arno/etesync-android
1
0
Fork 0
mirror of https://github.com/etesync/android synced 2024-11-15 12:28:57 +00:00
Code Issues Releases Wiki Activity
d712238700
etesync-android/doc/rfc4918-webdav.txt
rfc2822 a12942c606 Support for read-only calendars (closes #126) 
* relevant RFCs go into the doc/ directory for reference purposes
* read-only calendar collections are set as read-only in Android
* HTTP exception refactoring to mark 4xx HTTP errors as hard sync errors (numAuthExcetions/numParseExceptions) for Android sync manager
* query current-user-privilege-set for resources, detect read-only resources
* show read-only resources as read-only in SelectCollectionsFragment
* minor refactoring (DavProp.*)
2014-03-09 15:12:59 +01:00

7116 lines
270 KiB
Plaintext
Raw Blame History

This file contains invisible Unicode characters

This file contains invisible Unicode characters that are indistinguishable to humans but may be processed differently by a computer. If you think that this is intentional, you can safely ignore this warning. Use the Escape button to reveal them.

Network Working Group L. Dusseault, Ed.
Request for Comments: 4918 CommerceNet
Obsoletes: 2518 June 2007
Category: Standards Track
HTTP Extensions for Web Distributed Authoring and Versioning (WebDAV)
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
Web Distributed Authoring and Versioning (WebDAV) consists of a set
of methods, headers, and content-types ancillary to HTTP/1.1 for the
management of resource properties, creation and management of
resource collections, URL namespace manipulation, and resource
locking (collision avoidance).
RFC 2518 was published in February 1999, and this specification
obsoletes RFC 2518 with minor revisions mostly due to
interoperability experience.
Dusseault Standards Track [Page 1]
RFC 4918 WebDAV June 2007
Table of Contents
1. Introduction ....................................................7
2. Notational Conventions ..........................................8
3. Terminology .....................................................8
4. Data Model for Resource Properties .............................10
4.1. The Resource Property Model ...............................10
4.2. Properties and HTTP Headers ...............................10
4.3. Property Values ...........................................10
4.3.1. Example - Property with Mixed Content ..............12
4.4. Property Names ............................................14
4.5. Source Resources and Output Resources .....................14
5. Collections of Web Resources ...................................14
5.1. HTTP URL Namespace Model ..................................15
5.2. Collection Resources ......................................15
6. Locking ........................................................17
6.1. Lock Model ................................................18
6.2. Exclusive vs. Shared Locks ................................19
6.3. Required Support ..........................................20
6.4. Lock Creator and Privileges ...............................20
6.5. Lock Tokens ...............................................21
6.6. Lock Timeout ..............................................21
6.7. Lock Capability Discovery .................................22
6.8. Active Lock Discovery .....................................22
7. Write Lock .....................................................23
7.1. Write Locks and Properties ................................24
7.2. Avoiding Lost Updates .....................................24
7.3. Write Locks and Unmapped URLs .............................25
7.4. Write Locks and Collections ...............................26
7.5. Write Locks and the If Request Header .....................28
7.5.1. Example - Write Lock and COPY ......................28
7.5.2. Example - Deleting a Member of a Locked
Collection .........................................29
7.6. Write Locks and COPY/MOVE .................................30
7.7. Refreshing Write Locks ....................................30
8. General Request and Response Handling ..........................31
8.1. Precedence in Error Handling ..............................31
8.2. Use of XML ................................................31
8.3. URL Handling ..............................................32
8.3.1. Example - Correct URL Handling .....................32
8.4. Required Bodies in Requests ...............................33
8.5. HTTP Headers for Use in WebDAV ............................33
8.6. ETag ......................................................33
8.7. Including Error Response Bodies ...........................34
8.8. Impact of Namespace Operations on Cache Validators ........34
9. HTTP Methods for Distributed Authoring .........................35
9.1. PROPFIND Method ...........................................35
9.1.1. PROPFIND Status Codes ..............................37
Dusseault Standards Track [Page 2]
RFC 4918 WebDAV June 2007
9.1.2. Status Codes for Use in 'propstat' Element .........37
9.1.3. Example - Retrieving Named Properties ..............38
9.1.4. Example - Using 'propname' to Retrieve All
Property Names .....................................39
9.1.5. Example - Using So-called 'allprop' ................41
9.1.6. Example - Using 'allprop' with 'include' ...........43
9.2. PROPPATCH Method ..........................................44
9.2.1. Status Codes for Use in 'propstat' Element .........44
9.2.2. Example - PROPPATCH ................................45
9.3. MKCOL Method ..............................................46
9.3.1. MKCOL Status Codes .................................47
9.3.2. Example - MKCOL ....................................47
9.4. GET, HEAD for Collections .................................48
9.5. POST for Collections ......................................48
9.6. DELETE Requirements .......................................48
9.6.1. DELETE for Collections .............................49
9.6.2. Example - DELETE ...................................49
9.7. PUT Requirements ..........................................50
9.7.1. PUT for Non-Collection Resources ...................50
9.7.2. PUT for Collections ................................51
9.8. COPY Method ...............................................51
9.8.1. COPY for Non-collection Resources ..................51
9.8.2. COPY for Properties ................................52
9.8.3. COPY for Collections ...............................52
9.8.4. COPY and Overwriting Destination Resources .........53
9.8.5. Status Codes .......................................54
9.8.6. Example - COPY with Overwrite ......................55
9.8.7. Example - COPY with No Overwrite ...................55
9.8.8. Example - COPY of a Collection .....................56
9.9. MOVE Method ...............................................56
9.9.1. MOVE for Properties ................................57
9.9.2. MOVE for Collections ...............................57
9.9.3. MOVE and the Overwrite Header ......................58
9.9.4. Status Codes .......................................59
9.9.5. Example - MOVE of a Non-Collection .................60
9.9.6. Example - MOVE of a Collection .....................60
9.10. LOCK Method ..............................................61
9.10.1. Creating a Lock on an Existing Resource ...........61
9.10.2. Refreshing Locks ..................................62
9.10.3. Depth and Locking .................................62
9.10.4. Locking Unmapped URLs .............................63
9.10.5. Lock Compatibility Table ..........................63
9.10.6. LOCK Responses ....................................63
9.10.7. Example - Simple Lock Request .....................64
9.10.8. Example - Refreshing a Write Lock .................65
9.10.9. Example - Multi-Resource Lock Request .............66
9.11. UNLOCK Method ............................................68
9.11.1. Status Codes ......................................68
Dusseault Standards Track [Page 3]
RFC 4918 WebDAV June 2007
9.11.2. Example - UNLOCK ..................................69
10. HTTP Headers for Distributed Authoring ........................69
10.1. DAV Header ...............................................69
10.2. Depth Header .............................................70
10.3. Destination Header .......................................71
10.4. If Header ................................................72
10.4.1. Purpose ...........................................72
10.4.2. Syntax ............................................72
10.4.3. List Evaluation ...................................73
10.4.4. Matching State Tokens and ETags ...................74
10.4.5. If Header and Non-DAV-Aware Proxies ...............74
10.4.6. Example - No-tag Production .......................75
10.4.7. Example - Using "Not" with No-tag Production ......75
10.4.8. Example - Causing a Condition to Always
Evaluate to True ..................................75
10.4.9. Example - Tagged List If Header in COPY ...........76
10.4.10. Example - Matching Lock Tokens with
Collection Locks .................................76
10.4.11. Example - Matching ETags on Unmapped URLs ........76
10.5. Lock-Token Header ........................................77
10.6. Overwrite Header .........................................77
10.7. Timeout Request Header ...................................78
11. Status Code Extensions to HTTP/1.1 ............................78
11.1. 207 Multi-Status .........................................78
11.2. 422 Unprocessable Entity .................................78
11.3. 423 Locked ...............................................78
11.4. 424 Failed Dependency ....................................79
11.5. 507 Insufficient Storage .................................79
12. Use of HTTP Status Codes ......................................79
12.1. 412 Precondition Failed ..................................79
12.2. 414 Request-URI Too Long .................................79
13. Multi-Status Response .........................................80
13.1. Response Headers .........................................80
13.2. Handling Redirected Child Resources ......................81
13.3. Internal Status Codes ....................................81
14. XML Element Definitions .......................................81
14.1. activelock XML Element ...................................81
14.2. allprop XML Element ......................................82
14.3. collection XML Element ...................................82
14.4. depth XML Element ........................................82
14.5. error XML Element ........................................82
14.6. exclusive XML Element ....................................83
14.7. href XML Element .........................................83
14.8. include XML Element ......................................83
14.9. location XML Element .....................................83
14.10. lockentry XML Element ...................................84
14.11. lockinfo XML Element ....................................84
14.12. lockroot XML Element ....................................84
Dusseault Standards Track [Page 4]
RFC 4918 WebDAV June 2007
14.13. lockscope XML Element ...................................84
14.14. locktoken XML Element ...................................85
14.15. locktype XML Element ....................................85
14.16. multistatus XML Element .................................85
14.17. owner XML Element .......................................85
14.18. prop XML Element ........................................86
14.19. propertyupdate XML Element ..............................86
14.20. propfind XML Element ....................................86
14.21. propname XML Element ....................................87
14.22. propstat XML Element ....................................87
14.23. remove XML Element ......................................87
14.24. response XML Element ....................................88
14.25. responsedescription XML Element .........................88
14.26. set XML Element .........................................88
14.27. shared XML Element ......................................89
14.28. status XML Element ......................................89
14.29. timeout XML Element .....................................89
14.30. write XML Element .......................................89
15. DAV Properties ................................................90
16. Precondition/Postcondition XML Elements .......................98
17. XML Extensibility in DAV .....................................101
18. DAV Compliance Classes .......................................103
18.1. Class 1 .................................................103
18.2. Class 2 .................................................103
18.3. Class 3 .................................................103
19. Internationalization Considerations ..........................104
20. Security Considerations ......................................105
20.1. Authentication of Clients ...............................105
20.2. Denial of Service .......................................106
20.3. Security through Obscurity ..............................106
20.4. Privacy Issues Connected to Locks .......................106
20.5. Privacy Issues Connected to Properties ..................107
20.6. Implications of XML Entities ............................107
20.7. Risks Connected with Lock Tokens ........................108
20.8. Hosting Malicious Content ...............................108
21. IANA Considerations ..........................................109
21.1. New URI Schemes .........................................109
21.2. XML Namespaces ..........................................109
21.3. Message Header Fields ...................................109
21.3.1. DAV ..............................................109
21.3.2. Depth ............................................110
21.3.3. Destination ......................................110
21.3.4. If ...............................................110
21.3.5. Lock-Token .......................................110
21.3.6. Overwrite ........................................111
21.3.7. Timeout ..........................................111
21.4. HTTP Status Codes .......................................111
22. Acknowledgements .............................................112
Dusseault Standards Track [Page 5]
RFC 4918 WebDAV June 2007
23. Contributors to This Specification ...........................113
24. Authors of RFC 2518 ..........................................113
25. References ...................................................114
25.1. Normative References.....................................114
25.2. Informative References ..................................115
Appendix A. Notes on Processing XML Elements ....................117
A.1. Notes on Empty XML Elements ..............................117
A.2. Notes on Illegal XML Processing ..........................117
A.3. Example - XML Syntax Error ...............................117
A.4. Example - Unexpected XML Element .........................118
Appendix B. Notes on HTTP Client Compatibility ...................119
Appendix C. The 'opaquelocktoken' Scheme and URIs ................120
Appendix D. Lock-null Resources ..................................120
D.1. Guidance for Clients Using LOCK to Create Resources ......121
Appendix E. Guidance for Clients Desiring to Authenticate ........121
Appendix F. Summary of Changes from RFC 2518 .....................123
F.1. Changes for Both Client and Server Implementations .......123
F.2. Changes for Server Implementations .......................125
F.3. Other Changes ............................................126
Dusseault Standards Track [Page 6]
RFC 4918 WebDAV June 2007
1. Introduction
This document describes an extension to the HTTP/1.1 protocol that
allows clients to perform remote Web content authoring operations.
This extension provides a coherent set of methods, headers, request
entity body formats, and response entity body formats that provide
operations for:
Properties: The ability to create, remove, and query information
about Web pages, such as their authors, creation dates, etc.
Collections: The ability to create sets of documents and to retrieve
a hierarchical membership listing (like a directory listing in a file
system).
Locking: The ability to keep more than one person from working on a
document at the same time. This prevents the "lost update problem",
in which modifications are lost as first one author, then another,
writes changes without merging the other author's changes.
Namespace Operations: The ability to instruct the server to copy and
move Web resources, operations that change the mapping from URLs to
resources.
Requirements and rationale for these operations are described in a
companion document, "Requirements for a Distributed Authoring and
Versioning Protocol for the World Wide Web" [RFC2291].
This document does not specify the versioning operations suggested by
[RFC2291]. That work was done in a separate document, "Versioning
Extensions to WebDAV" [RFC3253].
The sections below provide a detailed introduction to various WebDAV
abstractions: resource properties (Section 4), collections of
resources (Section 5), locks (Section 6) in general, and write locks
(Section 7) specifically.
These abstractions are manipulated by the WebDAV-specific HTTP
methods (Section 9) and the extra HTTP headers (Section 10) used with
WebDAV methods. General considerations for handling HTTP requests
and responses in WebDAV are found in Section 8.
While the status codes provided by HTTP/1.1 are sufficient to
describe most error conditions encountered by WebDAV methods, there
are some errors that do not fall neatly into the existing categories.
This specification defines extra status codes developed for WebDAV
methods (Section 11) and describes existing HTTP status codes
(Section 12) as used in WebDAV. Since some WebDAV methods may
Dusseault Standards Track [Page 7]
RFC 4918 WebDAV June 2007
operate over many resources, the Multi-Status response (Section 13)
has been introduced to return status information for multiple
resources. Finally, this version of WebDAV introduces precondition
and postcondition (Section 16) XML elements in error response bodies.
WebDAV uses XML ([REC-XML]) for property names and some values, and
also uses XML to marshal complicated requests and responses. This
specification contains DTD and text definitions of all properties
(Section 15) and all other XML elements (Section 14) used in
marshalling. WebDAV includes a few special rules on extending WebDAV
XML marshalling in backwards-compatible ways (Section 17).
Finishing off the specification are sections on what it means for a
resource to be compliant with this specification (Section 18), on
internationalization support (Section 19), and on security
(Section 20).
2. Notational Conventions
Since this document describes a set of extensions to the HTTP/1.1
protocol, the augmented BNF used herein to describe protocol elements
is exactly the same as described in Section 2.1 of [RFC2616],
including the rules about implied linear whitespace. Since this
augmented BNF uses the basic production rules provided in Section 2.2
of [RFC2616], these rules apply to this document as well. Note this
is not the standard BNF syntax used in other RFCs.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
Note that in natural language, a property like the "creationdate"
property in the "DAV:" XML namespace is sometimes referred to as
"DAV:creationdate" for brevity.
3. Terminology
URI/URL - A Uniform Resource Identifier and Uniform Resource Locator,
respectively. These terms (and the distinction between them) are
defined in [RFC3986].
URI/URL Mapping - A relation between an absolute URI and a resource.
Since a resource can represent items that are not network
retrievable, as well as those that are, it is possible for a resource
to have zero, one, or many URI mappings. Mapping a resource to an
"http" scheme URI makes it possible to submit HTTP protocol requests
to the resource using the URI.
Dusseault Standards Track [Page 8]
RFC 4918 WebDAV June 2007
Path Segment - Informally, the characters found between slashes ("/")
in a URI. Formally, as defined in Section 3.3 of [RFC3986].
Collection - Informally, a resource that also acts as a container of
references to child resources. Formally, a resource that contains a
set of mappings between path segments and resources and meets the
requirements defined in Section 5.
Internal Member (of a Collection) - Informally, a child resource of a
collection. Formally, a resource referenced by a path segment
mapping contained in the collection.
Internal Member URL (of a Collection) - A URL of an internal member,
consisting of the URL of the collection (including trailing slash)
plus the path segment identifying the internal member.
Member (of a Collection) - Informally, a "descendant" of a
collection. Formally, an internal member of the collection, or,
recursively, a member of an internal member.
Member URL (of a Collection) - A URL that is either an internal
member URL of the collection itself, or is an internal member URL of
a member of that collection.
Property - A name/value pair that contains descriptive information
about a resource.
Live Property - A property whose semantics and syntax are enforced by
the server. For example, the live property DAV:getcontentlength has
its value, the length of the entity returned by a GET request,
automatically calculated by the server.
Dead Property - A property whose semantics and syntax are not
enforced by the server. The server only records the value of a dead
property; the client is responsible for maintaining the consistency
of the syntax and semantics of a dead property.
Principal - A distinct human or computational actor that initiates
access to network resources.
State Token - A URI that represents a state of a resource. Lock
tokens are the only state tokens defined in this specification.
Dusseault Standards Track [Page 9]
RFC 4918 WebDAV June 2007
4. Data Model for Resource Properties
4.1. The Resource Property Model
Properties are pieces of data that describe the state of a resource.
Properties are data about data.
Properties are used in distributed authoring environments to provide
for efficient discovery and management of resources. For example, a
'subject' property might allow for the indexing of all resources by
their subject, and an 'author' property might allow for the discovery
of what authors have written which documents.
The DAV property model consists of name/value pairs. The name of a
property identifies the property's syntax and semantics, and provides
an address by which to refer to its syntax and semantics.
There are two categories of properties: "live" and "dead". A live
property has its syntax and semantics enforced by the server. Live
properties include cases where a) the value of a property is
protected and maintained by the server, and b) the value of the
property is maintained by the client, but the server performs syntax
checking on submitted values. All instances of a given live property
MUST comply with the definition associated with that property name.
A dead property has its syntax and semantics enforced by the client;
the server merely records the value of the property verbatim.
4.2. Properties and HTTP Headers
Properties already exist, in a limited sense, in HTTP message
headers. However, in distributed authoring environments, a
relatively large number of properties are needed to describe the
state of a resource, and setting/returning them all through HTTP
headers is inefficient. Thus, a mechanism is needed that allows a
principal to identify a set of properties in which the principal is
interested and to set or retrieve just those properties.
4.3. Property Values
The value of a property is always a (well-formed) XML fragment.
XML has been chosen because it is a flexible, self-describing,
structured data format that supports rich schema definitions, and
because of its support for multiple character sets. XML's self-
describing nature allows any property's value to be extended by
adding elements. Clients will not break when they encounter
extensions because they will still have the data specified in the
original schema and MUST ignore elements they do not understand.
Dusseault Standards Track [Page 10]
RFC 4918 WebDAV June 2007
XML's support for multiple character sets allows any human-readable
property to be encoded and read in a character set familiar to the
user. XML's support for multiple human languages, using the "xml:
lang" attribute, handles cases where the same character set is
employed by multiple human languages. Note that xml:lang scope is
recursive, so an xml:lang attribute on any element containing a
property name element applies to the property value unless it has
been overridden by a more locally scoped attribute. Note that a
property only has one value, in one language (or language MAY be left
undefined); a property does not have multiple values in different
languages or a single value in multiple languages.
A property is always represented with an XML element consisting of
the property name, called the "property name element". The simplest
example is an empty property, which is different from a property that
does not exist:
<R:title xmlns:R="http://www.example.com/ns/"></R:title>
The value of the property appears inside the property name element.
The value may be any kind of well-formed XML content, including both
text-only and mixed content. Servers MUST preserve the following XML
Information Items (using the terminology from [REC-XML-INFOSET]) in
storage and transmission of dead properties:
For the property name Element Information Item itself:
[namespace name]
[local name]
[attributes] named "xml:lang" or any such attribute in scope
[children] of type element or character
On all Element Information Items in the property value:
[namespace name]
[local name]
[attributes]
[children] of type element or character
Dusseault Standards Track [Page 11]
RFC 4918 WebDAV June 2007
On Attribute Information Items in the property value:
[namespace name]
[local name]
[normalized value]
On Character Information Items in the property value:
[character code]
Since prefixes are used in some XML vocabularies (XPath and XML
Schema, for example), servers SHOULD preserve, for any Information
Item in the value:
[prefix]
XML Infoset attributes not listed above MAY be preserved by the
server, but clients MUST NOT rely on them being preserved. The above
rules would also apply by default to live properties, unless defined
otherwise.
Servers MUST ignore the XML attribute xml:space if present and never
use it to change whitespace handling. Whitespace in property values
is significant.
4.3.1. Example - Property with Mixed Content
Consider a dead property 'author' created by the client as follows:
<D:prop xml:lang="en" xmlns:D="DAV:">
<x:author xmlns:x='http://example.com/ns'>
<x:name>Jane Doe</x:name>
<!-- Jane's contact info -->
<x:uri type='email'
added='2005-11-26'>mailto:jane.doe@example.com</x:uri>
<x:uri type='web'
added='2005-11-27'>http://www.example.com</x:uri>
<x:notes xmlns:h='http://www.w3.org/1999/xhtml'>
Jane has been working way <h:em>too</h:em> long on the
long-awaited revision of <![CDATA[<RFC2518>]]>.
</x:notes>
</x:author>
</D:prop>
Dusseault Standards Track [Page 12]
RFC 4918 WebDAV June 2007
When this property is requested, a server might return:
<D:prop xmlns:D='DAV:'><author
xml:lang='en'
xmlns:x='http://example.com/ns'
xmlns='http://example.com/ns'
xmlns:h='http://www.w3.org/1999/xhtml'>
<x:name>Jane Doe</x:name>
<x:uri added="2005-11-26" type="email"
>mailto:jane.doe@example.com</x:uri>
<x:uri added="2005-11-27" type="web"
>http://www.example.com</x:uri>
<x:notes>
Jane has been working way <h:em>too</h:em> long on the
long-awaited revision of &lt;RFC2518&gt;.
</x:notes>
</author>
</D:prop>
Note in this example:
o The [prefix] for the property name itself was not preserved, being
non-significant, whereas all other [prefix] values have been
preserved,
o attribute values have been rewritten with double quotes instead of
single quotes (quoting style is not significant), and attribute
order has not been preserved,
o the xml:lang attribute has been returned on the property name
element itself (it was in scope when the property was set, but the
exact position in the response is not considered significant as
long as it is in scope),
o whitespace between tags has been preserved everywhere (whitespace
between attributes not so),
o CDATA encapsulation was replaced with character escaping (the
reverse would also be legal),
o the comment item was stripped (as would have been a processing
instruction item).
Implementation note: there are cases such as editing scenarios where
clients may require that XML content is preserved character by
character (such as attribute ordering or quoting style). In this
case, clients should consider using a text-only property value by
escaping all characters that have a special meaning in XML parsing.
Dusseault Standards Track [Page 13]
RFC 4918 WebDAV June 2007
4.4. Property Names
A property name is a universally unique identifier that is associated
with a schema that provides information about the syntax and
semantics of the property.
Because a property's name is universally unique, clients can depend
upon consistent behavior for a particular property across multiple
resources, on the same and across different servers, so long as that
property is "live" on the resources in question, and the
implementation of the live property is faithful to its definition.
The XML namespace mechanism, which is based on URIs ([RFC3986]), is
used to name properties because it prevents namespace collisions and
provides for varying degrees of administrative control.
The property namespace is flat; that is, no hierarchy of properties
is explicitly recognized. Thus, if a property A and a property A/B
exist on a resource, there is no recognition of any relationship
between the two properties. It is expected that a separate
specification will eventually be produced that will address issues
relating to hierarchical properties.
Finally, it is not possible to define the same property twice on a
single resource, as this would cause a collision in the resource's
property namespace.
4.5. Source Resources and Output Resources
Some HTTP resources are dynamically generated by the server. For
these resources, there presumably exists source code somewhere
governing how that resource is generated. The relationship of source
files to output HTTP resources may be one to one, one to many, many
to one, or many to many. There is no mechanism in HTTP to determine
whether a resource is even dynamic, let alone where its source files
exist or how to author them. Although this problem would usefully be
solved, interoperable WebDAV implementations have been widely
deployed without actually solving this problem, by dealing only with
static resources. Thus, the source vs. output problem is not solved
in this specification and has been deferred to a separate document.
5. Collections of Web Resources
This section provides a description of a type of Web resource, the
collection, and discusses its interactions with the HTTP URL
namespace and with HTTP methods. The purpose of a collection
resource is to model collection-like objects (e.g., file system
directories) within a server's namespace.
Dusseault Standards Track [Page 14]
RFC 4918 WebDAV June 2007
All DAV-compliant resources MUST support the HTTP URL namespace model
specified herein.
5.1. HTTP URL Namespace Model
The HTTP URL namespace is a hierarchical namespace where the
hierarchy is delimited with the "/" character.
An HTTP URL namespace is said to be consistent if it meets the
following conditions: for every URL in the HTTP hierarchy there
exists a collection that contains that URL as an internal member URL.
The root, or top-level collection of the namespace under
consideration, is exempt from the previous rule. The top-level
collection of the namespace under consideration is not necessarily
the collection identified by the absolute path '/' -- it may be
identified by one or more path segments (e.g., /servlets/webdav/...)
Neither HTTP/1.1 nor WebDAV requires that the entire HTTP URL
namespace be consistent -- a WebDAV-compatible resource may not have
a parent collection. However, certain WebDAV methods are prohibited
from producing results that cause namespace inconsistencies.
As is implicit in [RFC2616] and [RFC3986], any resource, including
collection resources, MAY be identified by more than one URI. For
example, a resource could be identified by multiple HTTP URLs.
5.2. Collection Resources
Collection resources differ from other resources in that they also
act as containers. Some HTTP methods apply only to a collection, but
some apply to some or all of the resources inside the container
defined by the collection. When the scope of a method is not clear,
the client can specify what depth to apply. Depth can be either zero
levels (only the collection), one level (the collection and directly
contained resources), or infinite levels (the collection and all
contained resources recursively).
A collection's state consists of at least a set of mappings between
path segments and resources, and a set of properties on the
collection itself. In this document, a resource B will be said to be
contained in the collection resource A if there is a path segment
mapping that maps to B and that is contained in A. A collection MUST
contain at most one mapping for a given path segment, i.e., it is
illegal to have the same path segment mapped to more than one
resource.
Dusseault Standards Track [Page 15]
RFC 4918 WebDAV June 2007
Properties defined on collections behave exactly as do properties on
non-collection resources. A collection MAY have additional state
such as entity bodies returned by GET.
For all WebDAV-compliant resources A and B, identified by URLs "U"
and "V", respectively, such that "V" is equal to "U/SEGMENT", A MUST
be a collection that contains a mapping from "SEGMENT" to B. So, if
resource B with URL "http://example.com/bar/blah" is WebDAV compliant
and if resource A with URL "http://example.com/bar/" is WebDAV
compliant, then resource A must be a collection and must contain
exactly one mapping from "blah" to B.
Although commonly a mapping consists of a single segment and a
resource, in general, a mapping consists of a set of segments and a
resource. This allows a server to treat a set of segments as
equivalent (i.e., either all of the segments are mapped to the same
resource, or none of the segments are mapped to a resource). For
example, a server that performs case-folding on segments will treat
the segments "ab", "Ab", "aB", and "AB" as equivalent. A client can
then use any of these segments to identify the resource. Note that a
PROPFIND result will select one of these equivalent segments to
identify the mapping, so there will be one PROPFIND response element
per mapping, not one per segment in the mapping.
Collection resources MAY have mappings to non-WebDAV-compliant
resources in the HTTP URL namespace hierarchy but are not required to
do so. For example, if resource X with URL
"http://example.com/bar/blah" is not WebDAV compliant and resource A
with "URL http://example.com/bar/" identifies a WebDAV collection,
then A may or may not have a mapping from "blah" to X.
If a WebDAV-compliant resource has no WebDAV-compliant internal
members in the HTTP URL namespace hierarchy, then the WebDAV-
compliant resource is not required to be a collection.
There is a standing convention that when a collection is referred to
by its name without a trailing slash, the server MAY handle the
request as if the trailing slash were present. In this case, it
SHOULD return a Content-Location header in the response, pointing to
the URL ending with the "/". For example, if a client invokes a
method on http://example.com/blah (no trailing slash), the server may
respond as if the operation were invoked on http://example.com/blah/
(trailing slash), and should return a Content-Location header with
the value http://example.com/blah/. Wherever a server produces a URL
referring to a collection, the server SHOULD include the trailing
slash. In general, clients SHOULD use the trailing slash form of
collection names. If clients do not use the trailing slash form the
client needs to be prepared to see a redirect response. Clients will
Dusseault Standards Track [Page 16]
RFC 4918 WebDAV June 2007
find the DAV:resourcetype property more reliable than the URL to find
out if a resource is a collection.
Clients MUST be able to support the case where WebDAV resources are
contained inside non-WebDAV resources. For example, if an OPTIONS
response from "http://example.com/servlet/dav/collection" indicates
WebDAV support, the client cannot assume that
"http://example.com/servlet/dav/" or its parent necessarily are
WebDAV collections.
A typical scenario in which mapped URLs do not appear as members of
their parent collection is the case where a server allows links or
redirects to non-WebDAV resources. For instance, "/col/link" might
not appear as a member of "/col/", although the server would respond
with a 302 status to a GET request to "/col/link"; thus, the URL
"/col/link" would indeed be mapped. Similarly, a dynamically-
generated page might have a URL mapping from "/col/index.html", thus
this resource might respond with a 200 OK to a GET request yet not
appear as a member of "/col/".
Some mappings to even WebDAV-compliant resources might not appear in
the parent collection. An example for this case are servers that
support multiple alias URLs for each WebDAV-compliant resource. A
server may implement case-insensitive URLs, thus "/col/a" and
"/col/A" identify the same resource, yet only either "a" or "A" is
reported upon listing the members of "/col". In cases where a server
treats a set of segments as equivalent, the server MUST expose only
one preferred segment per mapping, consistently chosen, in PROPFIND
responses.
6. Locking
The ability to lock a resource provides a mechanism for serializing
access to that resource. Using a lock, an authoring client can
provide a reasonable guarantee that another principal will not modify
a resource while it is being edited. In this way, a client can
prevent the "lost update" problem.
This specification allows locks to vary over two client-specified
parameters, the number of principals involved (exclusive vs. shared)
and the type of access to be granted. This document defines locking
for only one access type, write. However, the syntax is extensible,
and permits the eventual specification of locking for other access
types.
Dusseault Standards Track [Page 17]
RFC 4918 WebDAV June 2007
6.1. Lock Model
This section provides a concise model for how locking behaves. Later
sections will provide more detail on some of the concepts and refer
back to these model statements. Normative statements related to LOCK
and UNLOCK method handling can be found in the sections on those
methods, whereas normative statements that cover any method are
gathered here.
1. A lock either directly or indirectly locks a resource.
2. A resource becomes directly locked when a LOCK request to a URL
of that resource creates a new lock. The "lock-root" of the new
lock is that URL. If at the time of the request, the URL is not
mapped to a resource, a new empty resource is created and
directly locked.
3. An exclusive lock (Section 6.2) conflicts with any other kind of
lock on the same resource, whether either lock is direct or
indirect. A server MUST NOT create conflicting locks on a
resource.
4. For a collection that is locked with a depth-infinity lock L, all
member resources are indirectly locked. Changes in membership of
such a collection affect the set of indirectly locked resources:
* If a member resource is added to the collection, the new
member resource MUST NOT already have a conflicting lock,
because the new resource MUST become indirectly locked by L.
* If a member resource stops being a member of the collection,
then the resource MUST no longer be indirectly locked by L.
5. Each lock is identified by a single globally unique lock token
(Section 6.5).
6. An UNLOCK request deletes the lock with the specified lock token.
After a lock is deleted, no resource is locked by that lock.
7. A lock token is "submitted" in a request when it appears in an
"If" header (Section 7, "Write Lock", discusses when token
submission is required for write locks).
8. If a request causes the lock-root of any lock to become an
unmapped URL, then the lock MUST also be deleted by that request.
Dusseault Standards Track [Page 18]
RFC 4918 WebDAV June 2007
6.2. Exclusive vs. Shared Locks
The most basic form of lock is an exclusive lock. Exclusive locks
avoid having to deal with content change conflicts, without requiring
any coordination other than the methods described in this
specification.
However, there are times when the goal of a lock is not to exclude
others from exercising an access right but rather to provide a
mechanism for principals to indicate that they intend to exercise
their access rights. Shared locks are provided for this case. A
shared lock allows multiple principals to receive a lock. Hence any
principal that has both access privileges and a valid lock can use
the locked resource.
With shared locks, there are two trust sets that affect a resource.
The first trust set is created by access permissions. Principals who
are trusted, for example, may have permission to write to the
resource. Among those who have access permission to write to the
resource, the set of principals who have taken out a shared lock also
must trust each other, creating a (typically) smaller trust set
within the access permission write set.
Starting with every possible principal on the Internet, in most
situations the vast majority of these principals will not have write
access to a given resource. Of the small number who do have write
access, some principals may decide to guarantee their edits are free
from overwrite conflicts by using exclusive write locks. Others may
decide they trust their collaborators will not overwrite their work
(the potential set of collaborators being the set of principals who
have write permission) and use a shared lock, which informs their
collaborators that a principal may be working on the resource.
The WebDAV extensions to HTTP do not need to provide all of the
communications paths necessary for principals to coordinate their
activities. When using shared locks, principals may use any out-of-
band communication channel to coordinate their work (e.g., face-to-
face interaction, written notes, post-it notes on the screen,
telephone conversation, email, etc.) The intent of a shared lock is
to let collaborators know who else may be working on a resource.
Shared locks are included because experience from Web-distributed
authoring systems has indicated that exclusive locks are often too
rigid. An exclusive lock is used to enforce a particular editing
process: take out an exclusive lock, read the resource, perform
edits, write the resource, release the lock. This editing process
has the problem that locks are not always properly released, for
example, when a program crashes or when a lock creator leaves without
Dusseault Standards Track [Page 19]
RFC 4918 WebDAV June 2007
unlocking a resource. While both timeouts (Section 6.6) and
administrative action can be used to remove an offending lock,
neither mechanism may be available when needed; the timeout may be
long or the administrator may not be available.
A successful request for a new shared lock MUST result in the
generation of a unique lock associated with the requesting principal.
Thus, if five principals have taken out shared write locks on the
same resource, there will be five locks and five lock tokens, one for
each principal.
6.3. Required Support
A WebDAV-compliant resource is not required to support locking in any
form. If the resource does support locking, it may choose to support
any combination of exclusive and shared locks for any access types.
The reason for this flexibility is that locking policy strikes to the
very heart of the resource management and versioning systems employed
by various storage repositories. These repositories require control
over what sort of locking will be made available. For example, some
repositories only support shared write locks, while others only
provide support for exclusive write locks, while yet others use no
locking at all. As each system is sufficiently different to merit
exclusion of certain locking features, this specification leaves
locking as the sole axis of negotiation within WebDAV.
6.4. Lock Creator and Privileges
The creator of a lock has special privileges to use the lock to
modify the resource. When a locked resource is modified, a server
MUST check that the authenticated principal matches the lock creator
(in addition to checking for valid lock token submission).
The server MAY allow privileged users other than the lock creator to
destroy a lock (for example, the resource owner or an administrator).
The 'unlock' privilege in [RFC3744] was defined to provide that
permission.
There is no requirement for servers to accept LOCK requests from all
users or from anonymous users.
Note that having a lock does not confer full privilege to modify the
locked resource. Write access and other privileges MUST be enforced
through normal privilege or authentication mechanisms, not based on
the possible obscurity of lock token values.
Dusseault Standards Track [Page 20]
RFC 4918 WebDAV June 2007
6.5. Lock Tokens
A lock token is a type of state token that identifies a particular
lock. Each lock has exactly one unique lock token generated by the
server. Clients MUST NOT attempt to interpret lock tokens in any
way.
Lock token URIs MUST be unique across all resources for all time.
This uniqueness constraint allows lock tokens to be submitted across
resources and servers without fear of confusion. Since lock tokens
are unique, a client MAY submit a lock token in an If header on a
resource other than the one that returned it.
When a LOCK operation creates a new lock, the new lock token is
returned in the Lock-Token response header defined in Section 10.5,
and also in the body of the response.
Servers MAY make lock tokens publicly readable (e.g., in the DAV:
lockdiscovery property). One use case for making lock tokens
readable is so that a long-lived lock can be removed by the resource
owner (the client that obtained the lock might have crashed or
disconnected before cleaning up the lock). Except for the case of
using UNLOCK under user guidance, a client SHOULD NOT use a lock
token created by another client instance.
This specification encourages servers to create Universally Unique
Identifiers (UUIDs) for lock tokens, and to use the URI form defined
by "A Universally Unique Identifier (UUID) URN Namespace"
([RFC4122]). However, servers are free to use any URI (e.g., from
another scheme) so long as it meets the uniqueness requirements. For
example, a valid lock token might be constructed using the
"opaquelocktoken" scheme defined in Appendix C.
Example: "urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6"
6.6. Lock Timeout
A lock MAY have a limited lifetime. The lifetime is suggested by the
client when creating or refreshing the lock, but the server
ultimately chooses the timeout value. Timeout is measured in seconds
remaining until lock expiration.
The timeout counter MUST be restarted if a refresh lock request is
successful (see Section 9.10.2). The timeout counter SHOULD NOT be
restarted at any other time.
If the timeout expires, then the lock SHOULD be removed. In this
case the server SHOULD act as if an UNLOCK method was executed by the
Dusseault Standards Track [Page 21]
RFC 4918 WebDAV June 2007
server on the resource using the lock token of the timed-out lock,
performed with its override authority.
Servers are advised to pay close attention to the values submitted by
clients, as they will be indicative of the type of activity the
client intends to perform. For example, an applet running in a
browser may need to lock a resource, but because of the instability
of the environment within which the applet is running, the applet may
be turned off without warning. As a result, the applet is likely to
ask for a relatively small timeout value so that if the applet dies,
the lock can be quickly harvested. However, a document management
system is likely to ask for an extremely long timeout because its
user may be planning on going offline.
A client MUST NOT assume that just because the timeout has expired,
the lock has immediately been removed.
Likewise, a client MUST NOT assume that just because the timeout has
not expired, the lock still exists. Clients MUST assume that locks
can arbitrarily disappear at any time, regardless of the value given
in the Timeout header. The Timeout header only indicates the
behavior of the server if extraordinary circumstances do not occur.
For example, a sufficiently privileged user may remove a lock at any
time, or the system may crash in such a way that it loses the record
of the lock's existence.
6.7. Lock Capability Discovery
Since server lock support is optional, a client trying to lock a
resource on a server can either try the lock and hope for the best,
or perform some form of discovery to determine what lock capabilities
the server supports. This is known as lock capability discovery. A
client can determine what lock types the server supports by
retrieving the DAV:supportedlock property.
Any DAV-compliant resource that supports the LOCK method MUST support
the DAV:supportedlock property.
6.8. Active Lock Discovery
If another principal locks a resource that a principal wishes to
access, it is useful for the second principal to be able to find out
who the first principal is. For this purpose the DAV:lockdiscovery
property is provided. This property lists all outstanding locks,
describes their type, and MAY even provide the lock tokens.
Any DAV-compliant resource that supports the LOCK method MUST support
the DAV:lockdiscovery property.
Dusseault Standards Track [Page 22]
RFC 4918 WebDAV June 2007
7. Write Lock
This section describes the semantics specific to the write lock type.
The write lock is a specific instance of a lock type, and is the only
lock type described in this specification.
An exclusive write lock protects a resource: it prevents changes by
any principal other than the lock creator and in any case where the
lock token is not submitted (e.g., by a client process other than the
one holding the lock).
Clients MUST submit a lock-token they are authorized to use in any
request that modifies a write-locked resource. The list of
modifications covered by a write-lock include:
1. A change to any of the following aspects of any write-locked
resource:
* any variant,
* any dead property,
* any live property that is lockable (a live property is
lockable unless otherwise defined.)
2. For collections, any modification of an internal member URI. An
internal member URI of a collection is considered to be modified
if it is added, removed, or identifies a different resource.
More discussion on write locks and collections is found in
Section 7.4.
3. A modification of the mapping of the root of the write lock,
either to another resource or to no resource (e.g., DELETE).
Of the methods defined in HTTP and WebDAV, PUT, POST, PROPPATCH,
LOCK, UNLOCK, MOVE, COPY (for the destination resource), DELETE, and
MKCOL are affected by write locks. All other HTTP/WebDAV methods
defined so far -- GET in particular -- function independently of a
write lock.
The next few sections describe in more specific terms how write locks
interact with various operations.
Dusseault Standards Track [Page 23]
RFC 4918 WebDAV June 2007
7.1. Write Locks and Properties
While those without a write lock may not alter a property on a
resource it is still possible for the values of live properties to
change, even while locked, due to the requirements of their schemas.
Only dead properties and live properties defined as lockable are
guaranteed not to change while write locked.
7.2. Avoiding Lost Updates
Although the write locks provide some help in preventing lost
updates, they cannot guarantee that updates will never be lost.
Consider the following scenario:
Two clients A and B are interested in editing the resource
'index.html'. Client A is an HTTP client rather than a WebDAV
client, and so does not know how to perform locking.
Client A doesn't lock the document, but does a GET, and begins
editing.
Client B does LOCK, performs a GET and begins editing.
Client B finishes editing, performs a PUT, then an UNLOCK.
Client A performs a PUT, overwriting and losing all of B's changes.
There are several reasons why the WebDAV protocol itself cannot
prevent this situation. First, it cannot force all clients to use
locking because it must be compatible with HTTP clients that do not
comprehend locking. Second, it cannot require servers to support
locking because of the variety of repository implementations, some of
which rely on reservations and merging rather than on locking.
Finally, being stateless, it cannot enforce a sequence of operations
like LOCK / GET / PUT / UNLOCK.
WebDAV servers that support locking can reduce the likelihood that
clients will accidentally overwrite each other's changes by requiring
clients to lock resources before modifying them. Such servers would
effectively prevent HTTP 1.0 and HTTP 1.1 clients from modifying
resources.
WebDAV clients can be good citizens by using a lock / retrieve /
write /unlock sequence of operations (at least by default) whenever
they interact with a WebDAV server that supports locking.
Dusseault Standards Track [Page 24]
RFC 4918 WebDAV June 2007
HTTP 1.1 clients can be good citizens, avoiding overwriting other
clients' changes, by using entity tags in If-Match headers with any
requests that would modify resources.
Information managers may attempt to prevent overwrites by
implementing client-side procedures requiring locking before
modifying WebDAV resources.
7.3. Write Locks and Unmapped URLs
WebDAV provides the ability to send a LOCK request to an unmapped URL
in order to reserve the name for use. This is a simple way to avoid
the lost-update problem on the creation of a new resource (another
way is to use If-None-Match header specified in Section 14.26 of
[RFC2616]). It has the side benefit of locking the new resource
immediately for use of the creator.
Note that the lost-update problem is not an issue for collections
because MKCOL can only be used to create a collection, not to
overwrite an existing collection. When trying to lock a collection
upon creation, clients can attempt to increase the likelihood of
getting the lock by pipelining the MKCOL and LOCK requests together
(but because this doesn't convert two separate operations into one
atomic operation, there's no guarantee this will work).
A successful lock request to an unmapped URL MUST result in the
creation of a locked (non-collection) resource with empty content.
Subsequently, a successful PUT request (with the correct lock token)
provides the content for the resource. Note that the LOCK request
has no mechanism for the client to provide Content-Type or Content-
Language, thus the server will use defaults or empty values and rely
on the subsequent PUT request for correct values.
A resource created with a LOCK is empty but otherwise behaves in
every way as a normal resource. It behaves the same way as a
resource created by a PUT request with an empty body (and where a
Content-Type and Content-Language was not specified), followed by a
LOCK request to the same resource. Following from this model, a
locked empty resource:
o Can be read, deleted, moved, and copied, and in all ways behaves
as a regular non-collection resource.
o Appears as a member of its parent collection.
o SHOULD NOT disappear when its lock goes away (clients must
therefore be responsible for cleaning up their own mess, as with
any other operation or any non-empty resource).
Dusseault Standards Track [Page 25]
RFC 4918 WebDAV June 2007
o MAY NOT have values for properties like DAV:getcontentlanguage
that haven't been specified yet by the client.
o Can be updated (have content added) with a PUT request.
o MUST NOT be converted into a collection. The server MUST fail a
MKCOL request (as it would with a MKCOL request to any existing
non-collection resource).
o MUST have defined values for DAV:lockdiscovery and DAV:
supportedlock properties.
o The response MUST indicate that a resource was created, by use of
the "201 Created" response code (a LOCK request to an existing
resource instead will result in 200 OK). The body must still
include the DAV:lockdiscovery property, as with a LOCK request to
an existing resource.
The client is expected to update the locked empty resource shortly
after locking it, using PUT and possibly PROPPATCH.
Alternatively and for backwards compatibility to [RFC2518], servers
MAY implement Lock-Null Resources (LNRs) instead (see definition in
Appendix D). Clients can easily interoperate both with servers that
support the old model LNRs and the recommended model of "locked empty
resources" by only attempting PUT after a LOCK to an unmapped URL,
not MKCOL or GET, and by not relying on specific properties of LNRs.
7.4. Write Locks and Collections
There are two kinds of collection write locks. A depth-0 write lock
on a collection protects the collection properties plus the internal
member URLs of that one collection, while not protecting the content
or properties of member resources (if the collection itself has any
entity bodies, those are also protected). A depth-infinity write
lock on a collection provides the same protection on that collection
and also provides write lock protection on every member resource.
Expressed otherwise, a write lock of either kind protects any request
that would create a new resource in a write locked collection, any
request that would remove an internal member URL of a write locked
collection, and any request that would change the segment name of any
internal member.
Thus, a collection write lock protects all the following actions:
o DELETE a collection's direct internal member,
Dusseault Standards Track [Page 26]
RFC 4918 WebDAV June 2007
o MOVE an internal member out of the collection,
o MOVE an internal member into the collection,
o MOVE to rename an internal member within a collection,
o COPY an internal member into a collection, and
o PUT or MKCOL request that would create a new internal member.
The collection's lock token is required in addition to the lock token
on the internal member itself, if it is locked separately.
In addition, a depth-infinity lock affects all write operations to
all members of the locked collection. With a depth-infinity lock,
the resource identified by the root of the lock is directly locked,
and all its members are indirectly locked.
o Any new resource added as a descendant of a depth-infinity locked
collection becomes indirectly locked.
o Any indirectly locked resource moved out of the locked collection
into an unlocked collection is thereafter unlocked.
o Any indirectly locked resource moved out of a locked source
collection into a depth-infinity locked target collection remains
indirectly locked but is now protected by the lock on the target
collection (the target collection's lock token will thereafter be
required to make further changes).
If a depth-infinity write LOCK request is issued to a collection
containing member URLs identifying resources that are currently
locked in a manner that conflicts with the new lock (see Section 6.1,
point 3), the request MUST fail with a 423 (Locked) status code, and
the response SHOULD contain the 'no-conflicting-lock' precondition.
If a lock request causes the URL of a resource to be added as an
internal member URL of a depth-infinity locked collection, then the
new resource MUST be automatically protected by the lock. For
example, if the collection /a/b/ is write locked and the resource /c
is moved to /a/b/c, then resource /a/b/c will be added to the write
lock.
Dusseault Standards Track [Page 27]
RFC 4918 WebDAV June 2007
7.5. Write Locks and the If Request Header
A user agent has to demonstrate knowledge of a lock when requesting
an operation on a locked resource. Otherwise, the following scenario
might occur. In the scenario, program A, run by User A, takes out a
write lock on a resource. Program B, also run by User A, has no
knowledge of the lock taken out by program A, yet performs a PUT to
the locked resource. In this scenario, the PUT succeeds because
locks are associated with a principal, not a program, and thus
program B, because it is acting with principal A's credential, is
allowed to perform the PUT. However, had program B known about the
lock, it would not have overwritten the resource, preferring instead
to present a dialog box describing the conflict to the user. Due to
this scenario, a mechanism is needed to prevent different programs
from accidentally ignoring locks taken out by other programs with the
same authorization.
In order to prevent these collisions, a lock token MUST be submitted
by an authorized principal for all locked resources that a method may
change or the method MUST fail. A lock token is submitted when it
appears in an If header. For example, if a resource is to be moved
and both the source and destination are locked, then two lock tokens
must be submitted in the If header, one for the source and the other
for the destination.
7.5.1. Example - Write Lock and COPY
>>Request
COPY /~fielding/index.html HTTP/1.1
Host: www.example.com
Destination: http://www.example.com/users/f/fielding/index.html
If: <http://www.example.com/users/f/fielding/index.html>
(<urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6>)
>>Response
HTTP/1.1 204 No Content
In this example, even though both the source and destination are
locked, only one lock token must be submitted (the one for the lock
on the destination). This is because the source resource is not
modified by a COPY, and hence unaffected by the write lock. In this
example, user agent authentication has previously occurred via a
mechanism outside the scope of the HTTP protocol, in the underlying
transport layer.
Dusseault Standards Track [Page 28]
RFC 4918 WebDAV June 2007
7.5.2. Example - Deleting a Member of a Locked Collection
Consider a collection "/locked" with an exclusive, depth-infinity
write lock, and an attempt to delete an internal member "/locked/
member":
>>Request
DELETE /locked/member HTTP/1.1
Host: example.com
>>Response
HTTP/1.1 423 Locked
Content-Type: application/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<D:error xmlns:D="DAV:">
<D:lock-token-submitted>
<D:href>/locked/</D:href>
</D:lock-token-submitted>
</D:error>
Thus, the client would need to submit the lock token with the request
to make it succeed. To do that, various forms of the If header (see
Section 10.4) could be used.
"No-Tag-List" format:
If: (<urn:uuid:150852e2-3847-42d5-8cbe-0f4f296f26cf>)
"Tagged-List" format, for "http://example.com/locked/":
If: <http://example.com/locked/>
(<urn:uuid:150852e2-3847-42d5-8cbe-0f4f296f26cf>)
"Tagged-List" format, for "http://example.com/locked/member":
If: <http://example.com/locked/member>
(<urn:uuid:150852e2-3847-42d5-8cbe-0f4f296f26cf>)
Note that, for the purpose of submitting the lock token, the actual
form doesn't matter; what's relevant is that the lock token appears
in the If header, and that the If header itself evaluates to true.
Dusseault Standards Track [Page 29]
RFC 4918 WebDAV June 2007
7.6. Write Locks and COPY/MOVE
A COPY method invocation MUST NOT duplicate any write locks active on
the source. However, as previously noted, if the COPY copies the
resource into a collection that is locked with a depth-infinity lock,
then the resource will be added to the lock.
A successful MOVE request on a write locked resource MUST NOT move
the write lock with the resource. However, if there is an existing
lock at the destination, the server MUST add the moved resource to
the destination lock scope. For example, if the MOVE makes the
resource a child of a collection that has a depth-infinity lock, then
the resource will be added to that collection's lock. Additionally,
if a resource with a depth-infinity lock is moved to a destination
that is within the scope of the same lock (e.g., within the URL
namespace tree covered by the lock), the moved resource will again be
added to the lock. In both these examples, as specified in
Section 7.5, an If header must be submitted containing a lock token
for both the source and destination.
7.7. Refreshing Write Locks
A client MUST NOT submit the same write lock request twice. Note
that a client is always aware it is resubmitting the same lock
request because it must include the lock token in the If header in
order to make the request for a resource that is already locked.
However, a client may submit a LOCK request with an If header but
without a body. A server receiving a LOCK request with no body MUST
NOT create a new lock -- this form of the LOCK request is only to be
used to "refresh" an existing lock (meaning, at minimum, that any
timers associated with the lock MUST be reset).
Clients may submit Timeout headers of arbitrary value with their lock
refresh requests. Servers, as always, may ignore Timeout headers
submitted by the client, and a server MAY refresh a lock with a
timeout period that is different than the previous timeout period
used for the lock, provided it advertises the new value in the LOCK
refresh response.
If an error is received in response to a refresh LOCK request, the
client MUST NOT assume that the lock was refreshed.
Dusseault Standards Track [Page 30]
RFC 4918 WebDAV June 2007
8. General Request and Response Handling
8.1. Precedence in Error Handling
Servers MUST return authorization errors in preference to other
errors. This avoids leaking information about protected resources
(e.g., a client that finds that a hidden resource exists by seeing a
423 Locked response to an anonymous request to the resource).
8.2. Use of XML
In HTTP/1.1, method parameter information was exclusively encoded in
HTTP headers. Unlike HTTP/1.1, WebDAV encodes method parameter
information either in an XML ([REC-XML]) request entity body, or in
an HTTP header. The use of XML to encode method parameters was
motivated by the ability to add extra XML elements to existing
structures, providing extensibility; and by XML's ability to encode
information in ISO 10646 character sets, providing
internationalization support.
In addition to encoding method parameters, XML is used in WebDAV to
encode the responses from methods, providing the extensibility and
internationalization advantages of XML for method output, as well as
input.
When XML is used for a request or response body, the Content-Type
type SHOULD be application/xml. Implementations MUST accept both
text/xml and application/xml in request and response bodies. Use of
text/xml is deprecated.
All DAV-compliant clients and resources MUST use XML parsers that are
compliant with [REC-XML] and [REC-XML-NAMES]. All XML used in either
requests or responses MUST be, at minimum, well formed and use
namespaces correctly. If a server receives XML that is not well-
formed, then the server MUST reject the entire request with a 400
(Bad Request). If a client receives XML that is not well-formed in a
response, then the client MUST NOT assume anything about the outcome
of the executed method and SHOULD treat the server as malfunctioning.
Note that processing XML submitted by an untrusted source may cause
risks connected to privacy, security, and service quality (see
Section 20). Servers MAY reject questionable requests (even though
they consist of well-formed XML), for instance, with a 400 (Bad
Request) status code and an optional response body explaining the
problem.
Dusseault Standards Track [Page 31]
RFC 4918 WebDAV June 2007
8.3. URL Handling
URLs appear in many places in requests and responses.
Interoperability experience with [RFC2518] showed that many clients
parsing Multi-Status responses did not fully implement the full
Reference Resolution defined in Section 5 of [RFC3986]. Thus,
servers in particular need to be careful in handling URLs in
responses, to ensure that clients have enough context to be able to
interpret all the URLs. The rules in this section apply not only to
resource URLs in the 'href' element in Multi-Status responses, but
also to the Destination and If header resource URLs.
The sender has a choice between two approaches: using a relative
reference, which is resolved against the Request-URI, or a full URI.
A server MUST ensure that every 'href' value within a Multi-Status
response uses the same format.
WebDAV only uses one form of relative reference in its extensions,
the absolute path.
Simple-ref = absolute-URI | ( path-absolute [ "?" query ] )
The absolute-URI, path-absolute and query productions are defined in
Sections 4.3, 3.3, and 3.4 of [RFC3986].
Within Simple-ref productions, senders MUST NOT:
o use dot-segments ("." or ".."), or
o have prefixes that do not match the Request-URI (using the
comparison rules defined in Section 3.2.3 of [RFC2616]).
Identifiers for collections SHOULD end in a '/' character.
8.3.1. Example - Correct URL Handling
Consider the collection http://example.com/sample/ with the internal
member URL http://example.com/sample/a%20test and the PROPFIND
request below:
>>Request:
PROPFIND /sample/ HTTP/1.1
Host: example.com
Depth: 1
Dusseault Standards Track [Page 32]
RFC 4918 WebDAV June 2007
In this case, the server should return two 'href' elements containing
either
o 'http://example.com/sample/' and
'http://example.com/sample/a%20test', or
o '/sample/' and '/sample/a%20test'
Note that even though the server may be storing the member resource
internally as 'a test', it has to be percent-encoded when used inside
a URI reference (see Section 2.1 of [RFC3986]). Also note that a
legal URI may still contain characters that need to be escaped within
XML character data, such as the ampersand character.
8.4. Required Bodies in Requests
Some of these new methods do not define bodies. Servers MUST examine
all requests for a body, even when a body was not expected. In cases
where a request body is present but would be ignored by a server, the
server MUST reject the request with 415 (Unsupported Media Type).
This informs the client (which may have been attempting to use an
extension) that the body could not be processed as the client
intended.
8.5. HTTP Headers for Use in WebDAV
HTTP defines many headers that can be used in WebDAV requests and
responses. Not all of these are appropriate in all situations and
some interactions may be undefined. Note that HTTP 1.1 requires the
Date header in all responses if possible (see Section 14.18,
[RFC2616]).
The server MUST do authorization checks before checking any HTTP
conditional header.
8.6. ETag
HTTP 1.1 recommends the use of ETags rather than modification dates,
for cache control, and there are even stronger reasons to prefer
ETags for authoring. Correct use of ETags is even more important in
a distributed authoring environment, because ETags are necessary
along with locks to avoid the lost-update problem. A client might
fail to renew a lock, for example, when the lock times out and the
client is accidentally offline or in the middle of a long upload.
When a client fails to renew the lock, it's quite possible the
resource can still be relocked and the user can go on editing, as
long as no changes were made in the meantime. ETags are required for
the client to be able to distinguish this case. Otherwise, the
Dusseault Standards Track [Page 33]
RFC 4918 WebDAV June 2007
client is forced to ask the user whether to overwrite the resource on
the server without even being able to tell the user if it has
changed. Timestamps do not solve this problem nearly as well as
ETags.
Strong ETags are much more useful for authoring use cases than weak
ETags (see Section 13.3.3 of [RFC2616]). Semantic equivalence can be
a useful concept but that depends on the document type and the
application type, and interoperability might require some agreement
or standard outside the scope of this specification and HTTP. Note
also that weak ETags have certain restrictions in HTTP, e.g., these
cannot be used in If-Match headers.
Note that the meaning of an ETag in a PUT response is not clearly
defined either in this document or in RFC 2616 (i.e., whether the
ETag means that the resource is octet-for-octet equivalent to the
body of the PUT request, or whether the server could have made minor
changes in the formatting or content of the document upon storage).
This is an HTTP issue, not purely a WebDAV issue.
Because clients may be forced to prompt users or throw away changed
content if the ETag changes, a WebDAV server SHOULD NOT change the
ETag (or the Last-Modified time) for a resource that has an unchanged
body and location. The ETag represents the state of the body or
contents of the resource. There is no similar way to tell if
properties have changed.
8.7. Including Error Response Bodies
HTTP and WebDAV did not use the bodies of most error responses for
machine-parsable information until the specification for Versioning
Extensions to WebDAV introduced a mechanism to include more specific
information in the body of an error response (Section 1.6 of
[RFC3253]). The error body mechanism is appropriate to use with any
error response that may take a body but does not already have a body
defined. The mechanism is particularly appropriate when a status
code can mean many things (for example, 400 Bad Request can mean
required headers are missing, headers are incorrectly formatted, or
much more). This error body mechanism is covered in Section 16.
8.8. Impact of Namespace Operations on Cache Validators
Note that the HTTP response headers "Etag" and "Last-Modified" (see
[RFC2616], Sections 14.19 and 14.29) are defined per URL (not per
resource), and are used by clients for caching. Therefore servers
must ensure that executing any operation that affects the URL
namespace (such as COPY, MOVE, DELETE, PUT, or MKCOL) does preserve
their semantics, in particular:
Dusseault Standards Track [Page 34]
RFC 4918 WebDAV June 2007
o For any given URL, the "Last-Modified" value MUST increment every
time the representation returned upon GET changes (within the
limits of timestamp resolution).
o For any given URL, an "ETag" value MUST NOT be reused for
different representations returned by GET.
In practice this means that servers
o might have to increment "Last-Modified" timestamps for every
resource inside the destination namespace of a namespace operation
unless it can do so more selectively, and
o similarly, might have to re-assign "ETag" values for these
resources (unless the server allocates entity tags in a way so
that they are unique across the whole URL namespace managed by the
server).
Note that these considerations also apply to specific use cases, such
as using PUT to create a new resource at a URL that has been mapped
before, but has been deleted since then.
Finally, WebDAV properties (such as DAV:getetag and DAV:
getlastmodified) that inherit their semantics from HTTP headers must
behave accordingly.
9. HTTP Methods for Distributed Authoring
9.1. PROPFIND Method
The PROPFIND method retrieves properties defined on the resource
identified by the Request-URI, if the resource does not have any
internal members, or on the resource identified by the Request-URI
and potentially its member resources, if the resource is a collection
that has internal member URLs. All DAV-compliant resources MUST
support the PROPFIND method and the propfind XML element
(Section 14.20) along with all XML elements defined for use with that
element.
A client MUST submit a Depth header with a value of "0", "1", or
"infinity" with a PROPFIND request. Servers MUST support "0" and "1"
depth requests on WebDAV-compliant resources and SHOULD support
"infinity" requests. In practice, support for infinite-depth
requests MAY be disabled, due to the performance and security
concerns associated with this behavior. Servers SHOULD treat a
request without a Depth header as if a "Depth: infinity" header was
included.
Dusseault Standards Track [Page 35]
RFC 4918 WebDAV June 2007
A client may submit a 'propfind' XML element in the body of the
request method describing what information is being requested. It is
possible to:
o Request particular property values, by naming the properties
desired within the 'prop' element (the ordering of properties in
here MAY be ignored by the server),
o Request property values for those properties defined in this
specification (at a minimum) plus dead properties, by using the
'allprop' element (the 'include' element can be used with
'allprop' to instruct the server to also include additional live
properties that may not have been returned otherwise),
o Request a list of names of all the properties defined on the
resource, by using the 'propname' element.
A client may choose not to submit a request body. An empty PROPFIND
request body MUST be treated as if it were an 'allprop' request.
Note that 'allprop' does not return values for all live properties.
WebDAV servers increasingly have expensively-calculated or lengthy
properties (see [RFC3253] and [RFC3744]) and do not return all
properties already. Instead, WebDAV clients can use propname
requests to discover what live properties exist, and request named
properties when retrieving values. For a live property defined
elsewhere, that definition can specify whether or not that live
property would be returned in 'allprop' requests.
All servers MUST support returning a response of content type text/
xml or application/xml that contains a multistatus XML element that
describes the results of the attempts to retrieve the various
properties.
If there is an error retrieving a property, then a proper error
result MUST be included in the response. A request to retrieve the
value of a property that does not exist is an error and MUST be noted
with a 'response' XML element that contains a 404 (Not Found) status
value.
Consequently, the 'multistatus' XML element for a collection resource
MUST include a 'response' XML element for each member URL of the
collection, to whatever depth was requested. It SHOULD NOT include
any 'response' elements for resources that are not WebDAV-compliant.
Each 'response' element MUST contain an 'href' element that contains
the URL of the resource on which the properties in the prop XML
element are defined. Results for a PROPFIND on a collection resource
are returned as a flat list whose order of entries is not
Dusseault Standards Track [Page 36]
RFC 4918 WebDAV June 2007
significant. Note that a resource may have only one value for a
property of a given name, so the property may only show up once in
PROPFIND responses.
Properties may be subject to access control. In the case of
'allprop' and 'propname' requests, if a principal does not have the
right to know whether a particular property exists, then the property
MAY be silently excluded from the response.
Some PROPFIND results MAY be cached, with care, as there is no cache
validation mechanism for most properties. This method is both safe
and idempotent (see Section 9.1 of [RFC2616]).
9.1.1. PROPFIND Status Codes
This section, as with similar sections for other methods, provides
some guidance on error codes and preconditions or postconditions
(defined in Section 16) that might be particularly useful with
PROPFIND.
403 Forbidden - A server MAY reject PROPFIND requests on collections
with depth header of "Infinity", in which case it SHOULD use this
error with the precondition code 'propfind-finite-depth' inside the
error body.
9.1.2. Status Codes for Use in 'propstat' Element
In PROPFIND responses, information about individual properties is
returned inside 'propstat' elements (see Section 14.22), each
containing an individual 'status' element containing information
about the properties appearing in it. The list below summarizes the
most common status codes used inside 'propstat'; however, clients
should be prepared to handle other 2/3/4/5xx series status codes as
well.
200 OK - A property exists and/or its value is successfully returned.
401 Unauthorized - The property cannot be viewed without appropriate
authorization.
403 Forbidden - The property cannot be viewed regardless of
authentication.
404 Not Found - The property does not exist.
Dusseault Standards Track [Page 37]
RFC 4918 WebDAV June 2007
9.1.3. Example - Retrieving Named Properties
>>Request
PROPFIND /file HTTP/1.1
Host: www.example.com
Content-type: application/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<D:propfind xmlns:D="DAV:">
<D:prop xmlns:R="http://ns.example.com/boxschema/">
<R:bigbox/>
<R:author/>
<R:DingALing/>
<R:Random/>
</D:prop>
</D:propfind>
>>Response
HTTP/1.1 207 Multi-Status
Content-Type: application/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<D:multistatus xmlns:D="DAV:">
<D:response xmlns:R="http://ns.example.com/boxschema/">
<D:href>http://www.example.com/file</D:href>
<D:propstat>
<D:prop>
<R:bigbox>
<R:BoxType>Box type A</R:BoxType>
</R:bigbox>
<R:author>
<R:Name>J.J. Johnson</R:Name>
</R:author>
</D:prop>
<D:status>HTTP/1.1 200 OK</D:status>
</D:propstat>
<D:propstat>
<D:prop><R:DingALing/><R:Random/></D:prop>
<D:status>HTTP/1.1 403 Forbidden</D:status>
<D:responsedescription> The user does not have access to the
DingALing property.
</D:responsedescription>
</D:propstat>
Dusseault Standards Track [Page 38]
RFC 4918 WebDAV June 2007
</D:response>
<D:responsedescription> There has been an access violation error.
</D:responsedescription>
</D:multistatus>
In this example, PROPFIND is executed on a non-collection resource
http://www.example.com/file. The propfind XML element specifies the
name of four properties whose values are being requested. In this
case, only two properties were returned, since the principal issuing
the request did not have sufficient access rights to see the third
and fourth properties.
9.1.4. Example - Using 'propname' to Retrieve All Property Names
>>Request
PROPFIND /container/ HTTP/1.1
Host: www.example.com
Content-Type: application/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<propfind xmlns="DAV:">
<propname/>
</propfind>
>>Response
HTTP/1.1 207 Multi-Status
Content-Type: application/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<multistatus xmlns="DAV:">
<response>
<href>http://www.example.com/container/</href>
<propstat>
<prop xmlns:R="http://ns.example.com/boxschema/">
<R:bigbox/>
<R:author/>
<creationdate/>
<displayname/>
<resourcetype/>
<supportedlock/>
</prop>
<status>HTTP/1.1 200 OK</status>
Dusseault Standards Track [Page 39]
RFC 4918 WebDAV June 2007
</propstat>
</response>
<response>
<href>http://www.example.com/container/front.html</href>
<propstat>
<prop xmlns:R="http://ns.example.com/boxschema/">
<R:bigbox/>
<creationdate/>
<displayname/>
<getcontentlength/>
<getcontenttype/>
<getetag/>
<getlastmodified/>
<resourcetype/>
<supportedlock/>
</prop>
<status>HTTP/1.1 200 OK</status>
</propstat>
</response>
</multistatus>
In this example, PROPFIND is invoked on the collection resource
http://www.example.com/container/, with a propfind XML element
containing the propname XML element, meaning the name of all
properties should be returned. Since no Depth header is present, it
assumes its default value of "infinity", meaning the name of the
properties on the collection and all its descendants should be
returned.
Consistent with the previous example, resource
http://www.example.com/container/ has six properties defined on it:
bigbox and author in the "http://ns.example.com/boxschema/"
namespace, and creationdate, displayname, resourcetype, and
supportedlock in the "DAV:" namespace.
The resource http://www.example.com/container/index.html, a member of
the "container" collection, has nine properties defined on it, bigbox
in the "http://ns.example.com/boxschema/" namespace and creationdate,
displayname, getcontentlength, getcontenttype, getetag,
getlastmodified, resourcetype, and supportedlock in the "DAV:"
namespace.
This example also demonstrates the use of XML namespace scoping and
the default namespace. Since the "xmlns" attribute does not contain
a prefix, the namespace applies by default to all enclosed elements.
Hence, all elements that do not explicitly state the namespace to
which they belong are members of the "DAV:" namespace.
Dusseault Standards Track [Page 40]
RFC 4918 WebDAV June 2007
9.1.5. Example - Using So-called 'allprop'
Note that 'allprop', despite its name, which remains for backward-
compatibility, does not return every property, but only dead
properties and the live properties defined in this specification.
>>Request
PROPFIND /container/ HTTP/1.1
Host: www.example.com
Depth: 1
Content-Type: application/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<D:propfind xmlns:D="DAV:">
<D:allprop/>
</D:propfind>
>>Response
HTTP/1.1 207 Multi-Status
Content-Type: application/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<D:multistatus xmlns:D="DAV:">
<D:response>
<D:href>/container/</D:href>
<D:propstat>
<D:prop xmlns:R="http://ns.example.com/boxschema/">
<R:bigbox><R:BoxType>Box type A</R:BoxType></R:bigbox>
<R:author><R:Name>Hadrian</R:Name></R:author>
<D:creationdate>1997-12-01T17:42:21-08:00</D:creationdate>
<D:displayname>Example collection</D:displayname>
<D:resourcetype><D:collection/></D:resourcetype>
<D:supportedlock>
<D:lockentry>
<D:lockscope><D:exclusive/></D:lockscope>
<D:locktype><D:write/></D:locktype>
</D:lockentry>
<D:lockentry>
<D:lockscope><D:shared/></D:lockscope>
<D:locktype><D:write/></D:locktype>
</D:lockentry>
</D:supportedlock>
</D:prop>
Dusseault Standards Track [Page 41]
RFC 4918 WebDAV June 2007
<D:status>HTTP/1.1 200 OK</D:status>
</D:propstat>
</D:response>
<D:response>
<D:href>/container/front.html</D:href>
<D:propstat>
<D:prop xmlns:R="http://ns.example.com/boxschema/">
<R:bigbox><R:BoxType>Box type B</R:BoxType>
</R:bigbox>
<D:creationdate>1997-12-01T18:27:21-08:00</D:creationdate>
<D:displayname>Example HTML resource</D:displayname>
<D:getcontentlength>4525</D:getcontentlength>
<D:getcontenttype>text/html</D:getcontenttype>
<D:getetag>"zzyzx"</D:getetag>
<D:getlastmodified
>Mon, 12 Jan 1998 09:25:56 GMT</D:getlastmodified>
<D:resourcetype/>
<D:supportedlock>
<D:lockentry>
<D:lockscope><D:exclusive/></D:lockscope>
<D:locktype><D:write/></D:locktype>
</D:lockentry>
<D:lockentry>
<D:lockscope><D:shared/></D:lockscope>
<D:locktype><D:write/></D:locktype>
</D:lockentry>
</D:supportedlock>
</D:prop>
<D:status>HTTP/1.1 200 OK</D:status>
</D:propstat>
</D:response>
</D:multistatus>
In this example, PROPFIND was invoked on the resource
http://www.example.com/container/ with a Depth header of 1, meaning
the request applies to the resource and its children, and a propfind
XML element containing the allprop XML element, meaning the request
should return the name and value of all the dead properties defined
on the resources, plus the name and value of all the properties
defined in this specification. This example illustrates the use of
relative references in the 'href' elements of the response.
The resource http://www.example.com/container/ has six properties
defined on it: 'bigbox' and 'author in the
"http://ns.example.com/boxschema/" namespace, DAV:creationdate, DAV:
displayname, DAV:resourcetype, and DAV:supportedlock.
Dusseault Standards Track [Page 42]
RFC 4918 WebDAV June 2007
The last four properties are WebDAV-specific, defined in Section 15.
Since GET is not supported on this resource, the get* properties
(e.g., DAV:getcontentlength) are not defined on this resource. The
WebDAV-specific properties assert that "container" was created on
December 1, 1997, at 5:42:21PM, in a time zone 8 hours west of GMT
(DAV:creationdate), has a name of "Example collection" (DAV:
displayname), a collection resource type (DAV:resourcetype), and
supports exclusive write and shared write locks (DAV:supportedlock).
The resource http://www.example.com/container/front.html has nine
properties defined on it:
'bigbox' in the "http://ns.example.com/boxschema/" namespace (another
instance of the "bigbox" property type), DAV:creationdate, DAV:
displayname, DAV:getcontentlength, DAV:getcontenttype, DAV:getetag,
DAV:getlastmodified, DAV:resourcetype, and DAV:supportedlock.
The DAV-specific properties assert that "front.html" was created on
December 1, 1997, at 6:27:21PM, in a time zone 8 hours west of GMT
(DAV:creationdate), has a name of "Example HTML resource" (DAV:
displayname), a content length of 4525 bytes (DAV:getcontentlength),
a MIME type of "text/html" (DAV:getcontenttype), an entity tag of
"zzyzx" (DAV:getetag), was last modified on Monday, January 12, 1998,
at 09:25:56 GMT (DAV:getlastmodified), has an empty resource type,
meaning that it is not a collection (DAV:resourcetype), and supports
both exclusive write and shared write locks (DAV:supportedlock).
9.1.6. Example - Using 'allprop' with 'include'
>>Request
PROPFIND /mycol/ HTTP/1.1
Host: www.example.com
Depth: 1
Content-Type: application/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<D:propfind xmlns:D="DAV:">
<D:allprop/>
<D:include>
<D:supported-live-property-set/>
<D:supported-report-set/>
</D:include>
</D:propfind>
Dusseault Standards Track [Page 43]
RFC 4918 WebDAV June 2007
In this example, PROPFIND is executed on the resource
http://www.example.com/mycol/ and its internal member resources. The
client requests the values of all live properties defined in this
specification, plus all dead properties, plus two more live
properties defined in [RFC3253]. The response is not shown.
9.2. PROPPATCH Method
The PROPPATCH method processes instructions specified in the request
body to set and/or remove properties defined on the resource
identified by the Request-URI.
All DAV-compliant resources MUST support the PROPPATCH method and
MUST process instructions that are specified using the
propertyupdate, set, and remove XML elements. Execution of the
directives in this method is, of course, subject to access control
constraints. DAV-compliant resources SHOULD support the setting of
arbitrary dead properties.
The request message body of a PROPPATCH method MUST contain the
propertyupdate XML element.
Servers MUST process PROPPATCH instructions in document order (an
exception to the normal rule that ordering is irrelevant).
Instructions MUST either all be executed or none executed. Thus, if
any error occurs during processing, all executed instructions MUST be
undone and a proper error result returned. Instruction processing
details can be found in the definition of the set and remove
instructions in Sections 14.23 and 14.26.
If a server attempts to make any of the property changes in a
PROPPATCH request (i.e., the request is not rejected for high-level
errors before processing the body), the response MUST be a Multi-
Status response as described in Section 9.2.1.
This method is idempotent, but not safe (see Section 9.1 of
[RFC2616]). Responses to this method MUST NOT be cached.
9.2.1. Status Codes for Use in 'propstat' Element
In PROPPATCH responses, information about individual properties is
returned inside 'propstat' elements (see Section 14.22), each
containing an individual 'status' element containing information
about the properties appearing in it. The list below summarizes the
most common status codes used inside 'propstat'; however, clients
should be prepared to handle other 2/3/4/5xx series status codes as
well.
Dusseault Standards Track [Page 44]
RFC 4918 WebDAV June 2007
200 (OK) - The property set or change succeeded. Note that if this
appears for one property, it appears for every property in the
response, due to the atomicity of PROPPATCH.
403 (Forbidden) - The client, for reasons the server chooses not to
specify, cannot alter one of the properties.
403 (Forbidden): The client has attempted to set a protected
property, such as DAV:getetag. If returning this error, the server
SHOULD use the precondition code 'cannot-modify-protected-property'
inside the response body.
409 (Conflict) - The client has provided a value whose semantics are
not appropriate for the property.
424 (Failed Dependency) - The property change could not be made
because of another property change that failed.
507 (Insufficient Storage) - The server did not have sufficient space
to record the property.
9.2.2. Example - PROPPATCH
>>Request
PROPPATCH /bar.html HTTP/1.1
Host: www.example.com
Content-Type: application/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<D:propertyupdate xmlns:D="DAV:"
xmlns:Z="http://ns.example.com/standards/z39.50/">
<D:set>
<D:prop>
<Z:Authors>
<Z:Author>Jim Whitehead</Z:Author>
<Z:Author>Roy Fielding</Z:Author>
</Z:Authors>
</D:prop>
</D:set>
<D:remove>
<D:prop><Z:Copyright-Owner/></D:prop>
</D:remove>
</D:propertyupdate>
Dusseault Standards Track [Page 45]
RFC 4918 WebDAV June 2007
>>Response
HTTP/1.1 207 Multi-Status
Content-Type: application/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<D:multistatus xmlns:D="DAV:"
xmlns:Z="http://ns.example.com/standards/z39.50/">
<D:response>
<D:href>http://www.example.com/bar.html</D:href>
<D:propstat>
<D:prop><Z:Authors/></D:prop>
<D:status>HTTP/1.1 424 Failed Dependency</D:status>
</D:propstat>
<D:propstat>
<D:prop><Z:Copyright-Owner/></D:prop>
<D:status>HTTP/1.1 409 Conflict</D:status>
</D:propstat>
<D:responsedescription> Copyright Owner cannot be deleted or
altered.</D:responsedescription>
</D:response>
</D:multistatus>
In this example, the client requests the server to set the value of
the "Authors" property in the
"http://ns.example.com/standards/z39.50/" namespace, and to remove
the property "Copyright-Owner" in the same namespace. Since the
Copyright-Owner property could not be removed, no property
modifications occur. The 424 (Failed Dependency) status code for the
Authors property indicates this action would have succeeded if it
were not for the conflict with removing the Copyright-Owner property.
9.3. MKCOL Method
MKCOL creates a new collection resource at the location specified by
the Request-URI. If the Request-URI is already mapped to a resource,
then the MKCOL MUST fail. During MKCOL processing, a server MUST
make the Request-URI an internal member of its parent collection,
unless the Request-URI is "/". If no such ancestor exists, the
method MUST fail. When the MKCOL operation creates a new collection
resource, all ancestors MUST already exist, or the method MUST fail
with a 409 (Conflict) status code. For example, if a request to
create collection /a/b/c/d/ is made, and /a/b/c/ does not exist, the
request must fail.
When MKCOL is invoked without a request body, the newly created
collection SHOULD have no members.
Dusseault Standards Track [Page 46]
RFC 4918 WebDAV June 2007
A MKCOL request message may contain a message body. The precise
behavior of a MKCOL request when the body is present is undefined,
but limited to creating collections, members of a collection, bodies
of members, and properties on the collections or members. If the
server receives a MKCOL request entity type it does not support or
understand, it MUST respond with a 415 (Unsupported Media Type)
status code. If the server decides to reject the request based on
the presence of an entity or the type of an entity, it should use the
415 (Unsupported Media Type) status code.
This method is idempotent, but not safe (see Section 9.1 of
[RFC2616]). Responses to this method MUST NOT be cached.
9.3.1. MKCOL Status Codes
In addition to the general status codes possible, the following
status codes have specific applicability to MKCOL:
201 (Created) - The collection was created.
403 (Forbidden) - This indicates at least one of two conditions: 1)
the server does not allow the creation of collections at the given
location in its URL namespace, or 2) the parent collection of the
Request-URI exists but cannot accept members.
405 (Method Not Allowed) - MKCOL can only be executed on an unmapped
URL.
409 (Conflict) - A collection cannot be made at the Request-URI until
one or more intermediate collections have been created. The server
MUST NOT create those intermediate collections automatically.
415 (Unsupported Media Type) - The server does not support the
request body type (although bodies are legal on MKCOL requests, since
this specification doesn't define any, the server is likely not to
support any given body type).
507 (Insufficient Storage) - The resource does not have sufficient
space to record the state of the resource after the execution of this
method.
9.3.2. Example - MKCOL
This example creates a collection called /webdisc/xfiles/ on the
server www.example.com.
Dusseault Standards Track [Page 47]
RFC 4918 WebDAV June 2007
>>Request
MKCOL /webdisc/xfiles/ HTTP/1.1
Host: www.example.com
>>Response
HTTP/1.1 201 Created
9.4. GET, HEAD for Collections
The semantics of GET are unchanged when applied to a collection,
since GET is defined as, "retrieve whatever information (in the form
of an entity) is identified by the Request-URI" [RFC2616]. GET, when
applied to a collection, may return the contents of an "index.html"
resource, a human-readable view of the contents of the collection, or
something else altogether. Hence, it is possible that the result of
a GET on a collection will bear no correlation to the membership of
the collection.
Similarly, since the definition of HEAD is a GET without a response
message body, the semantics of HEAD are unmodified when applied to
collection resources.
9.5. POST for Collections
Since by definition the actual function performed by POST is
determined by the server and often depends on the particular
resource, the behavior of POST when applied to collections cannot be
meaningfully modified because it is largely undefined. Thus, the
semantics of POST are unmodified when applied to a collection.
9.6. DELETE Requirements
DELETE is defined in [RFC2616], Section 9.7, to "delete the resource
identified by the Request-URI". However, WebDAV changes some DELETE
handling requirements.
A server processing a successful DELETE request:
MUST destroy locks rooted on the deleted resource
MUST remove the mapping from the Request-URI to any resource.
Thus, after a successful DELETE operation (and in the absence of
other actions), a subsequent GET/HEAD/PROPFIND request to the target
Request-URI MUST return 404 (Not Found).
Dusseault Standards Track [Page 48]
RFC 4918 WebDAV June 2007
9.6.1. DELETE for Collections
The DELETE method on a collection MUST act as if a "Depth: infinity"
header was used on it. A client MUST NOT submit a Depth header with
a DELETE on a collection with any value but infinity.
DELETE instructs that the collection specified in the Request-URI and
all resources identified by its internal member URLs are to be
deleted.
If any resource identified by a member URL cannot be deleted, then
all of the member's ancestors MUST NOT be deleted, so as to maintain
URL namespace consistency.
Any headers included with DELETE MUST be applied in processing every
resource to be deleted.
When the DELETE method has completed processing, it MUST result in a
consistent URL namespace.
If an error occurs deleting a member resource (a resource other than
the resource identified in the Request-URI), then the response can be
a 207 (Multi-Status). Multi-Status is used here to indicate which
internal resources could NOT be deleted, including an error code,
which should help the client understand which resources caused the
failure. For example, the Multi-Status body could include a response
with status 423 (Locked) if an internal resource was locked.
The server MAY return a 4xx status response, rather than a 207, if
the request failed completely.
424 (Failed Dependency) status codes SHOULD NOT be in the 207 (Multi-
Status) response for DELETE. They can be safely left out because the
client will know that the ancestors of a resource could not be
deleted when the client receives an error for the ancestor's progeny.
Additionally, 204 (No Content) errors SHOULD NOT be returned in the
207 (Multi-Status). The reason for this prohibition is that 204 (No
Content) is the default success code.
9.6.2. Example - DELETE
>>Request
DELETE /container/ HTTP/1.1
Host: www.example.com
Dusseault Standards Track [Page 49]
RFC 4918 WebDAV June 2007
>>Response
HTTP/1.1 207 Multi-Status
Content-Type: application/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<d:multistatus xmlns:d="DAV:">
<d:response>
<d:href>http://www.example.com/container/resource3</d:href>
<d:status>HTTP/1.1 423 Locked</d:status>
<d:error><d:lock-token-submitted/></d:error>
</d:response>
</d:multistatus>
In this example, the attempt to delete
http://www.example.com/container/resource3 failed because it is
locked, and no lock token was submitted with the request.
Consequently, the attempt to delete http://www.example.com/container/
also failed. Thus, the client knows that the attempt to delete
http://www.example.com/container/ must have also failed since the
parent cannot be deleted unless its child has also been deleted.
Even though a Depth header has not been included, a depth of infinity
is assumed because the method is on a collection.
9.7. PUT Requirements
9.7.1. PUT for Non-Collection Resources
A PUT performed on an existing resource replaces the GET response
entity of the resource. Properties defined on the resource may be
recomputed during PUT processing but are not otherwise affected. For
example, if a server recognizes the content type of the request body,
it may be able to automatically extract information that could be
profitably exposed as properties.
A PUT that would result in the creation of a resource without an
appropriately scoped parent collection MUST fail with a 409
(Conflict).
A PUT request allows a client to indicate what media type an entity
body has, and whether it should change if overwritten. Thus, a
client SHOULD provide a Content-Type for a new resource if any is
known. If the client does not provide a Content-Type for a new
resource, the server MAY create a resource with no Content-Type
assigned, or it MAY attempt to assign a Content-Type.
Dusseault Standards Track [Page 50]
RFC 4918 WebDAV June 2007
Note that although a recipient ought generally to treat metadata
supplied with an HTTP request as authoritative, in practice there's
no guarantee that a server will accept client-supplied metadata
(e.g., any request header beginning with "Content-"). Many servers
do not allow configuring the Content-Type on a per-resource basis in
the first place. Thus, clients can't always rely on the ability to
directly influence the content type by including a Content-Type
request header.
9.7.2. PUT for Collections
This specification does not define the behavior of the PUT method for
existing collections. A PUT request to an existing collection MAY be
treated as an error (405 Method Not Allowed).
The MKCOL method is defined to create collections.
9.8. COPY Method
The COPY method creates a duplicate of the source resource identified
by the Request-URI, in the destination resource identified by the URI
in the Destination header. The Destination header MUST be present.
The exact behavior of the COPY method depends on the type of the
source resource.
All WebDAV-compliant resources MUST support the COPY method.
However, support for the COPY method does not guarantee the ability
to copy a resource. For example, separate programs may control
resources on the same server. As a result, it may not be possible to
copy a resource to a location that appears to be on the same server.
This method is idempotent, but not safe (see Section 9.1 of
[RFC2616]). Responses to this method MUST NOT be cached.
9.8.1. COPY for Non-collection Resources
When the source resource is not a collection, the result of the COPY
method is the creation of a new resource at the destination whose
state and behavior match that of the source resource as closely as
possible. Since the environment at the destination may be different
than at the source due to factors outside the scope of control of the
server, such as the absence of resources required for correct
operation, it may not be possible to completely duplicate the
behavior of the resource at the destination. Subsequent alterations
to the destination resource will not modify the source resource.
Subsequent alterations to the source resource will not modify the
destination resource.
Dusseault Standards Track [Page 51]
RFC 4918 WebDAV June 2007
9.8.2. COPY for Properties
After a successful COPY invocation, all dead properties on the source
resource SHOULD be duplicated on the destination resource. Live
properties described in this document SHOULD be duplicated as
identically behaving live properties at the destination resource, but
not necessarily with the same values. Servers SHOULD NOT convert
live properties into dead properties on the destination resource,
because clients may then draw incorrect conclusions about the state
or functionality of a resource. Note that some live properties are
defined such that the absence of the property has a specific meaning
(e.g., a flag with one meaning if present, and the opposite if
absent), and in these cases, a successful COPY might result in the
property being reported as "Not Found" in subsequent requests.
When the destination is an unmapped URL, a COPY operation creates a
new resource much like a PUT operation does. Live properties that
are related to resource creation (such as DAV:creationdate) should
have their values set accordingly.
9.8.3. COPY for Collections
The COPY method on a collection without a Depth header MUST act as if
a Depth header with value "infinity" was included. A client may
submit a Depth header on a COPY on a collection with a value of "0"
or "infinity". Servers MUST support the "0" and "infinity" Depth
header behaviors on WebDAV-compliant resources.
An infinite-depth COPY instructs that the collection resource
identified by the Request-URI is to be copied to the location
identified by the URI in the Destination header, and all its internal
member resources are to be copied to a location relative to it,
recursively through all levels of the collection hierarchy. Note
that an infinite-depth COPY of /A/ into /A/B/ could lead to infinite
recursion if not handled correctly.
A COPY of "Depth: 0" only instructs that the collection and its
properties, but not resources identified by its internal member URLs,
are to be copied.
Any headers included with a COPY MUST be applied in processing every
resource to be copied with the exception of the Destination header.
The Destination header only specifies the destination URI for the
Request-URI. When applied to members of the collection identified by
the Request-URI, the value of Destination is to be modified to
reflect the current location in the hierarchy. So, if the Request-
URI is /a/ with Host header value http://example.com/ and the
Dusseault Standards Track [Page 52]
RFC 4918 WebDAV June 2007
Destination is http://example.com/b/, then when
http://example.com/a/c/d is processed, it must use a Destination of
http://example.com/b/c/d.
When the COPY method has completed processing, it MUST have created a
consistent URL namespace at the destination (see Section 5.1 for the
definition of namespace consistency). However, if an error occurs
while copying an internal collection, the server MUST NOT copy any
resources identified by members of this collection (i.e., the server
must skip this subtree), as this would create an inconsistent
namespace. After detecting an error, the COPY operation SHOULD try
to finish as much of the original copy operation as possible (i.e.,
the server should still attempt to copy other subtrees and their
members that are not descendants of an error-causing collection).
So, for example, if an infinite-depth copy operation is performed on
collection /a/, which contains collections /a/b/ and /a/c/, and an
error occurs copying /a/b/, an attempt should still be made to copy
/a/c/. Similarly, after encountering an error copying a non-
collection resource as part of an infinite-depth copy, the server
SHOULD try to finish as much of the original copy operation as
possible.
If an error in executing the COPY method occurs with a resource other
than the resource identified in the Request-URI, then the response
MUST be a 207 (Multi-Status), and the URL of the resource causing the
failure MUST appear with the specific error.
The 424 (Failed Dependency) status code SHOULD NOT be returned in the
207 (Multi-Status) response from a COPY method. These responses can
be safely omitted because the client will know that the progeny of a
resource could not be copied when the client receives an error for
the parent. Additionally, 201 (Created)/204 (No Content) status
codes SHOULD NOT be returned as values in 207 (Multi-Status)
responses from COPY methods. They, too, can be safely omitted
because they are the default success codes.
9.8.4. COPY and Overwriting Destination Resources
If a COPY request has an Overwrite header with a value of "F", and a
resource exists at the Destination URL, the server MUST fail the
request.
When a server executes a COPY request and overwrites a destination
resource, the exact behavior MAY depend on many factors, including
WebDAV extension capabilities (see particularly [RFC3253]). For
Dusseault Standards Track [Page 53]
RFC 4918 WebDAV June 2007
example, when an ordinary resource is overwritten, the server could
delete the target resource before doing the copy, or could do an in-
place overwrite to preserve live properties.
When a collection is overwritten, the membership of the destination
collection after the successful COPY request MUST be the same
membership as the source collection immediately before the COPY.
Thus, merging the membership of the source and destination
collections together in the destination is not a compliant behavior.
In general, if clients require the state of the destination URL to be
wiped out prior to a COPY (e.g., to force live properties to be
reset), then the client could send a DELETE to the destination before
the COPY request to ensure this reset.
9.8.5. Status Codes
In addition to the general status codes possible, the following
status codes have specific applicability to COPY:
201 (Created) - The source resource was successfully copied. The
COPY operation resulted in the creation of a new resource.
204 (No Content) - The source resource was successfully copied to a
preexisting destination resource.
207 (Multi-Status) - Multiple resources were to be affected by the
COPY, but errors on some of them prevented the operation from taking
place. Specific error messages, together with the most appropriate
of the source and destination URLs, appear in the body of the multi-
status response. For example, if a destination resource was locked
and could not be overwritten, then the destination resource URL
appears with the 423 (Locked) status.
403 (Forbidden) - The operation is forbidden. A special case for
COPY could be that the source and destination resources are the same
resource.
409 (Conflict) - A resource cannot be created at the destination
until one or more intermediate collections have been created. The
server MUST NOT create those intermediate collections automatically.
412 (Precondition Failed) - A precondition header check failed, e.g.,
the Overwrite header is "F" and the destination URL is already mapped
to a resource.
Dusseault Standards Track [Page 54]
RFC 4918 WebDAV June 2007
423 (Locked) - The destination resource, or resource within the
destination collection, was locked. This response SHOULD contain the
'lock-token-submitted' precondition element.
502 (Bad Gateway) - This may occur when the destination is on another
server, repository, or URL namespace. Either the source namespace
does not support copying to the destination namespace, or the
destination namespace refuses to accept the resource. The client may
wish to try GET/PUT and PROPFIND/PROPPATCH instead.
507 (Insufficient Storage) - The destination resource does not have
sufficient space to record the state of the resource after the
execution of this method.
9.8.6. Example - COPY with Overwrite
This example shows resource
http://www.example.com/~fielding/index.html being copied to the
location http://www.example.com/users/f/fielding/index.html. The 204
(No Content) status code indicates that the existing resource at the
destination was overwritten.
>>Request
COPY /~fielding/index.html HTTP/1.1
Host: www.example.com
Destination: http://www.example.com/users/f/fielding/index.html
>>Response
HTTP/1.1 204 No Content
9.8.7. Example - COPY with No Overwrite
The following example shows the same copy operation being performed,
but with the Overwrite header set to "F." A response of 412
(Precondition Failed) is returned because the destination URL is
already mapped to a resource.
>>Request
COPY /~fielding/index.html HTTP/1.1
Host: www.example.com
Destination: http://www.example.com/users/f/fielding/index.html
Overwrite: F
Dusseault Standards Track [Page 55]
RFC 4918 WebDAV June 2007
>>Response
HTTP/1.1 412 Precondition Failed
9.8.8. Example - COPY of a Collection
>>Request
COPY /container/ HTTP/1.1
Host: www.example.com
Destination: http://www.example.com/othercontainer/
Depth: infinity
>>Response
HTTP/1.1 207 Multi-Status
Content-Type: application/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<d:multistatus xmlns:d="DAV:">
<d:response>
<d:href>http://www.example.com/othercontainer/R2/</d:href>
<d:status>HTTP/1.1 423 Locked</d:status>
<d:error><d:lock-token-submitted/></d:error>
</d:response>
</d:multistatus>
The Depth header is unnecessary as the default behavior of COPY on a
collection is to act as if a "Depth: infinity" header had been
submitted. In this example, most of the resources, along with the
collection, were copied successfully. However, the collection R2
failed because the destination R2 is locked. Because there was an
error copying R2, none of R2's members were copied. However, no
errors were listed for those members due to the error minimization
rules.
9.9. MOVE Method
The MOVE operation on a non-collection resource is the logical
equivalent of a copy (COPY), followed by consistency maintenance
processing, followed by a delete of the source, where all three
actions are performed in a single operation. The consistency
maintenance step allows the server to perform updates caused by the
move, such as updating all URLs, other than the Request-URI that
identifies the source resource, to point to the new destination
resource.
Dusseault Standards Track [Page 56]
RFC 4918 WebDAV June 2007
The Destination header MUST be present on all MOVE methods and MUST
follow all COPY requirements for the COPY part of the MOVE method.
All WebDAV-compliant resources MUST support the MOVE method.
Support for the MOVE method does not guarantee the ability to move a
resource to a particular destination. For example, separate programs
may actually control different sets of resources on the same server.
Therefore, it may not be possible to move a resource within a
namespace that appears to belong to the same server.
If a resource exists at the destination, the destination resource
will be deleted as a side-effect of the MOVE operation, subject to
the restrictions of the Overwrite header.
This method is idempotent, but not safe (see Section 9.1 of
[RFC2616]). Responses to this method MUST NOT be cached.
9.9.1. MOVE for Properties
Live properties described in this document SHOULD be moved along with
the resource, such that the resource has identically behaving live
properties at the destination resource, but not necessarily with the
same values. Note that some live properties are defined such that
the absence of the property has a specific meaning (e.g., a flag with
one meaning if present, and the opposite if absent), and in these
cases, a successful MOVE might result in the property being reported
as "Not Found" in subsequent requests. If the live properties will
not work the same way at the destination, the server MAY fail the
request.
MOVE is frequently used by clients to rename a file without changing
its parent collection, so it's not appropriate to reset all live
properties that are set at resource creation. For example, the DAV:
creationdate property value SHOULD remain the same after a MOVE.
Dead properties MUST be moved along with the resource.
9.9.2. MOVE for Collections
A MOVE with "Depth: infinity" instructs that the collection
identified by the Request-URI be moved to the address specified in
the Destination header, and all resources identified by its internal
member URLs are to be moved to locations relative to it, recursively
through all levels of the collection hierarchy.
The MOVE method on a collection MUST act as if a "Depth: infinity"
header was used on it. A client MUST NOT submit a Depth header on a
MOVE on a collection with any value but "infinity".
Dusseault Standards Track [Page 57]
RFC 4918 WebDAV June 2007
Any headers included with MOVE MUST be applied in processing every
resource to be moved with the exception of the Destination header.
The behavior of the Destination header is the same as given for COPY
on collections.
When the MOVE method has completed processing, it MUST have created a
consistent URL namespace at both the source and destination (see
Section 5.1 for the definition of namespace consistency). However,
if an error occurs while moving an internal collection, the server
MUST NOT move any resources identified by members of the failed
collection (i.e., the server must skip the error-causing subtree), as
this would create an inconsistent namespace. In this case, after
detecting the error, the move operation SHOULD try to finish as much
of the original move as possible (i.e., the server should still
attempt to move other subtrees and the resources identified by their
members that are not descendants of an error-causing collection).
So, for example, if an infinite-depth move is performed on collection
/a/, which contains collections /a/b/ and /a/c/, and an error occurs
moving /a/b/, an attempt should still be made to try moving /a/c/.
Similarly, after encountering an error moving a non-collection
resource as part of an infinite-depth move, the server SHOULD try to
finish as much of the original move operation as possible.
If an error occurs with a resource other than the resource identified
in the Request-URI, then the response MUST be a 207 (Multi-Status),
and the errored resource's URL MUST appear with the specific error.
The 424 (Failed Dependency) status code SHOULD NOT be returned in the
207 (Multi-Status) response from a MOVE method. These errors can be
safely omitted because the client will know that the progeny of a
resource could not be moved when the client receives an error for the
parent. Additionally, 201 (Created)/204 (No Content) responses
SHOULD NOT be returned as values in 207 (Multi-Status) responses from
a MOVE. These responses can be safely omitted because they are the
default success codes.
9.9.3. MOVE and the Overwrite Header
If a resource exists at the destination and the Overwrite header is
"T", then prior to performing the move, the server MUST perform a
DELETE with "Depth: infinity" on the destination resource. If the
Overwrite header is set to "F", then the operation will fail.
Dusseault Standards Track [Page 58]
RFC 4918 WebDAV June 2007
9.9.4. Status Codes
In addition to the general status codes possible, the following
status codes have specific applicability to MOVE:
201 (Created) - The source resource was successfully moved, and a new
URL mapping was created at the destination.
204 (No Content) - The source resource was successfully moved to a
URL that was already mapped.
207 (Multi-Status) - Multiple resources were to be affected by the
MOVE, but errors on some of them prevented the operation from taking
place. Specific error messages, together with the most appropriate
of the source and destination URLs, appear in the body of the multi-
status response. For example, if a source resource was locked and
could not be moved, then the source resource URL appears with the 423
(Locked) status.
403 (Forbidden) - Among many possible reasons for forbidding a MOVE
operation, this status code is recommended for use when the source
and destination resources are the same.
409 (Conflict) - A resource cannot be created at the destination
until one or more intermediate collections have been created. The
server MUST NOT create those intermediate collections automatically.
Or, the server was unable to preserve the behavior of the live
properties and still move the resource to the destination (see
'preserved-live-properties' postcondition).
412 (Precondition Failed) - A condition header failed. Specific to
MOVE, this could mean that the Overwrite header is "F" and the
destination URL is already mapped to a resource.
423 (Locked) - The source or the destination resource, the source or
destination resource parent, or some resource within the source or
destination collection, was locked. This response SHOULD contain the
'lock-token-submitted' precondition element.
502 (Bad Gateway) - This may occur when the destination is on another
server and the destination server refuses to accept the resource.
This could also occur when the destination is on another sub-section
of the same server namespace.
Dusseault Standards Track [Page 59]
RFC 4918 WebDAV June 2007
9.9.5. Example - MOVE of a Non-Collection
This example shows resource
http://www.example.com/~fielding/index.html being moved to the
location http://www.example.com/users/f/fielding/index.html. The
contents of the destination resource would have been overwritten if
the destination URL was already mapped to a resource. In this case,
since there was nothing at the destination resource, the response
code is 201 (Created).
>>Request
MOVE /~fielding/index.html HTTP/1.1
Host: www.example.com
Destination: http://www.example/users/f/fielding/index.html
>>Response
HTTP/1.1 201 Created
Location: http://www.example.com/users/f/fielding/index.html
9.9.6. Example - MOVE of a Collection
>>Request
MOVE /container/ HTTP/1.1
Host: www.example.com
Destination: http://www.example.com/othercontainer/
Overwrite: F
If: (<urn:uuid:fe184f2e-6eec-41d0-c765-01adc56e6bb4>)
(<urn:uuid:e454f3f3-acdc-452a-56c7-00a5c91e4b77>)
>>Response
HTTP/1.1 207 Multi-Status
Content-Type: application/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<d:multistatus xmlns:d='DAV:'>
<d:response>
<d:href>http://www.example.com/othercontainer/C2/</d:href>
<d:status>HTTP/1.1 423 Locked</d:status>
<d:error><d:lock-token-submitted/></d:error>
</d:response>
</d:multistatus>
Dusseault Standards Track [Page 60]
RFC 4918 WebDAV June 2007
In this example, the client has submitted a number of lock tokens
with the request. A lock token will need to be submitted for every
resource, both source and destination, anywhere in the scope of the
method, that is locked. In this case, the proper lock token was not
submitted for the destination
http://www.example.com/othercontainer/C2/. This means that the
resource /container/C2/ could not be moved. Because there was an
error moving /container/C2/, none of /container/C2's members were
moved. However, no errors were listed for those members due to the
error minimization rules. User agent authentication has previously
occurred via a mechanism outside the scope of the HTTP protocol, in
an underlying transport layer.
9.10. LOCK Method
The following sections describe the LOCK method, which is used to
take out a lock of any access type and to refresh an existing lock.
These sections on the LOCK method describe only those semantics that
are specific to the LOCK method and are independent of the access
type of the lock being requested.
Any resource that supports the LOCK method MUST, at minimum, support
the XML request and response formats defined herein.
This method is neither idempotent nor safe (see Section 9.1 of
[RFC2616]). Responses to this method MUST NOT be cached.
9.10.1. Creating a Lock on an Existing Resource
A LOCK request to an existing resource will create a lock on the
resource identified by the Request-URI, provided the resource is not
already locked with a conflicting lock. The resource identified in
the Request-URI becomes the root of the lock. LOCK method requests
to create a new lock MUST have an XML request body. The server MUST
preserve the information provided by the client in the 'owner'
element in the LOCK request. The LOCK request MAY have a Timeout
header.
When a new lock is created, the LOCK response:
o MUST contain a body with the value of the DAV:lockdiscovery
property in a prop XML element. This MUST contain the full
information about the lock just granted, while information about
other (shared) locks is OPTIONAL.
o MUST include the Lock-Token response header with the token
associated with the new lock.
Dusseault Standards Track [Page 61]
RFC 4918 WebDAV June 2007
9.10.2. Refreshing Locks
A lock is refreshed by sending a LOCK request to the URL of a
resource within the scope of the lock. This request MUST NOT have a
body and it MUST specify which lock to refresh by using the 'If'
header with a single lock token (only one lock may be refreshed at a
time). The request MAY contain a Timeout header, which a server MAY
accept to change the duration remaining on the lock to the new value.
A server MUST ignore the Depth header on a LOCK refresh.
If the resource has other (shared) locks, those locks are unaffected
by a lock refresh. Additionally, those locks do not prevent the
named lock from being refreshed.
The Lock-Token header is not returned in the response for a
successful refresh LOCK request, but the LOCK response body MUST
contain the new value for the DAV:lockdiscovery property.
9.10.3. Depth and Locking
The Depth header may be used with the LOCK method. Values other than
0 or infinity MUST NOT be used with the Depth header on a LOCK
method. All resources that support the LOCK method MUST support the
Depth header.
A Depth header of value 0 means to just lock the resource specified
by the Request-URI.
If the Depth header is set to infinity, then the resource specified
in the Request-URI along with all its members, all the way down the
hierarchy, are to be locked. A successful result MUST return a
single lock token. Similarly, if an UNLOCK is successfully executed
on this token, all associated resources are unlocked. Hence, partial
success is not an option for LOCK or UNLOCK. Either the entire
hierarchy is locked or no resources are locked.
If the lock cannot be granted to all resources, the server MUST
return a Multi-Status response with a 'response' element for at least
one resource that prevented the lock from being granted, along with a
suitable status code for that failure (e.g., 403 (Forbidden) or 423
(Locked)). Additionally, if the resource causing the failure was not
the resource requested, then the server SHOULD include a 'response'
element for the Request-URI as well, with a 'status' element
containing 424 Failed Dependency.
If no Depth header is submitted on a LOCK request, then the request
MUST act as if a "Depth:infinity" had been submitted.
Dusseault Standards Track [Page 62]
RFC 4918 WebDAV June 2007
9.10.4. Locking Unmapped URLs
A successful LOCK method MUST result in the creation of an empty
resource that is locked (and that is not a collection) when a
resource did not previously exist at that URL. Later on, the lock
may go away but the empty resource remains. Empty resources MUST
then appear in PROPFIND responses including that URL in the response
scope. A server MUST respond successfully to a GET request to an
empty resource, either by using a 204 No Content response, or by
using 200 OK with a Content-Length header indicating zero length
9.10.5. Lock Compatibility Table
The table below describes the behavior that occurs when a lock
request is made on a resource.
+--------------------------+----------------+-------------------+
| Current State | Shared Lock OK | Exclusive Lock OK |
+--------------------------+----------------+-------------------+
| None | True | True |
| Shared Lock | True | False |
| Exclusive Lock | False | False* |
+--------------------------+----------------+-------------------+
Legend: True = lock may be granted. False = lock MUST NOT be
granted. *=It is illegal for a principal to request the same lock
twice.
The current lock state of a resource is given in the leftmost column,
and lock requests are listed in the first row. The intersection of a
row and column gives the result of a lock request. For example, if a
shared lock is held on a resource, and an exclusive lock is
requested, the table entry is "false", indicating that the lock must
not be granted.
9.10.6. LOCK Responses
In addition to the general status codes possible, the following
status codes have specific applicability to LOCK:
200 (OK) - The LOCK request succeeded and the value of the DAV:
lockdiscovery property is included in the response body.
201 (Created) - The LOCK request was to an unmapped URL, the request
succeeded and resulted in the creation of a new resource, and the
value of the DAV:lockdiscovery property is included in the response
body.
Dusseault Standards Track [Page 63]
RFC 4918 WebDAV June 2007
409 (Conflict) - A resource cannot be created at the destination
until one or more intermediate collections have been created. The
server MUST NOT create those intermediate collections automatically.
423 (Locked), potentially with 'no-conflicting-lock' precondition
code - There is already a lock on the resource that is not compatible
with the requested lock (see lock compatibility table above).
412 (Precondition Failed), with 'lock-token-matches-request-uri'
precondition code - The LOCK request was made with an If header,
indicating that the client wishes to refresh the given lock.
However, the Request-URI did not fall within the scope of the lock
identified by the token. The lock may have a scope that does not
include the Request-URI, or the lock could have disappeared, or the
token may be invalid.
9.10.7. Example - Simple Lock Request
>>Request
LOCK /workspace/webdav/proposal.doc HTTP/1.1
Host: example.com
Timeout: Infinite, Second-4100000000
Content-Type: application/xml; charset="utf-8"
Content-Length: xxxx
Authorization: Digest username="ejw",
realm="ejw@example.com", nonce="...",
uri="/workspace/webdav/proposal.doc",
response="...", opaque="..."
<?xml version="1.0" encoding="utf-8" ?>
<D:lockinfo xmlns:D='DAV:'>
<D:lockscope><D:exclusive/></D:lockscope>
<D:locktype><D:write/></D:locktype>
<D:owner>
<D:href>http://example.org/~ejw/contact.html</D:href>
</D:owner>
</D:lockinfo>
>>Response
HTTP/1.1 200 OK
Lock-Token: <urn:uuid:e71d4fae-5dec-22d6-fea5-00a0c91e6be4>
Content-Type: application/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<D:prop xmlns:D="DAV:">
Dusseault Standards Track [Page 64]
RFC 4918 WebDAV June 2007
<D:lockdiscovery>
<D:activelock>
<D:locktype><D:write/></D:locktype>
<D:lockscope><D:exclusive/></D:lockscope>
<D:depth>infinity</D:depth>
<D:owner>
<D:href>http://example.org/~ejw/contact.html</D:href>
</D:owner>
<D:timeout>Second-604800</D:timeout>
<D:locktoken>
<D:href
>urn:uuid:e71d4fae-5dec-22d6-fea5-00a0c91e6be4</D:href>
</D:locktoken>
<D:lockroot>
<D:href
>http://example.com/workspace/webdav/proposal.doc</D:href>
</D:lockroot>
</D:activelock>
</D:lockdiscovery>
</D:prop>
This example shows the successful creation of an exclusive write lock
on resource http://example.com/workspace/webdav/proposal.doc. The
resource http://example.org/~ejw/contact.html contains contact
information for the creator of the lock. The server has an activity-
based timeout policy in place on this resource, which causes the lock
to automatically be removed after 1 week (604800 seconds). Note that
the nonce, response, and opaque fields have not been calculated in
the Authorization request header.
9.10.8. Example - Refreshing a Write Lock
>>Request
LOCK /workspace/webdav/proposal.doc HTTP/1.1
Host: example.com
Timeout: Infinite, Second-4100000000
If: (<urn:uuid:e71d4fae-5dec-22d6-fea5-00a0c91e6be4>)
Authorization: Digest username="ejw",
realm="ejw@example.com", nonce="...",
uri="/workspace/webdav/proposal.doc",
response="...", opaque="..."
Dusseault Standards Track [Page 65]
RFC 4918 WebDAV June 2007
>>Response
HTTP/1.1 200 OK
Content-Type: application/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<D:prop xmlns:D="DAV:">
<D:lockdiscovery>
<D:activelock>
<D:locktype><D:write/></D:locktype>
<D:lockscope><D:exclusive/></D:lockscope>
<D:depth>infinity</D:depth>
<D:owner>
<D:href>http://example.org/~ejw/contact.html</D:href>
</D:owner>
<D:timeout>Second-604800</D:timeout>
<D:locktoken>
<D:href
>urn:uuid:e71d4fae-5dec-22d6-fea5-00a0c91e6be4</D:href>
</D:locktoken>
<D:lockroot>
<D:href
>http://example.com/workspace/webdav/proposal.doc</D:href>
</D:lockroot>
</D:activelock>
</D:lockdiscovery>
</D:prop>
This request would refresh the lock, attempting to reset the timeout
to the new value specified in the timeout header. Notice that the
client asked for an infinite time out but the server choose to ignore
the request. In this example, the nonce, response, and opaque fields
have not been calculated in the Authorization request header.
9.10.9. Example - Multi-Resource Lock Request
>>Request
LOCK /webdav/ HTTP/1.1
Host: example.com
Timeout: Infinite, Second-4100000000
Depth: infinity
Content-Type: application/xml; charset="utf-8"
Content-Length: xxxx
Authorization: Digest username="ejw",
realm="ejw@example.com", nonce="...",
Dusseault Standards Track [Page 66]
RFC 4918 WebDAV June 2007
uri="/workspace/webdav/proposal.doc",
response="...", opaque="..."
<?xml version="1.0" encoding="utf-8" ?>
<D:lockinfo xmlns:D="DAV:">
<D:locktype><D:write/></D:locktype>
<D:lockscope><D:exclusive/></D:lockscope>
<D:owner>
<D:href>http://example.org/~ejw/contact.html</D:href>
</D:owner>
</D:lockinfo>
>>Response
HTTP/1.1 207 Multi-Status
Content-Type: application/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<D:multistatus xmlns:D="DAV:">
<D:response>
<D:href>http://example.com/webdav/secret</D:href>
<D:status>HTTP/1.1 403 Forbidden</D:status>
</D:response>
<D:response>
<D:href>http://example.com/webdav/</D:href>
<D:status>HTTP/1.1 424 Failed Dependency</D:status>
</D:response>
</D:multistatus>
This example shows a request for an exclusive write lock on a
collection and all its children. In this request, the client has
specified that it desires an infinite-length lock, if available,
otherwise a timeout of 4.1 billion seconds, if available. The
request entity body contains the contact information for the
principal taking out the lock -- in this case, a Web page URL.
The error is a 403 (Forbidden) response on the resource
http://example.com/webdav/secret. Because this resource could not be
locked, none of the resources were locked. Note also that the a
'response' element for the Request-URI itself has been included as
required.
In this example, the nonce, response, and opaque fields have not been
calculated in the Authorization request header.
Dusseault Standards Track [Page 67]
RFC 4918 WebDAV June 2007
9.11. UNLOCK Method
The UNLOCK method removes the lock identified by the lock token in
the Lock-Token request header. The Request-URI MUST identify a
resource within the scope of the lock.
Note that use of the Lock-Token header to provide the lock token is
not consistent with other state-changing methods, which all require
an If header with the lock token. Thus, the If header is not needed
to provide the lock token. Naturally, when the If header is present,
it has its normal meaning as a conditional header.
For a successful response to this method, the server MUST delete the
lock entirely.
If all resources that have been locked under the submitted lock token
cannot be unlocked, then the UNLOCK request MUST fail.
A successful response to an UNLOCK method does not mean that the
resource is necessarily unlocked. It means that the specific lock
corresponding to the specified token no longer exists.
Any DAV-compliant resource that supports the LOCK method MUST support
the UNLOCK method.
This method is idempotent, but not safe (see Section 9.1 of
[RFC2616]). Responses to this method MUST NOT be cached.
9.11.1. Status Codes
In addition to the general status codes possible, the following
status codes have specific applicability to UNLOCK:
204 (No Content) - Normal success response (rather than 200 OK, since
200 OK would imply a response body, and an UNLOCK success response
does not normally contain a body).
400 (Bad Request) - No lock token was provided.
403 (Forbidden) - The currently authenticated principal does not have
permission to remove the lock.
409 (Conflict), with 'lock-token-matches-request-uri' precondition -
The resource was not locked, or the request was made to a Request-URI
that was not within the scope of the lock.
Dusseault Standards Track [Page 68]
RFC 4918 WebDAV June 2007
9.11.2. Example - UNLOCK
>>Request
UNLOCK /workspace/webdav/info.doc HTTP/1.1
Host: example.com
Lock-Token: <urn:uuid:a515cfa4-5da4-22e1-f5b5-00a0451e6bf7>
Authorization: Digest username="ejw"
realm="ejw@example.com", nonce="...",
uri="/workspace/webdav/proposal.doc",
response="...", opaque="..."
>>Response
HTTP/1.1 204 No Content
In this example, the lock identified by the lock token
"urn:uuid:a515cfa4-5da4-22e1-f5b5-00a0451e6bf7" is successfully
removed from the resource
http://example.com/workspace/webdav/info.doc. If this lock included
more than just one resource, the lock is removed from all resources
included in the lock.
In this example, the nonce, response, and opaque fields have not been
calculated in the Authorization request header.
10. HTTP Headers for Distributed Authoring
All DAV headers follow the same basic formatting rules as HTTP
headers. This includes rules like line continuation and how to
combine (or separate) multiple instances of the same header using
commas.
WebDAV adds two new conditional headers to the set defined in HTTP:
the If and Overwrite headers.
10.1. DAV Header
DAV = "DAV" ":" #( compliance-class )
compliance-class = ( "1" | "2" | "3" | extend )
extend = Coded-URL | token
; token is defined in RFC 2616, Section 2.2
Coded-URL = "<" absolute-URI ">"
; No linear whitespace (LWS) allowed in Coded-URL
; absolute-URI defined in RFC 3986, Section 4.3
Dusseault Standards Track [Page 69]
RFC 4918 WebDAV June 2007
This general-header appearing in the response indicates that the
resource supports the DAV schema and protocol as specified. All DAV-
compliant resources MUST return the DAV header with compliance-class
"1" on all OPTIONS responses. In cases where WebDAV is only
supported in part of the server namespace, an OPTIONS request to non-
WebDAV resources (including "/") SHOULD NOT advertise WebDAV support.
The value is a comma-separated list of all compliance class
identifiers that the resource supports. Class identifiers may be
Coded-URLs or tokens (as defined by [RFC2616]). Identifiers can
appear in any order. Identifiers that are standardized through the
IETF RFC process are tokens, but other identifiers SHOULD be Coded-
URLs to encourage uniqueness.
A resource must show class 1 compliance if it shows class 2 or 3
compliance. In general, support for one compliance class does not
entail support for any other, and in particular, support for
compliance class 3 does not require support for compliance class 2.
Please refer to Section 18 for more details on compliance classes
defined in this specification.
Note that many WebDAV servers do not advertise WebDAV support in
response to "OPTIONS *".
As a request header, this header allows the client to advertise
compliance with named features when the server needs that
information. Clients SHOULD NOT send this header unless a standards
track specification requires it. Any extension that makes use of
this as a request header will need to carefully consider caching
implications.
10.2. Depth Header
Depth = "Depth" ":" ("0" | "1" | "infinity")
The Depth request header is used with methods executed on resources
that could potentially have internal members to indicate whether the
method is to be applied only to the resource ("Depth: 0"), to the
resource and its internal members only ("Depth: 1"), or the resource
and all its members ("Depth: infinity").
The Depth header is only supported if a method's definition
explicitly provides for such support.
The following rules are the default behavior for any method that
supports the Depth header. A method may override these defaults by
defining different behavior in its definition.
Dusseault Standards Track [Page 70]
RFC 4918 WebDAV June 2007
Methods that support the Depth header may choose not to support all
of the header's values and may define, on a case-by-case basis, the
behavior of the method if a Depth header is not present. For
example, the MOVE method only supports "Depth: infinity", and if a
Depth header is not present, it will act as if a "Depth: infinity"
header had been applied.
Clients MUST NOT rely upon methods executing on members of their
hierarchies in any particular order or on the execution being atomic
unless the particular method explicitly provides such guarantees.
Upon execution, a method with a Depth header will perform as much of
its assigned task as possible and then return a response specifying
what it was able to accomplish and what it failed to do.
So, for example, an attempt to COPY a hierarchy may result in some of
the members being copied and some not.
By default, the Depth header does not interact with other headers.
That is, each header on a request with a Depth header MUST be applied
only to the Request-URI if it applies to any resource, unless
specific Depth behavior is defined for that header.
If a source or destination resource within the scope of the Depth
header is locked in such a way as to prevent the successful execution
of the method, then the lock token for that resource MUST be
submitted with the request in the If request header.
The Depth header only specifies the behavior of the method with
regards to internal members. If a resource does not have internal
members, then the Depth header MUST be ignored.
10.3. Destination Header
The Destination request header specifies the URI that identifies a
destination resource for methods such as COPY and MOVE, which take
two URIs as parameters.
Destination = "Destination" ":" Simple-ref
If the Destination value is an absolute-URI (Section 4.3 of
[RFC3986]), it may name a different server (or different port or
scheme). If the source server cannot attempt a copy to the remote
server, it MUST fail the request. Note that copying and moving
resources to remote servers is not fully defined in this
specification (e.g., specific error conditions).
Dusseault Standards Track [Page 71]
RFC 4918 WebDAV June 2007
If the Destination value is too long or otherwise unacceptable, the
server SHOULD return 400 (Bad Request), ideally with helpful
information in an error body.
10.4. If Header
The If request header is intended to have similar functionality to
the If-Match header defined in Section 14.24 of [RFC2616]. However,
the If header handles any state token as well as ETags. A typical
example of a state token is a lock token, and lock tokens are the
only state tokens defined in this specification.
10.4.1. Purpose
The If header has two distinct purposes:
o The first purpose is to make a request conditional by supplying a
series of state lists with conditions that match tokens and ETags
to a specific resource. If this header is evaluated and all state
lists fail, then the request MUST fail with a 412 (Precondition
Failed) status. On the other hand, the request can succeed only
if one of the described state lists succeeds. The success
criteria for state lists and matching functions are defined in
Sections 10.4.3 and 10.4.4.
o Additionally, the mere fact that a state token appears in an If
header means that it has been "submitted" with the request. In
general, this is used to indicate that the client has knowledge of
that state token. The semantics for submitting a state token
depend on its type (for lock tokens, please refer to Section 6).
Note that these two purposes need to be treated distinctly: a state
token counts as being submitted independently of whether the server
actually has evaluated the state list it appears in, and also
independently of whether or not the condition it expressed was found
to be true.
10.4.2. Syntax
If = "If" ":" ( 1*No-tag-list | 1*Tagged-list )
No-tag-list = List
Tagged-list = Resource-Tag 1*List
List = "(" 1*Condition ")"
Condition = ["Not"] (State-token | "[" entity-tag "]")
; entity-tag: see Section 3.11 of [RFC2616]
; No LWS allowed between "[", entity-tag and "]"
Dusseault Standards Track [Page 72]
RFC 4918 WebDAV June 2007
State-token = Coded-URL
Resource-Tag = "<" Simple-ref ">"
; Simple-ref: see Section 8.3
; No LWS allowed in Resource-Tag
The syntax distinguishes between untagged lists ("No-tag-list") and
tagged lists ("Tagged-list"). Untagged lists apply to the resource
identified by the Request-URI, while tagged lists apply to the
resource identified by the preceding Resource-Tag.
A Resource-Tag applies to all subsequent Lists, up to the next
Resource-Tag.
Note that the two list types cannot be mixed within an If header.
This is not a functional restriction because the No-tag-list syntax
is just a shorthand notation for a Tagged-list production with a
Resource-Tag referring to the Request-URI.
Each List consists of one or more Conditions. Each Condition is
defined in terms of an entity-tag or state-token, potentially negated
by the prefix "Not".
Note that the If header syntax does not allow multiple instances of
If headers in a single request. However, the HTTP header syntax
allows extending single header values across multiple lines, by
inserting a line break followed by whitespace (see [RFC2616], Section
4.2).
10.4.3. List Evaluation
A Condition that consists of a single entity-tag or state-token
evaluates to true if the resource matches the described state (where
the individual matching functions are defined below in
Section 10.4.4). Prefixing it with "Not" reverses the result of the
evaluation (thus, the "Not" applies only to the subsequent entity-tag
or state-token).
Each List production describes a series of conditions. The whole
list evaluates to true if and only if each condition evaluates to
true (that is, the list represents a logical conjunction of
Conditions).
Each No-tag-list and Tagged-list production may contain one or more
Lists. They evaluate to true if and only if any of the contained
lists evaluates to true (that is, if there's more than one List, that
List sequence represents a logical disjunction of the Lists).
Dusseault Standards Track [Page 73]
RFC 4918 WebDAV June 2007
Finally, the whole If header evaluates to true if and only if at
least one of the No-tag-list or Tagged-list productions evaluates to
true. If the header evaluates to false, the server MUST reject the
request with a 412 (Precondition Failed) status. Otherwise,
execution of the request can proceed as if the header wasn't present.
10.4.4. Matching State Tokens and ETags
When performing If header processing, the definition of a matching
state token or entity tag is as follows:
Identifying a resource: The resource is identified by the URI along
with the token, in tagged list production, or by the Request-URI in
untagged list production.
Matching entity tag: Where the entity tag matches an entity tag
associated with the identified resource. Servers MUST use either the
weak or the strong comparison function defined in Section 13.3.3 of
[RFC2616].
Matching state token: Where there is an exact match between the state
token in the If header and any state token on the identified
resource. A lock state token is considered to match if the resource
is anywhere in the scope of the lock.
Handling unmapped URLs: For both ETags and state tokens, treat as if
the URL identified a resource that exists but does not have the
specified state.
10.4.5. If Header and Non-DAV-Aware Proxies
Non-DAV-aware proxies will not honor the If header, since they will
not understand the If header, and HTTP requires non-understood
headers to be ignored. When communicating with HTTP/1.1 proxies, the
client MUST use the "Cache-Control: no-cache" request header so as to
prevent the proxy from improperly trying to service the request from
its cache. When dealing with HTTP/1.0 proxies, the "Pragma: no-
cache" request header MUST be used for the same reason.
Because in general clients may not be able to reliably detect non-
DAV-aware intermediates, they are advised to always prevent caching
using the request directives mentioned above.
Dusseault Standards Track [Page 74]
RFC 4918 WebDAV June 2007
10.4.6. Example - No-tag Production
If: (<urn:uuid:181d4fae-7d8c-11d0-a765-00a0c91e6bf2>
["I am an ETag"])
(["I am another ETag"])
The previous header would require that the resource identified in the
Request-URI be locked with the specified lock token and be in the
state identified by the "I am an ETag" ETag or in the state
identified by the second ETag "I am another ETag".
To put the matter more plainly one can think of the previous If
header as expressing the condition below:
(
is-locked-with(urn:uuid:181d4fae-7d8c-11d0-a765-00a0c91e6bf2) AND
matches-etag("I am an ETag")
)
OR
(
matches-etag("I am another ETag")
)
10.4.7. Example - Using "Not" with No-tag Production
If: (Not <urn:uuid:181d4fae-7d8c-11d0-a765-00a0c91e6bf2>
<urn:uuid:58f202ac-22cf-11d1-b12d-002035b29092>)
This If header requires that the resource must not be locked with a
lock having the lock token
urn:uuid:181d4fae-7d8c-11d0-a765-00a0c91e6bf2 and must be locked by a
lock with the lock token
urn:uuid:58f202ac-22cf-11d1-b12d-002035b29092.
10.4.8. Example - Causing a Condition to Always Evaluate to True
There may be cases where a client wishes to submit state tokens, but
doesn't want the request to fail just because the state token isn't
current anymore. One simple way to do this is to include a Condition
that is known to always evaluate to true, such as in:
If: (<urn:uuid:181d4fae-7d8c-11d0-a765-00a0c91e6bf2>)
(Not <DAV:no-lock>)
"DAV:no-lock" is known to never represent a current lock token. Lock
tokens are assigned by the server, following the uniqueness
requirements described in Section 6.5, therefore cannot use the
"DAV:" scheme. Thus, by applying "Not" to a state token that is
Dusseault Standards Track [Page 75]
RFC 4918 WebDAV June 2007
known not to be current, the Condition always evaluates to true.
Consequently, the whole If header will always evaluate to true, and
the lock token urn:uuid:181d4fae-7d8c-11d0-a765-00a0c91e6bf2 will be
submitted in any case.
10.4.9. Example - Tagged List If Header in COPY
>>Request
COPY /resource1 HTTP/1.1
Host: www.example.com
Destination: /resource2
If: </resource1>
(<urn:uuid:181d4fae-7d8c-11d0-a765-00a0c91e6bf2>
[W/"A weak ETag"]) (["strong ETag"])
In this example, http://www.example.com/resource1 is being copied to
http://www.example.com/resource2. When the method is first applied
to http://www.example.com/resource1, resource1 must be in the state
specified by "(<urn:uuid:181d4fae-7d8c-11d0-a765-00a0c91e6bf2> [W/"A
weak ETag"]) (["strong ETag"])". That is, either it must be locked
with a lock token of "urn:uuid:181d4fae-7d8c-11d0-a765-00a0c91e6bf2"
and have a weak entity tag W/"A weak ETag" or it must have a strong
entity tag "strong ETag".
10.4.10. Example - Matching Lock Tokens with Collection Locks
DELETE /specs/rfc2518.txt HTTP/1.1
Host: www.example.com
If: <http://www.example.com/specs/>
(<urn:uuid:181d4fae-7d8c-11d0-a765-00a0c91e6bf2>)
For this example, the lock token must be compared to the identified
resource, which is the 'specs' collection identified by the URL in
the tagged list production. If the 'specs' collection is not locked
by a lock with the specified lock token, the request MUST fail.
Otherwise, this request could succeed, because the If header
evaluates to true, and because the lock token for the lock affecting
the affected resource has been submitted.
10.4.11. Example - Matching ETags on Unmapped URLs
Consider a collection "/specs" that does not contain the member
"/specs/rfc2518.doc". In this case, the If header
If: </specs/rfc2518.doc> (["4217"])
Dusseault Standards Track [Page 76]
RFC 4918 WebDAV June 2007
will evaluate to false (the URI isn't mapped, thus the resource
identified by the URI doesn't have an entity matching the ETag
"4217").
On the other hand, an If header of
If: </specs/rfc2518.doc> (Not ["4217"])
will consequently evaluate to true.
Note that, as defined above in Section 10.4.4, the same
considerations apply to matching state tokens.
10.5. Lock-Token Header
Lock-Token = "Lock-Token" ":" Coded-URL
The Lock-Token request header is used with the UNLOCK method to
identify the lock to be removed. The lock token in the Lock-Token
request header MUST identify a lock that contains the resource
identified by Request-URI as a member.
The Lock-Token response header is used with the LOCK method to
indicate the lock token created as a result of a successful LOCK
request to create a new lock.
10.6. Overwrite Header
Overwrite = "Overwrite" ":" ("T" | "F")
The Overwrite request header specifies whether the server should
overwrite a resource mapped to the destination URL during a COPY or
MOVE. A value of "F" states that the server must not perform the
COPY or MOVE operation if the destination URL does map to a resource.
If the overwrite header is not included in a COPY or MOVE request,
then the resource MUST treat the request as if it has an overwrite
header of value "T". While the Overwrite header appears to duplicate
the functionality of using an "If-Match: *" header (see [RFC2616]),
If-Match applies only to the Request-URI, and not to the Destination
of a COPY or MOVE.
If a COPY or MOVE is not performed due to the value of the Overwrite
header, the method MUST fail with a 412 (Precondition Failed) status
code. The server MUST do authorization checks before checking this
or any conditional header.
All DAV-compliant resources MUST support the Overwrite header.
Dusseault Standards Track [Page 77]
RFC 4918 WebDAV June 2007
10.7. Timeout Request Header
TimeOut = "Timeout" ":" 1#TimeType
TimeType = ("Second-" DAVTimeOutVal | "Infinite")
; No LWS allowed within TimeType
DAVTimeOutVal = 1*DIGIT
Clients MAY include Timeout request headers in their LOCK requests.
However, the server is not required to honor or even consider these
requests. Clients MUST NOT submit a Timeout request header with any
method other than a LOCK method.
The "Second" TimeType specifies the number of seconds that will
elapse between granting of the lock at the server, and the automatic
removal of the lock. The timeout value for TimeType "Second" MUST
NOT be greater than 2^32-1.
See Section 6.6 for a description of lock timeout behavior.
11. Status Code Extensions to HTTP/1.1
The following status codes are added to those defined in HTTP/1.1
[RFC2616].
11.1. 207 Multi-Status
The 207 (Multi-Status) status code provides status for multiple
independent operations (see Section 13 for more information).
11.2. 422 Unprocessable Entity
The 422 (Unprocessable Entity) status code means the server
understands the content type of the request entity (hence a
415(Unsupported Media Type) status code is inappropriate), and the
syntax of the request entity is correct (thus a 400 (Bad Request)
status code is inappropriate) but was unable to process the contained
instructions. For example, this error condition may occur if an XML
request body contains well-formed (i.e., syntactically correct), but
semantically erroneous, XML instructions.
11.3. 423 Locked
The 423 (Locked) status code means the source or destination resource
of a method is locked. This response SHOULD contain an appropriate
precondition or postcondition code, such as 'lock-token-submitted' or
'no-conflicting-lock'.
Dusseault Standards Track [Page 78]
RFC 4918 WebDAV June 2007
11.4. 424 Failed Dependency
The 424 (Failed Dependency) status code means that the method could
not be performed on the resource because the requested action
depended on another action and that action failed. For example, if a
command in a PROPPATCH method fails, then, at minimum, the rest of
the commands will also fail with 424 (Failed Dependency).
11.5. 507 Insufficient Storage
The 507 (Insufficient Storage) status code means the method could not
be performed on the resource because the server is unable to store
the representation needed to successfully complete the request. This
condition is considered to be temporary. If the request that
received this status code was the result of a user action, the
request MUST NOT be repeated until it is requested by a separate user
action.
12. Use of HTTP Status Codes
These HTTP codes are not redefined, but their use is somewhat
extended by WebDAV methods and requirements. In general, many HTTP
status codes can be used in response to any request, not just in
cases described in this document. Note also that WebDAV servers are
known to use 300-level redirect responses (and early interoperability
tests found clients unprepared to see those responses). A 300-level
response MUST NOT be used when the server has created a new resource
in response to the request.
12.1. 412 Precondition Failed
Any request can contain a conditional header defined in HTTP (If-
Match, If-Modified-Since, etc.) or the "If" or "Overwrite"
conditional headers defined in this specification. If the server
evaluates a conditional header, and if that condition fails to hold,
then this error code MUST be returned. On the other hand, if the
client did not include a conditional header in the request, then the
server MUST NOT use this status code.
12.2. 414 Request-URI Too Long
This status code is used in HTTP 1.1 only for Request-URIs, not URIs
in other locations.
Dusseault Standards Track [Page 79]
RFC 4918 WebDAV June 2007
13. Multi-Status Response
A Multi-Status response conveys information about multiple resources
in situations where multiple status codes might be appropriate. The
default Multi-Status response body is a text/xml or application/xml
HTTP entity with a 'multistatus' root element. Further elements
contain 200, 300, 400, and 500 series status codes generated during
the method invocation. 100 series status codes SHOULD NOT be recorded
in a 'response' XML element.
Although '207' is used as the overall response status code, the
recipient needs to consult the contents of the multistatus response
body for further information about the success or failure of the
method execution. The response MAY be used in success, partial
success and also in failure situations.
The 'multistatus' root element holds zero or more 'response' elements
in any order, each with information about an individual resource.
Each 'response' element MUST have an 'href' element to identify the
resource.
A Multi-Status response uses one out of two distinct formats for
representing the status:
1. A 'status' element as child of the 'response' element indicates
the status of the message execution for the identified resource
as a whole (for instance, see Section 9.6.2). Some method
definitions provide information about specific status codes
clients should be prepared to see in a response. However,
clients MUST be able to handle other status codes, using the
generic rules defined in Section 10 of [RFC2616].
2. For PROPFIND and PROPPATCH, the format has been extended using
the 'propstat' element instead of 'status', providing information
about individual properties of a resource. This format is
specific to PROPFIND and PROPPATCH, and is described in detail in
Sections 9.1 and 9.2.
13.1. Response Headers
HTTP defines the Location header to indicate a preferred URL for the
resource that was addressed in the Request-URI (e.g., in response to
successful PUT requests or in redirect responses). However, use of
this header creates ambiguity when there are URLs in the body of the
response, as with Multi-Status. Thus, use of the Location header
with the Multi-Status response is intentionally undefined.
Dusseault Standards Track [Page 80]
RFC 4918 WebDAV June 2007
13.2. Handling Redirected Child Resources
Redirect responses (300-303, 305, and 307) defined in HTTP 1.1
normally take a Location header to indicate the new URI for the
single resource redirected from the Request-URI. Multi-Status
responses contain many resource addresses, but the original
definition in [RFC2518] did not have any place for the server to
provide the new URI for redirected resources. This specification
does define a 'location' element for this information (see
Section 14.9). Servers MUST use this new element with redirect
responses in Multi-Status.
Clients encountering redirected resources in Multi-Status MUST NOT
rely on the 'location' element being present with a new URI. If the
element is not present, the client MAY reissue the request to the
individual redirected resource, because the response to that request
can be redirected with a Location header containing the new URI.
13.3. Internal Status Codes
Sections 9.2.1, 9.1.2, 9.6.1, 9.8.3, and 9.9.2 define various status
codes used in Multi-Status responses. This specification does not
define the meaning of other status codes that could appear in these
responses.
14. XML Element Definitions
In this section, the final line of each section gives the element
type declaration using the format defined in [REC-XML]. The "Value"
field, where present, specifies further restrictions on the allowable
contents of the XML element using BNF (i.e., to further restrict the
values of a PCDATA element). Note that all of the elements defined
here may be extended according to the rules defined in Section 17.
All elements defined here are in the "DAV:" namespace.
14.1. activelock XML Element
Name: activelock
Purpose: Describes a lock on a resource.
<!ELEMENT activelock (lockscope, locktype, depth, owner?, timeout?,
locktoken?, lockroot)>
Dusseault Standards Track [Page 81]
RFC 4918 WebDAV June 2007
14.2. allprop XML Element
Name: allprop
Purpose: Specifies that all names and values of dead properties and
the live properties defined by this document existing on the
resource are to be returned.
<!ELEMENT allprop EMPTY >
14.3. collection XML Element
Name: collection
Purpose: Identifies the associated resource as a collection. The
DAV:resourcetype property of a collection resource MUST contain
this element. It is normally empty but extensions may add sub-
elements.
<!ELEMENT collection EMPTY >
14.4. depth XML Element
Name: depth
Purpose: Used for representing depth values in XML content (e.g.,
in lock information).
Value: "0" | "1" | "infinity"
<!ELEMENT depth (#PCDATA) >
14.5. error XML Element
Name: error
Purpose: Error responses, particularly 403 Forbidden and 409
Conflict, sometimes need more information to indicate what went
wrong. In these cases, servers MAY return an XML response body
with a document element of 'error', containing child elements
identifying particular condition codes.
Description: Contains at least one XML element, and MUST NOT
contain text or mixed content. Any element that is a child of the
'error' element is considered to be a precondition or
postcondition code. Unrecognized elements MUST be ignored.
<!ELEMENT error ANY >
Dusseault Standards Track [Page 82]
RFC 4918 WebDAV June 2007
14.6. exclusive XML Element
Name: exclusive
Purpose: Specifies an exclusive lock.
<!ELEMENT exclusive EMPTY >
14.7. href XML Element
Name: href
Purpose: MUST contain a URI or a relative reference.
Description: There may be limits on the value of 'href' depending
on the context of its use. Refer to the specification text where
'href' is used to see what limitations apply in each case.
Value: Simple-ref
<!ELEMENT href (#PCDATA)>
14.8. include XML Element
Name: include
Purpose: Any child element represents the name of a property to be
included in the PROPFIND response. All elements inside an
'include' XML element MUST define properties related to the
resource, although possible property names are in no way limited
to those property names defined in this document or other
standards. This element MUST NOT contain text or mixed content.
<!ELEMENT include ANY >
14.9. location XML Element
Name: location
Purpose: HTTP defines the "Location" header (see [RFC2616], Section
14.30) for use with some status codes (such as 201 and the 300
series codes). When these codes are used inside a 'multistatus'
element, the 'location' element can be used to provide the
accompanying Location header value.
Dusseault Standards Track [Page 83]
RFC 4918 WebDAV June 2007
Description: Contains a single href element with the same value
that would be used in a Location header.
<!ELEMENT location (href)>
14.10. lockentry XML Element
Name: lockentry
Purpose: Defines the types of locks that can be used with the
resource.
<!ELEMENT lockentry (lockscope, locktype) >
14.11. lockinfo XML Element
Name: lockinfo
Purpose: The 'lockinfo' XML element is used with a LOCK method to
specify the type of lock the client wishes to have created.
<!ELEMENT lockinfo (lockscope, locktype, owner?) >
14.12. lockroot XML Element
Name: lockroot
Purpose: Contains the root URL of the lock, which is the URL
through which the resource was addressed in the LOCK request.
Description: The href element contains the root of the lock. The
server SHOULD include this in all DAV:lockdiscovery property
values and the response to LOCK requests.
<!ELEMENT lockroot (href) >
14.13. lockscope XML Element
Name: lockscope
Purpose: Specifies whether a lock is an exclusive lock, or a shared
lock.
<!ELEMENT lockscope (exclusive | shared) >
Dusseault Standards Track [Page 84]
RFC 4918 WebDAV June 2007
14.14. locktoken XML Element
Name: locktoken
Purpose: The lock token associated with a lock.
Description: The href contains a single lock token URI, which
refers to the lock.
<!ELEMENT locktoken (href) >
14.15. locktype XML Element
Name: locktype
Purpose: Specifies the access type of a lock. At present, this
specification only defines one lock type, the write lock.
<!ELEMENT locktype (write) >
14.16. multistatus XML Element
Name: multistatus
Purpose: Contains multiple response messages.
Description: The 'responsedescription' element at the top level is
used to provide a general message describing the overarching
nature of the response. If this value is available, an
application may use it instead of presenting the individual
response descriptions contained within the responses.
<!ELEMENT multistatus (response*, responsedescription?) >
14.17. owner XML Element
Name: owner
Purpose: Holds client-supplied information about the creator of a
lock.
Description: Allows a client to provide information sufficient for
either directly contacting a principal (such as a telephone number
or Email URI), or for discovering the principal (such as the URL
Dusseault Standards Track [Page 85]
RFC 4918 WebDAV June 2007
of a homepage) who created a lock. The value provided MUST be
treated as a dead property in terms of XML Information Item
preservation. The server MUST NOT alter the value unless the
owner value provided by the client is empty. For a certain amount
of interoperability between different client implementations, if
clients have URI-formatted contact information for the lock
creator suitable for user display, then clients SHOULD put those
URIs in 'href' child elements of the 'owner' element.
Extensibility: MAY be extended with child elements, mixed content,
text content or attributes.
<!ELEMENT owner ANY >
14.18. prop XML Element
Name: prop
Purpose: Contains properties related to a resource.
Description: A generic container for properties defined on
resources. All elements inside a 'prop' XML element MUST define
properties related to the resource, although possible property
names are in no way limited to those property names defined in
this document or other standards. This element MUST NOT contain
text or mixed content.
<!ELEMENT prop ANY >
14.19. propertyupdate XML Element
Name: propertyupdate
Purpose: Contains a request to alter the properties on a resource.
Description: This XML element is a container for the information
required to modify the properties on the resource.
<!ELEMENT propertyupdate (remove | set)+ >
14.20. propfind XML Element
Name: propfind
Dusseault Standards Track [Page 86]
RFC 4918 WebDAV June 2007
Purpose: Specifies the properties to be returned from a PROPFIND
method. Four special elements are specified for use with
'propfind': 'prop', 'allprop', 'include', and 'propname'. If
'prop' is used inside 'propfind', it MUST NOT contain property
values.
<!ELEMENT propfind ( propname | (allprop, include?) | prop ) >
14.21. propname XML Element
Name: propname
Purpose: Specifies that only a list of property names on the
resource is to be returned.
<!ELEMENT propname EMPTY >
14.22. propstat XML Element
Name: propstat
Purpose: Groups together a prop and status element that is
associated with a particular 'href' element.
Description: The propstat XML element MUST contain one prop XML
element and one status XML element. The contents of the prop XML
element MUST only list the names of properties to which the result
in the status element applies. The optional precondition/
postcondition element and 'responsedescription' text also apply to
the properties named in 'prop'.
<!ELEMENT propstat (prop, status, error?, responsedescription?) >
14.23. remove XML Element
Name: remove
Purpose: Lists the properties to be removed from a resource.
Description: Remove instructs that the properties specified in prop
should be removed. Specifying the removal of a property that does
not exist is not an error. All the XML elements in a 'prop' XML
element inside of a 'remove' XML element MUST be empty, as only
the names of properties to be removed are required.
<!ELEMENT remove (prop) >
Dusseault Standards Track [Page 87]
RFC 4918 WebDAV June 2007
14.24. response XML Element
Name: response
Purpose: Holds a single response describing the effect of a method
on resource and/or its properties.
Description: The 'href' element contains an HTTP URL pointing to a
WebDAV resource when used in the 'response' container. A
particular 'href' value MUST NOT appear more than once as the
child of a 'response' XML element under a 'multistatus' XML
element. This requirement is necessary in order to keep
processing costs for a response to linear time. Essentially, this
prevents having to search in order to group together all the
responses by 'href'. There are, however, no requirements
regarding ordering based on 'href' values. The optional
precondition/postcondition element and 'responsedescription' text
can provide additional information about this resource relative to
the request or result.
<!ELEMENT response (href, ((href*, status)|(propstat+)),
error?, responsedescription? , location?) >
14.25. responsedescription XML Element
Name: responsedescription
Purpose: Contains information about a status response within a
Multi-Status.
Description: Provides information suitable to be presented to a
user.
<!ELEMENT responsedescription (#PCDATA) >
14.26. set XML Element
Name: set
Purpose: Lists the property values to be set for a resource.
Description: The 'set' element MUST contain only a 'prop' element.
The elements contained by the 'prop' element inside the 'set'
element MUST specify the name and value of properties that are set
on the resource identified by Request-URI. If a property already
exists, then its value is replaced. Language tagging information
appearing in the scope of the 'prop' element (in the "xml:lang"
Dusseault Standards Track [Page 88]
RFC 4918 WebDAV June 2007
attribute, if present) MUST be persistently stored along with the
property, and MUST be subsequently retrievable using PROPFIND.
<!ELEMENT set (prop) >
14.27. shared XML Element
Name: shared
Purpose: Specifies a shared lock.
<!ELEMENT shared EMPTY >
14.28. status XML Element
Name: status
Purpose: Holds a single HTTP status-line.
Value: status-line (defined in Section 6.1 of [RFC2616])
<!ELEMENT status (#PCDATA) >
14.29. timeout XML Element
Name: timeout
Purpose: The number of seconds remaining before a lock expires.
Value: TimeType (defined in Section 10.7)
<!ELEMENT timeout (#PCDATA) >
14.30. write XML Element
Name: write
Purpose: Specifies a write lock.
<!ELEMENT write EMPTY >
Dusseault Standards Track [Page 89]
RFC 4918 WebDAV June 2007
15. DAV Properties
For DAV properties, the name of the property is also the same as the
name of the XML element that contains its value. In the section
below, the final line of each section gives the element type
declaration using the format defined in [REC-XML]. The "Value"
field, where present, specifies further restrictions on the allowable
contents of the XML element using BNF (i.e., to further restrict the
values of a PCDATA element).
A protected property is one that cannot be changed with a PROPPATCH
request. There may be other requests that would result in a change
to a protected property (as when a LOCK request affects the value of
DAV:lockdiscovery). Note that a given property could be protected on
one type of resource, but not protected on another type of resource.
A computed property is one with a value defined in terms of a
computation (based on the content and other properties of that
resource, or even of some other resource). A computed property is
always a protected property.
COPY and MOVE behavior refers to local COPY and MOVE operations.
For properties defined based on HTTP GET response headers (DAV:get*),
the header value could include LWS as defined in [RFC2616], Section
4.2. Server implementors SHOULD strip LWS from these values before
using as WebDAV property values.
15.1. creationdate Property
Name: creationdate
Purpose: Records the time and date the resource was created.
Value: date-time (defined in [RFC3339], see the ABNF in Section
5.6.)
Protected: MAY be protected. Some servers allow DAV:creationdate
to be changed to reflect the time the document was created if that
is more meaningful to the user (rather than the time it was
uploaded). Thus, clients SHOULD NOT use this property in
synchronization logic (use DAV:getetag instead).
COPY/MOVE behavior: This property value SHOULD be kept during a
MOVE operation, but is normally re-initialized when a resource is
created with a COPY. It should not be set in a COPY.
Dusseault Standards Track [Page 90]
RFC 4918 WebDAV June 2007
Description: The DAV:creationdate property SHOULD be defined on all
DAV compliant resources. If present, it contains a timestamp of
the moment when the resource was created. Servers that are
incapable of persistently recording the creation date SHOULD
instead leave it undefined (i.e. report "Not Found").
<!ELEMENT creationdate (#PCDATA) >
15.2. displayname Property
Name: displayname
Purpose: Provides a name for the resource that is suitable for
presentation to a user.
Value: Any text.
Protected: SHOULD NOT be protected. Note that servers implementing
[RFC2518] might have made this a protected property as this is a
new requirement.
COPY/MOVE behavior: This property value SHOULD be preserved in COPY
and MOVE operations.
Description: Contains a description of the resource that is
suitable for presentation to a user. This property is defined on
the resource, and hence SHOULD have the same value independent of
the Request-URI used to retrieve it (thus, computing this property
based on the Request-URI is deprecated). While generic clients
might display the property value to end users, client UI designers
must understand that the method for identifying resources is still
the URL. Changes to DAV:displayname do not issue moves or copies
to the server, but simply change a piece of meta-data on the
individual resource. Two resources can have the same DAV:
displayname value even within the same collection.
<!ELEMENT displayname (#PCDATA) >
15.3. getcontentlanguage Property
Name: getcontentlanguage
Purpose: Contains the Content-Language header value (from Section
14.12 of [RFC2616]) as it would be returned by a GET without
accept headers.
Value: language-tag (language-tag is defined in Section 3.10 of
[RFC2616])
Dusseault Standards Track [Page 91]
RFC 4918 WebDAV June 2007
Protected: SHOULD NOT be protected, so that clients can reset the
language. Note that servers implementing [RFC2518] might have
made this a protected property as this is a new requirement.
COPY/MOVE behavior: This property value SHOULD be preserved in COPY
and MOVE operations.
Description: The DAV:getcontentlanguage property MUST be defined on
any DAV-compliant resource that returns the Content-Language
header on a GET.
<!ELEMENT getcontentlanguage (#PCDATA) >
15.4. getcontentlength Property
Name: getcontentlength
Purpose: Contains the Content-Length header returned by a GET
without accept headers.
Value: See Section 14.13 of [RFC2616].
Protected: This property is computed, therefore protected.
Description: The DAV:getcontentlength property MUST be defined on
any DAV-compliant resource that returns the Content-Length header
in response to a GET.
COPY/MOVE behavior: This property value is dependent on the size of
the destination resource, not the value of the property on the
source resource.
<!ELEMENT getcontentlength (#PCDATA) >
15.5. getcontenttype Property
Name: getcontenttype
Purpose: Contains the Content-Type header value (from Section 14.17
of [RFC2616]) as it would be returned by a GET without accept
headers.
Value: media-type (defined in Section 3.7 of [RFC2616])
Protected: Potentially protected if the server prefers to assign
content types on its own (see also discussion in Section 9.7.1).
Dusseault Standards Track [Page 92]
RFC 4918 WebDAV June 2007
COPY/MOVE behavior: This property value SHOULD be preserved in COPY
and MOVE operations.
Description: This property MUST be defined on any DAV-compliant
resource that returns the Content-Type header in response to a
GET.
<!ELEMENT getcontenttype (#PCDATA) >
15.6. getetag Property
Name: getetag
Purpose: Contains the ETag header value (from Section 14.19 of
[RFC2616]) as it would be returned by a GET without accept
headers.
Value: entity-tag (defined in Section 3.11 of [RFC2616])
Protected: MUST be protected because this value is created and
controlled by the server.
COPY/MOVE behavior: This property value is dependent on the final
state of the destination resource, not the value of the property
on the source resource. Also note the considerations in
Section 8.8.
Description: The getetag property MUST be defined on any DAV-
compliant resource that returns the Etag header. Refer to Section
3.11 of RFC 2616 for a complete definition of the semantics of an
ETag, and to Section 8.6 for a discussion of ETags in WebDAV.
<!ELEMENT getetag (#PCDATA) >
15.7. getlastmodified Property
Name: getlastmodified
Purpose: Contains the Last-Modified header value (from Section
14.29 of [RFC2616]) as it would be returned by a GET method
without accept headers.
Value: rfc1123-date (defined in Section 3.3.1 of [RFC2616])
Protected: SHOULD be protected because some clients may rely on the
value for appropriate caching behavior, or on the value of the
Last-Modified header to which this property is linked.
Dusseault Standards Track [Page 93]
RFC 4918 WebDAV June 2007
COPY/MOVE behavior: This property value is dependent on the last
modified date of the destination resource, not the value of the
property on the source resource. Note that some server
implementations use the file system date modified value for the
DAV:getlastmodified value, and this can be preserved in a MOVE
even when the HTTP Last-Modified value SHOULD change. Note that
since [RFC2616] requires clients to use ETags where provided, a
server implementing ETags can count on clients using a much better
mechanism than modification dates for offline synchronization or
cache control. Also note the considerations in Section 8.8.
Description: The last-modified date on a resource SHOULD only
reflect changes in the body (the GET responses) of the resource.
A change in a property only SHOULD NOT cause the last-modified
date to change, because clients MAY rely on the last-modified date
to know when to overwrite the existing body. The DAV:
getlastmodified property MUST be defined on any DAV-compliant
resource that returns the Last-Modified header in response to a
GET.
<!ELEMENT getlastmodified (#PCDATA) >
15.8. lockdiscovery Property
Name: lockdiscovery
Purpose: Describes the active locks on a resource
Protected: MUST be protected. Clients change the list of locks
through LOCK and UNLOCK, not through PROPPATCH.
COPY/MOVE behavior: The value of this property depends on the lock
state of the destination, not on the locks of the source resource.
Recall that locks are not moved in a MOVE operation.
Description: Returns a listing of who has a lock, what type of lock
he has, the timeout type and the time remaining on the timeout,
and the associated lock token. Owner information MAY be omitted
if it is considered sensitive. If there are no locks, but the
server supports locks, the property will be present but contain
zero 'activelock' elements. If there are one or more locks, an
'activelock' element appears for each lock on the resource. This
property is NOT lockable with respect to write locks (Section 7).
<!ELEMENT lockdiscovery (activelock)* >
Dusseault Standards Track [Page 94]
RFC 4918 WebDAV June 2007
15.8.1. Example - Retrieving DAV:lockdiscovery
>>Request
PROPFIND /container/ HTTP/1.1
Host: www.example.com
Content-Length: xxxx
Content-Type: application/xml; charset="utf-8"
<?xml version="1.0" encoding="utf-8" ?>
<D:propfind xmlns:D='DAV:'>
<D:prop><D:lockdiscovery/></D:prop>
</D:propfind>
>>Response
HTTP/1.1 207 Multi-Status
Content-Type: application/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<D:multistatus xmlns:D='DAV:'>
<D:response>
<D:href>http://www.example.com/container/</D:href>
<D:propstat>
<D:prop>
<D:lockdiscovery>
<D:activelock>
<D:locktype><D:write/></D:locktype>
<D:lockscope><D:exclusive/></D:lockscope>
<D:depth>0</D:depth>
<D:owner>Jane Smith</D:owner>
<D:timeout>Infinite</D:timeout>
<D:locktoken>
<D:href
>urn:uuid:f81de2ad-7f3d-a1b2-4f3c-00a0c91a9d76</D:href>
</D:locktoken>
<D:lockroot>
<D:href>http://www.example.com/container/</D:href>
</D:lockroot>
</D:activelock>
</D:lockdiscovery>
</D:prop>
<D:status>HTTP/1.1 200 OK</D:status>
</D:propstat>
</D:response>
</D:multistatus>
Dusseault Standards Track [Page 95]
RFC 4918 WebDAV June 2007
This resource has a single exclusive write lock on it, with an
infinite timeout.
15.9. resourcetype Property
Name: resourcetype
Purpose: Specifies the nature of the resource.
Protected: SHOULD be protected. Resource type is generally decided
through the operation creating the resource (MKCOL vs PUT), not by
PROPPATCH.
COPY/MOVE behavior: Generally a COPY/MOVE of a resource results in
the same type of resource at the destination.
Description: MUST be defined on all DAV-compliant resources. Each
child element identifies a specific type the resource belongs to,
such as 'collection', which is the only resource type defined by
this specification (see Section 14.3). If the element contains
the 'collection' child element plus additional unrecognized
elements, it should generally be treated as a collection. If the
element contains no recognized child elements, it should be
treated as a non-collection resource. The default value is empty.
This element MUST NOT contain text or mixed content. Any custom
child element is considered to be an identifier for a resource
type.
Example: (fictional example to show extensibility)
<x:resourcetype xmlns:x="DAV:">
<x:collection/>
<f:search-results xmlns:f="http://www.example.com/ns"/>
</x:resourcetype>
15.10. supportedlock Property
Name: supportedlock
Purpose: To provide a listing of the lock capabilities supported by
the resource.
Protected: MUST be protected. Servers, not clients, determine what
lock mechanisms are supported.
Dusseault Standards Track [Page 96]
RFC 4918 WebDAV June 2007
COPY/MOVE behavior: This property value is dependent on the kind of
locks supported at the destination, not on the value of the
property at the source resource. Servers attempting to COPY to a
destination should not attempt to set this property at the
destination.
Description: Returns a listing of the combinations of scope and
access types that may be specified in a lock request on the
resource. Note that the actual contents are themselves controlled
by access controls, so a server is not required to provide
information the client is not authorized to see. This property is
NOT lockable with respect to write locks (Section 7).
<!ELEMENT supportedlock (lockentry)* >
15.10.1. Example - Retrieving DAV:supportedlock
>>Request
PROPFIND /container/ HTTP/1.1
Host: www.example.com
Content-Length: xxxx
Content-Type: application/xml; charset="utf-8"
<?xml version="1.0" encoding="utf-8" ?>
<D:propfind xmlns:D="DAV:">
<D:prop><D:supportedlock/></D:prop>
</D:propfind>
>>Response
HTTP/1.1 207 Multi-Status
Content-Type: application/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<D:multistatus xmlns:D="DAV:">
<D:response>
<D:href>http://www.example.com/container/</D:href>
<D:propstat>
<D:prop>
<D:supportedlock>
<D:lockentry>
<D:lockscope><D:exclusive/></D:lockscope>
<D:locktype><D:write/></D:locktype>
</D:lockentry>
<D:lockentry>
<D:lockscope><D:shared/></D:lockscope>
Dusseault Standards Track [Page 97]
RFC 4918 WebDAV June 2007
<D:locktype><D:write/></D:locktype>
</D:lockentry>
</D:supportedlock>
</D:prop>
<D:status>HTTP/1.1 200 OK</D:status>
</D:propstat>
</D:response>
</D:multistatus>
16. Precondition/Postcondition XML Elements
As introduced in Section 8.7, extra information on error conditions
can be included in the body of many status responses. This section
makes requirements on the use of the error body mechanism and
introduces a number of precondition and postcondition codes.
A "precondition" of a method describes the state of the server that
must be true for that method to be performed. A "postcondition" of a
method describes the state of the server that must be true after that
method has been completed.
Each precondition and postcondition has a unique XML element
associated with it. In a 207 Multi-Status response, the XML element
MUST appear inside an 'error' element in the appropriate 'propstat or
'response' element depending on whether the condition applies to one
or more properties or to the resource as a whole. In all other error
responses where this specification's 'error' body is used, the
precondition/postcondition XML element MUST be returned as the child
of a top-level 'error' element in the response body, unless otherwise
negotiated by the request, along with an appropriate response status.
The most common response status codes are 403 (Forbidden) if the
request should not be repeated because it will always fail, and 409
(Conflict) if it is expected that the user might be able to resolve
the conflict and resubmit the request. The 'error' element MAY
contain child elements with specific error information and MAY be
extended with any custom child elements.
This mechanism does not take the place of using a correct numeric
status code as defined here or in HTTP, because the client must
always be able to take a reasonable course of action based only on
the numeric code. However, it does remove the need to define new
numeric codes. The new machine-readable codes used for this purpose
are XML elements classified as preconditions and postconditions, so
naturally, any group defining a new condition code can use their own
namespace. As always, the "DAV:" namespace is reserved for use by
IETF-chartered WebDAV working groups.
Dusseault Standards Track [Page 98]
RFC 4918 WebDAV June 2007
A server supporting this specification SHOULD use the XML error
whenever a precondition or postcondition defined in this document is
violated. For error conditions not specified in this document, the
server MAY simply choose an appropriate numeric status and leave the
response body blank. However, a server MAY instead use a custom
condition code and other supporting text, because even when clients
do not automatically recognize condition codes, they can be quite
useful in interoperability testing and debugging.
Example - Response with precondition code
>>Response
HTTP/1.1 423 Locked
Content-Type: application/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<D:error xmlns:D="DAV:">
<D:lock-token-submitted>
<D:href>/workspace/webdav/</D:href>
</D:lock-token-submitted>
</D:error>
In this example, a client unaware of a depth-infinity lock on the
parent collection "/workspace/webdav/" attempted to modify the
collection member "/workspace/webdav/proposal.doc".
Some other useful preconditions and postconditions have been defined
in other specifications extending WebDAV, such as [RFC3744] (see
particularly Section 7.1.1), [RFC3253], and [RFC3648].
All these elements are in the "DAV:" namespace. If not specified
otherwise, the content for each condition's XML element is defined to
be empty.
Name: lock-token-matches-request-uri
Use with: 409 Conflict
Purpose: (precondition) -- A request may include a Lock-Token header
to identify a lock for the UNLOCK method. However, if the
Request-URI does not fall within the scope of the lock identified
by the token, the server SHOULD use this error. The lock may have
a scope that does not include the Request-URI, or the lock could
have disappeared, or the token may be invalid.
Dusseault Standards Track [Page 99]
RFC 4918 WebDAV June 2007
Name: lock-token-submitted (precondition)
Use with: 423 Locked
Purpose: The request could not succeed because a lock token should
have been submitted. This element, if present, MUST contain at
least one URL of a locked resource that prevented the request. In
cases of MOVE, COPY, and DELETE where collection locks are
involved, it can be difficult for the client to find out which
locked resource made the request fail -- but the server is only
responsible for returning one such locked resource. The server
MAY return every locked resource that prevented the request from
succeeding if it knows them all.
<!ELEMENT lock-token-submitted (href+) >
Name: no-conflicting-lock (precondition)
Use with: Typically 423 Locked
Purpose: A LOCK request failed due the presence of an already
existing conflicting lock. Note that a lock can be in conflict
although the resource to which the request was directed is only
indirectly locked. In this case, the precondition code can be
used to inform the client about the resource that is the root of
the conflicting lock, avoiding a separate lookup of the
"lockdiscovery" property.
<!ELEMENT no-conflicting-lock (href)* >
Name: no-external-entities
Use with: 403 Forbidden
Purpose: (precondition) -- If the server rejects a client request
because the request body contains an external entity, the server
SHOULD use this error.
Name: preserved-live-properties
Use with: 409 Conflict
Purpose: (postcondition) -- The server received an otherwise-valid
MOVE or COPY request, but cannot maintain the live properties with
the same behavior at the destination. It may be that the server
Dusseault Standards Track [Page 100]
RFC 4918 WebDAV June 2007
only supports some live properties in some parts of the
repository, or simply has an internal error.
Name: propfind-finite-depth
Use with: 403 Forbidden
Purpose: (precondition) -- This server does not allow infinite-depth
PROPFIND requests on collections.
Name: cannot-modify-protected-property
Use with: 403 Forbidden
Purpose: (precondition) -- The client attempted to set a protected
property in a PROPPATCH (such as DAV:getetag). See also
[RFC3253], Section 3.12.
17. XML Extensibility in DAV
The XML namespace extension ([REC-XML-NAMES]) is used in this
specification in order to allow for new XML elements to be added
without fear of colliding with other element names. Although WebDAV
request and response bodies can be extended by arbitrary XML
elements, which can be ignored by the message recipient, an XML
element in the "DAV:" namespace SHOULD NOT be used in the request or
response body unless that XML element is explicitly defined in an
IETF RFC reviewed by a WebDAV working group.
For WebDAV to be both extensible and backwards-compatible, both
clients and servers need to know how to behave when unexpected or
unrecognized command extensions are received. For XML processing,
this means that clients and servers MUST process received XML
documents as if unexpected elements and attributes (and all children
of unrecognized elements) were not there. An unexpected element or
attribute includes one that may be used in another context but is not
expected here. Ignoring such items for purposes of processing can of
course be consistent with logging all information or presenting for
debugging.
This restriction also applies to the processing, by clients, of DAV
property values where unexpected XML elements SHOULD be ignored
unless the property's schema declares otherwise.
This restriction does not apply to setting dead DAV properties on the
server where the server MUST record all XML elements.
Dusseault Standards Track [Page 101]
RFC 4918 WebDAV June 2007
Additionally, this restriction does not apply to the use of XML where
XML happens to be the content type of the entity body, for example,
when used as the body of a PUT.
Processing instructions in XML SHOULD be ignored by recipients.
Thus, specifications extending WebDAV SHOULD NOT use processing
instructions to define normative behavior.
XML DTD fragments are included for all the XML elements defined in
this specification. However, correct XML will not be valid according
to any DTD due to namespace usage and extension rules. In
particular:
o Elements (from this specification) are in the "DAV:" namespace,
o Element ordering is irrelevant unless otherwise stated,
o Extension attributes MAY be added,
o For element type definitions of "ANY", the normative text
definition for that element defines what can be in it and what
that means.
o For element type definitions of "#PCDATA", extension elements MUST
NOT be added.
o For other element type definitions, including "EMPTY", extension
elements MAY be added.
Note that this means that elements containing elements cannot be
extended to contain text, and vice versa.
With DTD validation relaxed by the rules above, the constraints
described by the DTD fragments are normative (see for example
Appendix A). A recipient of a WebDAV message with an XML body MUST
NOT validate the XML document according to any hard-coded or
dynamically-declared DTD.
Note that this section describes backwards-compatible extensibility
rules. There might also be times when an extension is designed not
to be backwards-compatible, for example, defining an extension that
reuses an XML element defined in this document but omitting one of
the child elements required by the DTDs in this specification.
Dusseault Standards Track [Page 102]
RFC 4918 WebDAV June 2007
18. DAV Compliance Classes
A DAV-compliant resource can advertise several classes of compliance.
A client can discover the compliance classes of a resource by
executing OPTIONS on the resource and examining the "DAV" header
which is returned. Note particularly that resources, rather than
servers, are spoken of as being compliant. That is because
theoretically some resources on a server could support different
feature sets. For example, a server could have a sub-repository
where an advanced feature like versioning was supported, even if that
feature was not supported on all sub-repositories.
Since this document describes extensions to the HTTP/1.1 protocol,
minimally all DAV-compliant resources, clients, and proxies MUST be
compliant with [RFC2616].
A resource that is class 2 or class 3 compliant must also be class 1
compliant.
18.1. Class 1
A class 1 compliant resource MUST meet all "MUST" requirements in all
sections of this document.
Class 1 compliant resources MUST return, at minimum, the value "1" in
the DAV header on all responses to the OPTIONS method.
18.2. Class 2
A class 2 compliant resource MUST meet all class 1 requirements and
support the LOCK method, the DAV:supportedlock property, the DAV:
lockdiscovery property, the Time-Out response header and the Lock-
Token request header. A class 2 compliant resource SHOULD also
support the Timeout request header and the 'owner' XML element.
Class 2 compliant resources MUST return, at minimum, the values "1"
and "2" in the DAV header on all responses to the OPTIONS method.
18.3. Class 3
A resource can explicitly advertise its support for the revisions to
[RFC2518] made in this document. Class 1 MUST be supported as well.
Class 2 MAY be supported. Advertising class 3 support in addition to
class 1 and 2 means that the server supports all the requirements in
this specification. Advertising class 3 and class 1 support, but not
class 2, means that the server supports all the requirements in this
specification except possibly those that involve locking support.
Dusseault Standards Track [Page 103]
RFC 4918 WebDAV June 2007
Example:
DAV: 1, 3
19. Internationalization Considerations
In the realm of internationalization, this specification complies
with the IETF Character Set Policy [RFC2277]. In this specification,
human-readable fields can be found either in the value of a property,
or in an error message returned in a response entity body. In both
cases, the human-readable content is encoded using XML, which has
explicit provisions for character set tagging and encoding, and
requires that XML processors read XML elements encoded, at minimum,
using the UTF-8 [RFC3629] and UTF-16 [RFC2781] encodings of the ISO
10646 multilingual plane. XML examples in this specification
demonstrate use of the charset parameter of the Content-Type header
(defined in [RFC3023]), as well as XML charset declarations.
XML also provides a language tagging capability for specifying the
language of the contents of a particular XML element. The "xml:lang"
attribute appears on an XML element to identify the language of its
content and attributes. See [REC-XML] for definitions of values and
scoping.
WebDAV applications MUST support the character set tagging, character
set encoding, and the language tagging functionality of the XML
specification. Implementors of WebDAV applications are strongly
encouraged to read "XML Media Types" [RFC3023] for instruction on
which MIME media type to use for XML transport, and on use of the
charset parameter of the Content-Type header.
Names used within this specification fall into four categories: names
of protocol elements such as methods and headers, names of XML
elements, names of properties, and names of conditions. Naming of
protocol elements follows the precedent of HTTP, using English names
encoded in US-ASCII for methods and headers. Since these protocol
elements are not visible to users, and are simply long token
identifiers, they do not need to support multiple languages.
Similarly, the names of XML elements used in this specification are
not visible to the user and hence do not need to support multiple
languages.
WebDAV property names are qualified XML names (pairs of XML namespace
name and local name). Although some applications (e.g., a generic
property viewer) will display property names directly to their users,
it is expected that the typical application will use a fixed set of
properties, and will provide a mapping from the property name and
namespace to a human-readable field when displaying the property name
Dusseault Standards Track [Page 104]
RFC 4918 WebDAV June 2007
to a user. It is only in the case where the set of properties is not
known ahead of time that an application need display a property name
to a user. We recommend that applications provide human-readable
property names wherever feasible.
For error reporting, we follow the convention of HTTP/1.1 status
codes, including with each status code a short, English description
of the code (e.g., 423 (Locked)). While the possibility exists that
a poorly crafted user agent would display this message to a user,
internationalized applications will ignore this message, and display
an appropriate message in the user's language and character set.
Since interoperation of clients and servers does not require locale
information, this specification does not specify any mechanism for
transmission of this information.
20. Security Considerations
This section is provided to detail issues concerning security
implications of which WebDAV applications need to be aware.
All of the security considerations of HTTP/1.1 (discussed in
[RFC2616]) and XML (discussed in [RFC3023]) also apply to WebDAV. In
addition, the security risks inherent in remote authoring require
stronger authentication technology, introduce several new privacy
concerns, and may increase the hazards from poor server design.
These issues are detailed below.
20.1. Authentication of Clients
Due to their emphasis on authoring, WebDAV servers need to use
authentication technology to protect not just access to a network
resource, but the integrity of the resource as well. Furthermore,
the introduction of locking functionality requires support for
authentication.
A password sent in the clear over an insecure channel is an
inadequate means for protecting the accessibility and integrity of a
resource as the password may be intercepted. Since Basic
authentication for HTTP/1.1 performs essentially clear text
transmission of a password, Basic authentication MUST NOT be used to
authenticate a WebDAV client to a server unless the connection is
secure. Furthermore, a WebDAV server MUST NOT send a Basic
authentication challenge in a WWW-Authenticate header unless the
connection is secure. An example of a secure connection would be a
Transport Layer Security (TLS) connection employing a strong cipher
suite and server authentication.
Dusseault Standards Track [Page 105]
RFC 4918 WebDAV June 2007
WebDAV applications MUST support the Digest authentication scheme
[RFC2617]. Since Digest authentication verifies that both parties to
a communication know a shared secret, a password, without having to
send that secret in the clear, Digest authentication avoids the
security problems inherent in Basic authentication while providing a
level of authentication that is useful in a wide range of scenarios.
20.2. Denial of Service
Denial-of-service attacks are of special concern to WebDAV servers.
WebDAV plus HTTP enables denial-of-service attacks on every part of a
system's resources.
o The underlying storage can be attacked by PUTting extremely large
files.
o Asking for recursive operations on large collections can attack
processing time.
o Making multiple pipelined requests on multiple connections can
attack network connections.
WebDAV servers need to be aware of the possibility of a denial-of-
service attack at all levels. The proper response to such an attack
MAY be to simply drop the connection. Or, if the server is able to
make a response, the server MAY use a 400-level status request such
as 400 (Bad Request) and indicate why the request was refused (a 500-
level status response would indicate that the problem is with the
server, whereas unintentional DoS attacks are something the client is
capable of remedying).
20.3. Security through Obscurity
WebDAV provides, through the PROPFIND method, a mechanism for listing
the member resources of a collection. This greatly diminishes the
effectiveness of security or privacy techniques that rely only on the
difficulty of discovering the names of network resources. Users of
WebDAV servers are encouraged to use access control techniques to
prevent unwanted access to resources, rather than depending on the
relative obscurity of their resource names.
20.4. Privacy Issues Connected to Locks
When submitting a lock request, a user agent may also submit an
'owner' XML field giving contact information for the person taking
out the lock (for those cases where a person, rather than a robot, is
taking out the lock). This contact information is stored in a DAV:
lockdiscovery property on the resource, and can be used by other
Dusseault Standards Track [Page 106]
RFC 4918 WebDAV June 2007
collaborators to begin negotiation over access to the resource.
However, in many cases, this contact information can be very private,
and should not be widely disseminated. Servers SHOULD limit read
access to the DAV:lockdiscovery property as appropriate.
Furthermore, user agents SHOULD provide control over whether contact
information is sent at all, and if contact information is sent,
control over exactly what information is sent.
20.5. Privacy Issues Connected to Properties
Since property values are typically used to hold information such as
the author of a document, there is the possibility that privacy
concerns could arise stemming from widespread access to a resource's
property data. To reduce the risk of inadvertent release of private
information via properties, servers are encouraged to develop access
control mechanisms that separate read access to the resource body and
read access to the resource's properties. This allows a user to
control the dissemination of their property data without overly
restricting access to the resource's contents.
20.6. Implications of XML Entities
XML supports a facility known as "external entities", defined in
Section 4.2.2 of [REC-XML], which instructs an XML processor to
retrieve and include additional XML. An external XML entity can be
used to append or modify the document type declaration (DTD)
associated with an XML document. An external XML entity can also be
used to include XML within the content of an XML document. For non-
validating XML, such as the XML used in this specification, including
an external XML entity is not required by XML. However, XML does
state that an XML processor may, at its discretion, include the
external XML entity.
External XML entities have no inherent trustworthiness and are
subject to all the attacks that are endemic to any HTTP GET request.
Furthermore, it is possible for an external XML entity to modify the
DTD, and hence affect the final form of an XML document, in the worst
case, significantly modifying its semantics or exposing the XML
processor to the security risks discussed in [RFC3023]. Therefore,
implementers must be aware that external XML entities should be
treated as untrustworthy. If a server chooses not to handle external
XML entities, it SHOULD respond to requests containing external
entities with the 'no-external-entities' condition code.
There is also the scalability risk that would accompany a widely
deployed application that made use of external XML entities. In this
situation, it is possible that there would be significant numbers of
requests for one external XML entity, potentially overloading any
Dusseault Standards Track [Page 107]
RFC 4918 WebDAV June 2007
server that fields requests for the resource containing the external
XML entity.
Furthermore, there's also a risk based on the evaluation of "internal
entities" as defined in Section 4.2.2 of [REC-XML]. A small,
carefully crafted request using nested internal entities may require
enormous amounts of memory and/or processing time to process. Server
implementers should be aware of this risk and configure their XML
parsers so that requests like these can be detected and rejected as
early as possible.
20.7. Risks Connected with Lock Tokens
This specification encourages the use of "A Universally Unique
Identifier (UUID) URN Namespace" ([RFC4122]) for lock tokens
(Section 6.5), in order to guarantee their uniqueness across space
and time. Version 1 UUIDs (defined in Section 4) MAY contain a
"node" field that "consists of an IEEE 802 MAC address, usually the
host address. For systems with multiple IEEE addresses, any
available one can be used". Since a WebDAV server will issue many
locks over its lifetime, the implication is that it may also be
publicly exposing its IEEE 802 address.
There are several risks associated with exposure of IEEE 802
addresses. Using the IEEE 802 address:
o It is possible to track the movement of hardware from subnet to
subnet.
o It may be possible to identify the manufacturer of the hardware
running a WebDAV server.
o It may be possible to determine the number of each type of
computer running WebDAV.
This risk only applies to host-address-based UUID versions. Section
4 of [RFC4122] describes several other mechanisms for generating
UUIDs that do not involve the host address and therefore do not
suffer from this risk.
20.8. Hosting Malicious Content
HTTP has the ability to host programs that are executed on client
machines. These programs can take many forms including Web scripts,
executables, plug-in modules, and macros in documents. WebDAV does
not change any of the security concerns around these programs, yet
often WebDAV is used in contexts where a wide range of users can
publish documents on a server. The server might not have a close
Dusseault Standards Track [Page 108]
RFC 4918 WebDAV June 2007
trust relationship with the author that is publishing the document.
Servers that allow clients to publish arbitrary content can usefully
implement precautions to check that content published to the server
is not harmful to other clients. Servers could do this by techniques
such as restricting the types of content that is allowed to be
published and running virus and malware detection software on
published content. Servers can also mitigate the risk by having
appropriate access restriction and authentication of users that are
allowed to publish content to the server.
21. IANA Considerations
21.1. New URI Schemes
This specification defines two URI schemes:
1. the "opaquelocktoken" scheme defined in Appendix C, and
2. the "DAV" URI scheme, which historically was used in [RFC2518] to
disambiguate WebDAV property and XML element names and which
continues to be used for that purpose in this specification and
others extending WebDAV. Creation of identifiers in the "DAV:"
namespace is controlled by the IETF.
Note that defining new URI schemes for XML namespaces is now
discouraged. "DAV:" was defined before standard best practices
emerged.
21.2. XML Namespaces
XML namespaces disambiguate WebDAV property names and XML elements.
Any WebDAV user or application can define a new namespace in order to
create custom properties or extend WebDAV XML syntax. IANA does not
need to manage such namespaces, property names, or element names.
21.3. Message Header Fields
The message header fields below should be added to the permanent
registry (see [RFC3864]).
21.3.1. DAV
Header field name: DAV
Applicable protocol: http
Status: standard
Dusseault Standards Track [Page 109]
RFC 4918 WebDAV June 2007
Author/Change controller: IETF
Specification document: this specification (Section 10.1)
21.3.2. Depth
Header field name: Depth
Applicable protocol: http
Status: standard
Author/Change controller: IETF
Specification document: this specification (Section 10.2)
21.3.3. Destination
Header field name: Destination
Applicable protocol: http
Status: standard
Author/Change controller: IETF
Specification document: this specification (Section 10.3)
21.3.4. If
Header field name: If
Applicable protocol: http
Status: standard
Author/Change controller: IETF
Specification document: this specification (Section 10.4)
21.3.5. Lock-Token
Header field name: Lock-Token
Applicable protocol: http
Status: standard
Dusseault Standards Track [Page 110]
RFC 4918 WebDAV June 2007
Author/Change controller: IETF
Specification document: this specification (Section 10.5)
21.3.6. Overwrite
Header field name: Overwrite
Applicable protocol: http
Status: standard
Author/Change controller: IETF
Specification document: this specification (Section 10.6)
21.3.7. Timeout
Header field name: Timeout
Applicable protocol: http
Status: standard
Author/Change controller: IETF
Specification document: this specification (Section 10.7)
21.4. HTTP Status Codes
This specification defines the HTTP status codes
o 207 Multi-Status (Section 11.1)
o 422 Unprocessable Entity (Section 11.2),
o 423 Locked (Section 11.3),
o 424 Failed Dependency (Section 11.4) and
o 507 Insufficient Storage (Section 11.5),
to be updated in the registry at
<http://www.iana.org/assignments/http-status-codes>.
Note: the HTTP status code 102 (Processing) has been removed in this
specification; its IANA registration should continue to reference RFC
2518.
Dusseault Standards Track [Page 111]
RFC 4918 WebDAV June 2007
22. Acknowledgements
A specification such as this thrives on piercing critical review and
withers from apathetic neglect. The authors gratefully acknowledge
the contributions of the following people, whose insights were so
valuable at every stage of our work.
Contributors to RFC 2518
Terry Allen, Harald Alvestrand, Jim Amsden, Becky Anderson, Alan
Babich, Sanford Barr, Dylan Barrell, Bernard Chester, Tim Berners-
Lee, Dan Connolly, Jim Cunningham, Ron Daniel, Jr., Jim Davis, Keith
Dawson, Mark Day, Brian Deen, Martin Duerst, David Durand, Lee
Farrell, Chuck Fay, Wesley Felter, Roy Fielding, Mark Fisher, Alan
Freier, George Florentine, Jim Gettys, Phill Hallam-Baker, Dennis
Hamilton, Steve Henning, Mead Himelstein, Alex Hopmann, Andre van der
Hoek, Ben Laurie, Paul Leach, Ora Lassila, Karen MacArthur, Steven
Martin, Larry Masinter, Michael Mealling, Keith Moore, Thomas Narten,
Henrik Nielsen, Kenji Ota, Bob Parker, Glenn Peterson, Jon Radoff,
Saveen Reddy, Henry Sanders, Christopher Seiwald, Judith Slein, Mike
Spreitzer, Einar Stefferud, Greg Stein, Ralph Swick, Kenji Takahashi,
Richard N. Taylor, Robert Thau, John Turner, Sankar Virdhagriswaran,
Fabio Vitali, Gregory Woodhouse, and Lauren Wood.
Two from this list deserve special mention. The contributions by
Larry Masinter have been invaluable; he both helped the formation of
the working group and patiently coached the authors along the way.
In so many ways he has set high standards that we have toiled to
meet. The contributions of Judith Slein were also invaluable; by
clarifying the requirements and in patiently reviewing version after
version, she both improved this specification and expanded our minds
on document management.
We would also like to thank John Turner for developing the XML DTD.
The authors of RFC 2518 were Yaron Goland, Jim Whitehead, A. Faizi,
Steve Carter, and D. Jensen. Although their names had to be removed
due to IETF author count restrictions, they can take credit for the
majority of the design of WebDAV.
Additional Acknowledgements for This Specification
Significant contributors of text for this specification are listed as
contributors in the section below. We must also gratefully
acknowledge Geoff Clemm, Joel Soderberg, and Dan Brotsky for hashing
out specific text on the list or in meetings. Joe Hildebrand and
Cullen Jennings helped close many issues. Barry Lind described an
additional security consideration and Cullen Jennings provided text
Dusseault Standards Track [Page 112]
RFC 4918 WebDAV June 2007
for that consideration. Jason Crawford tracked issue status for this
document for a period of years, followed by Elias Sinderson.
23. Contributors to This Specification
Julian Reschke
<green/>bytes GmbH
Hafenweg 16, 48155 Muenster, Germany
EMail: julian.reschke@greenbytes.de
Elias Sinderson
University of California, Santa Cruz
1156 High Street, Santa Cruz, CA 95064
EMail: elias@cse.ucsc.edu
Jim Whitehead
University of California, Santa Cruz
1156 High Street, Santa Cruz, CA 95064
EMail: ejw@soe.ucsc.edu
24. Authors of RFC 2518
Y. Y. Goland
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052-6399
EMail: yarong@microsoft.com
E. J. Whitehead, Jr.
Dept. Of Information and Computer Science
University of California, Irvine
Irvine, CA 92697-3425
EMail: ejw@ics.uci.edu
A. Faizi
Netscape
685 East Middlefield Road
Mountain View, CA 94043
EMail: asad@netscape.com
Dusseault Standards Track [Page 113]
RFC 4918 WebDAV June 2007
S. R. Carter
Novell
1555 N. Technology Way
M/S ORM F111
Orem, UT 84097-2399
EMail: srcarter@novell.com
D. Jensen
Novell
1555 N. Technology Way
M/S ORM F111
Orem, UT 84097-2399
EMail: dcjensen@novell.com
25. References
25.1. Normative References
[REC-XML] Bray, T., Paoli, J., Sperberg-McQueen, C., Maler,
E., and F. Yergeau, "Extensible Markup Language
(XML) 1.0 (Fourth Edition)", W3C REC-xml-20060816,
August 2006,
<http://www.w3.org/TR/2006/REC-xml-20060816/>.
[REC-XML-INFOSET] Cowan, J. and R. Tobin, "XML Information Set
(Second Edition)", W3C REC-xml-infoset-20040204,
February 2004, <http://www.w3.org/TR/2004/
REC-xml-infoset-20040204/>.
[REC-XML-NAMES] Bray, T., Hollander, D., Layman, A., and R. Tobin,
"Namespaces in XML 1.0 (Second Edition)", W3C REC-
xml-names-20060816, August 2006, <http://
www.w3.org/TR/2006/REC-xml-names-20060816/>.
[RFC2119] Bradner, S., "Key words for use in RFCs to
Indicate Requirement Levels", BCP 14, RFC 2119,
March 1997.
[RFC2277] Alvestrand, H., "IETF Policy on Character Sets and
Languages", BCP 18, RFC 2277, January 1998.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee,
"Hypertext Transfer Protocol -- HTTP/1.1",
RFC 2616, June 1999.
Dusseault Standards Track [Page 114]
RFC 4918 WebDAV June 2007
[RFC2617] Franks, J., Hallam-Baker, P., Hostetler, J.,
Lawrence, S., Leach, P., Luotonen, A., and L.
Stewart, "HTTP Authentication: Basic and Digest
Access Authentication", RFC 2617, June 1999.
[RFC3339] Klyne, G., Ed. and C. Newman, "Date and Time on
the Internet: Timestamps", RFC 3339, July 2002.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of
ISO 10646", STD 63, RFC 3629, November 2003.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter,
"Uniform Resource Identifier (URI): Generic
Syntax", STD 66, RFC 3986, January 2005.
[RFC4122] Leach, P., Mealling, M., and R. Salz, "A
Universally Unique IDentifier (UUID) URN
Namespace", RFC 4122, July 2005.
25.2. Informative References
[RFC2291] Slein, J., Vitali, F., Whitehead, E., and D.
Durand, "Requirements for a Distributed Authoring
and Versioning Protocol for the World Wide Web",
RFC 2291, February 1998.
[RFC2518] Goland, Y., Whitehead, E., Faizi, A., Carter, S.,
and D. Jensen, "HTTP Extensions for Distributed
Authoring -- WEBDAV", RFC 2518, February 1999.
[RFC2781] Hoffman, P. and F. Yergeau, "UTF-16, an encoding
of ISO 10646", RFC 2781, February 2000.
[RFC3023] Murata, M., St. Laurent, S., and D. Kohn, "XML
Media Types", RFC 3023, January 2001.
[RFC3253] Clemm, G., Amsden, J., Ellison, T., Kaler, C., and
J. Whitehead, "Versioning Extensions to WebDAV
(Web Distributed Authoring and Versioning)",
RFC 3253, March 2002.
[RFC3648] Whitehead, J. and J. Reschke, Ed., "Web
Distributed Authoring and Versioning (WebDAV)
Ordered Collections Protocol", RFC 3648,
December 2003.
Dusseault Standards Track [Page 115]
RFC 4918 WebDAV June 2007
[RFC3744] Clemm, G., Reschke, J., Sedlar, E., and J.
Whitehead, "Web Distributed Authoring and
Versioning (WebDAV) Access Control Protocol",
RFC 3744, May 2004.
[RFC3864] Klyne, G., Nottingham, M., and J. Mogul,
"Registration Procedures for Message Header
Fields", BCP 90, RFC 3864, September 2004.
Dusseault Standards Track [Page 116]
RFC 4918 WebDAV June 2007
Appendix A. Notes on Processing XML Elements
A.1. Notes on Empty XML Elements
XML supports two mechanisms for indicating that an XML element does
not have any content. The first is to declare an XML element of the
form <A></A>. The second is to declare an XML element of the form
<A/>. The two XML elements are semantically identical.
A.2. Notes on Illegal XML Processing
XML is a flexible data format that makes it easy to submit data that
appears legal but in fact is not. The philosophy of "Be flexible in
what you accept and strict in what you send" still applies, but it
must not be applied inappropriately. XML is extremely flexible in
dealing with issues of whitespace, element ordering, inserting new
elements, etc. This flexibility does not require extension,
especially not in the area of the meaning of elements.
There is no kindness in accepting illegal combinations of XML
elements. At best, it will cause an unwanted result and at worst it
can cause real damage.
A.3. Example - XML Syntax Error
The following request body for a PROPFIND method is illegal.
<?xml version="1.0" encoding="utf-8" ?>
<D:propfind xmlns:D="DAV:">
<D:allprop/>
<D:propname/>
</D:propfind>
The definition of the propfind element only allows for the allprop or
the propname element, not both. Thus, the above is an error and must
be responded to with a 400 (Bad Request).
Imagine, however, that a server wanted to be "kind" and decided to
pick the allprop element as the true element and respond to it. A
client running over a bandwidth limited line who intended to execute
a propname would be in for a big surprise if the server treated the
command as an allprop.
Additionally, if a server were lenient and decided to reply to this
request, the results would vary randomly from server to server, with
some servers executing the allprop directive, and others executing
the propname directive. This reduces interoperability rather than
increasing it.
Dusseault Standards Track [Page 117]
RFC 4918 WebDAV June 2007
A.4. Example - Unexpected XML Element
The previous example was illegal because it contained two elements
that were explicitly banned from appearing together in the propfind
element. However, XML is an extensible language, so one can imagine
new elements being defined for use with propfind. Below is the
request body of a PROPFIND and, like the previous example, must be
rejected with a 400 (Bad Request) by a server that does not
understand the expired-props element.
<?xml version="1.0" encoding="utf-8" ?>
<D:propfind xmlns:D="DAV:"
xmlns:E="http://www.example.com/standards/props/">
<E:expired-props/>
</D:propfind>
To understand why a 400 (Bad Request) is returned, let us look at the
request body as the server unfamiliar with expired-props sees it.
<?xml version="1.0" encoding="utf-8" ?>
<D:propfind xmlns:D="DAV:"
xmlns:E="http://www.example.com/standards/props/">
</D:propfind>
As the server does not understand the 'expired-props' element,
according to the WebDAV-specific XML processing rules specified in
Section 17, it must process the request as if the element were not
there. Thus, the server sees an empty propfind, which by the
definition of the propfind element is illegal.
Please note that had the extension been additive, it would not
necessarily have resulted in a 400 (Bad Request). For example,
imagine the following request body for a PROPFIND:
<?xml version="1.0" encoding="utf-8" ?>
<D:propfind xmlns:D="DAV:"
xmlns:E="http://www.example.com/standards/props/">
<D:propname/>
<E:leave-out>*boss*</E:leave-out>
</D:propfind>
The previous example contains the fictitious element leave-out. Its
purpose is to prevent the return of any property whose name matches
the submitted pattern. If the previous example were submitted to a
server unfamiliar with 'leave-out', the only result would be that the
'leave-out' element would be ignored and a propname would be
executed.
Dusseault Standards Track [Page 118]
RFC 4918 WebDAV June 2007
Appendix B. Notes on HTTP Client Compatibility
WebDAV was designed to be, and has been found to be, backward-
compatible with HTTP 1.1. The PUT and DELETE methods are defined in
HTTP and thus may be used by HTTP clients as well as WebDAV-aware
clients, but the responses to PUT and DELETE have been extended in
this specification in ways that only a WebDAV client would be
entirely prepared for. Some theoretical concerns were raised about
whether those responses would cause interoperability problems with
HTTP-only clients, and this section addresses those concerns.
Since any HTTP client ought to handle unrecognized 400-level and 500-
level status codes as errors, the following new status codes should
not present any issues: 422, 423, and 507 (424 is also a new status
code but it appears only in the body of a Multistatus response.) So,
for example, if an HTTP client attempted to PUT or DELETE a locked
resource, the 423 Locked response ought to result in a generic error
presented to the user.
The 207 Multistatus response is interesting because an HTTP client
issuing a DELETE request to a collection might interpret a 207
response as a success, even though it does not realize the resource
is a collection and cannot understand that the DELETE operation might
have been a complete or partial failure. That interpretation isn't
entirely justified, because a 200-level response indicates that the
server "received, understood, and accepted" the request, not that the
request resulted in complete success.
One option is that a server could treat a DELETE of a collection as
an atomic operation, and use either 204 No Content in case of
success, or some appropriate error response (400 or 500 level) for an
error. This approach would indeed maximize backward compatibility.
However, since interoperability tests and working group discussions
have not turned up any instances of HTTP clients issuing a DELETE
request against a WebDAV collection, this concern is more theoretical
than practical. Thus, servers are likely to be completely successful
at interoperating with HTTP clients even if they treat any collection
DELETE request as a WebDAV request and send a 207 Multi-Status
response.
In general, server implementations are encouraged to use the detailed
responses and other mechanisms defined in this document rather than
make changes for theoretical interoperability concerns.
Dusseault Standards Track [Page 119]
RFC 4918 WebDAV June 2007
Appendix C. The 'opaquelocktoken' Scheme and URIs
The 'opaquelocktoken' URI scheme was defined in [RFC2518] (and
registered by IANA) in order to create syntactically correct and
easy-to-generate URIs out of UUIDs, intended to be used as lock
tokens and to be unique across all resources for all time.
An opaquelocktoken URI is constructed by concatenating the
'opaquelocktoken' scheme with a UUID, along with an optional
extension. Servers can create new UUIDs for each new lock token. If
a server wishes to reuse UUIDs, the server MUST add an extension, and
the algorithm generating the extension MUST guarantee that the same
extension will never be used twice with the associated UUID.
OpaqueLockToken-URI = "opaquelocktoken:" UUID [Extension]
; UUID is defined in Section 3 of [RFC4122]. Note that LWS
; is not allowed between elements of
; this production.
Extension = path
; path is defined in Section 3.3 of [RFC3986]
Appendix D. Lock-null Resources
The original WebDAV model for locking unmapped URLs created "lock-
null resources". This model was over-complicated and some
interoperability and implementation problems were discovered. The
new WebDAV model for locking unmapped URLs (see Section 7.3) creates
"locked empty resources". Lock-null resources are deprecated. This
section discusses the original model briefly because clients MUST be
able to handle either model.
In the original "lock-null resource" model, which is no longer
recommended for implementation:
o A lock-null resource sometimes appeared as "Not Found". The
server responds with a 404 or 405 to any method except for PUT,
MKCOL, OPTIONS, PROPFIND, LOCK, UNLOCK.
o A lock-null resource does however show up as a member of its
parent collection.
o The server removes the lock-null resource entirely (its URI
becomes unmapped) if its lock goes away before it is converted to
a regular resource. Recall that locks go away not only when they
expire or are unlocked, but are also removed if a resource is
renamed or moved, or if any parent collection is renamed or moved.
Dusseault Standards Track [Page 120]
RFC 4918 WebDAV June 2007
o The server converts the lock-null resource into a regular resource
if a PUT request to the URL is successful.
o The server converts the lock-null resource into a collection if a
MKCOL request to the URL is successful (though interoperability
experience showed that not all servers followed this requirement).
o Property values were defined for DAV:lockdiscovery and DAV:
supportedlock properties but not necessarily for other properties
like DAV:getcontenttype.
Clients can easily interoperate both with servers that support the
old model "lock-null resources" and the recommended model of "locked
empty resources" by only attempting PUT after a LOCK to an unmapped
URL, not MKCOL or GET.
D.1. Guidance for Clients Using LOCK to Create Resources
A WebDAV client implemented to this specification might find servers
that create lock-null resources (implemented before this
specification using [RFC2518]) as well as servers that create locked
empty resources. The response to the LOCK request will not indicate
what kind of resource was created. There are a few techniques that
help the client deal with either type.
If the client wishes to avoid accidentally creating either lock-
null or empty locked resources, an "If-Match: *" header can be
included with LOCK requests to prevent the server from creating a
new resource.
If a LOCK request creates a resource and the client subsequently
wants to overwrite that resource using a COPY or MOVE request, the
client should include an "Overwrite: T" header.
If a LOCK request creates a resource and the client then decides
to get rid of that resource, a DELETE request is supposed to fail
on a lock-null resource and UNLOCK should be used instead. But
with a locked empty resource, UNLOCK doesn't make the resource
disappear. Therefore, the client might have to try both requests
and ignore an error in one of the two requests.
Appendix E. Guidance for Clients Desiring to Authenticate
Many WebDAV clients that have already been implemented have account
settings (similar to the way email clients store IMAP account
settings). Thus, the WebDAV client would be able to authenticate
with its first couple requests to the server, provided it had a way
to get the authentication challenge from the server with realm name,
Dusseault Standards Track [Page 121]
RFC 4918 WebDAV June 2007
nonce, and other challenge information. Note that the results of
some requests might vary according to whether or not the client is
authenticated -- a PROPFIND might return more visible resources if
the client is authenticated, yet not fail if the client is anonymous.
There are a number of ways the client might be able to trigger the
server to provide an authentication challenge. This appendix
describes a couple approaches that seem particularly likely to work.
The first approach is to perform a request that ought to require
authentication. However, it's possible that a server might handle
any request even without authentication, so to be entirely safe, the
client could add a conditional header to ensure that even if the
request passes permissions checks, it's not actually handled by the
server. An example of following this approach would be to use a PUT
request with an "If-Match" header with a made-up ETag value. This
approach might fail to result in an authentication challenge if the
server does not test authorization before testing conditionals as is
required (see Section 8.5), or if the server does not need to test
authorization.
Example - forcing auth challenge with write request
>>Request
PUT /forceauth.txt HTTP/1.1
Host: www.example.com
If-Match: "xxx"
Content-Type: text/plain
Content-Length: 0
The second approach is to use an Authorization header (defined in
[RFC2617]), which is likely to be rejected by the server but which
will then prompt a proper authentication challenge. For example, the
client could start with a PROPFIND request containing an
Authorization header containing a made-up Basic userid:password
string or with actual plausible credentials. This approach relies on
the server responding with a "401 Unauthorized" along with a
challenge if it receives an Authorization header with an unrecognized
username, invalid password, or if it doesn't even handle Basic
authentication. This seems likely to work because of the
requirements of RFC 2617:
Dusseault Standards Track [Page 122]
RFC 4918 WebDAV June 2007
"If the origin server does not wish to accept the credentials sent
with a request, it SHOULD return a 401 (Unauthorized) response. The
response MUST include a WWW-Authenticate header field containing at
least one (possibly new) challenge applicable to the requested
resource."
There's a slight problem with implementing that recommendation in
some cases, because some servers do not even have challenge
information for certain resources. Thus, when there's no way to
authenticate to a resource or the resource is entirely publicly
available over all accepted methods, the server MAY ignore the
Authorization header, and the client will presumably try again later.
Example - forcing auth challenge with Authorization header
>>Request
PROPFIND /docs/ HTTP/1.1
Host: www.example.com
Authorization: Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ==
Content-type: application/xml; charset="utf-8"
Content-Length: xxxx
[body omitted]
Appendix F. Summary of Changes from RFC 2518
This section lists major changes between this document and RFC 2518,
starting with those that are likely to result in implementation
changes. Servers will advertise support for all changes in this
specification by returning the compliance class "3" in the DAV
response header (see Sections 10.1 and 18.3).
F.1. Changes for Both Client and Server Implementations
Collections and Namespace Operations
o The semantics of PROPFIND 'allprop' (Section 9.1) have been
relaxed so that servers return results including, at a minimum,
the live properties defined in this specification, but not
necessarily return other live properties. The 'allprop' directive
therefore means something more like "return all properties that
are supposed to be returned when 'allprop' is requested" -- a set
of properties that may include custom properties and properties
defined in other specifications if those other specifications so
require. Related to this, 'allprop' requests can now be extended
with the 'include' syntax to include specific named properties,
Dusseault Standards Track [Page 123]
RFC 4918 WebDAV June 2007
thereby avoiding additional requests due to changed 'allprop'
semantics.
o Servers are now allowed to reject PROPFIND requests with Depth:
Infinity. Clients that used this will need to be able to do a
series of Depth:1 requests instead.
o Multi-Status response bodies now can transport the value of HTTP's
Location response header in the new 'location' element. Clients
may use this to avoid additional roundtrips to the server when
there is a 'response' element with a 3xx status (see
Section 14.24).
o The definition of COPY has been relaxed so that it doesn't require
servers to first delete the target resources anymore (this was a
known incompatibility with [RFC3253]). See Section 9.8.
Headers and Marshalling
o The Destination and If request headers now allow absolute paths in
addition to full URIs (see Section 8.3). This may be useful for
clients operating through a reverse proxy that does rewrite the
Host request header, but not WebDAV-specific headers.
o This specification adopts the error marshalling extensions and the
"precondition/postcondition" terminology defined in [RFC3253] (see
Section 16). Related to that, it adds the "error" XML element
inside multistatus response bodies (see Section 14.5, however note
that it uses a format different from the one recommended in RFC
3253).
o Senders and recipients are now required to support the UTF-16
character encoding in XML message bodies (see Section 19).
o Clients are now required to send the Depth header on PROPFIND
requests, although servers are still encouraged to support clients
that don't.
Locking
o RFC 2518's concept of "lock-null resources" (LNRs) has been
replaced by a simplified approach, the "locked empty resources"
(see Section 7.3). There are some aspects of lock-null resources
clients cannot rely on anymore, namely, the ability to use them to
create a locked collection or the fact that they disappear upon
UNLOCK when no PUT or MKCOL request was issued. Note that servers
are still allowed to implement LNRs as per RFC 2518.
Dusseault Standards Track [Page 124]
RFC 4918 WebDAV June 2007
o There is no implicit refresh of locks anymore. Locks are only
refreshed upon explicit request (see Section 9.10.2).
o Clarified that the DAV:owner value supplied in the LOCK request
must be preserved by the server just like a dead property
(Section 14.17). Also added the DAV:lockroot element
(Section 14.12), which allows clients to discover the root of
lock.
F.2. Changes for Server Implementations
Collections and Namespace Operations
o Due to interoperability problems, allowable formats for contents
of 'href' elements in multistatus responses have been limited (see
Section 8.3).
o Due to lack of implementation, support for the 'propertybehavior'
request body for COPY and MOVE has been removed. Instead,
requirements for property preservation have been clarified (see
Sections 9.8 and 9.9).
Properties
o Strengthened server requirements for storage of property values,
in particular persistence of language information (xml:lang),
whitespace, and XML namespace information (see Section 4.3).
o Clarified requirements on which properties should be writable by
the client; in particular, setting "DAV:displayname" should be
supported by servers (see Section 15).
o Only 'rfc1123-date' productions are legal as values for DAV:
getlastmodified (see Section 15.7).
Headers and Marshalling
o Servers are now required to do authorization checks before
processing conditional headers (see Section 8.5).
Locking
o Strengthened requirement to check identity of lock creator when
accessing locked resources (see Section 6.4). Clients should be
aware that lock tokens returned to other principals can only be
used to break a lock, if at all.
Dusseault Standards Track [Page 125]
RFC 4918 WebDAV June 2007
o Section 8.10.4 of [RFC2518] incorrectly required servers to return
a 409 status where a 207 status was really appropriate. This has
been corrected (Section 9.10).
F.3. Other Changes
The definition of collection state has been fixed so it doesn't vary
anymore depending on the Request-URI (see Section 5.2).
The DAV:source property introduced in Section 4.6 of [RFC2518] was
removed due to lack of implementation experience.
The DAV header now allows non-IETF extensions through URIs in
addition to compliance class tokens. It also can now be used in
requests, although this specification does not define any associated
semantics for the compliance classes defined in here (see
Section 10.1).
In RFC 2518, the definition of the Depth header (Section 9.2)
required that, by default, request headers would be applied to each
resource in scope. Based on implementation experience, the default
has now been reversed (see Section 10.2).
The definitions of HTTP status code 102 ([RFC2518], Section 10.1) and
the Status-URI response header (Section 9.7) have been removed due to
lack of implementation.
The TimeType format used in the Timeout request header and the
"timeout" XML element used to be extensible. Now, only the two
formats defined by this specification are allowed (see Section 10.7).
Author's Address
Lisa Dusseault (editor)
CommerceNet
2064 Edgewood Dr.
Palo Alto, CA 94303
US
EMail: ldusseault@commerce.net
Dusseault Standards Track [Page 126]
RFC 4918 WebDAV June 2007
Full Copyright Statement
Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
Dusseault Standards Track [Page 127]
Reference in New Issue View Git Blame Copy Permalink