in a collection. Properties defined on collections behave exactly
as do properties on non-collection resources.

For all WebDAV compliant resources A and B, identified by URIs U and
V, for which U is immediately relative to V, B MUST be a collection
that has U as an internal member URI. So, if the resource with URL
http://foo.com/bar/blah is WebDAV compliant and if the resource with
URL http://foo.com/bar/ is WebDAV compliant then the resource with
URL http://foo.com/bar/ must be a collection and must contain URL
http://foo.com/bar/blah as an internal member.

Collection resources MAY list the URLs of non-WebDAV compliant
children in the HTTP URL namespace hierarchy as internal members but
are not required to do so. For example, if the resource with URL
http://foo.com/bar/blah is not WebDAV compliant and the URL
http://foo.com/bar/ identifies a collection then URL
http://foo.com/bar/blah may or may not be an internal member of the
collection with URL http://foo.com/bar/.

If a WebDAV compliant resource has no WebDAV compliant children 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 trailing slash is
automatically appended. Due to this, a resource may accept a URI
without a trailing "/" to point to a collection. In this case it
SHOULD return a Content-Location header in the response pointing to
the URI ending with the "/". For example, if a client invokes a
method on http://foo.bar/blah (no trailing slash), the resource
http://foo.bar/blah/ (trailing slash) may respond as if the
operation were invoked on it, and should return a content-location

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header with http://foo.bar/blah/ in it. In general clients SHOULD
use the "/" form of collection names.

A resource MAY be a collection but not be WebDAV compliant. That
is, the resource may comply with all the rules set out in this
specification regarding how a collection is to behave without
necessarily supporting all methods that a WebDAV compliant resource
is required to support. In such a case the resource may return the
DAV:resourcetype property with the value DAV:collection but MUST NOT
return a DAV header containing the value "1" on an OPTIONS response.

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

5.3 Source Resources and Output Resources

For many resources, the entity returned by a GET method exactly
matches the persistent state of the resource, for example, a GIF
file stored on a disk. For this simple case, the URI at which a
resource is accessed is identical to the URI at which the source
(the persistent state) of the resource is accessed. This is also
the case for HTML source files that are not processed by the server
prior to transmission.

However, the server can sometimes process HTML resources before they
are transmitted as a return entity body. For example, a server-
side-include directive within an HTML file might instruct a server
to replace the directive with another value, such as the current
date. In this case, what is returned by GET (HTML plus date)
differs from the persistent state of the resource (HTML plus
directive). Typically there is no way to access the HTML resource
containing the unprocessed directive.

Sometimes the entity returned by GET is the output of a data-
producing process that is described by one or more source resources
(that may not even have a location in the URI namespace). A single
data-producing process may dynamically generate the state of a
potentially large number of output resources. An example of this is
a CGI script that describes a "finger" gateway process that maps
part of the namespace of a server into finger requests, such as
http://www.foo.bar.org/finger_gateway/user@host.

In the absence of distributed authoring capabilities, it is
acceptable to have no mapping of source resource(s) to the URI
namespace. In fact, preventing access to the source resource(s) has
desirable security benefits. However, if remote editing of the
source resource(s) is desired, the source resource(s) should be
given a location in the URI namespace. This source location should

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not be one of the locations at which the generated output is
retrievable, since in general it is impossible for the server to
differentiate requests for source resources from requests for
process output resources. There is often a many-to-many
relationship between source resources and output resources.

On WebDAV compliant servers the URI of the source resource(s) may be
stored in a link on the output resource with type DAV:source (see
section 13.10 for a description of the source link property).
Storing the source URIs in links on the output resources places the
burden of discovering the source on the authoring client. Note that
the value of a source link is not guaranteed to point to the correct
source. Source links may break or incorrect values may be entered.
Also note that not all servers will allow the client to set the
source link value. For example a server which generates source
links on the fly for its CGI files will most likely not allow a
client to set the source link value.

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.

6.1 Exclusive Vs. Shared Locks

The most basic form of lock is an exclusive lock. This is a lock
where the access right in question is only granted to a single
principal. The need for this arbitration results from a desire to
avoid having to merge results.

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 with appropriate access can get the lock.

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

Expires Dec 2002 14 WebDAV (RFC2518) bis June 2002

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 owner leaves without
unlocking a resource. While both timeouts 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.

6.2 Required Support

A WebDAV compliant server is not required to support locking in any
form. If the server 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.

Expires Dec 2002 15 WebDAV (RFC2518) bis June 2002

6.3 Lock Tokens

A lock token is a type of state token, represented as a URI, which
identifies a particular lock. A lock token is returned by every
successful LOCK operation in the lockdiscovery property in the
response body, and can also be found through lock discovery on a
resource.

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.

This specification provides a lock token URI scheme called
opaquelocktoken that meets the uniqueness requirements. However
resources are free to return any URI scheme so long as it meets the
uniqueness requirements.

Having a lock token provides no special access rights. Anyone can
find out anyone else's lock token by performing lock discovery.
Locks MUST be enforced based upon whatever authentication mechanism
is used by the server, not based on the secrecy of the token values.

6.4 opaquelocktoken Lock Token URI Scheme

The opaquelocktoken URI scheme is designed to be unique across all
resources for all time. Due to this uniqueness quality, a client
may submit an opaque lock token in an If header on a resource other
than the one that returned it.

All resources MUST recognize the opaquelocktoken scheme and, at
minimum, recognize that the lock token does not refer to an
outstanding lock on the resource.

In order to guarantee uniqueness across all resources for all time
the opaquelocktoken requires the use of the Universal Unique
Identifier (UUID) mechanism, as described in [ISO-11578].

Opaquelocktoken generators, however, have a choice of how they
create these tokens. They can either generate a new UUID for every
lock token they create or they can create a single UUID and then
add extension characters. If the second method is selected then the
program generating the extensions MUST guarantee that the same
extension will never be used twice with the associated UUID.

OpaqueLockToken-URI = "opaquelocktoken:" UUID [Extension] ; The
UUID production is the string representation of a UUID, as defined
in [ISO-11578]. Note that white space (LWS) is not allowed between
elements of this production.

Extension = path ; path is defined in section 3.2.1 of RFC 2068
[RFC2068]

Expires Dec 2002 16 WebDAV (RFC2518) bis June 2002

6.5 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. Lock capability discovery differs from discovery of
supported access control types, since there may be access control
types without corresponding lock types. A client can determine what
lock types the server supports by retrieving the supportedlock
property.

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

6.6 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 lockdiscovery
property is provided. This property lists all outstanding locks,
describes their type, and where available, provides their lock
token.

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

6.7 Usage Considerations

Although the locking mechanisms specified here 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

Expires Dec 2002 17 WebDAV (RFC2518) bis June 2002

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.

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 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.

7.1 Methods Restricted by Write Locks

A write lock MUST prevent a principal without the lock from
successfully executing a PUT, POST, PROPPATCH, LOCK, UNLOCK, MOVE,
DELETE, or MKCOL on the locked resource. All other current methods,
GET in particular, function independently of the lock.

Note, however, that as new methods are created it will be necessary
to specify how they interact with a write lock.

7.2 Write Locks and Lock Tokens

A successful request for an exclusive or shared write lock MUST
result in the generation of a unique lock token associated with the
requesting principal. Thus if five principals have a shared write
lock on the same resource there will be five lock tokens, one for
each principal.

Expires Dec 2002 18 WebDAV (RFC2518) bis June 2002

7.3 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 to respect locks
are guaranteed not to change while write locked.

7.4 Write Locks and Unmapped URLs

It is possible to lock an unmapped URL in order to lock 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 HTTP 1.1). It has the side benefit of locking
the new resource immediately for use of the creator.

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. In order to immediately lock a collection upon
creation, clients may attempt to pipeline the MKCOL and LOCK
requests together.

A lock request to an unmapped URL should result in the creation of a
resource that is locked. A subsequent PUT request with the correct
lock token should normally succeed, and provides the content,
content-type, content-language and other information as appropriate.

In this situation, WebDAV servers compliant with RFC2518 MAY create
"lock-null" resources which are special and unusual resources. A
lock-null resource:

- responds with a 404 or 405 to any DAV method except for PUT,
MKCOL, OPTIONS, PROPFIND, LOCK, UNLOCK.
- Appears as a member of its parent collection.
- Disappears (becomes once more an unmapped URL) if its lock goes
away before it is converted to a regular resource. (This must
also happen if it is renamed or moved, or if any parent collection
is renamed or moved, because locks are tied to URLs).
- May be turned into a regular resource when a PUT request to the
URL is successful. Ceases to be a lock-null resource.
- May be turned into a collection when a MKCOL request to the URL is
successful. Ceases to be a lock-null resource
- Has defined values for lockdiscovery and supportedlock properties.

However, interoperability and compliance problems have been found
with lock-null resources. Therefore, they are deprecated. WebDAV
servers compliant with this document SHOULD create regular locked
empty resources, which behave in every way as if they were a normal
resource. A locked empty resource:

- Can be downloaded, deleted, moved, copied, and in all ways behave
as a regular resource, not a lock-null resource.

Expires Dec 2002 19 WebDAV (RFC2518) bis June 2002

- Appears as a member of its parent collection.
- SHOULD NOT disappear when its lock goes away (clients must
therefore be responsible for cleaning up their own mess, as with
any other operation)
- SHOULD default to a content-type of "application/octet-stream".
- SHOULD default to reasonable, or reasonably blank, values for
other properties like getcontentlanguage.
- May have content added with a PUT request. MUST be able to change
content type.
- MUST NOT be turned into a collection. A MKCOL request must fail
as it would to any existing resource.
- MUST have defined values for lockdiscovery and supportedlock
properties.
- 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 lockdiscovery property, as with a LOCK request to an
existing resource.

Clients can easily interoperate with either kind of server (both
exist) by only attempting PUT after a LOCK to an unmapped URL, not
MKCOL or GET.

7.5 Write Locks and Collections

A write lock on a collection, whether created by a "Depth: 0" or
"Depth: infinity" lock request, prevents the addition or removal of
member URIs of the collection by non-lock owners. As a consequence,
when a principal issues a PUT or POST request to create a new
resource under a URI which needs to be an internal member of a write
locked collection to maintain HTTP namespace consistency, or issues
a DELETE to remove a resource which has a URI which is an existing
internal member URI of a write locked collection, this request MUST
fail if the principal does not have a write lock on the collection.

However, if a write lock request is issued to a collection
containing member URIs identifying resources that are currently
locked in a manner which conflicts with the write lock, the request
MUST fail with a 423 (Locked) status code.

If a lock owner causes the URI of a resource to be added as an
internal member URI of a locked collection then the new resource
MUST be automatically added to the lock. This is the only mechanism
that allows a resource to be added to a write lock. Thus, 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.

7.6 Write Locks and the If Request Header

Expires Dec 2002 20 WebDAV (RFC2518) bis June 2002

If a user agent is not required to have knowledge about a lock when
requesting an operation on a locked resource, the following scenario
might occur. 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 AÆs 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 in the If header for all locked resources
that a method may interact with or the method MUST fail. For
example, if a resource is to be moved and both the source and
destination are locked then two lock tokens must be submitted, one
for the source and the other for the destination.

7.6.1 Example - Write Lock

>>Request

COPY /~fielding/index.html HTTP/1.1
Host: www.ics.uci.edu
Destination: http://www.ics.uci.edu/users/f/fielding/index.html
If: <http://www.ics.uci.edu/users/f/fielding/index.html>
(<opaquelocktoken: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, 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.

7.7 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

Expires Dec 2002 21 WebDAV (RFC2518) bis June 2002

resource into a collection that is locked with "Depth: infinity",
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, the resource is subject
to being added to an existing lock at the destination, as specified
Comment : If a resource has in section 7.5. For example, if the MOVE makes the resource a child a "move lock" on it (a new of a collection that is locked with "Depth: infinity", then the type I just made up) then resource will be added to that collection's lock. Additionally, if a the MOVE should fail JUST because it is locked. resource locked with "Depth: infinity" is moved to a destination
that is within the scope of the same lock (e.g., within the
namespace tree covered by the lock), the moved resource will again
be a added to the lock. In both these examples, as specified in
section 7.6, an If header must be submitted containing a lock token
for both the source and destination.

7.8 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 method with an If header but
without a body. This form of LOCK MUST only be used to "refresh" a
lock. Meaning, at minimum, that any timers associated with the lock
MUST be re-set.

A server may return a Timeout header with a lock refresh that is
different than the Timeout header returned when the lock was
originally requested. Additionally clients may submit Timeout
headers of arbitrary value with their lock refresh requests.
Servers, as always, may ignore Timeout headers submitted by the
client.

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

8 HTTP Methods for Distributed Authoring

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

Expires Dec 2002 22 WebDAV (RFC2518) bis June 2002

8.1 PROPFIND

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 URIs. All DAV compliant
resources MUST support the PROPFIND method and the propfind XML
element (section Error! Reference source not found.) along with all
XML elements defined for use with that element.

A client may submit a Depth header with a value of "0", "1", or
"infinity" with a PROPFIND on a collection resource with internal
member URIs. DAV compliant servers MUST support the "0", "1" and
"infinity" behaviors. By default, the PROPFIND method without a
Depth header MUST act as if a "Depth: infinity" header was included.

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 request particular property values, all property
values, or a list of the names of the resourceÆs properties. A
client may choose not to submit a request body. An empty PROPFIND
request body MUST be treated as a request for the names and values
of all properties.

Clients MUST not send allprop requests in any form (either the empty
body PROPFIND or the specific allprop element), because allprop is
being removed. WebDAV servers increasingly have expensively-
calculated or lengthy properties (see [RFC3253] and [TODO: ref ACL
RFC when available]) and do not return all properties already.
Instead, WebDAV clients can use propname requests to discover what
properties exist, and request named properties when retrieving
values. A WebDAV server MAY omit certain live properties from other
specifications when responding to an allprop request from an older
client, and MAY return only custom (dead) properties and those
defined in this specification.

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 which does not exist is an error and MUST be
noted, if the response uses a multistatus XML element, with a
response XML element which contains a 404 (Not Found) status value.

Consequently, the multistatus XML element for a collection resource
with member URIs MUST include a response XML element for each member
URI of the collection, to whatever depth was requested. Each
response XML element MUST contain an href XML element that gives the
URI of the resource on which the properties in the prop XML element

Expires Dec 2002 23 WebDAV (RFC2518) bis June 2002

are defined. Results for a PROPFIND on a collection resource with
internal member URIs are returned as a flat list whose order of
entries is not significant.

In the case of allprop and propname, if a principal does not have
the right to know whether a particular property exists then the
property should be silently excluded from the response.

The results of this method SHOULD NOT be cached.

8.1.1 Example - Retrieving Named Properties

>>Request

PROPFIND /file HTTP/1.1
Host: www.foo.bar
Content-type: text/xml; charset="utf-8"
Content-Length: xxxx

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

>>Response

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

<?xml version="1.0" encoding="utf-8" ?>
<D:multistatus xmlns:D="DAV:">
<D:response xmlns:R="http://www.foo.bar/boxschema/">
<D:href>http://www.foo.bar/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>

Expires Dec 2002 24 WebDAV (RFC2518) bis June 2002

<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>
</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.foo.bar/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.

8.1.2 Example - Using propname to Retrieve all Property Names

>>Request

PROPFIND /container/ HTTP/1.1
Host: www.foo.bar
Content-Type: text/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: text/xml; charset="utf-8"
Content-Length: xxxx

<?xml version="1.0" encoding="utf-8" ?>
<multistatus xmlns="DAV:">
<response>
<href>http://www.foo.bar/container/</href>
<propstat>
<prop xmlns:R="http://www.foo.bar/boxschema/">
<R:bigbox/>

Expires Dec 2002 25 WebDAV (RFC2518) bis June 2002

<R:author/>
<creationdate/>
<displayname/>
<resourcetype/>
<supportedlock/>
</prop>
<status>HTTP/1.1 200 OK</status>
</propstat>
</response>
<response>
<href>http://www.foo.bar/container/front.html</href>
<propstat>
<prop xmlns:R="http://www.foo.bar/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.foo.bar/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 progeny should be returned.

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

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

Expires Dec 2002 26 WebDAV (RFC2518) bis June 2002

This example also demonstrates the use of XML namespace scoping, and
the default namespace. Since the "xmlns" attribute does not contain
an explicit "shorthand name" (prefix) letter, the namespace applies
by default to all enclosed elements. Hence, all elements which do
not explicitly state the namespace to which they belong are members
of the "DAV:" namespace schema.

8.2 PROPPATCH

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 of the DAV schema.
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. Instruction processing MUST occur in
the order instructions are received (i.e., from top to bottom).
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 section Error! Reference source not found..

8.2.1 Status Codes for use with 207 (Multi-Status)

The following are examples of response codes one would expect to be
used in a 207 (Multi-Status) response for this method. Note,
however, that unless explicitly prohibited any 2/3/4/5xx series
response code may be used in a 207 (Multi-Status) response.

200 (OK) - The command succeeded. As there can be a mixture of sets
and removes in a body, a 201 (Created) seems inappropriate.

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

409 (Conflict) - The client has provided a value whose semantics are
not appropriate for the property. This includes trying to set read-
only properties.

423 (Locked) - The specified resource is locked and the client
either is not a lock owner or the lock type requires a lock token to
be submitted and the client did not submit it.

Expires Dec 2002 27 WebDAV (RFC2518) bis June 2002

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

8.2.2 Example - PROPPATCH

>>Request

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

<?xml version="1.0" encoding="utf-8" ?>
<D:propertyupdate xmlns:D="DAV:"
xmlns:Z="http://www.w3.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>

>>Response

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

<?xml version="1.0" encoding="utf-8" ?>
<D:multistatus xmlns:D="DAV:"
xmlns:Z="http://www.w3.com/standards/z39.50">
<D:response>
<D:href>http://www.foo.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>

Expires Dec 2002 28 WebDAV (RFC2518) bis June 2002

<D:responsedescription> Copyright Owner can not 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://www.w3.com/standards/z39.50/"
namespace, and to remove the property "Copyright-Owner" in the
"http://www.w3.com/standards/z39.50/" 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.

8.3 MKCOL Method

The MKCOL method is used to create a new collection. All DAV
compliant resources MUST support the MKCOL method.

8.3.1 Request

MKCOL creates a new collection resource at the location specified by
the Request-URI. If the resource identified by the Request-URI is
non-null then the MKCOL MUST fail. During MKCOL processing, a
server MUST make the Request-URI a 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 neither /a/b/ nor /a/b/c/
exists, the request must fail.

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

A MKCOL request message may contain a message body. The behavior of
a MKCOL request when the body is present is 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. The exact
behavior of MKCOL for various request media types is undefined in
this document, and will be specified in separate documents.

8.3.2 Status Codes

Responses from a MKCOL request MUST NOT be cached as MKCOL has non-
idempotent semantics.

Expires Dec 2002 29 WebDAV (RFC2518) bis June 2002

201 (Created) - The collection or structured resource was created in
its entirety.

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 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 a
deleted/non-existent resource.

409 (Conflict) - A collection cannot be made at the Request-URI
until one or more intermediate collections have been created.

415 (Unsupported Media Type)- The server does not support the
request type of the body.

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

8.3.3 Example - MKCOL

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

>>Request

MKCOL /webdisc/xfiles/ HTTP/1.1
Host: www.server.org

>>Response

HTTP/1.1 201 Created

8.4 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" [RFC2068]. 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.

Expires Dec 2002 30 WebDAV (RFC2518) bis June 2002

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.

8.5 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.

8.6 DELETE

8.6.1 DELETE for Non-Collection Resources

If the DELETE method is issued to a non-collection resource whose
URIs are an internal member of one or more collections, then during
DELETE processing a server MUST remove any URI for the resource
identified by the Request-URI from collections which contain it as a
member.

8.6.2 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 URIs are to be
deleted.

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

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). 424 (Failed Dependency) errors SHOULD NOT be in the
207 (Multi-Status). 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.

Expires Dec 2002 31 WebDAV (RFC2518) bis June 2002

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.

8.6.2.1 Example - DELETE

>>Request

DELETE /container/ HTTP/1.1
Host: www.foo.bar

>>Response

HTTP/1.1 207 Multi-Status
Content-Type: text/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.foo.bar/container/resource3</d:href>
<d:status>HTTP/1.1 423 Locked</d:status>
</d:response>
</d:multistatus>

In this example the attempt to delete
http://www.foo.bar/container/resource3 failed because it is locked,
and no lock token was submitted with the request. Consequently, the
attempt to delete http://www.foo.bar/container/ also failed. Thus
the client knows that the attempt to delete
http://www.foo.bar/container/ must have also failed since the parent
can not 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.

8.7 PUT

8.7.1 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).

Expires Dec 2002 32 WebDAV (RFC2518) bis June 2002

8.7.2 PUT for Collections

As defined in the HTTP/1.1 specification [RFC2068], the "PUT method
requests that the enclosed entity be stored under the supplied
Request-URI." Since submission of an entity representing a
collection would implicitly encode creation and deletion of
resources, this specification intentionally does not define a
transmission format for creating a collection using PUT. Instead,
the MKCOL method is defined to create collections.

8.8 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.

8.8.1 COPY for HTTP/1.1 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. After a successful COPY invocation, all properties on the
source resource MUST be duplicated on the destination resource,
subject to modifying headers and XML elements, following the
definition for copying properties. 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.

8.8.2 COPY for Properties

Live properties described in this document SHOULD be duplicated as
identically behaving live properties at the destination resource.
If a property cannot be copied live, then its value MUST be

Expires Dec 2002 33 WebDAV (RFC2518) bis June 2002

duplicated, octet-for-octet, in an identically named, dead property
on the destination resource.

8.8.3 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". DAV compliant servers MUST support the "0" and
"infinity" Depth header behaviors.

A COPY of depth infinity 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.

A COPY of "Depth: 0" only instructs that the collection and its
properties but not resources identified by its internal member URIs,
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://fun.com/ and the
Destination is http://fun.com/b/ then when http://fun.com/a/c/d is
processed it must use a Destination of http://fun.com/b/c/d.

When the COPY method has completed processing it MUST have created a
consistent 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 descendents 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.

Expires Dec 2002 34 WebDAV (RFC2518) bis June 2002

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).

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.

8.8.4 COPY and the Overwrite Header

If a resource exists at the destination and the Overwrite header is
"T" then prior to performing the copy 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.

8.8.5 Status Codes

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
pre-existing 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. E.g. if a destination resource was locked and could
not be overwritten, then the destination resource URL appears with
the 423 (Locked) status.

403 (Forbidden) û The source and destination URIs are the same.

409 (Conflict) û A resource cannot be created at the destination
until one or more intermediate collections have been created.

412 (Precondition Failed) û A precondition failed, e.g. the
Overwrite header is "F" and the state of the destination resource is
non-null.

423 (Locked) - The destination resource was locked.

502 (Bad Gateway) - This may occur when the destination is on
another server and the destination server refuses to accept the
resource.

Expires Dec 2002 35 WebDAV (RFC2518) bis June 2002

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

8.8.6 Example - COPY with Overwrite

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

>>Request

COPY /~fielding/index.html HTTP/1.1
Host: www.ics.uci.edu
Destination: http://www.ics.uci.edu/users/f/fielding/index.html

>>Response

HTTP/1.1 204 No Content

8.8.7 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 resource
has a non-null state.

>>Request

COPY /~fielding/index.html HTTP/1.1
Host: www.ics.uci.edu
Destination: http://www.ics.uci.edu/users/f/fielding/index.html
Overwrite: F

>>Response

HTTP/1.1 412 Precondition Failed

8.8.8 Example - COPY of a Collection

>>Request

COPY /container/ HTTP/1.1
Host: www.foo.bar
Destination: http://www.foo.bar/othercontainer/

Expires Dec 2002 36 WebDAV (RFC2518) bis June 2002

Depth: infinity

>>Response

HTTP/1.1 207 Multi-Status
Content-Type: text/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.foo.bar/othercontainer/R2/</d:href>
<d:status>HTTP/1.1 423 Locked</d:status>
</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 given in section 8.8.3.

8.9 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 atomically. The consistency maintenance step
allows the server to perform updates caused by the move, such as
updating all URIs other than the Request-URI which identify the
source resource, to point to the new destination resource.
Consequently, 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 DAV compliant resources MUST support the MOVE
method. However, 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.

Expires Dec 2002 37 WebDAV (RFC2518) bis June 2002

8.9.1 MOVE for Properties

The behavior of properties on a MOVE MUST be the same as specified
in section 8.8.2.

8.9.2 MOVE for Collections

A MOVE with "Depth: infinity" instructs that the collection
identified by the Request-URI be moved to the URI specified in the
Destination header, and all resources identified by its internal
member URIs 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".

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 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 descendents 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).

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)

Expires Dec 2002 38 WebDAV (RFC2518) bis June 2002

responses from a MOVE. These responses can be safely omitted
because they are the default success codes.

8.9.3 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.

8.9.4 Status Codes

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

204 (No Content) - The source resource was successfully moved to a
pre-existing destination resource.

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. E.g. if a source resource was locked and could not
be moved, then the source resource URL appears with the 423 (Locked)
status.

403 (Forbidden) û The source and destination URIs are the same.

409 (Conflict) û A resource cannot be created at the destination
until one or more intermediate collections have been created.

412 (Precondition Failed) û A condition failed, e.g. the Overwrite
header is "F" and the state of the destination resource is non-null.

423 (Locked) - The source or the destination resource was locked.

502 (Bad Gateway) - This may occur when the destination is on
another server and the destination server refuses to accept the
resource.

8.9.5 Example - MOVE of a Non-Collection

This example shows resource
http://www.ics.uci.edu/~fielding/index.html being moved to the
location http://www.ics.uci.edu/users/f/fielding/index.html. The
contents of the destination resource would have been overwritten if
the destination resource had been non-null. In this case, since
there was nothing at the destination resource, the response code is
201 (Created).

Expires Dec 2002 39 WebDAV (RFC2518) bis June 2002

>>Request

MOVE /~fielding/index.html HTTP/1.1
Host: www.ics.uci.edu
Destination: http://www.ics.uci.edu/users/f/fielding/index.html

>>Response

HTTP/1.1 201 Created
Location: http://www.ics.uci.edu/users/f/fielding/index.html

8.9.6 Example - MOVE of a Collection

>>Request

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

>>Response

HTTP/1.1 207 Multi-Status
Content-Type: text/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.foo.bar/othercontainer/C2/</d:href>
<d:status>HTTP/1.1 423 Locked</d:status>
</d:response>
</d:multistatus>

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.foo.bar/othercontainer/C2/.
This means that the resource /container/C2/ could not be moved.
Because there was an error copying /container/C2/, none of
/container/C2's members were copied. However no errors were listed
for those members due to the error minimization rules given in
section 8.8.3. User agent authentication has previously occurred

Expires Dec 2002 40 WebDAV (RFC2518) bis June 2002

via a mechanism outside the scope of the HTTP protocol, in an
underlying transport layer.

8.10 LOCK Method

The following sections describe the LOCK method, which is used to
take out a lock of any access type. 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 which supports the LOCK method MUST, at minimum,
support the XML request and response formats defined herein.

8.10.1 Operation

A LOCK method invocation creates the lock specified by the lockinfo
XML element on the Request-URI. Lock method requests SHOULD have a
XML request body which contains an owner XML element for this lock
request, unless this is a refresh request. The server MUST preserve
the information provided by the client in the owner field when the
lock information is requested. The LOCK request may have a Timeout
header.

Clients MUST assume that locks may 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. The response MUST contain the value of the
lockdiscovery property in a prop XML element.

In order to indicate the lock token associated with a newly created
lock, a Lock-Token response header MUST be included in the response
for every successful LOCK request for a new lock. Note that the
Lock-Token header would not be returned in the response for a
successful refresh LOCK request because a new lock was not created.

8.10.2 The Effect of Locks on Properties and Collections

The scope of a lock is the entire state of the resource, including
its body and associated properties. As a result, a lock on a
resource MUST also lock the resource's properties.

For collections, a lock also affects the ability to add or remove
members. The nature of the effect depends upon the type of access
control involved.

Expires Dec 2002 41 WebDAV (RFC2518) bis June 2002

8.10.3 Locking Replicated Resources

A resource may be made available through more than one URI. However
locks apply to resources, not URIs. Therefore a LOCK request on a
resource MUST NOT succeed if can not be honored by all the URIs
through which the resource is addressable.

8.10.4 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 internal members, all the way
down the hierarchy, are to be locked. A successful result MUST
return a single lock token which represents all the resources that
have been locked. If an UNLOCK is successfully executed on this
token, all associated resources are unlocked. If the lock cannot be
granted to all resources, a 409 (Conflict) status code MUST be
returned with a response entity body containing a multistatus XML
element describing which resource(s) prevented the lock from being
granted. Hence, partial success is not an option. Either the
entire hierarchy is locked or no resources are locked.

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

8.10.5 Interaction with other Methods

The interaction of a LOCK with various methods is dependent upon the
lock type. However, independent of lock type, a successful DELETE
of a resource MUST cause all of its locks to be removed.

8.10.6 Lock Compatibility Table

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

CURRENT LOCK STATE/ SHARED EXCLUSIVE
LOCK REQUEST LOCK LOCK
None True True
Shared Lock True False
Exclusive Lock False False*

Expires Dec 2002 42 WebDAV (RFC2518) bis June 2002

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
the lock must not be granted.

8.10.7 Status Codes

200 (OK) - The lock request succeeded and the value of the
lockdiscovery property is included in the body.

409 (Conflict) û A resource cannot be created at the destination
until one or more intermediate collections have been created.

412 (Precondition Failed) - The included lock token was not
enforceable on this resource or the server could not satisfy the
request in the lockinfo XML element.

423 (Locked) - The resource is locked, so the method has been
rejected.
8.10.8 Example - Simple Lock Request

>>Request

LOCK /workspace/webdav/proposal.doc HTTP/1.1
Host: webdav.sb.aol.com
Timeout: Infinite, Second-4100000000
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
Authorization: Digest username="ejw",
realm="ejw@webdav.sb.aol.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://www.ics.uci.edu/~ejw/contact.html</D:href>
</D:owner>
</D:lockinfo>

Expires Dec 2002 43 WebDAV (RFC2518) bis June 2002

>>Response

HTTP/1.1 200 OK
Lock-Token: <opaquelocktoken:e71d4fae-5dec-22d6-fea5-00a0c91e6be4>
Content-Type: text/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://www.ics.uci.edu/~ejw/contact.html
</D:href>
</D:owner>
<D:timeout>Second-604800</D:timeout>
<D:locktoken>
<D:href>opaquelocktoken:e71d4fae-5dec-22d6-fea5-
00a0c91e6be4</D:href>
</D:locktoken>
</D:activelock>
</D:lockdiscovery>
</D:prop>

This example shows the successful creation of an exclusive write
lock on resource
http://webdav.sb.aol.com/workspace/webdav/proposal.doc. The
resource http://www.ics.uci.edu/~ejw/contact.html contains contact
information for the owner 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.

Note that the locktoken href element would not contain any
whitespace. The line return appearing in this document is only for
formatting.

8.10.9 Example - Refreshing a Write Lock

>>Request

LOCK /workspace/webdav/proposal.doc HTTP/1.1

Expires Dec 2002 44 WebDAV (RFC2518) bis June 2002

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

>>Response

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

This request would refresh the lock, resetting any time outs.
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.

8.10.10 Example - Multi-Resource Lock Request

>>Request

LOCK /webdav/ HTTP/1.1
Host: webdav.sb.aol.com
Timeout: Infinite, Second-4100000000

Expires Dec 2002 45 WebDAV (RFC2518) bis June 2002

Depth: infinity
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
Authorization: Digest username="ejw",
realm="ejw@webdav.sb.aol.com", nonce="...",
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://www.ics.uci.edu/~ejw/contact.html</D:href>
</D:owner>
</D:lockinfo>

>>Response

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

<?xml version="1.0" encoding="utf-8" ?>
<D:multistatus xmlns:D="DAV:">
<D:response>
<D:href>http://webdav.sb.aol.com/webdav/secret</D:href>
<D:status>HTTP/1.1 403 Forbidden</D:status>
</D:response>
<D:response>
<D:href>http://webdav.sb.aol.com/webdav/</D:href>
<D:propstat>
<D:prop><D:lockdiscovery/></D:prop>
<D:status>HTTP/1.1 424 Failed Dependency</D:status>
</D:propstat>
</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://webdav.sb.aol.com/webdav/secret. Because this resource could
not be locked, none of the resources were locked. Note also that
the lockdiscovery property for the Request-URI has been included as

Expires Dec 2002 46 WebDAV (RFC2518) bis June 2002

required. In this example the lockdiscovery property is empty which
means that there are no outstanding locks on the resource.

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

8.11 UNLOCK Method

The UNLOCK method removes the lock identified by the lock token in
the Lock-Token request header from the Request-URI, and all other
resources included in the lock. If all resources which have been
locked under the submitted lock token can not be unlocked then the
UNLOCK request MUST fail.

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

8.11.1 Example - UNLOCK

>>Request

UNLOCK /workspace/webdav/info.doc HTTP/1.1
Host: webdav.sb.aol.com
Lock-Token: <opaquelocktoken:a515cfa4-5da4-22e1-f5b5-00a0451e6bf7>
Authorization: Digest username="ejw",
realm="ejw@webdav.sb.aol.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
"opaquelocktoken:a515cfa4-5da4-22e1-f5b5-00a0451e6bf7" is
successfully removed from the resource
http://webdav.sb.aol.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. The 204 (No Content) status code is
used instead of 200 (OK) because there is no response entity body.

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

9 HTTP Headers for Distributed Authoring

Expires Dec 2002 47 WebDAV (RFC2518) bis June 2002

9.1 DAV Header

DAV = "DAV" ":" "1" ["," "2"] ["," 1#extend]

This header indicates that the resource supports the DAV schema and
protocol as specified. All DAV compliant resources MUST return the
DAV header on all OPTIONS responses.

The value is a list of all compliance classes that the resource
supports. Note that above a comma has already been added to the 2.
This is because a resource can not be level 2 compliant unless it is
also level 1 compliant. Please refer to section Error! Reference
source not found. for more details. In general, however, support for
one compliance class does not entail support for any other.

9.2 Depth Header

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

The Depth header is used with methods executed on resources which
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 immediate children, ("Depth: 1"), or the resource
and all its progeny ("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.

Methods which 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 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.

Expires Dec 2002 48 WebDAV (RFC2518) bis June 2002

Any headers on a method that has a defined interaction with the
Depth header MUST be applied to all resources in the scope of the
method except where alternative behavior is explicitly defined. For
example, an If-Match header will have its value applied against
every resource in the method's scope and will cause the method to
fail if the header fails to match.

If a resource, source or destination, within the scope of the method
with a 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 children. If a resource does not have internal
children then the Depth header MUST be ignored.

Please note, however, that it is always an error to submit a value
for the Depth header that is not allowed by the method's definition.
Thus submitting a "Depth: 1" on a COPY, even if the resource does
not have internal members, will result in a 400 (Bad Request). The
method should fail not because the resource doesn't have internal
members, but because of the illegal value in the header.

9.3 Destination Header

Destination = "Destination" ":" absoluteURI

The Destination header specifies the URI which identifies a
destination resource for methods such as COPY and MOVE, which take
two URIs as parameters. Note that the absoluteURI production is
defined in [RFC2396].

9.4 If Header

If = "If" ":" ( 1*No-tag-list | 1*Tagged-list)
No-tag-list = List
Tagged-list = Resource 1*List
Resource = Coded-URL
List = "(" 1*(["Not"](State-token | "[" entity-tag "]")) ")"
State-token = Coded-URL
Coded-URL = "<" absoluteURI ">"

The If header is intended to have similar functionality to the If-
Match header defined in section 14.25 of [RFC2068]. However the If
header is intended for use with any URI which represents state
information, referred to as a state token, about a resource 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.

Expires Dec 2002 49 WebDAV (RFC2518) bis June 2002

All DAV compliant resources MUST honor the If header.

The If header's purpose is to describe a series of state lists. If
the state of the resource to which the header is applied does not
match any of the specified state lists then the request MUST fail
with a 412 (Precondition Failed). If one of the described state
lists matches the state of the resource then the request may
succeed.

Note that the absoluteURI production is defined in [RFC2396].

9.4.1 No-tag-list Production

The No-tag-list production describes a series of state tokens and
ETags. If multiple No-tag-list productions are used then one only
needs to match the state of the resource for the method to be
allowed to continue.

If a method, due to the presence of a Depth or Destination header,
is applied to multiple resources then the No-tag-list production
MUST be applied to each resource the method is applied to.

9.4.1.1 Example - No-tag-list If Header

If: (<locktoken:a-write-lock-token> ["I am an ETag"]) (["I am
another ETag"])

The previous header would require that any resources within the
scope of the method must either be locked with the specified lock
token and 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
being in the form (or (and <locktoken:a-write-lock-token> ["I am an
ETag"]) (and ["I am another ETag"])).

9.4.2 Tagged-list Production

The tagged-list production scopes a list production. That is, it
specifies that the lists following the resource specification only
apply to the specified resource. The scope of the resource
production begins with the list production immediately following the
resource production and ends with the next resource production, if
any.

When the If header is applied to a particular resource, the Tagged-
list productions MUST be searched to determine if any of the listed
resources match the operand resource(s) for the current method. If
none of the resource productions match the current resource then the
header MUST be ignored. If one of the resource productions does

Expires Dec 2002 50 WebDAV (RFC2518) bis June 2002

match the name of the resource under consideration then the list
productions following the resource production MUST be applied to the
resource in the manner specified in the previous section.

The same URI MUST NOT appear more than once in a resource production
in an If header.

9.4.2.1 Example - Tagged List If header

COPY /resource1 HTTP/1.1
Host: www.foo.bar
Destination: http://www.foo.bar/resource2
If: <http://www.foo.bar/resource1> (<locktoken:a-write-lock-token>
[W/"A weak ETag"]) (["strong ETag"])
<http://www.bar.bar/random>(["another strong ETag"])

In this example http://www.foo.bar/resource1 is being copied to
http://www.foo.bar/resource2. When the method is first applied to
http://www.foo.bar/resource1, resource1 must be in the state
specified by "(<locktoken:a-write-lock-token> [W/"A weak ETag"])
(["strong ETag"])", that is, it either must be locked with a lock
token of "locktoken:a-write-lock-token" and have a weak entity tag
W/"A weak ETag" or it must have a strong entity tag "strong ETag".

That is the only success condition since the resource
http://www.bar.bar/random never has the method applied to it (the
only other resource listed in the If header) and
http://www.foo.bar/resource2 is not listed in the If header.

9.4.3 not Production

Every state token or ETag is either current, and hence describes the
state of a resource, or is not current, and does not describe the
state of a resource. The boolean operation of matching a state token
or ETag to the current state of a resource thus resolves to a true
or false value. The not production is used to reverse that value.
The scope of the not production is the state-token or entity-tag
immediately following it.

If: (Not <locktoken:write1> <locktoken:write2>)

When submitted with a request, this If header requires that all
operand resources must not be locked with locktoken:write1 and must
be locked with locktoken:write2.

9.4.4 Matching Function

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

Expires Dec 2002 51 WebDAV (RFC2518) bis June 2002

Matching entity tag: Where the entity tag matches an entity tag
associated with that resource.

Matching state token: Where there is an exact match between the
state token in the If header and any state token on the resource.

9.4.5 If Header and Non-DAV Compliant Proxies

Non-DAV compliant 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 "Cache-Control: no-cache" request header MUST be used 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.

9.5 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.

9.6 Overwrite Header

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

The Overwrite header specifies whether the server should overwrite
the state of a non-null destination resource during a COPY or MOVE.
A value of "F" states that the server must not perform the COPY or
MOVE operation if the state of the destination resource is non-null.
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 the If-Match: * header of HTTP/1.1, 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.

All DAV compliant resources MUST support the Overwrite header.

Expires Dec 2002 52 WebDAV (RFC2518) bis June 2002

9.7 Status-URI Response Header

The Status-URI response header may be used with the 102 (Processing)
status code to inform the client as to the status of a method.

Status-URI = "Status-URI" ":" *(Status-Code Coded-URL) ; Status-Code
is defined in 6.1.1 of [RFC2068]

The URIs listed in the header are source resources which have been
affected by the outstanding method. The status code indicates the
resolution of the method on the identified resource. So, for
example, if a MOVE method on a collection is outstanding and a 102
(Processing) response with a Status-URI response header is returned,
the included URIs will indicate resources that have had move
attempted on them and what the result was.

9.8 Timeout Request Header

TimeOut = "Timeout" ":" 1#TimeType
TimeType = ("Second-" DAVTimeOutVal | "Infinite" | Other)
DAVTimeOutVal = 1*digit
Other = "Extend" field-value ; See section 4.2 of [RFC2068]

Clients may include Timeout 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.

A Timeout request header MUST contain at least one TimeType and may
contain multiple TimeType entries. The purpose of listing multiple
TimeType entries is to indicate multiple different values and value
types that are acceptable to the client. The client lists the
TimeType entries in order of preference.

Timeout response values MUST use a Second value, Infinite, or a
TimeType the client has indicated familiarity with. The server may
assume a client is familiar with any TimeType submitted in a Timeout
header.

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.

The timeout counter SHOULD NOT be restarted any time an owner of the
lock sends a method to any member of the lock, including unsupported
methods, or methods which are unsuccessful. However the lock MUST
be refreshed if a refresh LOCK method is successfully received.

Expires Dec 2002 53 WebDAV (RFC2518) bis June 2002

If the timeout expires then the lock may be lost. Specifically, if
the server wishes to harvest the lock upon time-out, the server
SHOULD act as if an UNLOCK method was executed by the server on the
resource using the lock token of the timed-out lock, performed with
its override authority. Thus logs should be updated with the
disposition of the lock, notifications should be sent, etc., just as
they would be for an UNLOCK request.

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 off-line.

A client MUST NOT assume that just because the time-out has expired
the lock has been lost.

10 Status Code Extensions to HTTP/1.1

The following status codes are added to those defined in HTTP/1.1
[RFC2068].

10.1 102 Processing

The 102 (Processing) status code is an interim response used to
inform the client that the server has accepted the complete request,
but has not yet completed it. This status code SHOULD only be sent
when the server has a reasonable expectation that the request will
take significant time to complete. As guidance, if a method is
taking longer than 20 seconds (a reasonable, but arbitrary value) to
process the server SHOULD return a 102 (Processing) response. The
server MUST send a final response after the request has been
completed.

Methods can potentially take a long period of time to process,
especially methods that support the Depth header. In such cases the
client may time-out the connection while waiting for a response. To
prevent this the server may return a 102 (Processing) status code to
indicate to the client that the server is still processing the
method.

10.2 207 Multi-Status

Expires Dec 2002 54 WebDAV (RFC2518) bis June 2002

The 207 (Multi-Status) status code provides status for multiple
independent operations (see section Error! Reference source not
found. for more information).

10.3 422 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.

10.4 423 Locked

The 423 (Locked) status code means the source or destination
resource of a method is locked.

10.5 424 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).

10.6 507 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 which 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.

11 Multi-Status Response

The default 207 (Multi-Status) response body is a text/xml or
application/xml HTTP entity that contains a single XML element
called multistatus, which contains a set of XML elements called
response which 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.

Expires Dec 2002 55 WebDAV (RFC2518) bis June 2002

12 XML Element Definitions

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).

12.1 activelock XML Element

Name: activelock
Namespace: DAV:
Purpose: Describes a lock on a resource.

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

12.1.1 depth XML Element

Name: depth
Namespace: DAV:
Purpose: The value of the Depth header.
Value: "0" | "1" | "infinity"

<!ELEMENT depth (#PCDATA) >

12.1.2 locktoken XML Element

Name: locktoken
Namespace: DAV:
Purpose: The lock token associated with a lock.
Description: The href contains one or more opaque lock token
URIs which all refer to the same lock (i.e., the
OpaqueLockToken-URI production in section 6.4).

<!ELEMENT locktoken (href+) >

12.1.3 timeout XML Element

Name: timeout
Namespace: DAV:
Purpose: The timeout associated with a lock

Expires Dec 2002 56 WebDAV (RFC2518) bis June 2002

Value: TimeType ;Defined in section 23.2.

<!ELEMENT timeout (#PCDATA) >

12.2 collection XML Element

Name: collection
Namespace: DAV:
Purpose: Identifies the associated resource as a collection. The
resourcetype property of a collection resource MUST have
this value.

<!ELEMENT collection EMPTY >

12.3 href XML Element

Name: href
Namespace: DAV:
Purpose: Identifies the content of the element as a URI.
Value: URI ; See section 3.2.1 of [RFC2068]

<!ELEMENT href (#PCDATA)>

12.4 link XML Element

Name: link
Namespace: DAV:
Purpose: Identifies the property as a link and contains the source
and destination of that link.
Description: The link XML element is used to provide the
sources and destinations of a link. The name of the
property containing the link XML element provides the type
of the link. Link is a multi-valued element, so multiple
links may be used together to indicate multiple links with
the same type. The values in the href XML elements inside
the src and dst XML elements of the link XML element MUST
NOT be rejected if they point to resources which do not
exist.

<!ELEMENT link (src+, dst+) >

12.4.1 dst XML Element

Name: dst

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Namespace: DAV:
Purpose: Indicates the destination of a link
Value: URI

<!ELEMENT dst (#PCDATA) >

12.4.2 src XML Element

Name: src
Namespace: DAV:
Purpose: Indicates the source of a link.
Value: URI

<!ELEMENT src (#PCDATA) >

12.5 lockentry XML Element

Name: lockentry
Namespace: DAV:
Purpose: Defines the types of locks that can be used with the
resource.

<!ELEMENT lockentry (lockscope, locktype) >

12.6 lockinfo XML Element

Name: lockinfo
Namespace: DAV:
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?) >

12.7 lockscope XML Element

Name: lockscope
Namespace: DAV:
Purpose: Specifies whether a lock is an exclusive lock, or a shared
lock.

<!ELEMENT lockscope (exclusive | shared) >

Expires Dec 2002 58 WebDAV (RFC2518) bis June 2002

12.7.1 exclusive XML Element

Name: exclusive
Namespace: DAV:
Purpose: Specifies an exclusive lock

<!ELEMENT exclusive EMPTY >

12.7.2 shared XML Element

Name: shared
Namespace: DAV:
Purpose: Specifies a shared lock

<!ELEMENT shared EMPTY >

12.8 locktype XML Element

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

<!ELEMENT locktype (write) >

12.8.1 write XML Element

Name: write
Namespace: DAV:
Purpose: Specifies a write lock.

<!ELEMENT write EMPTY >

12.9 multistatus XML Element

Name: multistatus
Namespace: DAV:
Purpose: Contains multiple response messages.
Description: The responsedescription 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.

Expires Dec 2002 59 WebDAV (RFC2518) bis June 2002

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

12.9.1 response XML Element

Name: response
Namespace: DAV:
Purpose: Holds a single response describing the effect of a method
on resource and/or its properties.
Description: A particular href 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.

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

12.9.1.1 propstat XML Element

Name: propstat
Namespace: DAV:
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.

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

12.9.1.2 status XML Element

Name: status
Namespace: DAV:
Purpose: Holds a single HTTP status-line
Value: status-line ;status-line defined in [RFC2068]

<!ELEMENT status (#PCDATA) >

12.9.2 responsedescription XML Element

Name: responsedescription

Expires Dec 2002 60 WebDAV (RFC2518) bis June 2002

Namespace: DAV:
Purpose: Contains a message that can be displayed to the user
explaining the nature of the response.
Description: This XML element provides information suitable
to be presented to a user.

<!ELEMENT responsedescription (#PCDATA) >

12.10 owner XML Element

Name: owner
Namespace: DAV:
Purpose: Provides information about the principal taking out a lock.
Description: The owner XML element provides 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 of a homepage) who owns a lock.

<!ELEMENT owner ANY>

12.11 prop XML element

Name: prop
Namespace: DAV:
Purpose: Contains properties related to a resource.
Description: The prop XML element is a generic container for
properties defined on resources. All elements inside a
prop XML element MUST define properties related to the
resource. No other elements may be used inside of a prop
element.

<!ELEMENT prop ANY>

12.12 propertyupdate XML element

Name: propertyupdate
Namespace: DAV:
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. This XML element is multi-valued.

<!ELEMENT propertyupdate (remove | set)+ >

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12.12.1 remove XML element

Name: remove
Namespace: DAV:
Purpose: Lists the DAV 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) >

12.12.2 set XML element

Name: set
Namespace: DAV:
Purpose: Lists the DAV property values to be set for a resource.
Description: The set XML element MUST contain only a prop
XML element. The elements contained by the prop XML
element inside the set XML 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 in
the property's value (in the "xml:lang" attribute, if
present) MUST be persistently stored along with the
property, and MUST be subsequently retrievable using
PROPFIND.

<!ELEMENT set (prop) >

12.13 propfind XML Element

Name: propfind
Namespace: DAV:
Purpose: Specifies the properties to be returned from a PROPFIND
method. Two special elements are specified for use with
propfind, allprop and propname. If prop is used inside
propfind it MUST only contain property names, not values.

<!ELEMENT propfind (allprop | propname | prop) >

12.13.1 allprop XML Element

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Name: allprop
Namespace: DAV:
Purpose: The allprop XML element specifies that all property names
and values on the resource are to be returned.

<!ELEMENT allprop EMPTY >

12.13.2 propname XML Element

Name: propname
Namespace: DAV:
Purpose: The propname XML element specifies that only a list of
property names on the resource is to be returned.

<!ELEMENT propname EMPTY >

Expires Dec 2002 63 WebDAV (RFC2518) bis June 2002

13 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).

13.1 creationdate Property

Name: creationdate
Namespace: DAV:
Purpose: Records the time and date the resource was created.
Value: date-time ; See Appendix 2
Description: The creationdate property should be defined on
all DAV compliant resources. If present, it contains a
timestamp of the moment when the resource was created
(i.e., the moment it had non-null state). This property is
live and protected.

<!ELEMENT creationdate (#PCDATA) >

13.2 displayname Property

Name: displayname
Namespace: DAV:
Purpose: Provides a name for the resource that is suitable for
presentation to a user.
Description: The displayname property should be defined on
all DAV compliant resources. If present, the property
contains a description of the resource that is suitable for
presentation to a user. This property is live and MAY be
protected.

<!ELEMENT displayname (#PCDATA) >

13.3 getcontentlanguage Property

Name: getcontentlanguage
Namespace: DAV:
Purpose: Contains the Content-Language header returned by a GET
without accept headers

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Description: The getcontentlanguage property MUST be defined
on any DAV compliant resource that returns the Content-
Language header on a GET. This property is live and MAY be
protected.
Value: language-tag ;language-tag is defined in section 14.13 of
[RFC2068]

<!ELEMENT getcontentlanguage (#PCDATA) >

13.4 getcontentlength Property

Name: getcontentlength
Namespace: DAV:
Purpose: Contains the Content-Length header returned by a GET
without accept headers.
Description: The getcontentlength property MUST be defined
on any DAV compliant resource that returns the Content-
Length header in response to a GET. This property is live
and protected.
Value: content-length ; see section 14.14 of [RFC2068]

<!ELEMENT getcontentlength (#PCDATA) >

13.5 getcontenttype Property

Name: getcontenttype
Namespace: DAV:
Purpose: Contains the Content-Type header returned by a GET without
accept headers.
Description: This getcontenttype property MUST be defined on
any DAV compliant resource that returns the Content-Type
header in response to a GET. This property is live and MAY
be protected.
Value: media-type ; defined in section 3.7 of [RFC2068]

<!ELEMENT getcontenttype (#PCDATA) >

13.6 getetag Property

Name: getetag
Namespace: DAV:
Purpose: Contains the ETag header returned by a GET without accept
headers.

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Description: The getetag property MUST be defined on any DAV
compliant resource that returns the Etag header. This
property is live and protected.
Value: entity-tag ; defined in section 3.11 of [RFC2068]

<!ELEMENT getetag (#PCDATA) >

13.7 getlastmodified Property

Name: getlastmodified
Namespace: DAV:
Purpose: Contains the Last-Modified header returned by a GET method
without accept headers.
Description: Note that the last-modified date on a resource
may reflect changes in any part of the state of the
resource, not necessarily just a change to the response to
the GET method. For example, a change in a property may
cause the last-modified date to change. The getlastmodified
property MUST be defined on any DAV compliant resource that
returns the Last-Modified header in response to a GET. This
property is live and protected.
Value: HTTP-date ; defined in section 3.3.1 of [RFC2068]

<!ELEMENT getlastmodified (#PCDATA) >

13.8 lockdiscovery Property

Name: lockdiscovery
Namespace: DAV:
Purpose: Describes the active locks on a resource
Description: The lockdiscovery property 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. The server is free to withhold any or all of
this information if the requesting principal does not have
sufficient access rights to see the requested data. This
property is live and protected.

<!ELEMENT lockdiscovery (activelock)* >

13.8.1 Example - Retrieving the lockdiscovery Property

>>Request

PROPFIND /container/ HTTP/1.1

Expires Dec 2002 66 WebDAV (RFC2518) bis June 2002

Host: www.foo.bar
Content-Length: xxxx
Content-Type: text/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: text/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.foo.bar/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>opaquelocktoken:f81de2ad-7f3d-a1b2-4f3c-
00a0c91a9d76</D:href>
</D:locktoken>
</D:activelock>
</D:lockdiscovery>
</D:prop>
<D:status>HTTP/1.1 200 OK</D:status>
</D:propstat>
</D:response>
</D:multistatus>

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

13.9 resourcetype Property

Name: resourcetype
Namespace: DAV:

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Purpose: Specifies the nature of the resource.
Description: The resourcetype property MUST be defined on
all DAV compliant resources. The default value is empty.
This property is live and protected.

<!ELEMENT resourcetype ANY >

13.10 source Property

Name: source
Namespace: DAV:
Purpose: The destination of the source link identifies the resource
that contains the unprocessed source of the linkÆs source.
Description: The source of the link (src) is typically the
URI of the output resource on which the link is defined,
and there is typically only one destination (dst) of the
link, which is the URI where the unprocessed source of the
resource may be accessed. When more than one link
destination exists, this specification asserts no policy on
ordering. This property is live and MAY be protected.

<!ELEMENT source (link)* >

13.10.1 Example - A source Property

<?xml version="1.0" encoding="utf-8" ?>
<D:prop xmlns:D="DAV:" xmlns:F="http://www.foocorp.com/Project/">
<D:source>
<D:link>
<F:projfiles>Source</F:projfiles>
<D:src>http://foo.bar/program</D:src>
<D:dst>http://foo.bar/src/main.c</D:dst>
</D:link>
<D:link>
<F:projfiles>Library</F:projfiles>
<D:src>http://foo.bar/program</D:src>
<D:dst>http://foo.bar/src/main.lib</D:dst>
</D:link>
<D:link>
<F:projfiles>Makefile</F:projfiles>
<D:src>http://foo.bar/program</D:src>
<D:dst>http://foo.bar/src/makefile</D:dst>
</D:link>
</D:source>
</D:prop>

Expires Dec 2002 68 WebDAV (RFC2518) bis June 2002

In this example the resource http://foo.bar/program has a source
property that contains three links. Each link contains three
elements, two of which, src and dst, are part of the DAV schema
defined in this document, and one which is defined by the schema
http://www.foocorp.com/project/ (Source, Library, and Makefile). A
client which only implements the elements in the DAV spec will not
understand the foocorp elements and will ignore them, thus seeing
the expected source and destination links. An enhanced client may
know about the foocorp elements and be able to present the user with
additional information about the links. This example demonstrates
the power of XML markup, allowing element values to be enhanced
without breaking older clients.

13.11 supportedlock Property

Name: supportedlock
Namespace: DAV:
Purpose: To provide a listing of the lock capabilities supported by
the resource.
Description: The supportedlock property of a resource
returns a listing of the combinations of scope and access
types which 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 live and protected.

<!ELEMENT supportedlock (lockentry)* >

13.11.1 Example - Retrieving the supportedlock Property

>>Request

PROPFIND /container/ HTTP/1.1
Host: www.foo.bar
Content-Length: xxxx
Content-Type: text/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: text/xml; charset="utf-8"

Expires Dec 2002 69 WebDAV (RFC2518) bis June 2002

Content-Length: xxxx

<?xml version="1.0" encoding="utf-8" ?>
<D:multistatus xmlns:D="DAV:">
<D:response>
<D:href>http://www.foo.bar/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>
<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>

14 Instructions for Processing XML in DAV

All DAV compliant resources MUST ignore any unknown XML element and
all its children encountered while processing a DAV method that uses
XML as its command language.

This restriction also applies to the processing, by clients, of DAV
property values where unknown 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 unknown XML elements.

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.

Since XML can be transported as text/xml or application/xml, a DAV
server MUST accept DAV method requests with XML parameters
transported as either text/xml or application/xml, and DAV client
MUST accept XML responses using either text/xml or application/xml.

Expires Dec 2002 70 WebDAV (RFC2518) bis June 2002

15 DAV Compliance Classes

A DAV compliant resource can choose from two 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.

Since this document describes extensions to the HTTP/1.1 protocol,
minimally all DAV compliant resources, clients, and proxies MUST be
compliant with [RFC2068].

Compliance classes are not necessarily sequential. A resource that
is class 2 compliant must also be class 1 compliant; but if
additional compliance classes are defined later, a resource that is
class 1, 2, and 4 compliant might not be class 3 compliant. Also
note that identifiers other than numbers may be used as compliance
class identifiers.

15.1 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.

15.2 Class 2

A class 2 compliant resource MUST meet all class 1 requirements and
support the LOCK method, the supportedlock property, the
lockdiscovery property, the Time-Out response header and the Lock-
Token request header. A class "2" compliant resource SHOULD also
support the Time-Out 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.

16 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 [UTF-8] encoding of the ISO
10646 multilingual plane. XML examples in this specification

Expires Dec 2002 71 WebDAV (RFC2518) bis June 2002

demonstrate use of the charset parameter of the Content-Type header,
as defined in [RFC2376], as well as the XML "encoding" attribute,
which together provide charset identification information for MIME
and XML processors.

XML also provides a language tagging capability for specifying the
language of the contents of a particular XML element. XML uses
either IANA registered language tags (see [RFC1766]) or ISO 639
language tags [ISO-639] in the "xml:lang" attribute of an XML
element to identify the language of its content and attributes.

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" [RFC2376] 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 three categories:
names of protocol elements such as methods and headers, names of XML
elements, and names of properties. Naming of protocol elements
follows the precedent of HTTP, using English names encoded in
USASCII for methods and headers. Since these protocol elements are
not visible to users, and are in fact simply long token identifiers,
they do not need to support encoding in multiple character sets.
Similarly, though the names of XML elements used in this
specification are English names encoded in UTF-8, these names are
not visible to the user, and hence do not need to support multiple
character set encodings.

The name of a property defined on a resource is a URI. Although
some applications (e.g., a generic property viewer) will display
property URIs 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 URI to a human-readable
field when displaying the property name 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 URI 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.

Expires Dec 2002 72 WebDAV (RFC2518) bis June 2002

17 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
[RFC2068]) and XML (discussed in [RFC2376]) 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.

17.1 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 Basic
authentication credentials in a WWW-Authenticate header unless the
connection is secure. Examples of secure connections include a
Transport Layer Security (TLS) connection employing a strong cipher
suite with mutual authentication of client and server, or a
connection over a network which is physically secure, for example,
an isolated network in a building with restricted access.

WebDAV applications MUST support the Digest authentication scheme
[RFC2069]. 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 which is useful in a wide range of
scenarios.

17.2 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.

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

Expires Dec 2002 73 WebDAV (RFC2518) bis June 2002

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

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.

17.3 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.

17.4 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 lockdiscovery
property on the resource, and can be used by other 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
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.

17.5 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.

Expires Dec 2002 74 WebDAV (RFC2518) bis June 2002

17.6 Reduction of Security due to Source Link

HTTP/1.1 warns against providing read access to script code because
it may contain sensitive information. Yet WebDAV, via its source
link facility, can potentially provide a URI for script resources so
they may be authored. For HTTP/1.1, a server could reasonably
prevent access to source resources due to the predominance of read-
only access. WebDAV, with its emphasis on authoring, encourages
read and write access to source resources, and provides the source
link facility to identify the source. This reduces the security
benefits of eliminating access to source resources. Users and
administrators of WebDAV servers should be very cautious when
allowing remote authoring of scripts, limiting read and write access
to the source resources to authorized principals.

17.7 Implications of XML External Entities

XML supports a facility known as "external entities", defined in
section 4.2.2 of [REC-XML], which instruct 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 [REC-XML].
However, [REC-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 [RFC2376].
Therefore, implementers must be aware that external XML entities
should be treated as untrustworthy.

There is also the scalability risk that would accompany a widely
deployed application which 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 server which fields requests for the resource
containing the external XML entity.

17.8 Risks Connected with Lock Tokens

This specification, in section 6.4, requires the use of Universal
Unique Identifiers (UUIDs) for lock tokens, in order to guarantee
their uniqueness across space and time. UUIDs, as defined in [ISO-
11578], contain a "node" field which "consists of the IEEE address,

Expires Dec 2002 75 WebDAV (RFC2518) bis June 2002

usually the host address. For systems with multiple IEEE 802 nodes,
any available node address can be used." Since a WebDAV server will
issue many locks over its lifetime, the implication is that it will
also be publicly exposing its IEEE 802 address.

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

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

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

* It may be possible to determine the number of each type of
computer running WebDAV.
Section 23.4 of this specification details an alternate mechanism
for generating the "node" field of a UUID without using an IEEE 802
address, which alleviates the risks associated with exposure of IEEE
802 addresses by using an alternate source of uniqueness.

18 IANA Considerations

This document defines two namespaces, the namespace of property
names, and the namespace of WebDAV-specific XML elements used within
property values.

URIs are used for both names, for several reasons. Assignment of a
URI does not require a request to a central naming authority, and
hence allow WebDAV property names and XML elements to be quickly
defined by any WebDAV user or application. URIs also provide a
unique address space, ensuring that the distributed users of WebDAV
will not have collisions among the property names and XML elements
they create.

This specification defines a distinguished set of property names and
XML elements that are understood by all WebDAV applications. The
property names and XML elements in this specification are all
derived from the base URI DAV: by adding a suffix to this URI, for
example, DAV:creationdate for the "creationdate" property.

This specification also defines a URI scheme for the encoding of
lock tokens, the opaquelocktoken URI scheme described in section
6.4.

To ensure correct interoperation based on this specification, IANA
must reserve the URI namespaces starting with "DAV:" and with
"opaquelocktoken:" for use by this specification, its revisions, and
related WebDAV specifications.

Expires Dec 2002 76 WebDAV (RFC2518) bis June 2002

19 Intellectual Property

The following notice is copied from RFC 2026 [RFC2026], section
10.4, and describes the position of the IETF concerning intellectual
property claims made against this document.

The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to
pertain to the implementation or use other technology described in
this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the
IETF's procedures with respect to rights in standards-track and
standards-related documentation can be found in BCP-11. Copies of
claims of rights made available for publication and any assurances
of licenses to be made available, or the result of an attempt made
to obtain a general license or permission for the use of such
proprietary rights by implementors or users of this specification
can be obtained from the IETF Secretariat.

The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
Director.

20 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.

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, both in helping the formation
of the working group and in patiently coaching the authors along the
way. In so many ways he has set high standards we have toiled to

Expires Dec 2002 77 WebDAV (RFC2518) bis June 2002

meet. The contributions of Judith Slein in clarifying the
requirements, and in patiently reviewing draft after draft, both
improved this specification and expanded our minds on document
management.

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

Expires Dec 2002 78 WebDAV (RFC2518) bis June 2002

21 References

21.1 Normative References

[RFC1766] H. T. Alvestrand, "Tags for the Identification of
Languages." RFC 1766. Uninett. March, 1995.

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

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

[RFC2396] T. Berners-Lee, R. Fielding, L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax." RFC 2396.
MIT/LCS, U.C. Irvine, Xerox. August, 1998.

[REC-XML]T. Bray, J. Paoli, C. M. Sperberg-McQueen, "Extensible
Markup Language (XML)." World Wide Web Consortium
Recommendation REC-xml-19980210.
http://www.w3.org/TR/1998/REC-xml-19980210.

[REC-XML-NAMES] T. Bray, D. Hollander, A. Layman, "Name Spaces in
XML" World Wide Web Consortium Recommendation REC-xml-names.
http://www.w3.org/TR/REC-xml-names-19990114/

[RFC2069] J. Franks, P. Hallam-Baker, J. Hostetler, P. Leach, A.
Luotonen, E. Sink, and L. Stewart. "An Extension to HTTP :
Digest Access Authentication" RFC 2069. Northwestern
University, CERN, Spyglass Inc., Microsoft Corp., Netscape
Communications Corp., Spyglass Inc., Open Market Inc. January
1997.

[RFC2068] R. Fielding, J. Gettys, J. Mogul, H. Frystyk, T.
Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1." RFC
2068. U.C. Irvine, DEC, MIT/LCS. January, 1997.

[ISO-639] ISO (International Organization for Standardization).
ISO 639:1988. "Code for the representation of names of
languages."

[ISO-8601] ISO (International Organization for Standardization).
ISO 8601:1988. "Data elements and interchange formats -
Information interchange - Representation of dates and times."

Expires Dec 2002 79 WebDAV (RFC2518) bis June 2002

[ISO-11578] ISO (International Organization for Standardization).
ISO/IEC 11578:1996. "Information technology - Open Systems
Interconnection - Remote Procedure Call (RPC)"

[RFC2141] R. Moats, "URN Syntax." RFC 2141. AT&T. May, 1997.

[UTF-8] F. Yergeau, "UTF-8, a transformation format of Unicode
and ISO 10646." RFC 2279. Alis Technologies. January, 1998.

21.2 Informational References

[RFC2026] S. Bradner, "The Internet Standards Process - Revision
3." RFC 2026, BCP 9. Harvard University. October, 1996.

[RFC1807] R. Lasher, D. Cohen, "A Format for Bibliographic
Records," RFC 1807. Stanford, Myricom. June, 1995.

[WF] C. Lagoze, "The Warwick Framework: A Container Architecture
for Diverse Sets of Metadata", D-Lib Magazine, July/August
1996.
http://www.dlib.org/dlib/july96/lagoze/07lagoze.html

[USMARC] Network Development and MARC Standards, Office, ed.
1994. "USMARC Format for Bibliographic Data", 1994.
Washington, DC: Cataloging Distribution Service, Library of
Congress.

[REC-PICS] J. Miller, T. Krauskopf, P. Resnick, W. Treese, "PICS
Label Distribution Label Syntax and Communication Protocols"
Version 1.1, World Wide Web Consortium Recommendation REC-
PICS-labels-961031. http://www.w3.org/pub/WWW/TR/REC-PICS-
labels-961031.html.

[RFC2291] J. A. Slein, F. Vitali, E. J. Whitehead, Jr., D.
Durand, "Requirements for Distributed Authoring and
Versioning Protocol for the World Wide Web." RFC 2291. Xerox,
Univ. of Bologna, U.C. Irvine, Boston Univ. February, 1998.

[RFC2413] S. Weibel, J. Kunze, C. Lagoze, M. Wolf, "Dublin Core
Metadata for Resource Discovery." RFC 2413. OCLC, UCSF,
Cornell, Reuters. September, 1998.

[RFC2376] E. Whitehead, M. Murata, "XML Media Types." RFC 2376.
U.C. Irvine, Fuji Xerox Info. Systems. July 1998.

Expires Dec 2002 80 WebDAV (RFC2518) bis June 2002

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

Expires Dec 2002 81 WebDAV (RFC2518) bis June 2002

22 Authors' Addresses

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

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

L. Dusseault
Xythos Software, Inc.
25 Maiden Lane, 6th floor
San Francisco
Email: lisa@xythos.com

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23 Appendices

23.1 Appendix 1 - WebDAV Document Type Definition

This section provides a document type definition, following the
rules in [REC-XML], for the XML elements used in the protocol stream
and in the values of properties. It collects the element definitions
given in sections 12 and 13.

<!DOCTYPE webdav-1.0 [

<!ELEMENT href (#PCDATA) >
<!ELEMENT prop ANY >

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

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

<!ELEMENT lockscope (exclusive | shared) >
<!ELEMENT exclusive EMPTY >
<!ELEMENT shared EMPTY >

<!ELEMENT depth (#PCDATA) >
<!ELEMENT owner ANY >
<!ELEMENT timeout (#PCDATA) >
<!ELEMENT locktoken (href+) >

<!ELEMENT link (src+, dst+) >
<!ELEMENT dst (#PCDATA) >
<!ELEMENT src (#PCDATA) >

<!ELEMENT multistatus (response+, responsedescription?) >
<!ELEMENT response (href, ((href*, status)|(propstat+)),
responsedescription?) >
<!ELEMENT status (#PCDATA) >
<!ELEMENT propstat (prop, status, responsedescription?) >

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<!ELEMENT responsedescription (#PCDATA) >

<!ELEMENT propertyupdate (remove | set)+ >
<!ELEMENT remove (prop) >
<!ELEMENT set (prop) >

<!ELEMENT propfind (allprop | propname | prop) >
<!ELEMENT allprop EMPTY >
<!ELEMENT propname EMPTY >

<!ELEMENT collection EMPTY >

<!ELEMENT creationdate (#PCDATA) >
<!ELEMENT displayname (#PCDATA) >
<!ELEMENT getcontentlanguage (#PCDATA) >
<!ELEMENT getcontentlength (#PCDATA) >
<!ELEMENT getcontenttype (#PCDATA) >
<!ELEMENT getetag (#PCDATA) >
<!ELEMENT getlastmodified (#PCDATA) >
<!ELEMENT lockdiscovery (activelock)* >
<!ELEMENT resourcetype ANY >
<!ELEMENT source (link)* >
<!ELEMENT supportedlock (lockentry)* >
]>

23.2 Appendix 2 - ISO 8601 Date and Time Profile

The creationdate property specifies the use of the ISO 8601 date
format [ISO-8601]. This section defines a profile of the ISO 8601
date format for use with this specification. This profile is quoted
from an Internet-Draft by Chris Newman, and is mentioned here to
properly attribute his work.

date-time = full-date "T" full-time

full-date = date-fullyear "-" date-month "-" date-mday
full-time = partial-time time-offset

date-fullyear = 4DIGIT
date-month = 2DIGIT ; 01-12
date-mday = 2DIGIT ; 01-28, 01-29, 01-30, 01-31 based on
month/year
time-hour = 2DIGIT ; 00-23

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time-minute = 2DIGIT ; 00-59
time-second = 2DIGIT ; 00-59, 00-60 based on leap second rules
time-secfrac = "." 1*DIGIT
time-numoffset = ("+" / "-") time-hour ":" time-minute
time-offset = "Z" / time-numoffset

partial-time = time-hour ":" time-minute ":" time-second
[time-secfrac]

Numeric offsets are calculated as local time minus UTC (Coordinated
Universal Time). So the equivalent time in UTC can be determined by
subtracting the offset from the local time. For example, 18:50:00-
04:00 is the same time as 22:58:00Z.

If the time in UTC is known, but the offset to local time is
unknown, this can be represented with an offset of "-00:00". This
differs from an offset of "Z" which implies that UTC is the
preferred reference point for the specified time.

23.3 Appendix 3 - Notes on Processing XML Elements

23.3.1 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.

It is a violation of the XML specification to use the <A></A> form if
the associated DTD declares the element to be EMPTY (e.g., <!ELEMENT A
EMPTY>). If such a statement is included, then the empty element
format, <A/> must be used. If the element is not declared to be
EMPTY, then either form <A></A> or <A/> may be used for empty elements.

23.3.2 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 white space, 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.

Expires Dec 2002 85 WebDAV (RFC2518) bis June 2002

23.3.2.1 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.

23.3.2.2 Example - Unknown 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.foo.bar/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.foo.bar/standards/props/">
</D:propfind>

Expires Dec 2002 86 WebDAV (RFC2518) bis June 2002

As the server does not understand the expired-props element,
according to the WebDAV-specific XML processing rules specified in
section 14, it must ignore it. 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.foo.bar/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.

23.4 Appendix 4: UUID Node Generation

UUIDs, as defined in [ISO-11578], contain a "node" field that
contains one of the IEEE 802 addresses for the server machine. As
noted in section 17, there are several security risks associated
with exposing a machine's IEEE 802 address. This section provides an
alternate mechanism for generating the "node" field of a UUID which
does not employ an IEEE 802 address. WebDAV servers MAY use this
algorithm for creating the node field when generating UUIDs. The
text in this section is originally from an Internet-Draft by Paul
Leach and Rich Salz, who are noted here to properly attribute their
work.

The ideal solution is to obtain a 47 bit cryptographic quality
random number, and use it as the low 47 bits of the node ID, with
the most significant bit of the first octet of the node ID set to 1.
This bit is the unicast/multicast bit, which will never be set in
IEEE 802 addresses obtained from network cards; hence, there can
never be a conflict between UUIDs generated by machines with and
without network cards.

If a system does not have a primitive to generate cryptographic
quality random numbers, then in most systems there are usually a
fairly large number of sources of randomness available from which
one can be generated. Such sources are system specific, but often
include:

- the percent of memory in use

Expires Dec 2002 87 WebDAV (RFC2518) bis June 2002

- the size of main memory in bytes
- the amount of free main memory in bytes
- the size of the paging or swap file in bytes
- free bytes of paging or swap file
- the total size of user virtual address space in bytes
- the total available user address space bytes
- the size of boot disk drive in bytes
- the free disk space on boot drive in bytes
- the current time
- the amount of time since the system booted
- the individual sizes of files in various system directories
- the creation, last read, and modification times of files in
various system directories
- the utilization factors of various system resources (heap, etc.)
- current mouse cursor position
- current caret position
- current number of running processes, threads
- handles or IDs of the desktop window and the active window
- the value of stack pointer of the caller
- the process and thread ID of caller
- various processor architecture specific performance counters
(instructions executed, cache misses, TLB misses)

(Note that it is precisely the above kinds of sources of randomness
that are used to seed cryptographic quality random number generators
on systems without special hardware for their construction.)

In addition, items such as the computer's name and the name of the
operating system, while not strictly speaking random, will help
differentiate the results from those obtained by other systems.

The exact algorithm to generate a node ID using these data is system
specific, because both the data available and the functions to
obtain them are often very system specific. However, assuming that
one can concatenate all the values from the randomness sources into
a buffer, and that a cryptographic hash function such as MD5 is
available, then any 6 bytes of the MD5 hash of the buffer, with the
multicast bit (the high bit of the first byte) set will be an
appropriately random node ID.

Other hash functions, such as SHA-1, can also be used. The only
requirement is that the result be suitably random _ in the sense
that the outputs from a set uniformly distributed inputs are
themselves uniformly distributed, and that a single bit change in
the input can be expected to cause half of the output bits to
change.

24 Full Copyright Statement

Expires Dec 2002 88 WebDAV (RFC2518) bis June 2002

This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph
are included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.

The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.

This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Expires Dec 2002 89

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