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 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 on June 1, 2006. 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 Reschke Expires June 1, 2006 [Page 1] Internet-Draft Mounting WebDAV servers November 2005 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 , which may be joined by sending a message with subject "subscribe" to . Discussions of the WEBDAV working group are archived at . 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 . Reschke Expires June 1, 2006 [Page 2] Internet-Draft Mounting WebDAV servers November 2005 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 Reschke Expires June 1, 2006 [Page 3] Internet-Draft Mounting WebDAV servers November 2005 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. Reschke Expires June 1, 2006 [Page 4] Internet-Draft Mounting WebDAV servers November 2005 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". 3.1 dm:mount The element acts as container for all the remaining elements defined by this protocol. 3.2 dm:url The mandatory element provides the HTTP URL of the WebDAV collection that should be mounted by the client. 3.3 dm:open The optional 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 (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 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 Reschke Expires June 1, 2006 [Page 5] Internet-Draft Mounting WebDAV servers November 2005 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 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 .. View this collection in your WebDAV client .. (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 Reschke Expires June 1, 2006 [Page 6] Internet-Draft Mounting WebDAV servers November 2005 (4) Server returns "davmount" document HTTP/1.1 200 OK Content-Type: application/davmount+xml Content-Length: xxx Cache-Control: private http://www.example.com/user42/ inbox/ 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 Reschke Expires June 1, 2006 [Page 7] Internet-Draft Mounting WebDAV servers November 2005 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 Intended usage: COMMON Author/Change controller: IESG 7. Security Considerations All security considerations connected to HTTP/WebDAV and XML apply Reschke Expires June 1, 2006 [Page 8] Internet-Draft Mounting WebDAV servers November 2005 for this specification as well, namely [RFC2518] (Section 17) and [RFC3470] (Section 7). In addition, client implementers must be careful when implementing the 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, . 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. Reschke Expires June 1, 2006 [Page 9] Internet-Draft Mounting WebDAV servers November 2005 [WEBARCH] Walsh, N. and I. Jacobs, "Architecture of the World Wide Web, Volume One", W3C REC REC-webarch-20041215, December 2004, . 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 ). 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" () 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 Reschke Expires June 1, 2006 [Page 10] Internet-Draft Mounting WebDAV servers November 2005 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; Reschke Expires June 1, 2006 [Page 11] Internet-Draft Mounting WebDAV servers November 2005 } 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); Reschke Expires June 1, 2006 [Page 12] Internet-Draft Mounting WebDAV servers November 2005 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(" element missing."); WScript.Quit(2); } var ie = new ActiveXObject("InternetExplorer.Application"); ie.Navigate("about:blank"); var doc = ie.Document; Reschke Expires June 1, 2006 [Page 13] Internet-Draft Mounting WebDAV servers November 2005 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 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 element. Update acknowledgments. Incorporate some of JimW's suggestions in abstract and introduction. Expand security considerations regarding 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. Reschke Expires June 1, 2006 [Page 14] Internet-Draft Mounting WebDAV servers November 2005 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. Reschke Expires June 1, 2006 [Page 15] Internet-Draft Mounting WebDAV servers November 2005 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 Reschke Expires June 1, 2006 [Page 16] Internet-Draft Mounting WebDAV servers November 2005 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. 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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. Reschke Expires June 1, 2006 [Page 17]