Internet DRAFT - draft-reschke-webdav-locking
draft-reschke-webdav-locking
Network Working Group J. Reschke
Internet-Draft greenbytes
Updates: 2518 (if approved) October 5, 2005
Expires: April 8, 2006
Web Distributed Authoring and Versioning (WebDAV) Locking Protocol
draft-reschke-webdav-locking-08
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Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This document specifies a set of methods and headers ancillary to
HTTP/1.1 (RFC2616) and Distributed Authoring and Versioning (WebDAV,
RFC2518) for the management of resource locking (collision
avoidance). It updates those sections from RFC2518 that specify
WebDAV's locking features.
Editorial Note (to be removed by RFC Editor before publication)
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[[docstate: Note that this document is not a product of the WebDAV
working group. It is just an experiment to study the feasability of
extracing the locking feature into a separate specification.
--reschke]]
Distribution of this document is unlimited. Please send comments to
the WebDAV working group at <mailto:w3c-dist-auth@w3.org>, which may
be joined by sending a message with subject "subscribe" to
<mailto:w3c-dist-auth-request@w3.org>. Discussions of the WEBDAV
working group are archived at
<http://lists.w3.org/Archives/Public/w3c-dist-auth/>.
An issues list and XML and HTML versions of this draft are available
from
<http://greenbytes.de/tech/webdav/#draft-reschke-webdav-locking>.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . 6
1.2 Method Preconditions and Postconditions . . . . . . . . . 6
1.3 Document Organization . . . . . . . . . . . . . . . . . . 7
2. Overview of Locking . . . . . . . . . . . . . . . . . . . . . 7
2.1 Exclusive Vs. Shared Locks . . . . . . . . . . . . . . . . 7
2.1.1 Lock Compatibility Table . . . . . . . . . . . . . . . 9
2.2 Required Support . . . . . . . . . . . . . . . . . . . . . 9
2.3 Lock Tokens . . . . . . . . . . . . . . . . . . . . . . . 9
2.4 Lock Capability Discovery . . . . . . . . . . . . . . . . 10
2.5 Status of a lock . . . . . . . . . . . . . . . . . . . . . 10
2.5.1 Lock Access Type . . . . . . . . . . . . . . . . . . . 11
2.5.2 Lock Scope . . . . . . . . . . . . . . . . . . . . . . 11
2.5.3 Lock Root . . . . . . . . . . . . . . . . . . . . . . 11
2.5.4 Lock Depth . . . . . . . . . . . . . . . . . . . . . . 11
2.5.5 Client-supplied Lock Owner Information (optional) . . 11
2.5.6 Lock Creator (optional) . . . . . . . . . . . . . . . 11
2.5.7 Lock Timeout . . . . . . . . . . . . . . . . . . . . . 12
2.6 Active Lock Discovery . . . . . . . . . . . . . . . . . . 12
2.7 Usage Considerations . . . . . . . . . . . . . . . . . . . 12
3. Write Lock . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.1 Methods Restricted by Write Locks . . . . . . . . . . . . 14
3.2 Write Locks and Properties . . . . . . . . . . . . . . . . 14
3.3 Write Locks and Collections . . . . . . . . . . . . . . . 14
3.4 Write Locks and the If Request Header . . . . . . . . . . 15
3.4.1 Example - Write Lock . . . . . . . . . . . . . . . . . 15
3.5 Write Locks and COPY/MOVE . . . . . . . . . . . . . . . . 16
4. Properties . . . . . . . . . . . . . . . . . . . . . . . . . . 16
4.1 Common XML elements used in property values . . . . . . . 16
4.1.1 Lock Scopes . . . . . . . . . . . . . . . . . . . . . 16
4.1.2 Lock Types . . . . . . . . . . . . . . . . . . . . . . 16
4.2 DAV:lockdiscovery property . . . . . . . . . . . . . . . . 16
4.2.1 Examples for the DAV:lockdiscovery . . . . . . . . . . 18
4.3 DAV:supportedlock property . . . . . . . . . . . . . . . . 18
4.3.1 Examples for the DAV:supportedlock property . . . . . 19
5. LOCK Method . . . . . . . . . . . . . . . . . . . . . . . . . 19
5.1 Creating Locks . . . . . . . . . . . . . . . . . . . . . . 19
5.1.1 Marshalling . . . . . . . . . . . . . . . . . . . . . 19
5.1.2 Postconditions . . . . . . . . . . . . . . . . . . . . 20
5.1.3 Example - Simple Lock Request . . . . . . . . . . . . 21
5.1.4 Example - Multi-Resource Lock Request . . . . . . . . 23
5.2 Refreshing Locks . . . . . . . . . . . . . . . . . . . . . 24
5.2.1 Marshalling . . . . . . . . . . . . . . . . . . . . . 24
5.2.2 Preconditions . . . . . . . . . . . . . . . . . . . . 24
5.2.3 Postconditions . . . . . . . . . . . . . . . . . . . . 24
5.2.4 Example - Refreshing a Write Lock . . . . . . . . . . 25
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6. UNLOCK Method . . . . . . . . . . . . . . . . . . . . . . . . 26
6.1 Marshalling . . . . . . . . . . . . . . . . . . . . . . . 26
6.2 Preconditions . . . . . . . . . . . . . . . . . . . . . . 26
6.2.1 DAV:lock-token-matches precondition . . . . . . . . . 26
6.2.2 DAV:lock-removal-allowed precondition . . . . . . . . 26
6.3 Postconditions . . . . . . . . . . . . . . . . . . . . . . 27
6.3.1 DAV:lock-removed postcondition . . . . . . . . . . . . 27
6.4 Example - UNLOCK . . . . . . . . . . . . . . . . . . . . . 27
7. Additional status codes . . . . . . . . . . . . . . . . . . . 27
7.1 423 Locked . . . . . . . . . . . . . . . . . . . . . . . . 27
8. Additional marshalling and method semantics for other
methods . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
8.1 Additional marshalling . . . . . . . . . . . . . . . . . . 28
8.1.1 DAV:name-allowed precondition . . . . . . . . . . . . 28
8.1.2 DAV:parent-resource-must-be-non-null precondition . . 28
8.2 Additional method semantics (preconditions) . . . . . . . 28
8.2.1 DAV:lock-token-submission-allowed precondition . . . . 28
8.2.2 DAV:need-lock-token precondition . . . . . . . . . . . 28
8.3 Additional method semantics (postconditions) . . . . . . . 29
8.3.1 DAV:lock-removed postcondition . . . . . . . . . . . . 29
9. Headers . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
9.1 Lock-Token request/response header . . . . . . . . . . . . 30
9.2 Timeout request header . . . . . . . . . . . . . . . . . . 30
10. Capability discovery . . . . . . . . . . . . . . . . . . . . 31
10.1 OPTIONS method . . . . . . . . . . . . . . . . . . . . . . 31
11. Security considerations . . . . . . . . . . . . . . . . . . 31
11.1 Privacy Issues Connected to Locks . . . . . . . . . . . . 31
12. Internationalization Considerations . . . . . . . . . . . . 32
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . 32
14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 32
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 32
15.1 Normative References . . . . . . . . . . . . . . . . . . . 32
15.2 Informative References . . . . . . . . . . . . . . . . . . 33
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 33
A. Collected Locking Semantics . . . . . . . . . . . . . . . . . 33
A.1 Directly vs Indirectly . . . . . . . . . . . . . . . . . . 33
A.2 Creating Locks . . . . . . . . . . . . . . . . . . . . . . 34
A.3 Lock Inheritance . . . . . . . . . . . . . . . . . . . . . 34
A.4 Removing Locks . . . . . . . . . . . . . . . . . . . . . . 34
A.5 Submitting Lock Tokens . . . . . . . . . . . . . . . . . . 34
A.6 Locked State . . . . . . . . . . . . . . . . . . . . . . . 34
A.7 URL protection . . . . . . . . . . . . . . . . . . . . . . 34
A.8 Exclusive vs Shared . . . . . . . . . . . . . . . . . . . 35
B. Changes to RFC2518 . . . . . . . . . . . . . . . . . . . . . . 35
B.1 Removed/Deprecated features . . . . . . . . . . . . . . . 35
B.1.1 Implicit lock refresh . . . . . . . . . . . . . . . . 35
B.1.2 Lock-null resources . . . . . . . . . . . . . . . . . 35
B.2 Additional features . . . . . . . . . . . . . . . . . . . 35
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B.2.1 DAV:lockroot element in DAV:activelock . . . . . . . . 36
B.2.2 Error Marshalling . . . . . . . . . . . . . . . . . . 36
C. Text to be integrated from RFC2518 . . . . . . . . . . . . . . 36
C.1 HTTP Methods for Distributed Authoring . . . . . . . . . . 36
C.1.1 LOCK Method . . . . . . . . . . . . . . . . . . . . . 36
C.2 HTTP Headers for Distributed Authoring . . . . . . . . . . 36
C.2.1 If Header . . . . . . . . . . . . . . . . . . . . . . 36
D. 'opaquelocktoken' URI Scheme . . . . . . . . . . . . . . . . . 36
E. Change Log (to be removed by RFC Editor before publication) . 37
E.1 Since draft-reschke-webdav-locking-00 . . . . . . . . . . 37
E.2 Since draft-reschke-webdav-locking-01 . . . . . . . . . . 37
E.3 Since draft-reschke-webdav-locking-02 . . . . . . . . . . 37
E.4 Since draft-reschke-webdav-locking-03 . . . . . . . . . . 38
E.5 Since draft-reschke-webdav-locking-04 . . . . . . . . . . 38
E.6 Since draft-reschke-webdav-locking-05 . . . . . . . . . . 38
E.7 Since draft-reschke-webdav-locking-06 . . . . . . . . . . 38
E.8 Since draft-reschke-webdav-locking-07 . . . . . . . . . . 38
F. Resolved issues (to be removed by RFC Editor before
publication) . . . . . . . . . . . . . . . . . . . . . . . . . 38
F.1 import-gulp . . . . . . . . . . . . . . . . . . . . . . . 39
G. Open issues (to be removed by RFC Editor prior to
publication) . . . . . . . . . . . . . . . . . . . . . . . . . 39
G.1 edit . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
G.2 safeness_and_idempotence . . . . . . . . . . . . . . . . . 39
G.3 099_COPYMOVE_LOCKED_STATUS_CODE_CLARIFICATION . . . . . . 39
G.4 100_COPYMOVE_LOCKED_STATUS_DESCRIPTION . . . . . . . . . . 39
G.5 066_MUST_AN_IF_HEADER_CHECK_THE_ROOT_OF_URL . . . . . . . 40
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Intellectual Property and Copyright Statements . . . . . . . . 43
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1. Introduction
This document describes the "locking" extension to the Web
Distributed Authoring and Versioning (WebDAV) protocol that allows to
keep more than one person from working on a document at the same
time. This helps preventing the "lost update problem," in which
modifications are lost as first one author then another writes
changes without merging the other author's changes.
1.1 Terminology
The terminology used here follows and extends that in the WebDAV
Distributed Authoring Protocol specification [RFC2518].
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].
Since this document describes a set of extensions to the WebDAV
Distributed Authoring Protocol [RFC2518], itself an extension to the
HTTP/1.1 protocol, the augmented BNF used here to describe protocol
elements is exactly the same as described in Section 2.1 of
[RFC2616]. Since this augmented BNF uses the basic production rules
provided in Section 2.2 of [RFC2616], these rules apply to this
document as well.
This document uses XML DTD fragments ([XML]) as a purely notational
convention. WebDAV request and response bodies cannot be validated
due to the specific extensibility rules defined in section 23 of
[RFC2518] and due to the fact that all XML elements defined by this
specification use the XML namespace name "DAV:". In particular:
o Element names use the "DAV:" namespace.
o Element ordering is irrelevant.
o Extension elements/attributes (elements/attributes not already
defined as valid child elements) may be added anywhere, except
when explicitly stated otherwise.
1.2 Method Preconditions and Postconditions
A "precondition" of a method describes the state on the server that
must be true for that method to be performed. A "postcondition" of a
method describes the state on the server that must be true after that
method has completed. If a method precondition or postcondition for
a request is not satisfied and unless a more specific HTTP status
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code applies, the response status of the request MUST be either 403
(Forbidden) if the request should not be repeated because it will
always fail, or 409 (Conflict) if it is expected that the user might
be able to resolve the conflict and resubmit the request.
In order to allow better client handling of error responses, a
distinct XML element type is associated with each method precondition
and postcondition of a request. When a particular precondition is
not satisfied or a particular postcondition cannot be achieved, the
appropriate XML element MUST be returned as the child of a top-level
DAV:error element in the response body, unless otherwise negotiated
by the request. In a 207 Multi-Status response, the DAV:error
element would appear in the appropriate DAV:responsedescription
element.
1.3 Document Organization
Sections 2 and 3 provide an overview of the locking feature in
general and write locks in particular. Additional new live
properties for feature discovery and lock discovery are defined in
Section 4. Sections 5 and 6 discuss the LOCK and UNLOCK method.
HTTP headers, status codes and additional marshalling for existing
WebDAV methods are defined in Sections 7 through 9.
Appendix A gives a complete summary of the locking semantics defined
by this document. Subsequent appendices discuss changes from
RFC2518, and the "opaquelocktoken" URI scheme.
2. Overview of 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.
2.1 Exclusive Vs. Shared Locks
The most basic form of lock is an exclusive lock. This is a lock
where the access right in question is only granted to a single
principal. The need for this arbitration results from a desire to
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avoid having to merge results.
However, there are times when the goal of a lock is not to exclude
others from exercising an access right but rather to provide a
mechanism for principals to indicate that they intend to exercise
their access rights. Shared locks are provided for this case. A
shared lock allows multiple principals to receive a lock. Hence any
principal with appropriate access can get the lock.
With shared locks there are two trust sets that affect a resource.
The first trust set is created by access permissions. Principals who
are trusted, for example, may have permission to write to the
resource. Among those who have access permission to write to the
resource, the set of principals who have taken out a shared lock also
must trust each other, creating a (typically) smaller trust set
within the access permission write set.
Starting with every possible principal on the Internet, in most
situations the vast majority of these principals will not have write
access to a given resource. Of the small number who do have write
access, some principals may decide to guarantee their edits are free
from overwrite conflicts by using exclusive write locks. Others may
decide they trust their collaborators will not overwrite their work
(the potential set of collaborators being the set of principals who
have write permission) and use a shared lock, which informs their
collaborators that a principal may be working on the resource.
This specification does 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. With a shared lock, another user can at least
take out another shared lock and start modifying the resource.
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2.1.1 Lock Compatibility Table
The table below describes the behavior that occurs when a lock
request is made on a resource.
+-------------------------+--------------------+--------------------+
| Current lock state / | Shared Lock | Exclusive Lock |
| Lock request | | |
+-------------------------+--------------------+--------------------+
| None | True | True |
| Shared Lock | True | False |
| Exclusive Lock | False | False* |
+-------------------------+--------------------+--------------------+
Legend: True = lock may be granted. False = lock MUST NOT be
granted. *=It is illegal for a principal to request the same lock
twice.
The current lock state of a resource is given in the leftmost column,
and lock requests are listed in the first row. The intersection of a
row and column gives the result of a lock request. For example, if a
shared lock is held on a resource, and an exclusive lock is
requested, the table entry is "false", indicating the lock must not
be granted.
2.2 Required Support
A WebDAV compliant server is not required to support locking in any
form. If the server does support locking it may choose to support
any combination of exclusive and shared locks for any access types.
The reason for this flexibility is that locking policy strikes to the
very heart of the resource management and versioning systems employed
by various storage repositories. These repositories require control
over what sort of locking will be made available. For example, some
repositories only support shared write locks while others only
provide support for exclusive write locks while yet others use no
locking at all. As each system is sufficiently different to merit
exclusion of certain locking features, this specification leaves
locking as the sole axis of negotiation within WebDAV.
2.3 Lock Tokens
A lock token is a type of state token, represented as a URI, which
identifies a particular lock (see [RFC2518], section 9.4, for a
definition of state tokens). A lock token is returned by every
successful LOCK operation in the Lock-Token response header. The
lock token also appears in the value of the DAV:lockdiscovery
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property, the value of which is returned in the body of the response
to a successful LOCK operation (note that this property also includes
the tokens of other current locks on the resource).
Lock token URIs MUST be unique across all resources for all time.
This uniqueness constraint allows lock tokens to be submitted across
resources and servers without fear of confusion.
This specification provides a lock token URI scheme called
"opaquelocktoken" that meets the uniqueness requirements. However
servers are free to use any URI scheme so long as it meets the
uniqueness requirements (for example, the "urn:uuid" URN namespace
defined in [RFC4122]). Note that only URI schemes registered by the
IETF can ensure uniqueness.
Submitting 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.
2.4 Lock Capability Discovery
Since server lock support is optional, a client trying to lock a
resource on a server can either try the lock and hope for the best,
or perform some form of discovery to determine what lock capabilities
the server supports. This is known as lock capability discovery.
Lock capability discovery differs from discovery of supported access
control types, since there may be access control types without
corresponding lock types. A client can determine what lock types the
server supports by retrieving the DAV:supportedlock property defined
in Section 4.3.
2.5 Status of a lock
A lock is identified by a URI (the lock token URI) but in general, it
does not have a HTTP URL, and thus can not be directly manipulated
using HTTP methods. Instead, this specification defines the new
methods LOCK (creating and refreshing locks, see Section 5) and
UNLOCK (removing locks, see Section 6) that act indirectly on locks.
A lock has state that can be indirectly observed by using the DAV:
lockdiscovery property defined in Section 4.2. At a minimum, the
state of a lock consists of the items defined in the sections below.
After lock creation, all parts of the state with the exception of the
timeout value are immutable.
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2.5.1 Lock Access Type
At present, this specification only defines one lock access type, the
"write" lock defined in Section 3.
2.5.2 Lock Scope
A lock has either exclusive or shared scope (see Section 2.1).
2.5.3 Lock Root
A lock is created as effect of a LOCK (creation) method request. The
lock root is the URL to which this request was adressed.
2.5.4 Lock Depth
A "depth 0" lock only affects the resource to which the LOCK request
was adressed to (the lock root). This resource is said to be
"directly locked" by the lock.
On the other hand, a "depth infinity" lock on a collection
additionally affects all members of that collection. These resources
are said to be "indirectly locked" by the lock. A "depth infinity"
lock on a non-collection resource behaves exactly the same way as a
"depth 0" lock.
2.5.5 Client-supplied Lock Owner Information (optional)
Clients can submit information about the lock owner when creating a
lock. This information should be 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).
Owner information is kept with the lock so that it can be returned in
the DAV:lockdiscovery property upon request. Note that this
information is entirely client-controlled, thus a server MUST store
the information faithfully just like if it appeared in a WebDAV dead
property (see [RFC2518], section 4).
2.5.6 Lock Creator (optional)
When a lock has been created by an authenticated principal, the
server SHOULD keep information about that principal with the lock.
This enables the server to subsequently check whether a lock
identified by a lock token submitted in a request belongs to the same
principal on whose behalf the lock was initially created (see
Section 8.2.1 below).
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2.5.7 Lock Timeout
In general, a lock expires after a certain amount of time. This time
can be specified in the LOCK creation request (however servers are
not required to honor this request).
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.
The timers used for timeout expiry can be reset by the client by
submitting a LOCK refresh 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. 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, an administrator 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.
2.6 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 DAV:lockdiscovery
property is provided. This property lists all outstanding locks,
describes their type, and where available, provides their lock token.
2.7 Usage Considerations
Although the locking mechanisms specified here provide some help in
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preventing lost updates, they cannot guarantee that updates will
never be lost. Consider the following scenario:
o 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.
o Client A doesn't lock the document, but does a GET and begins
editing.
o Client B does LOCK, performs a GET and begins editing.
o Client B finishes editing, performs a PUT, then an UNLOCK.
o Client A performs a PUT, overwriting and losing all of B's
changes.
There are several reasons why the WebDAV protocol itself cannot
prevent this situation. First, it cannot force all clients to use
locking because it must be compatible with HTTP clients that do not
comprehend locking. Second, it cannot require servers to support
locking because of the variety of repository implementations, some of
which rely on reservations and merging rather than on locking.
Finally, being stateless, it cannot enforce a sequence of operations
like LOCK / GET / PUT / UNLOCK.
WebDAV servers that support locking can reduce the likelihood that
clients will accidentally overwrite each other's changes by requiring
clients to lock resources before modifying them. Such servers would
effectively prevent HTTP 1.0 and HTTP 1.1 clients from modifying
resources.
WebDAV clients can be good citizens by using a lock / retrieve /
write /unlock sequence of operations (at least by default) whenever
they interact with a WebDAV server that supports locking.
HTTP 1.1 clients can be good citizens, avoiding overwriting other
clients' changes, by using entity tags in If-Match headers with any
requests that would modify resources.
Information managers may attempt to prevent overwrites by
implementing client-side procedures requiring locking before
modifying WebDAV resources.
3. 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
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lock type described in this specification.
3.1 Methods Restricted by Write Locks
If a request would modify the content for a locked resource, a dead
property of a locked resource, a live property that is defined to be
lockable for a locked resource, or an internal member URI of a locked
collection, the request MUST fail unless the lock-token for that lock
is submitted in the request. An internal member URI of a collection
is considered to be modified if it is added, removed, or identifies a
different resource
3.2 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.
3.3 Write Locks and Collections
A write lock on a collection, whether created by a "Depth: 0" or
"Depth: infinity" lock request, prevents the addition or removal of
member URIs of the collection by non-lock owners. As a consequence,
when a principal issues a PUT or POST request to create a new
resource under a URI which needs to be an internal member of a write
locked collection to maintain HTTP namespace consistency, or issues a
DELETE to remove an internal member URI of a write locked collection,
this request MUST fail if the principal does not have a write lock on
the collection.
However, if a write lock request is issued to a collection containing
member URIs identifying resources that are currently locked in a
manner which conflicts with the write lock, the request MUST fail
with a 423 (Locked) status code (Note that this can only occur for a
request of a "Depth: infinity" write lock).
If a lock owner causes the URI of a resource to be added as an
internal member URI 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.
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3.4 Write Locks and the If Request Header
If a user agent is not required to have knowledge about a lock when
requesting an operation on a locked resource, the following scenario
might occur. Program A, run by User A, takes out a write lock on a
resource. Program B, also run by User A, has no knowledge of the
lock taken out by Program A, yet performs a PUT to the locked
resource. In this scenario, the PUT succeeds because locks are
associated with a principal, not a program, and thus program B,
because it is acting with principal A's credential, is allowed to
perform the PUT. However, had program B known about the lock, it
would not have overwritten the resource, preferring instead to
present a dialog box describing the conflict to the user. Due to
this scenario, a mechanism is needed to prevent different programs
from accidentally ignoring locks taken out by other programs with the
same authorization.
In order to prevent these collisions a lock token MUST be submitted
in the If header for all locked resources that a method may interact
with or the method MUST fail. For example, if a resource is to be
moved and both the source and destination are locked then two lock
tokens must be submitted, one for the source and the other for the
destination.
Servers SHOULD restrict usage of the lock token to exactly the
authenticated principal who created the lock.
3.4.1 Example - Write Lock
>>Request
COPY /~fielding/index.html HTTP/1.1
Host: example.com
Destination: http://example.com/users/f/fielding/index.html
If: <http://example.com/users/f/fielding/index.html>
(<opaquelocktoken:f81d4fae-7dec-11d0-a765-00a0c91e6bf6>)
>>Response
HTTP/1.1 204 No Content
In this example, even though both the source and destination are
locked, only one lock token must be submitted, for the lock on the
destination. This is because the source resource is not modified by
a COPY, and hence unaffected by the write lock. In this example,
user agent authentication has previously occurred via a mechanism
outside the scope of the HTTP protocol, in the underlying transport
layer.
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3.5 Write Locks and COPY/MOVE
A COPY method invocation MUST NOT duplicate any write locks active on
the source. However, as previously noted, if the COPY copies the
resource into a collection that is locked with "Depth: infinity",
then the resource will be added to the lock.
A successful MOVE request on a write locked resource MUST NOT move
the write lock with the resource. However, the resource is subject
to being added to an existing lock at the destination, as specified
in Section 3.3. 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 3.4, an If
header must be submitted containing a lock token for both the source
and destination.
4. Properties
Any DAV compliant resource that supports the LOCK method MUST support
the DAV:activelock and DAV:lockdiscovery properties defined below.
4.1 Common XML elements used in property values
4.1.1 Lock Scopes
<!ELEMENT lockscope (exclusive | shared) >
<!ELEMENT exclusive EMPTY >
<!ELEMENT shared EMPTY >
4.1.2 Lock Types
<!ELEMENT locktype (write) >
<!ELEMENT write EMPTY >
4.2 DAV:lockdiscovery property
The DAV:lockdiscovery property returns a listing of who has a lock,
what type of lock he has, the timeout type, the time remaining on the
timeout, the associated lock token and the root of the lock. The
server is free to withhold any or all of this information if the
requesting principal does not have sufficient access rights to see
the requested data.
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<!ELEMENT lockdiscovery (activelock)* >
<!ELEMENT activelock (lockscope, locktype, depth, owner?,
timeout?, locktoken?, lockroot) >
depth: the value of the Depth header (see Section 2.5.4; takes the
values "0" or "infinity").
<!ELEMENT depth (#PCDATA) >
owner: provides information about the principal taking out a lock
(see Section 2.5.5).
<!ELEMENT owner ANY>
timeout: the time remaining until timeout of a lock (see
Section 2.5.7).
<!ELEMENT timeout (#PCDATA) >
locktoken: the lock token associated with a lock; the href element
contains the lock token.
<!ELEMENT locktoken (href) >
<!-- href: defined in [RFC2518], Section 12.3 -->
lockroot: the URL that was specified as Request-URI in the LOCK
creation request; the href element contains the URL (see
Section 2.5.3).
<!ELEMENT lockroot (href) >
<!-- href: defined in [RFC2518], Section 12.3 -->
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4.2.1 Examples for the DAV:lockdiscovery
DAV:lockdiscovery property for a resource that has two shared write
locks on it, with infinite timeouts:
<D:lockdiscovery xmlns:D="DAV:">
<D:activelock>
<D:locktype><D:write/></D:locktype>
<D:lockscope><D:shared/></D:lockscope>
<D:depth>0</D:depth>
<D:owner>Jane Smith</D:owner>
<D:timeout>Infinite</D:timeout>
<D:locktoken>
<D:href
>opaquelocktoken:f81de2ad-7f3d-a1b2-4f3c-00a0c91a9d76</D:href>
</D:locktoken>
<D:lockroot>
<D:href
>http://example.com/container/</D:href>
</D:lockroot>
</D:activelock>>
<D:activelock>
<D:locktype><D:write/></D:locktype>
<D:lockscope><D:shared/></D:lockscope>
<D:depth>0</D:depth>
<D:owner>John Doe</D:owner>
<D:timeout>Infinite</D:timeout>
<D:locktoken>
<D:href
>opaquelocktoken:f81de2ad-7f3d-a1b2-4f3c-00a0c91a9d77</D:href>
</D:locktoken>
<D:lockroot>
<D:href
>http://example.com/container/</D:href>
</D:lockroot>
</D:activelock>
</D:lockdiscovery>
DAV:lockdiscovery property for a resource with no locks on it:
<D:lockdiscovery xmlns:D="DAV:"/>
4.3 DAV:supportedlock property
The DAV: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
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themselves controlled by access controls so a server is not required
to provide information the client is not authorized to see.
<!ELEMENT supportedlock (lockentry)* >
<!ELEMENT lockentry (lockscope, locktype) >
4.3.1 Examples for the DAV:supportedlock property
DAV:supportedlock property for a resource that supports both
exclusive and shares write locks:
<D:supportedlock xmlns:D="DAV:">
<D:lockentry>
<D:lockscope><D:exclusive/></D:lockscope>
<D:locktype><D:write/></D:locktype>
</D:lockentry>
<D:lockentry>
<D:lockscope><D:shared/></D:lockscope>
<D:locktype><D:write/></D:locktype>
</D:lockentry>
</D:supportedlock>
DAV:supportedlock property for a resource that doesn't support any
locks at all:
<D:supportedlock xmlns:D="DAV:"/>
5. LOCK Method
The following sections describe the LOCK method, which is used to
take out a lock of any access type or to refresh an existing lock.
5.1 Creating Locks
A LOCK method invocation with non-empty request body creates the lock
specified by the lockinfo XML element on the resource identified by
the Request-URI.
If the Request-URI identifies a null resource, the invocation MUST
create a new resource with empty content.
5.1.1 Marshalling
The request MAY include a "Timeout" header to be used as the timeout
value for the lock to be created (see Section 9.2). However, the
server is not required to honor or even consider this request.
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The request MAY include a "Depth" header specifying either "0" or
"infinity" (see [RFC2518], section 9.2). If no "Depth" header is
submitted then the request MUST act as if a "Depth:infinity" had been
specified.
The request body MUST be a DAV:lockinfo element:
<!ELEMENT lockinfo (lockscope, locktype, owner?) >
DAV:lockscope, DAV:locktype and DAV:owner are defined in Section 4.
The response body for a successful request MUST be a DAV:prop XML
element, containing the new value for the DAV:lockdiscovery property
defined in Section 4.2. The lock token URI for the new lock MUST be
returned in the "Lock-Token" response header (see Section 9.1).
If a "Depth: infinity" lock request fails because the lock could not
be granted to all resource, a 207 (Multistatus) 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.
5.1.2 Postconditions
5.1.2.1 DAV:create-lock postcondition
The request MUST have created a new lock on the resource identified
by the Request-URI, having all the lock properties specified in the
request (with the exception of the Timeout request header). The
request MUST have allocated a distinct new lock token URI for the new
lock, and that URI MUST NOT ever identify anything other than that
lock.
5.1.2.2 DAV:create-resource postcondition
If the Request-URI identified a null resource, the method MUST have
created a new resource with empty content.
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5.1.3 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="..."
<?xml version="1.0" encoding="utf-8" ?>
<D:lockinfo xmlns:D='DAV:'>
<D:lockscope><D:exclusive/></D:lockscope>
<D:locktype><D:write/></D:locktype>
<D:owner>
<D:href>http://example.org/~ejw/contact.html</D:href>
</D:owner>
</D:lockinfo>
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>>Response
HTTP/1.1 200 OK
Lock-Token: <opaquelocktoken:e71d4fae-5dec-22d6-fea5-00a0c91e6be4>
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<D:prop xmlns:D="DAV:">
<D:lockdiscovery>
<D:activelock>
<D:locktype><D:write/></D:locktype>
<D:lockscope><D:exclusive/></D:lockscope>
<D:depth>Infinity</D:depth>
<D:owner>
<D:href
>http://example.org/~ejw/contact.html</D:href>
</D:owner>
<D:timeout>Second-604800</D:timeout>
<D:locktoken>
<D:href
>opaquelocktoken:e71d4fae-5dec-22d6-fea5-00a0c91e6be4</D:href>
</D:locktoken>
<D:lockroot>
<D:href
>http://example.com/workspace/webdav/proposal.doc</D:href>
</D:lockroot>
</D:activelock>
</D:lockdiscovery>
</D:prop>
This example shows the successful creation of an exclusive write lock
on resource http://example.com/workspace/webdav/proposal.doc. The
resource http:/example.org/~ejw/contact.html contains contact
information for the 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).
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5.1.4 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="..."
<?xml version="1.0" encoding="utf-8" ?>
<D:lockinfo xmlns:D="DAV:">
<D:locktype><D:write/></D:locktype>
<D:lockscope><D:exclusive/></D:lockscope>
<D:owner>
<D:href>http://example.org/~ejw/contact.html</D:href>
</D:owner>
</D:lockinfo>
>>Response
HTTP/1.1 207 Multi-Status
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<D:multistatus xmlns:D="DAV:">
<D:response>
<D:href>/webdav/secret</D:href>
<D:status>HTTP/1.1 403 Forbidden</D:status>
</D:response>
<D:response>
<D:href>/webdav/</D:href>
<D:status>HTTP/1.1 424 Failed Dependency</D:status>
</D:response>
</D:multistatus>
This example shows a request for an exclusive write lock on a
collection and all its children. In this request, the client has
specified that it desires an infinite length lock, if available,
otherwise a timeout of 4.1 billion seconds, if available. The
request entity body contains the contact information for the
principal taking out the lock, in this case a web page URL.
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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.
5.2 Refreshing Locks
A LOCK request with no request body is a "LOCK refresh" request.
It's purpose is to restart all timers associated with a lock.
5.2.1 Marshalling
The request MUST include an "If" header that contains the lock tokens
of the locks to be refreshed (note there may be multiple in the case
of shared locks).
The request MAY include a "Timeout" header to be used as the new
timeout value for the lock(s) to be refreshed (see Section 9.2).
The request MAY include a "Depth" header specifying either "0" or
"infinity" (see [RFC2518], section 9.2) which MUST be ignored when
present.
The response to a successful lock refresh request MUST contain the
value of the current DAV:lockdiscovery property in a prop XML
element.
5.2.2 Preconditions
5.2.2.1 DAV:lock-submission-allowed precondition
See Section 8.2.1.
5.2.3 Postconditions
5.2.3.1 DAV:locks-refreshed postcondition
Timers associated with the those locks submitted in the "If" request
header whose lock root is the resource identified by the Request-URI
MUST be reset to their original value (or alternatively to the new
value given in the "Timeout" request header).
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5.2.4 Example - Refreshing a Write Lock
>>Request
LOCK /workspace/webdav/proposal.doc HTTP/1.1
Host: example.com
Timeout: Infinite, Second-4100000000
If: (<opaquelocktoken:e71d4fae-5dec-22d6-fea5-00a0c91e6be4>)
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
<?xml version="1.0" encoding="utf-8" ?>
<D:prop xmlns:D="DAV:">
<D:lockdiscovery>
<D:activelock>
<D:locktype><D:write/></D:locktype>
<D:lockscope><D:exclusive/></D:lockscope>
<D:depth>Infinity</D:depth>
<D:owner>
<D:href
>http://example.org/~ejw/contact.html</D:href>
</D:owner>
<D:timeout>Second-604800</D:timeout>
<D:locktoken>
<D:href
>opaquelocktoken:e71d4fae-5dec-22d6-fea5-00a0c91e6be4</D:href>
</D:locktoken>
<D:lockroot>
<D:href
>http://example.com/workspace/webdav/proposal.doc</D:href>
</D:lockroot>
</D:activelock>
</D:lockdiscovery>
</D:prop>
This request would refresh the lock, resetting any time outs. Notice
that the client asked for an infinite time out but the server choose
to ignore the request.
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6. UNLOCK Method
The UNLOCK method removes the lock identified by the lock token in
the Lock-Token request header from the resource identified by the
Request-URI, and all other resources included in the lock. Note that
the UNLOCK request may be submitted to any resource locked by that
lock (even those that are locked indirectly).
If all resources which have been locked under the submitted lock
token can not be unlocked then the UNLOCK request MUST fail.
Any DAV compliant resource which supports the LOCK method MUST
support the UNLOCK method.
A server MAY allow principals other than a lock owner to unlock a
resource. In this case, this capability SHOULD be under access
control (see [RFC3744], section 3.5). Note that there is a tradeoff
in allowing non-owners of a lock to unlock a resource. It can be
beneficial to allow non-lock owners to perform UNLOCK requests
because it allows the adminstrator of the server to configure the
server to grant longer lock timeouts because the administrator knows
that there is a process in place to allow users to deal with
forgotten locks left by other users. On the other hand, a
disadvantage of unlocking someone else's lock is that can create a
situation where two users are working on modifications to the same
resource at the same time which can result in a client having to
perform an merge that wasn't previously planned.
6.1 Marshalling
The request MUST include a "Lock-Token" header (see Section 9.1) that
identifies the lock to be removed.
6.2 Preconditions
6.2.1 DAV:lock-token-matches precondition
The lock identified by the "Lock-Token" request header exists, and
the resource identified by the Request-URI indeed is directly locked
by the specified lock.
6.2.2 DAV:lock-removal-allowed precondition
As dicussed above, the principal authenticated for the UNLOCK request
MUST be allowed to remove the identified lock (note that servers that
support the "WebDAV Access Control Protocol" should use the DAV:need-
privileges precondition defined in section 7.1.1 of [RFC3744]).
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6.3 Postconditions
6.3.1 DAV:lock-removed postcondition
The lock MUST have been removed from all resources included in the
lock.
6.4 Example - UNLOCK
>>Request
UNLOCK /workspace/webdav/info.doc HTTP/1.1
Host: example.com
Lock-Token: <opaquelocktoken:a515cfa4-5da4-22e1-f5b5-00a0451e6bf7>
Authorization: Digest username="ejw",
realm="ejw@example.com", nonce="...",
uri="/workspace/webdav/proposal.doc",
response="...", opaque="..."
>>Response
HTTP/1.1 204 No Content
In this example, the lock identified by the lock token
"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. Note that clients MUST interpret any of the
success status codes defined in [RFC2616], section 10.2 as success
codes. 204 (No Content) was used here merely for consistency with the
example in [RFC2518], section 8.11.1). The remainder of the document
discusses Capability Discovery, Security Considerations,
Internationalization Considerations and IANA Considerations.
Appendices discuss changes from RFC2518 (Appendix B) and the
"opaquelocktoken" URI scheme (Appendix D).
7. Additional status codes
7.1 423 Locked
The 423 (Locked) status code means the source or destination resource
of a method is locked.
8. Additional marshalling and method semantics for other methods
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8.1 Additional marshalling
This section defines additional condition names (see Section 1.2)
that apply to all methods.
8.1.1 DAV:name-allowed precondition
If a request such as COPY, LOCK, MOVE, PUT or MKCOL is going to
create a new internal member URI inside a collection resource, the
last path segment of that URI must specify a name that is available
as a resource name (for instance, servers may disallow path segments
that -- after being URI-unescaped -- aren't valid UTF-8 octet
sequences). [[anchor41: Copied from
draft-ietf-webdav-redirectref-protocol. --reschke]]
8.1.2 DAV:parent-resource-must-be-non-null precondition
If a request such as COPY, LOCK, MOVE, PUT or MKCOL is going to
create a new internal member URI inside a collection resource, that
collection resource must be non-null. [[anchor43: Copied from
draft-ietf-webdav-redirectref-protocol. --reschke]]
8.2 Additional method semantics (preconditions)
This section defines names (see Section 1.2) for new conditions
introduced by locking semantics. Otherwise noted otherwise, they
apply to all methods.
8.2.1 DAV:lock-token-submission-allowed precondition
If the server restricts usage of the lock token inside an "If"
request header to specific principals, the authenticated principal
for this request MUST be one of them.
8.2.2 DAV:need-lock-token precondition
If a request would modify the content for a locked resource, a dead
property of a locked resource, a live property that is defined to be
lockable for a locked resource, or an internal member URI of a locked
collection, the request MUST fail unless the lock-token for that lock
is submitted in the request. An internal member URI of a collection
is considered to be modified if it is added, removed, or identifies a
different resource.
<!ELEMENT need-lock-token (href)* >
Servers SHOULD insert DAV:href elements for the URLs of each root of
a lock for which a lock token was needed, unless that URL identies
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the same resource to that the request was sent.
8.2.2.1 Example
In the example below, a client unaware of a "Depth: infinity" lock on
the parent collection "/workspace/webdav/" attempts to modify the
collection member "/workspace/webdav/proposal.doc".
>>Request
PUT /workspace/webdav/proposal.doc HTTP/1.1
Host: example.com
>>Response
HTTP/1.1 423 Locked
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<D:error xmlns:D="DAV:">
<D:need-lock-token>
<D:href>/workspace/webdav/</D:href>
</D:need-lock-token>
</D:error>
8.3 Additional method semantics (postconditions)
8.3.1 DAV:lock-removed postcondition
If an operation (such as a MOVE or a DELETE request) causes a
directly locked resource to no longer be mapped to the lock-root of
that lock, that lock MUST have been deleted by that request.
8.3.1.1 Example
In this example, a client renames a collection "/workspace/webdav"
containing the locked member "/workspace/webdav/proposal.doc" (with
lock token "urn:uuid:FC28D97C-569E-411e-86BC-D30A233DD8A2").
>>Request
MOVE /workspace/webdav/ HTTP/1.1
Host: example.com
Destination: http://example.com/workspace/deltav/
If: </workspace/webdav/proposal.doc>
(<urn:uuid:FC28D97C-569E-411e-86BC-D30A233DD8A2>)
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>>Response
HTTP/1.1 201 Created
After executing the MOVE request, the member resource will now be
mapped to "/workspace/deltav/proposal.doc", but not to "/workspace/
webdav/proposal.doc" anymore. Therefore, the lock will be removed.
9. Headers
9.1 Lock-Token request/response header
Lock-Token = "Lock-Token" ":" Coded-URL
; Coded-URL: see [RFC2518], Section 9.4.
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.
Note that the "Lock-Token" request header does not contribute to the
precondition checks defined for the HTTP status 412 (see [RFC2616],
section 10.4.13).
9.2 Timeout request header
TimeOut = "Timeout" ":" 1#TimeType
TimeType = (TimeTypeSec | "Infinite" | Other)
TypeTypeSec = "Second-" 1*digit
Other = "Extend" field-value
; field-value: see [RFC2616], Section 4.2
(Linear white space (LWS) MUST NOT be used inside "TimeTypeSec".)
Clients MUST NOT submit a Timeout request header with any method
other than a LOCK method.
A Timeout request header MUST contain at least one TimeType and may
contain multiple TimeType entries. The purpose of listing multiple
TimeType entries is to indicate multiple different values and value
types that are acceptable to the client. The client lists the
TimeType entries in order of preference.
Timeout response values MUST use a Second value, Infinite, or a
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TimeType the client has indicated familiarity with. The server may
assume a client is familiar with any TimeType submitted in a Timeout
header.
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.
10. Capability discovery
10.1 OPTIONS method
If the server supports locking, it MUST return both the compliance
class names "2" and "locking" as fields in the "DAV" response header
(see [RFC2518], section 9.1) from an OPTIONS request on any resource
implemented by that server. A value of "2" or "locking" in the "DAV"
response header MUST indicate that the server meets all class "1"
requirements defined in [RFC2518] and supports all MUST level
requirements and REQUIRED features specified in this document,
including:
o LOCK and UNLOCK methods,
o DAV:lockdiscovery and DAV:supportedlock properties,
o "Time-Out" request header, "Lock-Token" request and response
header.
Note that for servers implementing this specification, the compliance
classes "2" and "locking" are synonymous. However, new clients can
take advantage of the new "locking" compliance class to detect server
support for changes introduced by this specification (see
Appendix B).
11. Security considerations
All security considerations mentioned in [RFC2518] also apply to this
document. Additionally, lock tokens introduce new privacy issues
discussed below.
11.1 Privacy Issues Connected to Locks
When submitting a lock request a user agent may also submit an owner
XML field giving contact information for the person taking out the
lock (for those cases where a person, rather than a robot, is taking
out the lock). This contact information is stored in a DAV:
lockdiscovery property on the resource, and can be used by other
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collaborators to begin negotiation over access to the resource.
However, in many cases this contact information can be very private,
and should not be widely disseminated. Servers SHOULD limit read
access to the DAV:lockdiscovery property as appropriate.
Furthermore, user agents SHOULD provide control over whether contact
information is sent at all, and if contact information is sent,
control over exactly what information is sent.
12. Internationalization Considerations
All internationalization considerations mentioned in [RFC2518] also
apply to this document.
13. IANA Considerations
This specification updates the definition of the "opaquelocktoken"
URI scheme described in Appendix D, registered my means of [RFC2518],
section 6.4. There are no additional IANA considerations.
14. Acknowledgements
This document is the collaborative product of
o the authors,
o the maintainers of RFC2518bis - Jason Crawford and Lisa Dusseault
- and
o the original authors of RFC2518 - Steve Carter, Asad Faizi, Yaron
Goland, Del Jensen and Jim Whitehead.
This document has also benefited from thoughtful discussion by Mark
Anderson, Dan Brotksy, Geoff Clemm, Jim Davis, Stefan Eissing,
Rickard Falk, Eric Glass, Stanley Guan, Larry Masinter, Joe Orton,
Juergen Pill, Elias Sinderson, Greg Stein, Kevin Wiggen, and other
members of the WebDAV working group.
15. References
15.1 Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2518] Goland, Y., Whitehead, E., Faizi, A., Carter, S., and D.
Jensen, "HTTP Extensions for Distributed Authoring --
WEBDAV", RFC 2518, February 1999.
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[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005.
[RFC4122] Leach, P., Mealling, M., and R. Salz, "A UUID URN
Namespace", RFC 4122, July 2005.
[XML] Bray, T., Paoli, J., Sperberg-McQueen, C., Maler, E., and
F. Yergeau, "Extensible Markup Language (XML) 1.0 (Third
Edition)", W3C REC-xml-20040204, February 2004,
<http://www.w3.org/TR/2004/REC-xml-20040204>.
15.2 Informative References
[RFC3744] Clemm, G., Reschke, J., Sedlar, E., and J. Whitehead, "Web
Distributed Authoring and Versioning (WebDAV) Access
Control Protocol", RFC 3744, May 2004.
Author's Address
Julian F. Reschke
greenbytes GmbH
Salzmannstrasse 152
Muenster, NW 48159
Germany
Phone: +49 251 2807760
Fax: +49 251 2807761
Email: julian.reschke@greenbytes.de
URI: http://greenbytes.de/tech/webdav/
Appendix A. Collected Locking Semantics
This section provides a complete summary of the semantics for (write)
locks.
A.1 Directly vs Indirectly
A lock either directly or indirectly locks a resource. (See
Section 2.5.4)
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A.2 Creating Locks
A LOCK request with a non-empty body creates a new lock, and the
resource identified by the Request-URI is directly locked by that
lock. The "lock-root" of the new lock is the Request-URI. If at the
time of the request, the Request-URI is not mapped to a resource, a
new resource with empty content MUST be created by the request. (See
Section 5.1)
A.3 Lock Inheritance
If a collection is directly locked by a depth:infinity lock, all
members of that collection (other than the collection itself) are
indirectly locked by that lock. In particular, if an internal member
resource is added to a collection that is locked by a depth:infinity
lock, and if the resource is not locked by that lock, then the
resource becomes indirectly locked by that lock. Conversely, if a
resource is indirectly locked with a depth:infinity lock, and if the
result of deleting an internal member URI is that the resource is no
longer a member of the collection that is directly locked by that
lock, then the resource is no longer locked by that lock. (See 2.5.4
and 3.5).
A.4 Removing Locks
An UNLOCK request deletes the lock with the specified lock token.
The Request-URI of the request MUST identify a resource that is
either directly or indirectly locked by that lock. After a lock is
deleted, no resource is locked by that lock. (See Section 6)
A.5 Submitting Lock Tokens
A lock token is "submitted" in a request when it appears in an "If"
request header. (See Section 3.4)
A.6 Locked State
If a request would modify the content for a locked resource, a dead
property of a locked resource, a live property that is defined to be
lockable for a locked resource, or an internal member URI of a locked
collection, the request MUST fail unless the lock-token for that lock
is submitted in the request. An internal member URI of a collection
is considered to be modified if it is added, removed, or identifies a
different resource. (See 3.1 and 8.2.2).
A.7 URL protection
If a request causes a directly locked resource to no longer be mapped
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to the lock-root of that lock, then the request MUST fail unless the
lock-token for that lock is submitted in the request. If the request
succeeds, then that lock MUST have been deleted by that request.
(See 3.5, 8.2.2 and 8.3.1)
A.8 Exclusive vs Shared
If a request would cause a resource to be locked by two different
exclusive locks, the request MUST fail. (See Section 2.1)
Appendix B. Changes to RFC2518
See Section 10 for a description about how clients can discover
support for this version of the WebDAV Locking protocol.
B.1 Removed/Deprecated features
B.1.1 Implicit lock refresh
In section 9.8, [RFC2518] specifies that locks should be refreshed
implicitly every time "...any time an owner of the lock sends a
method to any member of the lock, including unsupported methods, or
methods which are unsuccessful." This features has been removed
(locks need to be refreshed explicitly using the LOCK method).
Compatibility consideration: clients historically have never relied
on this feature as it was never implemented in widely deployed WebDAV
servers.
B.1.2 Lock-null resources
In section 7.4, [RFC2518] specifies a special resource type called
"lock-null resource" that's being created when a LOCK method request
is applied to a null resource. In practice, no real interoperability
was achieved because many servers failed to implement this feature
properly and few clients (if any) ever relied on that particular
functionality.
Removing this feature also means that there is no atomic way to
create a collection in locked state, but in practice, this doesn't
seem to be a problem.
Compatibility consideration: there do not seem to be any widely
deployed clients that actually relied on "lock-null resources".
B.2 Additional features
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B.2.1 DAV:lockroot element in DAV:activelock
Clients can take advantage of the new DAV:lockroot element to
discover the URL to which the LOCK request (that created the lock)
was applied.
Compatibility consideration: clients will have to fail gracefully
when communicating with older servers that do not support the new
element.
B.2.2 Error Marshalling
Clients can take advantage of additional, detailed error information
using the DAV:error element defined in Section 1.2.
Compatibility consideration: old clients should not even notice the
additional informations. New clients SHOULD handle absence of
additional error information gracefully.
Appendix C. Text to be integrated from RFC2518
C.1 HTTP Methods for Distributed Authoring
C.1.1 LOCK Method
C.1.1.1 Locking Replicated Resources
A resource may be made available through more than one URI. However
locks apply to resources, not URIs. Therefore a LOCK request on a
resource MUST NOT succeed if can not be honored by all the URIs
through which the resource is addressable.
C.2 HTTP Headers for Distributed Authoring
C.2.1 If Header
[[anchor61: Add "If" header considerations: --reschke]]
Appendix D. 'opaquelocktoken' URI Scheme
The opaquelocktoken URI scheme is designed to be unique across all
resources for all time. Due to this uniqueness quality, a client may
submit an opaque lock token in an If header on a resource other than
the one that returned it.
All resources MUST recognize the opaquelocktoken scheme and, at
minimum, recognize that the lock token does not refer to an
outstanding lock on the resource.
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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 Section 4 of [RFC4122].
OpaqueLockToken-URI = "opaquelocktoken:" UUID [path]
; UUID: see [RFC4122], Section 3.
; path: see [RFC3986], Section 3.3.
Appendix E. Change Log (to be removed by RFC Editor before publication)
E.1 Since draft-reschke-webdav-locking-00
Add and resolve issue "rfc2606-compliance". Resolve issues "extract-
locking", "updated-rfc2068", "022_COPY_OVERWRITE_LOCK_NULL",
"025_LOCK_REFRESH_BY_METHODS", "037_DEEP_LOCK_ERROR_STATUS",
"039_MISSING_LOCK_TOKEN", "040_LOCK_ISSUES_01", "040_LOCK_ISSUES_02",
"040_LOCK_ISSUES_05", "043_NULL_LOCK_SLASH_URL",
"065_UNLOCK_WHAT_URL", "077_LOCK_NULL_STATUS_CREATION",
"080_DEFER_LOCK_NULL_RESOURCES_IN_SPEC",
"089_FINDING_THE_ROOT_OF_A_DEPTH_LOCK",
"101_LOCKDISCOVERY_FORMAT_FOR_MULTIPLE_SHARED_LOCKS",
"109_HOW_TO_FIND_THE_ROOT_OF_A_LOCK" and
"111_MULTIPLE_TOKENS_PER_LOCK". Add issue "import-gulp". Start work
on moving text from RFC2518 excerpts into new sections. Define new
compliance class "locking" (similar to "bis" in RFC2518bis, but only
relevant to locking). Reformatted "GULP" into separate subsections
for easier reference.
E.2 Since draft-reschke-webdav-locking-01
Update "008_URI_URL", "040_LOCK_ISSUES_06",
"063_LOCKS_SHOULD_THEY_USE_AN_IF_HEADER_TO_VERIFY",
"067_UNLOCK_NEEDS_IF_HEADER", "068_UNLOCK_WITHOUT_GOOD_TOKEN". Re-
opened "065_UNLOCK_WHAT_URL". Close
"070_LOCK_RENEWAL_SHOULD_NOT_USE_IF_HEADER". Rewrite UNLOCK and LOCK
refresh method descriptions. Fix page title (TXT version). Close
"052_LOCK_BODY_SHOULD_BE_MUST", "054_IF_AND_AUTH",
"060_LOCK_REFRESH_BODY" and "079_UNLOCK_BY_NON_LOCK_OWNER". Add and
resolve "8.10.1_lockdiscovery_on_failure". Started attempt to
clarify status code.
E.3 Since draft-reschke-webdav-locking-02
Resolve issues "040_LOCK_ISSUES_03", "040_LOCK_ISSUES_04",
"040_LOCK_ISSUES_08" "053_LOCK_INHERITANCE", "057_LOCK_SEMANTICS",
"067_UNLOCK_NEEDS_IF_HEADER" and "068_UNLOCK_WITHOUT_GOOD_TOKEN".
Resolve issue "065_UNLOCK_WHAT_URL"; update to new GULP version
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(5.7). Add and resolve new issue "7.5_DELETE_vs_URIs". Start work
on "additional marshalling" and "introduction". Update issues
"044_REPORT_OTHER_RESOURCE_LOCKED" and
"066_MUST_AN_IF_HEADER_CHECK_THE_ROOT_OF_URL".
E.4 Since draft-reschke-webdav-locking-03
Close issues "import-rfc3253-stuff", "008_URI_URL",
"015_MOVE_SECTION_6.4.1_TO_APPX", "044_REPORT_OTHER_RESOURCE_LOCKED",
"056_DEPTH_LOCK_AND_IF" and "072_LOCK_URL_WITH_NO_PARENT_COLLECTION".
Reformat condition name descriptions. Add mention of condition
failure signalling to "Changes" appendix. Start edit of header
descriptions (Depth, Timeout) and LOCK creation description. Open
and close issue "3.2_lockdiscovery_depth". Start work on intro.
E.5 Since draft-reschke-webdav-locking-04
Add description of the lock as a resource and it's state (merging in
Timeout semantics from old headers section). Close issues
"040_LOCK_ISSUES_06",
"063_LOCKS_SHOULD_THEY_USE_AN_IF_HEADER_TO_VERIFY" and
"088_DAVOWNER_FIELD_IS_CLIENT_CONTROLED". Move edited version of
"Write Lock" chapter.
E.6 Since draft-reschke-webdav-locking-05
Add and close issues "rfc2396bis" and "5.2.1-
depth_header_vs_lock_refresh". Fixed DAV:lockdiscovery example.
E.7 Since draft-reschke-webdav-locking-06
Add and resolve issues "uri_draft_ref", "abnf",
"D_delegate_UUID_definition" and "lock_state_auth_principal".
E.8 Since draft-reschke-webdav-locking-07
Editorial fixes (whitespace, duplicate DTD fragment, Document
Organization section). Resolve issue "import_gulp": keep the
semantics summary as normative appendix, also make it the first one
(no change tracking for the move). Add "lock-removed" postcondition.
Update urn:uuid reference.
Appendix F. Resolved issues (to be removed by RFC Editor before
publication)
Issues that were either rejected or resolved in this version of this
document.
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F.1 import-gulp
Type: change
julian.reschke@greenbytes.de (2004-05-25): Make specification text
compatible with GULP where it isn't. Integrate GULP as normative
specification of the locking behaviour.
Resolution (2005-05-16): Integrate GULP as is, let remaining text
refer to it where appropriate. Also add pointers from GULP back into
the main document. Rename section to "Collected Method Semantics.
Appendix G. Open issues (to be removed by RFC Editor prior to
publication)
G.1 edit
Type: edit
julian.reschke@greenbytes.de (2004-05-25): Umbrella issue for
editorial fixes/enhancements.
G.2 safeness_and_idempotence
Type: edit
julian.reschke@greenbytes.de (2005-03-02): Specify safeness and
idempotence of LOCK and UNLOCK methods.
G.3 099_COPYMOVE_LOCKED_STATUS_CODE_CLARIFICATION
Type: change
<http://lists.w3.org/Archives/Public/w3c-dist-auth/2002AprJun/
0079.html>
ccjason@us.ibm.com (): What resource should be flagged in the
multistatus response to locking issues in COPY/MOVE requests?
Resolution: Resolved to flag the locking errors at the source
resource that was affected by the problem. The details of how to
describe the error was deferred to a subsequent version of WebDAV. -
6/15/02 - 2518bis does not reflect this.
G.4 100_COPYMOVE_LOCKED_STATUS_DESCRIPTION
Type: change
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<http://lists.w3.org/Archives/Public/w3c-dist-auth/2002AprJun/
0079.html>
(): The method of describing the details of (beyond what resolved by
COPYMOVE_LOCKED_STATUS_CODE_CLARIFICATION) of the underlying cause of
various locking and ACL COPY/MOVE problems is deferred. Two
proposals were outlined in the discussion, but interest was not great
and we clearly don't have interoperability to take these proposals
forward.
G.5 066_MUST_AN_IF_HEADER_CHECK_THE_ROOT_OF_URL
Type: change
(): Right now the server uses the IF: header to verify that a client
knows what locks it has that are affected by an operation before it
allows the operation. Must the client provide the root URL of a
lock, any URL for a pertainent loc, or some specific URL in the IF:
header.
ccjason@us.ibm.com (): It is felt by the group that it's important
that the client not just own and hold the lock token, but that it
also know where the lock is rooted before it does tasks related to
that lock. This is just a point of info. The issue itself still
needs to be brought up and answered.still
julian.reschke@greenbytes.de (): Summary: current implementations do
not seem to care (see http://lists.w3.org/Archives/Public/
w3c-dist-auth/2004AprJun/0190.html). Suggestion to require clients
to specify the lock root anyway, because this is what the WG agreed
upon earlier.
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Index
4
423 Locked (status code) 27
C
Condition Names
DAV:create-lock (post) 20
DAV:create-resource (post) 20
DAV:lock-removal-allowed (pre) 26
DAV:lock-removed (post) 27, 29
DAV:lock-submission-allowed (pre) 24
DAV:lock-token-matches (pre) 26
DAV:lock-token-submission-allowed (pre) 28
DAV:locks-refreshed (post) 24
DAV:name-allowed (pre) 28
DAV:need-lock-token (pre) 28
DAV:parent-resource-must-be-non-null (pre) 28
D
DAV header
compliance class '2' 31
compliance class 'locking' 31
DAV:create-lock postcondition 20
DAV:create-resource postcondition 20
DAV:lock-removal-allowed precondition 26
DAV:lock-removed postcondition 27, 29
DAV:lock-submission-allowed precondition 24
DAV:lock-token-matches precondition 26
DAV:lock-token-submission-allowed precondition 28
DAV:lockdiscovery property 16
DAV:locks-refreshed postcondition 24
DAV:name-allowed precondition 28
DAV:need-lock-token precondition 28
DAV:parent-resource-must-be-non-null precondition 28
DAV:supportedlock property 18
H
Headers
Lock-Token 30
Timeout 30
L
LOCK method 19
lock creation 19
lock refresh 24
Lock-Token header 30
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M
Methods
LOCK (lock creation) 19
LOCK (lock refresh) 24
LOCK 19
UNLOCK 26
O
opaquelocktoken (URI scheme) 36
P
Properties
DAV:lockdiscovery 16
DAV:supportedlock 18
S
Status Codes
423 Locked 27
T
Timeout header 30
U
UNLOCK method 26
URI schemes
opaquelocktoken 36
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