Internet Draft L. Dusseault, Xythos
Document: draft-ietf-webdav-rfc2518bis-04.txt J. Crawford, IBM
Expires: Oct 2003
HTTP Extensions for Distributed Authoring - WebDAV RFC2518 bis
Status of this Memo
This document is an Internet-Draft and is in full conformance
with all provisions of Section 10 of RFC2026.
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The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Abstract
WebDAV consists of a set of methods, headers, and content-types
ancillary to HTTP/1.1 for the management of resource properties,
creation and management of resource collections, namespace
manipulation, and resource locking (collision avoidance).
RFC2518 was published in February 1998, and this draft makes minor
revisions mostly due to interoperability experience.
Table of Contents
1 Introduction...................................................6
2 Notational Conventions.........................................7
3 Terminology....................................................7
4 Data Model for Resource Properties.............................8
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4.1 The Resource Property Model..................................8
4.2 Existing Metadata Proposals..................................8
4.3 Properties and HTTP Headers..................................9
4.4 XML Usage....................................................9
4.5 Property Values.............................................10
4.6 Property Names..............................................11
5 Collections of Web Resources..................................11
5.1 HTTP URL Namespace Model....................................12
5.2 Collection Resources........................................12
5.3 Source Resources and Output Resources.......................13
6 Locking.......................................................14
6.1 Exclusive Vs. Shared Locks..................................14
6.2 Required Support............................................15
6.3 Lock Tokens.................................................16
6.4 opaquelocktoken Lock Token URI Scheme.......................16
6.5 Lock Capability Discovery...................................17
6.6 Active Lock Discovery.......................................17
6.7 Usage Considerations........................................17
7 Write Lock....................................................18
7.1 Methods Restricted by Write Locks...........................18
7.2 Write Locks and Lock Tokens.................................19
7.3 Write Locks and Properties..................................19
7.4 Write Locks and Unmapped URLs...............................19
7.5 Write Locks and Collections.................................21
7.6 Write Locks and the If Request Header.......................21
7.7 Write Locks and COPY/MOVE...................................22
7.8 Refreshing Write Locks......................................23
8 HTTP Methods for Distributed Authoring........................23
8.1 General request and response handling.......................23
8.1.1 Use of XML.................................................23
8.1.2 Required Bodies in Requests................................24
8.1.3 Use of Location header in responses........................24
8.1.4 Required Response Headers: Date............................24
8.1.5 ETag.......................................................24
8.1.6 Including error response bodies............................25
8.2 PROPFIND....................................................26
8.2.1 Example - Retrieving Named Properties......................28
8.2.2 Example - Retrieving Named and Dead Properties.............29
8.2.3 Example - Using propname to Retrieve all Property Names....30
8.2.4 PROPFIND Request Errors....................................31
8.3 PROPPATCH...................................................32
8.3.1 Status Codes for use with 207 (Multi-Status)...............32
8.3.2 Example - PROPPATCH........................................33
8.4 MKCOL Method................................................34
8.4.1 Example - MKCOL............................................35
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8.5 GET, HEAD for Collections...................................35
8.6 POST for Collections........................................36
8.7 DELETE......................................................36
8.7.1 Example - DELETE...........................................37
8.8 PUT.........................................................37
8.9 COPY Method.................................................38
8.9.1 COPY for Collections.......................................39
8.9.2 COPY and the Overwrite Header..............................40
8.9.3 Status Codes...............................................40
8.9.4 Example - COPY with Overwrite..............................41
8.10 MOVE Method................................................42
8.10.1 MOVE for Properties......................................43
8.10.2 MOVE for Collections.....................................43
8.10.3 MOVE and the Overwrite Header............................44
8.10.4 Status Codes.............................................44
8.10.5 Example - MOVE of a Non-Collection.......................45
8.11 LOCK Method................................................46
8.11.1 Example - Simple Lock Request............................50
8.11.2 Example - Refreshing a Write Lock........................51
8.11.3 Example - Multi-Resource Lock Request....................52
8.12 UNLOCK Method..............................................54
8.12.1 Example - UNLOCK.........................................54
9 HTTP Headers for Distributed Authoring........................55
9.1 DAV Header..................................................55
9.2 Depth Header................................................55
9.3 Destination Header..........................................57
9.4 Force-Authentication Header.................................57
9.5 If Header...................................................57
9.5.1 No-tag-list Production.....................................58
9.5.2 Example - No-tag-list If Header............................58
9.5.3 Tagged-list Production.....................................59
9.5.4 Example - Tagged List If header............................59
9.5.5 Not Production.............................................59
9.5.6 Matching Function..........................................60
9.5.7 If Header and Non-DAV Aware Proxies........................60
9.6 Lock-Token Header...........................................60
9.7 Overwrite Header............................................60
9.8 Status-URI Response Header..................................61
9.9 Timeout Request Header......................................61
10 Status Code Extensions to HTTP/1.1............................62
10.1 102 Processing.............................................62
10.2 207 Multi-Status...........................................63
10.3 422 Unprocessable Entity...................................63
10.4 423 Locked.................................................63
10.5 424 Failed Dependency......................................63
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10.6 507 Insufficient Storage...................................63
11 Use of HTTP Status Codes......................................63
11.1 301 Moved Permanently......................................63
11.2 302 Found..................................................64
11.3 400 Bad Request............................................64
11.4 403 Forbidden..............................................64
11.5 409 Conflict...............................................64
11.6 414 Request-URI Too Long...................................64
12 Multi-Status Response.........................................64
12.1 Responses requiring Location in Multi-Status...............65
13 XML Element Definitions.......................................65
13.1 activelock XML Element.....................................65
13.2 depth XML Element..........................................66
13.3 locktoken XML Element......................................66
13.4 lockroot XML Element.......................................66
13.5 timeout XML Element........................................66
13.6 collection XML Element.....................................67
13.7 href XML Element...........................................67
13.8 lockentry XML Element......................................67
13.9 lockinfo XML Element.......................................67
13.10 lockscope XML Element......................................67
13.11 exclusive XML Element......................................68
13.12 shared XML Element.........................................68
13.13 locktype XML Element.......................................68
13.14 write XML Element..........................................68
13.15 multistatus XML Element....................................68
13.16 response XML Element.......................................69
13.17 propstat XML Element.......................................69
13.18 status XML Element.........................................70
13.19 responsedescription XML Element............................70
13.20 owner XML Element..........................................70
13.21 prop XML element...........................................70
13.22 propertyupdate XML element.................................70
13.23 remove XML element.........................................71
13.24 set XML element............................................71
13.25 propfind XML Element.......................................71
13.26 allprop XML Element........................................72
13.27 propname XML Element.......................................72
13.28 deadprops XML Element......................................72
14 DAV Properties................................................72
14.1 creationdate Property......................................73
14.2 displayname Property.......................................73
14.3 getcontentlanguage Property................................74
14.4 getcontentlength Property..................................74
14.5 getcontenttype Property....................................74
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14.6 getetag Property...........................................75
14.7 getlastmodified Property...................................75
14.8 lockdiscovery Property.....................................76
14.8.1 Example - Retrieving the lockdiscovery Property..........76
14.9 resourcetype Property......................................77
14.10 supportedlock Property.....................................78
14.10.1 Example - Retrieving the supportedlock Property..........78
15 Instructions for Processing XML in DAV........................79
16 DAV Compliance Classes........................................80
16.1 Class 1....................................................80
16.2 Class 2....................................................80
16.3 Class "bis"................................................80
17 Internationalization Considerations...........................81
18 Security Considerations.......................................82
18.1 Authentication of Clients..................................82
18.2 Denial of Service..........................................83
18.3 Security through Obscurity.................................83
18.4 Privacy Issues Connected to Locks..........................83
18.5 Privacy Issues Connected to Properties.....................84
18.6 Implications of XML External Entities......................84
18.7 Risks Connected with Lock Tokens...........................85
19 IANA Considerations...........................................85
20 Intellectual Property.........................................86
21 Acknowledgements..............................................86
22 References....................................................88
22.1 Normative References.......................................88
22.2 Informational References...................................89
23 Authors' Addresses............................................90
24 Appendices....................................................91
24.1 Appendix 1 - WebDAV Document Type Definition...............91
24.2 Appendix 3 - Notes on Processing XML Elements..............92
24.2.1 Notes on Empty XML Elements..............................92
24.2.2 Notes on Illegal XML Processing..........................92
24.2.3 Example - XML Syntax Error...............................93
24.2.4 Example - Unknown XML Element............................93
24.3 Appendix 4: UUID Node Generation...........................94
25 Full Copyright Statement......................................96
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1 Introduction
This document describes an extension to the HTTP/1.1 protocol that
allows clients to perform remote web content authoring operations.
This extension provides a coherent set of methods, headers, request
entity body formats, and response entity body formats that provide
operations for:
Properties: The ability to create, remove, and query information
about Web pages, such as their authors, creation dates, etc. Also,
the ability to link pages of any media type to related pages.
Collections: The ability to create sets of documents and to retrieve
a hierarchical membership listing (like a directory listing in a
file system).
Locking: The ability to keep more than one person from working on a
document at the same time. This prevents the "lost update problem",
in which modifications are lost as first one author then another
writes changes without merging the other author's changes.
Namespace Operations: The ability to instruct the server to copy and
move Web resources.
Requirements and rationale for these operations are described in a
companion document, "Requirements for a Distributed Authoring and
Versioning Protocol for the World Wide Web" [RFC2291].
This standard does not specify the versioning operations suggested
by [RFC2291]. That work was done in a separate document, "Versioning
Extensions to WebDAV" [RFC3253].
The sections below provide a detailed introduction to resource
properties (section 4), collections of resources (section 5), and
locking operations (section 6). These sections introduce the
abstractions manipulated by the WebDAV-specific HTTP methods
described in section 8. Section 9 describes the new HTTP headers
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. New status codes developed for the WebDAV methods are
defined in section 10, and existing HTTP status codes as used in
WebDAV are described in section Error! Reference source not found..
Since some WebDAV methods may operate over many resources, the
Multi-Status response has been introduced to return status
information for multiple resources. The Multi-Status response is
described in section 12.
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WebDAV uses XML to marshal complicated request and response
information, as well as to express metadata. XML elements used in
this specification are defined in section 13. An informational DTD
is provided in Appendix 1. Section 15 explains how to process XML
appearing in WebDAV so that it truly is extensible.
WebDAV employs the property mechanism to store information about the
current state of the resource. For example, when a lock is taken
out on a resource, a lock information property describes the current
state of the lock. Section 13.28 defines the properties used within
the WebDAV specification.
Finishing off the specification are sections on what it means to be
compliant with this specification (section 16), on
internationalization support (section 17), and on security (section
18).
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 RFC 2119
[RFC2119].
3 Terminology
URI/URL - A Uniform Resource Identifier and Uniform Resource
Locator, respectively. These terms (and the distinction between
them) are defined in [RFC2396].
Collection - A resource that contains a set of URLs, which identify
and locate member resources and which meet the requirements in
section 5 of this specification.
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 in section 5.2).
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Property - A name/value pair that contains descriptive information
about a resource.
Live Property - A property whose semantics and syntax are enforced
by the server. For example, the live "getcontentlength" property
has its value, the length of the entity returned by a GET request,
automatically calculated by the server.
Dead Property - A property whose semantics and syntax are not
enforced by the server. The server only records the value of a dead
property; the client is responsible for maintaining the consistency
of the syntax and semantics of a dead property.
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 Existing Metadata Proposals
Properties have long played an essential role in the maintenance of
large document repositories, and many current proposals contain some
notion of a property, or discuss web metadata more generally. These
include PICS [REC-PICS], PICS-NG, XML, Web Collections, and several
proposals on representing relationships within HTML. Work on PICS-NG
and Web Collections has been subsumed by the Resource Description
Framework (RDF) metadata activity of the World Wide Web Consortium.
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RDF consists of a network-based data model and an XML representation
of that model.
Some proposals come from a digital library perspective. These
include the Dublin Core [RFC2413] metadata set and the Warwick
Framework [WF], a container architecture for different metadata
schemas. The literature includes many examples of metadata,
including MARC [USMARC], a bibliographic metadata format, and a
technical report bibliographic format employed by the Dienst system
[RFC1807]. Additionally, the proceedings from the first IEEE
Metadata conference describe many community-specific metadata sets.
Participants of the 1996 Metadata II Workshop in Warwick, UK [WF],
noted that "new metadata sets will develop as the networked
infrastructure matures" and "different communities will propose,
design, and be responsible for different types of metadata." These
observations can be corroborated by noting that many community-
specific sets of metadata already exist, and there is significant
motivation for the development of new forms of metadata as many
communities increasingly make their data available in digital form,
requiring a metadata format to assist data location and cataloging.
4.3 Properties and HTTP Headers
Properties already exist, in a limited sense, in HTTP message
headers. However, in distributed authoring environments a
relatively large number of properties are needed to describe the
state of a resource, and setting/returning them all through HTTP
headers is inefficient. Thus a mechanism is needed which allows a
principal to identify a set of properties in which the principal is
interested and to set or retrieve just those properties.
4.4 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 Extensible Markup Language (XML) [REC-XML]
request entity body, or in an HTTP header. The use of XML to encode
method parameters was motivated by the ability to add extra XML
elements to existing structures, providing extensibility; and by
XML's ability to encode information in ISO 10646 character sets,
providing internationalization support. As a rule of thumb,
parameters are encoded in XML entity bodies when they have unbounded
length, or when they may be shown to a human user and hence require
encoding in an ISO 10646 character set. Otherwise, parameters are
encoded within HTTP headers.
In addition to encoding method parameters, XML is used in WebDAV to
encode the responses from methods, providing the extensibility and
internationalization advantages of XML for method output, as well as
input.
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An XML DTD is included in an appendix for all the XML elements
defined in this specification. However, legal XML will not be valid
according to this DTD due to namespace usage and extension rules, so
the DTD is only informational.
The XML namespace extension is also used in this specification in
order to allow for new XML elements to be added without fear of
colliding with other element names. Although WebDAV request and
response bodies can be extended by arbitrary XML elements, which can
be ignored by the message recipient, an XML element in the "DAV:"
namespace SHOULD NOT be used in the request or response body unless
that XML element is explicitly defined in an IETF RFC reviewed by a
WebDAV working group.
Note that ôDAV:ö is a top-level URI identifier that was defined
solely to provide a namespace for WebDAV XML elements and property
names. This practice is discouraged in part because registration of
top-level URI identifiers is difficult. "DAV:" was defined as the
WebDAV namespace before standard best practices emerged, and this
namespace is kept and still used because of significant existing
deployments, but this should not be emulated.
4.5 Property Values
The value of a property is always a (wellformed) 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 will ignore elements they do not
understand. XML's support for multiple character sets allows any
human-readable property to be encoded and read in a character set
familiar to the user. XML's support for multiple human languages,
using the "xml:lang" attribute, 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.
A property is always represented in XML with an XML element
consisting of the property name. 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
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text-only and mixed content. When the property value contains
further XML elements, namespaces that are in scope for that part of
the XML document apply within the property value as well, and MUST
be preserved in server storage for retransmission later. Namespace
prefixes need not be preserved due to the rules of prefix
declaration in XML.
Attributes on the property name element may convey information about
the property, but are not considered part of the value. However,
when language information appears in the 'xml:lang' attribute on the
property name element, the language information MUST be preserved in
server storage for retransmission later.
The XML attribute xml:space MUST NOT be used to change white space
handling. White space in property values is significant.
4.6 Property Names
A property name is a universally unique identifier that is
associated with a schema that provides information about the syntax
and semantics of the property.
Because a property's name is universally unique, clients can depend
upon consistent behavior for a particular property across multiple
resources, on the same and across different servers, so long as that
property is "live" on the resources in question, and the
implementation of the live property is faithful to its definition.
The XML namespace mechanism, which is based on URIs [RFC2396], is
used to name properties because it prevents namespace collisions and
provides for varying degrees of administrative control.
The property namespace is flat; that is, no hierarchy of properties
is explicitly recognized. Thus, if a property A and a property A/B
exist on a resource, there is no recognition of any relationship
between the two properties. It is expected that a separate
specification will eventually be produced which will address issues
relating to hierarchical properties.
Finally, it is not possible to define the same property twice on a
single resource, as this would cause a collision in the resource's
property namespace.
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.
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All DAV compliant resources MUST support the HTTP URL namespace
model specified herein.
5.1 HTTP URL Namespace Model
The HTTP URL namespace is a hierarchical namespace where the
hierarchy is delimited with the "/" character.
An HTTP URL namespace is said to be consistent if it meets the
following conditions: for every URL in the HTTP hierarchy there
exists a collection that contains that URL as an internal member.
The root, or top-level collection of the namespace under
consideration is exempt from the previous rule.
Neither HTTP/1.1 nor WebDAV require that the entire HTTP URL
namespace be consistent. However, certain WebDAV methods are
prohibited from producing results that cause namespace
inconsistencies.
Although implicit in [RFC2616] and [RFC2396], any resource,
including collection resources, MAY be identified by more than one
URI. For example, a resource could be identified by multiple HTTP
URLs.
5.2 Collection Resources
A collection is a resource whose state consists of at least a list
of internal member 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
[RFC2396].
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
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.
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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.bar/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.bar/blah/.
Wherever a server produces a URL referring to a collection, the
server MUST include the trailing slash. In general clients SHOULD
use the "/" form of collection names.
A resource MAY be a collection but not be WebDAV compliant. That
is, the resource may comply with all the rules set out in this
specification regarding how a collection is to behave without
necessarily supporting all methods that a WebDAV compliant resource
is required to support. In such a case the resource may return the
DAV:resourcetype property with the value DAV:collection but MUST NOT
return a DAV header containing the value "1" on an OPTIONS response.
Clients MUST be able to support the case where WebDAV resources are
contained inside non-WebDAV resources. For example, if a OPTIONS
response from "http://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.
5.3 Source Resources and Output Resources
For many resources, the entity returned by a GET method exactly
matches the persistent state of the resource, for example, a GIF
file stored on a disk. For this simple case, the URL at which a
resource is accessed is identical to the URL at which the source
(the persistent state) of the resource is accessed. This is also
the case for HTML source files that are not processed by the server
prior to transmission.
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However, the server can sometimes process HTML resources before they
are transmitted as a return entity body. For example, a server-
side-include directive within an HTML file might instruct a server
to replace the directive with another value, such as the current
date. In this case, what is returned by GET (HTML plus date)
differs from the persistent state of the resource (HTML plus
directive). Typically there is no way to access the HTML resource
containing the unprocessed directive.
Sometimes the entity returned by GET is the output of a data-
producing process that is described by one or more source resources
(that may not even have a location in the URI namespace). A single
data-producing process may dynamically generate the state of a
potentially large number of output resources. An example of this is
a CGI script that describes a "finger" gateway process that maps
part of the namespace of a server into finger requests, such as
http://finger.example.com/finger_gateway/user@host.
Although this problem would usefully be solved, interoperable WebDAV
implementations have been widely deployed without actually solving
this problem. Thus, the source vs. output problem is not solved in
this specification, and has been deferred to a separate document.
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 (see 7.5). 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
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shared lock allows multiple principals to receive a lock. Hence any
principal with appropriate access can get the lock.
With shared locks there are two trust sets that affect a resource.
The first trust set is created by access permissions. Principals
who are trusted, for example, may have permission to write to the
resource. Among those who have access permission to write to the
resource, the set of principals who have taken out a shared lock
also must trust each other, creating a (typically) smaller trust set
within the access permission write set.
Starting with every possible principal on the Internet, in most
situations the vast majority of these principals will not have write
access to a given resource. Of the small number who do have write
access, some principals may decide to guarantee their edits are free
from overwrite conflicts by using exclusive write locks. Others may
decide they trust their collaborators will not overwrite their work
(the potential set of collaborators being the set of principals who
have write permission) and use a shared lock, which informs their
collaborators that a principal may be working on the resource.
The WebDAV extensions to HTTP do not need to provide all of the
communications paths necessary for principals to coordinate their
activities. When using shared locks, principals may use any out of
band communication channel to coordinate their work (e.g., face-to-
face interaction, written notes, post-it notes on the screen,
telephone conversation, Email, etc.) The intent of a shared lock is
to let collaborators know who else may be working on a resource.
Shared locks are included because experience from web distributed
authoring systems has indicated that exclusive locks are often too
rigid. An exclusive lock is used to enforce a particular editing
process: take out an exclusive lock, read the resource, perform
edits, write the resource, release the lock. This editing process
has the problem that locks are not always properly released, for
example when a program crashes, or when a lock owner leaves without
unlocking a resource. While both timeouts and administrative action
can be used to remove an offending lock, neither mechanism may be
available when needed; the timeout may be long or the administrator
may not be available.
6.2 Required Support
A WebDAV compliant 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
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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. A lock token is returned in the Lock-
Token header in the response to a successful LOCK operation. The
lock token also appears in the value of the lockdiscovery property,
the value of which is returned in the body of the response to a
successful LOCK operation (this property also includes the tokens of
other current locks on the resource). Finally, the lockdiscovery
property can be queried using PROPFIND and the token can be
discovered that way. Each lock has only one unique lock token.
Lock token URIs MUST be unique across all resources for all time.
This uniqueness constraint allows lock tokens to be submitted across
resources and servers without fear of confusion.
This specification provides a lock token URI scheme called
opaquelocktoken that meets the uniqueness requirements. However
resources are free to return any URI scheme so long as it meets the
uniqueness requirements.
Having a lock token provides no special access rights. Anyone can
find out anyone else's lock token by performing lock discovery.
Locks MUST be enforced based upon whatever authentication mechanism
is used by the server, not based on the secrecy of the token values.
6.4 opaquelocktoken Lock Token URI Scheme
The opaquelocktoken URI scheme is designed to be unique across all
resources for all time. Due to this uniqueness quality, a client
may submit an opaque lock token in an If header on a resource other
than the one that returned it.
In order to guarantee uniqueness across all resources for all time
the opaquelocktoken requires the use of the Universal Unique
Identifier (UUID) mechanism, as described in [ISO-11578].
Opaquelocktoken generators, however, have a choice of how they
create these tokens. They can either generate a new UUID for every
lock token they create or they can create a single UUID and then
add extension characters. If the second method is selected then the
program generating the extensions MUST guarantee that the same
extension will never be used twice with the associated UUID.
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OpaqueLockToken-URI = "opaquelocktoken:" UUID [Extension] ; The
UUID production is the string representation of a UUID, as defined
in [ISO-11578]. Note that white space (LWS) is not allowed between
elements of this production.
Extension = path ; path is defined in section 3.2.1 of [RFC2616]
6.5 Lock Capability Discovery
Since server lock support is optional, a client trying to lock a
resource on a server can either try the lock and hope for the best,
or perform some form of discovery to determine what lock
capabilities the server supports. This is known as lock capability
discovery. Lock capability discovery differs from discovery of
supported access control types, since there may be access control
types without corresponding lock types. A client can determine what
lock types the server supports by retrieving the supportedlock
property.
Any DAV compliant resource that supports the LOCK method MUST
support the supportedlock property.
6.6 Active Lock Discovery
If another principal locks a resource that a principal wishes to
access, it is useful for the second principal to be able to find out
who the first principal is. For this purpose the lockdiscovery
property is provided. This property lists all outstanding locks,
describes their type, and where available, provides their lock
token.
Any DAV compliant resource that supports the LOCK method MUST
support the lockdiscovery property.
6.7 Usage Considerations
Although the locking mechanisms specified here provide some help in
preventing lost updates, they cannot guarantee that updates will
never be lost. Consider the following scenario:
Two clients A and B are interested in editing the resource
'index.html'. Client A is an HTTP client rather than a WebDAV
client, and so does not know how to perform locking.
Client A doesn't lock the document, but does a GET and begins
editing.
Client B does LOCK, performs a GET and begins editing.
Client B finishes editing, performs a PUT, then an UNLOCK.
Client A performs a PUT, overwriting and losing all of B's changes.
WebDAV (RFC2518) bis June 2003
There are several reasons why the WebDAV protocol itself cannot
prevent this situation. First, it cannot force all clients to use
locking because it must be compatible with HTTP clients that do not
comprehend locking. Second, it cannot require servers to support
locking because of the variety of repository implementations, some
of which rely on reservations and merging rather than on locking.
Finally, being stateless, it cannot enforce a sequence of operations
like LOCK / GET / PUT / UNLOCK.
WebDAV servers that support locking can reduce the likelihood that
clients will accidentally overwrite each other's changes by
requiring clients to lock resources before modifying them. Such
servers would effectively prevent HTTP 1.0 and HTTP 1.1 clients from
modifying resources.
WebDAV clients can be good citizens by using a lock / retrieve /
write /unlock sequence of operations (at least by default) whenever
they interact with a WebDAV server that supports locking.
HTTP 1.1 clients can be good citizens, avoiding overwriting other
clients' changes, by using entity tags in If-Match headers with any
requests that would modify resources.
Information managers may attempt to prevent overwrites by
implementing client-side procedures requiring locking before
modifying WebDAV resources.
7 Write Lock
This section describes the semantics specific to the write lock
type. The write lock is a specific instance of a lock type, and is
the only lock type described in this specification.
Write locks prevent unauthorized changes to resources. In general
terms, changes affected by write locks include changes to:
- the content of the resource
- any dead property of the resource
- any live property defined to be lockable (all properties defined
in this specification are lockable)
- the direct membership of the resource, if it is a collection
- the URL/location of a resource
The next few sections describe in more specific terms how write
locks interact with various operations.
7.1 Methods Restricted by Write Locks
A write lock MUST prevent a principal without the lock from
successfully executing a PUT, POST, PROPPATCH, LOCK, UNLOCK, MOVE,
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DELETE, or MKCOL on the locked resource. All other current methods,
GET in particular, function independently of the lock.
Note, however, that as new methods are created it will be necessary
to specify how they interact with a write lock.
7.2 Write Locks and Lock Tokens
A successful request for an exclusive or shared write lock MUST
result in the generation of a unique lock token associated with the
requesting principal. Thus if five principals have a shared write
lock on the same resource there will be five lock tokens, one for
each principal.
7.3 Write Locks and Properties
While those without a write lock may not alter a property on a
resource it is still possible for the values of live properties to
change, even while locked, due to the requirements of their schemas.
Only dead properties and live properties defined to respect locks
are guaranteed not to change while write locked.
7.4 Write Locks and Unmapped URLs
It is possible to lock an unmapped URL in order to lock the name for
use. This is a simple way to avoid the lost-update problem on the
creation of a new resource (another way is to use If-None-Match
header specified in HTTP 1.1). It has the side benefit of locking
the new resource immediately for use of the creator.
The lost-update problem is not an issue for collections because
MKCOL can only be used to create a collection, not to overwrite an
existing collection. In order to immediately lock a collection upon
creation, clients may attempt to pipeline the MKCOL and LOCK
requests together.
A lock request to an unmapped URL should result in the creation of a
resource that is locked. A subsequent PUT request with the correct
lock token should normally succeed, and provides the content,
content-type, content-language and other information as appropriate.
In this situation, a WebDAV server that was implemented from RFC2518
MAY create "lock-null" resources which are special and unusual
resources. Historically, a lock-null resource:
- Responds with a 404 or 405 to any DAV method except for PUT,
MKCOL, OPTIONS, PROPFIND, LOCK, UNLOCK.
- Appears as a member of its parent collection.
- Disappears (becomes once more an unmapped URL) if its lock goes
away before it is converted to a regular resource. (This must
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also happen if it is renamed or moved, or if any parent collection
is renamed or moved, because locks are tied to URLs).
- May be turned into a regular resource when a PUT request to the
URL is successful. Ceases to be a lock-null resource.
- May be turned into a collection when a MKCOL request to the URL
is successful. Ceases to be a lock-null resource
- Has defined values for lockdiscovery and supportedlock
properties.
However, interoperability and compliance problems have been found
with lock-null resources. Therefore, they are deprecated. WebDAV
servers SHOULD create regular locked empty resources, which are and
behave in every way as normal resources. A locked empty resource:
- Can be read, deleted, moved, copied, and in all ways behave as a
regular resource, not a lock-null resource.
- Appears as a member of its parent collection.
- SHOULD NOT disappear when its lock goes away (clients must
therefore be responsible for cleaning up their own mess, as with
any other operation)
- SHOULD default to having no content type.
- MAY NOT have values for properties like getcontentlanguage which
havenÆt been specified yet by the client.
- May have content added with a PUT request. MUST be able to
change content type.
- MUST NOT be turned into a collection. A MKCOL request must fail
as it would to any existing resource.
- MUST have defined values for lockdiscovery and supportedlock
properties.
- The response MUST indicate that a resource was created, by use of
the "201 Created" response code (a LOCK request to an existing
resource instead will result in 200 OK). The body must still
include the lockdiscovery property, as with a LOCK request to an
existing resource.
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
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locked empty resources by only attempting PUT after a LOCK to an
unmapped URL, not MKCOL or GET.
7.5 Write Locks and Collections
A write lock on a collection, whether created by a "Depth: 0" or
"Depth: infinity" lock request, prevents the addition or removal of
member 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 PUT or
POST request to create a new resource in a write locked collection,
or issues a DELETE to remove a resource which has a URL which is an
existing internal member URL of a write locked collection, this
request MUST fail if the principal does not provide the correct lock
token for the locked collection.
In addition, a depth-infinity lock affects all write operations to
all descendents of the locked collection. With a depth-infinity
lock, the root of the lock is directly locked, and all its
descendants are indirectly locked.
- Any new resource added as a descendent of a depth-infinity locked
collection becomes indirectly locked.
- Any indirectly locked resource moved out of the locked collection
into an unlocked collection is thereafter unlocked.
- 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.
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.
7.6 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
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resource. In this scenario, the PUT succeeds because locks are
associated with a principal, not a program, and thus program B,
because it is acting with principal AÆs credential, is allowed to
perform the PUT. However, had program B known about the lock, it
would not have overwritten the resource, preferring instead to
present a dialog box describing the conflict to the user. Due to
this scenario, a mechanism is needed to prevent different programs
from accidentally ignoring locks taken out by other programs with
the same authorization.
In order to prevent these collisions a lock token MUST be submitted
by an authorized principal for all locked resources that a method
may change or the method MUST fail. A lock token is submitted when
it appears in an If header. For example, if a resource is to be
moved and both the source and destination are locked then two lock
tokens must be submitted in the if header, one for the source and
the other for the destination.
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.
7.7 Write Locks and COPY/MOVE
A COPY method invocation MUST NOT duplicate any write locks active
on the source. However, as previously noted, if the COPY copies the
resource into a collection that is locked with "Depth: infinity",
then the resource will be added to the lock.
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A successful MOVE request on a write locked resource MUST NOT move
the write lock with the resource. However, the resource is subject
to being added to an existing lock at the destination, as specified
in section 7.5. 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
namespace tree covered by the lock), the moved resource will again
be a added to the lock. In both these examples, as specified in
section 7.6, an If header must be submitted containing a lock token
for both the source and destination.
7.8 Refreshing Write Locks
A client MUST NOT submit the same write lock request twice. Note
that a client is always aware it is resubmitting the same lock
request because it must include the lock token in the If header in
order to make the request for a resource that is already locked.
However, a client may submit a LOCK method with an If header but
without a body. This form of LOCK MUST only be used to "refresh" a
lock. Meaning, at minimum, that any timers associated with the lock
MUST be re-set.
A server may return a Timeout header with a lock refresh that is
different than the Timeout header returned when the lock was
originally requested. Additionally clients may submit Timeout
headers of arbitrary value with their lock refresh requests.
Servers, as always, may ignore Timeout headers submitted by the
client. 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.
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 [REC-XML] and [REC-XMLNS]. All
XML used in either requests or responses MUST be, at minimum, well
formed and use namespaces correctly. If a server receives ill-
formed XML in a request it MUST reject the entire request with a 400
(Bad Request). If a client receives ill-formed XML in a response
then it MUST NOT assume anything about the outcome of the executed
method and SHOULD treat the server as malfunctioning.
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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 Use of Location header in responses
When the Location header is used in a response, it is used by the
server to indicate the preferred address for the target resource of
the request. Whenever the server has a preferred address, it should
use that address consistently. This means that when a response
contains a Location header, all the URLs in the response body (e.g.
a Multi-Status) should be consistent (most importantly, should use
the same host and port).
8.1.4 Required Response Headers: Date
Note that HTTP 1.1 requires the Date header in all responses if
possible.
8.1.5 ETag
HTTP 1.1 suggests 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
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 'getetag'
property.
Because clients may be forced to prompt users or throw away changed
content if the ETag changes, a WebDAV server MUST not change the
ETag (or getlastmodified value) for a resource when only its
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property values change. The ETag represents the state of the body or
contents of the resource. There is no similar way to tell if
properties have changed.
8.1.6 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 ôDAV:errorö element may
contain multiple elements describing specific errors. For error
conditions not specified in this document, the server MAY simply
choose an appropriate numeric status and leave the response body
blank.
HTTP/1.1 403 Conflict
Content-Type: text/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.
Status codes are specified in this document with the convention of
following the numeric error code with the XML error code. E.g.
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403/DAV:forbid-external-entities - response codes when the server
refuses to accept external XML entities in XML request bodies.
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 13.25) along with all XML elements defined for use
with that element.
A client may submit a Depth header with a value of "0", "1", or
"infinity" with a PROPFIND on a collection resource with internal
member URLs. 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 request:
- Request particular property values, by naming the properties
desired within the 'prop' element
- Request all dead property values, by using 'deadprops' element.
This can be combined with retrieving specific live properties
named as above. Servers advertising support for RFC2518bis MUST
support this feature.
- Request property values for those properties defined in this
specification plus dead properties, by using æallpropÆ element
- Request a list of names of all the properties defined on the
resource, by using the æpropnameÆ element.
A client may choose not to submit a request body. An empty PROPFIND
request body MUST be treated as if it were an æallpropÆ request.
Note that æallpropÆ does not return values for all live properties.
WebDAV servers increasingly have expensively-calculated or lengthy
properties (see [RFC3253] and [TODO: ref ACL RFC when available])
and do not return all properties already. Instead, WebDAV clients
can use propname requests to discover what 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
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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 gives the
URL of the resource on which the properties in the prop XML element
are defined. URLs for collections appearing in the results MUST end
in a slash character. 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.
A server enumerating the members of a collection using absolute URLs
in a PROPFIND response MUST use a common prefix in those URLs, and
that prefix MUST be the absolute URL used in the response to refer
to the parent collection.
Unless otherwise notified, clients may expect that the URL for the
parent collection in the PROPFIND response will be the same URL that
was used to refer to the parent collection in the PROPFIND request.
Servers MAY use an alternate URL for the parent collection in a
PROPFIND response, but in this case the server MUST include a
Content-Location header whose value is the fully-qualified URL used
by the server to refer to the parent collection in this response.
Clients expect the fully-qualified URLs of members of a collection
to have a common prefix which is the fully-qualified URL of the
parent collection itself.
URLs in a PROPFIND response body MAY be represented as fully-
qualified URLs, in which case they must all contain the full parent
collection URL (scheme, host, port, and absolute path).
Alternatively, these URLs MAY be absolute paths (not containing
scheme, host or port), but in this case they must all still contain
the full parent collection path.
If a server allows resource names to include characters that arenÆt
legal in HTTP URL paths, these characters must be URI-escaped on the
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wire. For example, it is illegal to use a space character or double-
quote in a URI [RFC2396]. URIs appearing in PROPFIND or PROPPATCH
XML bodies (or other XML marshalling defined in this specification)
must also be legal URIs.
Properties may be subject to access control. In the case of allprop
and propname, if a principal does not have the right to know whether
a particular property exists then the property should be silently
excluded from the response.
The results of this method SHOULD NOT be cached.
8.2.1 Example - Retrieving Named Properties
>>Request
PROPFIND /file HTTP/1.1
Host: www.example.com
Content-type: text/xml; charset="utf-8"
Content-Length: xxxx
>>Response
HTTP/1.1 207 Multi-Status
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
http://www.example.com/file
Box type A
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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.
8.2.2 Example - Retrieving Named and Dead Properties
>>Request
PROPFIND /mycol/ HTTP/1.1
Host: www.example.com
Depth: 1
Content-type: text/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
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two specific live properties plus all dead properties (names and
values). The response is not shown.
8.2.3 Example - Using propname to Retrieve all Property Names
>>Request
PROPFIND /container/ HTTP/1.1
Host: www.example.com
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
>>Response
HTTP/1.1 207 Multi-Status
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
http://www.example.com/container/
HTTP/1.1 200 OK
http://www.example.com/container/front.html
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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.
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 schema.
8.2.4 PROPFIND Request Errors
PROPFIND requests may also fail entirely, before the server even
gets a chance to evaluate individual properties. 404 (Not Found) and
401 (Unauthorized) are possible as with every request. These are
some other notable errors.
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403/DAV:propfind-infinite-depth-forbidden - A server MAY reject all
PROPFIND requests on collections with depth header of "Infinity", in
which case it should use this error.
8.3 PROPPATCH
The PROPPATCH method processes instructions specified in the request
body to set and/or remove properties defined on the resource
identified by the Request-URI.
All DAV compliant resources MUST support the PROPPATCH method and
MUST process instructions that are specified using the
propertyupdate, set, and remove XML elements. 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. Instructions MUST either all be executed or none
executed. Thus if any error occurs during processing all executed
instructions MUST be undone and a proper error result returned.
Instruction processing details can be found in the definition of the
set and remove instructions in sections 13.23 and section 13.24.
8.3.1 Status Codes for use with 207 (Multi-Status)
The following are examples of response codes one would expect to be
used in a 207 (Multi-Status) response for this method. Note,
however, that unless explicitly prohibited any 2/3/4/5xx series
response code may be used in a 207 (Multi-Status) response.
200 (OK) - The command succeeded. As there can be a mixture of sets
and removes in a body, a 201 (Created) seems inappropriate.
403 (Forbidden) - The client, for reasons the server chooses not to
specify, cannot alter one of the properties.
403/DAV:read-only-property: The client has attempted to set a read-
only property, such as getetag.
409 (Conflict) - The client has provided a value whose semantics are
not appropriate for the property.
423 (Locked) - The specified resource is locked and the client
either is not a lock owner or the lock type requires a lock token to
be submitted and the client did not submit it.
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: text/xml; charset="utf-8"
Content-Length: xxxx
Jim Whitehead
Roy Fielding
>>Response
HTTP/1.1 207 Multi-Status
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
http://www.example.com/bar.html
HTTP/1.1 424 Failed Dependency
HTTP/1.1 409 Conflict
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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 resource identified by the Request-URI is
non-null then the MKCOL MUST fail. During MKCOL processing, a
server MUST make the Request-URI a member of its parent collection,
unless the Request-URI is "/". If no such ancestor exists, the
method MUST fail. When the MKCOL operation creates a new collection
resource, all ancestors MUST already exist, or the method MUST fail
with a 409 (Conflict) status code. For example, if a request to
create collection /a/b/c/d/ is made, and neither /a/b/ nor /a/b/c/
exists, the request must fail.
When MKCOL is invoked without a request body, the newly created
collection SHOULD have no members.
A MKCOL request message may contain a message body. The behavior of
a MKCOL request when the body is present is limited to creating
collections, members of a collection, bodies of members and
properties on the collections or members. If the server receives a
MKCOL request entity type it does not support or understand it MUST
respond with a 415 (Unsupported Media Type) status code. 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. The exact behavior of MKCOL for various
request media types is undefined in this document, and will be
specified in separate documents.
Status Codes
Responses from a MKCOL request MUST NOT be cached as MKCOL has non-
idempotent semantics.
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201 (Created) - The collection or structured resource was created in
its entirety.
403 (Forbidden) - This indicates at least one of two conditions: 1)
the server does not allow the creation of collections at the given
location in its namespace, or 2) the parent collection of the
Request-URI exists but cannot accept members.
405 (Method Not Allowed) - MKCOL can only be executed on a
deleted/non-existent resource.
409 (Conflict) - A collection cannot be made at the Request-URI
until one or more intermediate collections have been created. The
server MUST NOT create those intermediate collections automatically.
415 (Unsupported Media Type) - The server does not support the
request type of the body.
507 (Insufficient Storage) - The resource does not have sufficient
space to record the state of the resource after the execution of
this method.
8.4.1 Example - MKCOL
This example creates a collection called /webdisc/xfiles/ on the
server www.example.com.
>>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.
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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 for Non-Collection Resources
When a client issues a DELETE request to a Request-URI mapping to a
non-collection resource, if the operation is successful the server
MUST remove that mapping. Thus, after a successful DELETE operation
(and in the absence of other actions) a subsequent GET/HEAD/PROPFIND
request to the target Request-URI would return 404 (Not Found).
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
namespace consistency.
Any headers included with DELETE MUST be applied in processing every
resource to be deleted.
When the DELETE method has completed processing it MUST result in a
consistent namespace.
If an error occurs 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.
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The server MAY return a 4xx status response, rather than a Multi-
Status, if the entire DELETE request failed and it canÆt identify
the internal resources that caused the DELETE to fail.
424 (Failed Dependency) errors SHOULD NOT be in the 207 (Multi-
Status). They can be safely left out because the client will know
that the ancestors of a resource could not be deleted when the
client receives an error for the ancestor's progeny. 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.
8.7.1 Example - DELETE
>>Request
DELETE /container/ HTTP/1.1
Host: www.example.com
>>Response
HTTP/1.1 207 Multi-Status
Content-Type: text/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
PUT for Non-Collection Resources
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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).
PUT for Collections
As defined in [RFC2616], the "PUT method requests that the enclosed
entity be stored under the supplied Request-URI." Since submission
of an entity representing a collection would implicitly encode
creation and deletion of resources, this specification intentionally
does not define a transmission format for creating a collection
using PUT. Instead, the MKCOL method is defined to create
collections.
8.9 COPY Method
The COPY method creates a duplicate of the source resource,
identified by the Request-URI, in the destination resource,
identified by the URI in the Destination header. The Destination
header MUST be present. The exact behavior of the COPY method
depends on the type of the source resource.
All WebDAV compliant resources MUST support the COPY method.
However, support for the COPY method does not guarantee the ability
to copy a resource. For example, separate programs may control
resources on the same server. As a result, it may not be possible
to copy a resource to a location that appears to be on the same
server.
COPY for HTTP/1.1 resources
When the source resource is not a collection the result of the COPY
method is the creation of a new resource at the destination whose
state and behavior match that of the source resource as closely as
possible. After a successful COPY invocation, all properties on the
source resource MUST be duplicated on the destination resource,
subject to modifying headers and XML elements, following the
definition for copying properties. Since the environment at the
destination may be different than at the source due to factors
outside the scope of control of the server, such as the absence of
resources required for correct operation, it may not be possible to
completely duplicate the behavior of the resource at the
destination. Subsequent alterations to the destination resource will
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not modify the source resource. Subsequent alterations to the
source resource will not modify the destination resource.
COPY for Properties
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. If a property cannot be
copied live, then its value MUST be duplicated, octet-for-octet, in
an identically named, dead property on the destination resource.
A COPY operation creates a new resource, much like a PUT operation
does. Live properties which are related to resource creation (such
as creationdate) should have their values set accordingly.
Dead properties must be duplicated exactly.
8.9.1 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://fun.com/ and the
Destination is http://fun.com/b/ then when http://fun.com/a/c/d is
processed it must use a Destination of http://fun.com/b/c/d.
When the COPY method has completed processing it MUST have created a
consistent namespace at the destination (see section 5.1 for the
definition of namespace consistency). However, if an error occurs
while copying an internal collection, the server MUST NOT copy any
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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.
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.
8.9.2 COPY and the Overwrite Header
If a resource exists at the destination and the Overwrite header is
"T" then prior to performing the copy the server MUST perform a
DELETE with "Depth: infinity" on the destination resource. If the
Overwrite header is set to "F" then the operation will fail.
8.9.3 Status Codes
201 (Created) - The source resource was successfully copied. The
copy operation resulted in the creation of a new resource.
204 (No Content) - The source resource was successfully copied to a
pre-existing destination resource.
207 (Multi-Status) - Multiple resources were to be affected by the
COPY, but errors on some of them prevented the operation from taking
place. Specific error messages, together with the most appropriate
of the source and destination URLs, appear in the body of the multi-
status response. E.g. if a destination resource was locked and could
not be overwritten, then the destination resource URL appears with
the 423 (Locked) status.
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403 (Forbidden) - The operation is forbidden. Possibly this is
because 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 failed, e.g. the
Overwrite header is "F" and the state of the destination resource is
non-null.
423 (Locked) - The destination resource was locked.
502 (Bad Gateway) - This may occur when the destination is on
another server, repository or context. Either the source context
does not support copying to the destination context, or the
destination context 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.
8.9.4 Example - COPY with Overwrite
This example shows resource
http://www.ics.uci.edu/~fielding/index.html being copied to the
location http://www.ics.uci.edu/users/f/fielding/index.html. The
204 (No Content) status code indicates the existing resource at the
destination was overwritten.
>>Request
COPY /~fielding/index.html HTTP/1.1
Host: www.ics.uci.edu
Destination: http://www.ics.uci.edu/users/f/fielding/index.html
>>Response
HTTP/1.1 204 No Content
Example - COPY with No Overwrite
The following example shows the same copy operation being performed,
but with the Overwrite header set to "F." A response of 412
(Precondition Failed) is returned because the destination resource
has a non-null state.
>>Request
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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
Example - COPY of a Collection
>>Request
COPY /container/ HTTP/1.1
Host: www.example.com
Destination: http://www.example.com/othercontainer/
Depth: infinity
>>Response
HTTP/1.1 207 Multi-Status
Content-Type: text/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 Method
The MOVE operation on a non-collection resource is the logical
equivalent of a copy (COPY), followed by consistency maintenance
processing, followed by a delete of the source, where all three
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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.
8.10.1 MOVE for Properties
Live properties described in this document MUST 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. If the live properties will not work the same way at
the destination, the server MUST fail the request (the client can
perform COPY then DELETE if it wants a MOVE to work that badly).
This can mean that the server removes a live property if that's the
most appropriate behavior for that live property at the destination.
A MOVE can be a rename operation, so it's not appropriate to reset
live properties which are set at resource creation. For example, the
creationdate property value SHOULD remain the same.
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".
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Any headers included with MOVE MUST be applied in processing every
resource to be moved with the exception of the Destination header.
The behavior of the Destination header is the same as given for COPY
on collections.
When the MOVE method has completed processing it MUST have created a
consistent namespace at both the source and destination (see section
5.1 for the definition of namespace consistency). However, if an
error occurs while moving an internal collection, the server MUST
NOT move any resources identified by members of the failed
collection (i.e., the server must skip the error-causing subtree),
as this would create an inconsistent namespace. In this case, after
detecting the error, the move operation SHOULD try to finish as much
of the original move as possible (i.e., the server should still
attempt to move other subtrees and the resources identified by their
members, that are not descendents of an error-causing collection).
So, for example, if an infinite depth move is performed on
collection /a/, which contains collections /a/b/ and /a/c/, and an
error occurs moving /a/b/, an attempt should still be made to try
moving /a/c/. Similarly, after encountering an error moving a non-
collection resource as part of an infinite depth move, the server
SHOULD try to finish as much of the original move operation as
possible.
If an error occurs with a resource other than the resource
identified in the Request-URI then the response MUST be a 207
(Multi-Status), 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
201 (Created) - The source resource was successfully moved, and a
new resource was created at the destination.
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204 (No Content) - The source resource was successfully moved to a
pre-existing destination resource.
207 (Multi-Status) - Multiple resources were to be affected by the
MOVE, but errors on some of them prevented the operation from taking
place. Specific error messages, together with the most appropriate
of the source and destination URLs, appear in the body of the multi-
status response. E.g. if a source resource was locked and could not
be moved, then the source resource URL appears with the 423 (Locked)
status.
403 (Forbidden) û The source and destination resources are the same.
409 (Conflict) û 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) û A condition failed, e.g. the Overwrite
header is "F" and the state of the destination resource is non-null.
423 (Locked) - The source or the destination resource was locked.
500/DAV:live-properties-not-preserved - The server was unable to
preserve the behavior of the live properties and still move the
resource to the destination.
502 (Bad Gateway) - This may occur when the destination is on
another server and the destination server refuses to accept the
resource.
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 resource had been non-null. 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
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Location: http://www.ics.uci.edu/users/f/fielding/index.html
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: text/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
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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.
Operation
A LOCK method invocation creates the lock specified by the lockinfo
XML element on the resource indicated 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 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. The response MUST contain the value of the
lockdiscovery property in a prop XML element.
In order to indicate the lock token associated with a newly created
lock, a Lock-Token response header MUST be included in the response
for every successful LOCK request for a new lock. Note that the
Lock-Token header would not be returned in the response for a
successful refresh LOCK request because a new lock was not created.
Refreshing Locks
A lock is refreshed by sending a new LOCK request to the resource
which is the root of the lock. A LOCK request to refresh a lock 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). This
request does not contain a body, but it may contain a Timeout
header. A server MAY accept the Timeout header to change the
duration remaining on the lock to the new value.
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.
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The Effect of Locks on Properties and Collections
The scope of a lock is the entire state of the resource, including
its body and associated properties. As a result, a lock on a
resource MUST also lock the resource's properties.
For collections, a lock also affects the ability to add or remove
members. The nature of the effect depends upon the type of access
control involved. This means that if a collection is locked, its
lock-token is required in all these cases:
- DELETE a collectionÆs direct internal member
- MOVE a member out of the collection
- MOVE a member into the collection, unless it overwrites a pre-
existing member
- MOVE to rename it within a collection,
- COPY a member into a collection, unless it overwrites a pre-
existing member
- PUT or MKCOL request which would create a new member.
The collectionÆs lock token is required in addition to the lock
token on the internal member itself, if it exists.
Locking Replicated Resources
A resource may be made available through more than one URI. However
locks apply to resources, not URIs. Therefore a LOCK request on a
resource MUST NOT succeed if can not be honored by all the URIs
through which the resource is addressable.
Depth and Locking
The Depth header may be used with the LOCK method. Values other
than 0 or infinity MUST NOT be used with the Depth header on a LOCK
method. All resources that support the LOCK method MUST support the
Depth header.
A Depth header of value 0 means to just lock the resource specified
by the Request-URI.
If the Depth header is set to infinity then the resource specified
in the Request-URI along with all its internal members, all the way
down the hierarchy, are to be locked. A successful result MUST
return a single lock token which represents all the resources that
have been locked. If an UNLOCK is successfully executed on this
token, all associated resources are unlocked. If the lock cannot be
granted to all resources, a 409 (Conflict) status code MUST be
returned with a response entity body containing a multistatus XML
element describing which resource(s) prevented the lock from being
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granted. Hence, partial success is not an option. Either the
entire hierarchy is locked or no resources are locked.
If no Depth header is submitted on a LOCK request then the request
MUST act as if a "Depth:infinity" had been submitted.
Interaction with other Methods
The interaction of a LOCK with various methods is dependent upon the
lock type. However, independent of lock type, a successful DELETE
of a resource MUST cause all of its direct locks to be removed.
Locking Unmapped URLs
A successful LOCK method MUST result in the creation of an empty
resource which is locked (and which is not a collection), when a
resource did not previously exist at that URL. Later on, the lock
may go away but the empty resource remains. Empty resources MUST
then appear in PROPFIND responses including that URL in the response
scope. A server MUST respond successfully to a GET request to an
empty resource, either by using a 204 No Content response, or by
using 200 OK with a Content-Length header indicating zero length and
no Content-Type.
Lock Compatibility Table
The table below describes the behavior that occurs when a lock
request is made on a resource.
Current State Shared Lock Request Exclusive Lock Request
--------------------------------------------------------------------
None True True
Shared Lock True False
Exclusive Lock False False*
Legend: True = lock may be granted. False = lock MUST NOT be
granted. *=It is illegal for a principal to request the same lock
twice.
The current lock state of a resource is given in the leftmost
column, and lock requests are listed in the first row. The
intersection of a row and column gives the result of a lock request.
For example, if a shared lock is held on a resource, and an
exclusive lock is requested, the table entry is "false", indicating
the lock must not be granted.
Status Codes
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200 (OK) - The lock request succeeded and the value of the
lockdiscovery property is included in the body.
409 (Conflict) û A resource cannot be created at the destination
until one or more intermediate collections have been created. The
server MUST NOT create those intermediate collections automatically.
412 (Precondition Failed) - The included lock token was not
enforceable on this resource or the server could not satisfy the
request in the lockinfo XML element.
423 (Locked) - The resource is locked, so the method has been
rejected.
8.11.1 Example - Simple Lock Request
>>Request
LOCK /workspace/webdav/proposal.doc HTTP/1.1
Host: example.com
Timeout: Infinite, Second-4100000000
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
Authorization: Digest username="ejw",
realm="ejw@example.com", nonce="...",
uri="/workspace/webdav/proposal.doc",
response="...", opaque="..."
http://www.ics.uci.edu/~ejw/contact.html
>>Response
HTTP/1.1 200 OK
Lock-Token:
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
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infinity
http://www.ics.uci.edu/~ejw/contact.html
Second-604800
opaquelocktoken:e71d4fae-5dec-22d6-fea5-
00a0c91e6be4
http://example.com/workspace/webdav
/proposal.doc
This example shows the successful creation of an exclusive write
lock on resource http://example.com/workspace/webdav/proposal.doc.
The resource http://www.ics.uci.edu/~ejw/contact.html contains
contact information for the owner of the lock. The server has an
activity-based timeout policy in place on this resource, which
causes the lock to automatically be removed after 1 week (604800
seconds). Note that the nonce, response, and opaque fields have not
been calculated in the Authorization request header.
Note that the locktoken and lockroot href elements would not contain
any whitespace. The line return appearing in this document is only
for formatting.
8.11.2 Example - Refreshing a Write Lock
>>Request
LOCK /workspace/webdav/proposal.doc HTTP/1.1
Host: example.com
Timeout: Infinite, Second-4100000000
Lock-Token:
Authorization: Digest username="ejw",
realm="ejw@example.com", nonce="...",
uri="/workspace/webdav/proposal.doc",
response="...", opaque="..."
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>>Response
HTTP/1.1 200 OK
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
infinity
http://www.ics.uci.edu/~ejw/contact.html
Second-604800
opaquelocktoken:e71d4fae-5dec-22d6-fea5-
00a0c91e6be4
http://example.com/workspace/webdav
/proposal.doc
This request would refresh the lock, attempting to reset the timeout
to the new value specified in the timeout header. Notice that the
client asked for an infinite time out but the server choose to
ignore the request. In this example, the nonce, response, and opaque
fields have not been calculated in the Authorization request header.
8.11.3 Example - Multi-Resource Lock Request
>>Request
LOCK /webdav/ HTTP/1.1
Host: example.com
Timeout: Infinite, Second-4100000000
Depth: infinity
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Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
Authorization: Digest username="ejw",
realm="ejw