Network Working GroupJ. Reschke
Internet-Draftgreenbytes
Intended status: Standards TrackOctober 2005
Expires: April 2006

Mounting WebDAV (Web Distributed Authoring and Versioning) servers
draft-reschke-webdav-mount-02

Note: a later version of this document has been published as RFC4709.

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Copyright Notice

Copyright © The Internet Society (2005). All Rights Reserved.

Abstract

 I  

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 protocol 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.

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>.


Table of Contents

Issues list

IdTypeStatusDateRaised By
wfimplopennotoptionalchangeclosed2005-09-22julian.reschke@greenbytes.de
editeditopen2005-09-17julian.reschke@greenbytes.de
 I  edit   (type: edit, status: open)
julian.reschke@greenbytes.de2005-09-17 Umbrella issue for editorial fixes/enhancements.
Associated changes in this document: <#rfc.change.edit.1>, 1, 3.3, 4, 4, 4, 4, 4, 4, 4, 4, 4, 7, 8, 8, 8, C.

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.

 I  

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 their "locker". Ideally, when a user clicks 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.

For completeness, Appendix A lists other approaches that have been implemented in existing clients.

2. Terminology

The terminology used here follows and extends 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:

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; it's URL is computed by concatenating this element's value with the URL obtained from the <dm:url> (Section 3.2) element  I  (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 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 a authentication dialogue.

4. Example

In the example below, the server instructs the user agent to mount the WebDAV URL "http://www.example.com/documents I /" in it I 's WebDAV client, and then to display the contents  I of the child collection "/user42/inbox I /", identified by the URL  I ""http://www.example.com/documents/user42/inbox I /".

>> Request:

GET /Coll/&mount-me HTTP/1.1
Host: www.example.com

>> Response:

HTTP/1.1 200 OK
Content-Type: application/davmount+xml
Content-Length: xxx

<dm:mount xmlns:dm="http://purl.org/NET/webdav/mount">
  <dm:url>http://www.example.com/documents I /</dm:url>
  <dm:open> I /user42/inbox I /</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:

MIME subtype name:

Mandatory parameters:

Optional parameters:

Encoding considerations:

Security considerations:

Interoperability considerations:

Published specification:

Additional information:

Person and email address to contact for further information:

Intended usage:

Author/Change controller:

7. Security Considerations

All security considerations connected to HTTP/WebDAV and XML apply 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 I  (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,  I Joe Gregorio, Michal Gregr I  and, Jim Luther, Jaroslav Mazanec I , 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.
[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/>.

A. Alternative approaches

A.1 ...through HTML/CSS extensions

Microsoft Internet Explorer implements a CSS extension that allows switching to it's 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:

(see [WEBARCH], Section 2.4)

B. Implementations

B.1 Example implementation for Webfolder client

 I  wfimplopennotoptional   (type: change, status: closed)
julian.reschke@greenbytes.de2005-09-22 Fix Webfolder reference impl not to require open element.
2005-09-22Resolution:Fixed.
Associated changes in this document: B.1, B.1.

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");
  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);
  }
  
 I   if (n2 == null) {
    WScript.Echo("<open> 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");
  
 I   var result = folder.navigate(n1.text + n2.text);
  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.

C. Change Log (to be removed by RFC Editor before publication)

C.1 Since draft-reschke-webdav-mount-00

Add implementations section; add sample implementation for Microsoft Webfolder client. Add acknowledgments section.

 I  

C.2 Since draft-reschke-webdav-mount-01

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.

Index

A D M

Author's Address

Julian F. Reschke
greenbytes GmbH
Salzmannstrasse 152
Muenster, NW 48159
Germany
Phone: +49 251 2807760
Fax: +49 251 2807761
EMail: julian.reschke@greenbytes.de
URI: http://greenbytes.de/tech/webdav/

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