XEP-0129: WebDAV File Transfers

This document specifies a method for completing file transfers between XMPP entities using WebDAV.

WARNING: This Standards-Track document is Experimental. Publication as an XMPP Extension Protocol does not imply approval of this proposal by the XMPP Standards Foundation. Implementation of the protocol described herein is encouraged in exploratory implementations, but production systems should not deploy implementations of this protocol until it advances to a status of Draft.

Document Information

Series: XEP
Number: 0129
Publisher: XMPP Standards Foundation
Status: Experimental
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Superseded By: None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
Wiki Page: <http://wiki.jabber.org/index.php/WebDAV File Transfers (XEP-0129)>

Author Information

Legal Notices

Discussion Venue

The preferred venue for discussion of this document is the Standards discussion list: <http://mail.jabber.org/mailman/listinfo/standards>.

Given that this XMPP Extension Protocol normatively references IETF technologies, discussion on the XSF-IETF list may also be appropriate (see <http://mail.jabber.org/mailman/listinfo/jsf-ietf> for details).

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

Relation to XMPP

The Extensible Messaging and Presence Protocol (XMPP) is defined in the XMPP Core (RFC 3920) and XMPP IM (RFC 3921) 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.

Conformance Terms

The following 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".

Table of Contents

1. Introduction

File Transfer [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.

Example 1. Initial PUT Request

  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.

Example 2. HTTP OK

  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.

Example 3. PROPPATCH Request

  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.

Example 4. Server Returns HTTP 207

  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 [9]. (The example below shows the file being sent to multiple users using the Extended Stanza Addressing [10] protocol.)

Example 5. Sender Generates XMPP Message with URL

  <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).

Example 6. Recipient GET Request

  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 [11]:

Example 7. Confirmation Request Sent via Message

<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:

Example 8. Server Returns File

  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 [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.

Example 9. Client Discovers Services

<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>
  

Example 10. Client Queries Service Regarding Supported Features

<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.

Notes

Revision History

END