WebDAV

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WebDAV
Communication protocol
OSI layerApplication
Port(s)80, 443
RFC(s)RFC 2518, RFC 4918
Websitewww.webdav.org

WebDAV (Web Distributed Authoring and Versioning) is a set of extensions to the Hypertext Transfer Protocol (HTTP), which allows user agents to collaboratively author contents directly in an HTTP web server by providing facilities for concurrency control and namespace operations, thus allowing Web to be viewed as a writeable, collaborative medium and not just a read-only medium.[1] WebDAV is defined in RFC 4918 by a working group of the Internet Engineering Task Force (IETF).[2]

The WebDAV protocol provides a framework for users to create, change and move documents on a server. The most important features 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 the locking of files. It takes advantage of existing technologies such as Transport Layer Security, digest access authentication or XML to satisfy those requirements.[3]

Many modern operating systems provide built-in client-side support for WebDAV.

History[edit]

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.[4][5] Tim Berners-Lee's original vision of the Web involved a medium for both reading and writing. In fact, Berners-Lee's first web browser, called WorldWideWeb, could 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 transcend that limitation.[6][7]

The meetings resulted in the formation of an IETF working group because the new effort would lead to extensions to HTTP, which the IETF had started to standardize.

As work began on the protocol, it became clear that handling both distributed authoring and versioning together 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. (The Delta-V extension added versioning later – see the Extensions section below.)

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.[8]

Implementation[edit]

WebDAV collaborative authoring in a compatible HTTP server

WebDAV extends the set of standard HTTP verbs and headers allowed for request methods. The added verbs include:

  • COPY: copy a resource from one uniform resource identifier (URI) to another
  • LOCK: put a lock on a resource. WebDAV supports both shared and exclusive locks.
  • MKCOL: create collections (also known as a directory)
  • MOVE: move a resource from one URI to another
  • PROPFIND: retrieve properties, stored as XML, from a web resource. It is also overloaded to allow one to retrieve the collection structure (also known as directory hierarchy) of a remote system.
  • PROPPATCH: change and delete multiple properties on a resource in a single atomic act
  • UNLOCK: remove a lock from a resource

Properties[edit]

The properties of WebDAV protocol are name–value pair, in which a "name" is a Uniform Resource Identifier (URI) and the "values" are expressed through XML elements. Furthremore the methods to handle the properties are PROPFIND and PROPPATCH.[9]

Server support[edit]

  • Apache HTTP Server provides WebDAV modules based on both davfs and Apache Subversion (svn).
  • Caddy has an optional WebDAV module[10]
  • EGroupware, a Groupware with full *DAV support: CalDAV, CardDAV and WebDAV for file manager[11]
  • lighttpd has an optional WebDAV module[12]
  • Mailfence offers WebDAV support through a virtual drive+ you can connect external drives to Mailfence Documents[13]
  • Nextcloud is a fork of ownCloud, and therefore also offers full WebDAV support[14]
  • Nginx has a very limited optional WebDAV module[15] and a third-party module[16]
  • ownCloud is a cloud storage PHP application which offers full WebDAV support[17]
  • SabreDAV is a PHP application that can be used on Apache or Nginx in lieu of their bundled modules
  • Seafile has an optional WebDAV configuration[18]
  • Microsoft IIS introduced limited support for WebDAV in IIS version 5 & 6, and full support for WebDAV in IIS 7.5.[19] (Note: full WebDAV support for IIS 7 was provided through a separate download that was discontinued in July 2021.[20])

Client support[edit]

Documents produced by the working group[edit]

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[edit]

  • 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[edit]

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.[22] The WebDAV Search specification attempts to pick up where the working group left off, and was published as RFC 5323 in November 2008.[23]

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 groupware, GroupDAV is a variant of WebDAV which allows client/server groupware systems to store and fetch objects such as calendar items and address book entries instead of web pages.

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[24] in favor of Exchange Web Services (EWS), a SOAP/XML based API.

Additional Windows-specific extensions[edit]

As part of the Windows Server Protocols (WSPP) documentation set,[25] Microsoft published the following protocol documents detailing extensions to WebDAV:

  • [MS-WDVME]: Web Distributed Authoring and Versioning (WebDAV) Protocol: Microsoft Extensions.[26] 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.[27] 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.[28] 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.[29] 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.

WebDAV clients[edit]

Client Creator Operating system support License Interface
Cyberduck David V. Kocher Windows, MacOSX GPL GUI
davfs2 GNOME team FUSE GPL VFS
davix CERN Windows, Linux, MacOSX LGPL CLI
GVfs GNOME team GNOME GPL VFS
KIO KDE team KDE GPL VFS
Konqueror KDE team KDE GPL GUI
GNOME Files GNOME team GNOME GPL GUI
SmartFTP SmartSoft Ltd Windows Proprietary GUI
WebDrive South River Technologies Windows, OS X, iOS, Droid Proprietary VFS
WinSCP Martin Přikryl Windows GPL CLI and GUI

WebDAV libraries[edit]

Libraries Creator Operating system or platform License Language
Apache Wink Apache Software foundation JVM Java
Apache Tomcat Apache Software foundation JVM Java
Apache Jackrabbit Apache Software foundation JVM ASF Java
sabre/dav fruux Windows, Linux, MacOSX New BSD PHP


Alternatives to WebDAV[edit]

  • File Transfer Protocol (FTP), a simple and widely adapted 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 ; and scp, a form of SFTP that runs as a single command similar to a regular cp (copy) command in the shell.
  • Rsync, a protocol and a command similar to scp, that can also skip rewriting identical files and portions of files, or skip newer files, etc.
  • 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. Commonly used for multimedia streaming over ethernet and widely supported by Smart TVs.[30]
  • 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
  • Wiki software, such as MediaWiki.
  • Linked Data Platform (LDP), a Linked Data specification defining a set of integration patterns for building RESTful HTTP services that are capable of read-write of RDF data.
  • Object storage such as OpenStack Swift or Amazon S3

See also[edit]

References[edit]

  1. ^ Whitehead & Goland 1999, p. 293.
  2. ^ Whitehead 1998, p. 34.
  3. ^ Whitehead & Goland 1999, p. 294.
  4. ^ "Proposed agenda for San Mateo Meeting". 1996.
  5. ^ "Brief mtg. summary". 1996.
  6. ^ "Re: Updated agenda".
  7. ^ Whitehead 1998, p. 40.
  8. ^ Whitehead 1998, p. 39-40.
  9. ^ Whitehead & Goland 1999, p. 299.
  10. ^ 28 Jul 2017. "http.webdav - Caddy User Guide". Retrieved 13 July 2018.
  11. ^ "Access to EGroupware via WebDAV (CalDAV/CardDAV)". Retrieved 14 October 2021.
  12. ^ "lighttpd mod webdav".
  13. ^ "WebDAV implementation of Mailfence". Retrieved 5 May 2020.
  14. ^ "Nextcloud 18 User Manual". nextcloud.com. Retrieved 22 February 2020.
  15. ^ "Module ngx_http_dav_module". nginx website. Retrieved 15 July 2016.
  16. ^ "Module nginx-dav-ext-module". github.com. Retrieved 2 August 2016.
  17. ^ "ownCloud Documentation". owncloud.com. Retrieved 23 July 2018.
  18. ^ "Seafile Community Manual". Retrieved 14 September 2021.
  19. ^ "Installing and Configuring WebDAV on IIS 7 and Later". docs.microsoft.com. Retrieved 20 October 2021.
  20. ^ "WebDAV Extension for IIS". IIS.net. Retrieved 20 October 2021.
  21. ^ "Using the WebDAV Redirector". microsoft.com. Retrieved 21 October 2021.
  22. ^ DASL Archived 2004-06-03 at the Wayback Machine
  23. ^ WebDav SEARCH
  24. ^ Discontinued Features: Exchange 2010 SP1 Help Microsoft TechNet
  25. ^ "WSPP – Windows Server Protocols documentation". 2011.
  26. ^ "MS-WDVME – Web Distributed Authoring and Versioning (WebDAV) Protocol: Microsoft Extensions". 2014.
  27. ^ "MS-WDV – Web Distributed Authoring and Versioning (WebDAV) Protocol: Client Extensions". 2011.
  28. ^ "MS-WDVSE – Web Distributed Authoring and Versioning (WebDAV) Protocol: Server Extensions". 2011.
  29. ^ "MS-WEBDAVE – Web Distributed Authoring and Versioning Error Extensions Protocol Specification". 2011.
  30. ^ Rau, Thomas (19 October 2017). "Filme, Musik & Bilder im Heimnetzwerk streamen". PC-WELT (in German). Retrieved 5 November 2020.

External links[edit]