XEP-0129: WebDAV File Transfers

1. Introduction¶

SI File Transfer (XEP-0096) [1] defines mechanisms for transferring files between Jabber users, and defines the preferred approach for file transfers in Jabber applications. Unfortunately, the mechanisms defined therein require that both the sender and recipient be online at the same time. However, sometimes it is desirable for the sender to initiate a file transfer while the recipient is offline. One way to make this possible is for the sender to upload the file to a unique URL, then inform the recipient of the URL. The sender could do this by uploading the file to their own web server, but not everyone has their own web server. Fortunately, there is a well-defined protocol for such file management operations: a set of HTTP extensions known as WebDAV and defined in RFC 2518 [2] (see also the revision-in-progress, rfc2518bis [3]).

The use case in which the recipient is offline is the main motivation for this document. Another WebDAV use case presents itself in environments that use, or even require, WebDAV for file transfers using other protocols (e.g., files attached to email messages). The usual rationale for such deployments is virus-checking: the file is put onto the WebDAV server (either by an end-user or a script that, for example, strips attached files off email messages) and then checked for viruses; only after the virus check successfully completes is the recipient allowed to retrieve the file. A further benefit of such deployments is that it enables the sender to provide the file to multiple recipients. Thus the approach defined herein provides the added benefit of being usable in generic WebDAV environments as well.

2. Requirements¶

This document addresses the following requirements:

1. Enable file transfers when recipient is offline.
2. Use WebDAV for file puts and gets.

3. Terminology¶

This document inherits terms from RFC 2518, RFC 2616 [4], and RFC 2617 [5].

4. Protocol Flow¶

The client SHOULD attempt to PUT the file on the server. [6] The PUT request MUST include an "If-None-Match" header as well as an "Authorization" header that specifies appropriate authentication information.

  PUT /missive.html HTTP/1.1
  Host: files.shakespeare.lit
  Authorization: Basic cm9tZW9AbW9udGFndWUubmV0
  If-None-Match: *
  Content-Length: xxx
  Content-Type: text/html

  [body omitted]

Prior to storing the file, the server MUST verify the user's authentication credentials via any supported method. When the file is stored, the server also MUST set the owner "live" property to ensure that only the user that originally posted this file is allowed to modify the file in any way. Other users MAY be allowed to see properties and retrieve the file (upon authentication) but MUST NOT be able to perform operations such as DELETE, MOVE, and PROPPATCH.

  HTTP/1.1 200 OK
  Date: Thu, 18 Dec 2003 15:01:20 GMT

In the absence of any other authorization method (e.g., RFC 3744 [7] or Security Assertion Markup Language [8]) in use by the deployed WebDAV server, the client SHOULD perform a PROPPATCH request to set the list of Jabber IDs authorized to retrieve this file, and the server MUST NOT allow access until this configuration is completed.

  PROPPATCH /missive.html HTTP/1.1
  Host: files.shakespeare.lit
  Authorization: Basic cm9tZW9AbW9udGFndWUubmV0
  Content-Type: text/xml
  Content-Length: 243

  <propertyupdate xmlns='DAV:'>
    <set>
      <prop>
	<jidlist xmlns='http://www.xmpp.org/extensions/xep-0129.html#ns'>
	  <jid>juliet@capulet.com</jid>
	  <jid>benvolio@montague.net/home</jid>
	  <jid>mercutio@capulet.com</jid>
	</jidlist>
      </prop>
    </set>
  </propertyupdate>

Note: The semantics of the JID list defined above are:

• If a JID is a bare JID (no resource), any fully-qualified form of that JID may access this resource (in the example above, this means that any resource of juliet@capulet.com may access this URL).
• If a JID includes a resource identifier, only that specific JID may access this URL (in the example above, this means that only the JID benvolio@montague.net/home may access this URL; benvolio@montague.net/other may not).
• If both a full JID and a bare JID are specified in a single JID list, the bare JID takes precedence.

The server responds when the properties have been updated. This is typically a 207 (MultiPart) response, which means that the body can contain multiple status codes, as shown in the following example.

  HTTP/1.1 207 MultiPart Response
  Date: Thu, 18 Dec 2003 15:03:20 GMT
  Content-Type: text/xml; charset=UTF-8
  Content-Length: 211

  <multistatus xmlns='DAV:'>
    <response>
      <href>http://files.shakespeare.lit/missive.html</href>
      <propstat>
	<prop><jidlist xmlns='http://www.xmpp.org/extensions/xep-0129#ns'/></prop>
	<status>HTTP/1.1 200 OK</status>
      </propstat>
    </response>
  </multistatus>

Now that the file is available via WebDAV and the client has specified what Jabber IDs may access the URL, the sender sends a message to the target user(s) containing the URL of the file, encapsulated via Out-of-Band Data (XEP-0066) [9]. (The example below shows the file being sent to multiple users using the Extended Stanza Addressing (XEP-0033) [10] protocol.)

  <message from='romeo@montague.net/pda' to='multicast.jabber.org'>
    <addresses xmlns='http://jabber.org/protocol/address'>
      <address type='to' jid='juliet@capulet.com'/>
      <address type='to' jid='benvolio@montague.net/home'/>
      <address type='cc' jid='mercutio@capulet.com'/>
    </addresses>
    <x xmlns='jabber:x:oob'>
      <url>http://files.shakespeare.lit/missive.html</url>
    </x>
  </message>

When the target recipients have received the message, they may then perform an HTTP GET to download the file (the following request is from juliet@capulet.com).

  GET /missive.html HTTP/1.1
  Host: files.shakespeare.lit
  Authorization: Digest username="juliet@capulet.com",
                 realm="xmpp",
                 nonce="ec2cc00f21f71acd35ab9be057970609",
                 uri="missive.html",
                 qop=auth,
                 nc=00000001,
                 cnonce="0a4f113b",
                 response="6629fae49393a05397450978507c4ef1",
                 opaque="5ccc069c403ebaf9f0171e9517f40e41"

The server then checks to ensure that the provided JID was specified via the jidlist property. If not, the server MUST return an HTTP 403 (Forbidden) error; if so, the server attempts to authorize the user via Verifying HTTP Requests via XMPP (XEP-0070) [11]:

<message type='normal'
         from='files.shakespeare.lit'
         to='juliet@capulet.com'>
  <thread>e0ffe42b28561960c6b12b944a092794b9683a38</thread>
  <confirm xmlns='http://jabber.org/protocol/http-auth'
           id='0a4f113b'
           method='GET'
           url='https://files.shakespeare.lit:9345/missive.html'/>
</message>

If the XEP-0070 verification is successful, the server then allows the file to be retrieved:

  HTTP/1.1 200 OK
  Date: Thu, 18 Dec 2003 18:00:00 GMT
  Content-Type: text/html
  Content-Length: xxx

  [body omitted]

5. Determining Support¶

In order to discover a WebDAV server that supports this protocol, a client SHOULD use Service Discovery (XEP-0030) [12]. Support for this protocol MUST be advertised by means of a service discovery feature named "http://www.xmpp.org/extensions/xep-0129.html#ns" (see Protocol Namespaces regarding issuance of one or more permanent namespaces). An example of the discovery flow is shown below.

<iq from='romeo@shakespeare.lit/home'
    id='disco1'
    to='shakespeare.lit'
    type='get'>
  <query xmlns='http://jabber.org/protocol/disco#items'/>
</iq>

<iq from='shakespeare.lit'
    id='disco1'
    to='romeo@shakespeare.lit/home'
    type='result'>
  <query xmlns='http://jabber.org/protocol/disco#items'>
    ...
    <item jid='files.shakespeare.lit'/>
    ...
  </query>
</iq>

<iq from='romeo@shakespeare.lit/home'
    id='disco2'
    to='files.shakespeare.lit'
    type='get'>
  <query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>

<iq from='files.shakespeare.lit'
    id='disco2'
    to='romeo@shakespeare.lit/home'
    type='result'>
  <query xmlns='http://jabber.org/protocol/disco#info'>
    ...
    <feature var='http://jabber.org/protocol/http-auth'/>
    <feature var='http://www.xmpp.org/extensions/xep-0129.html#ns'/>
    ...
  </query>
</iq>

The user now knows that the "files.shakespeare.lit" service supports this protocol.

6. Security Considerations¶

See RFC 2518, XMPP Core, and XEP-0070 for security considerations related to those protocols, which are used by the profile defined herein. The initiating client MUST ensure that appropriate access controls are specified, normally by performing a PROPPATCH request to set the list of Jabber IDs authorized to retrieve the file. The server MUST NOT allow access to the file until access controls have been specified. In addition, the server MUST NOT allow access to the file by any unauthorized entity.

7. IANA Considerations¶

This document requires no interaction with the Internet Assigned Numbers Authority (IANA) [13].

8. XMPP Registrar Considerations¶

9. XML Schema¶

<?xml version='1.0' encoding='UTF-8'?>

<xs:schema
    xmlns:xs='http://www.w3.org/2001/XMLSchema'
    targetNamespace='http://www.xmpp.org/extensions/xep-0129.html#ns'
    xmlns='http://www.xmpp.org/extensions/xep-0129.html#ns'
    elementFormDefault='qualified'>

  <xs:element name='jidlist'>
    <xs:complexType>
      <xs:sequence minOccurs='0' maxOccurs='unbounded'>
        <xs:element name='jid' type='xs:string'/>
      </xs:sequence>
    </xs:complexType>
  </xs:element>

</xs:schema>

10. Acknowledgements¶

Thanks to Lisa Dusseault and Julian Reschke for their feedback.

Appendices

Appendix A: Document Information¶

Series

XEP

Number

0129

Publisher

XMPP Standards Foundation

Status

Deferred

Type

Standards Track

Version

0.3

Last Updated

2007-04-19

Approving Body

XMPP Council

Dependencies

XMPP Core, RFC 2518, XEP-0030, XEP-0066, XEP-0070

Supersedes

None

Superseded By

None

Short Name

TO BE ASSIGNED

Source Control

HTML

This document in other formats: XML  PDF

Appendix B: Author Information¶

Peter Saint-Andre

Email

xsf@stpeter.im

JabberID

peter@jabber.org

URI

http://stpeter.im/

Dave Smith

Email

dizzyd@jabber.org

JabberID

dizzyd@jabber.org

Appendix C: Legal Notices¶

Appendix D: Relation to XMPP¶

The Extensible Messaging and Presence Protocol (XMPP) is defined in the XMPP Core (RFC 6120) and XMPP IM (RFC 6121) specifications contributed by the XMPP Standards Foundation to the Internet Standards Process, which is managed by the Internet Engineering Task Force in accordance with RFC 2026. Any protocol defined in this document has been developed outside the Internet Standards Process and is to be understood as an extension to XMPP rather than as an evolution, development, or modification of XMPP itself.

Appendix E: Discussion Venue¶

The primary venue for discussion of XMPP Extension Protocols is the <standards@xmpp.org> discussion list.

Discussion on other xmpp.org discussion lists might also be appropriate; see <http://xmpp.org/about/discuss.shtml> for a complete list.

Given that this XMPP Extension Protocol normatively references IETF technologies, discussion on the <xsf-ietf@xmpp.org> list might also be appropriate.

Errata can be sent to <editor@xmpp.org>.

Appendix F: Requirements Conformance¶

The following requirements keywords as used in this document are to be interpreted as described in RFC 2119: "MUST", "SHALL", "REQUIRED"; "MUST NOT", "SHALL NOT"; "SHOULD", "RECOMMENDED"; "SHOULD NOT", "NOT RECOMMENDED"; "MAY", "OPTIONAL".

Appendix G: Notes¶

Appendix H: Revision History¶

Note: Older versions of this specification might be available at http://xmpp.org/extensions/attic/

1. Version 0.3 (2007-04-19)¶

   Corrected to reflect changes to XEP-0070; incorporated WedDAV feedback.

   psa
2. Version 0.2 (2004-04-13)¶

   Added information about service discovery.

   psa
3. Version 0.1 (2004-03-12)¶

   Initial version.

   psa/ds

END