Web Distributed Authoring and Versioning (WebDAV) Locking Protocolgreenbytes GmbHSalzmannstrasse 152MuensterNW48159Germany+49 251 2807760+49 251 2807761julian.reschke@greenbytes.dehttp://greenbytes.de/tech/webdav/
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.
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.
This version of this document doesn't yet contain any new or
rewritten text - it only contains text copied verbatim fro RFC2518
and GULP. It's sole purpose is be a reference point for
all future changes.
Distribution of this document is unlimited. Please send comments to the
WebDAV working group at w3c-dist-auth@w3.org, which may be joined by sending a message with subject
"subscribe" to w3c-dist-auth-request@w3.org.
Discussions of the WEBDAV working group are archived at URL:
http://lists.w3.org/Archives/Public/w3c-dist-auth/.
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.
This version of this document doesn't yet contain any new or
rewritten text - it only contains text copied verbatim fro RFC2518
and GULP. It's sole purpose is be a reference point for
all future changes.
Distribution of this document is unlimited. Please send comments to the
WebDAV working group at w3c-dist-auth@w3.org, which may be joined by sending a message with subject
"subscribe" to w3c-dist-auth-request@w3.org.
Discussions of the WEBDAV working group are archived at URL:
http://lists.w3.org/Archives/Public/w3c-dist-auth/.
Locking extracted from RFC2518.
Finished as of draft 00.
Update references of RFC2068 to either RFC2396 or RFC2616.
Done.
Import error marshalling and terminology from RFC3253.
Make specification text compatible with GULP where it isn't. Integrate
GULP as normative specification of the locking behaviour.
Umbrella issue for editorial fixes/enhancements.
Perform a thorough review of the specification to ensure that URI and URL are used correctly, and consistently throughout.
Seems to have been deferred: http://lists.w3.org/Archives/Public/w3c-dist-auth/2002AprJun/0216.html,
but there is some follow on discussion on what exactly needs to be clarified:
http://lists.w3.org/Archives/Public/w3c-dist-auth/2002JulSep/0068.html,
but no specific action was concluded besides the fact that we don't need to wait for RFC2396 to be updated or request any changes/clarifications to that.
Upon cursory reading of the rfc 2518 sec 8.10.4 through 8.11 I was confused by
the plethoria of error codes. Nothing seems to unify them.
8.10.4 speaks of a return code of 409 Conflict if a lock can't be granted.
- Firstly, I can't tell if it is saying that the 409 is within the multistatus
body... or in the response header.
- Secondly, later text seems to use a different status codes and never
mentions this one again.
8.10.7 lists status codes
- 200 OK, 412 Precondition Failed, and 423 Locked are listed, but 409 Conflict
(mentioned above) is not.
- In the case of 412 Precondition Failed, the description the follows doesn't
seem to describe a "precondition failed". And it sounds like it's talking about
an access request that includes a "locktoken", not a LOCK request that generates
one.
- The 423 Locked condition also sort of sounds like it's talking about an
access request rather than a LOCK request.
8.10.10 lists LOCK status codes
- 207 Multistatus which was not mentioned above
- 403 Forbidden which was not mentioned above.
- 424 Failed dependency which was not mentioned above.
8.11 UNLOCK
- we don't mention what the failure response should look like.
- comment: 200 OK seems like a better response than 204 No Content. The
brief explanation isn't persuasive and seems to say that the response code
should serve the purpose of the Content-Length. header.
- we should probably explicitly say if an UNLOCK can only be done on the
original resource... and will fail even if the resource specified is locked by
virtue of being a child of the original resource. Or is this too obvious? I
know it's something easy to goof up in an implementation.
9.4 If header
- BNF suggests that IF's content must be all tagged or all untagged.
- doesn't say if there can be two If headers in a request. Might we want a
tagged one and an untagged one?
- I must be misunderstanding this, but it sounds to me like that state of a
resource(s) must match one of the locktokens listed in the request. But what if
some of the resources are locked and others are not. The unlocked resources
definitely won't contain state that's listed. Are we precluding operations on
regions that might not be entirely locked? -- Is this a valid observation or a
red herring?
9.4.1.1 If header - untagged example
- See my comment about regions that are not entirely locked.
9.4.2 If header -tagged state
- So if we've applied a lock with depth.... and now we're doing a DELETE on a
subtree of that tree and we've tagged the locktoken we've submitted, will this
prevent that locktoken from apply'ing to ALL the resources of the subtree... and
thus prevent the COPY from succeeding? Or are we supposed to tag the lock token
with the root of the LOCK even if that is not part of what we are deleting? Or
should the request use untagged locktokens?
9.4.3 If header - NOT operator
- Why do we want this? of course... why not? :-)
Overall, the If header seems backwards for locktokens. It's client driven
rather than server semantics driven. The only feature it seems to provide is
perhaps the ability for the client to request that the request be aborted if the
resource no longer is locked. Other than that it seems to complicate the simple
process of letting the server know what tokens you hold. I'd think we'd just
want a different header to declare what lock tokens we hold and let the server
(not the client) decide how they affect the success of the request.
This issue needs to be handled in the base protocol.
In some cases, such as when the parent collection of a resource is locked, a 423 (Locked) status code is returned even though the resource identified by the Request-URI is not locked. This can be confusing, since it is not possible for a client to easily discover which resource is causing the locked status code to be returned. An improved status report would indicate the resource causing the lock message.
Proposal to define a specific precondition element plus specific
child elements similar to RFC3744, section 7.1.1.
Section 8.10.1 states that a LOCK method request SHOULD have an XML request body. This SHOULD should instead be MUST.
Clarify that for creating LOCKs, it MUST have a request body which
SHOULD have the DAV:owner element. For LOCK refreshes, no body is
required.
The fact that use of authentication credentials with submission of lock
tokens is required should be strengthened in the document.
Submitting the lock token in an If header (usages != UNLOCK) SHOULD be
restricted to whatever the server thinks the "owner" of the lock is.
The specification is currently silent on how to use the If header for
submitting a locktoken when performing a DELETE in a Depth infinity locked
collection. Should the If header have both the collection URL and the
Request-URI, or just the Request-URI? An example of this is needed.
Clarify as part of integrating GULP. May need to test interop with existing
implementations.
At present, the WebDAV specification is not excruciatingly explicit that
writing to a locked resource requires the combination of the lock token,
plus an authentication principal. At one point, the spec. discusses an
"authorized" principal, but "authorized" is never explicitly defined.
Submitting the lock token in an If header (usages != UNLOCK) SHOULD be
restricted to whatever the server thinks the "owner" of the lock is.
Is the complexity of the IF header appropriate for the simple task o
verifying that a client knowingly owns a lock? The IF header seems to
serve a different purpose. One of those purposes is for the server to
verify that you have the lock token (and that you know the root of it?).
Another is for the client to check some preconditions before doing an
action. Another seems to be to specify what lock to refresh in a lock
refresh request. This seems to create ambiguity in our definition of the
semantics of the IF: header.
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 still leaves the lock
referesh issue unresolved.
Need Lock-Token header to indicate the lock to be refreshed.
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.
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
Shouldn't we be using an IF header to do an UNLOCK seeing as you need to
prove you are holding a lock before you can remove it? (This might be
contingent on 063_LOCKS_SHOULD_THEY_USE_AN_IF_HEADER_TO_VERIFY)
What should UNLOCK return if a bad token is provided or no token.
(This might be contingent on UNLOCK_NEEDS_IF_HEADER.)
The LOCK renewal request should not us an IF header to specify what lock is
being renewed. This limits the use of the IF header.
Need Lock-Token header to indicate the lock to be refreshed.
If a LOCK request is submitted to a URL that doesn't have a parent collection, what should be the correct response? Other methods, PUT, MKCOL, COPY, MOVE all require a 409 response in this case. Seems like LOCK should have this requirement as well.
Resolved that since LNRs no longer exist (see NULL_RESOURCE_CLARIFY) the
server should return 409. We should insure that the new text we add to
replace LNRs does not create an ambiguity: http://lists.w3.org/Archives/Public/w3c-dist-auth/2002JanMar/0164.html
At present, the specification is not explicit about who might be capable of
grabbing a lock token via lock discovery and the submitting it in UNLOCK
(and/or for a subsequent write operation). It is OK for the resource owner
to grab the lock token and do UNLOCK/write? Is it OK to have a "grab lock
token" privilege that can be assigned to anyone?
Resolved in part by putting it under ACL control:
http://lists.w3.org/Archives/Public/w3c-dist-auth/2002JanMar/0002.html
and the response that follows it.
The DAV:owner field of a lock is controlled by the locking client and should
not be manipulated by the server. This is the only place the client can
store info. The roundtrip details should match what we resolve for the
PROP_ROUNDTRIP issue. Examples should also be checked.
Resolved by repeated statement and no disagreement.
What resource should be flagged in the multistatus response to locking issues in COPY/MOVE requests?
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.
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.
Ensure that examples use only sample domains as per RFC2606.
Done.
The terminology used here follows and extends that in the WebDAV Distributed
Authoring Protocol specification .
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 .
This document uses XML DTD fragments
() as a purely notational convention.
WebDAV request and response bodies cannot be validated due to the specific
extensibility rules defined in section 23 of and due to the fact
that all XML elements defined by this specification use the XML namespace
name "DAV:". In particular:
Element names use the "DAV:" namespace.Element ordering is irrelevant.Extension elements/attributes (elements/attributes not already defined
as valid child elements) may be added anywhere, except when explicitly
stated otherwise.
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 the specific condition does not define a more specific
HTTP status code, 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.
The locking feature introduces the following properties for a resource.
At present, this specification only defines one lock type, the write lock.
If the DAV:lockdiscovery property is requested from an unlocked resource,
what is the correct response? Apache mod_dav responds with an empty mod_dav
sends an empty lockdiscovery element (<D:lockdiscovery/>) while IIS sends
an empty prop element (<D:prop/>), that is, it sends no lockdiscovery
element at all.
The difference shouldn't matter for clients, and they need to expect both.
In general, servers that DO support locks on that resource should return
an empty element.
Added example.
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.
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 themselves controlled by access controls so a server is
not required to provide information the client is not authorized to
see.
The 423 (Locked) status code means the source or destination resource
of a method is locked.
If the server supports locking, it MUST return both the compliance class names
"2" and "locking" as fields in the "DAV" response header (see ,
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
and supports all MUST level requirements and REQUIRED features
specified in this document, including:
LOCK and UNLOCK methods,DAV:lockdiscovery and DAV:supportedlock properties,"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 ).
All security considerations mentioned in also apply to
this document. Additionally, lock tokens introduce new privacy issues
discussed below.
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 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.
All internationalization considerations mentioned in also apply to
this document.
All IANA considerations mentioned in also apply to this document.
This specification updates the definition of the "opaquelocktoken" URI scheme
described in , registered
my means of , section 6.4. There are no additional
IANA considerations.
This document is the collaborative product of
the authors,the maintainers of the RFC2518bis - Jason Crawford and Lisa Dusseault - andthe 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, Larry Masinter,
Joe Orton, Juergen Pill, Elias Sinderson, Greg Stein, Kevin Wiggen,
and other members of the WebDAV working group.
Key words for use in RFCs to Indicate Requirement LevelsHarvard Universitysob@harvard.eduUniform Resource Identifiers (URI): Generic SyntaxWorld Wide Web Consortiumtimbl@w3.orgDepartment of Information and Computer Sciencefielding@ics.uci.eduXerox PARCmasinter@parc.xerox.comHTTP Extensions for Distributed Authoring -- WEBDAVMicrosoft Corporationyarong@microsoft.comDept. Of Information and Computer Science, University of California, Irvineejw@ics.uci.eduNetscapeasad@netscape.comNovellsrcarter@novell.comNovelldcjensen@novell.comHypertext Transfer Protocol -- HTTP/1.1University of Californiafielding@ics.uci.eduMIT Laboratory for Computer Sciencejg@w3.orgDigital Equipment Corporationmogul@wrl.dec.comW3 Consortiumfrystyk@w3.orgW3 Consortiumtimbl@w3.orgHypertext Transfer Protocol -- HTTP/1.1University of California, Irvinefielding@ics.uci.eduW3Cjg@w3.orgCompaq Computer Corporationmogul@wrl.dec.comMIT Laboratory for Computer Sciencefrystyk@w3.orgXerox Corporationmasinter@parc.xerox.comMicrosoft Corporationpaulle@microsoft.comW3Ctimbl@w3.orgISO/IEC 11578:1996. Information technology - Open
Systems Interconnection - Remote Procedure Call
(RPC)International Organization for Standardizationhttp://www.iso.chExtensible Markup Language (XML) 1.0 (Third Edition)Textuality and Netscapetbray@textuality.comMicrosoftjeanpa@microsoft.comUniversity of Illinois at Chicago and Text Encoding Initiativecmsmcq@uic.eduSun Microsystemseve.maler@east.sun.comfrancois@yergeau.com
See for a description about how clients
can discover support for this version of the WebDAV Locking protocol.
In section 9.8, 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 considerations
Clients historically have never relied on this feature as it was never
implemented in widely deployed WebDAV servers.
In section 7.4, 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 considerations
There do not seem to be any widely deployed clients that actually relied
on "lock-null resources".
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.
Compatiblity consideration
Clients will have to fail gracefully when communicating with older servers
that do not support the new property.
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.
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.
Shared locks... read locks...
Our justifcation for shared locks ("Shared locks are included because....")
seems faulty. It's not a mechansim for dealing with programs that forget to
release their locks. That remains a problem with shared locks. In this case
they'd forget to release a shared lock and block exclusive lock users. Timeouts
and administrative action are the solutions to this problem... not shared locks.
BTW, I'd think that the use of exclusive locks is just fine. I do have a
problem with shared locks though... or at least shared write locks. Although
they were relatively easy to define, I see them as solving a red herring problem
of multiple entites cooperatively writing using distinct locks. I say it's a
red herring because they don't know each other well enough to use the same lock
but they do know each other well enough to not step on each other. This seems
unlikely. As does the managing a compatibility matrix and getting all the
entities to abide by it.
OTOH I see another more common problem that is being overlooked. I see a class
of folks whose purpose is to not actually write to a (set of) resource(s), but
to simply prevent others from writing to it while they are looking at it.
Shared write locks do not necessarily do that because with a shared write lock.
someone else could grab a shared lock and go ahead and write. The only way to
block that is to get an exclusive write lock. But doing that prevents anyone
else from doing what you're doing despite it being pretty benign.
An expedient solution is to say that a shared write lock should not necessarily
give one the right to modify a resource. All it should do is prevent others
from writing. And then the purpose of an exclusive write lock is just to insure
that others can't get a lock and block you from writing. Now is this the
right solution? Probably not. There probably should be something called a
read lock that actually prevents writes as a side effect.... and would tend to
get used in shared mode.
Anyway, as it is, I think the shared write locks are a red herring and we're
missing something we are more likely to need... shared read locks.
Agreement that the rational for shared locks either needs to be rewritten
or deleted. However shared locks are a fact, and we shouldn't change the
semantics given in RFC2518.
The most basic form of lock is an exclusive lock. This is a lock
where the access right in question is only granted to a single
principal. The need for this arbitration results from a desire to
avoid having to merge results.
However, there are times when the goal of a lock is not to exclude
others from exercising an access right but rather to provide a
mechanism for principals to indicate that they intend to exercise
their access rights. Shared locks are provided for this case. A
shared lock allows multiple principals to receive a lock. Hence any
principal with appropriate access can get the lock.
With shared locks there are two trust sets that affect a resource.
The first trust set is created by access permissions. Principals who
are trusted, for example, may have permission to write to the
resource. Among those who have access permission to write to the
resource, the set of principals who have taken out a shared lock also
must trust each other, creating a (typically) smaller trust set
within the access permission write set.
Starting with every possible principal on the Internet, in most
situations the vast majority of these principals will not have write
access to a given resource. Of the small number who do have write
access, some principals may decide to guarantee their edits are free
from overwrite conflicts by using exclusive write locks. Others may
decide they trust their collaborators will not overwrite their work
(the potential set of collaborators being the set of principals who
have write permission) and use a shared lock, which informs their
collaborators that a principal may be working on the resource.
The WebDAV extensions to HTTP do not need to provide all of the
communications paths necessary for principals to coordinate their
activities. When using shared locks, principals may use any out of
band communication channel to coordinate their work (e.g., face-to-face
interaction, written notes, post-it notes on the screen,
telephone conversation, Email, etc.) The intent of a shared lock is
to let collaborators know who else may be working on a resource.
Shared locks are included because experience from web distributed
authoring systems has indicated that exclusive locks are often too
rigid. An exclusive lock is used to enforce a particular editing
process: take out an exclusive lock, read the resource, perform
edits, write the resource, release the lock. This editing process
has the problem that locks are not always properly released, for
example when a program crashes, or when a lock owner leaves without
unlocking a resource. While both timeouts and administrative action
can be used to remove an offending lock, neither mechanism may be
available when needed; the timeout may be long or the administrator
may not be available.
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.
A lock token is a type of state token, represented as a URI, which
identifies a particular lock. A lock token is returned by every
successful LOCK operation in the DAV:lockdiscovery property in the
response body, and can also be found through lock discovery on a
resource.
Lock token URIs MUST be unique across all resources for all time.
This uniqueness constraint allows lock tokens to be submitted across
resources and servers without fear of confusion.
Section 6.3: "... However resource are free to return any URI scheme so long
as it meets the uniqueness requirements."
This is technically correct, but it might also be useful to say that the scheme
should make the URI be readily recognizable as a *LOCK* state token in the
event that other types of state tokens exist. I mention this because we seem to
have created the possibility of other types of state tokens. -- Your call. :-)
Disagreement: any URI scheme can be used as a lock token. Specifications that
define other types of state tokens will have to take care of distinguishing
them inside an "If" header.
No change.
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.
Section 6.3: ""Having a lock token provides no special access rights..."
I suggest that the phrase "owned by another party" be added in this first
sentence to distinguish between owning and having. It speaks of "having" in
this sentence but not subsequently. In fact "submitting" might be an even
better word than having.
Agreed, use "submitting".
HavingSubmitting 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.
The opaquelocktoken URI scheme is designed to be unique across all
resources for all time. Due to this uniqueness quality, a client may
submit an opaque lock token in an If header on a resource other than
the one that returned it.
All resources MUST recognize the opaquelocktoken scheme and, at
minimum, recognize that the lock token does not refer to an
outstanding lock on the resource.
In order to guarantee uniqueness across all resources for all time
the opaquelocktoken requires the use of the Universal Unique
Identifier (UUID) mechanism, as described in .
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
. Note that white space (LWS) is not allowed between
elements of this production.
Extension = path ; path is defined in section 3.2.1 of RFC 2068
, section 3.3.
UUIDs, as defined in , contain a "node" field that
contains one of the IEEE 802 addresses for the server machine. As
noted in , 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 usethe size of main memory in bytesthe amount of free main memory in bytesthe size of the paging or swap file in bytesfree bytes of paging or swap filethe total size of user virtual address space in bytesthe total available user address space bytesthe size of boot disk drive in bytesthe free disk space on boot drive in bytesthe current timethe amount of time since the system bootedthe individual sizes of files in various system directoriesthe creation, last read, and modification times of files in
various system directoriesthe utilization factors of various system resources (heap, etc.)current mouse cursor positioncurrent caret positioncurrent number of running processes, threadshandles or IDs of the desktop window and the active windowthe value of stack pointer of the callerthe process and thread ID of callervarious processor architecture specific performance counters
(instructions executed, cache misses, TLB misses)
(Note that it is precisely the above kinds of sources of randomness
that are used to seed cryptographic quality random number generators
on systems without special hardware for their construction.)
In addition, items such as the computer's name and the name of the
operating system, while not strictly speaking random, will help
differentiate the results from those obtained by other systems.
The exact algorithm to generate a node ID using these data is system
specific, because both the data available and the functions to obtain
them are often very system specific. However, assuming that one can
concatenate all the values from the randomness sources into a buffer,
and that a cryptographic hash function such as MD5 is available, then
any 6 bytes of the MD5 hash of the buffer, with the multicast bit
(the high bit of the first byte) set will be an appropriately random
node ID.
Other hash functions, such as SHA-1, can also be used. The only
requirement is that the result be suitably random _ in the sense that
the outputs from a set uniformly distributed inputs are themselves
uniformly distributed, and that a single bit change in the input can
be expected to cause half of the output bits to change.
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.
Any DAV compliant resource that supports the LOCK method MUST support
the DAV:supportedlock property.
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.
Any DAV compliant resource that supports the LOCK method MUST support
the DAV:lockdiscovery property.
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.
Two clients A and B are interested in editing the resource 'index.html'.
Client A is an HTTP client rather than a WebDAV client,
and so does not know how to perform locking.
Client A doesn't lock the document, but does a GET and begins
editing.
Client B does LOCK, performs a GET and begins editing.
Client B finishes editing, performs a PUT, then an UNLOCK.
Client A performs a PUT, overwriting and losing all of B's changes.
There are several reasons why the WebDAV protocol itself cannot
prevent this situation. First, it cannot force all clients to use
locking because it must be compatible with HTTP clients that do not
comprehend locking. Second, it cannot require servers to support
locking because of the variety of repository implementations, some of
which rely on reservations and merging rather than on locking.
Finally, being stateless, it cannot enforce a sequence of operations
like LOCK / GET / PUT / UNLOCK.
WebDAV servers that support locking can reduce the likelihood that
clients will accidentally overwrite each other's changes by requiring
clients to lock resources before modifying them. Such servers would
effectively prevent HTTP 1.0 and HTTP 1.1 clients from modifying
resources.
WebDAV clients can be good citizens by using a lock / retrieve /
write /unlock sequence of operations (at least by default) whenever
they interact with a WebDAV server that supports locking.
HTTP 1.1 clients can be good citizens, avoiding overwriting other
clients' changes, by using entity tags in If-Match headers with any
requests that would modify resources.
Information managers may attempt to prevent overwrites by
implementing client-side procedures requiring locking before
modifying WebDAV resources.
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.
Section 7.1 Write lock.
I believe this definition of a write lock is not right... or not complete...
judging from what I read elsewhere. I believe one can do these operations
without a write lock... as long as someone else doesn't have a write lock on the
resources effected. I also believe it doesn't prevent LOCK requests in the case of shared locks.
Clarify as part of rewriting the general semantics. The point about shared locks
is correct, though.
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.
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.
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.
If URL Ub is locked, creating a lock-null resource, then if a COPY is performed listing Ub as the destination, COPY will remove the lock-null resource, removing the lock, then perform the copy. A note needs to be added stating that the delete performed by the Overwrite header is atomic with the rest of the operation.
See 080_DEFER_LOCK_NULL_RESOURCES_IN_SPEC
If a URL ending in a slash is null locked, is it legal to do a PUT to it? That is, does the URL ending in slash set the resource type to a collection, or does the first PUT/MKCOL set the resource to a ordinary, or collection resource.
See 080_DEFER_LOCK_NULL_RESOURCES_IN_SPEC
What status code should be returned when a lock null resource is created -
200 OK or 201 Created? A related issue is what status code should be
returned by a PUT or MKCOL on a lock-null resource? MKCOL is defined to be
201, PUT could be 200 or 201 (201 seems like a slightly better choice).
Resolved via the proposal to remove LNR and replace them with ordinary
resources and by the following wording: http://lists.w3.org/Archives/Public/w3c-dist-auth/2001JulSep/0129.html.
See 080_DEFER_LOCK_NULL_RESOURCES_IN_SPEC
Proposal to remove lock null resources from the spec until we are motivated
to have them or something equivalent. In the meantime, keep the spec silent
on the topic in order to avoid precluding LNR or the equivalent in a future
version of WebDAV.
LNRs removed. See discussions preceding conclusion:
http://lists.w3.org/Archives/Public/w3c-dist-auth/2001JulSep/0128.html and
http://lists.w3.org/Archives/Public/w3c-dist-auth/2001JulSep/0107.html.
Closes 022_COPY_OVERWRITE_LOCK_NULL,
043_NULL_LOCK_SLASH_URL,
077_LOCK_NULL_STATUS_CREATION.
It is possible to assert a write lock on a null resource in order to
lock the name.
A write locked null resource, referred to as a lock-null resource,
MUST respond with a 404 (Not Found) or 405 (Method Not Allowed) to
any HTTP/1.1 or DAV methods except for PUT, MKCOL, OPTIONS, PROPFIND,
LOCK, and UNLOCK. A lock-null resource MUST appear as a member of
its parent collection. Additionally the lock-null resource MUST have
defined on it all mandatory DAV properties. Most of these
properties, such as all the get* properties, will have no value as a
lock-null resource does not support the GET method. Lock-Null
resources MUST have defined values for lockdiscovery and
supportedlock properties.
Until a method such as PUT or MKCOL is successfully executed on the
lock-null resource the resource MUST stay in the lock-null state.
However, once a PUT or MKCOL is successfully executed on a lock-null
resource the resource ceases to be in the lock-null state.
If the resource is unlocked, for any reason, without a PUT, MKCOL, or
similar method having been successfully executed upon it then the
resource MUST return to the null state.
A write lock on a collection, whether created by a "Depth: 0" or
"Depth: infinity" lock request, prevents the addition or removal of
member URIs of the collection by non-lock owners. As a consequence,
when a principal issues a PUT or POST request to create a new
resource under a URI which needs to be an internal member of a write
locked collection to maintain HTTP namespace consistency, or issues a
DELETE to remove a resource which has a URI which is an existing
internal member URI of a write locked collection, this request MUST
fail if the principal does not have a write lock on the collection.
Section 7.5 Write Locks and Collections.
It says that if members are locked in a conflicting manner, then their
collection can't be locked. That seems ambiguously safe to say, but I suspect
that text should mention depth since if the parent lock request is depth 0, I
don't think we let the members lock state effect the success of the LOCK
request. The possible exception is what we said about protecting a URI that was
used to perform a lock (of a member of the collection). I'm not sure what we'd
like to say for that. In the advanced collection meetings we refered to these
being "protected" and avoided speaking about "lock"ing the URI. This creates an
odd situation though.
Clarify that this only applies to the attempt to depth-infinity lock
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.
Section 7.5
states, "If a lock owner causes the URI of a resource to be added as an
internal member URI of a locked collection then the new resource MUST be
automatically added to the lock." However, though this is the intent, the
specification does not explicitly state that this behavior only applies to
depth infinity locked collections. The words "Depth infinity" should be
added before the word "locked" in this sentence.
Clarify as part of integrating GULP.
If a lock owner causes the URI of a resource to be added as an
internal member URI of a locked collection then the new resource MUST
be automatically added to the lock. This is the only mechanism that
allows a resource to be added to a write lock. Thus, for example, if
the collection /a/b/ is write locked and the resource /c is moved to
/a/b/c then resource /a/b/c will be added to the write lock.
If a user agent is not required to have knowledge about a lock when
requesting an operation on a locked resource, the following scenario
might occur. Program A, run by User A, takes out a write lock on a
resource. Program B, also run by User A, has no knowledge of the
lock taken out by Program A, yet performs a PUT to the locked
resource. In this scenario, the PUT succeeds because locks are
associated with a principal, not a program, and thus program B,
because it is acting with principal A's credential, is allowed to
perform the PUT. However, had program B known about the lock, it
would not have overwritten the resource, preferring instead to
present a dialog box describing the conflict to the user. Due to
this scenario, a mechanism is needed to prevent different programs
from accidentally ignoring locks taken out by other programs with the
same authorization.
In order to prevent these collisions a lock token MUST be submitted
by an authorized principal in the If header for all locked resources
that a method may interact with or the method MUST fail. For
example, if a resource is to be moved and both the source and
destination are locked then two lock tokens must be submitted, one
for the source and the other for the destination.
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
It says that a lock doesn't move with a moved resource. Of course if the lock
is on the resource, not the URI, it should move with the resource. But then we
have the caveat that we are also protecting the LOCK'd URI. I think the rule
should be that if we submit the locktoken with the MOVE request, we are allowed
to have the LOCK move with the resource and the lock will now protect a
different URI. Also, ALL locks in the subtree must be submitted or the MOVE
must fail because otherwise it would break our URI protection rule.
No change: LOCKs are lost then the locked resource is moved. Will also
be clearer once GULP is incorporated.
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
. 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 , an If
header must be submitted containing a lock token for both the source
and destination.
A client MUST NOT submit the same write lock request twice. Note
that a client is always aware it is resubmitting the same lock
request because it must include the lock token in the If header in
order to make the request for a resource that is already locked.
Section 7.8
of RFC 2518 indicates that clients may submit a lock refresh without a body.
However, it implies that clients could submit a lock refresh with a body.
Server implementations have been disallowing a lock refresh with a body. It
might make sense to codify this practice, and disallow submission of a body
on a lock refresh.
Clarify that LOCK refresh MUST NOT have a request body. Also clarify
Lock-Token header vs If header.
However, a client may submit a LOCK method with an If header but
without a body. This form of LOCK MUST only be used to "refresh" a
lock. Meaning, at minimum, that any timers associated with the lock
MUST be re-set.
A server may return a Timeout header with a lock refresh that is
different than the Timeout header returned when the lock was
originally requested. Additionally clients may submit Timeout
headers of arbitrary value with their lock refresh requests.
Servers, as always, may ignore Timeout headers submitted by the
client.
If an error is received in response to a refresh LOCK request the
client SHOULD assume that the lock was not refreshed.
The following sections describe the LOCK method, which is used to
take out a lock of any access type. 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.
Make sure updated method description discusses
applying LOCK to null resources.
A LOCK method invocation creates the lock specified by the lockinfo
XML element on the resource identified by the Request-URI. Lock method requests SHOULD have a
XML request body which contains an owner XML element for this lock
request, unless this is a refresh request. 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, 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. The response MUST contain
the value of the DAV:lockdiscovery property in a prop XML element.
In order to indicate the lock token associated with a newly created
lock, a Lock-Token response header MUST be included in the response
for every successful LOCK request for a new lock. Note that the
Lock-Token header would not be returned in the response for a
successful refresh LOCK request because a new lock was not created.
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.
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.
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.
Section 8.10.4
states that if a lock cannot be granted to all resources in a hierarchy, a
409 status response must be issued. Yet, the example in
section 8.10.10 which demonstrates this uses a 207.
Comment: 207 is correct, fix the bad spec text.
Done.
If the Depth header is set to infinity then the resource specified in
the Request-URI along with all its internal members, all the way down
the hierarchy, are to be locked. A successful result MUST return a
single lock token which represents all the resources that have been
locked. If an UNLOCK is successfully executed on this token, all
associated resources are unlocked. If the lock cannot be granted to
all resources, a 409 (Conflict)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. 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.
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 locks to be removed.
The table below describes the behavior that occurs when a lock
request is made on a resource.
Current lock state / Lock requestShared LockExclusive LockNoneTrueTrueShared LockTrueFalseExclusive LockFalseFalse*
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.
200 (OK) - The lock request succeeded and the value of the
DAV:lockdiscovery property is included in the body.
412 (Precondition Failed) - The included lock token was not
enforceable on this resource or the server could not satisfy the
request in the lockinfo XML element.
423 (Locked) - The resource is locked, so the method has been
rejected.
Keith Wannamaker: Section 8.10.1
explicitly states that the response from a successful lock request MUST
include the Lock-Token header, yet the examples in 8.10.8, 8.10.9, and 8.10.10
aren't compliant with this requirement, and should be updated.
Make obvious editing changes to the examples: http://lists.w3.org/Archives/Public/w3c-dist-auth/2001JulSep/0229.html
Note that this only applies to the example for a successful lock
creation, not for refreshes.
This example shows the successful creation of an exclusive write lock
on resource http://webdav.sb.aol.com/workspace/webdav/proposal.dochttp://example.com/workspace/webdav/proposal.doc.
The resource http://www.ics.uci.edu/~ejw/contact.htmlhttp:/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).
Note that the nonce, response, and opaque fields have not been
calculated in the Authorization request header.
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. In this example, the nonce, response, and
opaque fields have not been calculated in the Authorization request
header.
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://webdav.sb.aolexample.com/webdav/secret. Because this resource could
not be locked, none of the resources were locked. Note also that the
DAV:lockdiscovery property for the Request-URI has been included as
required. In this example the DAV: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.
What do you return if the unlock request specifies a URL on which the lock
does not reside? What if it's on a URL that is locked by the lock, but
it's not the resource where the lock is rooted?
Resolution (as of May 31, 2004) from RFC2518 issues list:
Resolved that you can specify any URL locked by the lock you want to unlock.
(http://lists.w3.org/Archives/Public/w3c-dist-auth/2002JulSep/0027.html)
We should resolve the issue of UNLOCK'ing other URLs in a few days.
RFC2518bis-05 and GULP 5.6 agree that the resource identified by the
request URL must be directly locked.
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.
The Request-URI MUST identify the resource that is directly locked by that lock.
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.
In this example, the lock identified by the lock token
"opaquelocktoken:a515cfa4-5da4-22e1-f5b5-00a0451e6bf7" is
successfully removed from the resource
http://webdav.sb.aolexample.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.
Add description of compliance class "2".Add "Depth" header considerations:
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.
Add "If" header considerations:
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.
Clients may include Timeout 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.
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
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.
Jim Amsden: The specification requires a lock to be refreshed if any method is executed, by anybody, on a locked resource. This can cause some performance problems. More importantly, the semantics of this refresh do not seem to be right -- why should a random GET by a third party cause all locks to be refreshed?
We should remove the mention of this behavior in 2518: http://lists.w3.org/Archives/Public/w3c-dist-auth/2001JulSep/0137.html
The timeout counter SHOULD be restarted any time an owner of the lock
sends a method to any member of the lock, including unsupported
methods, or methods which are unsuccessful. However the lock MUST be
refreshed if a refresh LOCK method is successfully received.
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.
The 423 (Locked) status code means the source or destination resource
of a method is locked.
It would be good if a client could look at a locked resource that it was
planning to unlock and also find out if it's depth locked and where the
depth lock is rooted.
Proposed solution: http://lists.w3.org/Archives/Public/w3c-dist-auth/2002JulSep/0049.html
approved.
See also 109_HOW_TO_FIND_THE_ROOT_OF_A_LOCK
If one finds a locked resource, it might be one of several resource locked
by a depth lock. How does one determine the root of the lock?
Resolved to support a dav:lockroot element in the lock discovery property:
http://lists.w3.org/Archives/Public/w3c-dist-auth/2002JulSep/0053.html
See 089_FINDING_THE_ROOT_OF_A_DEPTH_LOCKactivelockDAV:Describes a lock on a resource.depthDAV:The value of the Depth header."0" | "1" | "infinity"12.1.2
states that a dav:locktoken tag can have multiple <dav:href> tags in it.
Is this right? And is it trying to suggest that a single (shared) lock might
have multiple locktokens?
It is resolved that section 12.1.2 was incorrect and that only a single
lock token URI should be allowed there. Also it is resolved that a lock
only has a single lock token.
locktokenDAV:The lock token associated with a lock.The href contains one or more opaque lock token URIs
which all refer to the same lock (i.e., the OpaqueLockToken-URI
production in ).the lock token.lockrootDAV:The URL of the resource that was addressed in the LOCK request.The href contains the URL of the resource to which the
LOCK request has been applied.timeoutDAV:The timeout associated with a lockTimeType ;Defined in lockentryDAV:Defines the types of locks that can be used with the
resource.lockinfoDAV:The lockinfo XML element is used with a LOCK method to
specify the type of lock the client wishes to have created.lockscopeDAV:Specifies whether a lock is an exclusive lock, or a
shared lock.exclusiveDAV:Specifies an exclusive locksharedDAV:Specifies a shared locklocktypeDAV:Specifies the access type of a lock. At present, this
specification only defines one lock type, the write lock.writeDAV:Specifies a write lock.ownerDAV:Provides information about the principal taking out a
lock.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.
There is some confusion on how a PROPFIND response should express the fact
that a resource has multiple shared locks on it. It was suggested that the
spec become clearer.
Resolved trivially that it's probably worthwhile to demonstrate a correct
response for this situation in one of the examples.
lockdiscoveryDAV:Describes the active locks on a resourceThe 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. 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.
This resource has
a single exclusive write lock on it, with an
infinite timeout.
two shared write locks on it, with infinite timeouts.
supportedlockDAV:To provide a listing of the lock capabilities supported
by the resource.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.
A class 2 compliant resource MUST meet all class 1 requirements and
support the LOCK method, the DAV:supportedlock property, the
DAV: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.
Furthermore,
the introduction of locking functionality requires support for
authentication.
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.
This specification also defines a URI scheme for the encoding of lock
tokens, the opaquelocktoken URI scheme described in .
Copied from .
A lock either directly or indirectly locks a resource.
A LOCK request with a non-empty body creates a new lock, and the
resource identified by the request-URL is directly locked by that lock.
The "lock-root" of the new lock is the request-URL. If at the time of
the request, the request-URL is not mapped to a resource, a new
resource with no content MUST be created by the request.
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.
An UNLOCK request deletes the lock with the specified lock token.
The request-URL of the request MUST identify the resource that
is directly locked by that lock. After a lock is deleted,
no resource is locked by that lock.
A lock token is "submitted" in a request when it appears in an If
header.
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.
If a request causes a directly locked resource to no longer be
mapped 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.
If a request would cause a resource to be locked by two different
exclusive locks, the request MUST fail.
A lock either directly or indirectly locks a resource.
A LOCK request with a non-empty body creates a new lock, and the
resource identified by the request-URL is directly locked by that lock. The
"lock-root" of the new lock is the request-URL. If at the time of
the request, the request-URL is not mapped to a resource, a new
resource with no content MUST be created by the request.
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.
An UNLOCK request deletes the lock with the specified lock token. The request-URL
of the request MUST identify the resource that
is directly locked by that lock. After a lock is deleted,
no resource is locked by that lock.
A lock token is "submitted" in a request when it appears in an "If" request
header.
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.
If a request causes a directly locked resource to no longer be
mapped 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.
If a request would cause a resource to be locked by two different
exclusive locks, the request MUST fail.
The discussion of generating UUID node fields without using the IEEE 802 address in section 6.4.1 can be moved to an appendix.
Plan: get rid of the section altogether and refer to draft-mealling-uuid-urn.
In the meantime, move the whole opaquelocktoken discussion into an appendix.
The opaquelocktoken URI scheme is designed to be unique across all
resources for all time. Due to this uniqueness quality, a client may
submit an opaque lock token in an If header on a resource other than
the one that returned it.
All resources MUST recognize the opaquelocktoken scheme and, at
minimum, recognize that the lock token does not refer to an
outstanding lock on the resource.
In order to guarantee uniqueness across all resources for all time
the opaquelocktoken requires the use of the Universal Unique
Identifier (UUID) mechanism, as described in .
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
. Note that white space (LWS) is not allowed between
elements of this production.
Extension = path ; path is defined in , section 3.3.
UUIDs, as defined in , contain a "node" field that
contains one of the IEEE 802 addresses for the server machine. As
noted in , 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 usethe size of main memory in bytesthe amount of free main memory in bytesthe size of the paging or swap file in bytesfree bytes of paging or swap filethe total size of user virtual address space in bytesthe total available user address space bytesthe size of boot disk drive in bytesthe free disk space on boot drive in bytesthe current timethe amount of time since the system bootedthe individual sizes of files in various system directoriesthe creation, last read, and modification times of files in
various system directoriesthe utilization factors of various system resources (heap, etc.)current mouse cursor positioncurrent caret positioncurrent number of running processes, threadshandles or IDs of the desktop window and the active windowthe value of stack pointer of the callerthe process and thread ID of callervarious processor architecture specific performance counters
(instructions executed, cache misses, TLB misses)
(Note that it is precisely the above kinds of sources of randomness
that are used to seed cryptographic quality random number generators
on systems without special hardware for their construction.)
In addition, items such as the computer's name and the name of the
operating system, while not strictly speaking random, will help
differentiate the results from those obtained by other systems.
The exact algorithm to generate a node ID using these data is system
specific, because both the data available and the functions to obtain
them are often very system specific. However, assuming that one can
concatenate all the values from the randomness sources into a buffer,
and that a cryptographic hash function such as MD5 is available, then
any 6 bytes of the MD5 hash of the buffer, with the multicast bit
(the high bit of the first byte) set will be an appropriately random
node ID.
Other hash functions, such as SHA-1, can also be used. The only
requirement is that the result be suitably random in the sense that
the outputs from a set uniformly distributed inputs are themselves
uniformly distributed, and that a single bit change in the input can
be expected to cause half of the output bits to change.
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.