Mounting WebDAV (Web Distributed Authoring and Versioning) servers

Status of this Memo

By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79.¶

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts.¶

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as “work in progress”.¶

The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt.¶

The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html.¶

This Internet-Draft will expire in March 2006.¶

Copyright Notice

Abstract

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.¶

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.¶

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: ¶

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.

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.¶

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" in it's WebDAV client, and then to display the contents the child collection "/user42/inbox", identified by the URL ""http://www.example.com/documents/user42/inbox".¶

>> 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</dm:url>
  <dm:open>/user42/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 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 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.¶

8. Acknowledgements

This draft has benefited from thoughtful discussion by Emile Baizel, Michal Gregr and Jaroslav Mazanec.

Appendix 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: ¶

"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

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;
  }
  
  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);
  }
  
  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");
  
  var result = folder.navigate(n1.text + n2.text);
  
  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.

Index

A D M

A
- application/mount+xml MIME type 6.1
D
- dm:mount 3.1
- dm:opent 3.3
- dm:url 3.2
- dm:username 3.4
M
- MIME type
  - application/mount+xml 6.1

Full Copyright Statement

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.¶

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.¶

Intellectual Property

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.¶