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Network Working Group Request for Comments: 4918 Obsoletes: 2518 Category: Standards Track |
L. Dusseault, Ed. CommerceNet June 2007 |
This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.
Copyright © The IETF Trust (2007).
Web Distributed Authoring and Versioning (WebDAV) consists of a set of methods, headers, and content-types ancillary to HTTP/1.1 for the management of resource properties, creation and management of resource collections, URL namespace manipulation, and resource locking (collision avoidance).
RFC 2518 was published in February 1999, and this specification
obsoletes RFC 2518 with minor revisions mostly due to
interoperability experience.
1. Introduction
2. Notational Conventions
3. Terminology
4. Data Model for Resource Properties
4.1. The Resource Property Model
4.2. Properties and HTTP Headers
4.3. Property Values
4.3.1. Example - Property with Mixed Content
4.4. Property Names
4.5. Source Resources and Output Resources
5. Collections of Web Resources
5.1. HTTP URL Namespace Model
5.2. Collection Resources
6. Locking
6.1. Lock Model
6.2. Exclusive vs. Shared Locks
6.3. Required Support
6.4. Lock Creator and Privileges
6.5. Lock Tokens
6.6. Lock Timeout
6.7. Lock Capability Discovery
6.8. Active Lock Discovery
7. Write Lock
7.1. Write Locks and Properties
7.2. Avoiding Lost Updates
7.3. Write Locks and Unmapped URLs
7.4. Write Locks and Collections
7.5. Write Locks and the If Request Header
7.5.1. Example - Write Lock and COPY
7.5.2. Example - Deleting a Member of a Locked
Collection
7.6. Write Locks and COPY/MOVE
7.7. Refreshing Write Locks
8. General Request and Response Handling
8.1. Precedence in Error Handling
8.2. Use of XML
8.3. URL Handling
8.3.1. Example - Correct URL Handling
8.4. Required Bodies in Requests
8.5. HTTP Headers for Use in WebDAV
8.6. ETag
8.7. Including Error Response Bodies
8.8. Impact of Namespace Operations on Cache Validators
9. HTTP Methods for Distributed Authoring
9.1. PROPFIND Method
9.1.1. PROPFIND Status Codes
9.1.2. Status Codes for Use in 'propstat' Element
9.1.3. Example - Retrieving Named Properties
9.1.4. Example - Using 'propname' to Retrieve All
Property Names
9.1.5. Example - Using So-called 'allprop'
9.1.6. Example - Using 'allprop' with 'include'
9.2. PROPPATCH Method
9.2.1. Status Codes for Use in 'propstat' Element
9.2.2. Example - PROPPATCH
9.3. MKCOL Method
9.3.1. MKCOL Status Codes
9.3.2. Example - MKCOL
9.4. GET, HEAD for Collections
9.5. POST for Collections
9.6. DELETE Requirements
9.6.1. DELETE for Collections
9.6.2. Example - DELETE
9.7. PUT Requirements
9.7.1. PUT for Non-Collection Resources
9.7.2. PUT for Collections
9.8. COPY Method
9.8.1. COPY for Non-collection Resources
9.8.2. COPY for Properties
9.8.3. COPY for Collections
9.8.4. COPY and Overwriting Destination Resources
9.8.5. Status Codes
9.8.6. Example - COPY with Overwrite
9.8.7. Example - COPY with No Overwrite
9.8.8. Example - COPY of a Collection
9.9. MOVE Method
9.9.1. MOVE for Properties
9.9.2. MOVE for Collections
9.9.3. MOVE and the Overwrite Header
9.9.4. Status Codes
9.9.5. Example - MOVE of a Non-Collection
9.9.6. Example - MOVE of a Collection
9.10. LOCK Method
9.10.1. Creating a Lock on an Existing Resource
9.10.2. Refreshing Locks
9.10.3. Depth and Locking
9.10.4. Locking Unmapped URLs
9.10.5. Lock Compatibility Table
9.10.6. LOCK Responses
9.10.7. Example - Simple Lock Request
9.10.8. Example - Refreshing a Write Lock
9.10.9. Example - Multi-Resource Lock Request
9.11. UNLOCK Method
9.11.1. Status Codes
9.11.2. Example - UNLOCK
10. HTTP Headers for Distributed Authoring
10.1. DAV Header
10.2. Depth Header
10.3. Destination Header
10.4. If Header
10.4.1. Purpose
10.4.2. Syntax
10.4.3. List Evaluation
10.4.4. Matching State Tokens and ETags
10.4.5. If Header and Non-DAV-Aware Proxies
10.4.6. Example - No-tag Production
10.4.7. Example - Using "Not" with No-tag Production
10.4.8. Example - Causing a Condition to Always
Evaluate to True
10.4.9. Example - Tagged List If Header in COPY
10.4.10. Example - Matching Lock Tokens with
Collection Locks
10.4.11. Example - Matching ETags on Unmapped URLs
10.5. Lock-Token Header
10.6. Overwrite Header
10.7. Timeout Request Header
11. Status Code Extensions to HTTP/1.1
11.1. 207 Multi-Status
11.2. 422 Unprocessable Entity
11.3. 423 Locked
11.4. 424 Failed Dependency
11.5. 507 Insufficient Storage
12. Use of HTTP Status Codes
12.1. 412 Precondition Failed
12.2. 414 Request-URI Too Long
13. Multi-Status Response
13.1. Response Headers
13.2. Handling Redirected Child Resources
13.3. Internal Status Codes
14. XML Element Definitions
14.1. activelock XML Element
14.2. allprop XML Element
14.3. collection XML Element
14.4. depth XML Element
14.5. error XML Element
14.6. exclusive XML Element
14.7. href XML Element
14.8. include XML Element
14.9. location XML Element
14.10. lockentry XML Element
14.11. lockinfo XML Element
14.12. lockroot XML Element
14.13. lockscope XML Element
14.14. locktoken XML Element
14.15. locktype XML Element
14.16. multistatus XML Element
14.17. owner XML Element
14.18. prop XML Element
14.19. propertyupdate XML Element
14.20. propfind XML Element
14.21. propname XML Element
14.22. propstat XML Element
14.23. remove XML Element
14.24. response XML Element
14.25. responsedescription XML Element
14.26. set XML Element
14.27. shared XML Element
14.28. status XML Element
14.29. timeout XML Element
14.30. write XML Element
15. DAV Properties
16. Precondition/Postcondition XML Elements
17. XML Extensibility in DAV
18. DAV Compliance Classes
18.1. Class 1
18.2. Class 2
18.3. Class 3
19. Internationalization Considerations
20. Security Considerations
20.1. Authentication of Clients
20.2. Denial of Service
20.3. Security through Obscurity
20.4. Privacy Issues Connected to Locks
20.5. Privacy Issues Connected to Properties
20.6. Implications of XML Entities
20.7. Risks Connected with Lock Tokens
20.8. Hosting Malicious Content
21. IANA Considerations
21.1. New URI Schemes
21.2. XML Namespaces
21.3. Message Header Fields
21.3.1. DAV
21.3.2. Depth
21.3.3. Destination
21.3.4. If
21.3.5. Lock-Token
21.3.6. Overwrite
21.3.7. Timeout
21.4. HTTP Status Codes
22. Acknowledgements
23. Contributors to This Specification
24. Authors of RFC 2518
25. References
25.1. Normative References
25.2. Informative References
Appendix A. Notes on Processing XML Elements
A.1. Notes on Empty XML Elements
A.2. Notes on Illegal XML Processing
A.3. Example - XML Syntax Error
A.4. Example - Unexpected XML Element
Appendix B. Notes on HTTP Client Compatibility
Appendix C. The 'opaquelocktoken' Scheme and URIs
Appendix D. Lock-null Resources
D.1. Guidance for Clients Using LOCK to Create Resources
Appendix E. Guidance for Clients Desiring to Authenticate
Appendix F. Summary of Changes from RFC 2518
F.1. Changes for Both Client and Server Implementations
F.2. Changes for Server Implementations
F.3. Other Changes
This document describes an extension to the HTTP/1.1 protocol that allows clients to perform remote Web content authoring operations. This extension provides a coherent set of methods, headers, request entity body formats, and response entity body formats that provide operations for:
Properties: The ability to create, remove, and query information about Web pages, such as their authors, creation dates, etc.
Collections: The ability to create sets of documents and to retrieve a hierarchical membership listing (like a directory listing in a file system).
Locking: The ability to keep more than one person from working on a document at the same time. This prevents the "lost update problem", in which modifications are lost as first one author, then another, writes changes without merging the other author's changes.
Namespace Operations: The ability to instruct the server to copy and move Web resources, operations that change the mapping from URLs to resources.
Requirements and rationale for these operations are described in a companion document, "Requirements for a Distributed Authoring and Versioning Protocol for the World Wide Web" [RFC2291].
This document does not specify the versioning operations suggested by [RFC2291]. That work was done in a separate document, "Versioning Extensions to WebDAV" [RFC3253].
The sections below provide a detailed introduction to various WebDAV abstractions: resource properties (Section 4), collections of resources (Section 5), locks (Section 6) in general, and write locks (Section 7) specifically.
These abstractions are manipulated by the WebDAV-specific HTTP methods (Section 9) and the extra HTTP headers (Section 10) used with WebDAV methods. General considerations for handling HTTP requests and responses in WebDAV are found in Section 8.
While the status codes provided by HTTP/1.1 are sufficient to describe most error conditions encountered by WebDAV methods, there are some errors that do not fall neatly into the existing categories. This specification defines extra status codes developed for WebDAV methods (Section 11) and describes existing HTTP status codes (Section 12) as used in WebDAV. Since some WebDAV methods may
operate over many resources, the Multi-Status response (Section 13) has been introduced to return status information for multiple resources. Finally, this version of WebDAV introduces precondition and postcondition (Section 16) XML elements in error response bodies.
WebDAV uses XML ([REC-XML]) for property names and some values, and also uses XML to marshal complicated requests and responses. This specification contains DTD and text definitions of all properties (Section 15) and all other XML elements (Section 14) used in marshalling. WebDAV includes a few special rules on extending WebDAV XML marshalling in backwards-compatible ways (Section 17).
Finishing off the specification are sections on what it means for a resource to be compliant with this specification (Section 18), on internationalization support (Section 19), and on security (Section 20).
Since this document describes a set of extensions to the HTTP/1.1 protocol, the augmented BNF used herein to describe protocol elements is exactly the same as described in Section 2.1 of [RFC2616], including the rules about implied linear whitespace. Since this augmented BNF uses the basic production rules provided in Section 2.2 of [RFC2616], these rules apply to this document as well. Note this is not the standard BNF syntax used in other RFCs.
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].
Note that in natural language, a property like the "creationdate" property in the "DAV:" XML namespace is sometimes referred to as "DAV:creationdate" for brevity.
URI/URL - A Uniform Resource Identifier and Uniform Resource Locator, respectively. These terms (and the distinction between them) are defined in [RFC3986].
URI/URL Mapping - A relation between an absolute URI and a resource. Since a resource can represent items that are not network retrievable, as well as those that are, it is possible for a resource to have zero, one, or many URI mappings. Mapping a resource to an "http" scheme URI makes it possible to submit HTTP protocol requests to the resource using the URI.
Path Segment - Informally, the characters found between slashes ("/") in a URI. Formally, as defined in Section 3.3 of [RFC3986].
Collection - Informally, a resource that also acts as a container of references to child resources. Formally, a resource that contains a set of mappings between path segments and resources and meets the requirements defined in Section 5.
Internal Member (of a Collection) - Informally, a child resource of a collection. Formally, a resource referenced by a path segment mapping contained in the collection.
Internal Member URL (of a Collection) - A URL of an internal member, consisting of the URL of the collection (including trailing slash) plus the path segment identifying the internal member.
Member (of a Collection) - Informally, a "descendant" of a collection. Formally, an internal member of the collection, or, recursively, a member of an internal member.
Member URL (of a Collection) - A URL that is either an internal member URL of the collection itself, or is an internal member URL of a member of that collection.
Property - A name/value pair that contains descriptive information about a resource.
Live Property - A property whose semantics and syntax are enforced by the server. For example, the live property DAV:getcontentlength has its value, the length of the entity returned by a GET request, automatically calculated by the server.
Dead Property - A property whose semantics and syntax are not enforced by the server. The server only records the value of a dead property; the client is responsible for maintaining the consistency of the syntax and semantics of a dead property.
Principal - A distinct human or computational actor that initiates access to network resources.
State Token - A URI that represents a state of a resource. Lock tokens are the only state tokens defined in this specification.
Properties are pieces of data that describe the state of a resource. Properties are data about data.
Properties are used in distributed authoring environments to provide for efficient discovery and management of resources. For example, a 'subject' property might allow for the indexing of all resources by their subject, and an 'author' property might allow for the discovery of what authors have written which documents.
The DAV property model consists of name/value pairs. The name of a property identifies the property's syntax and semantics, and provides an address by which to refer to its syntax and semantics.
There are two categories of properties: "live" and "dead". A live property has its syntax and semantics enforced by the server. Live properties include cases where a) the value of a property is protected and maintained by the server, and b) the value of the property is maintained by the client, but the server performs syntax checking on submitted values. All instances of a given live property MUST comply with the definition associated with that property name. A dead property has its syntax and semantics enforced by the client; the server merely records the value of the property verbatim.
Properties already exist, in a limited sense, in HTTP message headers. However, in distributed authoring environments, a relatively large number of properties are needed to describe the state of a resource, and setting/returning them all through HTTP headers is inefficient. Thus, a mechanism is needed that allows a principal to identify a set of properties in which the principal is interested and to set or retrieve just those properties.
The value of a property is always a (well-formed) XML fragment.
XML has been chosen because it is a flexible, self-describing, structured data format that supports rich schema definitions, and because of its support for multiple character sets. XML's self- describing nature allows any property's value to be extended by adding elements. Clients will not break when they encounter extensions because they will still have the data specified in the original schema and MUST ignore elements they do not understand.
XML's support for multiple character sets allows any human-readable property to be encoded and read in a character set familiar to the user. XML's support for multiple human languages, using the "xml: lang" attribute, handles cases where the same character set is employed by multiple human languages. Note that xml:lang scope is recursive, so an xml:lang attribute on any element containing a property name element applies to the property value unless it has been overridden by a more locally scoped attribute. Note that a property only has one value, in one language (or language MAY be left undefined); a property does not have multiple values in different languages or a single value in multiple languages.
A property is always represented with an XML element consisting of the property name, called the "property name element". The simplest example is an empty property, which is different from a property that does not exist:
<R:title xmlns:R="http://www.example.com/ns/"></R:title>
The value of the property appears inside the property name element. The value may be any kind of well-formed XML content, including both text-only and mixed content. Servers MUST preserve the following XML Information Items (using the terminology from [REC-XML-INFOSET]) in storage and transmission of dead properties:
For the property name Element Information Item itself:
[namespace name]
[local name]
[attributes] named "xml:lang" or any such attribute in scope
[children] of type element or character
On all Element Information Items in the property value:
[namespace name]
[local name]
[attributes]
[children] of type element or character
On Attribute Information Items in the property value:
[namespace name]
[local name]
[normalized value]
On Character Information Items in the property value:
[character code]
Since prefixes are used in some XML vocabularies (XPath and XML Schema, for example), servers SHOULD preserve, for any Information Item in the value:
[prefix]
XML Infoset attributes not listed above MAY be preserved by the server, but clients MUST NOT rely on them being preserved. The above rules would also apply by default to live properties, unless defined otherwise.
Servers MUST ignore the XML attribute xml:space if present and never use it to change whitespace handling. Whitespace in property values is significant.
Consider a dead property 'author' created by the client as follows:
<D:prop xml:lang="en" xmlns:D="DAV:">
<x:author xmlns:x='http://example.com/ns'>
<x:name>Jane Doe</x:name>
<!-- Jane's contact info -->
<x:uri type='email'
added='2005-11-26'>mailto:jane.doe@example.com</x:uri>
<x:uri type='web'
added='2005-11-27'>http://www.example.com</x:uri>
<x:notes xmlns:h='http://www.w3.org/1999/xhtml'>
Jane has been working way <h:em>too</h:em> long on the
long-awaited revision of <![CDATA[<RFC2518>]]>.
</x:notes>
</x:author>
</D:prop>
When this property is requested, a server might return:
<D:prop xmlns:D='DAV:'><author
xml:lang='en'
xmlns:x='http://example.com/ns'
xmlns='http://example.com/ns'
xmlns:h='http://www.w3.org/1999/xhtml'>
<x:name>Jane Doe</x:name>
<x:uri added="2005-11-26" type="email"
>mailto:jane.doe@example.com</x:uri>
<x:uri added="2005-11-27" type="web"
>http://www.example.com</x:uri>
<x:notes>
Jane has been working way <h:em>too</h:em> long on the
long-awaited revision of <RFC2518>.
</x:notes>
</author>
</D:prop>
Note in this example:
Implementation note: there are cases such as editing scenarios where clients may require that XML content is preserved character by character (such as attribute ordering or quoting style). In this case, clients should consider using a text-only property value by escaping all characters that have a special meaning in XML parsing.
A property name is a universally unique identifier that is associated with a schema that provides information about the syntax and semantics of the property.
Because a property's name is universally unique, clients can depend
upon consistent behavior for a particular property across multiple
resources, on the same and across different servers, so long as that
property is "live" on the resources in question, and the
implementation of the live property is faithful to its definition.
The XML namespace mechanism, which is based on URIs ([RFC3986]), is used to name properties because it prevents namespace collisions and provides for varying degrees of administrative control.
The property namespace is flat; that is, no hierarchy of properties is explicitly recognized. Thus, if a property A and a property A/B exist on a resource, there is no recognition of any relationship between the two properties. It is expected that a separate specification will eventually be produced that will address issues relating to hierarchical properties.
Finally, it is not possible to define the same property twice on a single resource, as this would cause a collision in the resource's property namespace.
Some HTTP resources are dynamically generated by the server. For these resources, there presumably exists source code somewhere governing how that resource is generated. The relationship of source files to output HTTP resources may be one to one, one to many, many to one, or many to many. There is no mechanism in HTTP to determine whether a resource is even dynamic, let alone where its source files exist or how to author them. Although this problem would usefully be solved, interoperable WebDAV implementations have been widely deployed without actually solving this problem, by dealing only with static resources. Thus, the source vs. output problem is not solved in this specification and has been deferred to a separate document.
This section provides a description of a type of Web resource, the collection, and discusses its interactions with the HTTP URL namespace and with HTTP methods. The purpose of a collection resource is to model collection-like objects (e.g., file system directories) within a server's namespace.
All DAV-compliant resources MUST support the HTTP URL namespace model specified herein.
The HTTP URL namespace is a hierarchical namespace where the hierarchy is delimited with the "/" character.
An HTTP URL namespace is said to be consistent if it meets the
following conditions: for every URL in the HTTP hierarchy there
exists a collection that contains that URL as an internal member URL.
The root, or top-level collection of the namespace under
consideration, is exempt from the previous rule. The top-level
collection of the namespace under consideration is not necessarily
the collection identified by the absolute path '/' -- it may be
identified by one or more path segments (e.g., /servlets/webdav/...)
Neither HTTP/1.1 nor WebDAV requires that the entire HTTP URL namespace be consistent -- a WebDAV-compatible resource may not have a parent collection. However, certain WebDAV methods are prohibited from producing results that cause namespace inconsistencies.
As is implicit in [RFC2616] and [RFC3986], any resource, including collection resources, MAY be identified by more than one URI. For example, a resource could be identified by multiple HTTP URLs.
Collection resources differ from other resources in that they also act as containers. Some HTTP methods apply only to a collection, but some apply to some or all of the resources inside the container defined by the collection. When the scope of a method is not clear, the client can specify what depth to apply. Depth can be either zero levels (only the collection), one level (the collection and directly contained resources), or infinite levels (the collection and all contained resources recursively).
A collection's state consists of at least a set of mappings between path segments and resources, and a set of properties on the collection itself. In this document, a resource B will be said to be contained in the collection resource A if there is a path segment mapping that maps to B and that is contained in A. A collection MUST contain at most one mapping for a given path segment, i.e., it is illegal to have the same path segment mapped to more than one resource.
Properties defined on collections behave exactly as do properties on non-collection resources. A collection MAY have additional state such as entity bodies returned by GET.
For all WebDAV-compliant resources A and B, identified by URLs "U" and "V", respectively, such that "V" is equal to "U/SEGMENT", A MUST be a collection that contains a mapping from "SEGMENT" to B. So, if resource B with URL "http://example.com/bar/blah" is WebDAV compliant and if resource A with URL "http://example.com/bar/" is WebDAV compliant, then resource A must be a collection and must contain exactly one mapping from "blah" to B.
Although commonly a mapping consists of a single segment and a resource, in general, a mapping consists of a set of segments and a resource. This allows a server to treat a set of segments as equivalent (i.e., either all of the segments are mapped to the same resource, or none of the segments are mapped to a resource). For example, a server that performs case-folding on segments will treat the segments "ab", "Ab", "aB", and "AB" as equivalent. A client can then use any of these segments to identify the resource. Note that a PROPFIND result will select one of these equivalent segments to identify the mapping, so there will be one PROPFIND response element per mapping, not one per segment in the mapping.
Collection resources MAY have mappings to non-WebDAV-compliant
resources in the HTTP URL namespace hierarchy but are not required to
do so. For example, if resource X with URL
"http://example.com/bar/blah" is not WebDAV compliant and resource A
with "URL http://example.com/bar/" identifies a WebDAV collection,
then A may or may not have a mapping from "blah" to X.
If a WebDAV-compliant resource has no WebDAV-compliant internal members in the HTTP URL namespace hierarchy, then the WebDAV- compliant resource is not required to be a collection.
There is a standing convention that when a collection is referred to by its name without a trailing slash, the server MAY handle the request as if the trailing slash were present. In this case, it SHOULD return a Content-Location header in the response, pointing to the URL ending with the "/". For example, if a client invokes a method on http://example.com/blah (no trailing slash), the server may respond as if the operation were invoked on http://example.com/blah/ (trailing slash), and should return a Content-Location header with the value http://example.com/blah/. Wherever a server produces a URL referring to a collection, the server SHOULD include the trailing slash. In general, clients SHOULD use the trailing slash form of collection names. If clients do not use the trailing slash form the client needs to be prepared to see a redirect response. Clients will
find the DAV:resourcetype property more reliable than the URL to find out if a resource is a collection.
Clients MUST be able to support the case where WebDAV resources are
contained inside non-WebDAV resources. For example, if an OPTIONS
response from "http://example.com/servlet/dav/collection" indicates
WebDAV support, the client cannot assume that
"http://example.com/servlet/dav/" or its parent necessarily are
WebDAV collections.
A typical scenario in which mapped URLs do not appear as members of their parent collection is the case where a server allows links or redirects to non-WebDAV resources. For instance, "/col/link" might not appear as a member of "/col/", although the server would respond with a 302 status to a GET request to "/col/link"; thus, the URL "/col/link" would indeed be mapped. Similarly, a dynamically- generated page might have a URL mapping from "/col/index.html", thus this resource might respond with a 200 OK to a GET request yet not appear as a member of "/col/".
Some mappings to even WebDAV-compliant resources might not appear in the parent collection. An example for this case are servers that support multiple alias URLs for each WebDAV-compliant resource. A server may implement case-insensitive URLs, thus "/col/a" and "/col/A" identify the same resource, yet only either "a" or "A" is reported upon listing the members of "/col". In cases where a server treats a set of segments as equivalent, the server MUST expose only one preferred segment per mapping, consistently chosen, in PROPFIND responses.
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.
This section provides a concise model for how locking behaves. Later sections will provide more detail on some of the concepts and refer back to these model statements. Normative statements related to LOCK and UNLOCK method handling can be found in the sections on those methods, whereas normative statements that cover any method are gathered here.
The most basic form of lock is an exclusive lock. Exclusive locks avoid having to deal with content change conflicts, without requiring any coordination other than the methods described in this specification.
However, there are times when the goal of a lock is not to exclude others from exercising an access right but rather to provide a mechanism for principals to indicate that they intend to exercise their access rights. Shared locks are provided for this case. A shared lock allows multiple principals to receive a lock. Hence any principal that has both access privileges and a valid lock can use the locked resource.
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 creator leaves without
unlocking a resource. While both timeouts (Section 6.6) 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 successful request for a new shared lock MUST result in the generation of a unique lock associated with the requesting principal. Thus, if five principals have taken out shared write locks on the same resource, there will be five locks and five lock tokens, one for each principal.
A WebDAV-compliant resource is not required to support locking in any form. If the resource does support locking, it may choose to support any combination of exclusive and shared locks for any access types.
The reason for this flexibility is that locking policy strikes to the very heart of the resource management and versioning systems employed by various storage repositories. These repositories require control over what sort of locking will be made available. For example, some repositories only support shared write locks, while others only provide support for exclusive write locks, while yet others use no locking at all. As each system is sufficiently different to merit exclusion of certain locking features, this specification leaves locking as the sole axis of negotiation within WebDAV.
The creator of a lock has special privileges to use the lock to modify the resource. When a locked resource is modified, a server MUST check that the authenticated principal matches the lock creator (in addition to checking for valid lock token submission).
The server MAY allow privileged users other than the lock creator to destroy a lock (for example, the resource owner or an administrator). The 'unlock' privilege in [RFC3744] was defined to provide that permission.
There is no requirement for servers to accept LOCK requests from all users or from anonymous users.
Note that having a lock does not confer full privilege to modify the locked resource. Write access and other privileges MUST be enforced through normal privilege or authentication mechanisms, not based on the possible obscurity of lock token values.
A lock token is a type of state token that identifies a particular lock. Each lock has exactly one unique lock token generated by the server. Clients MUST NOT attempt to interpret lock tokens in any way.
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. Since lock tokens are unique, a client MAY submit a lock token in an If header on a resource other than the one that returned it.
When a LOCK operation creates a new lock, the new lock token is returned in the Lock-Token response header defined in Section 10.5, and also in the body of the response.
Servers MAY make lock tokens publicly readable (e.g., in the DAV: lockdiscovery property). One use case for making lock tokens readable is so that a long-lived lock can be removed by the resource owner (the client that obtained the lock might have crashed or disconnected before cleaning up the lock). Except for the case of using UNLOCK under user guidance, a client SHOULD NOT use a lock token created by another client instance.
This specification encourages servers to create Universally Unique Identifiers (UUIDs) for lock tokens, and to use the URI form defined by "A Universally Unique Identifier (UUID) URN Namespace" ([RFC4122]). However, servers are free to use any URI (e.g., from another scheme) so long as it meets the uniqueness requirements. For example, a valid lock token might be constructed using the "opaquelocktoken" scheme defined in Appendix C.
Example: "urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6"
A lock MAY have a limited lifetime. The lifetime is suggested by the client when creating or refreshing the lock, but the server ultimately chooses the timeout value. Timeout is measured in seconds remaining until lock expiration.
The timeout counter MUST be restarted if a refresh lock request is successful (see Section 9.10.2). The timeout counter SHOULD NOT be restarted at any other time.
If the timeout expires, then the lock SHOULD be removed. In this case 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.
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 offline.
A client MUST NOT assume that just because the timeout has expired, the lock has immediately been removed.
Likewise, a client MUST NOT assume that just because the timeout has not expired, the lock still exists. Clients MUST assume that locks can arbitrarily disappear at any time, regardless of the value given in the Timeout header. The Timeout header only indicates the behavior of the server if extraordinary circumstances do not occur. For example, a sufficiently privileged user may remove a lock at any time, or the system may crash in such a way that it loses the record of the lock's existence.
Since server lock support is optional, a client trying to lock a resource on a server can either try the lock and hope for the best, or perform some form of discovery to determine what lock capabilities the server supports. This is known as lock capability discovery. A client can determine what lock types the server supports by retrieving the 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 MAY even provide the lock tokens.
Any DAV-compliant resource that supports the LOCK method MUST support the DAV:lockdiscovery property.
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.
An exclusive write lock protects a resource: it prevents changes by any principal other than the lock creator and in any case where the lock token is not submitted (e.g., by a client process other than the one holding the lock).
Clients MUST submit a lock-token they are authorized to use in any request that modifies a write-locked resource. The list of modifications covered by a write-lock include:
Of the methods defined in HTTP and WebDAV, PUT, POST, PROPPATCH, LOCK, UNLOCK, MOVE, COPY (for the destination resource), DELETE, and MKCOL are affected by write locks. All other HTTP/WebDAV methods defined so far -- GET in particular -- function independently of a write lock.
The next few sections describe in more specific terms how write locks interact with various operations.
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 as lockable are guaranteed not to change while write locked.
Although the write locks provide some help in preventing lost updates, they cannot guarantee that updates will never be lost. Consider the following scenario:
Two clients A and B are interested in editing the resource 'index.html'. Client A is an HTTP client rather than a WebDAV client, and so does not know how to perform locking.
Client A doesn't lock the document, but does a GET, and begins editing.
Client B does LOCK, performs a GET and begins editing.
Client B finishes editing, performs a PUT, then an UNLOCK.
Client A performs a PUT, overwriting and losing all of B's changes.
There are several reasons why the WebDAV protocol itself cannot prevent this situation. First, it cannot force all clients to use locking because it must be compatible with HTTP clients that do not comprehend locking. Second, it cannot require servers to support locking because of the variety of repository implementations, some of which rely on reservations and merging rather than on locking. Finally, being stateless, it cannot enforce a sequence of operations like LOCK / GET / PUT / UNLOCK.
WebDAV servers that support locking can reduce the likelihood that clients will accidentally overwrite each other's changes by requiring clients to lock resources before modifying them. Such servers would effectively prevent HTTP 1.0 and HTTP 1.1 clients from modifying resources.
WebDAV clients can be good citizens by using a lock / retrieve / write /unlock sequence of operations (at least by default) whenever they interact with a WebDAV server that supports locking.
HTTP 1.1 clients can be good citizens, avoiding overwriting other clients' changes, by using entity tags in If-Match headers with any requests that would modify resources.
Information managers may attempt to prevent overwrites by implementing client-side procedures requiring locking before modifying WebDAV resources.
WebDAV provides the ability to send a LOCK request to an unmapped URL in order to reserve the name for use. This is a simple way to avoid the lost-update problem on the creation of a new resource (another way is to use If-None-Match header specified in Section 14.26 of [RFC2616]). It has the side benefit of locking the new resource immediately for use of the creator.
Note that the lost-update problem is not an issue for collections because MKCOL can only be used to create a collection, not to overwrite an existing collection. When trying to lock a collection upon creation, clients can attempt to increase the likelihood of getting the lock by pipelining the MKCOL and LOCK requests together (but because this doesn't convert two separate operations into one atomic operation, there's no guarantee this will work).
A successful lock request to an unmapped URL MUST result in the creation of a locked (non-collection) resource with empty content. Subsequently, a successful PUT request (with the correct lock token) provides the content for the resource. Note that the LOCK request has no mechanism for the client to provide Content-Type or Content- Language, thus the server will use defaults or empty values and rely on the subsequent PUT request for correct values.
A resource created with a LOCK is empty but otherwise behaves in every way as a normal resource. It behaves the same way as a resource created by a PUT request with an empty body (and where a Content-Type and Content-Language was not specified), followed by a LOCK request to the same resource. Following from this model, a locked empty resource:
The client is expected to update the locked empty resource shortly after locking it, using PUT and possibly PROPPATCH.
Alternatively and for backwards compatibility to [RFC2518], servers MAY implement Lock-Null Resources (LNRs) instead (see definition in Appendix D). Clients can easily interoperate both with servers that support the old model LNRs and the recommended model of "locked empty resources" by only attempting PUT after a LOCK to an unmapped URL, not MKCOL or GET, and by not relying on specific properties of LNRs.
There are two kinds of collection write locks. A depth-0 write lock on a collection protects the collection properties plus the internal member URLs of that one collection, while not protecting the content or properties of member resources (if the collection itself has any entity bodies, those are also protected). A depth-infinity write lock on a collection provides the same protection on that collection and also provides write lock protection on every member resource.
Expressed otherwise, a write lock of either kind protects any request that would create a new resource in a write locked collection, any request that would remove an internal member URL of a write locked collection, and any request that would change the segment name of any internal member.
Thus, a collection write lock protects all the following actions:
The collection's lock token is required in addition to the lock token on the internal member itself, if it is locked separately.
In addition, a depth-infinity lock affects all write operations to all members of the locked collection. With a depth-infinity lock, the resource identified by the root of the lock is directly locked, and all its members are indirectly locked.
If a depth-infinity write LOCK request is issued to a collection containing member URLs identifying resources that are currently locked in a manner that conflicts with the new lock (see Section 6.1, point 3), the request MUST fail with a 423 (Locked) status code, and the response SHOULD contain the 'no-conflicting-lock' precondition.
If a lock request causes the URL of a resource to be added as an internal member URL of a depth-infinity locked collection, then the new resource MUST be automatically protected by the lock. 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.
A user agent has to demonstrate knowledge of a lock when requesting an operation on a locked resource. Otherwise, the following scenario might occur. In the scenario, 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 for all locked resources that a method may change or the method MUST fail. A lock token is submitted when it appears in an If header. For example, if a resource is to be moved and both the source and destination are locked, then two lock tokens must be submitted in the If header, one for the source and the other for the destination.
>>Request
COPY /~fielding/index.html HTTP/1.1
Host: www.example.com
Destination: http://www.example.com/users/f/fielding/index.html
If: <http://www.example.com/users/f/fielding/index.html>
(<urn:uuid: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 (the one 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.
Consider a collection "/locked" with an exclusive, depth-infinity write lock, and an attempt to delete an internal member "/locked/ member":
>>Request
DELETE /locked/member HTTP/1.1
Host: example.com
>>Response
HTTP/1.1 423 Locked
Content-Type: application/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<D:error xmlns:D="DAV:">
<D:lock-token-submitted>
<D:href>/locked/</D:href>
</D:lock-token-submitted>
</D:error>
Thus, the client would need to submit the lock token with the request to make it succeed. To do that, various forms of the If header (see Section 10.4) could be used.
"No-Tag-List" format:
If: (<urn:uuid:150852e2-3847-42d5-8cbe-0f4f296f26cf>)
"Tagged-List" format, for "http://example.com/locked/":
If: <http://example.com/locked/>
(<urn:uuid:150852e2-3847-42d5-8cbe-0f4f296f26cf>)
"Tagged-List" format, for "http://example.com/locked/member":
If: <http://example.com/locked/member>
(<urn:uuid:150852e2-3847-42d5-8cbe-0f4f296f26cf>)
Note that, for the purpose of submitting the lock token, the actual form doesn't matter; what's relevant is that the lock token appears in the If header, and that the If header itself evaluates to true.
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 a depth-infinity lock, 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, if there is an existing lock at the destination, the server MUST add the moved resource to the destination lock scope. For example, if the MOVE makes the resource a child of a collection that has a depth-infinity lock, then the resource will be added to that collection's lock. Additionally, if a resource with a depth-infinity lock is moved to a destination that is within the scope of the same lock (e.g., within the URL namespace tree covered by the lock), the moved resource will again be added to the lock. In both these examples, as specified in Section 7.5, 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.
However, a client may submit a LOCK request with an If header but without a body. A server receiving a LOCK request with no body MUST NOT create a new lock -- this form of the LOCK request is only to be used to "refresh" an existing lock (meaning, at minimum, that any timers associated with the lock MUST be reset).
Clients may submit Timeout headers of arbitrary value with their lock refresh requests. Servers, as always, may ignore Timeout headers submitted by the client, and a server MAY refresh a lock with a timeout period that is different than the previous timeout period used for the lock, provided it advertises the new value in the LOCK refresh response.
If an error is received in response to a refresh LOCK request, the client MUST NOT assume that the lock was refreshed.
Servers MUST return authorization errors in preference to other errors. This avoids leaking information about protected resources (e.g., a client that finds that a hidden resource exists by seeing a 423 Locked response to an anonymous request to the resource).
In HTTP/1.1, method parameter information was exclusively encoded in
HTTP headers. Unlike HTTP/1.1, WebDAV encodes method parameter
information either in an XML ([REC-XML]) request entity body, or in
an HTTP header. The use of XML to encode method parameters was
motivated by the ability to add extra XML elements to existing
structures, providing extensibility; and by XML's ability to encode
information in ISO 10646 character sets, providing
internationalization support.
In addition to encoding method parameters, XML is used in WebDAV to encode the responses from methods, providing the extensibility and internationalization advantages of XML for method output, as well as input.
When XML is used for a request or response body, the Content-Type type SHOULD be application/xml. Implementations MUST accept both text/xml and application/xml in request and response bodies. Use of text/xml is deprecated.
All DAV-compliant clients and resources MUST use XML parsers that are compliant with [REC-XML] and [REC-XML-NAMES]. All XML used in either requests or responses MUST be, at minimum, well formed and use namespaces correctly. If a server receives XML that is not well- formed, then the server MUST reject the entire request with a 400 (Bad Request). If a client receives XML that is not well-formed in a response, then the client MUST NOT assume anything about the outcome of the executed method and SHOULD treat the server as malfunctioning.
Note that processing XML submitted by an untrusted source may cause risks connected to privacy, security, and service quality (see Section 20). Servers MAY reject questionable requests (even though they consist of well-formed XML), for instance, with a 400 (Bad Request) status code and an optional response body explaining the problem.
URLs appear in many places in requests and responses.
Interoperability experience with [RFC2518] showed that many clients
parsing Multi-Status responses did not fully implement the full
Reference Resolution defined in Section 5 of [RFC3986]. Thus,
servers in particular need to be careful in handling URLs in
responses, to ensure that clients have enough context to be able to
interpret all the URLs. The rules in this section apply not only to
resource URLs in the 'href' element in Multi-Status responses, but
also to the Destination and If header resource URLs.
The sender has a choice between two approaches: using a relative reference, which is resolved against the Request-URI, or a full URI. A server MUST ensure that every 'href' value within a Multi-Status response uses the same format.
WebDAV only uses one form of relative reference in its extensions, the absolute path.
Simple-ref = absolute-URI | ( path-absolute [ "?" query ] )
The absolute-URI, path-absolute and query productions are defined in Sections 4.3, 3.3, and 3.4 of [RFC3986].
Within Simple-ref productions, senders MUST NOT:
Identifiers for collections SHOULD end in a '/' character.
Consider the collection http://example.com/sample/ with the internal member URL http://example.com/sample/a%20test and the PROPFIND request below:
>>Request:
PROPFIND /sample/ HTTP/1.1
Host: example.com
Depth: 1
In this case, the server should return two 'href' elements containing either
Note that even though the server may be storing the member resource internally as 'a test', it has to be percent-encoded when used inside a URI reference (see Section 2.1 of [RFC3986]). Also note that a legal URI may still contain characters that need to be escaped within XML character data, such as the ampersand character.
Some of these new methods do not define bodies. Servers MUST examine all requests for a body, even when a body was not expected. In cases where a request body is present but would be ignored by a server, the server MUST reject the request with 415 (Unsupported Media Type). This informs the client (which may have been attempting to use an extension) that the body could not be processed as the client intended.
HTTP defines many headers that can be used in WebDAV requests and responses. Not all of these are appropriate in all situations and some interactions may be undefined. Note that HTTP 1.1 requires the Date header in all responses if possible (see Section 14.18, [RFC2616]).
The server MUST do authorization checks before checking any HTTP conditional header.
HTTP 1.1 recommends the use of ETags rather than modification dates, for cache control, and there are even stronger reasons to prefer ETags for authoring. Correct use of ETags is even more important in a distributed authoring environment, because ETags are necessary along with locks to avoid the lost-update problem. A client might fail to renew a lock, for example, when the lock times out and the client is accidentally offline or in the middle of a long upload. When a client fails to renew the lock, it's quite possible the resource can still be relocked and the user can go on editing, as long as no changes were made in the meantime. ETags are required for the client to be able to distinguish this case. Otherwise, the
client is forced to ask the user whether to overwrite the resource on the server without even being able to tell the user if it has changed. Timestamps do not solve this problem nearly as well as ETags.
Strong ETags are much more useful for authoring use cases than weak ETags (see Section 13.3.3 of [RFC2616]). Semantic equivalence can be a useful concept but that depends on the document type and the application type, and interoperability might require some agreement or standard outside the scope of this specification and HTTP. Note also that weak ETags have certain restrictions in HTTP, e.g., these cannot be used in If-Match headers.
Note that the meaning of an ETag in a PUT response is not clearly defined either in this document or in RFC 2616 (i.e., whether the ETag means that the resource is octet-for-octet equivalent to the body of the PUT request, or whether the server could have made minor changes in the formatting or content of the document upon storage). This is an HTTP issue, not purely a WebDAV issue.
Because clients may be forced to prompt users or throw away changed content if the ETag changes, a WebDAV server SHOULD NOT change the ETag (or the Last-Modified time) for a resource that has an unchanged body and location. The ETag represents the state of the body or contents of the resource. There is no similar way to tell if properties have changed.
HTTP and WebDAV did not use the bodies of most error responses for machine-parsable information until the specification for Versioning Extensions to WebDAV introduced a mechanism to include more specific information in the body of an error response (Section 1.6 of [RFC3253]). The error body mechanism is appropriate to use with any error response that may take a body but does not already have a body defined. The mechanism is particularly appropriate when a status code can mean many things (for example, 400 Bad Request can mean required headers are missing, headers are incorrectly formatted, or much more). This error body mechanism is covered in Section 16.
Note that the HTTP response headers "Etag" and "Last-Modified" (see [RFC2616], Sections 14.19 and 14.29) are defined per URL (not per resource), and are used by clients for caching. Therefore servers must ensure that executing any operation that affects the URL namespace (such as COPY, MOVE, DELETE, PUT, or MKCOL) does preserve their semantics, in particular:
In practice this means that servers
Note that these considerations also apply to specific use cases, such as using PUT to create a new resource at a URL that has been mapped before, but has been deleted since then.
Finally, WebDAV properties (such as DAV:getetag and DAV:
getlastmodified) that inherit their semantics from HTTP headers must
behave accordingly.
The PROPFIND method retrieves properties defined on the resource
identified by the Request-URI, if the resource does not have any
internal members, or on the resource identified by the Request-URI
and potentially its member resources, if the resource is a collection
that has internal member URLs. All DAV-compliant resources MUST
support the PROPFIND method and the propfind XML element
(Section 14.20) along with all XML elements defined for use with that
element.
A client MUST submit a Depth header with a value of "0", "1", or "infinity" with a PROPFIND request. Servers MUST support "0" and "1" depth requests on WebDAV-compliant resources and SHOULD support "infinity" requests. In practice, support for infinite-depth requests MAY be disabled, due to the performance and security concerns associated with this behavior. Servers SHOULD treat a request without a Depth header as if a "Depth: infinity" header was included.
A client may submit a 'propfind' XML element in the body of the request method describing what information is being requested. It is possible to:
A client may choose not to submit a request body. An empty PROPFIND request body MUST be treated as if it were an 'allprop' request.
Note that 'allprop' does not return values for all live properties. WebDAV servers increasingly have expensively-calculated or lengthy properties (see [RFC3253] and [RFC3744]) and do not return all properties already. Instead, WebDAV clients can use propname requests to discover what live properties exist, and request named properties when retrieving values. For a live property defined elsewhere, that definition can specify whether or not that live property would be returned in 'allprop' requests.
All servers MUST support returning a response of content type text/ xml or application/xml that contains a multistatus XML element that describes the results of the attempts to retrieve the various properties.
If there is an error retrieving a property, then a proper error result MUST be included in the response. A request to retrieve the value of a property that does not exist is an error and MUST be noted with a 'response' XML element that contains a 404 (Not Found) status value.
Consequently, the 'multistatus' XML element for a collection resource MUST include a 'response' XML element for each member URL of the collection, to whatever depth was requested. It SHOULD NOT include any 'response' elements for resources that are not WebDAV-compliant. Each 'response' element MUST contain an 'href' element that contains the URL of the resource on which the properties in the prop XML element are defined. Results for a PROPFIND on a collection resource are returned as a flat list whose order of entries is not
significant. Note that a resource may have only one value for a property of a given name, so the property may only show up once in PROPFIND responses.
Properties may be subject to access control. In the case of 'allprop' and 'propname' requests, if a principal does not have the right to know whether a particular property exists, then the property MAY be silently excluded from the response.
Some PROPFIND results MAY be cached, with care, as there is no cache validation mechanism for most properties. This method is both safe and idempotent (see Section 9.1 of [RFC2616]).
This section, as with similar sections for other methods, provides some guidance on error codes and preconditions or postconditions (defined in Section 16) that might be particularly useful with PROPFIND.
403 Forbidden - A server MAY reject PROPFIND requests on collections with depth header of "Infinity", in which case it SHOULD use this error with the precondition code 'propfind-finite-depth' inside the error body.
In PROPFIND responses, information about individual properties is returned inside 'propstat' elements (see Section 14.22), each containing an individual 'status' element containing information about the properties appearing in it. The list below summarizes the most common status codes used inside 'propstat'; however, clients should be prepared to handle other 2/3/4/5xx series status codes as well.
200 OK - A property exists and/or its value is successfully returned.
401 Unauthorized - The property cannot be viewed without appropriate authorization.
403 Forbidden - The property cannot be viewed regardless of authentication.
404 Not Found - The property does not exist.
>>Request
PROPFIND /file HTTP/1.1
Host: www.example.com
Content-type: application/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<D:propfind xmlns:D="DAV:">
<D:prop xmlns:R="http://ns.example.com/boxschema/">
<R:bigbox/>
<R:author/>
<R:DingALing/>
<R:Random/>
</D:prop>
</D:propfind>
>>Response
HTTP/1.1 207 Multi-Status
Content-Type: application/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<D:multistatus xmlns:D="DAV:">
<D:response xmlns:R="http://ns.example.com/boxschema/">
<D:href>http://www.example.com/file</D:href>
<D:propstat>
<D:prop>
<R:bigbox>
<R:BoxType>Box type A</R:BoxType>
</R:bigbox>
<R:author>
<R:Name>J.J. Johnson</R:Name>
</R:author>
</D:prop>
<D:status>HTTP/1.1 200 OK</D:status>
</D:propstat>
<D:propstat>
<D:prop><R:DingALing/><R:Random/></D:prop>
<D:status>HTTP/1.1 403 Forbidden</D:status>
<D:responsedescription> The user does not have access to the
DingALing property.
</D:responsedescription>
</D:propstat>
</D:response>
<D:responsedescription> There has been an access violation error.
</D:responsedescription>
</D:multistatus>
In this example, PROPFIND is executed on a non-collection resource http://www.example.com/file. The propfind XML element specifies the name of four properties whose values are being requested. In this case, only two properties were returned, since the principal issuing the request did not have sufficient access rights to see the third and fourth properties.
>>Request
PROPFIND /container/ HTTP/1.1
Host: www.example.com
Content-Type: application/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<propfind xmlns="DAV:">
<propname/>
</propfind>
>>Response
HTTP/1.1 207 Multi-Status
Content-Type: application/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<multistatus xmlns="DAV:">
<response>
<href>http://www.example.com/container/</href>
<propstat>
<prop xmlns:R="http://ns.example.com/boxschema/">
<R:bigbox/>
<R:author/>
<creationdate/>
<displayname/>
<resourcetype/>
<supportedlock/>
</prop>
<status>HTTP/1.1 200 OK</status>
</propstat>
</response>
<response>
<href>http://www.example.com/container/front.html</href>
<propstat>
<prop xmlns:R="http://ns.example.com/boxschema/">
<R:bigbox/>
<creationdate/>
<displayname/>
<getcontentlength/>
<getcontenttype/>
<getetag/>
<getlastmodified/>
<resourcetype/>
<supportedlock/>
</prop>
<status>HTTP/1.1 200 OK</status>
</propstat>
</response>
</multistatus>
In this example, PROPFIND is invoked on the collection resource http://www.example.com/container/, with a propfind XML element containing the propname XML element, meaning the name of all properties should be returned. Since no Depth header is present, it assumes its default value of "infinity", meaning the name of the properties on the collection and all its descendants should be returned.
Consistent with the previous example, resource
http://www.example.com/container/ has six properties defined on it:
bigbox and author in the "http://ns.example.com/boxschema/"
namespace, and creationdate, displayname, resourcetype, and
supportedlock in the "DAV:" namespace.
The resource http://www.example.com/container/index.html, a member of
the "container" collection, has nine properties defined on it, bigbox
in the "http://ns.example.com/boxschema/" namespace and creationdate,
displayname, getcontentlength, getcontenttype, getetag,
getlastmodified, resourcetype, and supportedlock in the "DAV:"
namespace.
This example also demonstrates the use of XML namespace scoping and the default namespace. Since the "xmlns" attribute does not contain a prefix, the namespace applies by default to all enclosed elements. Hence, all elements that do not explicitly state the namespace to which they belong are members of the "DAV:" namespace.
Note that 'allprop', despite its name, which remains for backward- compatibility, does not return every property, but only dead properties and the live properties defined in this specification.
>>Request
PROPFIND /container/ HTTP/1.1
Host: www.example.com
Depth: 1
Content-Type: application/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<D:propfind xmlns:D="DAV:">
<D:allprop/>
</D:propfind>
>>Response
HTTP/1.1 207 Multi-Status
Content-Type: application/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<D:multistatus xmlns:D="DAV:">
<D:response>
<D:href>/container/</D:href>
<D:propstat>
<D:prop xmlns:R="http://ns.example.com/boxschema/">
<R:bigbox><R:BoxType>Box type A</R:BoxType></R:bigbox>
<R:author><R:Name>Hadrian</R:Name></R:author>
<D:creationdate>1997-12-01T17:42:21-08:00</D:creationdate>
<D:displayname>Example collection</D:displayname>
<D:resourcetype><D:collection/></D:resourcetype>
<D:supportedlock>
<D:lockentry>
<D:lockscope><D:exclusive/></D:lockscope>
<D:locktype><D:write/></D:locktype>
</D:lockentry>
<D:lockentry>
<D:lockscope><D:shared/></D:lockscope>
<D:locktype><D:write/></D:locktype>
</D:lockentry>
</D:supportedlock>
</D:prop>
<D:status>HTTP/1.1 200 OK</D:status>
</D:propstat>
</D:response>
<D:response>
<D:href>/container/front.html</D:href>
<D:propstat>
<D:prop xmlns:R="http://ns.example.com/boxschema/">
<R:bigbox><R:BoxType>Box type B</R:BoxType>
</R:bigbox>
<D:creationdate>1997-12-01T18:27:21-08:00</D:creationdate>
<D:displayname>Example HTML resource</D:displayname>
<D:getcontentlength>4525</D:getcontentlength>
<D:getcontenttype>text/html</D:getcontenttype>
<D:getetag>"zzyzx"</D:getetag>
<D:getlastmodified
>Mon, 12 Jan 1998 09:25:56 GMT</D:getlastmodified>
<D:resourcetype/>
<D:supportedlock>
<D:lockentry>
<D:lockscope><D:exclusive/></D:lockscope>
<D:locktype><D:write/></D:locktype>
</D:lockentry>
<D:lockentry>
<D:lockscope><D:shared/></D:lockscope>
<D:locktype><D:write/></D:locktype>
</D:lockentry>
</D:supportedlock>
</D:prop>
<D:status>HTTP/1.1 200 OK</D:status>
</D:propstat>
</D:response>
</D:multistatus>
In this example, PROPFIND was invoked on the resource
http://www.example.com/container/ with a Depth header of 1, meaning
the request applies to the resource and its children, and a propfind
XML element containing the allprop XML element, meaning the request
should return the name and value of all the dead properties defined
on the resources, plus the name and value of all the properties
defined in this specification. This example illustrates the use of
relative references in the 'href' elements of the response.
The resource http://www.example.com/container/ has six properties
defined on it: 'bigbox' and 'author in the
"http://ns.example.com/boxschema/" namespace, DAV:creationdate, DAV:
displayname, DAV:resourcetype, and DAV:supportedlock.
The last four properties are WebDAV-specific, defined in Section 15. Since GET is not supported on this resource, the get* properties (e.g., DAV:getcontentlength) are not defined on this resource. The WebDAV-specific properties assert that "container" was created on December 1, 1997, at 5:42:21PM, in a time zone 8 hours west of GMT (DAV:creationdate), has a name of "Example collection" (DAV: displayname), a collection resource type (DAV:resourcetype), and supports exclusive write and shared write locks (DAV:supportedlock).
The resource http://www.example.com/container/front.html has nine properties defined on it:
'bigbox' in the "http://ns.example.com/boxschema/" namespace (another instance of the "bigbox" property type), DAV:creationdate, DAV: displayname, DAV:getcontentlength, DAV:getcontenttype, DAV:getetag, DAV:getlastmodified, DAV:resourcetype, and DAV:supportedlock.
The DAV-specific properties assert that "front.html" was created on December 1, 1997, at 6:27:21PM, in a time zone 8 hours west of GMT (DAV:creationdate), has a name of "Example HTML resource" (DAV: displayname), a content length of 4525 bytes (DAV:getcontentlength), a MIME type of "text/html" (DAV:getcontenttype), an entity tag of "zzyzx" (DAV:getetag), was last modified on Monday, January 12, 1998, at 09:25:56 GMT (DAV:getlastmodified), has an empty resource type, meaning that it is not a collection (DAV:resourcetype), and supports both exclusive write and shared write locks (DAV:supportedlock).
>>Request
PROPFIND /mycol/ HTTP/1.1
Host: www.example.com
Depth: 1
Content-Type: application/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<D:propfind xmlns:D="DAV:">
<D:allprop/>
<D:include>
<D:supported-live-property-set/>
<D:supported-report-set/>
</D:include>
</D:propfind>
In this example, PROPFIND is executed on the resource
http://www.example.com/mycol/ and its internal member resources. The
client requests the values of all live properties defined in this
specification, plus all dead properties, plus two more live
properties defined in [RFC3253]. The response is not shown.
The PROPPATCH method processes instructions specified in the request body to set and/or remove properties defined on the resource identified by the Request-URI.
All DAV-compliant resources MUST support the PROPPATCH method and
MUST process instructions that are specified using the
propertyupdate, set, and remove XML elements. Execution of the
directives in this method is, of course, subject to access control
constraints. DAV-compliant resources SHOULD support the setting of
arbitrary dead properties.
The request message body of a PROPPATCH method MUST contain the propertyupdate XML element.
Servers MUST process PROPPATCH instructions in document order (an exception to the normal rule that ordering is irrelevant). Instructions MUST either all be executed or none executed. Thus, if any error occurs during processing, all executed instructions MUST be undone and a proper error result returned. Instruction processing details can be found in the definition of the set and remove instructions in Sections 14.23 and 14.26.
If a server attempts to make any of the property changes in a PROPPATCH request (i.e., the request is not rejected for high-level errors before processing the body), the response MUST be a Multi- Status response as described in Section 9.2.1.
This method is idempotent, but not safe (see Section 9.1 of [RFC2616]). Responses to this method MUST NOT be cached.
In PROPPATCH responses, information about individual properties is returned inside 'propstat' elements (see Section 14.22), each containing an individual 'status' element containing information about the properties appearing in it. The list below summarizes the most common status codes used inside 'propstat'; however, clients should be prepared to handle other 2/3/4/5xx series status codes as well.
200 (OK) - The property set or change succeeded. Note that if this appears for one property, it appears for every property in the response, due to the atomicity of PROPPATCH.
403 (Forbidden) - The client, for reasons the server chooses not to specify, cannot alter one of the properties.
403 (Forbidden): The client has attempted to set a protected property, such as DAV:getetag. If returning this error, the server SHOULD use the precondition code 'cannot-modify-protected-property' inside the response body.
409 (Conflict) - The client has provided a value whose semantics are not appropriate for the property.
424 (Failed Dependency) - The property change could not be made because of another property change that failed.
507 (Insufficient Storage) - The server did not have sufficient space to record the property.
>>Request
PROPPATCH /bar.html HTTP/1.1
Host: www.example.com
Content-Type: application/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<D:propertyupdate xmlns:D="DAV:"
xmlns:Z="http://ns.example.com/standards/z39.50/">
<D:set>
<D:prop>
<Z:Authors>
<Z:Author>Jim Whitehead</Z:Author>
<Z:Author>Roy Fielding</Z:Author>
</Z:Authors>
</D:prop>
</D:set>
<D:remove>
<D:prop><Z:Copyright-Owner/></D:prop>
</D:remove>
</D:propertyupdate>
>>Response
HTTP/1.1 207 Multi-Status
Content-Type: application/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<D:multistatus xmlns:D="DAV:"
xmlns:Z="http://ns.example.com/standards/z39.50/">
<D:response>
<D:href>http://www.example.com/bar.html</D:href>
<D:propstat>
<D:prop><Z:Authors/></D:prop>
<D:status>HTTP/1.1 424 Failed Dependency</D:status>
</D:propstat>
<D:propstat>
<D:prop><Z:Copyright-Owner/></D:prop>
<D:status>HTTP/1.1 409 Conflict</D:status>
</D:propstat>
<D:responsedescription> Copyright Owner cannot be deleted or
altered.</D:responsedescription>
</D:response>
</D:multistatus>
In this example, the client requests the server to set the value of
the "Authors" property in the
"http://ns.example.com/standards/z39.50/" namespace, and to remove
the property "Copyright-Owner" in the same namespace. Since the
Copyright-Owner property could not be removed, no property
modifications occur. The 424 (Failed Dependency) status code for the
Authors property indicates this action would have succeeded if it
were not for the conflict with removing the Copyright-Owner property.
MKCOL creates a new collection resource at the location specified by the Request-URI. If the Request-URI is already mapped to a resource, then the MKCOL MUST fail. During MKCOL processing, a server MUST make the Request-URI an internal member of its parent collection, unless the Request-URI is "/". If no such ancestor exists, the method MUST fail. When the MKCOL operation creates a new collection resource, all ancestors MUST already exist, or the method MUST fail with a 409 (Conflict) status code. For example, if a request to create collection /a/b/c/d/ is made, and /a/b/c/ does not exist, the request must fail.
When MKCOL is invoked without a request body, the newly created collection SHOULD have no members.
A MKCOL request message may contain a message body. The precise behavior of a MKCOL request when the body is present is undefined, but limited to creating collections, members of a collection, bodies of members, and properties on the collections or members. If the server receives a MKCOL request entity type it does not support or understand, it MUST respond with a 415 (Unsupported Media Type) status code. If the server decides to reject the request based on the presence of an entity or the type of an entity, it should use the 415 (Unsupported Media Type) status code.
This method is idempotent, but not safe (see Section 9.1 of [RFC2616]). Responses to this method MUST NOT be cached.
In addition to the general status codes possible, the following status codes have specific applicability to MKCOL:
201 (Created) - The collection was created.
403 (Forbidden) - This indicates at least one of two conditions: 1) the server does not allow the creation of collections at the given location in its URL namespace, or 2) the parent collection of the Request-URI exists but cannot accept members.
405 (Method Not Allowed) - MKCOL can only be executed on an unmapped URL.
409 (Conflict) - A collection cannot be made at the Request-URI until one or more intermediate collections have been created. The server MUST NOT create those intermediate collections automatically.
415 (Unsupported Media Type) - The server does not support the request body type (although bodies are legal on MKCOL requests, since this specification doesn't define any, the server is likely not to support any given body type).
507 (Insufficient Storage) - The resource does not have sufficient space to record the state of the resource after the execution of this method.
This example creates a collection called /webdisc/xfiles/ on the server www.example.com.
>>Request
MKCOL /webdisc/xfiles/ HTTP/1.1
Host: www.example.com
>>Response
HTTP/1.1 201 Created
The semantics of GET are unchanged when applied to a collection, since GET is defined as, "retrieve whatever information (in the form of an entity) is identified by the Request-URI" [RFC2616]. GET, when applied to a collection, may return the contents of an "index.html" resource, a human-readable view of the contents of the collection, or something else altogether. Hence, it is possible that the result of a GET on a collection will bear no correlation to the membership of the collection.
Similarly, since the definition of HEAD is a GET without a response message body, the semantics of HEAD are unmodified when applied to collection resources.
Since by definition the actual function performed by POST is determined by the server and often depends on the particular resource, the behavior of POST when applied to collections cannot be meaningfully modified because it is largely undefined. Thus, the semantics of POST are unmodified when applied to a collection.
DELETE is defined in [RFC2616], Section 9.7, to "delete the resource identified by the Request-URI". However, WebDAV changes some DELETE handling requirements.
A server processing a successful DELETE request:
MUST destroy locks rooted on the deleted resource
MUST remove the mapping from the Request-URI to any resource.
Thus, after a successful DELETE operation (and in the absence of other actions), a subsequent GET/HEAD/PROPFIND request to the target Request-URI MUST return 404 (Not Found).
The DELETE method on a collection MUST act as if a "Depth: infinity" header was used on it. A client MUST NOT submit a Depth header with a DELETE on a collection with any value but infinity.
DELETE instructs that the collection specified in the Request-URI and all resources identified by its internal member URLs are to be deleted.
If any resource identified by a member URL cannot be deleted, then all of the member's ancestors MUST NOT be deleted, so as to maintain URL namespace consistency.
Any headers included with DELETE MUST be applied in processing every resource to be deleted.
When the DELETE method has completed processing, it MUST result in a consistent URL namespace.
If an error occurs deleting a member resource (a resource other than the resource identified in the Request-URI), then the response can be a 207 (Multi-Status). Multi-Status is used here to indicate which internal resources could NOT be deleted, including an error code, which should help the client understand which resources caused the failure. For example, the Multi-Status body could include a response with status 423 (Locked) if an internal resource was locked.
The server MAY return a 4xx status response, rather than a 207, if the request failed completely.
424 (Failed Dependency) status codes SHOULD NOT be in the 207 (Multi- Status) response for DELETE. They can be safely left out because the client will know that the ancestors of a resource could not be deleted when the client receives an error for the ancestor's progeny. Additionally, 204 (No Content) errors SHOULD NOT be returned in the 207 (Multi-Status). The reason for this prohibition is that 204 (No Content) is the default success code.
>>Request
DELETE /container/ HTTP/1.1
Host: www.example.com
>>Response
HTTP/1.1 207 Multi-Status
Content-Type: application/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<d:multistatus xmlns:d="DAV:">
<d:response>
<d:href>http://www.example.com/container/resource3</d:href>
<d:status>HTTP/1.1 423 Locked</d:status>
<d:error><d:lock-token-submitted/></d:error>
</d:response>
</d:multistatus>
In this example, the attempt to delete
http://www.example.com/container/resource3 failed because it is
locked, and no lock token was submitted with the request.
Consequently, the attempt to delete http://www.example.com/container/
also failed. Thus, the client knows that the attempt to delete
http://www.example.com/container/ must have also failed since the
parent cannot be deleted unless its child has also been deleted.
Even though a Depth header has not been included, a depth of infinity
is assumed because the method is on a collection.
A PUT performed on an existing resource replaces the GET response entity of the resource. Properties defined on the resource may be recomputed during PUT processing but are not otherwise affected. For example, if a server recognizes the content type of the request body, it may be able to automatically extract information that could be profitably exposed as properties.
A PUT that would result in the creation of a resource without an appropriately scoped parent collection MUST fail with a 409 (Conflict).
A PUT request allows a client to indicate what media type an entity body has, and whether it should change if overwritten. Thus, a client SHOULD provide a Content-Type for a new resource if any is known. If the client does not provide a Content-Type for a new resource, the server MAY create a resource with no Content-Type assigned, or it MAY attempt to assign a Content-Type.
Note that although a recipient ought generally to treat metadata supplied with an HTTP request as authoritative, in practice there's no guarantee that a server will accept client-supplied metadata (e.g., any request header beginning with "Content-"). Many servers do not allow configuring the Content-Type on a per-resource basis in the first place. Thus, clients can't always rely on the ability to directly influence the content type by including a Content-Type request header.
This specification does not define the behavior of the PUT method for existing collections. A PUT request to an existing collection MAY be treated as an error (405 Method Not Allowed).
The MKCOL method is defined to create collections.
The COPY method creates a duplicate of the source resource identified by the Request-URI, in the destination resource identified by the URI in the Destination header. The Destination header MUST be present. The exact behavior of the COPY method depends on the type of the source resource.
All WebDAV-compliant resources MUST support the COPY method. However, support for the COPY method does not guarantee the ability to copy a resource. For example, separate programs may control resources on the same server. As a result, it may not be possible to copy a resource to a location that appears to be on the same server.
This method is idempotent, but not safe (see Section 9.1 of [RFC2616]). Responses to this method MUST NOT be cached.
When the source resource is not a collection, the result of the COPY method is the creation of a new resource at the destination whose state and behavior match that of the source resource as closely as possible. Since the environment at the destination may be different than at the source due to factors outside the scope of control of the server, such as the absence of resources required for correct operation, it may not be possible to completely duplicate the behavior of the resource at the destination. Subsequent alterations to the destination resource will not modify the source resource. Subsequent alterations to the source resource will not modify the destination resource.
After a successful COPY invocation, all dead properties on the source resource SHOULD be duplicated on the destination resource. Live properties described in this document SHOULD be duplicated as identically behaving live properties at the destination resource, but not necessarily with the same values. Servers SHOULD NOT convert live properties into dead properties on the destination resource, because clients may then draw incorrect conclusions about the state or functionality of a resource. Note that some live properties are defined such that the absence of the property has a specific meaning (e.g., a flag with one meaning if present, and the opposite if absent), and in these cases, a successful COPY might result in the property being reported as "Not Found" in subsequent requests.
When the destination is an unmapped URL, a COPY operation creates a new resource much like a PUT operation does. Live properties that are related to resource creation (such as DAV:creationdate) should have their values set accordingly.
The COPY method on a collection without a Depth header MUST act as if a Depth header with value "infinity" was included. A client may submit a Depth header on a COPY on a collection with a value of "0" or "infinity". Servers MUST support the "0" and "infinity" Depth header behaviors on WebDAV-compliant resources.
An infinite-depth COPY instructs that the collection resource identified by the Request-URI is to be copied to the location identified by the URI in the Destination header, and all its internal member resources are to be copied to a location relative to it, recursively through all levels of the collection hierarchy. Note that an infinite-depth COPY of /A/ into /A/B/ could lead to infinite recursion if not handled correctly.
A COPY of "Depth: 0" only instructs that the collection and its properties, but not resources identified by its internal member URLs, are to be copied.
Any headers included with a COPY MUST be applied in processing every resource to be copied with the exception of the Destination header.
The Destination header only specifies the destination URI for the Request-URI. When applied to members of the collection identified by the Request-URI, the value of Destination is to be modified to reflect the current location in the hierarchy. So, if the Request- URI is /a/ with Host header value http://example.com/ and the
Destination is http://example.com/b/, then when
http://example.com/a/c/d is processed, it must use a Destination of
http://example.com/b/c/d.
When the COPY method has completed processing, it MU