XEP-0221: Data Forms Media Element

This specification defines an XMPP protocol extension for including media data in XEP-0004 data forms.

NOTICE: This document is currently within Last Call or under consideration by the XMPP Council for advancement to the next stage in the XSF standards process.

Document Information

Series: XEP
Number: 0221
Publisher: XMPP Standards Foundation
Status: Proposed
Type: Standards Track
Version: 0.4
Last Updated: 2008-07-27
Approving Body: XMPP Council
Dependencies: XMPP Core, XEP-0004
Supersedes: None
Superseded By: None
Short Name: NOT_YET_ASSIGNED
Wiki Page: <http://wiki.jabber.org/index.php/Data Forms Media Element (XEP-0221)>

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>.

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

In certain protocols that make use of Data Forms [1], it can be helpful to include media data such as small images. One example of such a "using protocol" is CAPTCHA Forms [2]. This document defines a method for including media data in a data form.

2. Media Element

The root element for media data is <media/>. This element MUST be qualified by the "urn:xmpp:tmp:media-element' namespace (see Protocol Namespaces regarding issuance of one or more permanent namespaces). The <media/> element MUST be contained within a <field/> element qualified by the 'jabber:x:data' namespace.

If the media is an image or video then the <media/> element SHOULD include 'height' and 'width' attributes specifying the recommended display size of the media in pixels.

The <media/> element SHOULD contain at least one <uri/> element to specify the out-of-band location of the media data. [3] If included, the <uri/> element MUST contain a URI that indicates the location and MUST include a 'type' attribute that specifies the MIME type of the media.

The 'type' attribute of the <uri/> element is REQUIRED. The value of the 'type' attribute MUST match the syntax specified in RFC 2045 [4]. That is, the value MUST include a top-level media type, the "/" character, and a subtype; in addition, it MAY include one or more optional parameters (e.g., the "audio/ogg" MIME type in the example shown below includes a "codecs" parameter as specified in RFC 4281 [5]). The "type/subtype" string SHOULD be registered in the IANA MIME Media Types Registry [6], but MAY be an unregistered or yet-to-be-registered value.

The <media/> element MAY also contain one or more <data/> elements for distributing the media in-band. The <data/> element MUST be qualified by the 'urn:xmpp:tmp:data-element' as defined in Data Element [7]. The encoded data SHOULD NOT be larger than 8 kilobytes. [8]

Example 1. Audio Media Element

<media xmlns='urn:xmpp:tmp:media-element'>
  <uri type='audio/x-wav'>
    http://victim.example.com/challenges/speech.wav?F3A6292C
  </uri>
  <uri type='audio/ogg; codecs=speex'>
    http://victim.example.com/challenges/speech.ogg?F3A6292C
  </uri>
  <uri type='audio/mpeg'>
    http://victim.example.com/challenges/speech.mp3?F3A6292C
  </uri>
  <data xmlns='urn:xmpp:tmp:data-element' 
        alt='An audio file'
        type='audio/ogg; codecs=speex'>
    [ ... base64-encoded-audio ... ]
  </data>
</media>
  

The following example is provided only for the purpose of illustration; consult the specifications for using protocols to see canonical examples.

Example 2. Inclusion in Data Form

<x xmlns='jabber:x:data' type='form'>
  [ ... ]
  <field var='ocr'>
    <media xmlns='xmlns='urn:xmpp:tmp:media-element'
           height='80'
           width='290'>
      <uri type='image/jpeg'>
        http://www.victim.com/challenges/ocr.jpeg?F3A6292C
      </uri>
      <data xmlns='urn:xmpp:tmp:data-element'
            type='image/jpeg'> ** Base64 encoded image ** </data>
    </media>
  </field>
  [ ... ]
</x>
  

3. Security Considerations

The ability to include arbitrary binary data implies that it is possible to send scripts, applets, images, and executable code, which may be potentially harmful. To reduce the risk of such exposure, an implementation MAY choose to not display or process such data but instead either completely ignore the data, show only the value of the 'alt' attribute (if included), or prompt a human user for approval (either explicitly via user action or implicitly via a list of approved entities from whom the user will accept binary data without per-event approval).

4. IANA Considerations

This document requires no interaction with the Internet Assigned Numbers Authority (IANA) [9].

5. XMPP Registrar Considerations

6. XML Schema

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

<xs:schema
    xmlns:xs='http://www.w3.org/2001/XMLSchema'
    targetNamespace='urn:xmpp:tmp:media-element'
    xmlns='urn:xmpp:tmp:media-element'
    elementFormDefault='qualified'>

  <xs:import 
      namespace='urn:xmpp:tmp:data-element'/>

  <xs:element name='media'>
    <xs:complexType>
      <xs:sequence xmlns:data='urn:xmpp:tmp:data-element'>
        <xs:element ref='uri' minOccurs='0' maxOccurs='unbounded'/>
        <xs:element ref='data:data' minOccurs='0' maxOccurs='unbounded'/>
      </xs:sequence>
      <xs:attribute name='height' type='xs:unsignedShort' use='optional'/>
      <xs:attribute name='width' type='xs:unsignedShort' use='optional'/>
    </xs:complexType>
  </xs:element>

  <xs:element name='uri'>
    <xs:complexType>
      <xs:simpleContent>
        <xs:extension base='xs:string'>
          <xs:attribute name='type' type='xs:string' use='required'/>
        </xs:extension>
      </xs:simpleContent>
    </xs:complexType>
  </xs:element>

</xs:schema>
  

Notes

Revision History

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