WEBDAV Working Group Y. Goland, Microsoft
INTERNET-DRAFT E. J. Whitehead, Jr., U.C. Irvine
<draft-ietf-webdav-protocol-01> Asad Faizi, Netscape
Stephen R. Carter, Novell
Del Jensen, Novell
Expires January 15, 1997 July 13, 1997
Extensions for Distributed Authoring and Versioning
on the
World Wide Web -- WEBDAV
Status of this Memo
This document is an Internet-Draft. 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 made obsolete 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".
To learn the current status of any Internet-Draft, please check
the "1id-abstracts.txt" listing contained in the Internet-Drafts
Shadow Directories on ftp.is.co.za (Africa), nic.nordu.net
(Europe), munnari.oz.au (Pacific Rim), ds.internic.net (US East
Coast), or ftp.isi.edu (US West Coast).
Distribution of this document is unlimited. Please send comments
to the Distributed Authoring and Versioning (WEBDAV) working
group at <w3c-dist-auth@w3.org>, which may be joined by sending a
message with subject "subscribe" to <w3c-dist-auth-
request@w3.org>.
Discussions of the WEBDAV working group are archived at
<URL:http://www.w3.org/pub/WWW/Archives/Public/w3c-dist-auth>.
Abstract
This Document specifies a set of methods and content-types
ancillary to HTTP/1.1 for the management of resource properties,
simple name space manipulation,
simple resource locking (collision avoidance) and resource
version control.
Table of Contents
Abstract
1 Terminology
2 Data Model and Methods for DAV Properties
2.1 Introduction
2.1.1............................The DAV Property
2.1.2.................Existing Metadata Proposals
2.1.3.................Properties and HTTP Headers
2.2 A Property Model for HTTP Resources
2.2.1....................................Overview
2.2.2..........................Property Namespace
2.2.3.........................Property Attributes
2.2.4.....................................Schemas
2.3 DAV Schema
2.3.1..............................Live Attribute
2.3.2..........................ReadOnly Attribute
2.3.3....................................Elements
2.4 Property Identifiers
2.4.1..........................Problem Definition
2.4.2........................Solution Requirement
2.4.3...........................DAV URL Parameter
2.4.4...............................Name Encoding
2.4.5...........Compatibility with legacy systems
2.5 Link XML Element
2.5.1.........................Problem Description
2.5.2.......................Solution Requirements
2.5.3............................Link XML Element
2.5.4.............................Src XML Element
2.5.5.............................Dst XML Element
2.5.6.....................................Example
2.6 Properties and Methods
2.6.1......................................DELETE
2.6.2.........................................GET
2.6.3............................PROPPATCH Method
2.6.4.........................................PUT
2.6.5......................................SEARCH
3 A Proposal for Collections of Web Resources and Name Space
Operations
3.1 Observations on the HTTP Object Model
3.1.1........................Collection Resources
3.1.2Creation and Retrieval of Collection Resources
3.1.3.......Source Resources and Output Resources
3.2 MKCOL Method
3.2.1.........................Problem Description
3.2.2.......................Solution Requirements
3.2.3.....................................Request
3.2.4....................................Response
3.2.5.....................................Example
3.3 INDEX Method
3.3.1.........................Problem Description
3.3.2.......................Solution Requirements
3.3.3.................................The Request
3.3.4................................The Response
3.3.5.......................Response Message Body
3.3.6.....................................Example
3.4 Behavior of RFC 2068 Methods on Collections
3.4.1...................GET, HEAD for Collections
3.4.2........................POST for Collections
3.4.3.........................PUT for Collections
3.4.4......................DELETE for Collections
3.5 COPY Method
3.5.1.........................Problem Description
3.5.2.......................Solution Requirements
3.5.3.................................The Request
3.5.4................................The Response
3.5.5....................................Examples
3.6 MOVE Method
3.6.1.........................Problem Description
3.6.2.......................Solution Requirements
3.6.3.................................The Request
3.6.4................................The Response
3.6.5....................................Examples
3.7 Multi-Status Response
3.7.1..........................Problem Definition
3.7.2.......................Solution Requirements
3.7.3.......................Multi-Status Response
3.7.4.....................................Example
3.8 ADDREF Method
3.8.1..........................Problem Definition
3.8.2.......................Solution Requirements
3.8.3.................................The Request
3.9 DELREF Method
3.9.1..........................Problem Definition
3.9.2.......................Solution Requirements
3.9.3.................................The Request
3.10 PATCH Method
3.10.1.........................Problem Definition
3.10.2......................Solution Requirements
3.10.3................................The Request
3.10.4.........application/XML elements for PATCH
3.10.5...............................The Response
3.10.6...................................Examples
3.11 Headers
3.11.1......................................Depth
3.11.2................................Destination
3.11.3....................Enforce-Live-Properties
3.11.4.......................Duplicate-Properties
3.11.5..................................Overwrite
3.11.6.............................Destroy Header
3.11.7...................Collection-Member Header
3.12 Links
3.12.1..................Source Link Property Type
4 State Tokens
4.1 Overview
4.1.1.........................Problem Description
4.1.2.......................Solution Requirements
4.2 State Token Syntax
4.3 State Token Conditional Headers
4.3.1..............................If-State-Match
4.3.2.........................If-None-State-Match
4.4 State Token Header
4.5 E-Tags
5 Locking
5.1 Problem Description - Overview
5.1.1..................Exclusive Vs. Shared Locks
5.1.2............................Required Support
5.2 LOCK Method
5.2.1...................................Operation
5.2.2The Effect of Locks on Properties and Containers
5.2.3................Locking Replicated Resources
5.2.4..............Interaction with other Methods
5.2.5....................Lock Compatibility Table
5.2.6................................Status Codes
5.2.7.....................................Example
5.2.8....................Lock-Info Request Header
5.2.9........................Owner Request Header
5.2.10............................Time-Out Header
5.2.11.........................State-Token Header
5.3 Write Lock
5.4 Lock Tokens
5.4.1.........................Problem Description
5.4.2...........................Proposed Solution
5.4.3.......................Lock Token Definition
5.5 UNLOCK Method
5.5.1..........................Problem Definition
5.5.2.....................................Example
5.6 Discovery Mechanisms
5.6.1.........................Lock Type Discovery
5.6.2.......................Active Lock Discovery
6 Version Control
7 Internationalization Support
8 Security Considerations
9 Acknowledgements
10 References
11 Authors' Addresses
Appendix 1 - Content Type Application/XML
Syntax
XML element
Entity-Name
Close
XML Encoding
Markup Modifier
XML Syntax Shorthand
Appendix 2 - Parameter Syntax for Content-Type Application/XML
Schema Content-Type Parameter
Appendix 3 URI Path Encoding
Problem Definition
Solution Requirement
Path Component
Appendix 4 - XML URI
Appendix 5 - XML elements
Ref XML element
Namespace
Namespace XML element
AS XML element
Required XML element
The XML URI and Namespace
1 Terminology
Collection - A resource that contains member resources.
Member Resource - a resource referred to by a collection. There
are two types of member resources: external and internal.
Internal Member Resource - the name given to a member resource of
a collection whose URI is relative to the URI of the collection.
External Member Resource - a member resource with an absolute URI
that is not relative to its parents URI.
Properties Also known as small-chunk metadata, a hierarchical
set of name/value pairs that describe a resource.
Live Properties Properties whose semantics and syntax are
enforced by the server. For example, a live read-only property
that is enforced by the server would disallow PUTs to the
associated resource.
Dead properties Properties whose semantics and syntax are not
enforced by the server. A dead read-only property would not be
enforced by the server and thus would not be used by the server as
a reason to disallow a PUT on the associated resource.
2 Data Model and Methods for DAV Properties
2.1 Introduction
2.1.1 The DAV Property
Properties are pieces of data that describe the state of a
resource. Properties are data about data. The term property is
used within this specification to disambiguate the concept from
the overloaded terms metadata and attribute.
Properties are used within 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.
2.1.2 Existing Metadata Proposals
Properties have a long played an essential role in the maintenance
of large document repositories, and many current proposals contain
some notion of a property. These include PICS [Miller et al.,
1996], PICS-NG, the Rel/Rev draft [Maloney, 1996], Web
Collections, XML [Bray, 1997], several proposals on representing
relationships within HTML, digital signature manifests (DCMF), and
a position paper on Web metadata architecture [Berners-Lee, 1997].
Some proposals come from a digital library perspective. These
include the Dublin Core [Weibel et al., 1995] metadata set and the
Warwick Framework [Lagoze, 1996], a container architecture for
different metadata schemas. The literature includes many examples
of metadata, including MARC [MARC, 1994], a bibliographic metadata
format, RFC 1807 [Lasher, Cohen, 1995], a technical report
bibliographic format employed by the Dienst system, and the
proceedings from the first IEEE Metadata conference describe many
community-specific metadata sets.
Participants of the 1996 Metadata II Workshop in Warwick, UK
[Lagoze, 1996], 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.
2.1.3 Properties and HTTP Headers
Properties already exist, in a limited sense, within HTTP through
the use of message headers. However, in distributed authoring
environments a relatively large number of properties are needed to
fully describe the state of a resource, and setting/returning them
all through HTTP 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 then set or retrieve just
those properties.
2.2 A Property Model for HTTP Resources
2.2.1 Overview
The DAV property model is based on name/value/attribute triples.
The name of a property identifies the propertys syntax and
semantics, and provides an address with which to refer to a
property. The value of a property is an octet stream. The
attributes of a property are a set of name/value pairs that are
not directly addressable. Attributes are retrieved in conjunction
with retrieving a property, and are set when changing a propertys
value. This specification defines two attributes, live, which
indicates if the propertys syntax and semantics is enforced by
the server, and readonly, which indicates that the propertys
value may be retrieved but not set.
2.2.2 Property Namespace
2.2.2.1 Problem Definition
The requirement is to be able to associate a value with a property
name on a resource and to be able to directly address that value.
2.2.2.2 Solution Requirement
Ideally a property namespace should work well with extant property
implementations as well as database systems. The DAV property
namespace has been specified with the following two facts in mind:
Namespaces associated with flat file systems are certainly
ubiquitous.
Many databases use a fixed schema mechanism, which makes
efficient implementation of hierarchical properties
difficult. Specifically, each property has a random set of
children; the best a relational database can do is provide
a table with name and value, where the value is a series
of indexes into other tables and each index represents a
specific value. However most RDBS do not provide for table
pointers, only index values. Such a system would have to
be jury-rigged to handle table pointers. In addition,
indexing systems are optimized for a small set of
relatively large tables; hierarchical property systems
tend toward many properties, each with different numbers
and types of children, thus potentially requiring a table
for each child.
It would seem best to implement a flat property namespace,
inducing a natural isomorphism between DAV and most native
file systems. Adopting such a model should not restrict RDBS
from taking full advantage of their search facilities.
However, it seems that future trends might be toward
hierarchical properties. As such, DAV requirements []
stipulate that the design of the flat property system MUST
be such that it will be possible to add true hierarchical
properties later without breaking downlevel clients.
Specifically, a flat client MUST be able to speak to a
hierarchical server and a hierarchical client MUST be able
to speak to a flat server. Worst case either way MUST be
that the request fails.
2.2.2.3 Property Names
A property name identifies both the syntax and semantics of
the propertys value. It is critical that property names do
not collide, e.g., two principals defining the same property
name with two different meanings.
The URI framework provides for a mechanism to prevent
namespace collision and for varying degrees of
administrative control. Rather than reinvent these desirable
features, DAV properties make use of them by requiring that
all DAV property names MUST be URIs.
The property namespace is flat, that is, it is not possible
to string together a series of property names in order to
refer to a hierarchy of properties. Thus it is possible to
refer to a property A but not a property A/B.
2.2.3 Property Attributes
The attributes of a property provide information about the
property. Note that a property contains information about a
resource.
Attributes consist of name/value pairs whose value MUST be a
string. Attributes are not directly addressable, rather they
are retrieved and defined in the context of other property
operations. For example, if one retrieves a property value,
the attributes will also be returned. If one sets a property
value, one may also specify the values for its attributes.
All attributes on a server MUST be live. This means that the
server MUST only record attributes with syntax and semantics
the server understands and enforces. This normally means
that clients can not define new attributes on a property;
clients may only make use of the attributes supported by the
server.
If a client submits an attribute when setting a property
then the server MUST NOT record the property unless it
accepts the values specified for the corresponding
attributes. Thus, if a property value is submitted with a
live attribute then the server MUST NOT record the value
unless the server understands and enforces the syntax and
semantics of the property.
2.2.4 Schemas
A schema is a group of property names, attributes, and XML
elements.
It is often useful to indicate support for a particular
schema in a request or a response. Schema discovery is also
useful for determining if a system supports a group of
properties, attributes, or XML elements. A property does not
necessarily contain sufficient information to identify any
schema(s) to which it may belong.
As with property names, schemas MUST use URIs as their
names.
2.3 DAV Schema
The DAV Schema is specified as
http://www.ietf.org/standards/dav/. This schema is used to
indicate support for
properties and attributes that can be defined on a resource
and
XML elements that can be returned in responses.
All DAV compliant servers MUST support the DAV schema.
2.3.1 Live Attribute
Name: http://www.ietf.org/standards/dav/live
Purpose: To indicate that the property has its syntax and
semantics enforced by the resource on which it is recorded.
Schema: http://www.ietf.org/standards/dav/
Parent: Any property
Values= = <><>
Description: This attribute is used to indicate that the
resource expressing the property understands and enforces
the syntax and semantics of the property. The absence of the
Live attribute in a response indicates to the client that
the corresponding property does not have its syntax and
semantics enforced by the resource on which it is recorded.
If a live attribute is included when setting the value of a
property then the server SHOULD set the property if the
property will be live and MUST NOT set the property if the
property will not be live.
2.3.2 ReadOnly Attribute
Name: http://www.ietf.org/standards/dav/readonly
Purpose: To indicate that a property can be retrieved, but
not set through the property mechanism.
Schema: http://www.ietf.org/standards/dav/
Parent: Any property
Values= = <><>
Description: This attribute is used to indicate that the
property can only be retrieved, not set through the property
mechanism. This attribute is not meant as an access control
mechanism but rather to reflect the fact that the property
is not designed to have its value set through the property
mechanism. If this attribute is included when setting the
value of a property, the request MUST be rejected since
accepting the value would violate ReadOnly attribute. A
server MUST NOT effect a property protocol element that is
inconsistent or ill-defined with respect to the elements
attribute state, were it to be expressed.
2.3.3 Elements
2.3.3.1 Prop XML element
Name: http://www.ietf.org/standards/dav/prop
Purpose: To specify the name and value of a property
Schema: http://www.ietf.org/standards/dav/
Parent: Any
Values: PropName PropValue
2.3.3.2 PropName XML element
Name: http://www.ietf.org/stnadards/dav/name
Purpose: To specify the name of a property, which MUST be a
URI.
Schema: http://www.ietf.org/standards/dav/
Parent: Prop
Values: URI
2.3.3.3 PropValue XML element
Name: http://www.ietf.org/standards/dav/propvalue
Purpose: To specify the value of a property.
Schema: http://www.ietf.org/standards/dav/
Parent: Prop
Values: The contents of a property.
2.4 Property Identifiers
2.4.1 Problem Definition
The addition of DAV properties to the HTTP object model
introduces the need for a mechanism to unambiguously refer
to either the body of the resource or the properties of a
resource.
2.4.2 Solution Requirement
The mechanism used for referring to the resource body must
also be usable for referring to the resources properties,
such that even non-DAV aware clients can retrieve DAV
properties.
2.4.3 DAV URL Parameter
To allow for the specification of property information in
the context of an http scheme URL, a switch is needed. The
switch indicates that following path segments specify a
property location. To this end the DAV param is introduced
for use with http scheme URLs. The path segment to the right
of the DAV param MUST be formatted according to the XML Link
standard, described in Appendix 3.
2.4.4 Name Encoding
Properties on a resource are given URIs as a name. Thus, in
order to be able to refer to a property one must be able to
put the propertys URI into an HTTP URI.
For example, the author property with full name
http://www.w3.org/standards/z39.50/author is defined on
http://somewhere.com/resource.
To create a reference to the author one would perform the
following steps.
Add the DAV parameter to the base URI,
http://somewhere.com/resource;DAV.
Add / to refer to the root of the resources property
namespace, http://somewhere.com/resource;DAV/.
Change the author propertys name into parameter format by
changing /s to !s and encasing the entire value in
parenthesis. The value must be encased in parenthesis in
order to indicate the / to ! translation. The
translation / to ! is done in order to prevent
confusion over segments boundaries, and to make sure that
the syntax for relative URIs remains well-defined.
http://somewhere.com/resource;DAV/(http:!!www.w3.org!stand
ards!z39.50!author).
The process is now complete, and the URL can be used in a
GET or PATCH to retrieve or alter the value. See appendix 3
for more information.
2.4.5 Compatibility with legacy systems
2.4.5.1 Problem Definition
The HTTP parameter space is uncontrolled, thus someone may
already be using a parameter with a value of DAV for some
end other than the one described here. Thus a client sending
a URI with a DAV param to a server may receive an unexpected
or inappropriate response.
2.4.5.2 Solution Requirement
A mechanism is needed to prevent namespace collisions.
2.4.5.3 Proposed Solution
All DAV compliant servers MUST honor the DAV param type on
http URLs. Thus if a client knows it is talking to a DAV
server, it can safely send an http URL with the DAV param.
The client may send the http URL with the DAV param
extension to a server that is not known to be DAV compliant
if the client uses PEP [Connolly, 1997] to prevent
collisions. The proper PEP header is:
DAVPEP = PEP: {{map DAV}{strength must}}
Note: this PEP header is not compliant with [Connolly,
1997]; the PEP authors have indicated they will change the
format to make the example legal.
2.5 Link XML Element
2.5.1 Problem Description
A mechanism is needed to associate resources with other
resources. These associations, also known as links, consist
of three values, a type describing the nature of the
association, the source of the link, and the destination of
the link. In the case of annotation, neither the source nor
the destination of a link need be the resource upon which
the link is recorded.
2.5.2 Solution Requirements
The association mechanism MUST make use of the DAV property
mechanism in order to make the existence of the associations
searchable.
2.5.3 Link XML Element
Name: http://www.ietf.org/standards/dav/link
Purpose: The XML document which is the value of a link.
Schema: http://www.ietf.org/standards/dav/
Values= An XML document which MUST have a src and dst XML
element.
Description: Link is used to provide the source and one or
more destinations of the link. The type of the property
provides the type of the link. Link is a multivalued
element,so multiple Links may be used together to indicate
multiple links with the same type.
2.5.4 Src XML Element
Name: http://www.ietf.org/standards/dav/src
Purpose: To indicate the source of a link.
Schema: http://www.ietf.org/standards/dav/
Parent: http://www.ietf.org/standards/dav/link
Values= URI
2.5.5 Dst XML Element
Name: http://www.ietf.org/standards/dav/Dst
Purpose: To indicate one or more destinations of a link
Schema: http://www.ietf.org/standards/dav/
Parent: http://www.ietf.org/standards/dav/link
Values= URI
2.5.6 Example
<XML>
<Namespace><Ref>http://www.ietf.org/standards/dav/</><A
S>D</></>
<D:Prop>
<Propname>Source</>
<Propvalue>
<XML:XML>
<Namespace>
<Ref>http://www.ietf.org/standards/
dav/</><AS>D</>
</>
<Namespace>
<Ref>http://www.foocorp.com/Project
/</><AS>F</>
</>
<D:Link>
<F:ProjectFiles>Source</>
<src>http://foo.bar/program</>
<dst>http://foo.bar/source/main.c</>
</>
<D:Link>
<F:ProjectFiles>Library</>
<src>http://foo.bar/program</>
<dst>http://foo.bar/source/main.lib</>
</>
<D:Link>
<F:ProjectFiles>Makefile</>
<src>http://foo.bar/program</>
<dst>http://foo.bar/source/makefile</>
</> </> </> </> </>
In this example the resource http://foo.bar/program has a
source property defined which 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.
2.6 Properties and Methods
2.6.1 DELETE
The delete method, when used on a property, causes the
property to be removed.
2.6.2 GET
A GET on a property returns the name of the property. Accept
types may be used to specify the format of the return value,
but all DAV compliant servers MUST at minimum support a
return type of application/XML. If application/XML is used
as the response format then it MUST include the
http://www.ietf.org/standards/dav/ schema.
2.6.2.1 Example
GET bar;DAV/(http:!!www.w3.org!standards!z39.50!Authors)
HTTP/1.1
Host: foo.com
HTTP/1.1 200 OK
Content-Type: application/xml
Content-Length: xxxx
E-tag: 1234
Last-Modified: xxxx
<XML>
<XML:Namespace><Ref>http://www.ietf.org/standards/dav/<
/><AS>D</></>
<XML:Namespace><Ref>http://www.w3.com/standards/z39.50/
</><AS>Z</></>
<D:prop>
<propname>Z:Authors</>
<propvalue>
<XML:XML>
<Namespace>
<Ref>http://www.ietf.org/standards/
dav/</>
<AS>D</>
</>
<Namespace>
<Ref>http://www.w3.com/standards/z39.50/
</>
<AS>Z</>
</>
<Z:Author>Jane Doe</>
<Z:Author>Joe Doe</>
<Z:Author>Lots oDoe</>
</> </> </> </>
GET bar;DAV/(Dublin:Producer) HTTP/1.1
Host: foo.com
HTTP/1.1 200 OK
Content-Type: application/xml
Content-Length: xxxx
E-tag: 2345
Last-Modified: xxxx
<XML>
<XML:Namespace><Ref>http://www.ietf.org/standards/dav/<
/><AS>D</></>
<XML:Namespace><Ref>Dublin</><AS>Du</></>
<D:prop>
<propname>Du:Producer</>
<propvalue><XML:XML>Marcus Doe</></>
</> </>
GET bar;DAV/ HTTP/1.1
Host: foo.com
HTTP/1.1 200 OK
Content-Type: application/xml
Content-Length: xxxx
E-tag; 1234
Last-Modified: xxxx
<XML>
<XML:Namespace><Ref>http://www.ietf.org/standards/dav/<
/><AS>D</></>
<XML:Namespace><Ref>http://www.w3.com/standards/z39.50/
</><AS>Z</></>
<XML:Namespace><Ref>Dublin</><AS>Du</></>
<D:prop>
<propname>Z:Authors</>
<propvalue>
<XML:XML>
<Namespace>
<Ref>http://www.ietf.org/standards/
dav/</>
<AS>D</>
</>
<Namespace>
<Ref>http://www.w3.com/standards/z39.50/
</>
<AS>Z</>
</>
<Z:Author>Jane Doe</>
<Z:Author>Joe Doe</>
<Z:Author>Lots oDoe</>
</> </> </>
<D:prop>
<propname>Du:Producer</>
<propvalue><XML:XML>Marcus Doe</></>
</> </>
2.6.3 PROPPATCH Method
The PROPPATCH method specifies how to alter a property. The
message body controls the actual action taken by a
PROPPATCH. All DAV compliant servers are required to support
the use of the application/XML content-type using the
http://www.ietf.org/standards/dav/proppatch/ schema in a
PROPPATCH method with a request-URI that points to the
resource upon which the property is defined.
The changes in a http://www.w3.com/standards/dav/proppatch/
request MUST be atomically executed, partial results are not
allowed.
2.6.3.1 Request URI
The request URI of a PROPPATCH method with the
http://www.ietf.org/standards/dav/proppatch/ schema MUST
point to the resource upon which the property is defined.
2.6.3.2 PropertyUpdate XML element
Name: http://www.ietf.org/standards/dav/PropertyUpdate
Purpose: To contain a request to alter the properties on a
resource.
Schema: http://www.ietf.org/standards/dav/
Parent: <XML>
Values= *(Create | Remove | Insert)
Description: This XML element is a container for the
information required to modify the properties on the
resource. This XML element is multivalued.
2.6.3.3 Create XML element
Name: http://www.ietf.org/standards/dav/create
Purpose: To create the DAV property specified inside the
Create XML element.
Schema: http://www.ietf.org/standards/dav/
Parent: http://www.ietf.org/standards/dav/PropertyUpdate
Values= Prop
Description: This XML element contains a Prop as the only
element. The PropName contains the name of the property to
be created or overwritten. The PropValue XML element
contains the value of the new property.
2.6.3.4 Remove XML element
Name: http://www.ietf.org/standards/dav/remove
Purpose: To remove the DAV property specified inside the
Remove XML element.
Schema: http://www.ietf.org/standards/dav/
Parent: http://www.ietf.org/standards/dav/PropertyUpdate
Values= PropName
Description: Remove specifies that the property specified in
PropName should be removed. Specifying the removal of a
property that does not exist is not an error.
2.6.3.5 Response Codes
200 OK The command succeeded. As there can be a mixture of
PUT and DELETEs in a body, a 201 Create seems inappropriate.
400 Bad Request The client has provide a value whose
syntax is illegal for the property.
401 Unauthorized The client does not have authorization to
alter one of the properties. This error also occurs if a
property is inherently read only.
403 Forbidden The client, for reasons the server chooses
not to specify, can not alter one of the properties.
405 Conflict The client has provided a value whose
semantics are not appropriate for the property.
413 Request Entity Too Long If a particular property is
too long to be recorded then a composite XML error will be
returned indicating the offending property.
2.6.3.6 Example
PROPPATCH bar;DAV/ HTTP/1.1
Host: www.foo.com
Content-Type: application/XML
Content-Length: xxxx
<XML>
<Namespace><Ref>http://www.ietf.org/standards/dav/</><A
S>D</></>
<Namespace><Ref>http://www.w3.com/standards/z39.50/</><
AS>Z</></>
<D:PropertyUpdate>
<Create><prop>
<propname>Z:authors</>
<propvalue>
<XML:XML>
<Namespace>
<Ref>http://www.ietf.org/standards/dav/proppatch/</>
<AS>D</>
</>
<Namespace>
<Ref>http://www.w3.com/standards/z39.50/</>
<AS>Z</>
</>
<Z:Author>Jim Whitehead</>
<Z:Author>Roy Fielding</>
</>
</>
<Remove><propname>Z:Copyright-Onwer</></>
</> </>
2.6.4 PUT
A PUT is specified in order to control what is returned by a
GET. However a GET on a property always returns some sort of
property containment format. As such PUT can not be used if
the Request-URI refers to a property.
2.6.5 SEARCH
2.6.5.1 Request-URI
The request-URI of the search method is the URI of the
resource. .
The Depth header MUST NOT be used on a SEARCH method which
contains a Limited-Search XML element (limited search).
2.6.5.2 Command Format
The message body stipulates the action of a SEARCH method.
This section defines an application/xml content type using
the http://www.ietf.org/standards/dav/ schema. This method
is not normally cacheable.
2.6.5.2.1 Limited-Search XML element
Name: http://www.ietf.org/standards/dav/limited-search
Purpose: To specify the set of matching properties
Schema: http://www.ietf.org/standards/dav/
Parent: <XML>
Values: The value is a single OR XML element. The OR element
may only contain AND XML elements, and MUST contain at least
one AND element.
Description: This property indicates a very limited search.
The search may only be on HTTP properties.
2.6.5.2.2 OR XML element
Name: http://www.ietf.org/standards/dav/or
Purpose: To take its members, evaluate them, get a true or
false result, or the results together, and have that be
the total result.
Schema: http://www.ietf.org/standards/dav/
Parent: Limited-Search XML element
Values: AND XML element.
2.6.5.2.3 AND XML element
Name: http://www.ietf.org/sandards/dav/and
Purpose: To take its members, evaluate them, get a true or
false result, and the results together, and have that be
the total result.
Schema: http://www.ietf.org/standards/dav
Parent: OR XML element
Values: Zero or one Name XML element, and zero or one Value
XML element. There MUST be at least one Name or Value XML
element.
2.6.5.2.4 Name XML element
Name: http://www.ietf.org/standards/dav/name
Purpose: To provide a pattern against which property names
are to be compared. If the name matches then the property
evaluates to true, otherwise false.
Schema: http://www.ietf.org/standards/dav/
Parent: AND XML element
Values: Match-Stream
2.6.5.2.5 Value XML element
Name: http://www.ietf.org/standards/dav/value
Purpose: To provide a pattern against which property values
are to be compared. If the value matches then the property
evaluates to true, otherwise false.
Schema: http://www.ietf.org/standards/dav/
Parent: AND XML element
Values: Match-Stream
2.6.5.2.6 Match-String XML element
Name: http://www.ietf.org/standards/dav/match-string
Purpose: To specify a search pattern to be matched against
an octet stream
Schema: http://www.ietf.org/standards/dav/
Parent: Name or Value XML element
Values: (* | ? | EncodedOctet)
EncodedOctet = <An EncodedOctet uses XML encoding to encode
* and ? as well as < and >
Description: This element provides a template against which
anything that can be expressed as an octet stream may be
compared. * is a wildcard that matches zero or more
unspecified contiguous octets. ? is a wildcard that
matches exactly one unspecified octet.
2.6.5.3 Response Format
The response is an application/xml message body which
contains a single SearchResult XML element whose contents
are a series of XML elements representing matching
properties.
2.6.5.3.1 SearchResult XML element
Name: http://www.ietf.org/standards/dav/searchresult
Purpose: To contain the results of a SEARCH request
Schema: http://www.ietf.org/standards/dav/
Parent: Any, usually <XML>
Values: Zero or more Prop XML elements (defined in
Properties draft)
Description: The SearchResult XML element provides the
context to inform the client that its contents are not just
some XML element, but an XML representation of the requested
property.
2.6.5.4 Example
SEARCH /container/ HTTP/1.1
Host: www.foo.bar
Content-Length: xxxx
Content-Type: application/xml
<XML>
<XML:Namespace>
<Ref>http://www.ietf.org/standards/dav/</>
<AS>S</>
</>
<S:limited-search>
<OR>
<AND>
<Name>*</>
</>
</>
</>
</>
HTTP/1.1 200 OK
Content-Type: application/xml
Content-Length: xxxxx
<XML>
<XML:Namespace>
<Ref>http://www.ietf.org/standards/dav/</>
<As>S</>
</>
<XML:Namespace>
<Ref>http://www.foo.bar/boxschema</>
<AS>R</>
</>
<S:SearchResult>
<Prop>
<PropName>R:bigbox</>
<PropValue>
<XML:XML>
<BoxType>Box type A</>
</>
</>
</>
<Prop>
<PropName>R:author</>
<PropValue>
<XML:XML>
<Name>J.J.
Dingleheimerschmidt</>
</>
</>
</>
</>
</>
The result will return all properties on the container and
its members. In this case only two properties were found,
one on the container and one on one of its members, both
properties are live.
3 A Proposal for Collections of Web Resources and Name
Space Operations
3.1 Observations on the HTTP Object Model
As a prerequisite for specification of collections and name
space operations for the Web, a model for collection
resources and for namespace topology must be given. This
section describes a new type of Web resource, the collection
resource, and provides a model for discussing the
relationship between the resources that are generated as the
result of a data-producing process, and the source resources
that describe the process.
3.1.1 Collection Resources
A collection is a Web resource type whose primary state is a
set of URIs and associated values that are recorded as
properties on the resource. The URIs identify resources
that are members of the collection. The values associated
with each URI include information such as the Last Modified
Date, Entity Tag, Creation Date, Content Type, Display Name,
and whether the member is a collection.
A member of a collection is either an internal member
resource, which MUST have a URI that is relative to the base
URI of the collection, or an external member resource, which
has a URI which is not relative to the base URI of the
collection. External member resources are further subdivided
into propagate members, which have recursive method
invocations propagated to them, and no-propagate members,
which do not.
A collection resource may be viewed and used as a compound
resource in which the collection is a container for a group
of related resources that, together, form a larger logical
unit. For example, a collection of HTML resources where
each resource is the chapter of a book can be viewed as a
compound resource representing the entire book.
Some methods, when invoked on a collection, affect the
entire collection. For example, it is possible to copy an
entire collection and its contents with just a single copy
method request. The model for performing these operations is
a tree traversal. The method is invoked on the collection,
which then performs the method on itself before propagating
the method to all its internal members and propagate
external members. If these are non-collection resources,
the request method is processed. However, if the request is
propagated to another collection, then the propagation
begins again. This sequence of actions causes the method to
be propagated as a tree traversal of the members of the
collections. It is incumbent upon the client to perform any
locking operation on the collection or subordinate members
that it deems necessary in order to maintain state
consistency during the execution of such methods.
3.1.2 Creation and Retrieval of Collection Resources
Since the existing HTTP methods for creating (PUT, POST) and
retrieving (GET) a resource were defined for non-collection
resources, it is not surprising that the semantics of these
methods do not transfer well to collections. For example,
the PUT method is defined to store the request entity under
the Request-URI. While a description format for a
collection can readily be constructed that could be used
with PUT, the implications of sending such a description to
the server are undesirable. For example, if a description
of a collection that omitted some existing resources were
PUT to a server, this might be interpreted as a command to
remove those members. This would extend PUT to perform
DELETE functionality, which is undesirable since it changes
the semantics of PUT, and makes it difficult to control
DELETE functionality with an access control scheme based on
methods.
While the POST method is sufficiently open-ended that a
create a collection POST command could be constructed,
this is undesirable because it would be difficult to provide
separate access control for collection creation and other
uses of POST if they both use the same method.
The GET method when applied to collections is also
problematic. While it might seem desirable to have GET
return a listing of the members of a collection, this is
foiled by the existence of the index.html de-facto
standard namespace redirection, in which a GET request on a
collection is automatically redirected to the index.html
resource.
Because of the difficulty of reusing some existing HTTP/1.1
methods for collections, two new resource creation/retrieval
methods are needed. This specification introduces the MKCOL
method for creating collection resources, and the INDEX
method for retrieving the contents of a collection.
The exact definition of the behavior of GET and PUT on
collections is defined later in this draft.
3.1.3 Source Resources and Output Resources
For many resources, the entity returned by GET exactly
matches the persistent state of the resource, for example, a
GIF file stored on a disk. For this simple case, the URL at
which a resource is accessed is identical to the URL 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, HTML files can sometimes be processed by the server
before being transmitted as a return entity body. Server-
side-include directives within an HTML file 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 file 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
URL 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 capability, the fact
that the source resource(s) for server generated output do
not have a mapping to the URI namespace is not a problem,
and has desirable security benefits. However, if remote
editing of the source resource(s) is desired, they should be
given a location in the URI namespace. This source location
should 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.
For DAV compliant servers all output resources which have a
single source resource (and that source resource has a URI),
the URI of the source resource SHOULD be stored in a single
link on the output resource with type DAV:/ Source. Note
that by storing the source URI in links on the output
resources, the burden of discovering the source is placed on
the authoring client.
In the general case, a large number of source resources can
comprise a data-producing process that generates many output
resources, creating a many-to-many relationship between
output resources and source resources. If each output
resource had links back to every source resource in the
data-producing process, there can be a potentially large
number of such links. Due to the potentially large number of
links, and the lack of a policy for ordering access to
multiple sources, explicit storage of source relationships
is limited to cases with only a single source resource.
3.2 MKCOL Method
3.2.1 Problem Description
The client needs a way to create a collection.
3.2.2 Solution Requirements
The solution:
Must ensure that a collection has been made (i.e. that it
responds to the INDEX method) as opposed to a non-
collection resource. If a collection could not be made, it
must indicate a failure to the principal.
Requires that the server MAY, if necessary, create any
intermediate collections so that the underlying storage
medium is self-consistent.
3.2.3 Request
The MKCOL method creates a new collection resource at the
location specified by the Request-URI. If the Request-URI
exists then MKCOL must fail.
During MKCOL processing, a server MAY add the Request-URI to
one or more collections within the servers controlled
namespace.
3.2.3.1 MKCOL Without Request Body
When MKCOL is invoked without a request body then the
collection created has no members.
3.2.3.2 MKCOL With Request Body
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.
3.2.3.3 Creating Multiple Collections
The server MAY create intermediate collections if they do
not already exist. For example, if the collection
http://server/a/ already exists in the servers namespace,
then while performing a MKCOL to create http://server/a/b/c/
the server may also create a collection at
http://server/a/b/.
3.2.4 Response
Responses from a MKCOL request are not cacheable, since
MKCOL has non-idempotent semantics.
201 (Created) - The structured resource was created in its
entirety.
403 (Forbidden) - The server does not allow the creation of
collections at the given location in its namespace.
415 (Unsupported Media Type) The server does not support
the request type of the body.
416 (Unprocessable Entity) - A new status code. The server
understands the content type of the request entity, but was
unable to process the contained instructions.
3.2.5 Example
This example creates a container collection called
/webdisc/xfiles/ on the server www.server.org.
MKCOL /webdisc/xfiles/ HTTP/1.1
Host: www.server.org
HTTP/1.1 201 Created
3.3 INDEX Method
3.3.1 Problem Description
A mechanism is needed to discover if a resource is a
collection and if so, list its members.
3.3.2 Solution Requirements
The solution:
must allow a client to discover the members of a collection
must always provide a machine-readable description of the
membership of a collection
3.3.3 The Request
The INDEX method returns a machine-readable representation
of the membership of the resource at the Request-URI. For a
collection, INDEX MUST return a machine-readable list of its
members. For other resources, the information returned by
INDEX is undefined, and MAY vary. The request message body
of an INDEX request SHOULD be ignored.
The Depth header can be used to indicate how much of a
result can be generated for the response. The specific
values allowed for the depth header when used with the INDEX
method are 1 and infinity. The 1 value indicates that the
internal and external member resources should be reported in
the result, infinity indicates that all internal and
external member resources and all their descendants should
be in the result. If the Depth header is not given, then 1
is assumed. Servers MUST honor a depth of 1. Servers MAY
honor infinity. If the server does not support the value of
the depth header then a 412 (Precondition failed) MUST be
returned.
3.3.4 The Response
200 (OK) The server MUST send an application/xml response
entity which describes the collection.
404 (Not Found) - Same behavior as HTTP 1.1. The server
never had the resource, or the server permanently deleted
the resource and has no knowledge that it ever existed. This
error code implies that, essentially, the server has no
information about the Request URI.
3.3.5 Response Message Body
The default INDEX response for a resource is an
application/xml HTTP entity (i.e., an Extensible Markup
Language (XML) document) that contains a single XML element
called collectionresource which describes the collection,
and a set of XML elements called memberesource which
describe the members of the collection.
The response from INDEX is cacheable, and SHOULD be
accompanied by an ETag header (see section 13.3.4 of RFC
2068). If GET and INDEX return different entities for the
same resource state, they MUST return different entity tags.
The server MUST transmit the following XML elements for each
member resource of a collection: Ref, IsCollection, Content-
Type, External. The server MUST transmit the following XML
elements if it can generate any meaningful values for them:
Creation-Date, Last-Modified, DisplayName, Content-Language.
The server SHOULD transmit Etag XML elements for each
member (see section 13.3.4 of RFC 2068).
The value of content-type, last-modified, and etag XML
elements MUST be identical to the value of the response
header field of the same name in the HTTP/1.1 specification.
Since the HTTP/1.1 header fields are described in terms of
the on-the-wire entity, the values presented by INDEX are
those that would be generated if the resource was accessed
using the GET method without content negotiation.
3.3.5.1 CollectionResource
Name: http://www.ietf.org/standards/dav/collectionresource
Purpose: Describes a collection
Schema: http://www.ietf.org/standards/dav/
Parent: <XML>
Value:MemberResource
3.3.5.2 MemberResource
Name: http://www.ietf.org/standards/dav/memberresource
Purpose: Describes a member of a collection
Schema: http://www.ietf.org/standards/dav/
Parent: CollectionResource
Value:Ref, IsCollection, Content-Type, External, Creation-
Date, Last-Modified, ETag, DisplayName (other XML elements
MAY also be present)
3.3.5.3 Ref
See XML definition.
3.3.5.4 IsCollection
Name: http://www.ietf.org/standards/dav/iscollection
Purpose: This is a boolean value which is set to true if
the entry is a collection
Schema: http://www.ietf.org/standards/dav/
Parent: MemberResource
Value:(true | false)
3.3.5.5 Content-Type
Name: http://www.ietf.org/standards/dav/content-type
Purpose: The content-type of the member resource.
Schema: http://www.ietf.org/standards/dav/
Parent: MemberResource
Value:media-type ; defined in Section 3.7 of [HTTP11]
If no meaningful content-type can be generated, then an
empty value MUST be given.
3.3.5.6 External
Name: http://www.ietf.org/standards/dav/external
Purpose: If present, this element indicates the resource is
an external member of the collection. If the value is
propagate, it is a propagate member, if the value is no-
propagate, it is a no-propagate member.
Schema: http://www.ietf.org/standards/dav/
Parent: MemberResource
Value:(propagate | no-propagate)
3.3.5.7 Creation-Date
Name: http://www.ietf.org/standards/dav/creation-date
Purpose: The date the resource was created.
Schema: http://www.ietf.org/standards/dav/
Parent: MemberResource
Value:The date MUST be given in RFC 1123 format (rfc-1123
production, defined in section 3.3.1 of [HTTP11]
3.3.5.8 Last-Modified
Name: http://www.ietf.org/standards/dav/last-modified
Purpose: The date the resource was last modified.
Schema: http://www.ietf.org/standards/dav/
Parent: MemberResource
Value:The date MUST be given in RFC 1123 format (rfc-1123
production, defined in section 3.3.1 of [HTTP11]
3.3.5.9 ETag
Name: http://www.ietf.org/standards/dav/etag
Purpose: The entity tag of the resource.
Schema: http://www.ietf.org/standards/dav/
Parent: MemberResource
Value:entity-tag ; defined in Section 3.11 of [HTTP11]
3.3.5.10 DisplayName
Name: http://www.ietf.org/standards/dav/displayname
Purpose: A name for the resource that is suitable for
presentation to a person
Schema: http://www.ietf.org/standards/dav/
Parent: MemberResource
Value:Any valid XML character data (from XML specification)
3.3.5.11 Content-Language
Name: http://www.ietf.org/standards/dav/content-language
Purpose: Describes the natural language(s) of the intended
audience for the resource.
Schema: http://www.ietf.org.standards/dav/
Parent: MemberResource
Value: 1#language-tag ;language-tag is defined in section
14.13 of RFC 2068
3.3.6 Example
INDEX /user/yarong/dav_drafts/ HTTP/1.1
Host: www.microsoft.com
Depth: 1
HTTP/1.1 200 OK
Content-Type: application/xml
Content-Length: xxx
Last-Modified: xxx
ETag: fooyyybar
<XML>
<XML:Namespace><Ref>http://www.ietf.org/standards/dav/<
/><As>D</></>
<D:CollectionResource>
<MemberResource>
<XML:Ref>namespace.doc</>
<IsCollection>false</>
<Content-Type>application/msword</>
<External>false</>
<Creation-Date>Thu, 20 Mar 1997 23:05:25
GMT</>
<Last-Modified>Fri, 22 Aug 1997 18:22:56
GMT</>
<Etag>8675309</>
<DisplayName>WebDAV Name Space Operations
Draft</>
<Content-Language>en</>
</> </>
</>
This example shows the result of the INDEX method applied to
the collection resource
http://www.microsoft.com/er/yarong/dav_drafts/. It returns
a response body in XML format, which gives information about
the containers sole member,
http://www.microsoft.com/users/yarong/dav_drafts/namespace.d
oc.
3.4 Behavior of RFC 2068 Methods on Collections
With the introduction of the collection resource type to the
HTTP object model, it is necessary to define the behavior of
the existing methods (defined in RFC 2068) when invoked on a
collection resource to avoid ambiguity. While some methods,
such as OPTIONS and TRACE behave identically when applied to
collections, GET, HEAD, POST, PUT, and DELETE require some
additional explanation.
3.4.1 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 [HTTP11]. 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, and hence it is possible the
result of a GET on a collection will bear no correlation to
the state of the collection.
Similarly, since the definition of HEAD is a GET without a
response message body, the semantics of HEAD do not require
any modification when applied to collection resources.
3.4.2 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 modified because it is largely undefined. Thus
the semantics of POST do not require any modification when
applied to a collection.
3.4.3 PUT for Collections
In HTTP/1.1, PUT stores the request entity under the
Request-URI, and hence its semantics are limited to non-
collection resources. If a PUT is invoked on a collection
resource it MUST fail.
When the PUT operation creates a new non-collection
resource, a server MAY add that resources URI to one or
more collections within the servers controlled namespace.
3.4.4 DELETE for Collections
When DELETE is applied to a collection resource, all
internal members MUST be recursively deleted. The
dav:link/propagate external members MUST be deleted and
their links must be removed. dav:link/nopropagate external
members MUST have only their link removed; the resources
MUST not be deleted.
The Depth header does not apply to the DELETE method. It
cannot be used to limit the extent of the operation. If it
is present it MUST be ignored.
When applied to any resource, the DELETE method deletes all
properties on the Request-URI.
During DELETE processing, a server MAY remove the URI of the
deleted resource(s) from collections within its controlled
namespace.
3.4.4.1 New Response Codes for DELETE
207 (Partial Success) Only some of the member resources were
deleted. The response entity will describe any errors.
500 (Server Error) The resource was in such a state that it
could not be deleted. The response entity will describe
reason for the error.
3.5 COPY Method
3.5.1 Problem Description
Currently, in order to create a copy of a resource, the
client must GET an entity and then PUT that entity to the
desired destination. This requires (1) an entity to be
transmitted to and from the server and (2) that the resource
be expressible as an entity with complete fidelity.
This is problematic because of the network traffic involved
in making a copy, and because there is often no way to fully
express a resource as an entity without a loss of fidelity.
3.5.2 Solution Requirements
The solution:
MUST allow a principal to create a copy of a resource
without having to transmit the resource to and from the
server.
3.5.3 The Request
The COPY method creates a duplicate of the source resource,
given by the Request-URI, in the destination resource, given
by the Destination header. The Destination header MUST be
present. The exact behavior of the COPY method depends on
the type of the source resource.
3.5.3.1 COPY for HTTP/1.1 resources
When the source resource is not a collection, and is not a
property, the body of the destination resource MUST be
octet-for-octet identical to the body of the source
resource. Alterations to the destination resource do not
modify the source resource. Alterations to the source
resource do not modify the destination resource. Thus, all
copies are performed by-value.
If the Duplicate-Properties header is false, then
properties SHOULD NOT be copied to the destination resource.
If the Duplicate-Properties header is false and the
Enforce-Live-Properties header is also present, the request
MUST fail with a 412 (Precondition Failed) status code.
[Ed. Note: what if resource to be copied has no properties,
and no properties are explicitly named in the header?]
All properties on a source resource SHOULD be duplicated on
the destination resource following the definition for
copying properties.
3.5.3.2 COPY for Properties
Live properties SHOULD be duplicated as identically behaving
live properties at the destination resource. Since they are
live properties, the server determines the syntax and
semantics (hence value) of these properties. Properties
named by the Enforce-Live-Properties header MUST be live on
the destination resource, or the method MUST fail. If a
property is not named by Enforce-Live-Properties and cannot
be copied live, then its value MUST be duplicated in an
identically named, dead resource on the destination
resource.
For every dead property defined on the source resource,
there SHOULD be an octet-for-octet identical dead property
on the destination resource.
3.5.3.3 COPY for Collections
The Depth and Overwrite headers govern the behavior of COPY
for collections.
When performing a recursive copy, all HTTP/1.1 request
headers are duplicated on the propagated method request
except for the precondition headers If-Modified-Since, If-
Match, If-None-Match, If-Range, If-Unmodified-Since, which
should only be applied to the Request-URI in order to
determine if the operation should be performed. The
Destination header MUST be rewritten to preserve the
membership of the destination collection, i.e., by appending
the relative URI of the member to the URI of the destination
collection.
A Depth of 0 indicates the collection MUST duplicate all
of its external members in a new collection at the
Destination. Since the COPY method is not propagated to its
members, no internal member resource is duplicated.
A Depth of 1 indicates the collection MUST propagate the
COPY to all internal, non-collection members. If the
Overwrite header is true the COPY method duplicates all of
its external members in a new collection at the Destination.
If the Overwrite header is false and the destination
resource is a collection, the COPY method does not duplicate
its external members, but is propagated to all internal,
non-collection members.
A Depth of infinity indicates the collection MUST
propagate the COPY method to all internal members. If the
Overwrite header is true, the COPY method MUST duplicate
all of its external members in a new collection at the
Destination. If the Overwrite header is false and the
destination resource is a collection, then the COPY method
does not duplicate its external members, but is propagated
to all internal members.
3.5.3.4 Type Interactions
If the destination resource identifies a property and the
source resource is not a property, then the copy SHOULD
fail.
If the destination resource identifies a collection and the
Overwrite header is true, prior to performing the copy,
the server MUST perform a DELETE operation on the
collection.
3.5.4 The Response
200 (OK) The source resource was successfully copied to a
pre-existing destination resource.
201 (Created) The source resource was successfully copied.
The copy operation resulted in the creation of a new
resource.
207 (Partial Success) Only some of the member resources were
copied. The return entity body describes the status code for
each resource.
412 (Precondition Failed) This status code MUST be returned
if the server was unable to maintain the liveness of the
properties listed in the Enforce-Live-Properties header, or
if the Overwrite header is false, and the state of the
destination resource is non-null.
500 (Server Error) The resource was in such a state that it
could not be copied. This may occur if the Destination
header indicated an external (from the point of view of the
server) resource and the server has no capability to copy to
an external resource.
502 (Bad Gateway) - This may occur when copying to external
resources and the destination server refused to accept the
resource.
3.5.5 Examples
3.5.5.1 Overwrite Example
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
contents of the destination resource were overwritten, if
non-null.
COPY /~fielding/index.html HTTP/1.1
Host: www.ics.uci.edu
Destination:
http://www.ics.uci.edu/users/f/fielding/index.html
Overwrite: true
HTTP/1.1 200 OK
3.5.5.2 No Overwrite Example
The following example shows the same copy operation being
performed, except with the Overwrite header set to false.
A response of 412, Precondition Failed, is returned because
the destination resource has a non-null state.
COPY /~fielding/index.html HTTP/1.1
Host: www.ics.uci.edu
Destination:
http://www.ics.uci.edu/users/f/fielding/index.html
HTTP/1.1 412 Precondition Failed
3.6 MOVE Method
3.6.1 Problem Description
The move operation on a resource is the logical equivalent
of a copy followed by a delete.
In HTTP 1.1, the procedure could be performed in several
steps. First, the client could issue a GET to retrieve a
representation of a resource, issue a DELETE to remove the
resource from the server, then use PUT to place the resource
on the server with a new URI. As is the case for COPY -
because of the network traffic involved in making a move,
and because there is often no way to fully express a
resource as an entity without a loss of fidelity - server
move functionality is preferable.
With a DAV server, a principal may accomplish this task by
issuing a COPY and then DELETE. Network load decreases, but
the server load may still be significant because the server
must create a duplicate resource. Were a server to know
beforehand that a principal intended to perform COPY and
DELETE operations in succession, it could avoid the creation
of a duplicate resource.
3.6.2 Solution Requirements
The solution:
Must prevent the unneeded transfer of entity bodies from and
to the server.
Must prevent the unneeded creation of copies by the server.
3.6.3 The Request
The MOVE method is defined as the logical equivalent of a
COPY followed by a DELETE of the source resource, performed
atomically.
3.6.4 The Response
200 (OK) - The resource was moved. A successful response
must contain the Content-Location header, set equal to the
URI in source. This lets caches properly flush any cached
entries for the source. Unfortunately the Content-Location
header only allows a single value so it is not possible for
caches unfamiliar with the MOVE method to properly clear
their caches.
207 (Partial Success) Only some of the member resources were
moved. The return entity body will give the status code for
each resource.
412 (Precondition Failed) This status code MUST be returned
if the server was unable to maintain the liveness of the
properties listed in the Enforce-Live-Properties header, or
if the Overwrite header is false, and the state of the
destination resource is non-null.
501 (Not Implemented) - This may occur if the Destination
header specifies a resource which is outside its domain of
control (e.g., stored on another server) resource and the
server either refuses or is incapable of moving to an
external resource.
502 (Bad Gateway) - This may occur when moving to external
resources and the destination server refused to accept the
resource.
3.6.5 Examples
3.6.5.1 Overwrite Example
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 were overwritten, if
non-null.
MOVE /~fielding/index.html HTTP/1.1
Host: www.ics.uci.edu
Destination:
http://www.ics.uci.edu/users/f/fielding/index.html
Overwrite: true
HTTP/1.1 200 OK
Content-Location:
http://www.ics.uci.edu/users/f/fielding/index.html
3.7 Multi-Status Response
3.7.1 Problem Definition
Certain methods (COPY, MOVE, and DELETE) when applied to a
collection might be recursively applied to all sub-members
of the collection. In this case, it is possible that the
operation will succeed on some member resources and fail on
others, thus generating a 207 (Partial Success) status code.
A principal may need to know which members of the
collection succeeded and which failed.
3.7.2 Solution Requirements
The solution must:
- communicate the status code and reason
- give the URI of the resource on which the method was
invoked
- be consistent with other return body formats
3.7.3 Multi-Status Response
The default multi-status response body is an application/xml
HTTP entity that contains a single XML element called
multiresponse, which contains a set of XML elements called
response, one for each 200, 300, 400, and 500 series status
code generated during the method invocation. 100 series
status codes MUST NOT be recorded in a response XML element.
Each response XML element contains two sub-entities, ref,
the URI of the resource on which the method was invoked, and
status, which holds the status-line from the method
invocation.
A multi-status response MUST be present when a 207 (Partial
Success) status code is returned by the initial method
invocation.
3.7.3.1 MultiResponse
Name:
http://www.ietf.org/standards/dav/multiresponse/multi
response
Purpose: Contains multiple response messages.
Schema: http://www.ietf.org/standards/dav/multiresponse/
Parent: <XML>
Value:1*Response
3.7.3.2 Response
Name:
http://www.ietf.org/standards/dav/multiresponse/respo
nse
Purpose: Holds a single response
Schema: http://www.ietf.org/standards/dav/multiresponse/
Parent: MultiResponse
Value:Ref, Status
3.7.3.3 Status
Name:
http://www.ietf.org/standards/dav/multiresponse/statu
s
Purpose: Holds a single HTTP status-line
Schema: http://www.ietf.org/standards/dav/multiresponse/
Parent: Response
Value:status-line ;status-line defined in [HTTP11]
3.7.4 Example
COPY /users/jdoe/collection/ HTTP/1.1
Host: www.doecorp.com
Destination:
http://www.doecorp.com/users/jdoe/othercollection/
Depth: infinity
Overwrite: false
HTTP/1.1 207 Partial Success
Content-Type: application/xml
Content-Length: xxx
<XML>
<XML:Namespace><Ref>http://www.ietf.org/standards/dav/multir
esponse/</><As>R</></>
<R:MultiResponse>
<Response>
<XML:Ref>http://www.doecorp.com/users/jdoe/collection/i
ndex.html</>
<Status>HTTP/1.1 412 Precondition Failed</>
</>
<Response>
<XML:Ref>http://www.doecorp.com/users/jdoe/collection/r
eport.html</>
<Status>HTTP/1.1 200 OK</>
</>
</>
</>
3.8 ADDREF Method
3.8.1 Problem Definition
There needs to be a way to add an external member to a
collection.
3.8.2 Solution Requirements
The solution must:
allow access control
allow referencing to URIs of external members
not require a body
3.8.3 The Request
The ADDREF method adds the URI specified in the Collection-
Member header as an external member to the collection
specified by the Request-URI. The value in the Collection-
Member header MUST be an absolute URI meeting the
requirements of an external member URI. The propagation
type of the external URI is specified in the Collection-
Member Header.
3.9 DELREF Method
3.9.1 Problem Definition
There needs to be a way to remove an external member from a
collection.
3.9.2 Solution Requirements
The solution must:
allow access control
allow referencing to URIs of external members
not require a body
3.9.3 The Request
The DELREF method removes the URI specified in the
Collection-Member header from the collection specified by
the Request-URI.
3.10 PATCH Method
3.10.1 Problem Definition
At present, if a principal wishes to modify a resource, they
must issue a GET against the resource, modify their local
copy of the resource, and then issue a PUT to place the
modified resource on the server. This procedure is
inefficient because the entire entity for a resource must be
transmitted to and from the server in order to make even
small changes. Ideally, the update entity transmitted to
the server should be proportional in size to the
modifications.
3.10.2 Solution Requirements
The solution must:
allow partial modification of a resource without having to
transmit the entire modified resource
allow byte-range patching
allows extensions so that patches can be done beyond simple
byte-range patching
allow ranges to be deleted, inserted, and replaced
3.10.3 The Request
The PATCH method contains a list of differences between the
original version of the resource identified by the Request-
URI and the desired content of the resource after the PATCH
action has been applied. The list of differences is in a
format defined by the media type of the entity (e.g.,
"application/diff") and must include sufficient information
to allow the server to convert the original version of the
resource to the desired version.
Since the semantics of PATCH are non-idempotent, responses
to this method are not cacheable.
If the request appears (at least initially) to be
acceptable, the server MUST transmit an interim 100 response
message after receiving the empty line terminating the
request headers and continue processing the request.
While server support for PATCH is optional, if a server does
support PATCH, it MUST support at least the application/xml
diff format defined below. Support for the VTML difference
format [VTML] is recommended, but not required.
3.10.4 application/XML elements for PATCH
The resourceupdate XML elementXML element contains a set of
XML sub-entities that describe modification operations. The
name and meaning of these XML elements is given below.
Processing of these directives MUST be performed in the
order encountered within the XML document. A directive
operates on the resource as modified by all previous
directives (executed in sequential order).
3.10.4.1 ResourceUpdate
Name:
http://www.ietf.org/standards/dav/patch/resourceupdat
e
Purpose: Contains an ordered set of changes to a non-
collection, non-property resource.
Schema: http://www.ietf.org/standards/dav/patch/
Parent: <XML>
Value:*(Insert | Delete | Replace)
3.10.4.2 Insert
Name: http://www.ietf.org/standards/dav/patch/insert
Purpose: Insert the XML elementXML elements contents
starting exactly at the specified octet.
Schema: http://www.ietf.org/standards/dav/patch/
Parent: ResourceUpdate
Value:The insert XML elementXML element MUST contain an
octet XML elementXML element that specifies an octet
position within the body of a resource. A value of end
specifies the end of the resource. The body of the insert
XML elementXML element contains the octets to be inserted.
3.10.4.3 Delete
Name: http://www.ietf.org/standards/dav/patch/delete
Purpose: Removes the specified range of octets.
Schema: http://www.ietf.org/standards/dav/patch/
Parent: ResourceUpdate
Value:The Delete XML elementXML element MUST contain an
octet-range XML elementXML element. The value of this XML
elementXML element is empty.
Discussion: The octets which are deleted are removed, which
means the resource is collapsed and the length of the
resource is decremented by the size of the octet range. It
is not appropriate to replace deleted octets with zeroed-out
octets, since zero is a valid octet value.
3.10.4.4 Replace
Name: http://www.ietf.org/standards/dav/patch/replace
Purpose: Replaces the specified range of octets with the
contents of the XML element. If the number of octets in the
XML element is different from the number of octets
specified, the update MUST be rejected.
Schema: http://www.ietf.org/standards/dav/patch/
Parent: ResourceUpdate
Value:The Replace XML element MUST contain an octet-range
XML element. The contents of the entity are the replacement
octets.
3.10.4.5 Octet-Range Attribute
Name:
http://www.ietf.org/standards/dav/patch/octet-range
Purpose: Specifies a range of octets which the enclosing
property effects.
Schema: http://www.ietf.org/standards/dav/patch/
Parent: Insert, Delete, Replace
Value: number [- (number | end)]
Number = 1*Digit
Description: Octet numbering begins with 0. If the octet
contains a single number then the operation is to begin at
that octet and to continue for a length specified by the
operation. In the case of a delete, this would mean to
delete but a single octet. In the case of an insert this
would mean to begin the insertion at the specified octet and
to continue for the length of the included value, extending
the resource if necessary. In the case of replace, the
replace begins at the specified octet and overwrites all
that follow to the length of the included value. Octet
values MUST specify locations in the state of the resource
prior to the processing of the PATCH method.
3.10.5 The Response
200 (OK) - The request entity body was processed without
error, resulting in an update to the state of the resource.
409 (Conflict) - If the update information in the request
message body does not make sense given the current state of
the resource (e.g., an instruction to delete a non-existent
line), this status code MAY be returned.
415 (Unsupported Media Type) - The server does not support
the content type of the update instructions in the request
message body.
416 (Unprocessable Entity) - A new status code. The server
understands the content type of the request entity, but was
unable to process the contained instructions.
3.10.6 Examples
3.10.6.1 HTML file modification
The following example shows a modification of the title and
contents of the HTML resource
http://www.example.org/hello.html.
Before:
<HTML>
<HEAD>
<TITLE>Hello world HTML page</TITLE>
</HEAD>
<BODY>
<P>Hello, world!</P>
</BODY>
</HTML>
PATCH Request: Response:
PATCH hello.html HTTP/1.1
Host: www.example.org
Content-Type: application/xml
Content-Length: xxx
HTTP/1.1 100 Continue
<XML>
<XML:Namespace><ref>http://www.ietf.org/standards/dav/p
atch/</><AS>D</></>
<D:ResourceUpdate>
<Replace><octet-range>14</>&003CTITLE&003ENew
Title&003C/TITLE&003E</>
<Delete><octet-range>38-50</>
<Insert><octet-range>86</>&003CP&003ENew
paragraph&003C/P&003E
</>
</></>
HTTP/1.1 200 OK
After:
<HTML>
<HEAD>
<TITLE>New Title</TITLE>
</HEAD>
<BODY>
<P>Hello, world!</P>
<P>New paragraph</P>
</BODY>
</HTML>
3.11 Headers
3.11.1 Depth
The Depth header determines the depth to which a method is
propagated on a resources children.
Depth = Depth : DepthToken
DepthToken = "0" | "1" | "infinity" | token
The optional token allows for extension. A server MUST
ignore a Depth header with an unknown value.
3.11.2 Destination
The Destination header specifies a destination resource for
methods such as COPY and MOVE, which take two URIs as
parameters.
Destination= Destination : URI
3.11.3 Enforce-Live-Properties
The Enforce-Live-Properties header specifies properties that
MUST be live after they are copied (moved) to the
destination resource of a copy (or move). If the value *
is given for the header, then it designates all live
properties on the source resource.
EnforceLiveProperties = "Enforce-Live-Properties :"
(* | 1#( Property-Name ))
Property-Name = <> URI <>
3.11.4 Duplicate-Properties
The Duplicate-Properties header instructs the server whether
to duplicate the source resources properties onto the
destination resource during a COPY or MOVE. A value of
false requires that the server MUST NOT duplicate on the
destination resource any properties that are defined on the
source resource. By default, the value of this header is
true, and a client MAY omit this header from a request
when its value is true.
Duplicate-Properties = Duplicate-Properties :
(true | false)
3.11.5 Overwrite
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 false states that the
server MUST NOT perform the COPY or MOVE operation if the
state of the destination resource is non-null. By default,
the value of Overwrite is false, and a client MAY omit
this header from a request when its value is false. 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.
Overwrite = Overwrite : (true | false)
3.11.6 Destroy Header
When deleting a resource the client often wishes to specify
exactly what sort of delete is being enacted. The Destroy
header, used with PEP, allows the client to specify the end
result they desire. The Destroy header is specified as
follows:
DestroyHeader = "Destroy" ":" #Choices
Choices = "VersionDestroy" | "NoUndelete" | "Undelete"
| Token
The Undelete token requests that, if possible, the resource
should be left in a state such that it can be undeleted. The
server is not required to honor this request.
The NoUndelete token requests that the resource MUST NOT be
left in a state such that it can be undeleted.
The VersionDestroy token includes the functionality of the
NoUndelete token and extends it to include having the server
remove all versioning references to the resource that it has
control over.
3.11.7 Collection-Member Header
The Collection-Member header specifies the URI of an
external resource to be added/deleted to/from a collection.
CollectionMember = Collection-Member : PropType SP
URI
PropType = propagation = (prop | noprop)
3.12 Links
3.12.1 Source Link Property Type
Name: http://www.ietf.org/standards/dav/link/source
Purpose: The destination of the source link identifies the
resource that contains the unprocessed source of the links
source.
Schema: http://www.ietf.org/standards/dav/link/
Parent: Any.
Value:An XML document with zero or more link XML elements.
Discussion: 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, DAV asserts no policy on partial
ordering.
4 State Tokens
4.1 Overview
4.1.1 Problem Description
There are times when a principal will want to predicate
successful execution of a method on the current state of a
resource. While HTTP/1.1 provides a mechanism for
conditional execution of methods using entity tags via the
If-Match and If-None-Match headers, the mechanism is not
sufficiently extensible to express conditional statements
involving more generic state indicators, such as lock
tokens.
The fundamental issue with entity tags is that they can only
be generated by a resource. However there are times when a
client will want to be able to share state tokens between
resources, potentially on different servers, as well as be
able to generate certain types of lock tokens without first
having to communicate with a server.
For example, a principal may wish to require that resource B
have a certain state in order for a method to successfully
execute on resource A. If the client submits an e-tag from
resource B to resource A, then A has no way of knowing that
the e-tag is meant to describe resource B.
Another example occurs when a principal wishes to predicate
the successful completion of a method on the absence of any
locks on a resource. It is not sufficient to submit an If-
None-Match: * as this refers to the existence of an entity,
not of a lock.
This draft defines the term state token as an identifier
for a state of a resource. The sections below define
requirements for state tokens and provide a state token
syntax, along with two new headers which can accept the new
state token syntax.
4.1.2 Solution Requirements
4.1.2.1 Syntax
Self-Describing. A state token must be self describing such
that upon inspecting a state token it is possible to
determine what sort of state token it is, what resource(s)
it applies to, and what state it represents.
This self-describing nature allows servers to accept tokens
from other servers and potentially be able to coordinate
state information cross resource and cross site through
standardized protocols. For example, the execution of a
request on resource A can be predicated on the state of
resource B, where A and B are potentially on different
servers.
Client Generable. The state token syntax must allow, when
appropriate, for clients to generate a state token without
having first communicated with a server.
One drawback of entity tags is that they are set by the
server, and there is no interoperable algorithm for
calculating an entity tag. Consequently, a client cannot
generate an entity tag from a particular state of a
resource. However, a state token which encodes an MD5 state
hash could be calculated by a client based on a client-held
state of a resource, and then submitted to a server in a
conditional method invocation.
Another potential use for client generable state tokens is
for a client to generate lock tokens with wild card fields,
and hence be able to express conditionals such as: only
execute this GET if there are no write locks on this
resource.
4.1.2.2 Conditonals
Universal. A solution must be applicable to all requests.
Positive and Negative. Conditional expressions must allow
for the expression of both positive and negative state
requirements.
4.2 State Token Syntax
State tokens are URLs employing the following syntax:
State-Token = StateToken: Type : Resources : State-
Info
Type = Type = Caret-encoded-URL
Resources = Res = Caret-encoded-URL
Caret-encoded-URL = ^ Resource ^
Resource = <A URI where all ^ characters are escaped>
State-Info = *(uchar | reserved) ; uchar, reserved defined
section 3.2.1 of RFC 2068
This proposal has created a new URL scheme for state tokens
because a state token names a network resource using its
normal name, which is typically state-invariant, along with
additional information that specifies a particular state of
the resource. Encoding the state information into the
native URL scheme of the network resource was not felt to be
safe, since freedom from name space collisions could not be
guaranteed. If this proposal is accepted, the StateToken URL
scheme will need to be defined and registered with IANA.
State Token URLs begin with the URL scheme name StateToken
rather than the name of the particular state token type they
represent in order to make the URL self describing. Thus it
is possible to examine the URL and know, at a minimum, that
it is a state token.
Labeled name/value pairs are used within the token to allow
new fields to be added. Processors of state tokens MUST be
prepared to accept the fields in whatever order they are
present and MUST ignore any fields they do not understand.
The Type field specifies the type of the state information
encoded in the state token. A URL is used in order to avoid
namespace collisions.
The Res field identifies the resource for which the state
token specifies a particular state. Since commas and spaces
are acceptable URL characters, a caret is used to delimit a
URL. Since a caret is an acceptable URL character, any
instances of it must be escaped using the % escape
convention.
The State-Info production is expanded upon in descriptions
of specific state token types, and is intended to contain
the state description information for a particular state
token.
4.3 State Token Conditional Headers
4.3.1 If-State-Match
If-State-Match = "If-State-Match" ":" (AND | OR) 1#(<
State-Token >)
The If-State-Match header is intended to have similar
functionality to the If-Match header defined in section
14.25 of RFC 2068.
If the AND keyword is used and all of the state tokens
identify the state of the resource, then the server MAY
perform the requested method. If the OR keyword is used and
any of the state tokens identifies the current state of the
resource, then server MAY perform the requested method. If
neither of the keyword requirements is met, the server MUST
NOT perform the requested method, and MUST return a 412
(Precondition Failed) response.
4.3.2 If-None-State-Match
If-None-State-Match = "If-None-State-Match" : 1#(<
State-Token >)
The If-None-State-Match header is intended to have similar
functionality to the If-None-Match header defined in section
14.26 of RFC 2068.
If any of the state tokens identifies the current state of
the resource, the server MUST NOT perform the requested
method. Instead, if the request method was GET, HEAD,
INDEX, or GETMETA, the server SHOULD respond with a 304 (Not
Modified) response, including the cache-related entity-
header fields (particularly ETag) of the current state of
the resource. For all other request methods, the server
MUST respond with a status of 412 (Precondition Failed).
If none of the state tokens identifies the current state of
the resource, the server MAY perform the requested method.
Note that the AND and OR keywords specified with the If-
State-Match header are intentionally not defined for If-
None-State-Match, because this functionality is not
required.
4.4 State Token Header
State-Token-Header = State-Token : 1#(< State-Token
>)
The State Token header is intended to have similar
functionality to the etag header defined in section 14.20 of
RFC 2068. The purpose of the tag is to return state tokens
defined on a resource in a response. The contents of the
state-token are not guaranteed to be exhaustive and are
generally used to return a new state token that has been
defined as the result of a method. For example, if a LOCK
method were successfully executed on a resource the response
would include a state token header with the lock state token
included.
4.5 E-Tags
E-tags have already been deployed using the If-Match and If-
None-Match headers. Introducing two mechanisms to express
e-tags would only confuse matters, therefore e-tags should
continue to be expressed using quoted strings and the If-
Match and If-None-Match headers.
5 Locking
5.1 Problem Description - Overview
Locking is used to arbitrate access to a resource amongst
principals that have equal access rights to that resource.
This draft allows locks to vary over two parameters, the
number of principals involved and the type of access to be
granted. This draft will only provide for the definition of
locking for one access type, write. However, the syntax is
extensible enough to allow for the specification of other
access types. It is a goal of this proposal that it use the
same access verbs as will be defined in the access control
draft.
5.1.1 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 constantly merge results. In
fact, many users so dislike having to merge that they would
rather serialize their access to a resource rather than have
to constantly perform merges.
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 right. 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 the resource, those who are not,
don't. Among those who have access permission to write the
resource, the set of principals who have taken out a shared
lock also must trust each other, creating a (probably)
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 in conjunction with a
precondition header (If-State-Match) that checks for
existence of the lock prior to writing the resource. Others
may decide they trust their collaborators (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 is potentially 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). The intent of a shared lock is to let
collaborators know who else is potentially working on a
resource..
Why not use exclusive write locks all the time? Experience
from initial Web distributed authoring systems has indicated
that exclusive write locks are often too rigid. An
exclusive write lock is used to enforce a particular editing
process: take out exclusive write lock, read the resource,
perform edits, write the resource, release the lock. What
happens if the lock isn't released? While the time-out
mechanism provides one solution, if you need to force the
release of a lock immediately, it doesn't help much.
Granted, an administrator can release the lock for you, but
this could become a significant burden for large sites.
Further, what if the administrator can't be reached
immediately?
Despite their potential problems, exclusive write locks are
extremely useful, since often a guarantee of freedom from
overwrite conflicts is exactly what is needed. The
solution: provide exclusive write locks, but also provide a
less strict mechanism in the form of shared locks which can
be used by a set of people who trust each other and who have
access to a communications channel external to HTTP which
can be used to negotiate writing to the resource.
5.1.2 Required Support
A DAV 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 server implementers
have said that they are willing to accept minimum
requirements on all services but locking. Locking policy
strikes to the very heart of their resource management and
versioning systems and they require control over what sort
of locking will be made available. For example, some systems
only support shared write locks while others only provide
support for exclusive write locks. As each system is
sufficiently different to merit exclusion of certain locking
features, the authors are proposing that locking be allowed
as the sole axis of negotiation within DAV.
5.2 LOCK Method
5.2.1 Operation
A lock method invocation creates the lock specified by the
Lock-Info header on the request-URI. Lock method requests
SHOULD NOT have a request body. A user-agent SHOULD submit
an Owner header field with a lock request.
A successful response to a lock invocation MUST include a
Lock-Token header. If the server supports a time based lock
removal mechanism on the resource, a successful lock
invocation SHOULD return a Time-Out header.
5.2.2 The Effect of Locks on Properties and Containers
By default a lock affects the entire state of the resource,
including its associated properties. As such it is illegal
to specify a lock on a property. For containers, a lock also
affects the ability to add or remove members. The nature of
the effect depends upon the type of access control involved.
The Depth header expresses the general semantics of a LOCK
method request when invoked on a collection (note that
specific lock types may restrict the effect of a lock, for
example limiting the allowable values of the Depth header):
A Depth header (defined in the namespace draft) may be used
on a LOCK method when the LOCK method is applied to a
collection resource. The legal values for Depth on a LOCK
are 0, 1, and Infinity. A Depth of 0 instructs the
resource to just lock the container. As previously
mentioned, depending on the type of lock, the lock affects
the ability to add or remove members of the container.
@.A Depth of 1 means that the container is locked and a LOCK
is executed on the containers propagate members with a
Depth of 0 and If-Range, If-Modified-Since, If-Unmodified-
Since, If-Match and If-None-Match headers are dropped.
However, the effects of the LOCK MUST be atomic in that
either the container and all of its members are locked or
no lock is granted. The result of a Depth 1 lock is a
single lock token which represents the lock on the
container and all of its members. This lock token may be
used in an If-State-Match or If-Not-State-Match header
against any of the resources covered by the lock. Since
the lock token represents a lock on all the resources, an
UNLOCK using that token will remove the lock from all
included resources, not just the resource the UNLOCK was
executed on.
@.A Depth of infinity means that the LOCK is recursively
executed, with a Depth of infinity, on the collection and
all of its propagate members and all of their propagate
members. As with a Depth of 1, the LOCK must be granted in
total or not at all. Otherwise the lock operates in the
same manner as a Depth of 1 lock.
The default behavior when locking a container is to act as
if a Depth: 0 header had been placed on the method.
5.2.3 Locking Replicated Resources
Some servers automatically replicate resources across
multiple URLs. In such a circumstance the server MAY only
accept a lock on one of the URLs if the server can guarantee
that the lock will be honored across all the URLs.
5.2.4 Interaction with other Methods
Only two methods, MOVE and DELETE, have side effects which
involve locks. When a resource is moved, its lock SHOULD be
moved with it. However this may not always be possible and
there is currently no proposal to create a header which
would specify that the lock request should fail if the
resources locks can not be maintained. A COPY MUST NOT copy
any locks on the source resource over to the destination
resource. Deleting a resource MUST remove all locks on the
resource.
5.2.5 Lock Compatibility Table
The table below describes the behavior that occurs when a
lock request is made on a resource.
Current lock state/ Shared Lock Exclusive Lock
Lock request
None True True
Shared Lock True False
Exclusive Lock False False*
Legend: True = lock MAY be granted. False = lock MUST NOT
be granted. *=if the principal requesting the lock is the
owner of the lock, the lock MAY be regranted.
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.
If an exclusive lock is re-requested by the principal who
owns the lock, the lock MAY be regranted. If the lock is
regranted, the same lock token that was previously issued
MUST be returned.
5.2.6 Status Codes
412 Precondition Failed The included state-token was not
enforceable on this resource.
416 Locked The resource is locked so the method has been
rejected.
5.2.7 Example
LOCK /workspace/webdav/proposal.doc HTTP/1.1
Host: webdav.sb.aol.com
Lock-Info: LockType=Write LockScope=Exclusive
Owner: <http://www.ics.uci.edu/~ejw/contact.html>
HTTP/1.1 200 OK
State-Token: StateToken:Type=^DAV:/LOCK/DAVLOCK^:Res=^http:/
/www.ics.uci.edu/workspace/webdav/proposal.doc^:LockType=Wri
te:LockScope=Exclusive:ServerID=12382349AdfFFF
Time-Out: ClockType=Activity TimeType=second;604800
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). The response has a Lock-Token
header that gives the state token URL for the lock token
generated by this lock request.
5.2.8 Lock-Info Request Header
The Lock-Info header specifies the scope and type of a lock
for a LOCK method request. The syntax specification below is
extensible, allowing new type and scope identifiers to be
added.
LockInfo = Lock-Info : DAVLockType SP DAVLockScope CRLF
DAVLockType = LockType = DAVLockTypeValue
DAVLockTypeValue = (Write | *(uchar | reserved))
DAVLockScope = LockScope = DAVLockScopeValue
DAVLockScopeValue = (Exclusive |Shared | *(uchar |
reserved))
5.2.9 Owner Request Header
5.2.9.1 Problem Description
When discovering the list of owners of locks on a resource,
a principal may want to be able to contact the owner
directly. For this to be possible the lock discovery
mechanism must provide enough information for the lock owner
to be contacted.
5.2.9.2 Solution Requirements
Not all systems have authentication procedures that provide
sufficient information to identify a particular user in a
way that is meaningful to a human. In addition, many systems
that do have sufficient information, such as a name and e-
mail address, do not have the ability to associate this
information with the lock discovery mechanism. Therefore a
means is needed to allow principals to provide
authentication in a manner which will be meaningful to a
human.
The From header (defined in RFC 2068), which contains only
an email mailbox, is not sufficient for the purposes of
quick identification. When desperately looking for someone
to remove a lock, e-mail is often not sufficient. A
telephone number (cell number, pager number, etc.) would be
better. Furthermore, the email address in the From field may
or may not support including the owners name and that name
is often set to an alias anyway. Therefore a header more
flexible than From is required.
5.2.9.3 Syntax
Owner = "Owner" ":" ((< URI >) | quoted-string)
The URI SHOULD provide a means for either directly
contacting the principal (such as a telephone number or e-
mail URI), or for discovering the principal (such as the
URL of a homepage). The quoted string SHOULD provide a
means for directly contacting the principal, such as a name
and telephone number.
5.2.10 Time-Out Header
5.2.10.1 Problem Description
In a perfect world principals take out locks, use the
resource as needed, and then remove the lock when it is no
longer needed. However, this scenario is frequently not
completed, leaving active but unused locks. Reasons for this
include client programs crashing and loosing information
about locks, users leaving their systems for the day and
forgetting to remove their locks, etc. As a result of this
behavior, servers need to establish a policy by which they
can remove a lock without input from the lock owner. Once
such a policy is instituted, the server also needs a
mechanism to inform the principal of the policy.
5.2.10.2 Solution Requirements
There are two basic lock removal policies, administrator and
time based remove. In the first case a principal other than
the lock owner has sufficient access rights to order the
lock removed, even though they did not take it out. User-
agents MUST assume that such a mechanism is available and
thus locks may arbitrarily disappear at any time. If their
actions require confirmation of the existence of a lock then
the If-State headers are available.
The second solution, is the time based removal policy.
Activity based systems set a timer as soon as the lock is
taken out. Every time a method is executed on the resource,
the timer is reset. If the timer runs out, the lock is
removed.
Finally, some systems only allow locks to exist for the
duration of a session, where a session is defined as the
time when the HTTP connection that was used to take out the
lock remains connected. This mechanism is used to allow
programs which are likely to be improperly exited, such as
JAVA programs running in a browser, to take out locks
without leaving a lot of ownerless locks around when they
are improperly exited.
5.2.10.3 Syntax
TimeOut = "Time-Out" ":" ((TimeOutType SP Session) |
TimeOutVal |
Session) CRLF
TimeOutType = ClockType SP TimeType
ClockType = ClockType = ClockTypeValue
ClockTypeValue = Activity
TimeType = TimeType = TimeTypeValue
TimeTypeValue = Second ; DAVTimeOutVal
DAVTimeOutVal = 1*digit
Session = Session = (Yes | No)
The Second TimeType specifies the number of seconds that
may elapse before the lock is automatically removed. A
server MUST not generate a time out value for second
greater than 2^32-1.
If no time based system is in use then a Time-Out header
MUST NOT be returned. The Time-Out header MUST only be
returned in a response to a LOCK request.When session is set
to yes then whatever clocktype and timetype is being used,
their effects are scoped within that particular session. So
an absolute lock with a ten day expiration period will only
remain active so long as the session remains active. A
DAVTimeOutVal value must be greater than zero.
Clients MAY include TimeOut headers in their LOCK requests.
However the server is not required to honor or even consider
the request. The primary purpose in allowing clients to
submit a TimeOut header is to inform the server if the
client is requesting a session based lock. If a timeout is
associated with the lock, the server MUST return a TimeOut
header with a valid value.
5.2.11 State-Token Header
5.2.11.1 Problem Definition
Program A, used by User A, takes out a write lock on a
resource. Program B, also run by User A, then proceeds to
perform a PUT to the locked resource. The PUT will succeed
because locks are associated with a principal, not a
program, and thus program B, because it is acting with
principal As credential, will be allowed to perform the
PUT. In reality program B had no knowledge of the lock and
had it had such knowledge, would not have overwritten the
resource. Hence, a mechanism is needed to prevent different
programs from accidentally ignoring locks taken out by other
programs with the same authorization.
5.2.11.2 Solution Requirement
The solution must not require principals to perform
discovery in order to prevent accidental overwrites as this
could cause race conditions.
The solution must not require that clients guess what sorts
of locks might be used and use if-state-match headers with
wildcards to prevent collisions. The problem with trying to
guess which locks are being used is that new lock types
might be introduced, and the program would not know to
guess them. So, for example, a client might put in an if-
state-match header with a wildcard specifying that if any
write lock is outstanding then the operation should fail.
However a new read/write lock could be introduced which the
client would not know to put in the header.
5.2.11.3 State-Token Header
The State-Token header is returned in a successful response
to the LOCK method or is used as a request header with the
UNLOCK method.
The State-Token header containing a lock token owned by the
request principal is used by the principal on arbitrary
method to indicate that the principal is aware of the
specified lock. If the State-Token header with the
appropriate lock token is not included the request MUST be
rejected, even though the requesting principal has
authorization to make modifications specified by the lock
type. This injunction does not apply to methods that are not
affected by the principals lock.
For example, Program A, used by user A, takes out a write
lock on a resource. Program A then makes a number of PUT
requests on the locked resource, all the requests contain a
State-Token header which includes the write lock state
token. Program B, also run by User A, then proceeds to
perform a PUT to the locked resource. However program B was
not aware of the existence of the lock and so does not
include the appropriate state-token header. The method is
rejected even though principal A is authorized to perform
the PUT. Program B can, if it so chooses, now perform lock
discovery and obtain the lock token. Note that program A and
B can perform GETs without using the state-token header
because the ability to perform a GET is not affected by a
write lock.
Note that having a lock state token provides no special
access rights. Anyone can find out anyone elses lock state
token by performing lock discovery. Locks are to be enforced
based upon whatever authentication mechanism is used by the
server, not based on the secrecy of the token values.
5.3 Write Lock
A write lock prevents a principal without the lock from
successfully executing a PUT, POST, DELETE, MKCOL,
PROPPATCH, PATCH, ADDREF or DELREF on the locked resource.
All other methods, GET in particular, function independent
of the lock.
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 to not
change while locked.
It is possible to assert a write lock on a null resource in
order to lock the name. Please note, however, that locking a
null resource effectively makes the resource non-null as the
resource now has lock related properties defined on it.
Write locking a container also prevents adding or removing
members of the container. This means that attempts to
PUT/POST a resource into the immediate name space of the
write locked container MUST fail if the principal requesting
the action does not have the write lock on the container. In
order to keep the behavior of locking containers consistent
all locks on containers MUST contain a Depth header equal to
infinity, any other value is illegal.
5.4 Lock Tokens
5.4.1 Problem Description
It is possible that once a lock has been granted it may be
removed without the lock owners knowledge. This can cause
serialization problems if the lock owner executes methods
thinking their lock is still in effect. Thus a mechanism is
needed for a principal to predicate the successful execution
of a message upon the continuing existence of a lock.
5.4.2 Proposed Solution
The proposed solution is to provide a lock token in the
response of a lock request. The lock token is a type of
state token and describes a particular lock. The same lock
token must never be repeated on a particular resource. This
prevents problems with long held outstanding lock tokens
being confused with newer tokens. This uniqueness
requirement is the same as for e-tags. This requirement also
allows for tokens to be submitted across resources and
servers without fear of confusion.
5.4.3 Lock Token Definition
The lock token is returned in the State-Token header in the
response to a LOCK method. The lock token can also be
discovered through lock discovery on a resource.
Lock-Token-URL = StateToken: Type : Resources : State-
Info
Type = Type = ^DAV:/LOCK/DAVLOCK^
Resources = Res = 1*(^ Caret-Encoded-URI ^)
Caret-Encoded-URI = <This is a URI which has all ^s %
encoded.>
State-Info = DAVLockScope : DAVLockType : ServerID ;
DAVLockScope, DAVLockType defined in Lock-Info header
ServerID = ServerID = *(uchar | reserved)
The ServerID is a field for use by the server. Its most
basic purpose is to put in a unique identifier to guarantee
that a server will never confuse an old lock token with a
newer one. However the server is free to use the field to
record whatever information it deems fit. The field is
opaque to clients.
5.5 UNLOCK Method
5.5.1 Problem Definition
The UNLOCK method removes the lock identified by the lock
token in the State-Token header from the Request-URI.
5.5.2 Example
UNLOCK /workspace/webdav/proposal.doc HTTP/1.1
Host: webdav.sb.aol.com
State-Token: StateToken:Type=^DAV:/LOCK/DAVLOCK^:Res=^http:/
/www.ics.uci.edu/workspace/webdav/proposal.doc^:LockType=Wri
te:LockScope=Exclusive:ServerID=12382349AdfFFF
HTTP/1.1 200 OK
In this example, the lock from example of Section 2.9 is
removed from the resource at
http://webdav.sb.aol.com/workspace/webdav/proposal.doc
5.6 Discovery Mechanisms
5.6.1 Lock Type Discovery
5.6.1.1 Problem Definition
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 can perform some form of discovery to
determine what lock types the server actually supports, then
formulate a supported request. This is known as lock type
discovery. Lock type discovery is not the same as
discovering what access control types are supported, as
there may be access control types without corresponding lock
types.
5.6.1.2 SupportedLock Property
Name: http://www.ietf.org/standards/dav/lock/supportedlock
Purpose: To provide a listing of the lock types supported by
the resource.
Schema: http://www.ietf.org/standards/dav/
Values: An XML document containing zero or more LockEntry
XML elements.
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. If
SupportedLock is available on * then it MUST define the
set of locks allowed on all resources on that server.
5.6.1.3 LOCKENTRY XML Element
Name: http://www.ietf.org/standards/dav/lockentry
Purpose: Defines a DAVLockType/LockScope pair which may be
legally used with a LOCK on the specified resource.
Schema: HYPERLINK http://www.ietf.org/standards/dav/
Parent: A SupportedLock entry
Values: LockType LockScope
5.6.1.4 LOCKTYPE XML Element
Name: http://www.ietf.org/standards/dav/locktype
Purpose: Lists a DAVLockType
Schema: http://www.ietf.org/standards/dav/
Parent: LOCKENTRY
Values: DAVLockTypeValue
5.6.1.5 LOCKSCOPE XML Element
Name: http://www.ietf.org/standards/dav/lockscope
Purpose: Lists a DAVLockScope
Schema: http://www.ietf.org/standards/dav/
Parent: LOCKENTRY
Values: DAVLockScopeValue
5.6.2 Active Lock Discovery
5.6.2.1 Problem Definition
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.
5.6.2.2 Solution Requirements
The lock discovery mechanism should provide a list of who
has the resource locked, what locks they have, and what
their lock tokens are. The lock tokens are useful in shared
lock situations where two principals in particular may want
to guarantee that they do not overwrite each other. The lock
tokens are also useful for administrative purposes so that
an administrator can remove a lock by referring to its
token.
5.6.2.3 LOCKDISCOVERY Property
Name: http://www.ietf.org/standards/dav/lockdiscovery
Purpose: To discover what locks are active on a resource
Schema: http://www.ietf.org/standards/dav/
Values= An XML document containing zero or more ActiveLock
XML elements.
Description: The LOCKDISCOVERY property returns a listing of
who has a lock, what type of lock they have, the time out
type and the time remaining on the time out, 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.
5.6.2.4 ACTIVELOCK XML Element
Name: http://www.ietf.org/standards/dav/activelock
Purpose: A multivalued XML element that describes a
particular active lock on a resource
Schema: http://www.ietf.org/standards/dav/
Parent: A LOCKDISCOVERY entry
Values= LOCKTYPE LOCKSCOPE OWNER TIMEOUT LOCKTOKEN
5.6.2.5 OWNER XML Element
Name: http://www.ietf.org/standards/dav/lock/owner
Purpose: Returns owner information
Schema: http://www.ietf.org/standards/dav/
Parent: ACTIVELOCK
Values= XML:REF | {any valid XML string}
5.6.2.6 TIMEOUT XML Element
Name: http://www.ietf.org/standards/dav/timeout
Purpose: Returns information about the timeout associated
with the lock
Schema: http://www.ietf.org/standards/dav/
Parent: ACTIVELOCK
Values= CLOCKTYPE TIMETYPE TIMEOUTVAL
5.6.2.7 CLOCKTYPE XML Element
Name: http://www.ietf.org/standards/dav/clocktype
Purpose: Returns the clock type used with this lock
Schema: http://www.ietf.org/standards/dav/
Parent: TIMEOUT
Values= ClockTypeValue
5.6.2.8 TIMETYPE XML Element
Name: http://www.ietf.org/standards/dav/clocktype
Purpose: Returns the time type used with this lock
Schema: http://www.ietf.org/standards/dav/
Parent: TIMEOUT
Values= TimeTypeValue
5.6.2.9 TIMEOUTVAL XML Element
Name: http://www.ietf.org/standards/dav/timeoutval
Purpose: Returns the amount of time left on the lock
Schema: http://www.ietf.org/standards/dav/
Parent: TIMEOUT
Values= DAVTimeOutVal
5.6.2.10 LOCKTOKEN XML Element
Name: http://www.ietf.org/standards/dav/statetoken
Purpose: Returns the lock token
Schema: http://www.ietf.org/standards/dav/
Parent: ACTIVELOCK
Values= XML:REF
Description: The REF contains a Lock-Token-URL.
6 Version Control
[TBD]
7 Internationalization Support
[TBD]
8 Security Considerations
[TBD]
9 Acknowledgements
Roy Fielding, Richard Taylor, Larry Masinter, Henry Sanders,
Judith Slein, Dan Connolly, David Durand, Henrik Nielsen,
Paul Leach. Kenji Ota, Kenji Takahashi. Jim Cunningham.
Others, TBD.
10 References
[Berners-Lee, 1997] T. Berners-Lee, "Metadata Architecture."
Unpublished white paper, January 1997.
http://www.w3.org/pub/WWW/DesignIssues/Metadata.html.
[Bray, 1997] T. Bray, C. M. Sperberg-McQueen, Extensible
Markup Language (XML): Part I. Syntax, WD-xml-lang.html,
http://www.w3.org/pub/WWW/TR/WD-xml-lang.html.
[Connolly, 1997] D. Connolly, R. Khare, H.F. Nielsen, PEP -
an Extension Mechanism for HTTP, Internet draft, work-in-
progress. draft-ietf-http-pep-03.txt,
ftp://ds.internic.net/internet-drafts/draft-ietf-http-pep-
03.txt.
[Lasher, Cohen, 1995] R. Lasher, D. Cohen, "A Format for
Bibliographic Records," RFC 1807. Stanford, Myricom. June,
1995.
[Maloney, 1996] M. Maloney, "Hypertext Links in HTML."
Internet draft (expired), work-in-progress, January, 1996.
[MARC, 1994] Network Development and MARC Standards, Office,
ed. 1994. "USMARC Format for Bibliographic Data", 1994.
Washington, DC: Cataloging Distribution Service, Library of
Congress.
[Miller et.al., 1996] J. Miller, T. Krauskopf, P. Resnick,
W. Treese, "PICS Label Distribution Label Syntax and
Communication Protocols" Version 1.1, W3C Recommendation
REC-PICS-labels-961031. http://www.w3.org/pub/WWW/TR/REC-
PICS-labels-961031.html.
[WebDAV, 1997] WEBDAV Design Team. A Proposal for Web
Metadata Operations. Unpublished manuscript.
http://www.ics.uci.edu/~ejw/authoring/proposals/metadata.htm
l
[Weibel et al., 1995] S. Weibel, J. Godby, E. Miller, R.
Daniel, "OCLC/NCSA Metadata Workshop Report."
http://purl.oclc.org/metadata/dublin_core_report.
[Yergeau, 1997] F. Yergeau, UTF-8, a transformation format
of Unicode and ISO 10646, Internet Draft, work-in-progress,
draft-yergeau-utf8-rev-00.txt,
http://www.internic.net/internet-drafts/draft-yergeau-utf8-
rev-00.txt.
11 Authors' Addresses
Yaron 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
Asad Faizi
Netscape
685 East Middlefield Road
Mountain View, CA 94043
Email: asad@netscape.com
Stephen R Carter
Novell
1555 N. Technology Way
M/S ORM F111
Orem, UT 84097-2399
Fax (801) 228 5176
Email srcarter@novell.com
Del Jensen
Novell
1555 N. Technology Way
M/S ORM F111
Orem, UT 84097-2399
Fax (801) 228 5176
Email dcjensen@novell.com
Appendix 1 - Content Type Application/XML
This is a digest of the XML data specification available at
http://www.w3.org/TR/WD-xml-lang.html
Syntax
The application/XML content type contains an XML document.
Its syntax is as defined below.
XML = XMLStart *XMLEntity Close
XMLStart = < XML >
XMLEntity= Open *(XMLText | XMLEntity) Close
Close = </> | </Entity-Name Markup>
Open = < Entity-Name *Attribute >
Attribute = Entity-Name = Quoted-String
XMLText = <An Octet Stream which uses XML encoding for <
and >>
Entity-Name = ([As-Tag :] Name) | (As-Tag :)
As-Tag = 1*Alpha
Name = (alpha | _) *(alpha | digit | . | - | _ |
other)
Other = <Other characters must be encoded>
XML element
An XML element, as defined in the BNF, is an open tag with
content followed by a close tag. In order to prevent
confusion with the term entity as used in HTTP, the term XML
element will be used.
The first XML element of a XML document MUST be the <XML>
XML element. This XML element tells the parser that it is
dealing with an XML document. So long as this XML element is
present the parser can be sure that it can parse the
document, even if XML has been extended. If XML is ever
altered in a manner that is not backwards compatible with
this specification then the content-type and the outer most
XML element MUST be changed.
Entity-Name
All XML element names must map to URIs. However due to
historical restrictions on what characters may appear in an
XML element name, URIs cannot be expressed in an XML element
name. This issue is dealt with in more detail in section 10.
Entity-Names without [AS] are relative URIs whose base is
the enclosing Entity-Name. If the enclosing Entity-Name is
<XML> then the Entity-Name MUST use an [AS].
Close
The close production marks the end of a XML element.
XML Encoding
In different contexts certain characters are reserved, for
example / can not be used in an XML element name and
>/< can not be used in a value. As such these values
must be encoded as follows:
Encoding = Decimal | Hex4
Decimal = & Non-Zero *(0 | Non-Zero)
Hex4 = &u- 4(Hex)
Non-Zero = 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
9
Hex = 0 | Non-Zero | A | B | C | D | E | F
The numbers MUST map to the UTF8 character encodings. Please
note that the & character must always be encoded.
Markup Modifier
The markup modifier, (-, after the end of an XML element)
instructs the principal how to treat a XML element with an
unknown name. If the modifier is used and the XML element is
not recognized then the XML element name MUST be stripped
and the XML elements contents promoted one level in the
parse tree. If the modifier is not used and the XML element
name is unknown then the XML element and its contents MUST
be ignored.
XML Syntax Shorthand
The following template is recommended for efficiently
providing a description of an XML element.
Name: The name of the XML element
Purpose: A one line description of the XML elements
purpose.
Schema: The schema, if any, that the XML element belongs to
Parent: XML elements that this XML element may be a child
of.
Values: A description, usually a BNF, of the simple and
compound values that the XML element supports.
Description: Further information.
Example: An example of the XML elements use.
Appendix 2 - Parameter Syntax for Content-Type
Application/XML
HTTP 1.1 provides for a mechanism to include a parameter
with a content type. In order to prevent namespace
collisions the parameters for application/XML must use the
following syntax:
Parameter = #(<>URI<> [= (token | Quoted-String)])
Schema Content-Type Parameter
Parameter = <> http://www.w3.org/standards/xml/content-
type/schema <> = <> #URI <>
The http://www.w3.org/standards/xml/content-type/schema/ URL
is used as a parameter to an application/xml content type.
The URL indicates that its value lists some subset of the
schemas defined in NameSpace parameters within the enclosed
document. The URI can also be used in requests to indicate
schemas that should appear in the result.
An example of the use of this parameter is to include it in
an accept-type header on a request to indicate that the
response should contain the specified namespace. Thus the
client is able to inform the server of its support for a
particular set of namespaces. The server is not required to
return a result with the specified namespaces.
Appendix 3 URI Path Encoding
Problem Definition
A mechanism is needed to refer to specific DAV properties in
a manner that can handle simple, composite, and multivalued
DAV properties.
Solution Requirement
The reference mechanism must use the standard URL syntax so
it can be used with both currently existing and future URLs.
For example, the syntax could be appended to an HTTP URL to
specify a HTTP property on that URL.
Path Component
URIPath = / [segment]
Segment = (( Abs-URI ) | Rel-URI)[Index]*( ; param)
Index = [( [-]*digit )]
Abs-URI = < An absolute or relative URI which has been URI-
Path encoded >
Rel-URI = < A relative URI for which URI-Encoding(Rel-URI)
== Rel-URI >
URI-Path encoding consists of the following algorithm:
URL encode all ! characters
Map all / characters to ! characters
Please note that all relative URIs are relative to the URI
in the path segment preceding them. Hence the URI in the
first path segment MUST be an absolute URI.
The purpose of the encoding is to allow URLs to be used as
segments without having to use % encoding on all the /
which produces a URL form which is extremely difficult for
humans to deal with, and which changes the semantics of the
URL.
Appendix 4 - XML URI
The XML scheme is to be registered with IANA as a reserved
namespace that will be owned by the XML group through the
W3C.
The new URI is defined as:
XML = XML : XML-Path
Appendix 5 - XML elements
Ref XML element
Name: XML:Ref
Purpose: A XML element that indicates that its contents are
a URI.
Schema: XML
Parent: Any
Value = URI
Namespace
Namespace XML element
Name: XML:Namespace
Purpose: To inform the parser that a particular schema is in
use and to provide a shorthand name for referring to XML
elements related to that schema.
Schema: XML
Parent: Any
Value = (Ref [AS])
Description: This XML element contains two XML elements, Ref
and AS. The purpose of the XML element is to inform the
parser that a schema, identified by the value of the Ref XML
element, is in use and, when appropriate, to provide a
shorthand name to refer XML elements derived from that
schema using the AS XML element. The AS mechanism is needed
for efficiency reasons and because a URI can not be fully
specified in an XML open tag. The Namespace XML elements
scope is all siblings and their children.
AS XML element
Name: XML:AS
Purpose: To provide a short name for the URI of the schema
provided in the Ref XML entity of a namespace XML entity.
Schema: XML
Parent: XML:Namespace
Value = 1*Alpha
Description: The AS XML entity is used to provide a
shorthand reference for the URI in the Ref XML entity of a
Namespace XML entity. The value contained in the AS XML
entity is generated at the XML producers discretion, the
only requirement is that all AS values MUST be unique within
the contents of the parent of the namespace element.
All XML entity open tags contain a name of the form As-
Tag:Name. The As-Tag is the value defined in an AS XML
entity inside of a Namespace. To resolve the As-Tag:Name
into a properly formatted URI replace As-Tag: with the URI
provided in the Ref that the AS was defined with. Also note
that AS value also applies to any URIs defined in a Ref
inside of Namespace.
For example,
<XML>
<XML:Namespace><Ref>http://blah;DAV/</><AS>B</></>
<XML:Namespace><Ref>B:(B:)/</><AS>C</></>
<C:Moo></>
</>
So B:(B:) translates to http://blah;DAV/(http:!!blah;DAV!)/
and C:Moo translates to
http://blah;DAV/(http:!!blah;DAV!)/Moo.
Required XML element
Name: XML:Required
Purpose: To indicate that the read MUST understand the
associated Namespace in order to successfully process the
XML document.
Schema: XML
Parent: XML:Namespace
Value: None
The XML URI and Namespace
In order to prevent a logical loop the XML namespace is said
to be declared, with the AS value of XML as a consequence
of the <XML> enclosing property.
Datatracker
Report a datatracker bug
draft-ietf-webdav-protocol-01
Internet-Draft
| Document | Document type |
This is an older version of an Internet-Draft that was ultimately published as RFC 2518.
Expired & archived
|
|
|---|---|---|---|
| Select version | |||
| Compare versions | |||
| Author | |||
| RFC stream |
|
||
| Other formats | |||
| Additional resources | Mailing list discussion |