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Network Working Group                                         J. ReschkeRequest for Comments: 4709                                    greenbytesCategory: Informational                                     October 2006Mounting Web Distributed Authoring and Versioning (WebDAV) ServersStatus of This Memo   This memo provides information for the Internet community.  It does   not specify an Internet standard of any kind.  Distribution of this   memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2006).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   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.Reschke                      Informational                      [Page 1]

RFC 4709                Mounting WebDAV Servers             October 2006Table of Contents1. Introduction ....................................................22. Terminology .....................................................33. Format ..........................................................33.1. dm:mount ...................................................43.2. dm:url .....................................................43.3. dm:open ....................................................43.4. dm:username ................................................44. Example .........................................................45. Internationalization Considerations .............................56. IANA Considerations .............................................66.1. MIME Type Registration .....................................67. Security Considerations .........................................88. Acknowledgements ................................................89. References ......................................................99.1. Normative References .......................................99.2. Informative References .....................................9Appendix A.  Alternative Approaches ...............................10A.1. ...Through HTML/CSS Extensions ............................10A.2. ...Through Custom URI Schemes .............................10Appendix B.  Implementations ......................................10B.1. Example Implementation for Webfolder Client ...............10B.2. Xythos ....................................................141.  Introduction   By definition, a Web Distributed Authoring and Versioning (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.Reschke                      Informational                      [Page 2]

RFC 4709                Mounting WebDAV Servers             October 20062.  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.3.  Format   A WebDAV mount request is encoded in a specific XML format ([XML])   with a well-defined MIME type (seeSection 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 inSection 3 of        [RFC3986] -->   <!ELEMENT open (#PCDATA) >   <!-- PCDATA value: path, as defined inSection 3 of        [RFC3986] -->   <!ELEMENT username (#PCDATA) >Reschke                      Informational                      [Page 3]

RFC 4709                Mounting WebDAV Servers             October 20063.1.  dm:mount   The <dm:mount> element acts as a 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 (seeSection 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   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.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 inSection 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.Reschke                      Informational                      [Page 4]

RFC 4709                Mounting WebDAV Servers             October 2006   (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>5.  Internationalization Considerations   This document does not introduce any new internationalization   considerations beyond those discussed in[RFC2518], Section 16.Reschke                      Informational                      [Page 5]

RFC 4709                Mounting WebDAV Servers             October 20066.  IANA Considerations6.1.  MIME Type Registration   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      [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.   Applications that use this media type:      SAP Netweaver Knowledge Management, Xythos Drive.Reschke                      Informational                      [Page 6]

RFC 4709                Mounting WebDAV Servers             October 2006   Additional information:      Magic number(s):         As specified for "application/xml" in[RFC3023], Section 3.2.      File extension(s):         .davmount      Fragment identifiers:         As specified for "application/xml" in[RFC3023], Section 5.      Base URI:         As specified in[RFC3023], Section 6.      Macintosh file type code(s):         TEXT   Person & email address to contact for further information:      Julian Reschke <julian.reschke@greenbytes.de>   Intended usage:      COMMON   Restrictions on usage:      None.   Author:      Julian Reschke   Change controller:      IESGReschke                      Informational                      [Page 7]

RFC 4709                Mounting WebDAV Servers             October 20067.  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 (seeSection 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).   The OPTIONAL <dm:username> element defined inSection 3.4 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.8.  Acknowledgements   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.Reschke                      Informational                      [Page 8]

RFC 4709                Mounting WebDAV Servers             October 20069.  References9.1.  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 (Fourth              Edition)", W3C REC-xml-20060816, August 2006,              <http://www.w3.org/TR/2006/REC-xml-20060816>.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-webarch-20041215, December 2004,              <http://www.w3.org/TR/2004/REC-webarch-20041215/>.Reschke                      Informational                      [Page 9]

RFC 4709                Mounting WebDAV Servers             October 2006Appendix A.  Alternative ApproachesA.1.  ...Through HTML/CSS Extensions   Microsoft Internet Explorer implements a Cascading Style Sheet (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   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 [WEBARCH], Section 2.4.)Appendix B.  ImplementationsB.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";Reschke                      Informational                     [Page 10]

RFC 4709                Mounting WebDAV Servers             October 2006   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);Reschke                      Informational                     [Page 11]

RFC 4709                Mounting WebDAV Servers             October 2006       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());Reschke                      Informational                     [Page 12]

RFC 4709                Mounting WebDAV Servers             October 2006   }   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);       }     }Reschke                      Informational                     [Page 13]

RFC 4709                Mounting WebDAV Servers             October 2006   }B.2.  Xythos   The "Xythos Drive" WebDAV client for WebDAV supports this   specification starting with version 4.4.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/Reschke                      Informational                     [Page 14]

RFC 4709                Mounting WebDAV Servers             October 2006Full Copyright Statement   Copyright (C) The Internet Society (2006).   This document is subject to the rights, licenses and restrictions   contained inBCP 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 inBCP 78 andBCP 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 athttp://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.Acknowledgement   Funding for the RFC Editor function is provided by the IETF   Administrative Support Activity (IASA).Reschke                      Informational                     [Page 15]