Mounting Web Distributed Authoring and Versioning (WebDAV) Serversgreenbytes GmbHHafenweg 16MuensterNW48155Germany+49 251 2807760+49 251 2807761[email protected]http://greenbytes.de/tech/webdav/
In current Web browsers, there is no uniform way to specify that a user
clicking on a link will be presented with an editable view of a
Web Distinguished Authoring and Versioning (WebDAV)
server. For example, it is frequently desirable to be able to click
on a link and have this link open a window that can handle drag-and-drop interaction with the resources of a WebDAV server.
This document specifies a mechanism and a document format that enables
WebDAV servers to send
"mounting" information to a WebDAV client. The
mechanism is designed to work on any platform and with any combination
of browser and WebDAV client, relying solely on the well-understood
dispatch of documents through their MIME type.
By definition, a Web Distributed Authoring and Versioning (WebDAV) server () is an HTTP
server as well (). Most WebDAV servers can be
(at least partly) operated from an HTML-based user interface in a web browser. However,
it is frequently desirable to be able to switch from an HTML-based view to
a presentation provided by a native WebDAV client, directly supporting
the authoring features defined in WebDAV and related specifications.
This document specifies a platform-neutral mechanism based on the dispatch
of documents through their MIME type. For completeness, lists other
approaches that have been implemented in existing clients.
For example, many educational institutions use WebDAV servers as a mechanism
for sharing documents among students. Each student owns a separate collection
structure on a WebDAV server, often called his/her "locker". Ideally, when
users click on a link in an HTML page provided by the university (perhaps
by their university Web portal), an editable view of their locker will appear.
The terminology used here follows that in the WebDAV Distributed
Authoring Protocol specification .
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD",
"SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be
interpreted as described in .
This document uses XML DTD fragments
() as a purely notational convention. In particular:
Element names use the namespace "http://purl.org/NET/webdav/mount". When
an XML element type in this namespace is referenced in this document outside
of the context of an XML fragment, the string "dm:" will be prefixed to the element name.
Element ordering is irrelevant.Extension elements/attributes (elements/attributes not already defined
as valid child elements) may be added anywhere, except when explicitly
stated otherwise.
A WebDAV mount request is encoded in a specific XML format ()
with a well-defined MIME type (see ).
The MIME type allows user agents to dispatch the content to a handler
specific to the system's WebDAV client.
The elements defined below use the namespace "http://purl.org/NET/webdav/mount".
<!ELEMENT mount (url, open?, username?) >
<!ELEMENT url (#PCDATA) >
<!-- PCDATA value: scheme ":" hier-part, as defined in of
-->
<!ELEMENT open (#PCDATA) >
<!-- PCDATA value: path, as defined in of
-->
<!ELEMENT username (#PCDATA) >
The <dm:mount> element acts as a container for all the remaining elements
defined by this protocol.
The mandatory <dm:url> element provides the HTTP URL of the WebDAV collection
that should be mounted by the client.
The optional <dm:open> element instructs the client to display the specified
child collection; its URL is computed by concatenating this element's
value with the URL obtained from the <dm:url> element
(see for a discussion about
why this element only supports displaying collections rather than opening
arbitrary documents).
The server can use the optional <dm:username> element to specify the name
of the currently authenticated principal. A client can use this value to select
a matching mount point (different users may have mounted the URL with
different credentials under different local mount points) or to provide
a meaningful default for
authentication against the server. It is common that a browser and
WebDAV client do not share HTTP connections, so including this information
in the mount document increases usability.
Implementation Note: If a <dm:username> element is present, public
caching of the document should be disallowed. Thus, appropriate 'Vary' or
'Cache-Control' headers are needed in the server response.
In the example below, the client first retrieves a representation of a
WebDAV collection using a generic Web browser (1). The returned HTML content
contains a hyperlink that identifies the "davmount" document
in the format defined in (2). The user follows this
link (3), which causes the server to return the "davmount" document to the user's
browser (4). The browser in turn passes the content to the application that
was registered to handle the "application/davmount+xml" MIME type, usually
the default WebDAV client on the client's system.
(1) Client retrieves representation of WebDAV collection "/user42/inbox/".
GET /user42/inbox/ HTTP/1.1
Host: www.example.com
(2) Server returns representation.
HTTP/1.1 200 OK
Content-Type: text/html
Content-Length: xxx
..
<a href="?action=davmount">View this collection in your
WebDAV client</a>
..
(note that the example shows only that part of the HTML page
that contains the relevant link)
(3) Client follows link to "davmount" document
GET /user42/inbox/?action=davmount HTTP/1.1
Host: www.example.com
(4) Server returns "davmount" document
HTTP/1.1 200 OK
Content-Type: application/davmount+xml
Content-Length: xxx
Cache-Control: private
<dm:mount xmlns:dm="http://purl.org/NET/webdav/mount">
<dm:url>http://www.example.com/user42/</dm:url>
<dm:open>inbox/</dm:open>
</dm:mount>
This document does not introduce any new internationalization considerations
beyond those discussed in .
Type name:
application
Subtype name:
davmount+xml
Required parameters:
none
Optional parameters:
"charset":
This parameter has identical semantics to the charset parameter of
the "application/xml" media type as specified in .
Encoding considerations:
Identical to those of "application/xml" as described in .
Security considerations:
As defined in this specification.
In addition, as this media type uses the "+xml" convention, it shares the same security considerations as described in .
Interoperability considerations:
There are no known interoperability issues.
Published specification:
This specification.
Applications that use this media type:
SAP Netweaver Knowledge Management, Xythos Drive.
Additional information:
Magic number(s):
As specified for "application/xml" in .
File extension(s):
.davmount
Fragment identifiers:
As specified for "application/xml" in .
Base URI:
As specified in .
Macintosh file type code(s):
TEXT
Person & email address to contact for further information:
Julian Reschke <[email protected]>
Intended usage:
COMMON
Restrictions on usage:
None.
Author:
Julian Reschke
Change controller:
IESG
All security considerations connected to HTTP/WebDAV and XML apply for
this specification as well, namely,
and .
In addition, client implementers must be careful when implementing the
<dm:open> element (see ). It MUST NOT
be used to initiate any action beyond displaying the contents of a
WebDAV collection (supporting
"opening" documents could be abused to trick a user into letting the operating
system's shell execute arbitrary content, possibly running it as an
executable program).
The OPTIONAL <dm:username> element defined in
allows the inclusion of user names into mount documents. However in some cases, user
name information is considered to be security sensitive. Should this
be the case, parties generating mount documents are advised to either not to
include user names, or to use access control to restrict access to the
information as desired.
This document has benefited from thoughtful discussion by Emile Baizel,
Spencer Dawkins, Lisa Dusseault, Stefan Eissing,
Joe Gregorio, Michal Gregr, Russ Housley, Jim Luther, Jaroslav Mazanec, and Jim Whitehead.
Key words for use in RFCs to Indicate Requirement LevelsHarvard University[email protected]HTTP Extensions for Distributed Authoring -- WEBDAVMicrosoft Corporation[email protected]Dept. Of Information and Computer Science, University of California, Irvine[email protected]Netscape[email protected]Novell[email protected]Novell[email protected]Hypertext Transfer Protocol -- HTTP/1.1University of California, Irvine[email protected]W3C[email protected]Compaq Computer Corporation[email protected]MIT Laboratory for Computer Science[email protected]Xerox Corporation[email protected]Microsoft Corporation[email protected]W3C[email protected]XML Media TypesIBM Tokyo Research Laboratory[email protected]simonstl.com[email protected]Skymoon Ventures[email protected]Extensible Markup Language (XML) 1.0 (Fourth Edition)Textuality and Netscape[email protected]Microsoft[email protected]University of Illinois at Chicago and Text Encoding Initiative[email protected]Sun Microsystems[email protected][email protected]Uniform Resource Identifier (URI): Generic SyntaxWorld Wide Web Consortium[email protected]Day Software[email protected]Adobe Systems Incorporated[email protected]
Guidelines for the Use of Extensible Markup Language (XML) within IETF ProtocolsVeriSign, Inc.21345 Ridgetop CircleDullesVA20166-6503US+1 703 948 3257[email protected]Dover Beach Consulting, Inc.POB 255268SacramentoCA95865-5268US+1 916 483 8878[email protected]Adobe Systems IncorporatedMail Stop W14345 Park Ave.San JoseCA95110US+1 408 536 3024[email protected]http://larry.masinter.netArchitecture of the World Wide Web, Volume OneSun Microsystems, Inc.W3Chttp://www.w3.org/People/Jacobs
Microsoft Internet Explorer implements a
Cascading Style Sheet (CSS) extension that allows
switching to its own WebDAV client ("Webfolder", see
). However, at the time
of this writing, this extension was not implemented by any other
user agent.
The "kio" library of the "K Desktop Enviroment" () uses
the URI scheme "webdav" to dispatch to the system's WebDAV client. This URI scheme
is not registered, nor is it supported on other platforms. Furthermore,
the W3C's "Architecture of the World Wide Web, Volume One"
explicitly advises against defining new schemes when existing schemes can be
used:
A specification SHOULD reuse an existing URI scheme (rather than create a new one)
when it provides the desired properties of identifiers and their relation to resources.
(See .)
The figure below shows a sample implementation of a dispatcher for
the application/davmount+xml datatype, suited for Win32 systems and the
Microsoft "Webfolder" client.
// sample implementation of application/davmount+xml
// dispatcher for Windows Webfolder client
//
// to install/uninstall:
// wscript davmount.js
//
// to open the webfolder:
// wscript davmount.js filename
// (where filename refers to an XML document with MIME type
// application/davmount+xml)
var EXTENSION = ".davmount";
var MIMETYPE = "application/davmount+xml";
var REGKW = "WebDAV.mount";
var NS = "xmlns:m='http://purl.org/NET/webdav/mount";
// remove keys/entries from the registry
function regdel(shell, key) {
try {
var x = shell.RegRead(key);
try {
shell.RegDelete(key);
}
catch(e) {
WScript.Echo("Error removing key " + key + ": " + e);
}
}
catch(e) {
// entry not present
}
}
// methods for registering/unregistering the handler
function install() {
var WshShell = new ActiveXObject("WScript.Shell");
if (WshShell == null) {
WScript.Echo("Couldn't instantiate WScript.Shell object");
return 2;
}
var fso = new ActiveXObject("Scripting.FileSystemObject");
var RegExt = "HKCR\\" + EXTENSION + "\\";
var RegMimeType = "HKCR\\MIME\\DataBase\\Content Type\\"
+ MIMETYPE + "\\";
var RegKw = "HKCR\\" + REGKW + "\\";
var extension = null;
try {
extension = WshShell.RegRead(RegMimeType + "Extension");
}
catch (e) {
}
if (extension == null) {
var but = WshShell.popup("Install the dispatcher for mime type "
+ MIMETYPE + "?", 0, MIMETYPE + " installation", 4);
if (but == 6) {
try {
WshShell.RegWrite(RegExt, REGKW);
WshShell.RegWrite(RegExt + "Content Type", MIMETYPE);
WshShell.RegWrite(RegMimeType + "Extension", EXTENSION);
WshShell.RegWrite(RegKw, "WebDAV Mount Request");
WshShell.RegWrite(RegKw + "DefaultIcon\\",
"shell32.dll,103");
var path = fso.getAbsolutePathName("davmount.js");
WshShell.RegWrite(RegKw + "shell\\open\\command\\",
"%SystemRoot%\\system32\\wscript.exe /nologo \""
+ path + "\" \"%1\"", "REG_EXPAND_SZ");
}
catch (e) {
WScript.Echo("Error writing to registry");
return 1;
}
return 0;
}
else {
return 1;
}
}
else {
var but = WshShell.popup("Remove the dispatcher for mime type "
+ MIMETYPE + "?", 0, MIMETYPE + " installation", 4);
if (but == 6) {
regdel(WshShell, RegExt + "Content Type");
regdel(WshShell, RegExt);
regdel(WshShell, RegKw + "shell\\open\\command\\");
regdel(WshShell, RegKw + "DefaultIcon\\");
regdel(WshShell, RegKw);
regdel(WshShell, RegMimeType + "Extension");
regdel(WshShell, RegMimeType);
return 0;
}
else {
return 1;
}
}
}
if (WScript.Arguments.length == 0) {
// install/uninstall
WScript.Quit(install());
}
else {
// try to invoke Webfolder
var inp = new ActiveXObject("MSXML2.DOMDocument");
var furi = encodeURI(WScript.Arguments(0));
if (! inp.load(furi)) {
WScript.Echo("Can't read from '"
+ WScript.Arguments(0) + "'!");
WScript.Quit(2);
}
inp.setProperty("SelectionLanguage", "XPath");
inp.setProperty("SelectionNamespaces",
"xmlns:m='http://purl.org/NET/webdav/mount'");
var n1 = inp.selectSingleNode("/m:mount/m:url");
var n2 = inp.selectSingleNode("/m:mount/m:open");
if (n1 == null) {
WScript.Echo("<url> element missing.");
WScript.Quit(2);
}
var ie = new ActiveXObject("InternetExplorer.Application");
ie.Navigate("about:blank");
var doc = ie.Document;
var folder = doc.createElement("span");
folder.addBehavior("#default#httpFolder");
var result = folder.navigate(n1.text +
(n2 == null ? "" : n2.text));
// close the window again when there was no <open> element
if (n2 == null) ie.Quit();
if (result != "OK") {
if (result == "PROTOCOL_NOT_SUPPORTED") {
WScript.Echo("This site doesn't seem to support WebDAV.");
WScript.Quit(1);
}
else {
WScript.Echo("Unexpected status: " + result);
WScript.Quit(2);
}
}
}
The "Xythos Drive" WebDAV client for WebDAV supports this specification
starting with version 4.4.