WebDAV L. Dusseault
Internet-Draft OSAF
Obsoletes: 2518 (if approved) November 2005
Expires: May 5, 2006
HTTP Extensions for Distributed Authoring - WebDAV
draft-ietf-webdav-rfc2518bis-09
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Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
WebDAV consists of a set of methods, headers, and content-types
ancillary to HTTP/1.1 for the management of resource properties,
creation and management of resource collections, URL namespace
manipulation, and resource locking (collision avoidance).
RFC2518 was published in February 1999, and this specification makes
minor revisions mostly due to interoperability experience.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 7
2. Notational Conventions . . . . . . . . . . . . . . . . . . . 9
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 10
4. Data Model for Resource Properties . . . . . . . . . . . . . 11
4.1. The Resource Property Model . . . . . . . . . . . . . . 11
4.2. Properties and HTTP Headers . . . . . . . . . . . . . . 11
4.3. XML Usage . . . . . . . . . . . . . . . . . . . . . . . 11
4.4. Property Values . . . . . . . . . . . . . . . . . . . . 12
4.4.1. Example - Property with Mixed Content . . . . . . . 14
4.5. Property Names . . . . . . . . . . . . . . . . . . . . . 15
4.6. Source Resources and Output Resources . . . . . . . . . 16
5. Collections of Web Resources . . . . . . . . . . . . . . . . 17
5.1. HTTP URL Namespace Model . . . . . . . . . . . . . . . . 17
5.2. Collection Resources . . . . . . . . . . . . . . . . . . 17
6. Locking . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
6.1. Exclusive Vs. Shared Locks . . . . . . . . . . . . . . . 19
6.2. Required Support . . . . . . . . . . . . . . . . . . . . 20
6.3. Lock Tokens . . . . . . . . . . . . . . . . . . . . . . 20
6.4. Lock Capability Discovery . . . . . . . . . . . . . . . 21
6.5. Active Lock Discovery . . . . . . . . . . . . . . . . . 21
6.6. Locks and Multiple Bindings . . . . . . . . . . . . . . 22
7. Write Lock . . . . . . . . . . . . . . . . . . . . . . . . . 23
7.1. Lock Owner . . . . . . . . . . . . . . . . . . . . . . . 23
7.2. Methods Restricted by Write Locks . . . . . . . . . . . 23
7.3. Write Locks and Lock Tokens . . . . . . . . . . . . . . 24
7.4. Write Locks and Properties . . . . . . . . . . . . . . . 24
7.5. Avoiding Lost Updates . . . . . . . . . . . . . . . . . 24
7.6. Write Locks and Unmapped URLs . . . . . . . . . . . . . 25
7.7. Write Locks and Collections . . . . . . . . . . . . . . 27
7.8. Write Locks and the If Request Header . . . . . . . . . 28
7.8.1. Example - Write Lock . . . . . . . . . . . . . . . . 29
7.9. Write Locks and COPY/MOVE . . . . . . . . . . . . . . . 29
7.10. Refreshing Write Locks . . . . . . . . . . . . . . . . . 30
8. HTTP Methods for Distributed Authoring . . . . . . . . . . . 31
8.1. General Request and Response Handling . . . . . . . . . 31
8.1.1. Use of XML . . . . . . . . . . . . . . . . . . . . . 31
8.1.2. Required Bodies in Requests . . . . . . . . . . . . 31
8.1.3. HTTP Headers for use in WebDAV . . . . . . . . . . . 31
8.1.4. ETag . . . . . . . . . . . . . . . . . . . . . . . . 31
8.1.5. Including error response bodies . . . . . . . . . . 32
8.2. PROPFIND . . . . . . . . . . . . . . . . . . . . . . . . 33
8.2.1. PROPFIND status codes . . . . . . . . . . . . . . . 35
8.2.2. Status codes for use with 207 (Multi-Status) . . . . 35
8.2.3. Example - Retrieving Named Properties . . . . . . . 35
8.2.4. Example - Retrieving Named and Dead Properties . . . 37
8.2.5. Example - Using 'propname' to Retrieve all
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Property Names . . . . . . . . . . . . . . . . . . . 37
8.2.6. Example - Using 'allprop' . . . . . . . . . . . . . 39
8.3. PROPPATCH . . . . . . . . . . . . . . . . . . . . . . . 41
8.3.1. Status Codes for use in 207 (Multi-Status) . . . . . 42
8.3.2. Example - PROPPATCH . . . . . . . . . . . . . . . . 43
8.4. MKCOL Method . . . . . . . . . . . . . . . . . . . . . . 44
8.4.1. MKCOL Status Codes . . . . . . . . . . . . . . . . . 45
8.4.2. Example - MKCOL . . . . . . . . . . . . . . . . . . 45
8.5. GET, HEAD for Collections . . . . . . . . . . . . . . . 46
8.6. POST for Collections . . . . . . . . . . . . . . . . . . 46
8.7. DELETE . . . . . . . . . . . . . . . . . . . . . . . . . 46
8.7.1. DELETE for Collections . . . . . . . . . . . . . . . 47
8.7.2. Example - DELETE . . . . . . . . . . . . . . . . . . 47
8.8. PUT . . . . . . . . . . . . . . . . . . . . . . . . . . 48
8.8.1. PUT for Non-Collection Resources . . . . . . . . . . 48
8.8.2. PUT for Collections . . . . . . . . . . . . . . . . 48
8.9. COPY . . . . . . . . . . . . . . . . . . . . . . . . . . 49
8.9.1. COPY for Non-collection Resources . . . . . . . . . 49
8.9.2. COPY for Properties . . . . . . . . . . . . . . . . 49
8.9.3. COPY for Collections . . . . . . . . . . . . . . . . 50
8.9.4. COPY and Overwriting Destination Resources . . . . . 51
8.9.5. Status Codes . . . . . . . . . . . . . . . . . . . . 51
8.9.6. Example - COPY with Overwrite . . . . . . . . . . . 52
8.9.7. Example - COPY with No Overwrite . . . . . . . . . . 53
8.9.8. Example - COPY of a Collection . . . . . . . . . . . 53
8.10. MOVE . . . . . . . . . . . . . . . . . . . . . . . . . . 54
8.10.1. MOVE for Properties . . . . . . . . . . . . . . . . 55
8.10.2. MOVE for Collections . . . . . . . . . . . . . . . . 55
8.10.3. MOVE and the Overwrite Header . . . . . . . . . . . 56
8.10.4. Status Codes . . . . . . . . . . . . . . . . . . . . 56
8.10.5. Example - MOVE of a Non-Collection . . . . . . . . . 57
8.10.6. Example - MOVE of a Collection . . . . . . . . . . . 58
8.11. LOCK Method . . . . . . . . . . . . . . . . . . . . . . 58
8.11.1. Refreshing Locks . . . . . . . . . . . . . . . . . . 59
8.11.2. Depth and Locking . . . . . . . . . . . . . . . . . 60
8.11.3. Locking Unmapped URLs . . . . . . . . . . . . . . . 60
8.11.4. Lock Compatibility Table . . . . . . . . . . . . . . 60
8.11.5. LOCK Responses . . . . . . . . . . . . . . . . . . . 61
8.11.6. Example - Simple Lock Request . . . . . . . . . . . 62
8.11.7. Example - Refreshing a Write Lock . . . . . . . . . 64
8.11.8. Example - Multi-Resource Lock Request . . . . . . . 65
8.12. UNLOCK Method . . . . . . . . . . . . . . . . . . . . . 66
8.12.1. Status Codes . . . . . . . . . . . . . . . . . . . . 66
8.12.2. Example - UNLOCK . . . . . . . . . . . . . . . . . . 67
9. HTTP Headers for Distributed Authoring . . . . . . . . . . . 68
9.1. DAV Header . . . . . . . . . . . . . . . . . . . . . . . 68
9.2. Depth Header . . . . . . . . . . . . . . . . . . . . . . 68
9.3. Destination Header . . . . . . . . . . . . . . . . . . . 70
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9.4. Force-Authentication Header . . . . . . . . . . . . . . 70
9.5. If Header . . . . . . . . . . . . . . . . . . . . . . . 70
9.5.1. No-tag-list Production . . . . . . . . . . . . . . . 71
9.5.2. Tagged-list Production . . . . . . . . . . . . . . . 71
9.5.3. Example - Tagged List If header in COPY . . . . . . 72
9.5.4. Not Production . . . . . . . . . . . . . . . . . . . 72
9.5.5. Matching Function . . . . . . . . . . . . . . . . . 73
9.5.6. If Header and Non-DAV Aware Proxies . . . . . . . . 73
9.6. Lock-Token Header . . . . . . . . . . . . . . . . . . . 74
9.7. Overwrite Header . . . . . . . . . . . . . . . . . . . . 74
9.8. Timeout Request Header . . . . . . . . . . . . . . . . . 74
10. Status Code Extensions to HTTP/1.1 . . . . . . . . . . . . . 76
10.1. 207 Multi-Status . . . . . . . . . . . . . . . . . . . . 76
10.2. 422 Unprocessable Entity . . . . . . . . . . . . . . . . 76
10.3. 423 Locked . . . . . . . . . . . . . . . . . . . . . . . 76
10.4. 424 Failed Dependency . . . . . . . . . . . . . . . . . 76
10.5. 507 Insufficient Storage . . . . . . . . . . . . . . . . 76
11. Use of HTTP Status Codes . . . . . . . . . . . . . . . . . . 77
11.1. 412 Precondition Failed . . . . . . . . . . . . . . . . 77
11.2. 414 Request-URI Too Long . . . . . . . . . . . . . . . . 77
12. Multi-Status Response . . . . . . . . . . . . . . . . . . . . 78
12.1. Response headers . . . . . . . . . . . . . . . . . . . . 78
12.2. URL Handling . . . . . . . . . . . . . . . . . . . . . . 78
12.3. Handling redirected child resources . . . . . . . . . . 79
12.4. Internal Status Codes . . . . . . . . . . . . . . . . . 79
13. XML Element Definitions . . . . . . . . . . . . . . . . . . . 80
13.1. activelock XML Element . . . . . . . . . . . . . . . . . 80
13.2. allprop XML Element . . . . . . . . . . . . . . . . . . 80
13.3. collection XML Element . . . . . . . . . . . . . . . . . 80
13.4. dead-props XML Element . . . . . . . . . . . . . . . . . 81
13.5. depth XML Element . . . . . . . . . . . . . . . . . . . 81
13.6. error XML Element . . . . . . . . . . . . . . . . . . . 81
13.7. exclusive XML Element . . . . . . . . . . . . . . . . . 82
13.8. href XML Element . . . . . . . . . . . . . . . . . . . . 82
13.9. location XML Element . . . . . . . . . . . . . . . . . . 82
13.10. lockentry XML Element . . . . . . . . . . . . . . . . . 83
13.11. lockinfo XML Element . . . . . . . . . . . . . . . . . . 83
13.12. lockroot XML Element . . . . . . . . . . . . . . . . . . 83
13.13. lockscope XML Element . . . . . . . . . . . . . . . . . 84
13.14. locktoken XML Element . . . . . . . . . . . . . . . . . 84
13.15. locktype XML Element . . . . . . . . . . . . . . . . . . 84
13.16. multistatus XML Element . . . . . . . . . . . . . . . . 85
13.17. owner XML Element . . . . . . . . . . . . . . . . . . . 85
13.18. prop XML element . . . . . . . . . . . . . . . . . . . . 85
13.19. propertyupdate XML element . . . . . . . . . . . . . . . 86
13.20. propfind XML Element . . . . . . . . . . . . . . . . . . 86
13.21. propname XML Element . . . . . . . . . . . . . . . . . . 86
13.22. propstat XML Element . . . . . . . . . . . . . . . . . . 87
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13.23. remove XML element . . . . . . . . . . . . . . . . . . . 87
13.24. response XML Element . . . . . . . . . . . . . . . . . . 87
13.25. responsedescription XML Element . . . . . . . . . . . . 88
13.26. set XML element . . . . . . . . . . . . . . . . . . . . 88
13.27. shared XML Element . . . . . . . . . . . . . . . . . . . 89
13.28. status XML Element . . . . . . . . . . . . . . . . . . . 89
13.29. timeout XML Element . . . . . . . . . . . . . . . . . . 89
13.30. write XML Element . . . . . . . . . . . . . . . . . . . 90
14. DAV Properties . . . . . . . . . . . . . . . . . . . . . . . 91
14.1. creationdate Property . . . . . . . . . . . . . . . . . 91
14.2. displayname Property . . . . . . . . . . . . . . . . . . 92
14.3. getcontentlanguage Property . . . . . . . . . . . . . . 92
14.4. getcontentlength Property . . . . . . . . . . . . . . . 93
14.5. getcontenttype Property . . . . . . . . . . . . . . . . 93
14.6. getetag Property . . . . . . . . . . . . . . . . . . . . 94
14.7. getlastmodified Property . . . . . . . . . . . . . . . . 94
14.8. lockdiscovery Property . . . . . . . . . . . . . . . . . 95
14.8.1. Example - Retrieving the lockdiscovery Property . . 96
14.9. resourcetype Property . . . . . . . . . . . . . . . . . 97
14.10. supportedlock Property . . . . . . . . . . . . . . . . . 98
14.10.1. Example - Retrieving the DAV:supportedlock
Property . . . . . . . . . . . . . . . . . . . . . . 99
15. Precondition/postcondition XML elements . . . . . . . . . . . 100
16. Instructions for Processing XML in DAV . . . . . . . . . . . 103
17. DAV Compliance Classes . . . . . . . . . . . . . . . . . . . 104
17.1. Class 1 . . . . . . . . . . . . . . . . . . . . . . . . 104
17.2. Class 2 . . . . . . . . . . . . . . . . . . . . . . . . 104
17.3. Class 'bis' . . . . . . . . . . . . . . . . . . . . . . 104
18. Internationalization Considerations . . . . . . . . . . . . . 106
19. Security Considerations . . . . . . . . . . . . . . . . . . . 108
19.1. Authentication of Clients . . . . . . . . . . . . . . . 108
19.2. Denial of Service . . . . . . . . . . . . . . . . . . . 108
19.3. Security through Obscurity . . . . . . . . . . . . . . . 109
19.4. Privacy Issues Connected to Locks . . . . . . . . . . . 109
19.5. Privacy Issues Connected to Properties . . . . . . . . . 109
19.6. Implications of XML Entities . . . . . . . . . . . . . . 110
19.7. Risks Connected with Lock Tokens . . . . . . . . . . . . 111
19.8. Hosting malicious scripts executed on client machines . 111
20. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 113
21. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 114
21.1. Previous Authors' Addresses . . . . . . . . . . . . . . 115
22. References . . . . . . . . . . . . . . . . . . . . . . . . . 116
22.1. Normative References . . . . . . . . . . . . . . . . . . 116
22.2. Informational References . . . . . . . . . . . . . . . . 116
Appendix A. Notes on Processing XML Elements . . . . . . . . . . 118
A.1. Notes on Empty XML Elements . . . . . . . . . . . . . . 118
A.2. Notes on Illegal XML Processing . . . . . . . . . . . . 118
A.3. Example - XML Syntax Error . . . . . . . . . . . . . . . 118
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A.4. Example - Unknown XML Element . . . . . . . . . . . . . 119
Appendix B. Notes on HTTP Client Compatibility . . . . . . . . . 120
Appendix C. The opaquelocktoken scheme and URIs . . . . . . . . 121
Appendix D. Summary of changes from RFC2518 . . . . . . . . . . 122
D.1. Changes Notable to Server Implementors . . . . . . . . . 122
D.2. Changes Notable to Client Implementors . . . . . . . . . 123
Appendix E. Change Log (to be removed by RFC Editor before
publication) . . . . . . . . . . . . . . . . . . . . 124
E.1. Changes from -05 to -06 . . . . . . . . . . . . . . . . 124
E.2. Changes in -07 . . . . . . . . . . . . . . . . . . . . . 124
E.3. Changes in -08 . . . . . . . . . . . . . . . . . . . . . 125
E.4. Changes in -09 . . . . . . . . . . . . . . . . . . . . . 126
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 128
Intellectual Property and Copyright Statements . . . . . . . . . 129
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1. Introduction
This document describes an extension to the HTTP/1.1 protocol that
allows clients to perform remote web content authoring operations.
This extension provides a coherent set of methods, headers, request
entity body formats, and response entity body formats that provide
operations for:
Properties: The ability to create, remove, and query information
about Web pages, such as their authors, creation dates, etc. Also,
the ability to link pages of any media type to related pages.
Collections: The ability to create sets of documents and to retrieve
a hierarchical membership listing (like a directory listing in a file
system).
Locking: The ability to keep more than one person from working on a
document at the same time. This prevents the "lost update problem",
in which modifications are lost as first one author then another
writes changes without merging the other author's changes.
Namespace Operations: The ability to instruct the server to copy and
move Web resources, operations which change the URL.
Requirements and rationale for these operations are described in a
companion document, "Requirements for a Distributed Authoring and
Versioning Protocol for the World Wide Web" [RFC2291].
This standard does not specify the versioning operations suggested by
[RFC2291]. That work was done in a separate document, "Versioning
Extensions to WebDAV" [RFC3253].
The sections below provide a detailed introduction to 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 8) and the new HTTP headers (Section 9) used with
WebDAV methods.
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 new status codes developed for WebDAV
methods (Section 10) and describes existing HTTP status codes
(Section 11) as used in WebDAV. Since some WebDAV methods may
operate over many resources, the Multi-Status response (Section 12)
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has been introduced to return status information for multiple
resources. Finally, this version of WebDAV introduces precondition
and postcondition (Section 15) XML elements in error response bodies.
WebDAV uses [XML] for property names and some values, and also uses
XML to marshal complicated request and response. This specification
contains DTD and text definitions of all all properties (Section 14)
and all other XML elements (Section 13) used in marshalling. WebDAV
includes a few special rules on how to process XML (Section 16)
appearing in WebDAV so that it truly is extensible.
Finishing off the specification are sections on what it means for a
resource to be compliant with this specification (Section 17), on
internationalization support (Section 18), and on security
(Section 19).
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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 white-space. Since this
augmented BNF uses the basic production rules provided in section 2.2
of [RFC2616], these rules apply to this document as well.
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.
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3. Terminology
URI/URL - A Uniform Resource Identifier and Uniform Resource Locator,
respectively. These terms (and the distinction between them) are
defined in [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.
Collection - A resource that contains a set of URLs, which identify
and locate member resources and which meet the collections
requirements (Section 5).
Member URL - A URL which is a member of the set of URLs contained by
a collection.
Internal Member URL - A Member URL that is immediately relative to
the URL of the collection (the definition of immediately relative is
given later (Section 5.2)).
Property - A name/value pair that contains descriptive information
about a resource.
Live Property - A property whose semantics and syntax are enforced by
the server. For example, the live 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 "principal" is a distinct human or computational actor
that initiates access to network resources.
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4. Data Model for Resource Properties
4.1. The Resource Property Model
Properties are pieces of data that describe the state of a resource.
Properties are data about data.
Properties are used in distributed authoring environments to provide
for efficient discovery and management of resources. For example, a
'subject' property might allow for the indexing of all resources by
their subject, and an 'author' property might allow for the discovery
of what authors have written which documents.
The DAV property model consists of name/value pairs. The name of a
property identifies the property's syntax and semantics, and provides
an address by which to refer to its syntax and semantics.
There are two categories of properties: "live" and "dead". A live
property has its syntax and semantics enforced by the server. Live
properties include cases where a) the value of a property is read-
only, maintained by the server, and b) the value of the property is
maintained by the client, but the server performs syntax checking on
submitted values. All instances of a given live property MUST comply
with the definition associated with that property name. A dead
property has its syntax and semantics enforced by the client; the
server merely records the value of the property verbatim.
4.2. 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 which allows a principal to
identify a set of properties in which the principal is interested and
to set or retrieve just those properties.
4.3. XML Usage
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] 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
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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 MIME 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.
The XML namespace extension [W3C.REC-xml-names-19990114] is also used
in this specification in order to allow for new XML elements to be
added without fear of colliding with other element names. Although
WebDAV request and response bodies can be extended by arbitrary XML
elements, which can be ignored by the message recipient, an XML
element in the "DAV:" namespace SHOULD NOT be used in the request or
response body unless that XML element is explicitly defined in an
IETF RFC reviewed by a WebDAV working group.
Note that "DAV:" uses a scheme name defined solely for the purpose of
creating this XML namespace. Defining new URI schemes for namespaces
is discouraged. "DAV:" was defined before standard best practices
emerged, and this namespace is still used only because of significant
existing deployments.
4.4. 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 new elements. Older 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.
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 a 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), not multiple values in different languages or a single
value in multiple languages.
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A property is always represented in XML 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:
The value of a 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. In the latter case, servers MUST
preserve certain aspects of the content (described using the
terminology from [W3C.REC-xml-infoset-20040204]).
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 value:
[namespace name]
[local name]
[attributes]
[children] of type element or character
On Attribute Information Items in the value:
[namespace name]
[local name]
[normalized value]
On Character Information Items in the value:
[character code]
Since prefixes are used in some XML query/handling tools, servers
SHOULD preserve, for any Information Item in the value:
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[prefix]
In dead properties (considered as content, like document bodies)
servers are encouraged to (MAY) preserve, for any Comment Information
Item in the value:
[content]
XML Infoset attributes not listed above MAY be preserved by the
server, but clients MUST NOT rely on them being preserved.
The XML attribute xml:space MUST NOT be used to change white space
handling. White space in property values is significant.
4.4.1. Example - Property with Mixed Content
Consider a dead property 'author' created by the client as follows:
Jane Doe
mailto:jane.doe@example.com
http://www.example.com
Jane has been working way too long on the
long-awaited revision of ]]>.
When this property is requested, a server might return:
Jane Doe
mailto:jane.doe@example.com
http://www.example.com
Jane has been working way too long on the
long-awaited revision of <RFC2518>.
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Note in this example:
o The [prefix] for the property name itself was not preserved, being
non-significant
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.
4.5. Property Names
A property name is a universally unique identifier that is associated
with a schema that provides information about the syntax and
semantics of the property.
Because a property's name is universally unique, clients can depend
upon consistent behavior for a particular property across multiple
resources, on the same and across different servers, so long as that
property is "live" on the resources in question, and the
implementation of the live property is faithful to its definition.
The XML namespace mechanism, which is based on URIs ([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
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between the two properties. It is expected that a separate
specification will eventually be produced which will address issues
relating to hierarchical properties.
Finally, it is not possible to define the same property twice on a
single resource, as this would cause a collision in the resource's
property namespace.
4.6. 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.
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5. Collections of Web Resources
This section provides a description of a new type of Web resource,
the collection, and discusses its interactions with the HTTP URL
namespace. The purpose of a collection resource is to model
collection-like objects (e.g., file system directories) within a
server's namespace.
All DAV compliant resources MUST support the HTTP URL namespace model
specified herein.
5.1. HTTP URL Namespace Model
The HTTP URL namespace is a hierarchical namespace where the
hierarchy is delimited with the "/" character.
An HTTP URL namespace is said to be consistent if it meets the
following conditions: for every URL in the HTTP hierarchy there
exists a collection that contains that URL as an internal member.
The root, or top-level collection of the namespace under
consideration is exempt from the previous rule. 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 require 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.
Although 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
A collection is a resource whose state consists of at least a list of
internal member URLs and a set of properties, but which may have
additional state such as entity bodies returned by GET. An internal
member URL MUST be immediately relative to a base URL of the
collection. That is, the internal member URL is equal to a
containing collection's URL plus an additional segment for non-
collection resources, or additional segment plus trailing slash "/"
for collection resources, where segment is defined in section 3.3 of
[RFC3986].
Any given internal member URL MUST only belong to the collection
once, i.e., it is illegal to have multiple instances of the same URL
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in a collection. Properties defined on collections behave exactly as
do properties on non-collection resources.
For all WebDAV compliant resources A and B, identified by URLs U and
V, for which U is immediately relative to V, B MUST be a collection
that has U as an internal member URL. So, if the resource with URL
http://example.com/bar/blah is WebDAV compliant and if the resource
with URL http://example.com/bar/ is WebDAV compliant then the
resource with URL http://example.com/bar/ must be a collection and
must contain URL http://example.com/bar/blah as an internal member.
Collection resources MAY list the URLs of non-WebDAV compliant
children in the HTTP URL namespace hierarchy as internal members but
are not required to do so. For example, if the resource with URL
http://example.com/bar/blah is not WebDAV compliant and the URL
http://example.com/bar/ identifies a collection then URL
http://example.com/bar/blah may or may not be an internal member of
the collection with URL http://example.com/bar/.
If a WebDAV compliant resource has no WebDAV compliant children in
the HTTP URL namespace hierarchy then the WebDAV compliant resource
is not required to be a collection.
There is a standing convention that when a collection is referred to
by its name without a trailing slash, the 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
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 a 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.
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6. Locking
The ability to lock a resource provides a mechanism for serializing
access to that resource. Using a lock, an authoring client can
provide a reasonable guarantee that another principal will not modify
a resource while it is being edited. In this way, a client can
prevent the "lost update" problem.
This specification allows locks to vary over two client-specified
parameters, the number of principals involved (exclusive vs. shared)
and the type of access to be granted. This document defines locking
for only one access type, write. However, the syntax is extensible,
and permits the eventual specification of locking for other access
types.
6.1. Exclusive Vs. Shared Locks
The most basic form of lock is an exclusive lock. Only one exclusive
lock may exist on any resource, whether it is directly or indirectly
locked (Section 7.7). Exclusive locks avoid having to merge results,
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 with appropriate access can use the lock.
With shared locks there are two trust sets that affect a resource.
The first trust set is created by access permissions. Principals who
are trusted, for example, may have permission to write to the
resource. Among those who have access permission to write to the
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.
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The WebDAV extensions to HTTP do not need to provide all of the
communications paths necessary for principals to coordinate their
activities. When using shared locks, principals may use any out of
band communication channel to coordinate their work (e.g., face-to-
face interaction, written notes, post-it notes on the screen,
telephone conversation, Email, etc.) The intent of a shared lock is
to let collaborators know who else may be working on a resource.
Shared locks are included because experience from web distributed
authoring systems has indicated that exclusive locks are often too
rigid. An exclusive lock is used to enforce a particular editing
process: take out an exclusive lock, read the resource, perform
edits, write the resource, release the lock. This editing process
has the problem that locks are not always properly released, for
example when a program crashes, or when a lock owner leaves without
unlocking a resource. While both timeouts and administrative action
can be used to remove an offending lock, neither mechanism may be
available when needed; the timeout may be long or the administrator
may not be available.
6.2. Required Support
A WebDAV compliant 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.
6.3. Lock Tokens
A lock token is a type of state token, represented as a URI, which
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.
When a LOCK operation creates a new lock, the new lock token is
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returned in the Lock-Token response header defined in Section 9.6,
and also in the body of the response.
Submitting a lock token does not confer full privilege to use the
lock token or modify the locked resource. Anyone can find out anyone
else's lock token by performing lock discovery. Write access and
other privileges MUST be enforced through normal privilege or
authentication mechanisms, not based on the slight obscurity of lock
token values.
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.
This specification encourages servers to create 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"
6.4. 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.
6.5. Active Lock Discovery
If another principal locks a resource that a principal wishes to
access, it is useful for the second principal to be able to find out
who the first principal is. For this purpose the DAV:lockdiscovery
property is provided. This property lists all outstanding locks,
describes their type, and MAY even provide the lock tokens.
Any DAV compliant resource that supports the LOCK method MUST support
the DAV:lockdiscovery property.
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6.6. Locks and Multiple Bindings
A resource may be made available through more than one URI. However
locks apply to resources, not URIs. Therefore a LOCK request on a
resource MUST NOT succeed if can not be honored by all the URIs
through which the resource is addressable.
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7. Write Lock
This section describes the semantics specific to the write lock type.
The write lock is a specific instance of a lock type, and is the only
lock type described in this specification.
An exclusive write lock will prevent parallel changes to a resource
by any principal other than the write lock holder. In general terms,
changes affected by write locks include changes to:
o the content of the resource
o any dead property of the resource
o any live property defined to be lockable (all properties defined
in this specification are lockable)
o the direct membership of the resource, if it is a collection
o the URL/location of a resource
The next few sections describe in more specific terms how write locks
interact with various operations.
7.1. Lock Owner
The creator of the lock is the lock owner. The server MUST restrict
the usage of the lock token to the lock owner (both for shared and
exclusive locks -- for multi-user shared lock cases, each
authenticated principal MUST obtain its own shared lock).
The server MAY allow privileged users other than the lock owner to
destroy a lock (for example, the resource owner or an administrator)
as a special case of lock usage.
If an anonymous user requests a lock, the server MAY refuse the
request.
7.2. Methods Restricted by Write Locks
A server MUST reject any write request that alters a write-locked
resource unless a valid lock token is provided. The write operations
defined in HTTP and WebDAV are PUT, POST, PROPPATCH, LOCK, UNLOCK,
MOVE, COPY (for the destination resource), DELETE, and MKCOL. All
other HTTP/WebDAV methods, GET in particular, function independently
of the lock. A shared write lock prevents the same operations,
however it also allows access by any principal that has a shared
write lock on the same resource.
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Note, however, that as new methods are created it will be necessary
to specify how they interact with a write lock.
7.3. Write Locks and Lock Tokens
A successful request for an exclusive or shared write lock MUST
result in the generation of a unique lock token associated with the
requesting principal. Thus if five principals have a shared write
lock on the same resource there will be five lock tokens, one for
each principal.
7.4. Write Locks and Properties
While those without a write lock may not alter a property on a
resource it is still possible for the values of live properties to
change, even while locked, due to the requirements of their schemas.
Only dead properties and live properties defined to respect locks are
guaranteed not to change while write locked.
7.5. 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
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clients will accidentally overwrite each other's changes by requiring
clients to lock resources before modifying them. Such servers would
effectively prevent HTTP 1.0 and HTTP 1.1 clients from modifying
resources.
WebDAV clients can be good citizens by using a lock / retrieve /
write /unlock sequence of operations (at least by default) whenever
they interact with a WebDAV server that supports locking.
HTTP 1.1 clients can be good citizens, avoiding overwriting other
clients' changes, by using entity tags in If-Match headers with any
requests that would modify resources.
Information managers may attempt to prevent overwrites by
implementing client-side procedures requiring locking before
modifying WebDAV resources.
7.6. Write Locks and Unmapped URLs
It is possible to lock an unmapped URL in order to lock the name for
use. This is a simple way to avoid the lost-update problem on the
creation of a new resource (another way is to use If-None-Match
header specified in HTTP 1.1). It has the side benefit of locking
the new resource immediately for use of the creator.
The lost-update problem is not an issue for collections because MKCOL
can only be used to create a collection, not to overwrite an existing
collection. When trying to lock a collection upon creation, clients
may 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 an locked resource with empty content. Subsequently, a
successful PUT request (with the correct lock token) provides the
content for the resource, and the server MUST also use the content-
type and content-language information from this request.
In this situation, a WebDAV server that was implemented from
[RFC2518] MAY create "lock-null" resources which are special and
unusual resources. Historically, a lock-null resource:
o Responds with a 404 or 405 to any DAV method except for PUT,
MKCOL, OPTIONS, PROPFIND, LOCK, UNLOCK.
o Appears as a member of its parent collection.
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o Disappears (URI becomes unmapped) if its lock goes away before it
is converted to a regular resource. (This must also happen if it
is renamed or moved, or if any parent collection is renamed or
moved, because locks are tied to URLs).
o May be turned into a regular resource when a PUT request to the
URL is successful. Ceases to be a lock-null resource.
o May be turned into a collection when a MKCOL request to the URL is
successful. Ceases to be a lock-null resource.
o Has defined values for DAV:lockdiscovery and DAV:supportedlock
properties.
However, interoperability and compliance problems have been found
with lock-null resources. Therefore, they are deprecated. WebDAV
servers SHOULD create regular locked empty resources, which are and
behave in every way as normal resources. A locked empty resource:
o Can be read, deleted, moved, copied, and in all ways behave as a
regular resource, not a lock-null 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)
o SHOULD default to having no content type.
o MAY NOT have values for properties like DAV:getcontentlanguage
which haven't been specified yet by the client.
o May have content added with a PUT request. MUST be able to change
content type.
o MUST NOT be turned into a collection. A MKCOL request must fail
as it would to any existing 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.
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The client is expected to update the locked empty resource shortly
after locking it, using PUT and possibly PROPPATCH. When the client
uses PUT to overwrite a locked empty resource the client MUST supply
a Content-Type if any is known. If the client supplies a Content-
Type value the server MUST set that value (this requirement actually
applies to any resource that is overwritten but is particularly
necessary for locked empty resources which are initially created with
no Content-Type.
Clients can easily interoperate both with servers that support the
deprecated lock-null resources and servers that support simpler
locked empty resources by only attempting PUT after a LOCK to an
unmapped URL, not MKCOL or GET.
7.7. Write Locks and Collections
A write lock on a collection, whether created by a "Depth: 0" or
"Depth: infinity" lock request, prevents the addition or removal of
member URLs of the collection by non-lock owners.
A zero-depth lock on a collection affects changes to the direct
membership of that collection. When a principal issues a write
request to create a new resource in a write locked collection, or
isses a DELETE, MOVE or other request that would remove an existing
internal member URL of a write locked collection or change the
binding name, this request MUST fail if the principal does not
provide the correct lock token for the locked collection.
This means that if a collection is locked (depth 0 or infinity), its
lock-token is required in all these cases:
o DELETE a collection's direct internal member
o MOVE a member out of the collection
o MOVE a member into the collection
o MOVE to rename a member within a collection
o COPY a member into a collection
o PUT or MKCOL request which would create a new 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 descendents of the locked collection. With a depth-infinity
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lock, the root of the lock is directly locked, and all its
descendants are indirectly locked.
o Any new resource added as a descendent 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 within the scope of 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 which conflicts with the write lock, the request
MUST fail with a 423 (Locked) status code, and the response SHOULD
contain the 'lock-token-present' precondition.
If a lock owner 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 added to the lock. This is the
only mechanism that allows a resource to be added to a write lock.
Thus, for example, if the collection /a/b/ is write locked and the
resource /c is moved to /a/b/c then resource /a/b/c will be added to
the write lock.
7.8. Write Locks and the If Request Header
If a user agent is not required to have knowledge about a lock when
requesting an operation on a locked resource, the following scenario
might occur. Program A, run by User A, takes out a write lock on a
resource. Program B, also run by User A, has no knowledge of the
lock taken out by Program A, yet performs a PUT to the locked
resource. In this scenario, the PUT succeeds because locks are
associated with a principal, not a program, and thus program B,
because it is acting with principal 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
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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.
7.8.1. Example - Write Lock
>>Request
COPY /~fielding/index.html HTTP/1.1
Host: www.ics.uci.edu
Destination: http://www.ics.uci.edu/users/f/fielding/index.html
If:
()
>>Response
HTTP/1.1 204 No Content
In this example, even though both the source and destination are
locked, only one lock token must be submitted, for the lock on the
destination. This is because the source resource is not modified by
a COPY, and hence unaffected by the write lock. In this example,
user agent authentication has previously occurred via a mechanism
outside the scope of the HTTP protocol, in the underlying transport
layer.
7.9. 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 "Depth: infinity",
then the resource will be added to the lock.
A successful MOVE request on a write locked resource MUST NOT move
the write lock with the resource. However, the resource is subject
to being added to an existing lock at the destination (see
Section 7.7). For example, if the MOVE makes the resource a child of
a collection that is locked with "Depth: infinity", then the resource
will be added to that collection's lock. Additionally, if a resource
locked with "Depth: infinity" 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 a added
to the lock. In both these examples, as specified in Section 7.8, an
If header must be submitted containing a lock token for both the
source and destination.
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7.10. Refreshing Write Locks
A client MUST NOT submit the same write lock request twice. Note
that a client is always aware it is resubmitting the same lock
request because it must include the lock token in the If header in
order to make the request for a resource that is already locked.
However, a client may submit a LOCK method with an If header but
without a body. This form of LOCK MUST only be used to "refresh" a
lock. Meaning, at minimum, that any timers associated with the lock
MUST be re-set.
A server may return a Timeout header with a lock refresh that is
different than the Timeout header returned when the lock was
originally requested. Additionally clients may submit Timeout
headers of arbitrary value with their lock refresh requests.
Servers, as always, may ignore Timeout headers submitted by the
client. Note that timeout is measured in seconds remaining until
expiration.
If an error is received in response to a refresh LOCK request the
client MUST NOT assume that the lock was refreshed.
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8. HTTP Methods for Distributed Authoring
8.1. General Request and Response Handling
8.1.1. Use of XML
Some of the following new HTTP methods use XML as a request and
response format. All DAV compliant clients and resources MUST use
XML parsers that are compliant with [XML] and XML Namespaces
[W3C.REC-xml-names-19990114]. 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 19). 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.
8.1.2. 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 they intended.
8.1.3. 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]).
8.1.4. ETag
HTTP 1.1 recommends the use of the ETag header in responses to GET
and PUT requests. 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
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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 client is forced
to ask the user whether to overwrite the resource on the server
without even being able to tell the user whether it has changed.
Timestamps do not solve this problem nearly as well as ETags.
WebDAV servers SHOULD support strong ETags for all resources that may
be PUT. If ETags are supported for a resource, the server MUST
return the ETag header in all PUT and GET responses to that resource,
as well as provide the same value for the DAV:getetag property.
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 DAV:getlastmodified value) for a resource that has an
unchanged body. The ETag represents the state of the body or
contents of the resource. There is no similar way to tell if
properties have changed.
8.1.5. Including error response bodies
HTTP and WebDAV did not use the bodies of most error responses for
machine-parsable information until DeltaV introduced a mechanism to
include more specific information in the body of an error response
(section 1.6 of [RFC3253]). The 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 mechanism does not take the place of using a correct numeric
error 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 error. However, it does remove the need to define new
numeric error codes, avoiding the confusion of who is allowed to
define such new codes. The codes used in this mechanism are XML
elements in a namespace, so naturally any group defining a new error
code can use their own namespace. As always, the "DAV:" namespace is
reserved for use by IETF-chartered WebDAV working groups.
A server supporting "bis" SHOULD include a specific XML error code in
a "DAV:error" response body element, when a specific XML error code
is defined in this document. The DAV:error element may contain
multiple elements describing specific errors. For error conditions
not specified in this document, the server MAY simply choose an
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appropriate numeric status and leave the response body blank.
8.1.5.1. Example - Response with precondition code
>>Response
HTTP/1.1 403 Forbidden
Content-Type: application/xml; charset="utf-8"
Content-Length: xxxx
In this specification, both the numeric and the XML error code are
defined for some failure situations, in which case the XML error code
must have the "DAV:" namespace, appear in the "error" root element,
and be returned in a body with the numeric error code specified.
8.2. PROPFIND
The PROPFIND method retrieves properties defined on the resource
identified by the Request-URI, if the resource does not have any
internal members, or on the resource identified by the Request-URI
and potentially its member resources, if the resource is a collection
that has internal member URLs. All DAV compliant resources MUST
support the PROPFIND method and the propfind XML element
(Section 13.20) along with all XML elements defined for use with that
element.
A client may submit a Depth header with a value of "0", "1", or
"infinity" with a PROPFIND on a collection resource. Servers MUST
support the "0", "1" and "infinity" behaviors on WebDAV-compliant
resources. By default, the PROPFIND method without a Depth header
MUST act as if a "Depth: infinity" header was included.
A client may submit a 'propfind' XML element in the body of the
request method describing what information is being requested. It is
possible to:
o Request particular property values, by naming the properties
desired within the 'prop' element (the ordering of properties in
here MAY be ignored by server)
o Request all dead property values, by using 'dead-props' element.
This can be combined with retrieving specific live properties
named as above. Servers advertising support for this
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specification MUST support this feature.
o Request property values for those properties defined in this
specification plus dead properties, by using 'allprop' element
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. A WebDAV server MAY omit certain
live properties from other specifications when responding to an
'allprop' request from an older client, and MAY return only custom
(dead) properties and those defined in this specification.
All servers MUST support returning a response of content type text/
xml or application/xml that contains a multistatus XML element that
describes the results of the attempts to retrieve the various
properties.
If there is an error retrieving a property then a proper error result
MUST be included in the response. A request to retrieve the value of
a property which does not exist is an error and MUST be noted, if the
response uses a 'multistatus' XML element, with a 'response' XML
element which contains a 404 (Not Found) status value.
Consequently, the 'multistatus' XML element for a collection resource
with member URLs MUST include a 'response' XML element for each
member URL of the collection, to whatever depth was requested. Each
'response' XML element MUST contain an 'href' XML 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 with internal member URLs are returned as a flat list whose
order of entries is not significant.
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.
The results of this method SHOULD NOT be cached.
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8.2.1. PROPFIND status codes
A server MAY fail an entire PROPFIND request with an appropriate
status code and MAY redirect the entire request. In addition, the
following error codes are specifically defined for PROPFIND requests:
403 Forbidden - A server MAY reject all 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.
8.2.2. Status codes for use with 207 (Multi-Status)
The following status codes are defined for use within the PROPFIND
Multi-Status response:
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.
8.2.3. Example - Retrieving Named Properties
>>Request
PROPFIND /file HTTP/1.1
Host: www.example.com
Content-type: application/xml; charset="utf-8"
Content-Length: xxxx
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>>Response
HTTP/1.1 207 Multi-Status
Content-Type: application/xml; charset="utf-8"
Content-Length: xxxx
http://www.example.com/file
Box type A
J.J. Johnson
HTTP/1.1 200 OK
HTTP/1.1 403 Forbidden
The user does not have access to the
DingALing property.
There has been an access violation error.
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.
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8.2.4. Example - Retrieving Named and Dead Properties
>>Request
PROPFIND /mycol/ HTTP/1.1
Host: www.example.com
Depth: 1
Content-type: application/xml; charset="utf-8"
Content-Length: xxxx
In this example, PROPFIND is executed on a collection resource
http://www.example.com/mycol/. The client requests the values of two
specific live properties plus all dead properties (names and values).
The response is not shown.
8.2.5. 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
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>>Response
HTTP/1.1 207 Multi-Status
Content-Type: application/xml; charset="utf-8"
Content-Length: xxxx
http://www.example.com/container/
HTTP/1.1 200 OK
http://www.example.com/container/front.html
HTTP/1.1 200 OK
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 descendents should be
returned.
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Consistent with the previous example, resource
http://www.example.com/container/ has six properties defined on it:
bigbox and author in the "http://www.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://www.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 which do not explicitly state the namespace to
which they belong are members of the "DAV:" namespace.
8.2.6. Example - Using '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
>>Response
HTTP/1.1 207 Multi-Status
Content-Type: application/xml; charset="utf-8"
Content-Length: xxxx
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/container/
Box type A
Hadrian
1997-12-01T17:42:21-08:00
Example collection
HTTP/1.1 200 OK
/container/front.html
Box type B
1997-12-01T18:27:21-08:00
Example HTML resource
4525
text/html
zzyzx
Monday, 12-Jan-98 09:25:56 GMT
HTTP/1.1 200 OK
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In this example, PROPFIND was invoked on the resource
http://www.foo.bar/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.foo.bar/container/ has six properties defined
on it: 'bigbox' and 'author in the "http://www.foo.bar/boxschema/"
namespace, DAV:creationdate, DAV:displayname, DAV:resourcetype, and
DAV:supportedlock.
The last four properties are WebDAV-specific, defined in Section 14.
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.foo.bar/container/front.html has nine
properties defined on it:
'bigbox' in the "http://www.foo.bar/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).
8.3. PROPPATCH
The PROPPATCH method processes instructions specified in the request
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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. Instruction processing MUST occur 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 Section 13.23 and Section 13.26.
8.3.1. Status Codes for use in 207 (Multi-Status)
The following are examples of response codes one would expect to be
used in a 207 (Multi-Status) response for this method. Note,
however, that unless explicitly prohibited any 2/3/4/5xx series
response code may be used in a 207 (Multi-Status) response.
200 (OK) - The 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 read-only
property, such as DAV:getetag. If returning this error, the server
SHOULD use the precondition code 'writable-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.
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8.3.2. Example - PROPPATCH
>>Request
PROPPATCH /bar.html HTTP/1.1
Host: www.example.com
Content-Type: application/xml; charset="utf-8"
Content-Length: xxxx
Jim Whitehead
Roy Fielding
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>>Response
HTTP/1.1 207 Multi-Status
Content-Type: application/xml; charset="utf-8"
Content-Length: xxxx
http://www.example.com/bar.html
HTTP/1.1 424 Failed Dependency
HTTP/1.1 409 Conflict
Copyright Owner can not be deleted or
altered.
In this example, the client requests the server to set the value of
the "Authors" property in the "http://www.w3.com/standards/z39.50/"
namespace, and to remove the property "Copyright-Owner" in the
"http://www.w3.com/standards/z39.50/" namespace. Since the
Copyright-Owner property could not be removed, no property
modifications occur. The 424 (Failed Dependency) status code for the
Authors property indicates this action would have succeeded if it
were not for the conflict with removing the Copyright-Owner property.
8.4. MKCOL Method
The MKCOL method is used to create a new collection. All WebDAV
compliant resources MUST support the 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 a member of its parent collection, unless the
Request-URI is "/". If no such ancestor exists, the method MUST
fail. When the MKCOL operation creates a new collection resource,
all ancestors MUST already exist, or the method MUST fail with a 409
(Conflict) status code. For example, if a request to create
collection /a/b/c/d/ is made, and /a/b/c/ does not exist, the request
must fail.
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When MKCOL is invoked without a request body, the newly created
collection SHOULD have no members.
A MKCOL request message may contain a message body. The 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.
8.4.1. MKCOL Status Codes
Responses from a MKCOL request MUST NOT be cached as MKCOL has non-
idempotent semantics. 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 (since this specification does not define any body
for MKCOL requests).
507 (Insufficient Storage) - The resource does not have sufficient
space to record the state of the resource after the execution of this
method.
8.4.2. Example - MKCOL
This example creates a collection called /webdisc/xfiles/ on the
server www.example.com.
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>>Request
MKCOL /webdisc/xfiles/ HTTP/1.1
Host: www.example.com
>>Response
HTTP/1.1 201 Created
8.5. 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.
8.6. POST for Collections
Since by definition the actual function performed by POST is
determined by the server and often depends on the particular
resource, the behavior of POST when applied to collections cannot be
meaningfully modified because it is largely undefined. Thus the
semantics of POST are unmodified when applied to a collection.
8.7. DELETE
DELETE is defined in [RFC2616], section 9.7, to "delete the resource
identified by the Request-URI". However, WebDAV changes some DELETE
handling requirements.
A server processing a successful DELETE request:
MUST destroy locks rooted on the deleted resource
MUST remove the mapping from the Request-URI to any resource.
Thus, after a successful DELETE operation (and in the absence of
other actions) a subsequent GET/HEAD/PROPFIND request to the target
Request-URI MUST return 404 (Not Found).
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8.7.1. 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 an internal 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 Multi-
Status, if the request failed.
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.
8.7.2. Example - DELETE
>>Request
DELETE /container/ HTTP/1.1
Host: www.example.com
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>>Response
HTTP/1.1 207 Multi-Status
Content-Type: application/xml; charset="utf-8"
Content-Length: xxxx
http://www.example.com/container/resource3
HTTP/1.1 423 Locked
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 can not be deleted unless its child has also been deleted.
Even though a Depth header has not been included, a depth of infinity
is assumed because the method is on a collection.
8.8. PUT
8.8.1. 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).
8.8.2. 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.
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8.9. COPY
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. The state of the resource to be copied is fixed at
the point the server begins processing the COPY request.
All WebDAV compliant resources MUST support the COPY method.
However, support for the COPY method does not guarantee the ability
to copy a resource. For example, separate programs may control
resources on the same server. As a result, it may not be possible to
copy a resource to a location that appears to be on the same server.
8.9.1. 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.
8.9.2. COPY for Properties
After a successful COPY invocation, all dead properties on the source
resource MUST be duplicated on the destination resource, along with
all properties as appropriate. 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.
A COPY operation creates a new resource, much like a PUT operation
does. Live properties which are related to resource creation (such
as DAV:creationdate) should have their values set accordingly.
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8.9.3. 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.
A COPY of depth infinity instructs that the collection resource
identified by the Request-URI is to be copied to the location
identified by the URI in the Destination header, and all its internal
member resources are to be copied to a location relative to it,
recursively through all levels of the collection hierarchy.
A COPY of "Depth: 0" only instructs that the collection and its
properties but not resources identified by its internal member 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 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 descendents of an error-causing collection).
So, for example, if an infinite depth copy operation is performed on
collection /a/, which contains collections /a/b/ and /a/c/, and an
error occurs copying /a/b/, an attempt should still be made to copy
/a/c/. Similarly, after encountering an error copying a non-
collection resource as part of an infinite depth copy, the server
SHOULD try to finish as much of the original copy operation as
possible.
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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.
8.9.4. 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]). Some
considerations:
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 source collection membership
could completely replace the destination collection membership, or
the source collection membership could be combined with the
destination collection membership.
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
or to force collection membership to be reset), then the client could
send a DELETE to the destination before the COPY request to ensure
this reset.
8.9.5. 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.
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204 (No Content) - The source resource was successfully copied to a
pre-existing destination resource.
207 (Multi-Status) - Multiple resources were to be affected by the
COPY, but errors on some of them prevented the operation from taking
place. Specific error messages, together with the most appropriate
of the source and destination URLs, appear in the body of the multi-
status response. E.g. if a destination resource was locked and could
not be overwritten, then the destination resource URL appears with
the 423 (Locked) status.
403 (Forbidden) - 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.
423 (Locked) - The destination resource, or resource within the
destination collection, was locked. This response SHOULD contain the
'lock-token-present' 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.
8.9.6. Example - COPY with Overwrite
This example shows resource
http://www.ics.uci.edu/~fielding/index.html being copied to the
location http://www.ics.uci.edu/users/f/fielding/index.html. The 204
(No Content) status code indicates the existing resource at the
destination was overwritten.
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>>Request
COPY /~fielding/index.html HTTP/1.1
Host: www.ics.uci.edu
Destination: http://www.ics.uci.edu/users/f/fielding/index.html
>>Response
HTTP/1.1 204 No Content
8.9.7. 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.ics.uci.edu
Destination: http://www.ics.uci.edu/users/f/fielding/index.html
Overwrite: F
>>Response
HTTP/1.1 412 Precondition Failed
8.9.8. Example - COPY of a Collection
>>Request
COPY /container/ HTTP/1.1
Host: www.example.com
Destination: http://www.example.com/othercontainer/
Depth: infinity
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>>Response
HTTP/1.1 207 Multi-Status
Content-Type: application/xml; charset="utf-8"
Content-Length: xxxx
http://www.example.com/othercontainer/R2/
HTTP/1.1 423 Locked
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.
8.10. MOVE
The MOVE operation on a non-collection resource is the logical
equivalent of a copy (COPY), followed by consistency maintenance
processing, followed by a delete of the source, where all three
actions are performed atomically. The consistency maintenance step
allows the server to perform updates caused by the move, such as
updating all URLs other than the Request-URI which identify the
source resource, to point to the new destination resource.
Consequently, the Destination header MUST be present on all MOVE
methods and MUST follow all COPY requirements for the COPY part of
the MOVE method. All WebDAV compliant resources MUST support the
MOVE method. However, support for the MOVE method does not guarantee
the ability to move a resource to a particular destination.
For example, separate programs may actually control different sets of
resources on the same server. Therefore, it may not be possible to
move a resource within a namespace that appears to belong to the same
server.
If a resource exists at the destination, the destination resource
will be deleted as a side-effect of the MOVE operation, subject to
the restrictions of the Overwrite header.
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8.10.1. 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 which 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.
8.10.2. 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".
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 descendents of an error-causing collection).
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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.
8.10.3. MOVE and the Overwrite Header
If a resource exists at the destination and the Overwrite header is
"T" then prior to performing the move the server MUST perform a
DELETE with "Depth: infinity" on the destination resource. If the
Overwrite header is set to "F" then the operation will fail.
8.10.4. 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. E.g. if a source resource was locked and could not
be moved, then the source resource URL appears with the 423 (Locked)
status.
403 (Forbidden) - Among many possible reasons for forbidding a MOVE
operation, this status code is recommended for use when the source
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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 state
of 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-present' 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.
8.10.5. Example - MOVE of a Non-Collection
This example shows resource
http://www.ics.uci.edu/~fielding/index.html being moved to the
location http://www.ics.uci.edu/users/f/fielding/index.html. The
contents of the destination resource would have been overwritten if
the destination 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.ics.uci.edu
Destination: http://www.ics.uci.edu/users/f/fielding/index.html
>>Response
HTTP/1.1 201 Created
Location: http://www.ics.uci.edu/users/f/fielding/index.html
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8.10.6. Example - MOVE of a Collection
>>Request
MOVE /container/ HTTP/1.1
Host: www.example.com
Destination: http://www.example.com/othercontainer/
Overwrite: F
If: ()
()
>>Response
HTTP/1.1 207 Multi-Status
Content-Type: application/xml; charset="utf-8"
Content-Length: xxxx
http://www.example.com/othercontainer/C2/
HTTP/1.1 423 Locked
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.
8.11. 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 which supports the LOCK method MUST, at minimum, support
the XML request and response formats defined herein.
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A LOCK method invocation to an unlocked resource creates a lock on
the resource identified by the Request-URI, which becomes the root of
the lock. Lock method requests to create a new lock MUST have a XML
request body which contains an owner XML element and other
information for this lock request. The server MUST preserve the
information provided by the client in the 'owner' field when the lock
information is requested. The LOCK request MAY have a Timeout
header.
Clients MUST assume that locks may arbitrarily disappear at any time,
regardless of the value given in the Timeout header. The Timeout
header only indicates the behavior of the server if extraordinary
circumstances do not occur. For example, a sufficiently privileged
user may remove a lock at any time or the system may crash in such a
way that it loses the record of the lock's existence.
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.
8.11.1. Refreshing Locks
A lock is refreshed by sending a LOCK request without a request body
to the URL of a resource within the scope of the lock. This request
MUST specify which lock to refresh by using the 'Lock-Token' header
with a single lock token (only one lock may be refreshed at a time).
It 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.
Note that in RFC2518, clients were indicated through the example in
the text to use the If header to specify what lock to refresh (rather
than the Lock-Token header). Servers are encouraged to continue to
support this as well as the Lock-Token header.
Note that the Lock-Token header is not be returned in the response
for a successful refresh LOCK request, but the LOCK response body
MUST contain the new value for the DAV:lockdiscovery body.
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8.11.2. Depth and Locking
The Depth header may be used with the LOCK method. Values other than
0 or infinity MUST NOT be used with the Depth header on a LOCK
method. All resources that support the LOCK method MUST support the
Depth header.
A Depth header of value 0 means to just lock the resource specified
by the Request-URI.
If the Depth header is set to infinity then the resource specified in
the Request-URI along with all its internal members, all the way down
the hierarchy, are to be locked. A successful result MUST return a
single lock token which represents all the resources that have been
locked. If an UNLOCK is successfully executed on this token, all
associated resources are unlocked. Hence, partial success is not an
option. 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 which prevented the lock from being granted, along with
a suitable status c