Network Working Group Y. Goland
Request for Comments: 2518 Microsoft
Category: Standards Track E. Whitehead
UC Irvine
A. Faizi
Netscape
S. Carter
Novell
D. Jensen
Novell
February 1999
HTTP Extensions for Distributed Authoring -- WEBDAV
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (1999). All Rights Reserved.
Abstract
This document specifies 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).
Table of Contents
ABSTRACT............................................................1
1 INTRODUCTION .....................................................5
2 NOTATIONAL CONVENTIONS ...........................................7
3 TERMINOLOGY ......................................................7
4 DATA MODEL FOR RESOURCE PROPERTIES ...............................8
4.1 The Resource Property Model ...................................8
4.2 Existing Metadata Proposals ...................................8
4.3 Properties and HTTP Headers ...................................9
4.4 Property Values ...............................................9
4.5 Property Names ...............................................10
4.6 Media Independent Links ......................................10
5 COLLECTIONS OF WEB RESOURCES ....................................11
5.1 HTTP URL Namespace Model .....................................11
5.2 Collection Resources .........................................11
5.3 Creation and Retrieval of Collection Resources ...............12
5.4 Source Resources and Output Resources ........................13
6 LOCKING .........................................................14
6.1 Exclusive Vs. Shared Locks ...................................14
6.2 Required Support .............................................16
6.3 Lock Tokens ..................................................16
6.4 opaquelocktoken Lock Token URI Scheme ........................16
6.4.1 Node Field Generation Without the IEEE 802 Address ........17
6.5 Lock Capability Discovery ....................................19
6.6 Active Lock Discovery ........................................19
6.7 Usage Considerations .........................................19
7 WRITE LOCK ......................................................20
7.1 Methods Restricted by Write Locks ............................20
7.2 Write Locks and Lock Tokens ..................................20
7.3 Write Locks and Properties ...................................20
7.4 Write Locks and Null Resources ...............................21
7.5 Write Locks and Collections ..................................21
7.6 Write Locks and the If Request Header ........................22
7.6.1 Example - Write Lock ......................................22
7.7 Write Locks and COPY/MOVE ....................................23
7.8 Refreshing Write Locks .......................................23
8 HTTP METHODS FOR DISTRIBUTED AUTHORING ..........................23
8.1 PROPFIND .....................................................24
8.1.1 Example - Retrieving Named Properties .....................25
8.1.2 Example - Using allprop to Retrieve All Properties ........26
8.1.3 Example - Using propname to Retrieve all Property Names ...29
8.2 PROPPATCH ....................................................31
8.2.1 Status Codes for use with 207 (Multi-Status) ..............31
8.2.2 Example - PROPPATCH .......................................32
8.3 MKCOL Method .................................................33
8.3.1 Request ...................................................33
8.3.2 Status Codes ..............................................33
8.3.3 Example - MKCOL ...........................................34
8.4 GET, HEAD for Collections ....................................34
8.5 POST for Collections .........................................35
8.6 DELETE .......................................................35
8.6.1 DELETE for Non-Collection Resources .......................35
8.6.2 DELETE for Collections ....................................36
8.7 PUT ..........................................................36
8.7.1 PUT for Non-Collection Resources ..........................36
8.7.2 PUT for Collections .......................................37
8.8 COPY Method ..................................................37
8.8.1 COPY for HTTP/1.1 resources ...............................37
8.8.2 COPY for Properties .......................................38
8.8.3 COPY for Collections ......................................38
8.8.4 COPY and the Overwrite Header .............................39
8.8.5 Status Codes ..............................................39
8.8.6 Example - COPY with Overwrite .............................40
8.8.7 Example - COPY with No Overwrite ..........................40
8.8.8 Example - COPY of a Collection ............................41
8.9 MOVE Method ..................................................42
8.9.1 MOVE for Properties .......................................42
8.9.2 MOVE for Collections ......................................42
8.9.3 MOVE and the Overwrite Header .............................43
8.9.4 Status Codes ..............................................43
8.9.5 Example - MOVE of a Non-Collection ........................44
8.9.6 Example - MOVE of a Collection ............................44
8.10 LOCK Method ..................................................45
8.10.1 Operation .................................................46
8.10.2 The Effect of Locks on Properties and Collections .........46
8.10.3 Locking Replicated Resources ..............................46
8.10.4 Depth and Locking .........................................46
8.10.5 Interaction with other Methods ............................47
8.10.6 Lock Compatibility Table ..................................47
8.10.7 Status Codes ..............................................48
8.10.8 Example - Simple Lock Request .............................48
8.10.9 Example - Refreshing a Write Lock .........................49
8.10.10 Example - Multi-Resource Lock Request ....................50
8.11 UNLOCK Method ................................................51
8.11.1 Example - UNLOCK ..........................................52
9 HTTP HEADERS FOR DISTRIBUTED AUTHORING ..........................52
9.1 DAV Header ...................................................52
9.2 Depth Header .................................................52
9.3 Destination Header ...........................................54
9.4 If Header ....................................................54
9.4.1 No-tag-list Production ....................................55
9.4.2 Tagged-list Production ....................................55
9.4.3 not Production ............................................56
9.4.4 Matching Function .........................................56
9.4.5 If Header and Non-DAV Compliant Proxies ...................57
9.5 Lock-Token Header ............................................57
9.6 Overwrite Header .............................................57
9.7 Status-URI Response Header ...................................57
9.8 Timeout Request Header .......................................58
10 STATUS CODE EXTENSIONS TO HTTP/1.1 ............................59
10.1 102 Processing ...............................................59
10.2 207 Multi-Status .............................................59
10.3 422 Unprocessable Entity .....................................60
10.4 423 Locked ...................................................60
10.5 424 Failed Dependency ........................................60
10.6 507 Insufficient Storage .....................................60
11 MULTI-STATUS RESPONSE .........................................60
12 XML ELEMENT DEFINITIONS .......................................61
12.1 activelock XML Element .......................................61
12.1.1 depth XML Element .........................................61
12.1.2 locktoken XML Element .....................................61
12.1.3 timeout XML Element .......................................61
12.2 collection XML Element .......................................62
12.3 href XML Element .............................................62
12.4 link XML Element .............................................62
12.4.1 dst XML Element ...........................................62
12.4.2 src XML Element ...........................................62
12.5 lockentry XML Element ........................................63
12.6 lockinfo XML Element .........................................63
12.7 lockscope XML Element ........................................63
12.7.1 exclusive XML Element .....................................63
12.7.2 shared XML Element ........................................63
12.8 locktype XML Element .........................................64
12.8.1 write XML Element .........................................64
12.9 multistatus XML Element ......................................64
12.9.1 response XML Element ......................................64
12.9.2 responsedescription XML Element ...........................65
12.10 owner XML Element ...........................................65
12.11 prop XML element ............................................66
12.12 propertybehavior XML element ................................66
12.12.1 keepalive XML element ....................................66
12.12.2 omit XML element .........................................67
12.13 propertyupdate XML element ..................................67
12.13.1 remove XML element .......................................67
12.13.2 set XML element ..........................................67
12.14 propfind XML Element ........................................68
12.14.1 allprop XML Element ......................................68
12.14.2 propname XML Element .....................................68
13 DAV PROPERTIES ................................................68
13.1 creationdate Property ........................................69
13.2 displayname Property .........................................69
13.3 getcontentlanguage Property ..................................69
13.4 getcontentlength Property ....................................69
13.5 getcontenttype Property ......................................70
13.6 getetag Property .............................................70
13.7 getlastmodified Property .....................................70
13.8 lockdiscovery Property .......................................71
13.8.1 Example - Retrieving the lockdiscovery Property ...........71
13.9 resourcetype Property ........................................72
13.10 source Property .............................................72
13.10.1 Example - A source Property ..............................72
13.11 supportedlock Property ......................................73
13.11.1 Example - Retrieving the supportedlock Property ..........73
14 INSTRUCTIONS FOR PROCESSING XML IN DAV ........................74
15 DAV COMPLIANCE CLASSES ........................................75
15.1 Class 1 ......................................................75
15.2 Class 2 ......................................................75
16 INTERNATIONALIZATION CONSIDERATIONS ...........................76
17 SECURITY CONSIDERATIONS .......................................77
17.1 Authentication of Clients ....................................77
17.2 Denial of Service ............................................78
17.3 Security through Obscurity ...................................78
17.4 Privacy Issues Connected to Locks ............................78
17.5 Privacy Issues Connected to Properties .......................79
17.6 Reduction of Security due to Source Link .....................79
17.7 Implications of XML External Entities ........................79
17.8 Risks Connected with Lock Tokens .............................80
18 IANA CONSIDERATIONS ...........................................80
19 INTELLECTUAL PROPERTY .........................................81
20 ACKNOWLEDGEMENTS ..............................................82
21 REFERENCES ....................................................82
21.1 Normative References .........................................82
21.2 Informational References .....................................83
22 AUTHORS' ADDRESSES ............................................84
23 APPENDICES ....................................................86
23.1 Appendix 1 - WebDAV Document Type Definition .................86
23.2 Appendix 2 - ISO 8601 Date and Time Profile ..................88
23.3 Appendix 3 - Notes on Processing XML Elements ................89
23.3.1 Notes on Empty XML Elements ...............................89
23.3.2 Notes on Illegal XML Processing ...........................89
23.4 Appendix 4 -- XML Namespaces for WebDAV ......................92
23.4.1 Introduction ..............................................92
23.4.2 Meaning of Qualified Names ................................92
24 FULL COPYRIGHT STATEMENT ......................................94
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].
The sections below provide a detailed introduction to resource
properties (section 4), collections of resources (section 5), and
locking operations (section 6). These sections introduce the
abstractions manipulated by the WebDAV-specific HTTP methods
described in section 8, "HTTP Methods for Distributed Authoring".
In HTTP/1.1, method parameter information was exclusively encoded in
HTTP headers. Unlike HTTP/1.1, WebDAV encodes method parameter
information either in an Extensible Markup Language (XML) [REC-XML]
request entity body, or in an HTTP header. The use of XML to encode
method parameters was motivated by the ability to add extra XML
elements to existing structures, providing extensibility; and by
XML's ability to encode information in ISO 10646 character sets,
providing internationalization support. As a rule of thumb,
parameters are encoded in XML entity bodies when they have unbounded
length, or when they may be shown to a human user and hence require
encoding in an ISO 10646 character set. Otherwise, parameters are
encoded within HTTP headers. Section 9 describes the new HTTP
headers used with WebDAV methods.
In addition to encoding method parameters, XML is used in WebDAV to
encode the responses from methods, providing the extensibility and
internationalization advantages of XML for method output, as well as
input.
XML elements used in this specification are defined in section 12.
The XML namespace extension (Appendix 4) 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.
While the status codes provided by HTTP/1.1 are sufficient to
describe most error conditions encountered by WebDAV methods, there
are some errors that do not fall neatly into the existing categories.
New status codes developed for the WebDAV methods are defined in
section 10. Since some WebDAV methods may operate over many
resources, the Multi-Status response has been introduced to return
status information for multiple resources. The Multi-Status response
is described in section 11.
WebDAV employs the property mechanism to store information about the
current state of the resource. For example, when a lock is taken out
on a resource, a lock information property describes the current
state of the lock. Section 13 defines the properties used within the
WebDAV specification.
Finishing off the specification are sections on what it means to be
compliant with this specification (section 15), on
internationalization support (section 16), and on security (section
17).
2 Notational Conventions
Since this document describes a set of extensions to the HTTP/1.1
protocol, the augmented BNF used herein to describe protocol elements
is exactly the same as described in section 2.1 of [RFC2068]. Since
this augmented BNF uses the basic production rules provided in
section 2.2 of [RFC2068], these rules apply to this document as well.
The key Words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC2119 [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 URIs, termed member
URIs, which identify member resources and meets the requirements in
section 5 of this specification.
Member URI - A URI which is a member of the set of URIs contained by
a collection.
Internal Member URI - A Member URI that is immediately relative to
the URI of the collection (the definition of immediately relative is
given in section 5.2).
Property - A name/value pair that contains descriptive information
about a resource.
Live Property - A property whose semantics and syntax are enforced by
the server. For example, the live "getcontentlength" property has
its value, the length of the entity returned by a GET request,
automatically calculated by the server.
Dead Property - A property whose semantics and syntax are not
enforced by the server. The server only records the value of a dead
property; the client is responsible for maintaining the consistency
of the syntax and semantics of a dead property.
Null Resource - A resource which responds with a 404 (Not Found) to
any HTTP/1.1 or DAV method except for PUT, MKCOL, OPTIONS and LOCK.
A NULL resource MUST NOT appear as a member of its parent collection.
4 Data Model for Resource Properties
4.1 The Resource Property Model
Properties are pieces of data that describe the state of a resource.
Properties are data about data.
Properties are used in distributed authoring environments to provide
for efficient discovery and management of resources. For example, a
'subject' property might allow for the indexing of all resources by
their subject, and an 'author' property might allow for the discovery
of what authors have written which documents.
The DAV property model consists of name/value pairs. The name of a
property identifies the property's syntax and semantics, and provides
an address by which to refer to its syntax and semantics.
There are two categories of properties: "live" and "dead". A live
property has its syntax and semantics enforced by the server. Live
properties include cases where a) the value of a property is read-
only, maintained by the server, and b) the value of the property is
maintained by the client, but the server performs syntax checking on
submitted values. All instances of a given live property MUST comply
with the definition associated with that property name. A dead
property has its syntax and semantics enforced by the client; the
server merely records the value of the property verbatim.
4.2 Existing Metadata Proposals
Properties have long played an essential role in the maintenance of
large document repositories, and many current proposals contain some
notion of a property, or discuss web metadata more generally. These
include PICS [REC-PICS], PICS-NG, XML, Web Collections, and several
proposals on representing relationships within Html. Work on PICS-NG
and Web Collections has been subsumed by the Resource Description
Framework (RDF) metadata activity of the World Wide Web Consortium.
RDF consists of a network-based data model and an XML representation
of that model.
Some proposals come from a digital library perspective. These
include the Dublin Core [RFC2413] metadata set and the Warwick
Framework [WF], a container architecture for different metadata
schemas. The literature includes many examples of metadata,
including MARC [USMARC], a bibliographic metadata format, and a
technical report bibliographic format employed by the Dienst system
[RFC1807]. Additionally, the proceedings from the first IEEE Metadata
conference describe many community-specific metadata sets.
Participants of the 1996 Metadata II Workshop in Warwick, UK [WF],
noted that "new metadata sets will develop as the networked
infrastructure matures" and "different communities will propose,
design, and be responsible for different types of metadata." These
observations can be corroborated by noting that many community-
specific sets of metadata already exist, and there is significant
motivation for the development of new forms of metadata as many
communities increasingly make their data available in digital form,
requiring a metadata format to assist data location and cataloging.
4.3 Properties and HTTP Headers
Properties already exist, in a limited sense, in HTTP message
headers. However, in distributed authoring environments a relatively
large number of properties are needed to describe the state of a
resource, and setting/returning them all through HTTP headers is
inefficient. Thus a mechanism is needed which allows a principal to
identify a set of properties in which the principal is interested and
to set or retrieve just those properties.
4.4 Property Values
The value of a property when eXPressed in XML MUST be well formed.
XML has been chosen because it is a flexible, self-describing,
structured data format that supports rich schema definitions, and
because of its support for multiple character sets. XML's self-
describing nature allows any property's value to be extended by
adding new elements. Older clients will not break when they
encounter extensions because they will still have the data specified
in the original schema and will ignore elements they do not
understand. XML's support for multiple character sets allows any
human-readable property to be encoded and read in a character set
familiar to the user. XML's support for multiple human languages,
using the "xml:lang" attribute, handles cases where the same
character set is employed by multiple human languages.
4.5 Property Names
A property name is a universally unique identifier that is associated
with a schema that provides information about the syntax and
semantics of the property.
Because a property's name is universally unique, clients can depend
upon consistent behavior for a particular property across multiple
resources, on the same and across different servers, so long as that
property is "live" on the resources in question, and the
implementation of the live property is faithful to its definition.
The XML namespace mechanism, which is based on URIs [RFC2396], is
used to name properties because it prevents namespace collisions and
provides for varying degrees of administrative control.
The property namespace is flat; that is, no hierarchy of properties
is explicitly recognized. Thus, if a property A and a property A/B
exist on a resource, there is no recognition of any relationship
between the two properties. It is expected that a separate
specification will eventually be produced which will address issues
relating to hierarchical properties.
Finally, it is not possible to define the same property twice on a
single resource, as this would cause a collision in the resource's
property namespace.
4.6 Media Independent Links
Although HTML resources support links to other resources, the Web
needs more general support for links between resources of any media
type (media types are also known as MIME types, or content types).
WebDAV provides such links. A WebDAV link is a special type of
property value, formally defined in section 12.4, that allows typed
connections to be established between resources of any media type.
The property value consists of source and destination Uniform
Resource Identifiers (URIs); the property name identifies the link
type.
5 Collections of Web Resources
This section provides a description of a new type of Web resource,
the collection, and discusses its interactions with the HTTP URL
namespace. The purpose of a collection resource is to model
collection-like objects (e.g., file system directories) within a
server's namespace.
All DAV compliant resources MUST support the HTTP URL namespace model
specified herein.
5.1 HTTP URL Namespace Model
The HTTP URL namespace is a hierarchical namespace where the
hierarchy is delimited with the "/" character.
An HTTP URL namespace is said to be consistent if it meets the
following conditions: for every URL in the HTTP hierarchy there
exists a collection that contains that URL as an internal member.
The root, or top-level collection of the namespace under
consideration is exempt from the previous rule.
Neither HTTP/1.1 nor WebDAV require that the entire HTTP URL
namespace be consistent. However, certain WebDAV methods are
prohibited from producing results that cause namespace
inconsistencies.
Although implicit in [RFC2068] and [RFC2396], any resource, including
collection resources, MAY be identified by more than one URI. For
example, a resource could be identified by multiple HTTP URLs.
5.2 Collection Resources
A collection is a resource whose state consists of at least a list of
internal member URIs and a set of properties, but which may have
additional state such as entity bodies returned by GET. An internal
member URI MUST be immediately relative to a base URI of the
collection. That is, the internal member URI is equal to a
containing collection's URI plus an additional segment for non-
collection resources, or additional segment plus trailing slash "/"
for collection resources, where segment is defined in section 3.3 of
[RFC2396].
Any given internal member URI MUST only belong to the collection
once, i.e., it is illegal to have multiple instances of the same URI
in a collection. Properties defined on collections behave exactly as
do properties on non-collection resources.
For all WebDAV compliant resources A and B, identified by URIs U and
V, for which U is immediately relative to V, B MUST be a collection
that has U as an internal member URI. So, if the resource with URL
http://foo.com/bar/blah is WebDAV compliant and if the resource with
URL http://foo.com/bar/ is WebDAV compliant then the resource with
URL http://foo.com/bar/ must be a collection and must contain URL
http://foo.com/bar/blah as an internal member.
Collection resources MAY list the URLs of non-WebDAV compliant
children in the HTTP URL namespace hierarchy as internal members but
are not required to do so. For example, if the resource with URL
http://foo.com/bar/blah is not WebDAV compliant and the URL
http://foo.com/bar/ identifies a collection then URL
http://foo.com/bar/blah may or may not be an internal member of the
collection with URL http://foo.com/bar/.
If a WebDAV compliant resource has no WebDAV compliant children in
the HTTP URL namespace hierarchy then the WebDAV compliant resource
is not required to be a collection.
There is a standing convention that when a collection is referred to
by its name without a trailing slash, the trailing slash is
automatically appended. Due to this, a resource may accept a URI
without a trailing "/" to point to a collection. In this case it
SHOULD return a content-location header in the response pointing to
the URI ending with the "/". For example, if a client invokes a
method on http://foo.bar/blah (no trailing slash), the resource
http://foo.bar/blah/ (trailing slash) may respond as if the operation
were invoked on it, and should return a content-location header with
http://foo.bar/blah/ in it. In general clients SHOULD use the "/"
form of collection names.
A resource MAY be a collection but not be WebDAV compliant. That is,
the resource may comply with all the rules set out in this
specification regarding how a collection is to behave without
necessarily supporting all methods that a WebDAV compliant resource
is required to support. In such a case the resource may return the
DAV:resourcetype property with the value DAV:collection but MUST NOT
return a DAV header containing the value "1" on an OPTIONS response.
5.3 Creation and Retrieval of Collection Resources
This document specifies the MKCOL method to create new collection
resources, rather than using the existing HTTP/1.1 PUT or POST
method, for the following reasons:
In HTTP/1.1, the PUT method is defined to store the request body at
the location specified by the Request-URI. While a description
format for a collection can readily be constructed for use with PUT,
the implications of sending such a description to the server are
undesirable. For example, if a description of a collection that
omitted some existing resources were PUT to a server, this might be
interpreted as a command to remove those members. This would extend
PUT to perform DELETE functionality, which is undesirable since it
changes the semantics of PUT, and makes it difficult to control
DELETE functionality with an Access control scheme based on methods.
While the POST method is sufficiently open-ended that a "create a
collection" POST command could be constructed, this is undesirable
because it would be difficult to separate access control for
collection creation from other uses of POST.
The exact definition of the behavior of GET and PUT on collections is
defined later in this document.
5.4 Source Resources and Output Resources
For many resources, the entity returned by a GET method exactly
matches the persistent state of the resource, for example, a GIF file
stored on a disk. For this simple case, the URI at which a resource
is accessed is identical to the URI at which the source (the
persistent state) of the resource is accessed. This is also the case
for HTML source files that are not processed by the server prior to
transmission.
However, the server can sometimes process HTML resources before they
are transmitted as a return entity body. For example, a server-
side-include directive within an HTML file might instruct a server to
replace the directive with another value, such as the current date.
In this case, what is returned by GET (HTML plus date) differs from
the persistent state of the resource (HTML plus directive).
Typically there is no way to access the HTML resource containing the
unprocessed directive.
Sometimes the entity returned by GET is the output of a data-
producing process that is described by one or more source resources
(that may not even have a location in the URI namespace). A single
data-producing process may dynamically generate the state of a
potentially large number of output resources. An example of this is
a CGI script that describes a "finger" gateway process that maps part
of the namespace of a server into finger requests, such as
http://www.foo.bar.org/finger_gateway/user@host.
In the absence of distributed authoring capabilities, it is
acceptable to have no mapping of source resource(s) to the URI
namespace. In fact, preventing access to the source resource(s) has
desirable security benefits. However, if remote editing of the
source resource(s) is desired, the source resource(s) should be given
a location in the URI namespace. This source location should not be
one of the locations at which the generated output is retrievable,
since in general it is impossible for the server to differentiate
requests for source resources from requests for process output
resources. There is often a many-to-many relationship between source
resources and output resources.
On WebDAV compliant servers the URI of the source resource(s) may be
stored in a link on the output resource with type DAV:source (see
section 13.10 for a description of the source link property).
Storing the source URIs in links on the output resources places the
burden of discovering the source on the authoring client. Note that
the value of a source link is not guaranteed to point to the correct
source. Source links may break or incorrect values may be entered.
Also note that not all servers will allow the client to set the
source link value. For example a server which generates source links
on the fly for its CGI files will most likely not allow a client to
set the source link value.
6 Locking
The ability to lock a resource provides a mechanism for serializing
access to that resource. Using a lock, an authoring client can
provide a reasonable guarantee that another principal will not modify
a resource while it is being edited. In this way, a client can
prevent the "lost update" problem.
This specification allows locks to vary over two client-specified
parameters, the number of principals involved (exclusive vs. shared)
and the type of access to be granted. This document defines locking
for only one access type, write. However, the syntax is extensible,
and permits the eventual specification of locking for other access
types.
6.1 Exclusive Vs. Shared Locks
The most basic form of lock is an exclusive lock. This is a lock
where the access right in question is only granted to a single
principal. The need for this arbitration results from a desire to
avoid having to merge results.
However, there are times when the goal of a lock is not to exclude
others from exercising an access right but rather to provide a
mechanism for principals to indicate that they intend to exercise
their access rights. Shared locks are provided for this case. A
shared lock allows multiple principals to receive a lock. Hence any
principal with appropriate access can get the lock.
With shared locks there are two trust sets that affect a resource.
The first trust set is created by access permissions. Principals who
are trusted, for example, may have permission to write to the
resource. Among those who have access permission to write to the
resource, the set of principals who have taken out a shared lock also
must trust each other, creating a (typically) smaller trust set
within the access permission write set.
Starting with every possible principal on the Internet, in most
situations the vast majority of these principals will not have write
access to a given resource. Of the small number who do have write
access, some principals may decide to guarantee their edits are free
from overwrite conflicts by using exclusive write locks. Others may
decide they trust their collaborators will not overwrite their work
(the potential set of collaborators being the set of principals who
have write permission) and use a shared lock, which informs their
collaborators that a principal may be working on the resource.
The WebDAV extensions to HTTP do not need to provide all of the
communications paths necessary for principals to coordinate their
activities. When using shared locks, principals may use any out of
band communication channel to coordinate their work (e.g., face-to-
face interaction, written notes, post-it notes on the screen,
telephone conversation, Email, etc.) The intent of a shared lock is
to let collaborators know who else may be working on a resource.
Shared locks are included because experience from web distributed
authoring systems has indicated that exclusive locks are often too
rigid. An exclusive lock is used to enforce a particular editing
process: take out an exclusive lock, read the resource, perform
edits, write the resource, release the lock. This editing process
has the problem that locks are not always properly released, for
example when a program crashes, or when a lock owner leaves without
unlocking a resource. While both timeouts and administrative action
can be used to remove an offending lock, neither mechanism may be
available when needed; the timeout may be long or the administrator
may not be available.
6.2 Required Support
A WebDAV compliant server is not required to support locking in any
form. If the server does support locking it may choose to support
any combination of exclusive and shared locks for any access types.
The reason for this flexibility is that locking policy strikes to the
very heart of the resource management and versioning systems employed
by various storage repositories. These repositories require control
over what sort of locking will be made available. For example, some
repositories only support shared write locks while others only
provide support for exclusive write locks while yet others use no
locking at all. As each system is sufficiently different to merit
exclusion of certain locking features, this specification leaves
locking as the sole axis of negotiation within WebDAV.
6.3 Lock Tokens
A lock token is a type of state token, represented as a URI, which
identifies a particular lock. A lock token is returned by every
successful LOCK operation in the lockdiscovery property in the
response body, and can also be found through lock discovery on a
resource.
Lock token URIs MUST be unique across all resources for all time.
This uniqueness constraint allows lock tokens to be submitted across
resources and servers without fear of confusion.
This specification provides a lock token URI scheme called
opaquelocktoken that meets the uniqueness requirements. However
resources are free to return any URI scheme so long as it meets the
uniqueness requirements.
Having a lock token provides no special access rights. Anyone can
find out anyone else's lock token by performing lock discovery.
Locks MUST be enforced based upon whatever authentication mechanism
is used by the server, not based on the secrecy of the token values.
6.4 opaquelocktoken Lock Token URI Scheme
The opaquelocktoken URI scheme is designed to be unique across all
resources for all time. Due to this uniqueness quality, a client may
submit an opaque lock token in an If header on a resource other than
the one that returned it.
All resources MUST recognize the opaquelocktoken scheme and, at
minimum, recognize that the lock token does not refer to an
outstanding lock on the resource.
In order to guarantee uniqueness across all resources for all time
the opaquelocktoken requires the use of the Universal Unique
Identifier (UUID) mechanism, as described in [ISO-11578].
Opaquelocktoken generators, however, have a choice of how they create
these tokens. They can either generate a new UUID for every lock
token they create or they can create a single UUID and then add
extension characters. If the second method is selected then the
program generating the extensions MUST guarantee that the same
extension will never be used twice with the associated UUID.
OpaqueLockToken-URI = "opaquelocktoken:" UUID [Extension] ; The UUID
production is the string representation of a UUID, as defined in
[ISO-11578]. Note that white space (LWS) is not allowed between
elements of this production.
Extension = path ; path is defined in section 3.2.1 of RFC2068
[RFC2068]
6.4.1 Node Field Generation Without the IEEE 802 Address
UUIDs, as defined in [ISO-11578], contain a "node" field that
contains one of the IEEE 802 addresses for the server machine. As
noted in section 17.8, there are several security risks associated
with exposing a machine's IEEE 802 address. This section provides an
alternate mechanism for generating the "node" field of a UUID which
does not employ an IEEE 802 address. WebDAV servers MAY use this
algorithm for creating the node field when generating UUIDs. The
text in this section is originally from an Internet-Draft by Paul
Leach and Rich Salz, who are noted here to properly attribute their
work.
The ideal solution is to oBTain a 47 bit cryptographic quality random
number, and use it as the low 47 bits of the node ID, with the most
significant bit of the first octet of the node ID set to 1. This bit
is the unicast/multicast bit, which will never be set in IEEE 802
addresses obtained from network cards; hence, there can never be a
conflict between UUIDs generated by machines with and without network
cards.
If a system does not have a primitive to generate cryptographic
quality random numbers, then in most systems there are usually a
fairly large number of sources of randomness available from which one
can be generated. Such sources are system specific, but often
include:
- the percent of memory in use
- the size of main memory in bytes
- the amount of free main memory in bytes
- the size of the paging or swap file in bytes
- free bytes of paging or swap file
- the total size of user virtual address space in bytes
- the total available user address space bytes
- the size of boot disk drive in bytes
- the free disk space on boot drive in bytes
- the current time
- the amount of time since the system booted
- the individual sizes of files in various system directories
- the creation, last read, and modification times of files in
various system directories
- the utilization factors of various system resources (heap, etc.)
- current mouse cursor position
- current caret position
- current number of running processes, threads
- handles or IDs of the desktop window and the active window
- the value of stack pointer of the caller
- the process and thread ID of caller
- various processor architecture specific performance counters
(instructions executed, cache misses, TLB misses)
(Note that it is precisely the above kinds of sources of randomness
that are used to seed cryptographic quality random number generators
on systems without special hardware for their construction.)
In addition, items such as the computer's name and the name of the
operating system, while not strictly speaking random, will help
differentiate the results from those obtained by other systems.
The exact algorithm to generate a node ID using these data is system
specific, because both the data available and the functions to obtain
them are often very system specific. However, assuming that one can
concatenate all the values from the randomness sources into a buffer,
and that a cryptographic hash function such as MD5 is available, then
any 6 bytes of the MD5 hash of the buffer, with the multicast bit
(the high bit of the first byte) set will be an appropriately random
node ID.
Other hash functions, such as SHA-1, can also be used. The only
requirement is that the result be suitably random _ in the sense that
the outputs from a set uniformly distributed inputs are themselves
uniformly distributed, and that a single bit change in the input can
be expected to cause half of the output bits to change.
6.5 Lock Capability Discovery
Since server lock support is optional, a client trying to lock a
resource on a server can either try the lock and hope for the best,
or perform some form of discovery to determine what lock capabilities
the server supports. This is known as lock capability discovery.
Lock capability discovery differs from discovery of supported access
control types, since there may be access control types without
corresponding lock types. A client can determine what lock types the
server supports by retrieving the supportedlock property.
Any DAV compliant resource that supports the LOCK method MUST support
the supportedlock property.
6.6 Active Lock Discovery
If another principal locks a resource that a principal wishes to
access, it is useful for the second principal to be able to find out
who the first principal is. For this purpose the lockdiscovery
property is provided. This property lists all outstanding locks,
describes their type, and where available, provides their lock token.
Any DAV compliant resource that supports the LOCK method MUST support
the lockdiscovery property.
6.7 Usage Considerations
Although the locking mechanisms specified here provide some help in
preventing lost updates, they cannot guarantee that updates will
never be lost. Consider the following scenario:
Two clients A and B are interested in editing the resource '
index.html'. Client A is an HTTP client rather than a WebDAV client,
and so does not know how to perform locking.
Client A doesn't lock the document, but does a GET and begins
editing.
Client B does LOCK, performs a GET and begins editing.
Client B finishes editing, performs a PUT, then an UNLOCK.
Client A performs a PUT, overwriting and losing all of B's changes.
There are several reasons why the WebDAV protocol itself cannot
prevent this situation. First, it cannot force all clients to use
locking because it must be compatible with HTTP clients that do not
comprehend locking. Second, it cannot require servers to support
locking because of the variety of repository implementations, some of
which rely on reservations and merging rather than on locking.
Finally, being stateless, it cannot enforce a sequence of operations
like LOCK / GET / PUT / UNLOCK.
WebDAV servers that support locking can reduce the likelihood that
clients will accidentally overwrite each other's changes by requiring
clients to lock resources before modifying them. Such servers would
effectively prevent HTTP 1.0 and HTTP 1.1 clients from modifying
resources.
WebDAV clients can be good citizens by using a lock / retrieve /
write /unlock sequence of operations (at least by default) whenever
they interact with a WebDAV server that supports locking.
HTTP 1.1 clients can be good citizens, avoiding overwriting other
clients' changes, by using entity tags in If-Match headers with any
requests that would modify resources.
Information managers may attempt to prevent overwrites by
implementing client-side procedures requiring locking before
modifying WebDAV resources.
7 Write Lock
This section describes the semantics specific to the write lock type.
The write lock is a specific instance of a lock type, and is the only
lock type described in this specification.
7.1 Methods Restricted by Write Locks
A write lock MUST prevent a principal without the lock from
successfully executing a PUT, POST, PROPPATCH, LOCK, UNLOCK, MOVE,
DELETE, or MKCOL on the locked resource. All other current methods,
GET in particular, function independently of the lock.
Note, however, that as new methods are created it will be necessary
to specify how they interact with a write lock.
7.2 Write Locks and Lock Tokens
A successful request for an exclusive or shared write lock MUST
result in the generation of a unique lock token associated with the
requesting principal. Thus if five principals have a shared write
lock on the same resource there will be five lock tokens, one for
each principal.
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 Null Resources
It is possible to assert a write lock on a null resource in order to
lock the name.
A write locked null resource, referred to as a lock-null resource,
MUST respond with a 404 (Not Found) or 405 (Method Not Allowed) to
any HTTP/1.1 or DAV methods except for PUT, MKCOL, OPTIONS, PROPFIND,
LOCK, and UNLOCK. A lock-null resource MUST appear as a member of
its parent collection. Additionally the lock-null resource MUST have
defined on it all mandatory DAV properties. Most of these
properties, such as all the get* properties, will have no value as a
lock-null resource does not support the GET method. Lock-Null
resources MUST have defined values for lockdiscovery and
supportedlock properties.
Until a method such as PUT or MKCOL is successfully executed on the
lock-null resource the resource MUST stay in the lock-null state.
However, once a PUT or MKCOL is successfully executed on a lock-null
resource the resource ceases to be in the lock-null state.
If the resource is unlocked, for any reason, without a PUT, MKCOL, or
similar method having been successfully executed upon it then the
resource MUST return to the null state.
7.5 Write Locks and Collections
A write lock on a collection, whether created by a "Depth: 0" or
"Depth: infinity" lock request, prevents the addition or removal of
member URIs of the collection by non-lock owners. As a consequence,
when a principal issues a PUT or POST request to create a new
resource under a URI which needs to be an internal member of a write
locked collection to maintain HTTP namespace consistency, or issues a
DELETE to remove a resource which has a URI which is an existing
internal member URI of a write locked collection, this request MUST
fail if the principal does not have a write lock on the collection.
However, if a write lock request is issued to a collection containing
member URIs identifying resources that are currently locked in a
manner which conflicts with the write lock, the request MUST fail
with a 423 (Locked) status code.
If a lock owner causes the URI of a resource to be added as an
internal member URI of a locked collection then the new resource MUST
be automatically added to the lock. This is the only mechanism that
allows a resource to be added to a write lock. Thus, for example, if
the collection /a/b/ is write locked and the resource /c is moved to
/a/b/c then resource /a/b/c will be added to the write lock.
7.6 Write Locks and the If Request Header
If a user agent is not required to have knowledge about a lock when
requesting an operation on a locked resource, the following scenario
might occur. Program A, run by User A, takes out a write lock on a
resource. Program B, also run by User A, has no knowledge of the
lock taken out by Program A, yet performs a PUT to the locked
resource. In this scenario, the PUT succeeds because locks are
associated with a principal, not a program, and thus program B,
because it is acting with principal A's credential, is allowed to
perform the PUT. However, had program B known about the lock, it
would not have overwritten the resource, preferring instead to
present a dialog box describing the conflict to the user. Due to
this scenario, a mechanism is needed to prevent different programs
from accidentally ignoring locks taken out by other programs with the
same authorization.
In order to prevent these collisions a lock token MUST be submitted
by an authorized principal in the If header for all locked resources
that a method may interact with or the method MUST fail. For
example, if a resource is to be moved and both the source and
destination are locked then two lock tokens must be submitted, one
for the source and the other for the destination.
7.6.1 Example - Write Lock
>>Request
COPY /~fielding/index.html HTTP/1.1
Host: www.ics.uci.edu
Destination: http://www.ics.uci.edu/users/f/fielding/index.html
If: <http://www.ics.uci.edu/users/f/fielding/index.html>
(<opaquelocktoken:f81d4fae-7dec-11d0-a765-00a0c91e6bf6>)
>>Response
HTTP/1.1 204 No Content
In this example, even though both the source and destination are
locked, only one lock token must be submitted, for the lock on the
destination. This is because the source resource is not modified by
a COPY, and hence unaffected by the write lock. In this example, user
agent authentication has previously occurred via a mechanism outside
the scope of the HTTP protocol, in the underlying transport layer.
7.7 Write Locks and COPY/MOVE
A COPY method invocation MUST NOT duplicate any write locks active on
the source. However, as previously noted, if the COPY copies the
resource into a collection that is locked with "Depth: infinity",
then the resource will be added to the lock.
A successful MOVE request on a write locked resource MUST NOT move
the write lock with the resource. However, the resource is subject to
being added to an existing lock at the destination, as specified 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.
If an error is received in response to a refresh LOCK request the
client SHOULD assume that the lock was not refreshed.
8 HTTP Methods for Distributed Authoring
The following new HTTP methods use XML as a request and response
format. All DAV compliant clients and resources MUST use XML parsers
that are compliant with [REC-XML]. All XML used in either requests
or responses MUST be, at minimum, well formed. If a server receives
ill-formed XML in a request it MUST reject the entire request with a
400 (Bad Request). If a client receives ill-formed XML in a response
then it MUST NOT assume anything about the outcome of the executed
method and SHOULD treat the server as malfunctioning.
8.1 PROPFIND
The PROPFIND method retrieves properties defined on the resource
identified by the Request-URI, if the resource does not have any
internal members, or on the resource identified by the Request-URI
and potentially its member resources, if the resource is a collection
that has internal member URIs. All DAV compliant resources MUST
support the PROPFIND method and the propfind XML element (section
12.14) along with all XML elements defined for use with that element.
A client may submit a Depth header with a value of "0", "1", or
"infinity" with a PROPFIND on a collection resource with internal
member URIs. DAV compliant servers MUST support the "0", "1" and
"infinity" behaviors. By default, the PROPFIND method without a Depth
header MUST act as if a "Depth: infinity" header was included.
A client may submit a propfind XML element in the body of the request
method describing what information is being requested. It is
possible to request particular property values, all property values,
or a list of the names of the resource's properties. A client may
choose not to submit a request body. An empty PROPFIND request body
MUST be treated as a request for the names and values of all
properties.
All servers MUST support returning a response of content type
text/xml or application/xml that contains a multistatus XML element
that describes the results of the attempts to retrieve the various
properties.
If there is an error retrieving a property then a proper error result
MUST be included in the response. A request to retrieve the value of
a property which does not exist is an error and MUST be noted, if the
response uses a multistatus XML element, with a response XML element
which contains a 404 (Not Found) status value.
Consequently, the multistatus XML element for a collection resource
with member URIs MUST include a response XML element for each member
URI of the collection, to whatever depth was requested. Each response
XML element MUST contain an href XML element that gives the URI of
the resource on which the properties in the prop XML element are
defined. Results for a PROPFIND on a collection resource with
internal member URIs are returned as a flat list whose order of
entries is not significant.
In the case of allprop and propname, if a principal does not have the
right to know whether a particular property exists then the property
should be silently excluded from the response.
The results of this method SHOULD NOT be cached.
8.1.1 Example - Retrieving Named Properties
>>Request
PROPFIND /file HTTP/1.1
Host: www.foo.bar
Content-type: text/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<D:propfind xmlns:D="DAV:">
<D:prop xmlns:R="http://www.foo.bar/boxschema/">
<R:bigbox/>
<R:author/>
<R:DingALing/>
<R:Random/>
</D:prop>
</D:propfind>
>>Response
HTTP/1.1 207 Multi-Status
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<D:multistatus xmlns:D="DAV:">
<D:response>
<D:href>http://www.foo.bar/file</D:href>
<D:propstat>
<D:prop xmlns:R="http://www.foo.bar/boxschema/">
<R:bigbox>
<R:BoxType>Box type A</R:BoxType>
</R:bigbox>
<R:author>
<R:Name>J.J. Johnson</R:Name>
</R:author>
</D:prop>
<D:status>HTTP/1.1 200 OK</D:status>
</D:propstat>
<D:propstat>
<D:prop><R:DingALing/><R:Random/></D:prop>
<D:status>HTTP/1.1 403 Forbidden</D:status>
<D:responsedescription> The user does not have access to
the DingALing property.
</D:responsedescription>
</D:propstat>
</D:response>
<D:responsedescription> There has been an access violation error.
</D:responsedescription>
</D:multistatus>
In this example, PROPFIND is executed on a non-collection resource
http://www.foo.bar/file. The propfind XML element specifies the name
of four properties whose values are being requested. In this case
only two properties were returned, since the principal issuing the
request did not have sufficient access rights to see the third and
fourth properties.
8.1.2 Example - Using allprop to Retrieve All Properties
>>Request
PROPFIND /container/ HTTP/1.1
Host: www.foo.bar
Depth: 1
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<D:propfind xmlns:D="DAV:">
<D:allprop/>
</D:propfind>
>>Response
HTTP/1.1 207 Multi-Status
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<D:multistatus xmlns:D="DAV:">
<D:response>
<D:href>http://www.foo.bar/container/</D:href>
<D:propstat>
<D:prop xmlns:R="http://www.foo.bar/boxschema/">
<R:bigbox>
<R:BoxType>Box type A</R:BoxType>
</R:bigbox>
<R:author>
<R:Name>Hadrian</R:Name>
</R:author>
<D:creationdate>
1997-12-01T17:42:21-08:00
</D:creationdate>
<D:displayname>
Example collection
</D:displayname>
<D:resourcetype><D:collection/></D:resourcetype>
<D:supportedlock>
<D:lockentry>
<D:lockscope><D:exclusive/></D:lockscope>
<D:locktype><D:write/></D:locktype>
</D:lockentry>
<D:lockentry>
<D:lockscope><D:shared/></D:lockscope>
<D:locktype><D:write/></D:locktype>
</D:lockentry>
</D:supportedlock>
</D:prop>
<D:status>HTTP/1.1 200 OK</D:status>
</D:propstat>
</D:response>
<D:response>
<D:href>http://www.foo.bar/container/front.html</D:href>
<D:propstat>
<D:prop xmlns:R="http://www.foo.bar/boxschema/">
<R:bigbox>
<R:BoxType>Box type B</R:BoxType>
</R:bigbox>
<D:creationdate>
1997-12-01T18:27:21-08:00
</D:creationdate>
<D:displayname>
Example HTML resource
</D:displayname>
<D:getcontentlength>
4525
</D:getcontentlength>
<D:getcontenttype>
text/html
</D:getcontenttype>
<D:getetag>
zzyzx
</D:getetag>
<D:getlastmodified>
Monday, 12-Jan-98 09:25:56 GMT
</D:getlastmodified>
<D:resourcetype/>
<D:supportedlock>
<D:lockentry>
<D:lockscope><D:exclusive/></D:lockscope>
<D:locktype><D:write/></D:locktype>
</D:lockentry>
<D:lockentry>
<D:lockscope><D:shared/></D:lockscope>
<D:locktype><D:write/></D:locktype>
</D:lockentry>
</D:supportedlock>
</D:prop>
<D:status>HTTP/1.1 200 OK</D:status>
</D:propstat>
</D:response>
</D:multistatus>
In this example, PROPFIND was invoked on the resource
http://www.foo.bar/container/ with a Depth header of 1, meaning the
request applies to the resource and its children, and a propfind XML
element containing the allprop XML element, meaning the request
should return the name and value of all properties defined on each
resource.
The resource http://www.foo.bar/container/ has six properties defined
on it:
http://www.foo.bar/boxschema/bigbox,
http://www.foo.bar/boxschema/author, DAV:creationdate,
DAV:displayname, DAV:resourcetype, and DAV:supportedlock.
The last four properties are WebDAV-specific, defined in section 13.
Since GET is not supported on this resource, the get* properties
(e.g., getcontentlength) are not defined on this resource. The DAV-
specific properties assert that "container" was created on December
1, 1997, at 5:42:21PM, in a time zone 8 hours west of GMT
(creationdate), has a name of "Example collection" (displayname), a
collection resource type (resourcetype), and supports exclusive write
and shared write locks (supportedlock).
The resource http://www.foo.bar/container/front.html has nine
properties defined on it:
http://www.foo.bar/boxschema/bigbox (another instance of the "bigbox"
property type), DAV:creationdate, DAV:displayname,
DAV:getcontentlength, DAV:getcontenttype, DAV:getetag,
DAV:getlastmodified, DAV:resourcetype, and DAV:supportedlock.
The DAV-specific properties assert that "front.html" was created on
December 1, 1997, at 6:27:21PM, in a time zone 8 hours west of GMT
(creationdate), has a name of "Example HTML resource" (displayname),
a content length of 4525 bytes (getcontentlength), a MIME type of
"text/html" (getcontenttype), an entity tag of "zzyzx" (getetag), was
last modified on Monday, January 12, 1998, at 09:25:56 GMT
(getlastmodified), has an empty resource type, meaning that it is not
a collection (resourcetype), and supports both exclusive write and
shared write locks (supportedlock).
8.1.3 Example - Using propname to Retrieve all Property Names
>>Request
PROPFIND /container/ HTTP/1.1
Host: www.foo.bar
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<propfind xmlns="DAV:">
<propname/>
</propfind>
>>Response
HTTP/1.1 207 Multi-Status
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<multistatus xmlns="DAV:">
<response>
<href>http://www.foo.bar/container/</href>
<propstat>
<prop xmlns:R="http://www.foo.bar/boxschema/">
<R:bigbox/>
<R:author/>
<creationdate/>
<displayname/>
<resourcetype/>
<supportedlock/>
</prop>
<status>HTTP/1.1 200 OK</status>
</propstat>
</response>
<response>
<href>http://www.foo.bar/container/front.html</href>
<propstat>
<prop xmlns:R="http://www.foo.bar/boxschema/">
<R:bigbox/>
<creationdate/>
<displayname/>
<getcontentlength/>
<getcontenttype/>
<getetag/>
<getlastmodified/>
<resourcetype/>
<supportedlock/>
</prop>
<status>HTTP/1.1 200 OK</status>
</propstat>
</response>
</multistatus>
In this example, PROPFIND is invoked on the collection resource
http://www.foo.bar/container/, with a propfind XML element containing
the propname XML element, meaning the name of all properties should
be returned. Since no Depth header is present, it assumes its
default value of "infinity", meaning the name of the properties on
the collection and all its progeny should be returned.
Consistent with the previous example, resource
http://www.foo.bar/container/ has six properties defined on it,
http://www.foo.bar/boxschema/bigbox,
http://www.foo.bar/boxschema/author, DAV:creationdate,
DAV:displayname, DAV:resourcetype, and DAV:supportedlock.
The resource http://www.foo.bar/container/index.html, a member of the
"container" collection, has nine properties defined on it,
http://www.foo.bar/boxschema/bigbox, DAV:creationdate,
DAV:displayname, DAV:getcontentlength, DAV:getcontenttype,
DAV:getetag, DAV:getlastmodified, DAV:resourcetype, and
DAV:supportedlock.
This example also demonstrates the use of XML namespace scoping, and
the default namespace. Since the "xmlns" attribute does not contain
an explicit "shorthand name" (prefix) letter, the namespace applies
by default to all enclosed elements. Hence, all elements which do
not explicitly state the namespace to which they belong are members
of the "DAV:" namespace schema.
8.2 PROPPATCH
The PROPPATCH method processes instructions specified in the request
body to set and/or remove properties defined on the resource
identified by the Request-URI.
All DAV compliant resources MUST support the PROPPATCH method and
MUST process instructions that are specified using the
propertyupdate, set, and remove XML elements of the DAV schema.
Execution of the directives in this method is, of course, subject to
access control constraints. DAV compliant resources SHOULD support
the setting of arbitrary dead properties.
The request message body of a PROPPATCH method MUST contain the
propertyupdate XML element. Instruction processing MUST occur in the
order instructions are received (i.e., from top to bottom).
Instructions MUST either all be executed or none executed. Thus if
any error occurs during processing all executed instructions MUST be
undone and a proper error result returned. Instruction processing
details can be found in the definition of the set and remove
instructions in section 12.13.
8.2.1 Status Codes for use with 207 (Multi-Status)
The following are examples of response codes one would expect to be
used in a 207 (Multi-Status) response for this method. Note,
however, that unless explicitly prohibited any 2/3/4/5xx series
response code may be used in a 207 (Multi-Status) response.
200 (OK) - The command succeeded. As there can be a mixture of sets
and removes in a body, a 201 (Created) seems inappropriate.
403 (Forbidden) - The client, for reasons the server chooses not to
specify, cannot alter one of the properties.
409 (Conflict) - The client has provided a value whose semantics are
not appropriate for the property. This includes trying to set read-
only properties.
423 (Locked) - The specified resource is locked and the client either
is not a lock owner or the lock type requires a lock token to be
submitted and the client did not submit it.
507 (Insufficient Storage) - The server did not have sufficient space
to record the property.
8.2.2 Example - PROPPATCH
>>Request
PROPPATCH /bar.html HTTP/1.1
Host: www.foo.com
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<D:propertyupdate xmlns:D="DAV:"
xmlns:Z="http://www.w3.com/standards/z39.50/">
<D:set>
<D:prop>
<Z:authors>
<Z:Author>Jim Whitehead</Z:Author>
<Z:Author>Roy Fielding</Z:Author>
</Z:authors>
</D:prop>
</D:set>
<D:remove>
<D:prop><Z:Copyright-Owner/></D:prop>
</D:remove>
</D:propertyupdate>
>>Response
HTTP/1.1 207 Multi-Status
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<D:multistatus xmlns:D="DAV:"
xmlns:Z="http://www.w3.com/standards/z39.50">
<D:response>
<D:href>http://www.foo.com/bar.html</D:href>
<D:propstat>
<D:prop><Z:Authors/></D:prop>
<D:status>HTTP/1.1 424 Failed Dependency</D:status>
</D:propstat>
<D:propstat>
<D:prop><Z:Copyright-Owner/></D:prop>
<D:status>HTTP/1.1 409 Conflict</D:status>
</D:propstat>
<D:responsedescription> Copyright Owner can not be deleted or
altered.</D:responsedescription>
</D:response>
</D:multistatus>
In this example, the client requests the server to set the value of
the http://www.w3.com/standards/z39.50/Authors property, and to
remove the property http://www.w3.com/standards/z39.50/Copyright-
Owner. Since the Copyright-Owner property could not be removed, no
property modifications occur. The 424 (Failed Dependency) status
code for the Authors property indicates this action would have
succeeded if it were not for the conflict with removing the
Copyright-Owner property.
8.3 MKCOL Method
The MKCOL method is used to create a new collection. All DAV
compliant resources MUST support the MKCOL method.
8.3.1 Request
MKCOL creates a new collection resource at the location specified by
the Request-URI. If the resource identified by the Request-URI is
non-null then the MKCOL MUST fail. During MKCOL processing, a server
MUST make the Request-URI a member of its parent collection, unless
the Request-URI is "/". If no such ancestor exists, the method MUST
fail. When the MKCOL operation creates a new collection resource,
all ancestors MUST already exist, or the method MUST fail with a 409
(Conflict) status code. For example, if a request to create
collection /a/b/c/d/ is made, and neither /a/b/ nor /a/b/c/ exists,
the request must fail.
When MKCOL is invoked without a request body, the newly created
collection SHOULD have no members.
A MKCOL request message may contain a message body. The behavior of
a MKCOL request when the body is present is limited to creating
collections, members of a collection, bodies of members and
properties on the collections or members. If the server receives a
MKCOL request entity type it does not support or understand it MUST
respond with a 415 (Unsupported Media Type) status code. The exact
behavior of MKCOL for various request media types is undefined in
this document, and will be specified in separate documents.
8.3.2 Status Codes
Responses from a MKCOL request MUST NOT be cached as MKCOL has non-
idempotent semantics.
201 (Created) - The collection or structured resource was created in
its entirety.
403 (Forbidden) - This indicates at least one of two conditions: 1)
the server does not allow the creation of collections at the given
location in its namespace, or 2) the parent collection of the
Request-URI exists but cannot accept members.
405 (Method Not Allowed) - MKCOL can only be executed on a
deleted/non-existent resource.
409 (Conflict) - A collection cannot be made at the Request-URI until
one or more intermediate collections have been created.
415 (Unsupported Media Type)- The server does not support the request
type of the body.
507 (Insufficient Storage) - The resource does not have sufficient
space to record the state of the resource after the execution of this
method.
8.3.3 Example - MKCOL
This example creates a collection called /webdisc/xfiles/ on the
server www.server.org.
>>Request
MKCOL /webdisc/xfiles/ HTTP/1.1
Host: www.server.org
>>Response
HTTP/1.1 201 Created
8.4 GET, HEAD for Collections
The semantics of GET are unchanged when applied to a collection,
since GET is defined as, "retrieve whatever information (in the form
of an entity) is identified by the Request-URI" [RFC2068]. GET when
applied to a collection may return the contents of an "index.html"
resource, a human-readable view of the contents of the collection, or
something else altogether. Hence it is possible that the result of a
GET on a collection will bear no correlation to the membership of the
collection.
Similarly, since the definition of HEAD is a GET without a response
message body, the semantics of HEAD are unmodified when applied to
collection resources.
8.5 POST for Collections
Since by definition the actual function performed by POST is
determined by the server and often depends on the particular
resource, the behavior of POST when applied to collections cannot be
meaningfully modified because it is largely undefined. Thus the
semantics of POST are unmodified when applied to a collection.
8.6 DELETE
8.6.1 DELETE for Non-Collection Resources
If the DELETE method is issued to a non-collection resource whose
URIs are an internal member of one or more collections, then during
DELETE processing a server MUST remove any URI for the resource
identified by the Request-URI from collections which contain it as a
member.
8.6.2 DELETE for Collections
The DELETE method on a collection MUST act as if a "Depth: infinity"
header was used on it. A client MUST NOT submit a Depth header with
a DELETE on a collection with any value but infinity.
DELETE instructs that the collection specified in the Request-URI and
all resources identified by its internal member URIs are to be
deleted.
If any resource identified by a member URI cannot be deleted then all
of the member's ancestors MUST NOT be deleted, so as to maintain
namespace consistency.
Any headers included with DELETE MUST be applied in processing every
resource to be deleted.
When the DELETE method has completed processing it MUST result in a
consistent namespace.
If an error occurs with a resource other than the resource identified
in the Request-URI then the response MUST be a 207 (Multi-Status).
424 (Failed Dependency) errors SHOULD NOT be in the 207 (Multi-
Status). They can be safely left out because the client will know
that the ancestors of a resource could not be deleted when the client
receives an error for the ancestor's progeny. Additionally 204 (No
Content) errors SHOULD NOT be returned in the 207 (Multi-Status).
The reason for this prohibition is that 204 (No Content) is the
default success code.
8.6.2.1 Example - DELETE
>>Request
DELETE /container/ HTTP/1.1
Host: www.foo.bar
>>Response
HTTP/1.1 207 Multi-Status
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<d:multistatus xmlns:d="DAV:">
<d:response>
<d:href>http://www.foo.bar/container/resource3</d:href>
<d:status>HTTP/1.1 423 Locked</d:status>
</d:response>
</d:multistatus>
In this example the attempt to delete
http://www.foo.bar/container/resource3 failed because it is locked,
and no lock token was submitted with the request. Consequently, the
attempt to delete http://www.foo.bar/container/ also failed. Thus the
client knows that the attempt to delete http://www.foo.bar/container/
must have also failed since the parent can not be deleted unless its
child has also been deleted. Even though a Depth header has not been
included, a depth of infinity is assumed because the method is on a
collection.
8.7 PUT
8.7.1 PUT for Non-Collection Resources
A PUT performed on an existing resource replaces the GET response
entity of the resource. Properties defined on the resource may be
recomputed during PUT processing but are not otherwise affected. For
example, if a server recognizes the content type of the request body,
it may be able to automatically extract information that could be
profitably exposed as properties.
A PUT that would result in the creation of a resource without an
appropriately scoped parent collection MUST fail with a 409
(Conflict).
8.7.2 PUT for Collections
As defined in the HTTP/1.1 specification [RFC2068], the "PUT method
requests that the enclosed entity be stored under the supplied
Request-URI." Since submission of an entity representing a
collection would implicitly encode creation and deletion of
resources, this specification intentionally does not define a
transmission format for creating a collection using PUT. Instead,
the MKCOL method is defined to create collections.
When the PUT operation creates a new non-collection resource all
ancestors MUST already exist. If all ancestors do not exist, the
method MUST fail with a 409 (Conflict) status code. For example, if
resource /a/b/c/d.html is to be created and /a/b/c/ does not exist,
then the request must fail.
8.8 COPY Method
The COPY method creates a duplicate of the source resource,
identified by the Request-URI, in the destination resource,
identified by the URI in the Destination header. The Destination
header MUST be present. The exact behavior of the COPY method
depends on the type of the source resource.
All WebDAV compliant resources MUST support the COPY method.
However, support for the COPY method does not guarantee the ability
to copy a resource. For example, separate programs may control
resources on the same server. As a result, it may not be possible to
copy a resource to a location that appears to be on the same server.
8.8.1 COPY for HTTP/1.1 resources
When the source resource is not a collection the result of the COPY
method is the creation of a new resource at the destination whose
state and behavior match that of the source resource as closely as
possible. After a successful COPY invocation, all properties on the
source resource MUST be duplicated on the destination resource,
subject to modifying headers and XML elements, following the
definition for copying properties. Since the environment at the
destination may be different than at the source due to factors
outside the scope of control of the server, such as the absence of
resources required for correct operation, it may not be possible to
completely duplicate the behavior of the resource at the destination.
Subsequent alterations to the destination resource will not modify
the source resource. Subsequent alterations to the source resource
will not modify the destination resource.
8.8.2. COPY for Properties
The following section defines how properties on a resource are
handled during a COPY operation.
Live properties SHOULD be duplicated as identically behaving live
properties at the destination resource. 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
subject to the effects of the propertybehavior XML element.
The propertybehavior XML element can specify that properties are
copied on best effort, that all live properties must be successfully
copied or the method must fail, or that a specified list of live
properties must be successfully copied or the method must fail. The
propertybehavior XML element is defined in section 12.12.
8.8.3 COPY for Collections
The COPY method on a collection without a Depth header MUST act as if
a Depth header with value "infinity" was included. A client may
submit a Depth header on a COPY on a collection with a value of "0"
or "infinity". DAV compliant servers MUST support the "0" and
"infinity" Depth header behaviors.
A COPY of depth infinity instructs that the collection resource
identified by the Request-URI is to be copied to the location
identified by the URI in the Destination header, and all its internal
member resources are to be copied to a location relative to it,
recursively through all levels of the collection hierarchy.
A COPY of "Depth: 0" only instructs that the collection and its
