Network Working Group J. Reschke
Internet-Draft greenbytes
Expires: June 1, 2006 November 28, 2005
Mounting WebDAV (Web Distributed Authoring and Versioning) servers
draft-reschke-webdav-mount-03
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Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
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
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 Web Distributed Authoring and Versioning (WebDAV) servers to
send "mounting" information to a WebDAV client. The mechanism is
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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.
Editorial Note (To be removed by RFC Editor before publication)
Please send comments to the Distributed Authoring and Versioning
(WebDAV) working group at <mailto:w3c-dist-auth@w3.org>, which may be
joined by sending a message with subject "subscribe" to
<mailto:w3c-dist-auth-request@w3.org>. Discussions of the WEBDAV
working group are archived at
<http://lists.w3.org/Archives/Public/w3c-dist-auth/>.
Note that although discussion takes place on the WebDAV working
group's mailing list, this is not a working group document.
XML versions, latest edits and the issues list for this document are
available from
<http://greenbytes.de/tech/webdav/#draft-reschke-webdav-mount>.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1 dm:mount . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.2 dm:url . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.3 dm:open . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.4 dm:username . . . . . . . . . . . . . . . . . . . . . . . 5
4. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Internationalization Considerations . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
6.1 MIME type registration . . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
9.1 Normative References . . . . . . . . . . . . . . . . . . . 9
9.2 Informative References . . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 10
A. Alternative approaches . . . . . . . . . . . . . . . . . . . . 10
A.1 ...through HTML/CSS extensions . . . . . . . . . . . . . . 10
A.2 ...through custom URI schemes . . . . . . . . . . . . . . 10
B. Implementations . . . . . . . . . . . . . . . . . . . . . . . 10
B.1 Example implementation for Webfolder client . . . . . . . 11
B.2 Xythos . . . . . . . . . . . . . . . . . . . . . . . . . . 14
C. Change Log (to be removed by RFC Editor before publication) . 14
C.1 Since draft-reschke-webdav-mount-00 . . . . . . . . . . . 14
C.2 Since draft-reschke-webdav-mount-01 . . . . . . . . . . . 14
C.3 Since draft-reschke-webdav-mount-02 . . . . . . . . . . . 14
D. Open issues (to be removed by RFC Editor prior to
publication) . . . . . . . . . . . . . . . . . . . . . . . . . 15
D.1 edit . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Intellectual Property and Copyright Statements . . . . . . . . 17
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1. Introduction
By definition, a WebDAV server ([RFC2518]) is an HTTP server as well
([RFC2616]). 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,
Appendix A 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.
2. Terminology
The terminology used here follows that in the WebDAV Distributed
Authoring Protocol specification [RFC2518].
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].
This document uses XML DTD fragments ([XML]) as a purely notational
convention. In particular:
o 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.
o Element ordering is irrelevant.
o Extension elements/attributes (elements/attributes not already
defined as valid child elements) may be added anywhere, except
when explicitly stated otherwise.
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3. Format
A WebDAV mount request is encoded in a specific XML format ([XML])
with a well-defined MIME type (see Section 6.1). 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 section 3 of
[RFC3986] -->
<!ELEMENT open (#PCDATA) >
<!-- PCDATA value: path, as defined in section 3 of
[RFC3986] -->
<!ELEMENT username (#PCDATA) >
3.1 dm:mount
The <dm:mount> element acts as container for all the remaining
elements defined by this protocol.
3.2 dm:url
The mandatory <dm:url> element provides the HTTP URL of the WebDAV
collection that should be mounted by the client.
3.3 dm:open
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> (Section 3.2)
element (see Section 7 for a discussion about why this element only
supports displaying collections rather than opening arbitrary
documents).
3.4 dm:username
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
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mount points) or to provide a meaningful default for authentication
against the server. It is common that 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.
4. Example
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 Section 3 (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
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(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>
5. Internationalization Considerations
This document does not introduce any new internationalization
considerations beyond those discussed in [RFC2518], Section 16.
6. IANA Considerations
6.1 MIME type registration
MIME media type name:
application
MIME subtype name:
davmount+xml
Mandatory parameters:
none
Optional parameters:
"charset": This parameter has identical semantics to the charset
parameter of the "application/xml" media type as specified in
[RFC3023].
Encoding considerations:
Identical to those of "application/xml" as described in [RFC3023],
section 3.2.
Security considerations:
As defined in this specification. In addition, as this media type
uses the "+xml" convention, it shares the same security
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considerations as described in [RFC3023], section 10.
Interoperability considerations:
There are no known interoperability issues.
Published specification:
This specification.
Additional information:
Magic number(s):
As specified for "application/xml" in [RFC3023], section 3.2.
File extension:
.davmount
Fragment identifiers:
As specified for "application/xml" in [RFC3023], section 5.
Base URI:
As specified in [RFC3023], section 6.
Macintosh File Type code:
TEXT
Person and email address to contact for further information:
Julian Reschke <julian.reschke@greenbytes.de>
Intended usage:
COMMON
Author/Change controller:
IESG
7. Security Considerations
All security considerations connected to HTTP/WebDAV and XML apply
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for this specification as well, namely [RFC2518] (Section 17) and
[RFC3470] (Section 7).
In addition, client implementers must be careful when implementing
the <dm:open> element (see Section 3.3). 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).
8. Acknowledgements
This draft has benefited from thoughtful discussion by Emile Baizel,
Spencer Dawkins, Stefan Eissing, Joe Gregorio, Michal Gregr, Jim
Luther, Jaroslav Mazanec, and Jim Whitehead.
9. References
9.1 Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2518] Goland, Y., Whitehead, E., Faizi, A., Carter, S., and D.
Jensen, "HTTP Extensions for Distributed Authoring --
WEBDAV", RFC 2518, February 1999.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC3023] Murata, M., St.Laurent, S., and D. Kohn, "XML Media
Types", RFC 3023, January 2001.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005.
[XML] Bray, T., Paoli, J., Sperberg-McQueen, C., Maler, E., and
F. Yergeau, "Extensible Markup Language (XML) 1.0 (Third
Edition)", W3C REC-xml-20040204, February 2004,
<http://www.w3.org/TR/2004/REC-xml-20040204>.
9.2 Informative References
[RFC3470] Hollenbeck, S., Rose, M., and L. Masinter, "Guidelines for
the Use of Extensible Markup Language (XML) within IETF
Protocols", RFC 3470, BCP 70, January 2003.
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[WEBARCH] Walsh, N. and I. Jacobs, "Architecture of the World Wide
Web, Volume One", W3C REC REC-webarch-20041215,
December 2004,
<http://www.w3.org/TR/2004/REC-webarch-20041215/>.
Author's Address
Julian F. Reschke
greenbytes GmbH
Hafenweg 16
Muenster, NW 48155
Germany
Phone: +49 251 2807760
Fax: +49 251 2807761
Email: julian.reschke@greenbytes.de
URI: http://greenbytes.de/tech/webdav/
Appendix A. Alternative approaches
A.1 ...through HTML/CSS extensions
Microsoft Internet Explorer implements a CSS extension that allows
switching to its own WebDAV client ("Webfolder", see <http://
msdn.microsoft.com/workshop/author/behaviors/reference/behaviors/
anchor.asp>). However, at the time of this writing this extension
was not implemented by any other user agent.
A.2 ...through custom URI schemes
The "kio" library of the "K Desktop Enviroment"
(<http://www.kde.org/>) uses the URI scheme "webdav" to dispatch to
the system's WebDAV client. This URI scheme is not registered, nor
supported on other platforms. Furthermore, 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 [WEBARCH], Section 2.4)
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B.1 Example implementation for Webfolder client
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;
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}
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);
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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");
if (! inp.load(WScript.Arguments(0))) {
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;
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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);
}
}
}
B.2 Xythos
The "Xythos Drive" WebDAV client for WebDAV supports this
specification starting with version 4.4.
Appendix C. Change Log (to be removed by RFC Editor before publication)
Add implementations section; add sample implementation for Microsoft
Webfolder client. Add acknowledgments section.
Be consistent in using trailing slashes on collection URLs in
examples. Fix webfolder reference impl not to require <open>
element. Update acknowledgments. Incorporate some of JimW's
suggestions in abstract and introduction. Expand security
considerations regarding <open> and fwd-reference it from the spec.
Author's address updated. Mainly editorial fixes after review by
Spencer Dawkins. Enhance rational for dm:username based of feedback
by Stefan Eissing.
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Appendix D. Open issues (to be removed by RFC Editor prior to
publication)
Type: edit
julian.reschke@greenbytes.de (2005-09-17): Umbrella issue for
editorial fixes/enhancements.
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Index
A
application/mount
xml MIME type 7
D
dm:mount 5
dm:opent 5
dm:url 5
dm:username 5
M
MIME type
application/mount 7
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to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
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