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Versions: 00 01 02 03 04 05 RFC 4709

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

Status of this Memo

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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)

Appendix B.  Implementations






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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)

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

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

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.

C.3  Since draft-reschke-webdav-mount-02

   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)

D.1  edit

   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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Intellectual Property Statement

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at
   ietf-ipr@ietf.org.


Disclaimer of Validity

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


Copyright Statement

   Copyright (C) The Internet Society (2005).  This document is subject
   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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