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WebDAV L. Dusseault
Internet-Draft OSAF
Expires: January 15, 2005 J. Crawford
IBM
July 17, 2004
HTTP Extensions for Distributed Authoring - WebDAV RFC2518 bis
draft-ietf-webdav-rfc2518bis-06
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as
Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at http://
www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on January 15, 2005.
Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
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.
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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) [15].
This standard does not specify the versioning operations suggested by
RFC2291 [15]. That work was done in a separate document, "Versioning
Extensions to WebDAV" (RFC3253) [18].
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 (Section
8) and the new HTTP headers used with WebDAV methods (Section 9).
While the status codes provided by HTTP/1.1 are sufficient to
describe most error conditions encountered by WebDAV methods, there
are some errors that do not fall neatly into the existing categories.
This specification defines new status codes developed for WebDAV
methods (Section 10) and describes existing HTTP status codes
(Section 11) as used in WebDAV. Since some WebDAV methods may
operate over many resources, the Multi-Status response (Section 12)
has been introduced to return status information for multiple
resources. Finally, this version of WebDAV introduces XML elements
in error response bodies in Section 15.
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WebDAV uses XML [11] to marshal complicated request and response
information, as well as to express metadata, so this specification
contains definitions of all XML elements used (Section 13). WebDAV
includes a few special rules on how to process XML (Section 16)
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.
Finishing off the specification are sections on what it means to be
compliant with this specification (Section 17), on
internationalization support (Section 18), and on security (Section
19).
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2. Notational Conventions
Since this document describes a set of extensions to the HTTP/1.1
protocol, the augmented BNF used herein to describe protocol elements
is exactly the same as described in section 2.1 of RFC2616 [8],
including the rules about implied linear white-space. Since this
augmented BNF uses the basic production rules provided in section 2.2
of RFC2616 [8], 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 [3].
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3. Terminology
URI/URL - A Uniform Resource Identifier and Uniform Resource Locator,
respectively. These terms (and the distinction between them) are
defined in RFC2396 [6].
Collection - A resource that contains a set of URLs, which identify
and locate member resources and which meet the collections
requirements (Section 5).
Member URL - A URL which is a member of the set of URLs contained by
a collection.
Internal Member URL - A Member URL that is immediately relative to
the URL of the collection (the definition of immediately relative is
given later (Section 5.2)).
Property - A name/value pair that contains descriptive information
about a resource.
Live Property - A property whose semantics and syntax are enforced by
the server. For example, the live "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.
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4. Data Model for Resource Properties
4.1 The Resource Property Model
Properties are pieces of data that describe the state of a resource.
Properties are data about data.
Properties are used in distributed authoring environments to provide
for efficient discovery and management of resources. For example, a
'subject' property might allow for the indexing of all resources by
their subject, and an 'author' property might allow for the discovery
of what authors have written which documents.
The DAV property model consists of name/value pairs. The name of a
property identifies the property's syntax and semantics, and provides
an address by which to refer to its syntax and semantics.
There are two categories of properties: "live" and "dead". A live
property has its syntax and semantics enforced by the server. Live
properties include cases where a) the value of a property is read-
only, maintained by the server, and b) the value of the property is
maintained by the client, but the server performs syntax checking on
submitted values. All instances of a given live property MUST comply
with the definition associated with that property name. A dead
property has its syntax and semantics enforced by the client; the
server merely records the value of the property verbatim.
4.2 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 [20], 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.
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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 XML [11] request entity body, or in an HTTP
header. The use of XML to encode method parameters was motivated by
the ability to add extra XML elements to existing structures,
providing extensibility; and by XML's ability to encode information
in ISO 10646 character sets, providing internationalization support.
In addition to encoding method parameters, XML is used in WebDAV to
encode the responses from methods, providing the extensibility and
internationalization advantages of XML for method output, as well as
input.
The XML namespace extension [10] is also used in this specification
in order to allow for new XML elements to be added without fear of
colliding with other element names. Although WebDAV request and
response bodies can be extended by arbitrary XML elements, which can
be ignored by the message recipient, an XML element in the "DAV:"
namespace SHOULD NOT be used in the request or response body unless
that XML element is explicitly defined in an IETF RFC reviewed by a
WebDAV working group.
Note that "DAV:" is a scheme name defined solely to provide a
namespace for WebDAV XML elements and property names. This practice
is discouraged in part because registration of new scheme names is
difficult. "DAV:" was defined as the WebDAV namespace before
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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 (well-formed) XML fragment.
XML has been chosen because it is a flexible, self-describing,
structured data format that supports rich schema definitions, and
because of its support for multiple character sets. XML's self-
describing nature allows any property's value to be extended by
adding new elements. Older clients will not break when they
encounter extensions because they will still have the data specified
in the original schema and 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
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.
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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 [6], 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.
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5. Collections of Web Resources
This section provides a description of a new type of Web resource,
the collection, and discusses its interactions with the HTTP URL
namespace. The purpose of a collection resource is to model
collection-like objects (e.g., file system directories) within a
server's namespace.
All DAV compliant resources MUST support the HTTP URL namespace model
specified herein.
5.1 HTTP URL Namespace Model
The HTTP URL namespace is a hierarchical namespace where the
hierarchy is delimited with the "/" character.
An HTTP URL namespace is said to be consistent if it meets the
following conditions: for every URL in the HTTP hierarchy there
exists a collection that contains that URL as an internal member.
The root, or top-level collection of the namespace under
consideration is exempt from the previous rule.
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 [8] and RFC2396 [6], 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 [6].
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.
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For all WebDAV compliant resources A and B, identified by URLs U and
V, for which U is immediately relative to V, B MUST be a collection
that has U as an internal member URL. So, if the resource with URL
http://example.com/bar/blah is WebDAV compliant and if the resource
with URL http://example.com/bar/ is WebDAV compliant then the
resource with URL http://example.com/bar/ must be a collection and
must contain URL http://example.com/bar/blah as an internal member.
Collection resources MAY list the URLs of non-WebDAV compliant
children in the HTTP URL namespace hierarchy as internal members but
are not required to do so. For example, if the resource with URL
http://example.com/bar/blah is not WebDAV compliant and the URL
http://example.com/bar/ identifies a collection then URL http://
example.com/bar/blah may or may not be an internal member of the
collection with URL http://example.com/bar/.
If a WebDAV compliant resource has no WebDAV compliant children in
the HTTP URL namespace hierarchy then the WebDAV compliant resource
is not required to be a collection.
There is a standing convention that when a collection is referred to
by its name without a trailing slash, the server MAY handle the
request as if the trailing slash were present. In this case it
SHOULD return a Content-Location header in the response, pointing to
the URL ending with the "/". For example, if a client invokes a
method on http://example.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.
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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.
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.
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6. Locking
The ability to lock a resource provides a mechanism for serializing
access to that resource. Using a lock, an authoring client can
provide a reasonable guarantee that another principal will not modify
a resource while it is being edited. In this way, a client can
prevent the "lost update" problem.
This specification allows locks to vary over two client-specified
parameters, the number of principals involved (exclusive vs. shared)
and the type of access to be granted. This document defines locking
for only one access type, write. However, the syntax is extensible,
and permits the eventual specification of locking for other access
types.
6.1 Exclusive Vs. Shared Locks
The most basic form of lock is an exclusive lock. Only one exclusive
lock may exist on any resource, whether it is directly or indirectly
locked (Section 7.5). 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
shared lock allows multiple principals to receive a lock. Hence any
principal with appropriate access can use the lock.
With shared locks there are two trust sets that affect a resource.
The first trust set is created by access permissions. Principals who
are trusted, for example, may have permission to write to the
resource. Among those who have access permission to write to the
resource, the set of principals who have taken out a shared lock also
must trust each other, creating a (typically) smaller trust set
within the access permission write set.
Starting with every possible principal on the Internet, in most
situations the vast majority of these principals will not have write
access to a given resource. Of the small number who do have write
access, some principals may decide to guarantee their edits are free
from overwrite conflicts by using exclusive write locks. Others may
decide they trust their collaborators will not overwrite their work
(the potential set of collaborators being the set of principals who
have write permission) and use a shared lock, which informs their
collaborators that a principal may be working on the resource.
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The WebDAV extensions to HTTP do not need to provide all of the
communications paths necessary for principals to coordinate their
activities. When using shared locks, principals may use any out of
band communication channel to coordinate their work (e.g., face-to-
face interaction, written notes, post-it notes on the screen,
telephone conversation, Email, etc.) The intent of a shared lock is
to let collaborators know who else may be working on a resource.
Shared locks are included because experience from web distributed
authoring systems has indicated that exclusive locks are often too
rigid. An exclusive lock is used to enforce a particular editing
process: take out an exclusive lock, read the resource, perform
edits, write the resource, release the lock. This editing process
has the problem that locks are not always properly released, for
example when a program crashes, or when a lock owner leaves without
unlocking a resource. While both timeouts and administrative action
can be used to remove an offending lock, neither mechanism may be
available when needed; the timeout may be long or the administrator
may not be available.
6.2 Required Support
A WebDAV compliant resource is not required to support locking in any
form. If the resource does support locking it may choose to support
any combination of exclusive and shared locks for any access types.
The reason for this flexibility is that locking policy strikes to the
very heart of the resource management and versioning systems employed
by various storage repositories. These repositories require control
over what sort of locking will be made available. For example, some
repositories only support shared write locks while others only
provide support for exclusive write locks while yet others use no
locking at all. As each system is sufficiently different to merit
exclusion of certain locking features, this specification leaves
locking as the sole axis of negotiation within WebDAV.
6.3 Lock Tokens
A lock token is a type of state token, represented as a URI, which
identifies a particular lock. 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.
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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. The IETF recommends using registered URI
schemes to ensure uniqueness.
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 [12].
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 [12]. Note that white space (LWS) is not allowed between
elements of this production.
Extension = path ; path is defined in section 3.3 of RFC2396 [6]
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. A
client can determine what lock types the server supports by
retrieving the supportedlock property.
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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 Avoiding Lost Updates
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.
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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.
6.8 Locks and Multiple Bindings
A resource may be made available through more than one URI. However
locks apply to resources, not URIs. Therefore a LOCK request on a
resource MUST NOT succeed if can not be honored by all the URIs
through which the resource is addressable.
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7. Write Lock
This section describes the semantics specific to the write lock type.
The write lock is a specific instance of a lock type, and is the only
lock type described in this specification.
Write locks prevent unauthorized changes to resources. In general
terms, changes affected by write locks include changes to:
o the content of the resource
o any dead property of the resource
o any live property defined to be lockable (all properties defined
in this specification are lockable)
o the direct membership of the resource, if it is a collection
o the URL/location of a resource
The next few sections describe in more specific terms how write locks
interact with various operations.
7.1 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 Unmapped URLs
It is possible to lock an unmapped URL in order to lock the name for
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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 an
locked resource with empty content. A subsequent PUT request with
the correct lock token SHOULD normally succeed, and this new request
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:
o Responds with a 404 or 405 to any DAV method except for PUT,
MKCOL, OPTIONS, PROPFIND, LOCK, UNLOCK.
o Appears as a member of its parent collection.
o Disappears (URI becomes unmapped) if its lock goes away before it
is converted to a regular resource. (This must also happen if it
is renamed or moved, or if any parent collection is renamed or
moved, because locks are tied to URLs).
o May be turned into a regular resource when a PUT request to the
URL is successful. Ceases to be a lock-null resource.
o May be turned into a collection when a MKCOL request to the URL is
successful. Ceases to be a lock-null resource.
o Has defined values for 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:
o Can be read, deleted, moved, copied, and in all ways behave as a
regular resource, not a lock-null resource.
o Appears as a member of its parent collection.
o SHOULD NOT disappear when its lock goes away (clients must
therefore be responsible for cleaning up their own mess, as with
any other operation)
o SHOULD default to having no content type.
o MAY NOT have values for properties like getcontentlanguage which
haven't been specified yet by the client.
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o May have content added with a PUT request. MUST be able to change
content type.
o MUST NOT be turned into a collection. A MKCOL request must fail
as it would to any existing resource.
o MUST have defined values for lockdiscovery and supportedlock
properties.
o The response MUST indicate that a resource was created, by use of
the "201 Created" response code (a LOCK request to an existing
resource instead will result in 200 OK). The body must still
include the 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
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 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.
o Any new resource added as a descendent of a depth-infinity locked
collection becomes indirectly locked.
o Any indirectly locked resource moved out of the locked collection
into an unlocked collection is thereafter unlocked.
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o Any indirectly locked resource moved out of a locked source
collection into a depth-infinity locked target collection remains
indirectly locked but is now within the scope of the lock on the
target collection (the target collection's lock token will
thereafter be required to make further changes).
If a depth-infinity write LOCK request is issued to a collection
containing member URLs identifying resources that are currently
locked in a manner which conflicts with the write lock, the request
MUST fail with a 423 (Locked) status code, and the response SHOULD
contain the 'missing-lock-token' precondition.
If a lock owner causes the URL of a resource to be added as an
internal member URL of a depth-infinity locked collection then the
new resource MUST be automatically added to the lock. This is the
only mechanism that allows a resource to be added to a write lock.
Thus, for example, if the collection /a/b/ is write locked and the
resource /c is moved to /a/b/c then resource /a/b/c will be added to
the write lock.
7.6 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 Aȡs 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.
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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.
A successful MOVE request on a write locked resource MUST NOT move
the write lock with the resource. However, the resource is subject
to being added to an existing lock at the destination (see Section
7.5). 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
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that a client is always aware it is resubmitting the same lock
request because it must include the lock token in the If header in
order to make the request for a resource that is already locked.
However, a client may submit a LOCK method with an If header but
without a body. This form of LOCK MUST only be used to "refresh" a
lock. Meaning, at minimum, that any timers associated with the lock
MUST be re-set.
A server may return a Timeout header with a lock refresh that is
different than the Timeout header returned when the lock was
originally requested. Additionally clients may submit Timeout
headers of arbitrary value with their lock refresh requests.
Servers, as always, may ignore Timeout headers submitted by the
client. Note that timeout is measured in seconds remaining until
expiration.
If an error is received in response to a refresh LOCK request the
client MUST NOT assume that the lock was refreshed.
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8. HTTP Methods for Distributed Authoring
8.1 General request and response handling
8.1.1 Use of XML
Some of the following new HTTP methods use XML as a request and
response format. All DAV compliant clients and resources MUST use
XML parsers that are compliant with XML [11] and XML Namespaces [10].
All XML used in either requests or responses MUST be, at minimum,
well formed and use namespaces correctly. If a server receives non-
wellformed 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.
8.1.2 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 recommends the use of the ETag header in responses to GET
and PUT requests. Correct use of ETags is even more important in a
distributed authoring environment, because ETags are necessary along
with locks to avoid the lost-update problem. A client might fail to
renew a lock, for example when the lock times out and the client is
accidentally offline or in the middle of a long upload. When a
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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 that has an unchanged body.
The ETag represents the state of the body or contents of the
resource. There is no similar way to tell if properties have
changed.
8.1.6 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 [18]). 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 ȼDAV:errorȫ 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.
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HTTP/1.1 403 Forbidden
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.
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. 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:
o Request particular property values, by naming the properties
desired within the 'prop' element (the ordering of properties in
here MAY be ignored by server)
o Request all dead property values, by using 'dead-props' element.
This can be combined with retrieving specific live properties
named as above. Servers advertising support for RFC2518bis MUST
support this feature.
o Request property values for those properties defined in this
specification plus dead properties, by using 'allprop' element
o Request a list of names of all the properties defined on the
resource, by using the 'propname' element.
A client may choose not to submit a request body. An empty PROPFIND
request body MUST be treated as if it were an 'allprop' request.
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Note that 'allprop' does not return values for all live properties.
WebDAV servers increasingly have expensively-calculated or lengthy
properties (see RFC3253 [18] and RFC3744 [19]) and do not return all
properties already. Instead, WebDAV clients can use propname
requests to discover what live properties exist, and request named
properties when retrieving values. A WebDAV server MAY omit certain
live properties from other specifications when responding to an
allprop request from an older client, and MAY return only custom
(dead) properties and those defined in this specification.
All servers MUST support returning a response of content type text/
xml or application/xml that contains a multistatus XML element that
describes the results of the attempts to retrieve the various
properties. The multistatus contains one response element for each
resource in the scope of the request (in no required order) or may be
empty if no resources match the request.
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
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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 arenȡt
legal in HTTP URL paths, these characters must be URI-escaped on the
wire. For example, it is illegal to use a space character or double-
quote in a URI [6]. URIs appearing in PROPFIND or PROPPATCH XML
bodies (or other XML marshalling defined in this specification) are
still subject to all URI rules, including forbidden characters.
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 MAY 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
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http://www.example.com/file
Box type A
J.J. Johnson
HTTP/1.1 200 OK
HTTP/1.1 403 Forbidden
The user does not have access to the
DingALing property.
There has been an access violation error.
In this example, PROPFIND is executed on a non-collection resource
http://www.example.com/file. The propfind XML element specifies the
name of four properties whose values are being requested. In this
case only two properties were returned, since the principal issuing
the request did not have sufficient access rights to see the third
and fourth properties.
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8.2.2 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 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/
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HTTP/1.1 200 OK
http://www.example.com/container/front.html
HTTP/1.1 200 OK
In this example, PROPFIND is invoked on the collection resource
http://www.example.com/container/, with a propfind XML element
containing the propname XML element, meaning the name of all
properties should be returned. Since no Depth header is present, it
assumes its default value of "infinity", meaning the name of the
properties on the collection and all its descendents should be
returned.
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,
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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.
403 Forbidden - A server MAY reject all PROPFIND requests on
collections with depth header of "Infinity", in which case it SHOULD
use this error with the element 'propfind-infinite-depth-forbidden'
inside the body.
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 (an exception to the normal rule that ordering is
irrelevant). Instructions MUST either all be executed or none
executed. Thus if any error occurs during processing all executed
instructions MUST be undone and a proper error result returned.
Instruction processing details can be found in the definition of the
set and remove instructions in sections 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
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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 (Forbidden): The client has attempted to set a read- only
property, such as getetag. If returning this error, the server
SHOULD use 'read-only-property' inside the response body.
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. This response SHOULD
contain the 'missing-lock-token' precondition element.
507 (Insufficient Storage) - The server did not have sufficient space
to record the property.
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
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>>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
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 /a/b/c/ does not exist, the request
must fail.
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When MKCOL is invoked without a request body, the newly created
collection SHOULD have no members.
A MKCOL request message may contain a message body. The 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.
8.4.1 MKCOL Status Codes
Responses from a MKCOL request MUST NOT be cached as MKCOL has non-
idempotent semantics.
201 (Created) - The collection was created.
403 (Forbidden) - This indicates at least one of two conditions: 1)
the server does not allow the creation of collections at the given
location in its namespace, or 2) the parent collection of the
Request-URI exists but cannot accept members.
405 (Method Not Allowed) - MKCOL can only be executed on an unmapped
URL.
409 (Conflict) - A collection cannot be made at the Request-URI until
one or more intermediate collections have been created. The server
MUST NOT create those intermediate collections automatically.
415 (Unsupported Media Type) - The server does not support the
request 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.
8.4.2 Example - MKCOL
This example creates a collection called /webdisc/xfiles/ on the
server www.example.com.
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>>Request
MKCOL /webdisc/xfiles/ HTTP/1.1
Host: www.example.com
>>Response
HTTP/1.1 201 Created
8.5 GET, HEAD for Collections
The semantics of GET are unchanged when applied to a collection,
since GET is defined as, "retrieve whatever information (in the form
of an entity) is identified by the Request-URI" [RFC2616]. GET when
applied to a collection may return the contents of an "index.html"
resource, a human-readable view of the contents of the collection, or
something else altogether. Hence it is possible that the result of a
GET on a collection will bear no correlation to the membership of the
collection.
Similarly, since the definition of HEAD is a GET without a response
message body, the semantics of HEAD are unmodified when applied to
collection resources.
8.6 POST for Collections
Since by definition the actual function performed by POST is
determined by the server and often depends on the particular
resource, the behavior of POST when applied to collections cannot be
meaningfully modified because it is largely undefined. Thus the
semantics of POST are unmodified when applied to a collection.
8.7 DELETE
8.7.1 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 MUST return 404 (Not Found).
8.7.2 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
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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.
The server MAY return a 4xx status response, rather than a Multi-
Status, if the entire DELETE request failed and it canȡt 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.
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8.7.3 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
8.8.1 PUT for Non-Collection Resources
A PUT performed on an existing resource replaces the GET response
entity of the resource. Properties defined on the resource may be
recomputed during PUT processing but are not otherwise affected. For
example, if a server recognizes the content type of the request body,
it may be able to automatically extract information that could be
profitably exposed as properties.
A PUT that would result in the creation of a resource without an
appropriately scoped parent collection MUST fail with a 409
(Conflict).
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8.8.2 PUT for Collections
As defined in RFC2616 [8], 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
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.
8.9.1 COPY for Non-collection Resources
When the source resource is not a collection the result of the COPY
method is the creation of a new resource at the destination whose
state and behavior match that of the source resource as closely as
possible. Since the environment at the destination may be different
than at the source due to factors outside the scope of control of the
server, such as the absence of resources required for correct
operation, it may not be possible to completely duplicate the
behavior of the resource at the destination. Subsequent alterations
to the destination resource will not modify the source resource.
Subsequent alterations to the source resource will not modify the
destination resource.
8.9.2 COPY for Properties
After a successful COPY invocation, all dead properties on the source
resource MUST be duplicated on the destination resource, along with
all properties as appropriate. Live properties described in this
document SHOULD be duplicated as identically behaving live properties
at the destination resource, but not necessarily with the same
values. 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.
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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.
8.9.3 COPY for Collections
The COPY method on a collection without a Depth header MUST act as if
a Depth header with value "infinity" was included. A client may
submit a Depth header on a COPY on a collection with a value of "0"
or "infinity". Servers MUST support the "0" and "infinity" Depth
header behaviors on WebDAV-compliant resources.
A COPY of depth infinity instructs that the collection resource
identified by the Request-URI is to be copied to the location
identified by the URI in the Destination header, and all its internal
member resources are to be copied to a location relative to it,
recursively through all levels of the collection hierarchy.
A COPY of "Depth: 0" only instructs that the collection and its
properties but not resources identified by its internal member URLs,
are to be copied.
Any headers included with a COPY MUST be applied in processing every
resource to be copied with the exception of the Destination header.
The Destination header only specifies the destination URI for the
Request-URI. When applied to members of the collection identified by
the Request-URI the value of Destination is to be modified to reflect
the current location in the hierarchy. So, if the Request-URI is /a/
with Host header value http://example.com/ and the Destination is
http://example.com/b/ then when http://example.com/a/c/d is processed
it must use a Destination of http://example.com/b/c/d.
When the COPY method has completed processing it MUST have created a
consistent namespace at the destination (see Section 8.7.2for the
definition of namespace consistency). However, if an error occurs
while copying an internal collection, the server MUST NOT copy any
resources identified by members of this collection (i.e., the server
must skip this subtree), as this would create an inconsistent
namespace. After detecting an error, the COPY operation SHOULD try
to finish as much of the original copy operation as possible (i.e.,
the server should still attempt to copy other subtrees and their
members, that are not descendents of an error-causing collection).
So, for example, if an infinite depth copy operation is performed on
collection /a/, which contains collections /a/b/ and /a/c/, and an
error occurs copying /a/b/, an attempt should still be made to copy /
a/c/. Similarly, after encountering an error copying a non-
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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.
8.9.4 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.
8.9.5 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.
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.
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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, or resource within the
destination collection, was locked. This response SHOULD contain the
'missing-lock-token' precondition element.
502 (Bad Gateway) - This may occur when the destination is on another
server, repository or namespace. Either the source namespace does
not support copying to the destination namespace, or the destination
namespace refuses to accept the resource. The client may wish to try
GET/PUT and PROPFIND/PROPPATCH instead.
507 (Insufficient Storage) - The destination resource does not have
sufficient space to record the state of the resource after the
execution of this method.
8.9.6 COPY Examples
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.
COPY with Overwrite
>>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
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.
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COPY with No Overwrite
>>Request
COPY /~fielding/index.html HTTP/1.1
Host: www.ics.uci.edu
Destination: http://www.ics.uci.edu/users/f/fielding/index.html
Overwrite: F
>>Response
HTTP/1.1 412 Precondition Failed
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.
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8.10 MOVE
The MOVE operation on a non-collection resource is the logical
equivalent of a copy (COPY), followed by consistency maintenance
processing, followed by a delete of the source, where all three
actions are performed atomically. The consistency maintenance step
allows the server to perform updates caused by the move, such as
updating all URLs other than the Request-URI which identify the
source resource, to point to the new destination resource.
Consequently, the Destination header MUST be present on all MOVE
methods and MUST follow all COPY requirements for the COPY part of
the MOVE method. All WebDAV compliant resources MUST support the
MOVE method. However, support for the MOVE method does not guarantee
the ability to move a resource to a particular destination.
For example, separate programs may actually control different sets of
resources on the same server. Therefore, it may not be possible to
move a resource within a namespace that appears to belong to the same
server.
If a resource exists at the destination, the destination resource
will be deleted as a side-effect of the MOVE operation, subject to
the restrictions of the Overwrite header.
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 reports the live property as "Not
Found" if that's the most appropriate behavior for that live property
at the destination, as long as the live property is still supported
with the same semantics.
MOVE is frequently used by clients to rename a file without changing
its parent collection, 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 after a MOVE.
Dead properties must be moved along with the resource.
8.10.2 MOVE for Collections
A MOVE with "Depth: infinity" instructs that the collection
identified by the Request-URI be moved to the address specified in
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the Destination header, and all resources identified by its internal
member URLs are to be moved to locations relative to it, recursively
through all levels of the collection hierarchy.
The MOVE method on a collection MUST act as if a "Depth: infinity"
header was used on it. A client MUST NOT submit a Depth header on a
MOVE on a collection with any value but "infinity".
Any headers included with MOVE MUST be applied in processing every
resource to be moved with the exception of the Destination header.
The behavior of the Destination header is the same as given for COPY
on collections.
When the MOVE method has completed processing it MUST have created a
consistent 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
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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.
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) - The source and destination resources are the same.
409 (Conflict) - A resource cannot be created at the destination
until one or more intermediate collections have been created. The
server MUST NOT create those intermediate collections automatically.
Or, the server was unable to preserve the behavior of the live
properties and still move the resource to the destination (see
'live-properties-not-preserved' postcondition).
412 (Precondition Failed) Ș 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, or some
resource within the source or destination collection, was locked.
This response SHOULD contain the 'missing-lock-token' precondition
element.
502 (Bad Gateway) - This may occur when the destination is on another
server and the destination server refuses to accept the resource.
This could also occur when the destination is on another sub-section
of the same server namespace.
8.10.5 Examples
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
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resource, the response code is 201 (Created).
MOVE of a Non-Collection
>>Request
MOVE /~fielding/index.html HTTP/1.1
Host: www.ics.uci.edu
Destination: http://www.ics.uci.edu/users/f/fielding/index.html
>>Response
HTTP/1.1 201 Created
Location: http://www.ics.uci.edu/users/f/fielding/index.html
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/
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C2's members were moved. However no errors were listed for those
members due to the error minimization rules. User agent
authentication has previously occurred via a mechanism outside the
scope of the HTTP protocol, in an underlying transport layer.
8.11 LOCK Method
The following sections describe the LOCK method, which is used to
take out a lock of any access type and to refresh an existing lock.
These sections on the LOCK method describe only those semantics that
are specific to the LOCK method and are independent of the access
type of the lock being requested.
Any resource which supports the LOCK method MUST, at minimum, support
the XML request and response formats defined herein.
A LOCK method invocation to an unlocked resource creates a lock on
the resource identified by the Request-URI, which becomes the root of
the lock. Lock method requests to create a new lock MUST have a XML
request body which contains an owner XML element and other
information for this lock request. The server MUST preserve the
information provided by the client in the owner field when the lock
information is requested. The LOCK request MAY have a Timeout
header.
Clients MUST assume that locks may arbitrarily disappear at any time,
regardless of the value given in the Timeout header. The Timeout
header only indicates the behavior of the server if extraordinary
circumstances do not occur. For example, a sufficiently privileged
user may remove a lock at any time or the system may crash in such a
way that it loses the record of the lock's existence. The response
MUST contain the value of the lockdiscovery property in a prop XML
element.
A success response to a LOCK request MUST include the Lock-Token
response header with the token associated with the new lock, and MUST
contain a body with the value of the 'lockdiscovery' property. 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.
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:
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o DELETE a collection's direct internal member
o MOVE a member out of the collection
o MOVE a member into the collection, unless it overwrites a pre-
existing member
o MOVE to rename it within a collection,
o COPY a member into a collection, unless it overwrites a pre-
existing member
o PUT or MKCOL request which would create a new member.
The collection's lock token is required in addition to the lock token
on the internal member itself, if it exists.
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.
8.11.1 Refreshing Locks
A lock is refreshed by sending a LOCK request without a body to a
resource within the scope 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 MUST 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. A server MUST
ignore the Depth header on a LOCK refresh, and the client SHOULD NOT
send the Depth header on a LOCK refresh as the server will not
convert the lock or confirm the depth.
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.
8.11.2 Depth and Locking
The Depth header may be used with the LOCK method. Values other than
0 or infinity MUST NOT be used with the Depth header on a LOCK
method. All resources that support the LOCK method MUST support the
Depth header.
A Depth header of value 0 means to just lock the resource specified
by the Request-URI.
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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 207 (Multi-Status) status code MUST be returned with
a response entity body containing a multistatus XML element
describing which resource(s) prevented the lock from being 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.
8.11.3 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.
8.11.4 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
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requested, the table entry is "false", indicating the lock must not
be granted.
8.11.5 LOCK responses
200 (OK) - The lock request succeeded and the value of the
lockdiscovery property is included in the body.
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) - 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 already. For consistency's
sake, this response SHOULD contain the 'missing-lock-token'
precondition element.
400 (Bad Request), with 'request-uri-must-match-lock-token'
precondition - The LOCK request was made with a Lock-Token header,
indicating that the client wishes to refresh the given lock.
However, the Request-URI did not fall within the scope of the lock
identified by the token. The lock may have a scope that does not
include the Request-URI, or the lock could have disappeared, or the
token may be invalid.
8.11.6 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
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>>Response
HTTP/1.1 200 OK
Lock-Token:
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 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.
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8.11.7 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="..."
>>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
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the request. In this example, the nonce, response, and opaque fields
have not been calculated in the Authorization request header.
8.11.8 Example - Multi-Resource Lock Request
>>Request
LOCK /webdav/ HTTP/1.1
Host: example.com
Timeout: Infinite, Second-4100000000
Depth: infinity
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/1.1 207 Multi-Status
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
http://example.com/webdav/secret
HTTP/1.1 403 Forbidden
http://example.com/webdav/
HTTP/1.1 424 Failed Dependency
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This example shows a request for an exclusive write lock on a
collection and all its children. In this request, the client has
specified that it desires an infinite length lock, if available,
otherwise a timeout of 4.1 billion seconds, if available. The
request entity body contains the contact information for the
principal taking out the lock, in this case a web page URL.
The error is a 403 (Forbidden) response on the resource http://
example.com/webdav/secret. Because this resource could not be
locked, none of the resources were locked. Note also that the
lockdiscovery property for the Request-URI has been included as
required. In this example the lockdiscovery property is empty which
means that there are no outstanding locks on the resource.
In this example, the nonce, response, and opaque fields have not been
calculated in the Authorization request header.
8.12 UNLOCK Method
The UNLOCK method removes the lock identified by the lock token in
the Lock-Token request header. The Request-URI MUST identify a
resource within the scope of the lock. The If header is not needed
to provide the lock token although servers SHOULD still evaluate the
If header and treat it as a conditional header.
For a successful response to this method, the server MUST remove the
lock from the resource identified by the Request-URI and from all
other resources included in the lock.
If all resources which have been locked under the submitted lock
token can not be unlocked then the UNLOCK request MUST fail.
A successful response to an UNLOCK method does not mean that the
resource is necessarily unlocked. It means that the specific lock
corresponding to the specified token no longer exists.
Any DAV compliant resource which supports the LOCK method MUST
support the UNLOCK method.
8.12.1 Status Codes
204 (No Content) - Normal success response
400 (Bad Request) - No lock token was provided (see
'missing-lock-token' precondition), or request was made to a
Request-URI that was not within the scope of the lock (see
'requesturi-must-match-lock-token' precondition).
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403 (Forbidden) - The currently authenticated principal does not have
permission to remove the lock (the server SHOULD use the
'need-privileges' precondition element).
412 (Precondition Failed) - The resource was not locked.
8.12.2 Example
>>Request
UNLOCK /workspace/webdav/info.doc HTTP/1.1
Host: example.com
Lock-Token:
Authorization: Digest username="ejw",
realm="ejw@example.com", nonce="...",
uri="/workspace/webdav/proposal.doc",
response="...", opaque="..."
>>Response
HTTP/1.1 204 No Content
In this example, the lock identified by the lock token
"opaquelocktoken:a515cfa4-5da4-22e1-f5b5-00a0451e6bf7" is
successfully removed from the resource http://example.com/workspace/
webdav/info.doc. If this lock included more than just one resource,
the lock is removed from all resources included in the lock. The 204
(No Content) status code is used instead of 200 (OK) because there is
no response entity body.
In this example, the nonce, response, and opaque fields have not been
calculated in the Authorization request header.
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9. HTTP Headers for Distributed Authoring
All DAV headers follow the same basic formatting rules as HTTP
headers. This includes rules like line continuation and how to
combine (or separate) multiple instances of the same header using
commas.
9.1 DAV Header
DAV = "DAV" ":" #( compliance-code )
compliance-code = ( "1" | "2" | "bis" | extend )
extend = Coded-URL | token
This general-header appearing in the response indicates that the
resource supports the DAV schema and protocol as specified. All DAV
compliant resources MUST return the DAV header on all OPTIONS
responses.
The value is a comma-separated list of all compliance class
identifiers that the resource supports. Class identifiers may be
Coded-URLs or tokens (as defined by [RFC2616]). Identifiers can
appear in any order. Identifiers that are standardized through the
IETF RFC process are tokens, but other identifiers SHOULD be Coded-
URLs to encourage uniqueness.
A resource must show class 1 compliance if it shows class 2 or "bis"
compliance. In general, support for one compliance class does not
entail support for any other. Please refer to section 16 for more
details on compliance classes defined in this specification.
This header must also appear on responses to OPTIONS requests to the
special '*' Request-URI as defined in HTTP/1.1. In this case it
means that the repository supports the named features in at least
some internal namespaces.
As an optional request header, this header allows the client to
advertise compliance with named features. Clients need not advertise
1, 2 or bis because a WebDAV server currently doesn't need that
information to decide how to respond to requests defined in this
specification or in HTTP/1.1. However, future extensions may define
client compliance codes. When used as a request header, the DAV
header MAY affect caching so this header SHOULD NOT be used on all
GET requests.
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9.2 Depth Header
Depth = "Depth" ":" ("0" | "1" | "infinity")
The Depth request header is used with methods executed on resources
which could potentially have internal members to indicate whether the
method is to be applied only to the resource ("Depth: 0"), to the
resource and its immediate children, ("Depth: 1"), or the resource
and all its progeny ("Depth: infinity").
The Depth header is only supported if a method's definition
explicitly provides for such support.
The following rules are the default behavior for any method that
supports the Depth header. A method may override these defaults by
defining different behavior in its definition.
Methods which support the Depth header may choose not to support all
of the header's values and may define, on a case by case basis, the
behavior of the method if a Depth header is not present. For
example, the MOVE method only supports "Depth: infinity" and if a
Depth header is not present will act as if a "Depth: infinity" header
had been applied.
Clients MUST NOT rely upon methods executing on members of their
hierarchies in any particular order or on the execution being atomic
unless the particular method explicitly provides such guarantees.
Upon execution, a method with a Depth header will perform as much of
its assigned task as possible and then return a response specifying
what it was able to accomplish and what it failed to do.
So, for example, an attempt to COPY a hierarchy may result in some of
the members being copied and some not.
Any headers on a method that has a defined interaction with the Depth
header MUST be applied to all resources in the scope of the method
except where alternative behavior is explicitly defined. For
example, an If-Match header will have its value applied against every
resource in the method's scope and will cause the method to fail if
the header fails to match.
If a resource, source or destination, within the scope of the method
with a Depth header is locked in such a way as to prevent the
successful execution of the method, then the lock token for that
resource MUST be submitted with the request in the If request header.
The Depth header only specifies the behavior of the method with
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regards to internal children. If a resource does not have internal
children then the Depth header MUST be ignored.
Please note, however, that it is always an error to submit a value
for the Depth header that is not allowed by the method's definition.
Thus submitting a "Depth: 1" on a COPY, even if the resource does not
have internal members, will result in a 400 (Bad Request). The
method should fail not because the resource doesn't have internal
members, but because of the illegal value in the header.
9.3 Destination Header
Destination = "Destination" ":" ( absoluteURI )
The Destination request header specifies the URI which identifies a
destination resource for methods such as COPY and MOVE, which take
two URIs as parameters. Note that the absoluteURI production is
defined in RFC2396 [6].
If the Destination value is an absolute URI, it may name a different
server (or different port or scheme). If the source server cannot
attempt a copy to the remote server, it MUST fail the request with a
502 (Bad Gateway) response. Servers MAY attempt to copy the resource
to the remote server using PUT/PROPPATCH or another mechanism.
9.4 Force-Authentication Header
Force-Authentication = "Force-Authentication" ":" Method
The Force-Authentication request header is used with the OPTIONS
method to specify that the client wants to be challenged for
authentication credentials to the resource identified by the
Request-URI. If present on a request to a WebDAV-compliant resource,
the server MUST respond with either 401 (Unauthorized) or 501 (Not
Implemented) status code. The Method value is used for the client to
indicate what method it intends to use first on the resource
identified in the Request-URI.
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9.5 If Header
If = "If" ":" ( 1*No-tag-list | 1*Tagged-list)
No-tag-list = List
Tagged-list = Resource 1*List
Resource = Coded-URL
List = #( "(" List | Clause ")" )
Clause = ["Not"] State-token | State-token
State-token = Coded-URL | "[" entity-tag "]"
Coded-URL = "<" absoluteURI ">"
The If request header is intended to have similar functionality to
the If- Match header defined in section 14.24 of RFC2616 [8].
However the If header is intended for use with any URI which
represents state information, referred to as a state token, about a
resource as well as ETags. A typical example of a state token is a
lock token, and lock tokens are the only state tokens defined in this
specification. The state token is a special token that
must never match an actual valid lock token. The purpose of this is
described in section 9.5.5.
The If header's purpose is to describe a series of state lists. If
the state of the resource to which the header is applied does not
match any of the specified state lists then the request MUST fail
with a 412 (Precondition Failed). If one of the described state
lists matches the state of the resource then the request may succeed.
The server must parse the If header when it appears on any request,
evaluate all the clauses, and if the conditional evaluates to false,
fail the request.
Note that the absoluteURI production is defined in RFC2396 [6].
RFC2518 originally defined the If header without comma separators.
This oversight meant that the If header couldn't be divided up among
multiple lines according to the HTTP header manipulation rules.
Servers supporting "bis" MUST be able to accept commas in If header
values. If the header has commas between tokens or clauses, the
header can be evaluated simply by removing the commas and proceeding
with the evaluation rules.
9.5.1 No-tag-list Production
The No-tag-list production describes a series of state tokens and
ETags. If multiple No-tag-list productions are used then one only
needs to match the state of the resource for the method to be allowed
to continue. All untagged tokens apply to the resource identified in
the Request-URI.
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Example - no-tag-list production
If: ( ["I am an ETag"]), (["I
am another ETag"])
The previous header would require that the resource identified in the
Request-URI be locked with the specified lock token and in the state
identified by the "I am an ETag" ETag or in the state identified by
the second ETag "I am another ETag". To put the matter more plainly
one can think of the previous If header as being in the form (or (and
["I am an ETag"]) (and ["I am
another ETag"])).
9.5.2 Tagged-list Production
The tagged-list production scopes a list production. That is, it
specifies that the lists following the resource specification only
apply to the specified resource. The scope of the resource
production begins with the list production immediately following the
resource production and ends with the next resource production, if
any. All clauses must be evaluated. If the state of the resource
named in the tag does not match any of the associated state lists
then the request MUST fail with a 412 (Precondition Failed).
The same URI MUST NOT appear more than once in a resource production
in an If header.
Example - Tagged List If header
COPY /resource1 HTTP/1.1
Host: www.example.com
Destination: http://www.example.com/resource2
If: ( [W/"A weak ETag"]), (["strong ETag"]),
(["another strong ETag"])
In this example http://www.example.com/resource1 is being copied to
http://www.example.com/resource2. When the method is first applied
to http://www.example.com/resource1, resource1 must be in the state
specified by "( [W/"A weak ETag"])
(["strong ETag"])", that is, it either must be locked with a lock
token of "locktoken:a-write-lock-token" and have a weak entity tag W/
"A weak ETag" or it must have a strong entity tag "strong ETag".
That is the only success condition since the resource http://
www.bar.bar/random never has the method applied to it (the only other
resource listed in the If header) and http://www.example.com/
resource2 is not listed in the If header.
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9.5.3 Not Production
Every state token or ETag is either current, and hence describes the
state of a resource, or is not current, and does not describe the
state of a resource. The boolean operation of matching a state token
or ETag to the current state of a resource thus resolves to a true or
false value. The "Not" production is used to reverse that value.
The scope of the not production is the state-token or entity-tag
immediately following it.
If: (Not )
When submitted with a request, this If header requires that all
operand resources must not be locked with locktoken:write1 and must
be locked with locktoken:write2.
The Not production is particularly useful with the ""
state token. The clause "Not " must evaluate to true.
Thus, any "OR" statement containing the clause "Not "
must also evaluate to true.
9.5.4 Matching Function
When performing If header processing, the definition of a matching
state token or entity tag is as follows.
Identifying a resource: The resource is identified by the URI along
with the token, in tagged list production, or by the Request-URI in
untagged list production.
Matching entity tag: Where the entity tag matches an entity tag
associated with the identified resource.
Matching state token: Where there is an exact match between the state
token in the If header and any state token on the identified
resource. A lock state token is considered to match if the resource
is anywhere in the scope of the lock.
Example - Matching lock tokens with collection locks
DELETE /specs/rfc2518.txt HTTP/1.1
Host: www.example.com
If: ()
For this example, the lock token must be compared to the identified
resource, which is the 'specs' collection identified by the URL in
the tagged list production. If the 'specs' collection is not locked
or has a lock with a different token, the request MUST fail. If the
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'specs' collection is locked (depth infinity) with that lock token,
then this request could succeed, both because the If header evaluates
to true, and because the lock token for the lock affecting the
affected resource has been provided. Alternatively, a request where
the 'rfc2518.txt' URL is associated with the lock token in the If
header could also succeed.
9.5.5 If Header and Non-DAV Aware Proxies
Non-DAV aware proxies will not honor the If header, since they will
not understand the If header, and HTTP requires non-understood
headers to be ignored. When communicating with HTTP/1.1 proxies, the
"Cache-Control: no-cache" request header MUST be used so as to
prevent the proxy from improperly trying to service the request from
its cache. When dealing with HTTP/1.0 proxies the "Pragma: no-
cache" request header MUST be used for the same reason.
9.6 Lock-Token Header
Lock-Token = "Lock-Token" ":" Coded-URL
The Lock-Token request header is used with the UNLOCK method to
identify the lock to be removed. The lock token in the Lock-Token
request header MUST identify a lock that contains the resource
identified by Request-URI as a member.
The Lock-Token response header is used with the LOCK method to
indicate the lock token created as a result of a successful LOCK
request to create a new lock.
9.7 Overwrite Header
Overwrite = "Overwrite" ":" ("T" | "F")
The Overwrite request header specifies whether the server should
overwrite the state of a non-null destination resource during a COPY
or MOVE. A value of "F" states that the server must not perform the
COPY or MOVE operation if the state of the destination resource is
non-null. If the overwrite header is not included in a COPY or MOVE
request then the resource MUST treat the request as if it has an
overwrite header of value "T". While the Overwrite header appears to
duplicate the functionality of the If-Match: * header of HTTP/1.1,
If-Match applies only to the Request-URI, and not to the Destination
of a COPY or MOVE.
If a COPY or MOVE is not performed due to the value of the Overwrite
header, the method MUST fail with a 412 (Precondition Failed) status
code.
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All DAV compliant resources MUST support the Overwrite header.
9.8 Timeout Request Header
TimeOut = "Timeout" ":" 1#TimeType
TimeType = ("Second-" DAVTimeOutVal | "Infinite")
DAVTimeOutVal = 1*digit
Clients may include Timeout request headers in their LOCK requests.
However, the server is not required to honor or even consider these
requests. Clients MUST NOT submit a Timeout request header with any
method other than a LOCK method.
Timeout response values MUST use a Second value or Infinite.
The "Second" TimeType specifies the number of seconds that will
elapse between granting of the lock at the server, and the automatic
removal of the lock. The timeout value for TimeType "Second" MUST
NOT be greater than 2^32-1.
The timeout counter MUST be restarted if a refresh LOCK request is
successful. The timeout counter SHOULD NOT be restarted at any other
time.
If the timeout expires then the lock may be lost. Specifically, if
the server wishes to harvest the lock upon time-out, the server
SHOULD act as if an UNLOCK method was executed by the server on the
resource using the lock token of the timed-out lock, performed with
its override authority. Thus logs should be updated with the
disposition of the lock, notifications should be sent, etc., just as
they would be for an UNLOCK request.
Servers are advised to pay close attention to the values submitted by
clients, as they will be indicative of the type of activity the
client intends to perform. For example, an applet running in a
browser may need to lock a resource, but because of the instability
of the environment within which the applet is running, the applet may
be turned off without warning. As a result, the applet is likely to
ask for a relatively small timeout value so that if the applet dies,
the lock can be quickly harvested. However, a document management
system is likely to ask for an extremely long timeout because its
user may be planning on going off-line.
A client MUST NOT assume that just because the time-out has expired
the lock has been lost. Likewise, a client MUST NOT assume that just
because the time-out has not expired, the lock still exists (and for
this reason, clients are strongly advised to use ETags as well).
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10. Status Code Extensions to HTTP/1.1
The following status codes are added to those defined in HTTP/1.1
RFC2616 [8].
10.1 102 Processing
The 102 (Processing) status code is an interim response used to
inform the client that the server has accepted the complete request,
but has not yet completed it. This status code SHOULD only be sent
when the server has a reasonable expectation that the request will
take significant time to complete. As guidance, if a method is
taking longer than 20 seconds (a reasonable, but arbitrary value) to
process the server SHOULD return a 102 (Processing) response. The
server MUST send a final response after the request has been
completed.
Methods can potentially take a long period of time to process,
especially methods that support the Depth header. In such cases the
client may time-out the connection while waiting for a response. To
prevent this the server may return a 102 (Processing) status code to
indicate to the client that the server is still processing the
method.
10.2 207 Multi-Status
The 207 (Multi-Status) status code provides status for multiple
independent operations (see Section 12 for more information).
10.3 422 Unprocessable Entity
The 422 (Unprocessable Entity) status code means the server
understands the content type of the request entity (hence a
415(Unsupported Media Type) status code is inappropriate), and the
syntax of the request entity is correct (thus a 400 (Bad Request)
status code is inappropriate) but was unable to process the contained
instructions. For example, this error condition may occur if an XML
request body contains well-formed (i.e., syntactically correct), but
semantically erroneous XML instructions.
10.4 423 Locked
The 423 (Locked) status code means the source or destination resource
of a method is locked. This response SHOULD contain the
'missing-lock-token' element and corresponding href in the error
body.
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10.5 424 Failed Dependency
The 424 (Failed Dependency) status code means that the method could
not be performed on the resource because the requested action
depended on another action and that action failed. For example, if a
command in a PROPPATCH method fails then, at minimum, the rest of the
commands will also fail with 424 (Failed Dependency).
10.6 507 Insufficient Storage
The 507 (Insufficient Storage) status code means the method could not
be performed on the resource because the server is unable to store
the representation needed to successfully complete the request. This
condition is considered to be temporary. If the request which
received this status code was the result of a user action, the
request MUST NOT be repeated until it is requested by a separate user
action.
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11. Use of HTTP Status Codes
11.1 301 Moved Permanently
Any WebDAV request may be redirected using this status code.
11.2 302 Found
Any WebDAV request may be redirected using this status code.
11.3 400 Bad Request
This code may be used if:
o the Host header is missing in any request
o The protocol version is HTTP/1.0
o Any header is improperly formatted
o The request method line is improperly formatted
11.4 403 Forbidden
To be used if the server does not ever accept this method on this
kind of resource. For example, if a PUT is not accepted on a
collection.
11.5 409 Conflict
The 409 Conflict is most typically returned when a method that
attempts to create a new resource must fail, because one of the
collections that resource depends on does not exist. However, other
types of conflicts are defined in specifications extending RFC2518.
Therefore, this can be returned in response to all methods.
11.6 414 Request-URI Too Long
This status code is used in HTTP 1.1 only for Request-URIs, because
full URIs arenȡt used in other headers. WebDAV specifies full URLs
in other headers, therefore this error may be used if the URI is too
long in other locations as well. This status code may be used in
response to any method in this specification.
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12. Multi-Status Response
The default 207 (Multi-Status) response body is a text/xml or
application/xml HTTP entity that contains a single XML element called
multistatus, which contains a set of XML elements called response
which contain 200, 300, 400, and 500 series status codes generated
during the method invocation. 100 series status codes SHOULD NOT be
recorded in a response XML element. The 207 status code itself MUST
NOT be considered a success response, it is only completely
successful if all response elements inside contain success status
codes.
The body of a 207 Multi-Status response MUST contain a URL associated
with each specific status code, so that the client can tell whether
the error occurred with the source resource, destination resource or
some other resource in the scope of the request. URLs for
collections appearing in the results SHOULD end in a '/' character.
When a Multi-Status body is returned in response to a PROPFIND or
another request with a single scope, all URLs appearing in the body
must be equal to or inside the request-URI, thus the URLs MAY be
absolute or MAY be relative.
o If the URLs are absolute, then the server MUST ensure that the
URLs have the same prefix (scheme, host, port, and path) as the
URL of the requested resource (which may be the same as the
Request-URI or may be the corrected in the response Location
header).
o If the URLs are relative, they MUST be resolved against the
Location header, if present, or as second choice against the
Request-URI.
When a Multi-Status body is returned in response to MOVE or COPY,
relative URIs resolution is ambiguous (the request had both a source
and a destination URL). Thus, URLs appearing in the responses to
MOVE or COPY SHOULD be absolute and fully-qualified URLs.
12.1 Responses requiring Location in Multi-Status
The 300-303, 305 and 307 responses defined in HTTP 1.1 normally take
a Location header to indicate where the client should make the
request. The Multi-Status response syntax as defined in RFC2518 did
not allow for the Location header information to be included in an
unambiguous way, so servers MAY choose not to use these status codes
in Multi-Status responses. If a clients receives this status code in
Multi-Status, the client MAY reissue the request to the individual
resource, so that the server can issue a response with a Location
header for each resource.
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Additionally, this specification defines a new element that servers
MAY use in the response element to provide a location value in
Multi-Status (see Section 13.29).
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13. XML Element Definitions
In this section, the final line of each section gives the element
type declaration using the format defined in XML [11]. The "Value"
field, where present, specifies further restrictions on the allowable
contents of the XML element using BNF (i.e., to further restrict the
values of a PCDATA element). The "Extensibility" field discusses how
the element may be extended in the future (or in existing extensions
to WebDAV.
All of the elements defined here may be extended by the addition of
attributes and child elements not defined in this specification.
13.1 activelock XML Element
Name: activelock
Namespace: DAV:
Purpose: Describes a lock on a resource.
Extensibility: MAY be extended with additional child elements or
attributes which SHOULD be ignored if not recognized.
13.2 depth XML Element
Name: depth
Namespace: DAV:
Purpose: The value of the Depth header.
Value: "0" | "1" | "infinity"
Extensibility: MAY be extended with attributes which SHOULD be
ignored.
13.3 locktoken XML Element
Name: locktoken
Namespace: DAV:
Purpose: The lock token associated with a lock.
Description: The href contains a single lock token URI which refers
to the lock (i.e., the OpaqueLockToken-URI production in section
6.4).
Extensibility: MAY be extended with additional child elements or
attributes which SHOULD be ignored if not recognized.
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13.4 lockroot XML Element
Name: lockroot
Namespace: DAV:
Purpose: Contains the root URL of the lock, which is the URL through
which the resource was addressed in the LOCK request.
Description: The href contains a URL with the address of the root of
the lock. The server SHOULD include this in all lockdiscovery
property values and the response to LOCK requests.
Extensibility: MAY be extended with additional child elements or
attributes which SHOULD be ignored if not recognized.
13.5 timeout XML Element
Name: timeout
Namespace: DAV:
Purpose: The number of seconds remaining before a lock expires.
Value: TimeType (defined in Section 9.8).
Extensibility: MAY be extended with attributes which SHOULD be
ignored.
13.6 collection XML Element
Name: collection
Namespace: DAV:
Purpose: Identifies the associated resource as a collection. The
resourcetype property of a collection resource MUST contain this
element. It is normally empty but extensions may add
sub-elements.
Extensibility: MAY be extended with child elements or attributes
which SHOULD be ignored if not recognized.
13.7 href XML Element
Name: href
Namespace: DAV:
Purpose: Identifies the content of the element as a URI. In many
situations, this URI MUST be a HTTP URI, and furthermore, it MUST
identify a WebDAV resource. There is one exception to this
general rule in the lockdiscovery property, where the lock token
(which is a URI but may not be a HTTP URI) is inside the href
element. Other specifications SHOULD be explicit if the href
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element is to contain non-HTTP URIs.
Value: URI (See section 3.2.1 of RFC2616 [8])
Extensibility: MAY be extended with attributes which SHOULD be
ignored.
13.8 lockentry XML Element
Name: lockentry
Namespace: DAV:
Purpose: Defines the types of locks that can be used with the
resource.
Extensibility: MAY be extended with additional child elements or
attributes which SHOULD be ignored if not recognized.
13.9 lockinfo XML Element
Name: lockinfo
Namespace: DAV:
Purpose: The lockinfo XML element is used with a LOCK method to
specify the type of lock the client wishes to have created.
Extensibility: MAY be extended with additional child elements or
attributes which SHOULD be ignored if not recognized.
13.10 lockscope XML Element
Name: lockscope
Namespace: DAV:
Purpose: Specifies whether a lock is an exclusive lock, or a shared
lock.
Extensibility: SHOULD NOT be extended with child elements. MAY be
extended with attributes which SHOULD be ignored.
13.11 exclusive XML Element
Name: exclusive
Namespace: DAV:
Purpose: Specifies an exclusive lock
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Extensibility: Normally empty, but MAY be extended with additional
child elements or attributes which SHOULD be ignored if not
recognized.
13.12 shared XML Element
Name: shared
Namespace: DAV:
Purpose: Specifies a shared lock
Extensibility: Normally empty, but MAY be extended with additional
child elements or attributes which SHOULD be ignored if not
recognized.
13.13 locktype XML Element
Name: locktype
Namespace: DAV:
Purpose: Specifies the access type of a lock. At present, this
specification only defines one lock type, the write lock.
Extensibility: MAY be extended with additional child elements or
attributes which SHOULD be ignored if not recognized.
13.14 write XML Element
Name: write
Namespace: DAV:
Purpose: Specifies a write lock.
Extensibility: Normally empty, but MAY be extended with additional
child elements or attributes which SHOULD be ignored if not
recognized.
13.15 multistatus XML Element
Name: multistatus
Namespace: DAV:
Purpose: Contains multiple response messages.
Description The responsedescription at the top level is used to
provide a general message describing the overarching nature of the
response. If this value is available an application may use it
instead of presenting the individual response descriptions
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contained within the responses.
Extensibility: MAY be extended with additional child elements or
attributes which SHOULD be ignored if not recognized.
13.16 response XML Element
Name: locktype
Namespace: DAV:
Purpose: Holds a single response describing the effect of a method
on resource and/or its properties.
Description: A particular href MUST NOT appear more than once as the
child of a response XML element under a multistatus XML element.
This requirement is necessary in order to keep processing costs
for a response to linear time. Essentially, this prevents having
to search in order to group together all the responses by href.
There are, however, no requirements regarding ordering based on
href values.
Extensibility: MAY be extended with additional child elements or
attributes which SHOULD be ignored if not recognized.
13.17 propstat XML Element
Name: propstat
Namespace: DAV:
Purpose: Groups together a prop and status element that is
associated with a particular href element.
Description: The propstat XML element MUST contain one prop XML
element and one status XML element. The contents of the prop XML
element MUST only list the names of properties to which the result
in the status element applies.
Extensibility: MAY be extended with additional child elements or
attributes which SHOULD be ignored if not recognized.
13.18 status XML Element
Name: status
Namespace: DAV:
Purpose: Holds a single HTTP status-line
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Value: status-line (status-line defined in RFC2616 [8]
Extensibility: MAY be extended with attributes which SHOULD be
ignored.
13.19 responsedescription XML Element
Name: responsedescription
Namespace: DAV:
Purpose: Contains a message that can be displayed to the user
explaining the nature of the response.
Description: This XML element provides information suitable to be
presented to a user.
Extensibility: MAY be extended with attributes which SHOULD be
ignored.
13.20 owner XML Element
Name: owner
Namespace: DAV:
Purpose: Provides information about the principal taking out a lock.
Description The owner XML element provides information sufficient for
either directly contacting a principal (such as a telephone number
or Email URI), or for discovering the principal (such as the URL
of a homepage) who owns a lock. This information is provided by
the client, and may only be altered by the server if the owner
value provided by the client is empty.
Extensibility MAY be extended with child elements, mixed content,
text content or attributes. Structured content, for example one
or more child elements containing URLs, is RECOMMENDED.
13.23 remove XML element
Name: remove
Namespace: DAV:
Purpose: Lists the DAV properties to be removed from a resource.
Description: Remove instructs that the properties specified in prop
should be removed. Specifying the removal of a property that does
not exist is not an error. All the XML elements in a prop XML
element inside of a remove XML element MUST be empty, as only the
names of properties to be removed are required.
Extensibility: MAY be extended with additional child elements or
attributes which SHOULD be ignored if not recognized.
13.24 set XML element
Name: set
Namespace: DAV:
Purpose: Lists the DAV property values to be set for a resource.
Description: The set XML element MUST contain only a prop XML
element. The elements contained by the prop XML element inside
the set XML element MUST specify the name and value of properties
that are set on the resource identified by Request-URI. If a
property already exists then its value is replaced. Language
tagging information appearing in the scope of the prop element (in
the "xml:lang" attribute, if present) MUST be persistently stored
along with the property, and MUST be subsequently retrievable
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using PROPFIND.
Extensibility: MAY be extended with additional child elements or
attributes which SHOULD be ignored if not recognized.
13.25 propfind XML Element
Name: propfind
Namespace: DAV:
Purpose: Specifies the properties to be returned from a PROPFIND
method. Four special elements are specified for use with
propfind: prop, dead-props, allprop and propname. If prop is used
inside propfind it MUST NOT contain property values.
Extensibility: MAY be extended with additional child elements or
attributes which SHOULD be ignored if not recognized, as long as
it still contains one of the required elements.
13.26 allprop XML Element
Name: allprop
Namespace: DAV:
Purpose: The allprop XML element specifies that all names and values
of dead properties and the live properties defined by this
document existing on the resource are to be returned.
Extensibility: Normally empty, but MAY be extended with additional
child elements or attributes which SHOULD be ignored if not
recognized.
13.27 propname XML Element
Name: propname
Namespace: DAV:
Purpose: The propname XML element specifies that only a list of
property names on the resource is to be returned.
Extensibility: Normally empty, but MAY be extended with additional
child elements or attributes which SHOULD be ignored if not
recognized.
13.28 dead-props XML Element
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Name: dead-props
Namespace: DAV:
Purpose: The dead-props XML element specifies that all dead
properties, names and values, should be returned in the response.
Extensibility: Normally empty, but MAY be extended with additional
child elements or attributes which SHOULD be ignored if not
recognized.
13.29 location XML Element
Name: location
Namespace: DAV:
Purpose: In normal responses (not Multi-Status), some status codes
go along with a Location header. When these status codes are used
in a Multi-Status response, this element is used instead.
Description: Contains a single href element with the same URI that
would be used in a Location header.
Extensibility: MAY be extended with additional child elements or
attributes which SHOULD be ignored if not recognized.
13.30 error XML Element
Name: error
Namespace: DAV:
Purpose: Error responses, particularly 403 Forbidden and 409
Conflict, sometimes need more information to indicate what went
wrong. When an error response contains a body in WebDAV, the body
is in XML with the root element 'error'. The 'error' tag SHOULD
include a standard error tag defined in this specification or
another specification. The 'error' tag MAY include custom error
tags (in custom namespaces) which a client can safely ignore.
Description: Contains any XML element
Extensibility: Fully extensible with additional child elements or
attributes which SHOULD be ignored if not recognized.
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14. DAV Properties
For DAV properties, the name of the property is also the same as the
name of the XML element that contains its value. In the section
below, the final line of each section gives the element type
declaration using the format defined in XML [11]. The "Value" field,
where present, specifies further restrictions on the allowable
contents of the XML element using BNF (i.e., to further restrict the
values of a PCDATA element). Note that a resource may have only one
value for a property of a given name, so the property may only show
up once in PROPFIND responses or PROPPATCH requests.
Some property values are calculated by the server and it is not
appropriate to allow client changes, thus they are protected.
Existing server implementations already have different sets of
RFC2518 properties protected, but clients can have some expectations
which properties are normally protected. The value of a protected
property may not be changed even by a user with permission to edit
other properties. The value of an unprotected property may be
changed by some users with appropriate permissions.
14.1 creationdate Property
Name: creationdate
Namespace: DAV:
Purpose: Records the time and date the resource was created.
Value: date-time (defined in RFC3339 [9], see the ABNF in section
5.6.)
Protected: MAY be protected. Some servers allow creationdate to be
changed to reflect the time the document was created if that is
more meaningful to the user (rather than the time it was
uploaded). Thus, clients SHOULD NOT use this property in
synchronization logic (use getetag instead).
COPY/MOVE behaviour: This property value SHOULD be kept during a
MOVE operation, but is normally re-initialized when a resource is
created with a COPY. It should not be set in a COPY.
Description: The creationdate property should be defined on all DAV
compliant resources. If present, it contains a timestamp of the
moment when the resource was created (i.e., the moment it had
non-null state).
Extensibility: MAY contain attributes which SHOULD be ignored if not
recognized.
14.2 displayname Property
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Name: displayname
Namespace: DAV:
Purpose: Provides a name for the resource that is suitable for
presentation to a user.
Value: Any text
Protected: Possibly
COPY/MOVE behaviour: This property value SHOULD be preserved in
local COPY and MOVE operations. It MAY be attempted to be set in
a COPY operation to a remote server.
Description: The displayname property should be defined on all DAV
compliant resources. If present, the property contains a
description of the resource that is suitable for presentation to a
user.
Extensibility: MAY contain attributes which SHOULD be ignored if not
recognized.
14.3 getcontentlanguage Property
Name: getcontentlanguage
Namespace: DAV:
Purpose: Contains the Content-Language header returned by a GET
without accept headers
Value: language-tag (language-tag is defined in section 14.13 of
RFC2616 [8])
Protected: SHOULD NOT be protected, so that clients can reset the
language.
COPY/MOVE behaviour: This property value SHOULD be preserved in
local COPY and MOVE operations. It SHOULD be attempted to be set
in a COPY operation to a remote server.
Description: The getcontentlanguage property MUST be defined on any
DAV compliant resource that returns the Content-Language header on
a GET.
Extensibility: MAY contain attributes which SHOULD be ignored if not
recognized.
14.4 getcontentlength Property
Name: getcontentlength
Namespace: DAV:
Purpose: Contains the Content-Length header returned by a GET
without accept headers.
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Value: content-length (see section 14.14 of RFC2616 [8])
Protected: SHOULD be protected so clients cannot set to misleading
values
Description: The getcontentlength property MUST be defined on any
DAV compliant resource that returns the Content-Length header in
response to a GET.
COPY/MOVE behaviour: This property value is dependent on the size of
the destination resource, not the value of the property on the
source resource.
Extensibility: MAY contain attributes which SHOULD be ignored if not
recognized.
14.5 getcontenttype Property
Name: getcontenttype
Namespace: DAV:
Purpose: Contains the Content-Type header returned by a GET without
accept headers.
Value: media-type (defined in section 3.7 of RFC2616 [8])
Protected: SHOULD NOT be protected, so clients may fix this value
COPY/MOVE behaviour: This property value SHOULD be preserved in
local COPY and MOVE operations. In a remote COPY operation that
is implemented through a PUT request, the PUT request must have
the appropriate Content-Type header.
Description: This getcontenttype property MUST be defined on any DAV
compliant resource that returns the Content-Type header in
response to a GET.
Extensibility: MAY contain attributes which SHOULD be ignored if not
recognized.
14.6 getetag Property
Name: getetag
Namespace: DAV:
Purpose: Contains the ETag header returned by a GET without accept
headers.
Value: entity-tag (defined in section 3.11 of RFC2616 [8])
Protected: MUST be protected because this value is created and
controlled by the server.
COPY/MOVE behaviour: This property value is dependent on the final
state of the destination resource, not the value of the property
on the source resource.
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Description: The getetag property MUST be defined on any DAV
compliant resource that returns the Etag header. Refer to RFC2616
for a complete definition of the semantics of an ETag. Note that
changes in properties or lock state MUST not cause a resourceȡs
ETag to change.
Extensibility: MAY contain attributes which SHOULD be ignored if not
recognized.
14.7 getlastmodified Property
Name: getlastmodified
Namespace: DAV:
Purpose: Contains the Last-Modified header returned by a GET method
without accept headers.
Value: HTTP-date (defined in section 3.3.1 of RFC2616 [8])
Protected: SHOULD be protected because some clients may rely on the
value for appropriate caching behavior, or on the value of the
Last-Modified header to which this property is linked.
COPY/MOVE behaviour: This property value is dependent on the last
modified date of the destination resource, not the value of the
property on the source resource. Note that some server
implementations use the file system date modified value for the
'getlastmodified' value, and this is preserved in a MOVE even when
the HTTP Last-Modified value SHOULD change. Thus, clients cannot
rely on this value for caching and SHOULD use ETags.
Description: Note that the last-modified date on a resource SHOULD
only reflect changes in the body (the GET responses) of the
resource. A change in a property only SHOULD NOT cause the
last-modified date to change, because clients MAY rely on the
last-modified date to know when to overwrite the existing body.
The getlastmodified property MUST be defined on any DAV compliant
resource that returns the Last- Modified header in response to a
GET.
Extensibility: MAY contain attributes which SHOULD be ignored if not
recognized.
14.8 lockdiscovery Property
Name: lockdiscovery
Namespace: DAV:
Purpose: Describes the active locks on a resource
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Protected: MUST be protected. Clients change the list of locks
through LOCK and UNLOCK, not through PROPPATCH.
COPY/MOVE behaviour: The value of this property depends on the lock
state of the destination, not on the locks of the source resource.
Recall that locks are not moved in a MOVE operation.
Description: The lockdiscovery property returns a listing of who has
a lock, what type of lock he has, the timeout type and the time
remaining on the timeout, and the associated lock token. If there
are no locks, but the server supports locks, the property will be
present but contain zero Ƚactivelockȡ elements. If there is one
or more lock, an Ƚactivelockȡ element appears for each lock on
the resource.
Extensibility: MAY be extended with additional child elements or
attributes which SHOULD be ignored if not recognized.
14.8.1 Example - Retrieving the lockdiscovery Property
>>Request
PROPFIND /container/ HTTP/1.1
Host: www.example.com
Content-Length: xxxx
Content-Type: text/xml; charset="utf-8"
>>Response
HTTP/1.1 207 Multi-Status
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
http://www.example.com/container/
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0
Jane Smith
Infinite
opaquelocktoken:f81de2ad-7f3d-a1b2-4f3c-
00a0c91a9d76
http://www.example.com/container/
HTTP/1.1 200 OK
This resource has a single exclusive write lock on it, with an
infinite timeout.
14.9 resourcetype Property
Name: resourcetype
Namespace: DAV:
Purpose: Specifies the nature of the resource.
Protected: SHOULD be protected. Resource type is generally decided
through the operation creating the resource (MKCOL vs PUT), not by
PROPPATCH.
COPY/MOVE behaviour: Generally a COPY/MOVE of a resource results in
the same type of resource at the destination. In a remote COPY,
the source server SHOULD NOT attempt to set this property.
Description: The resourcetype property MUST be defined on all DAV
compliant resources. The default value is empty.
Extensibility: MAY be extended with any child elements or attributes
which SHOULD be ignored if not recognized. If the element
contains the 'collection' child element plus additional
unrecognized elements/attributes, it should generally be treated
as a collection. If the element contains no recognized child
elements it should be treated as a non- collection
WebDAV-compliant resource.
Example: (fictional example to show extensibility)
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14.10 supportedlock Property
Name: supportedlock
Namespace: DAV:
Purpose: To provide a listing of the lock capabilities supported by
the resource.
Protected: MUST be protected. Servers determine what lock
mechanisms are supported, not clients.
COPY/MOVE behaviour: This property value is dependent on the kind of
locks supported at the destination, not on the value of the
property at the source resource. Servers attempting to COPY to a
destination should not attempt to set this property at the
destination.
Description: The supportedlock property of a resource returns a
listing of the combinations of scope and access types which may be
specified in a lock request on the resource. Note that the actual
contents are themselves controlled by access controls so a server
is not required to provide information the client is not
authorized to see.
Extensibility: MAY be extended with any child elements or attributes
which SHOULD be ignored if not recognized.
14.10.1 Example - Retrieving the supportedlock Property
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>>Request
PROPFIND /container/ HTTP/1.1
Host: www.example.com
Content-Length: xxxx
Content-Type: text/xml; charset="utf-8"
>>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
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15. Precondition/postcondition XML elements
The numerical status codes used in HTTP responses are not
sufficiently granular or informative for all purposes. Some
extensions to HTTP have used the error response body along with some
status codes in order to provide additiona machine-readable response
detail. The machine-readable codes are XML elements classified as
preconditions (generally client error or failure to meet the
conditions in order for the request to be considered) and
postconditions (generally server error or failure to respond
successfully to an otherwise valid request). The precondition or
postcondition XML element appears inside an 'error' element which is
the root of the XML body of the response. The 'error' root element
or the precondition or postcondition elements MAY contain additional
XML elements or attributes not defined in this specification.
XML elements in error response bodies were not used in RFC2518, but
were introduced in RFC2518bis. Thus, use of these informative
elements is RECOMMENDED. Even if clients do not automatically
recognize the error bodies they can be quite useful in
interoperability testing and debugging.
Name: external-entities-forbidden
Namespace: DAV:
Use with: 403 Forbidden
Purpose: (precondition) -- If the server rejects a client request
because the request body contains an external entity, the server
SHOULD use this error.
Name: requesturi-must-match-lock-token
Namespace: DAV:
Use with: 400 Bad Request
Purpose: (precondition) -- A request may include a Lock-Token header
to identify a lock for the purposes of an operation such as
refresh LOCK or UNLOCK. However, if the Request-URI doe not fall
within the scope of the lock identified by the token, the server
SHOULD use this error. The lock may have a scope that does not
include the Request-URI, or the lock could have disappeared, or
the token may be invalid.
Name: missing-lock-token
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Namespace: DAV:
Use with: 400 Bad Request
Purpose: (precondition) -- If the server rejects a request because
the request MUST have a lock token and is missing the lock token
header or header value (e.g. on an UNLOCK request), the server
SHOULD use this error.
Name: live-properties-not-preserved
Namespace: DAV:
Use with: 409 Conflict
Purpose: (postcondition) -- The server received an otherwise-valid
MOVE or COPY request, but cannot maintain the live properties with
the same behavior at the destination. It may be that the server
only supports some live properties in some parts of the
repository, or simply has an internal error.
Name: read-only-property
Namespace: DAV:
Use with: 403 Forbidden
Purpose: (precondition) -- The client attempted to set a read-only
property in a PROPPATCH (such as 'getetag').
Name: propfind-infinite-depth-forbidden
Namespace: DAV:
Use with: 403 Forbidden
Purpose: (precondition) -- This server does not allow infinite-depth
PROPFIND requests on collections.
Name: need-privileges
Namespace: DAV:
Use with: 403 Forbidden
Purpose: (precondition) -- The currently authenticated user simply
does not have the privileges required to do the requested
operation (e.g. UNLOCK a lock created by someone else).
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Name: missing-lock-token
Namespace: DAV:
Use with: 423 Locked
Purpose: (precondition) -- The request could not succeed because a
lock token should have been provided. This element, if present,
MUST contain the URL of a locked resource that prevented the
request. In cases of MOVE, COPY and DELETE where collection locks
are involved, it can be difficult for the client to find out which
locked resource made the request fail -- but the server is only
resonsible for returning one such locked resource. The server MAY
return every locked resource that prevented the request from
succeeding if it knows them all.
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16. Instructions for Processing XML in DAV
All DAV compliant resources MUST ignore any unknown XML element and
all its children encountered while processing a DAV method that uses
XML as its command language.
This restriction also applies to the processing, by clients, of DAV
property values where unknown XML elements SHOULD be ignored unless
the property's schema declares otherwise.
This restriction does not apply to setting dead DAV properties on the
server where the server MUST record unknown XML elements.
Additionally, this restriction does not apply to the use of XML where
XML happens to be the content type of the entity body, for example,
when used as the body of a PUT.
Since XML can be transported as text/xml or application/xml, a DAV
server MUST accept DAV method requests with XML parameters
transported as either text/xml or application/xml, and a DAV client
MUST accept XML responses using either text/xml or application/xml.
XML DTD fragments are included for all the XML elements defined in
this specification. However, legal XML may not be valid according to
any DTD due to namespace usage and extension rules, so the DTD is
only informational. A recipient of a WebDAV message with an XML body
MUST NOT validate the XML document according to any hard-coded or
dynamically-declared DTD.
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17. DAV Compliance Classes
A DAV compliant resource can advertise several classes of compliance.
A client can discover the compliance classes of a resource by
executing OPTIONS on the resource, and examining the "DAV" header
which is returned. Note particularly that resources are spoken of as
being compliant, rather than servers. That is because theoretically
some resources on a server could support different feature sets.
E.g. a server could have a sub-repository where an advanced feature
like server was supported, even if that feature was not supported on
all servers.
Since this document describes extensions to the HTTP/1.1 protocol,
minimally all DAV compliant resources, clients, and proxies MUST be
compliant with RFC2616 [8].
A resource that is class 2 compliant must also be class 1 compliant,
and a resource that is compliant with "bis" must also be class 1
compliant.
17.1 Class 1
A class 1 compliant resource MUST meet all "MUST" requirements in all
sections of this document.
Class 1 compliant resources MUST return, at minimum, the value "1" in
the DAV header on all responses to the OPTIONS method.
17.2 Class 2
A class 2 compliant resource MUST meet all class 1 requirements and
support the LOCK method, the supportedlock property, the
lockdiscovery property, the Time-Out response header and the Lock-
Token request header. A class "2" compliant resource SHOULD also
support the Time-Out request header and the owner XML element.
Class 2 compliant resources MUST return, at minimum, the values "1"
and "2" in the DAV header on all responses to the OPTIONS method.
17.3 Class 'bis'
A resource can explicitly advertise its support for the revisions to
RFC2518 made in this document. In particular, this allows clients to
use the Force-Authentication header on requests. Class 1 must be
supported as well. Class 2 MAY be supported.
A resource that supports bis MUST support:
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o the Force-Authentication header.
o Any behavior that it supports, in the manner specified in this
document, rather than in the manner specified in RFC2518, for all
client requests. A server MAY use an older behavior for specific
clients that are discovered to have interoperability problems with
the requirements of this specification, but MUST NOT use an older
behavior indiscriminately.
Example:
DAV: 1, bis
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18. Internationalization Considerations
In the realm of internationalization, this specification complies
with the IETF Character Set Policy RFC2277 [8]. In this
specification, human-readable fields can be found either in the value
of a property, or in an error message returned in a response entity
body. In both cases, the human-readable content is encoded using
XML, which has explicit provisions for character set tagging and
encoding, and requires that XML processors read XML elements encoded,
at minimum, using the UTF-8 RFC2279 [5] and UTF-16 encodings of the
ISO 10646 multilingual plane. XML examples in this specification
demonstrate use of the charset parameter of the Content-Type header,
as defined in RFC2376 [17], as well as the XML declarations which
provide charset identification information for MIME and XML
processors.
XML also provides a language tagging capability for specifying the
language of the contents of a particular XML element. The "xml:lang"
attribute appears on an XML element to identify the language of its
content and attributes. See XML [11] for definitions of values and
scoping.
WebDAV applications MUST support the character set tagging, character
set encoding, and the language tagging functionality of the XML
specification. Implementors of WebDAV applications are strongly
encouraged to read "XML Media Types" RFC2376 [17] for instruction on
which MIME media type to use for XML transport, and on use of the
charset parameter of the Content-Type header.
Names used within this specification fall into four categories: names
of protocol elements such as methods and headers, names of XML
elements, names of properties, and names of conditions. Naming of
protocol elements follows the precedent of HTTP, using English names
encoded in USASCII for methods and headers. Since these protocol
elements are not visible to users, and are simply long token
identifiers, they do not need to support multiple languages.
Similarly, the names of XML elements used in this specification are
not visible to the user and hence do not need to support multiple
languages.
WebDAV property names are qualified XML names (pairs of XML namespace
name and local name). Although some applications (e.g., a generic
property viewer) will display property names directly to their users,
it is expected that the typical application will use a fixed set of
properties, and will provide a mapping from the property name and
namespace to a human-readable field when displaying the property name
to a user. It is only in the case where the set of properties is not
known ahead of time that an application need display a property name
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URI to a user. We recommend that applications provide human-readable
property names wherever feasible.
For error reporting, we follow the convention of HTTP/1.1 status
codes, including with each status code a short, English description
of the code (e.g., 423 (Locked)). While the possibility exists that
a poorly crafted user agent would display this message to a user,
internationalized applications will ignore this message, and display
an appropriate message in the user's language and character set.
Since interoperation of clients and servers does not require locale
information, this specification does not specify any mechanism for
transmission of this information.
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19. Security Considerations
This section is provided to detail issues concerning security
implications of which WebDAV applications need to be aware.
All of the security considerations of HTTP/1.1 (discussed in RFC2616
[8]) and XML (discussed in RFC2376 [17]) also apply to WebDAV. In
addition, the security risks inherent in remote authoring require
stronger authentication technology, introduce several new privacy
concerns, and may increase the hazards from poor server design.
These issues are detailed below.
19.1 Authentication of Clients
Due to their emphasis on authoring, WebDAV servers need to use
authentication technology to protect not just access to a network
resource, but the integrity of the resource as well. Furthermore,
the introduction of locking functionality requires support for
authentication.
A password sent in the clear over an insecure channel is an
inadequate means for protecting the accessibility and integrity of a
resource as the password may be intercepted. Since Basic
authentication for HTTP/1.1 performs essentially clear text
transmission of a password, Basic authentication MUST NOT be used to
authenticate a WebDAV client to a server unless the connection is
secure. Furthermore, a WebDAV server MUST NOT send Basic
authentication credentials in a WWW-Authenticate header unless the
connection is secure. Examples of secure connections include a
Transport Layer Security (TLS) connection employing a strong cipher
suite with mutual authentication of client and server, or a
connection over a network which is physically secure, for example, an
isolated network in a building with restricted access.
WebDAV applications MUST support the Digest authentication scheme
RFC2069 [2]. Since Digest authentication verifies that both parties
to a communication know a shared secret, a password, without having
to send that secret in the clear, Digest authentication avoids the
security problems inherent in Basic authentication while providing a
level of authentication which is useful in a wide range of scenarios.
19.2 Denial of Service
Denial of service attacks are of special concern to WebDAV servers.
WebDAV plus HTTP enables denial of service attacks on every part of a
system's resources.
The underlying storage can be attacked by PUTting extremely large
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files.
Asking for recursive operations on large collections can attack
processing time.
Making multiple pipelined requests on multiple connections can attack
network connections.
WebDAV servers need to be aware of the possibility of a denial of
service attack at all levels.
19.3 Security through Obscurity
WebDAV provides, through the PROPFIND method, a mechanism for listing
the member resources of a collection. This greatly diminishes the
effectiveness of security or privacy techniques that rely only on the
difficulty of discovering the names of network resources. Users of
WebDAV servers are encouraged to use access control techniques to
prevent unwanted access to resources, rather than depending on the
relative obscurity of their resource names.
19.4 Privacy Issues Connected to Locks
When submitting a lock request a user agent may also submit an owner
XML field giving contact information for the person taking out the
lock (for those cases where a person, rather than a robot, is taking
out the lock). This contact information is stored in a lockdiscovery
property on the resource, and can be used by other collaborators to
begin negotiation over access to the resource. However, in many
cases this contact information can be very private, and should not be
widely disseminated. Servers SHOULD limit read access to the
lockdiscovery property as appropriate. Furthermore, user agents
SHOULD provide control over whether contact information is sent at
all, and if contact information is sent, control over exactly what
information is sent.
19.5 Privacy Issues Connected to Properties
Since property values are typically used to hold information such as
the author of a document, there is the possibility that privacy
concerns could arise stemming from widespread access to a resource's
property data. To reduce the risk of inadvertent release of private
information via properties, servers are encouraged to develop access
control mechanisms that separate read access to the resource body and
read access to the resource's properties. This allows a user to
control the dissemination of their property data without overly
restricting access to the resource's contents.
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19.6 Implications of XML External Entities
XML supports a facility known as "external entities", defined in
section 4.2.2 of XML [11], which instruct an XML processor to
retrieve and include additional XML. An external XML entity can be
used to append or modify the document type declaration (DTD)
associated with an XML document. An external XML entity can also be
used to include XML within the content of an XML document. For non-
validating XML, such as the XML used in this specification, including
an external XML entity is not required by XML [11]. However, XML
[11] does state that an XML processor may, at its discretion, include
the external XML entity.
External XML entities have no inherent trustworthiness and are
subject to all the attacks that are endemic to any HTTP GET request.
Furthermore, it is possible for an external XML entity to modify the
DTD, and hence affect the final form of an XML document, in the worst
case significantly modifying its semantics, or exposing the XML
processor to the security risks discussed in RFC2376 [17].
Therefore, implementers must be aware that external XML entities
should be treated as untrustworthy. If a server implementor chooses
not to handle external XML entities, it SHOULD respond to requests
containing external entities with the precondition defined above
(external-entities-forbidden).
There is also the scalability risk that would accompany a widely
deployed application which made use of external XML entities. In
this situation, it is possible that there would be significant
numbers of requests for one external XML entity, potentially
overloading any server which fields requests for the resource
containing the external XML entity.
19.7 Risks Connected with Lock Tokens
This specification, in section 6.4, requires the use of Universal
Unique Identifiers (UUIDs) for lock tokens, in order to guarantee
their uniqueness across space and time. UUIDs, as defined in
ISO-11578 [12], contain a "node" field which "consists of the IEEE
address, usually the host address. For systems with multiple IEEE
802 nodes, any available node address can be used." Since a WebDAV
server will issue many locks over its lifetime, the implication is
that it will also be publicly exposing its IEEE 802 address.
There are several risks associated with exposure of IEEE 802
addresses. Using the IEEE 802 address:
o It is possible to track the movement of hardware from subnet to
subnet.
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o It may be possible to identify the manufacturer of the hardware
running a WebDAV server.
o It may be possible to determine the number of each type of
computer running WebDAV.
Section 24.2 of this specification details an alternate mechanism for
generating the "node" field of a UUID without using an IEEE 802
address, which alleviates the risks associated with exposure of IEEE
802 addresses by using an alternate source of uniqueness.
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20. IANA Considerations
This document defines two namespaces, the namespace of property
names, and the namespace of WebDAV-specific XML elements used within
property values.
The use of XML namespaces means that unique WebDAV property names and
XML elements can be quickly defined by any WebDAV user or
application, without requiring IANA action.
This specification defines a distinguished set of property names and
XML elements that are understood by all WebDAV applications. The
property names and XML elements in this specification are all in the
"DAV:" namespace. In natural language, a property like the
"creationdate" property in the "DAV:" namespace is sometimes referred
to as "DAV:creationdate" for brevity.
This specification also defines a URI scheme for the encoding of lock
tokens, the opaquelocktoken URI scheme described in section 6.4.
To ensure correct interoperation based on this specification, IANA
must reserve the URI namespaces starting with "DAV:" and with
"opaquelocktoken:" for use by this specification, its revisions, and
related WebDAV specifications.
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21. Acknowledgements
A specification such as this thrives on piercing critical review and
withers from apathetic neglect. The authors gratefully acknowledge
the contributions of the following people, whose insights were so
valuable at every stage of our work.
Contributors to RFC2518
Terry Allen, Harald Alvestrand, Jim Amsden, Becky Anderson, Alan
Babich, Sanford Barr, Dylan Barrell, Bernard Chester, Tim Berners-
Lee, Dan Connolly, Jim Cunningham, Ron Daniel, Jr., Jim Davis, Keith
Dawson, Mark Day, Brian Deen, Martin Duerst, David Durand, Lee
Farrell, Chuck Fay, Wesley Felter, Roy Fielding, Mark Fisher, Alan
Freier, George Florentine, Jim Gettys, Phill Hallam-Baker, Dennis
Hamilton, Steve Henning, Mead Himelstein, Alex Hopmann, Andre van der
Hoek, Ben Laurie, Paul Leach, Ora Lassila, Karen MacArthur, Steven
Martin, Larry Masinter, Michael Mealling, Keith Moore, Thomas Narten,
Henrik Nielsen, Kenji Ota, Bob Parker, Glenn Peterson, Jon Radoff,
Saveen Reddy, Henry Sanders, Christopher Seiwald, Judith Slein, Mike
Spreitzer, Einar Stefferud, Greg Stein, Ralph Swick, Kenji Takahashi,
Richard N. Taylor, Robert Thau, John Turner, Sankar Virdhagriswaran,
Fabio Vitali, Gregory Woodhouse, and Lauren Wood.
Two from this list deserve special mention. The contributions by
Larry Masinter have been invaluable, both in helping the formation of
the working group and in patiently coaching the authors along the
way. In so many ways he has set high standards we have toiled to
meet. The contributions of Judith Slein in clarifying the
requirements, and in patiently reviewing draft after draft, both
improved this specification and expanded our minds on document
management.
We would also like to thank John Turner for developing the XML DTD.
The authors of RFC2518 were Yaron Goland, Jim Whitehead, A. Faizi,
Steve Carter and D. Jensen. Although their names had to be removed
due to IETF author count restrictions they can take credit for the
majority of the design of WebDAV.
Additional Contributors to This Specification
Valuable contributions to RFC2518 bis came from some already named.
New contributors must also be gratefully acknowledged. Julian
Reschke, Geoff Clemm, Joel Soderberg, and Dan Brotsky hashed out
specific text on the list or in meetings. Ilya Kirnos supplied text
for Force-Authentication header. Joe Hildebrand contributed as
co-chair.
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22. References
22.1 Normative References
[1] Noble, B., Nguyen, G., Satyanarayanan, M. and R. Katz, "Mobile
Network Tracing", RFC 2041, October 1996.
[2] Franks, J., Hallam-Baker, P., Hostetler, J., Leach, P.,
Luotonen, A., Sink, E. and L. Stewart, "An Extension to HTTP :
Digest Access Authentication", RFC 2069, January 1997.
[3] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[4] Alvestrand, H., "IETF Policy on Character Sets and Languages",
BCP 18, RFC 2277, January 1998.
[5] Yergeau, F., "UTF-8, a transformation format of ISO 10646", RFC
2279, January 1998.
[6] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 2396, August
1998.
[7] Goland, Y., Whitehead, E., Faizi, A., Carter, S. and D. Jensen,
"HTTP Extensions for Distributed Authoring -- WEBDAV", RFC
2518, February 1999.
[8] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L.,
Leach, P. and T. Berners-Lee, "Hypertext Transfer Protocol --
HTTP/1.1", RFC 2616, June 1999.
[9] Klyne, G. and C. Newman, "Date and Time on the Internet:
Timestamps", RFC 3339, July 2002.
[10] Bray, T., Hollander, D. and A. Layman, "Namespaces in XML", W3C
REC REC-xml-names-19990114, January 1999.
[11] Bray, T., Paoli, J., Sperberg-McQueen, C. and E. Maler,
"Extensible Markup Language (XML) 1.0 (Second Edition)", W3C
FirstEdition REC-xml-20001006, October 2000.
[12] International Organization for Standardization, "Information
technology - Open Systems Interconnection - Remote Procedure
Call (RPC)", ISO Standard 11578, 1996.
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22.2 Informational References
[13] Bradner, S., "The Internet Standards Process -- Revision 3",
BCP 9, RFC 2026, October 1996.
[14] Lasher, R. and D. Cohen, "A Format for Bibliographic Records",
RFC 1807, June 1995.
[15] Slein, J., Vitali, F., Whitehead, E. and D. Durand,
"Requirements for a Distributed Authoring and Versioning
Protocol for the World Wide Web", RFC 2291, February 1998.
[16] Weibel, S., Kunze, J., Lagoze, C. and M. Wolf, "Dublin Core
Metadata for Resource Discovery", RFC 2413, September 1998.
[17] Whitehead, E. and M. Makoto, "XML Media Types", RFC 2376, July
1998.
[18] Clemm, G., Amsden, J., Ellison, T., Kaler, C. and J. Whitehead,
"Versioning Extensions to WebDAV (Web Distributed Authoring and
Versioning)", RFC 3253, March 2002.
[19] Clemm, G., Reschke, J., Sedlar, E. and J. Whitehead, "Web
Distributed Authoring and Versioning (WebDAV) Access Control
Protocol", RFC 3744, May 2004.
[20] Krauskopf, T., Miller, J., Resnick, P. and W. Treese, "PICS 1.1
Label Distribution -- Label Syntax and Communication
Protocols", W3C REC REC-PICS-labels-961031, October 1996.
[21] Lagoze, C., "The Warwick Framework: A Container Architecture
for Diverse Sets of Metadata", July/August 1996, .
[22] Cataloging Distribution Service, Library of Congress,
Washington, DC, "Network Development and MARC Standards,
Office, ed. 1994. "USMARC Format for Bibliographic Data"",
1994.
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Authors' Addresses
Lisa Dusseault
Open Source Application Foundation
2064 Edgewood Dr.
Palo Alto, CA 94303
US
EMail: lisa@osafoundation.org
Jason L Crawford
IBM
P.O.Box 704
Yorktown Heights, NY 10598
US
EMail: nnjason8451@smallcue.com
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Appendix A. Previous Authors' Addresses
Editors of RFC2518
Y. Y. Goland Microsoft Corporation One Microsoft Way Redmond, WA
98052-6399 Email: yarong@microsoft.com
E. J. Whitehead, Jr. Dept. Of Information and Computer Science
University of California, Irvine Irvine, CA 92697-3425 Email:
ejw@ics.uci.edu
A. Faizi Netscape 685 East Middlefield Road Mountain View, CA 94043
Email: asad@netscape.com
S. R. Carter Novell 1555 N. Technology Way M/S ORM F111 Orem, UT
84097-2399 Email: srcarter@novell.com
D. Jensen Novell 1555 N. Technology Way M/S ORM F111 Orem, UT
84097-2399 Email: dcjensen@novell.com
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Appendix B. Appendices
B.1 Appendix 1 - Notes on Processing XML Elements
B.1.1 Notes on Empty XML Elements
XML supports two mechanisms for indicating that an XML element does
not have any content. The first is to declare an XML element of the
form . The second is to declare an XML element of the form
. The two XML elements are semantically identical.
B.1.2 Notes on Illegal XML Processing
XML is a flexible data format that makes it easy to submit data that
appears legal but in fact is not. The philosophy of "Be flexible in
what you accept and strict in what you send" still applies, but it
must not be applied inappropriately. XML is extremely flexible in
dealing with issues of white space, element ordering, inserting new
elements, etc. This flexibility does not require extension,
especially not in the area of the meaning of elements.
There is no kindness in accepting illegal combinations of XML
elements. At best it will cause an unwanted result and at worst it
can cause real damage.
B.1.3 Example - XML Syntax Error
The following request body for a PROPFIND method is illegal.
The definition of the propfind element only allows for the allprop or
the propname element, not both. Thus the above is an error and must
be responded to with a 400 (Bad Request).
Imagine, however, that a server wanted to be "kind" and decided to
pick the allprop element as the true element and respond to it. A
client running over a bandwidth limited line who intended to execute
a propname would be in for a big surprise if the server treated the
command as an allprop.
Additionally, if a server were lenient and decided to reply to this
request, the results would vary randomly from server to server, with
some servers executing the allprop directive, and others executing
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the propname directive. This reduces interoperability rather than
increasing it.
B.1.4 Example - Unknown XML Element
The previous example was illegal because it contained two elements
that were explicitly banned from appearing together in the propfind
element. However, XML is an extensible language, so one can imagine
new elements being defined for use with propfind. Below is the
request body of a PROPFIND and, like the previous example, must be
rejected with a 400 (Bad Request) by a server that does not
understand the expired-props element.
To understand why a 400 (Bad Request) is returned let us look at the
request body as the server unfamiliar with expired-props sees it.
As the server does not understand the expired-props element,
according to the WebDAV-specific XML processing rules specified in
Section 16, it must ignore it. Thus the server sees an empty
propfind, which by the definition of the propfind element is illegal.
Please note that had the extension been additive it would not
necessarily have resulted in a 400 (Bad Request). For example,
imagine the following request body for a PROPFIND:
*boss*
The previous example contains the fictitious element leave-out. Its
purpose is to prevent the return of any property whose name matches
the submitted pattern. If the previous example were submitted to a
server unfamiliar with leave-out, the only result would be that the
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leave-out element would be ignored and a propname would be executed.
B.2 Appendix 2: UUID Node Generation
UUIDs, as defined in ISO-11578 [12], contain a "node" field that
contains one of the IEEE 802 addresses for the server machine. As
noted in section 18, 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
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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.
B.3 Changes
B.3.1 Changes in -01
B.3.2 Changes in -06
Specified that a successful LOCK request to an unmapped URL creates a
new, empty locked resource.
Resolved UNLOCK_NEEDS_IF_HEADER by clarifying that only Lock-Token
header is needed on UNLOCK.
Added Section 15 on preconditions and postconditions and defined a
number of preconditions and postconditions. The 'missing-lock-token'
precondition resolves the REPORT_OTHER_RESOURCE_LOCKED issue.
Added example of matching lock token to URI in the case of a
collection lock in the If header section.
Removed ability for Destination header to take "abs_path" in order to
keep consistent with other places where client provides URLs (If
header, href element in request body)
Clarified the href element - that it generally contains HTTP URIs but
not always.
Attempted to fix the BNF describing the If header to allow commas
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Clarified presence of Depth header on LOCK refresh requests.
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