|RFC(s)||RFC 2518, RFC 4918|
Web Distributed Authoring and Versioning (WebDAV) is an extension of the Hypertext Transfer Protocol (HTTP) that allows clients to perform remote Web content authoring operations. A working group of the Internet Engineering Task Force (IETF) defined WebDAV in RFC 4918.
The WebDAV protocol makes the Web a readable and writable medium. It provides a framework for users to create, change and move documents on a server; typically a web server or web share. The most important features of the WebDAV protocol include the maintenance of properties about an author or modification date, namespace management, collections, and overwrite protection. Maintenance of properties includes such things as the creation, removal, and querying of file information. Namespace management deals with the ability to copy and move web pages within a server’s namespace. Collections deal with the creation, removal, and listing of various resources. Lastly, overwrite protection handles aspects related to locking of files.
The WebDAV working group concluded its work in March 2007, after the Internet Engineering Steering Group (IESG) accepted an incremental update to RFC 2518. Other extensions left unfinished at that time, such as the BIND method, have been finished by their individual authors, independent of the formal working group.
WebDAV began in 1996 when Jim Whitehead, a PhD graduate from UC Irvine, worked with the World Wide Web Consortium (W3C) to host two meetings to discuss the problem of distributed authoring on the World Wide Web with interested people. Tim Berners-Lee's original vision of the Web was that of a medium for both reading and writing. In fact, Berners-Lee's first web browser, called WorldWideWeb, was able to both view and edit web pages; but, as the Web grew, it became a read-only medium for most users. Whitehead and other like-minded people wanted to fix that limitation.
As work began on the protocol, it became clear that handling both distributed authoring and versioning would involve too much work and that the tasks would have to be separated. The WebDAV group focused on distributed authoring, and left versioning for the future. Versioning was added later by the Delta-V extension — see the Extensions section below.
The protocol consists of a set of new methods and headers for use in HTTP. The added methods include:
- PROPFIND — used to retrieve properties, stored as XML, from a web resource. It is also overloaded to allow one to retrieve the collection structure (a.k.a. directory hierarchy) of a remote system.
- PROPPATCH — used to change and delete multiple properties on a resource in a single atomic act
- MKCOL — used to create collections (a.k.a. a directory)
- COPY — used to copy a resource from one URI to another
- MOVE — used to move a resource from one URI to another
- LOCK — used to put a lock on a resource. WebDAV supports both shared and exclusive locks.
- UNLOCK — used to remove a lock from a resource
- The cross-platform Apache HTTP Server provides WebDAV modules based on both davfs and Apache Subversion (svn).
Linux users can mount WebDAV shares using the davfs2 and the fusedav file system modules which mount them as Coda or FUSE filesystems. KDE has native WebDAV support as part of kio_http. This enables the file managers Dolphin & Konqueror, and every other KDE application to interact directly with WebDAV servers. All applications using the GIO library, including the Nautilus file manager, have access to WebDAV through GNOME Virtual File System (GVFS). Many Linux distributions also include the cadaver command-line client interface, which provides an FTP-like command set.
Mac OS X version 10.0 and following support WebDAV shares natively as a type of filesystem. The system can mount WebDAV-enabled server directories to the filesystem using the traditional BSD mounting mechanism or through the "Connect to Server" dialog found in the Finder. Mac OS X version 10.1.1 introduced support for HTTP Digest Access authentication. Mac OS X 10.4 (Tiger) extended WebDAV interoperability to include support for the HTTPS scheme, proxies, and additional methods of authentication. The Finder presents a WebDAV share as an external disk, allowing users to interact with WebDAV just as they would with any other filesystem. Apple's iDisk, part of its former MobileMe service, used WebDAV for file access.
Microsoft introduced WebDAV client support in Microsoft Windows 98 with a feature called "Web folders". This client consisted of an OLE object which could be accessed by any OLE software, and was installed as an extension to Windows Explorer (the desktop/file manager) and was later included in Windows 2000. In Windows XP, Microsoft added the Web Client service also known as the WebDAV mini-redirector which is preferred by default over the old Web folders client. This newer client works as a system service at the network-redirector level (immediately above the file-system), allowing WebDAV shares to be assigned to a drive letter and used by any software. The redirector also allows WebDAV shares to be addressed via UNC paths (e.g. http://host/path/ is converted to \\host\path\) for compatibility with Windows filesystem APIs. Some versions of the redirector are reported to have some limitations in authentication support. In addition, WebDAV over HTTPS works only if a computer has KB892211-version files or newer installed. Otherwise Windows displays "The folder you entered does not appear to be valid. Please choose another" when adding a network resource. NOTE: 892211 has been superseded by KB907306. Windows Vista includes only the WebDAV redirector, but if you install a version of Office, Internet Explorer, OLE-DB or "Microsoft Update for Web Folders" you will get the original "Web folders" client. The update will only work on the 32-bit version of XP/Vista. Microsoft states that 64 bit versions of Windows will never support the "Web folders" client. Instead users are limited to using WebDAV via the native Web Client service redirector.
Alternatives to WebDAV
- File Transfer Protocol (FTP), a simple network protocol based on IP, allows users to transfer files between network hosts. FTPS extends FTP for secure traffic.
- SSH File Transfer Protocol (SFTP), an extension of the Secure Shell protocol (SSH) version 2.0, provides secure file-transfer capability
- A distributed file system such as the Server Message Block (SMB) protocol allows Microsoft Windows and open-source Samba clients to access and manage files and folders remotely on a suitable file server
- AtomPub, an HTTP-based protocol for creating and updating web resources, can be used for some of the use cases of WebDAV. It is based on standard HTTP verbs with standardized collection resources that behave somewhat like the WebDAV model of directories.
- CMIS, a standard consisting of a set of Web services for sharing information among disparate content repositories, seeks to ensure interoperability for people and applications using multiple content repositories; it has both SOAP- and AtomPub-based interfaces
Documents produced by the working group
The WebDAV working group produced several works:
- a requirements document: "Requirements for a Distributed Authoring and Versioning Protocol for the World Wide Web" RFC 2291, issued February 1998
- a base protocol document (excluding versioning, despite its title): "HTTP Extensions for Web Distributed Authoring and Versioning (WebDAV)" RFC 4918, issued June 2007 (which updates and supersedes "HTTP Extensions for Distributed Authoring — WebDAV" RFC 2518, issued February 1999)
- the ordered collections protocol: "Web Distributed Authoring and Versioning (WebDAV) Ordered Collections Protocol" RFC 3648, issued December 2003
- the access control protocol: "Web Distributed Authoring and Versioning (WebDAV) Access Control Protocol" RFC 3744, issued May 2004
- a quota specification: "Quota and Size Properties for Distributed Authoring and Versioning (DAV) Collections" RFC 4331, issued February 2006
- a redirect specification: "Web Distributed Authoring and Versioning (WebDAV) Redirect Reference Resources" RFC 4437, issued March 2006
Other documents published through IETF
- the versioning protocol: "Versioning Extensions to WebDAV (Web Distributed Authoring and Versioning)" RFC 3253 (created by the Delta-V working group)
- a specification of WebDAV property datatypes: "Datatypes for Web Distributed Authoring and Versioning (WebDAV) Properties" RFC 4316
- a document defining how to initiate mounting of a WebDAV resource: "Mounting Web Distributed Authoring and Versioning (WebDAV) Servers" RFC 4709
- a calendar access protocol: "Calendaring Extensions to WebDAV (CalDAV)" RFC 4791
- a query protocol: "Web Distributed Authoring and Versioning (WebDAV) SEARCH" RFC 5323
- an extension to the WebDAV ACL specification: "WebDAV Current Principal Extension" RFC 5397
- an extension to the WebDAV MKCOL method: "Extended MKCOL for Web Distributed Authoring and Versioning (WebDAV)" RFC 5689
- an extension of the collection model, defining creation and discovery of additional bindings to a resource: "Binding Extensions to Web Distributed Authoring and Versioning (WebDAV)" RFC 5842
- an application of POST to WebDAV collections: "Using POST to Add Members to Web Distributed Authoring and Versioning (WebDAV) Collections" RFC 5995
- an extension which allows synchronizing large collections efficiently: "Collection Synchronization for Web Distributed Authoring and Versioning (WebDAV)" RFC 6578
Extensions and derivatives
For versioning, the Delta-V protocol under the Web Versioning and Configuration Management working group adds resource revision tracking, published in RFC 3253.
For searching and locating, the DAV Searching and Locating (DASL) working group never produced any official standard although there are a number of implementations of its last draft. Work continued as non-working-group activity. The WebDAV Search specification attempts to pick up where the working group left off, and was published as RFC 5323 in November 2008.
For calendaring, CalDAV is a protocol allowing calendar access via WebDAV. CalDAV models calendar events as HTTP resources in iCalendar format, and models calendars containing events as WebDAV collections.
For MS Exchange interoperability, WebDAV can be used for reading/updating/deleting items in a mailbox or public folder. WebDAV for Exchange has been extended by Microsoft to accommodate working with messaging data. Exchange Server version 2000, 2003, and 2007 support WebDAV. However, WebDAV support has been discontinued in Exchange 2010 in favor of Exchange Web Services (EWS), a SOAP/XML based API.
Additional Windows-specific extensions
As part of the Windows Server Protocols (WSPP) documentation set, Microsoft published the following protocol documents detailing extensions to WebDAV:
- [MS-WDVME]: Web Distributed Authoring and Versioning (WebDAV) Protocol: Microsoft Extensions. These extensions include a new verb and new headers, and properties that enable previously unmanageable file types and optimize protocol interactions for file system clients. These extensions introduce new functionality into WebDAV, optimize processing, and eliminate the need for special-case processing.
- [MS-WDV]: Web Distributed Authoring and Versioning (WebDAV) Protocol: Client Extensions. The client extensions in this specification extend the WebDAV Protocol by introducing new headers that both enable the file types that are not currently manageable and optimize protocol interactions for file system clients. These extensions do not introduce new functionality into the WebDAV Protocol, but instead optimize processing and eliminate the need for special-case processing.
- [MS-WDVSE]: Web Distributed Authoring and Versioning (WebDAV) Protocol: Server Extensions. The server extensions in this specification extend WebDAV by introducing new HTTP request and response headers that both enable the file types that are not currently manageable and optimize protocol interactions for file system clients. This specification also introduces a new WebDAV method that is used to send search queries to disparate search providers.
- [MS-WEBDAVE]: Web Distributed Authoring and Versioning Error Extensions Protocol Specification. This SharePoint Front-End Protocol describes extended error codes and extended error handling mechanism specified in [MS-WDV] to enable compliant servers to report error condition details on a server response.
- "Realising the Full Potential of the Web".
- "Proposed agenda for San Mateo Meeting". 1996.
- "Brief mtg. summary". 1996.
- "Re: Updated agenda".
- Preliminary webdav support in kio_http
- indoglobal.com: KDE Konqueror
- Mac OS X Man Page for mount_webdav(8)
- Overview of Mac OS X File Systems
- "How documents are opened from a Web site in Office 2003". Microsoft Support. Microsoft. Retrieved 25 June 2012.
- WebDAV Mini-Redirector (MRXDAV.SYS) Versions and Issues List
- Windows Vista Client Setup Instructions
- Description of the Software Update for Web Folders: May 18, 2007. Support.microsoft.com. Retrieved on 2013-07-17.
- WebDav SEARCH
- Discontinued Features: Exchange 2010 SP1 Help Microsoft TechNet
- "WSPP – Windows Server Protocols documentation". 2011.
- "MS-WDVME – Web Distributed Authoring and Versioning (WebDAV) Protocol: Microsoft Extensions". 2014.
- "MS-WDV – Web Distributed Authoring and Versioning (WebDAV) Protocol: Client Extensions". 2011.
- "MS-WDVSE – Web Distributed Authoring and Versioning (WebDAV) Protocol: Server Extensions". 2011.
- "MS-WEBDAVE – Web Distributed Authoring and Versioning Error Extensions Protocol Specification". 2011.