WebDAV
From Wikipedia, the free encyclopedia
WebDAV was an IETF working group. The abbreviation stands for Web-based Distributed Authoring and Versioning. The term also refers to the set of extensions to the HTTP protocol that the group defined which allows users to collaboratively edit and manage files on remote web servers.
The WebDAV protocol's aim was to make the World Wide Web a readable and writable medium, in line with Tim Berners-Lee's original vision. It provides functionality to create, change and move documents on a remote server (typically a web server or "web share"). This is useful, among other things, for authoring the documents which a web server serves, but can also be used for general web-based file storage that can be accessed from anywhere. Important features in WebDAV protocol include locking (overwrite prevention), properties (creation, removal, and querying of information about author, modified date, etc.), name space management (ability to copy and move Web pages within a server's namespace) and collections (creation, removal, and listing of resources). Most modern operating systems provide built-in support for WebDAV. With the right client and a fast network, it can be almost as easy to use files on a WebDAV server as those stored in local directories.
The WebDAV working group has concluded its work in March 2007, after an incremental update to RFC2518 was accepted by the IESG. Other extensions that were unfinished at that point of time - such as the BIND protocol - will be finished by their individual authors outside a formal working group.
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[edit] History
WebDAV began when Jim Whitehead convinced the W3C to host two meetings where people interested in the problem of distributed authoring on the World Wide Web could get together to discuss possible solutions. The original vision of the World Wide Web as expounded by Tim Berners-Lee was a both readable and writable medium. In fact Berners-Lee's first web browser, called WorldWideWeb, was capable of both viewing and editing web pages. However as it grew the web became, for most users, a read-only medium. Whitehead and other like-minded people wanted to fix that limitation.[citation needed]
The group of people meeting at the W3C decided that the best way to proceed was to form an IETF working group. The IETF seemed a natural choice as the HTTP protocol was being standardized there and it was assumed that this new effort would lead to extensions to that protocol.
As work began on the protocol it became clear that handling both distributed authoring and versioning was just too much and that the tasks would have to be separated. The WebDAV working group therefore decided to focus on just distributed authoring and leave 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 and has the distinction of almost certainly being the first protocol ever to use XML.
[edit] Documents produced by the working group
The WebDAV working group has to date produced several works:
- a requirements document: "Requirements for a Distributed Authoring and Versioning Protocol for the World Wide Web" RFC 2291,
- a base protocol document: "HTTP Extensions for Distributed Authoring -- WEBDAV" RFC 2518,
- the ordered collections protocol: "Web Distributed Authoring and Versioning (WebDAV) Ordered Collections Protocol" RFC 3648,
- the access control protocol: "Web Distributed Authoring and Versioning (WebDAV) Access Control Protocol" RFC 3744,
- a quota specification: "Quota and Size Properties for Distributed Authoring and Versioning (DAV) Collections" RFC 4331,
- a redirect specification: "Web Distributed Authoring and Versioning (WebDAV) Redirect Reference Resources" RFC 4437, and
- an update to the base protocol document: "HTTP Extensions for Distributed Authoring -- WEBDAV" draft-ietf-webdav-rfc2518bis-18 (publication pending).
[edit] Documents not produced by the working group, but published through the 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, and
- a calendar access protocol: "Calendaring Extensions to WebDAV (CalDAV)" RFC 4791.
[edit] Overview of the protocol
WebDAV added the following methods to HTTP:
- PROPFIND — Used to retrieve properties, persisted as XML, from a 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. 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 — To remove a lock from a resource.
Resource is HTTP's name for a referent: that which is pointed to by a URI.
[edit] Extensions and derivatives
- For versioning, the Web Versioning and Configuration Management (Delta-V (Internet Protocol)) working group is the Versioning Extensions to WebDAV which put the V back into WebDAV.
- 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 continues as non-working-group activity, see DASL). However another, WebDav SEARCH attempts to pick up where it left off.
- 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.
[edit] Windows XP and the "mini redirector"
Microsoft introduced WebDAV client support in Windows 98 with a feature called "Web folders". This client was simply an extension to Windows Explorer (the desktop/file manager) and later included in Windows 2000. In Windows XP, Microsoft changed the client to the "WebDAV mini-redirector". This new client works at the filesystem level, allowing WebDAV shares to be assigned to a drive letter and used by all software. However, all versions of the redirector have serious bugs[1]. It has been known to try to convert HTTP URLs to UNC paths e.g http://host/path/ to \\host\path\. It also often uses Windows Domain authentication when answering HTTP basic-auth challenges. One known fix which may work around the first problem is to explicitly specify the port number in the URL e.g http://host:80/path/. This reportedly forces the use of the old "Web folders" client.
