XEP-0137: Publishing Stream Initiation Requests

Matthew Miller

Email: linuxwolf@outer-planes.net
JabberID: linuxwolf@outer-planes.net

Thomas Muldowney

Email: temas@jabber.org
JabberID: temas@jabber.org

Copyright

Permissions

Disclaimer of Warranty

Limitation of Liability

IPR Conformance

1. Introduction
2. Requirements
3. Use Cases
    3.1. Publishing an SI Request
    3.2. Integration with Data Forms
    3.3. Triggering the Stream Initiation Request
4. Implementation Notes
    4.1. Publish ID versus SI ID
5. Security Considerations
6. IANA Considerations
7. XMPP Registrar Considerations
    7.1. Protocol Namespaces
    7.2. Data Form Validation Datatypes
8. XML Schema
Notes
Revision History

3.1 Publishing an SI Request

A stream owner uses the <sipub/> element to announce that it can perform a specific SI request. This element can be sent to a publish-subscribe (XEP-0060) node, or sent directly to potential recipients within a <message/> stanza.

The format of the <sipub/> element is as follows:

Example 1. Sample <sipub/>

  <sipub xmlns='http://jabber.org/protocol/sipub'
         from='sender-jid'
         id='publish-0123'
         profile='si-profile'
         mime-type='mime/type'>
    <profile xmlns='si-profile' ...>...</profile>
  </sipub>
    

This format is nearly identical to that for the stream initiation <si/> element (see XEP-0095). The major difference is the lack of the feature negotiation for the stream methods, and the addition of a 'from' attribute.

The 'from' attribute SHOULD be present, and MUST be present if the stanza containing the <sipub/> is not from the stream owner (e.g., if the stream is advertised at a publish-subscribe node). If present, this attribute MUST be the valid JID for the stream owner.

The 'id' attribute is an opaque identifier. This attribute MUST be present, and MUST be a valid non-empty string. It uniquely identifies the published request at the potential sender.

As with stream initiation, the 'profile' attribute MUST be present, and MUST be the namespace URI governing the profile information. It identifies the format for the SI profile.

As with stream initiation, the 'mime-type' attribute SHOULD be present, and MUST be an IANA-registered content type. [5] It provides the receiver with additional information about what the data stream will be.

The <sipub/> element MUST contain an element qualified by the namespace specified by the 'profile' attribute (e.g., <file xmlns='http://jabber.org/protocol/si/profile/file-transfer'/> for file transfer). This is the additional information about the data stream.

The <sipub/> information is typically provided via pubsub:

Example 2. Sender advertises stream via publish-subscribe

<iq from='bard@shakespeare.lit/globe'
    to='pubsub.shakespeare.lit'
    id='ps1'>
  <pubsub xmlns='http://jabber.org/protocol/pubsub'>
    <publish node='characters'>
      <sipub xmlns='http://jabber.org/protocol/si-pub'
          from='bard@shakespeare.lit'
          id='publish-0123'
          mime-type='application/pdf'
          profile='http://jabber.org/protocol/si/profile/file-transfer'>
        <file xmlns='http://jabber.org/protocol/si/profile/file-transfer'
              name='NDA.pdf'
              size='138819'
              date='2004-01-28T10:07Z'>
          <desc>All Shakespearean characters must sign and return this NDA ASAP</desc>
        </file>
      </sipub>
    </publish>
  </pubsub>
</iq>
    

Example 3. Pubsub service pushes announcement to all subscribers

<message from='pubsub.shakespeare.lit' to='juliet@capulet.com/balcony'>
  <event xmlns='http://jabber.org/protocol/pubsub#event'>
    <items node='characters'>
      <item id='current'>
        <sipub xmlns='http://jabber.org/protocol/si-pub'
            from='bard@shakespeare.lit'
            id='publish-0123'
            mime-type='application/pdf'
            profile='http://jabber.org/protocol/si/profile/file-transfer'>
          <file xmlns='http://jabber.org/protocol/si/profile/file-transfer'
                name='NDA.pdf'
                size='138819'
                date='2004-01-28T10:07Z'>
            <desc>All Shakespearean characters must sign and return this NDA ASAP</desc>
          </file>
        </sipub>
      </item>
    </items>
  </event>
</message>
    

The <sipub/> element MAY also be included directly within a <message/> stanza sent to another entity (or multiple entities, e.g., in Multi-User Chat [6] or via Extended Stanza Addressing [7]). This can be especially useful for informing an offline entity about an available stream.

Example 4. Advertising a stream in a message stanza

<message from='romeo@montague.net/pda' to='juliet@capulet.com'>
  <sipub xmlns='http://jabber.org/protocol/si-pub'
      id='publish-0123'
      mime-type='application/pdf'
      profile='http://jabber.org/protocol/si/profile/file-transfer'>
    <file xmlns='http://jabber.org/protocol/si/profile/file-transfer'
          name='NDA.pdf'
          size='138819'
          date='2004-01-28T10:07Z'>
      <desc>All Shakespearean characters must sign and return this NDA ASAP</desc>
    </file>
  </sipub>
</message>
    

3.2 Integration with Data Forms

One of the goals of sipub is to integrate Stream Initiation with Data Forms to provide a "file upload" capability. This is accomplished via the datatypes specified in Data Forms Validation [8]. Each datatype is specific to the profile desired.

For example the datatype "sipub:file-transfer" is used to identify the file upload field(s) corresponding to XEP-0096:

Example 5. "Upload File" Data Forms Field

  <field var='file' type='text-single' label='File to Upload'>
    <validate xmlns='http://jabber.org/protocol/xdata-validate'
              datatype='sipub:file-transfer'/>
  </field>
    

When submitting such a form, a field's value(s) MUST be the <sipub/> identifier(s). Also, the submitter MUST provide an <sipub/> element within the data form for each file to be uploaded:

Example 6. Submitting an "Upload File" form

  <x xmlns='jabber:x:data' type='submit'>
    <field var='file'>
      <value>publish-0123</value>
    </field>
    <sipub xmlns='http://jabber.org/protocol/sipub'
           id='publish-0123'
           mime-type='text/html'
           profile='http://jabber.org/protocol/si/profile/file-transfer'>
      <file xmlns='http://jabber.org/protocol/si/profile/file-transfer'
            name='missive.html'
            size='1024'
            date='2005-07-21T11:21Z'/>
    </sipub>
  </x>
    

The form processor will use this to retrieve the file(s) to be uploaded.

3.3 Triggering the Stream Initiation Request

A potential receiver starts the stream initiation session by sending an IQ-get to the sender, using the <start xmlns='http://jabber.org/protocol/sipub'/> element. This element contains the 'id' attribute to specify which published stream to retrieve:

Example 7. Receiver requests start of stream

  <iq type='get'
      id='sipub-request-0'
      from='juliet@capulet.com/balcony'
      to='romeo@montague.net/pda'>
    <start xmlns='http://jabber.org/protocol/sipub'
           id='publish-0123'/>
  </iq>
    

If the sender accepts the request, it responds with an IQ-result containing a <starting/> element. This element indicates the stream initiation identifier to be used:

Example 8. Sender accepts request to start stream

  <iq type='result'
      id='sipub-request-0'
      from='romeo@montague.net/pda'
      to='juliet@capulet.com/balcony'>
    <starting xmlns='http://jabber.org/protocol/sipub'
              sid='session-87651234'/>
  </iq>
    

Then the sender begins the stream initiation negotiation:

Example 9. Sender starts negotiation

  <iq type='set'
      id='sipub-set-1'
      from='romeo@montague.net/pda'
      to='juliet@capulet.com/balcony'>
    <si xmlns='http://jabber.org/protocol/si'
        id='session-87651234'
        mime-type='text/html'
        profile='http://jabber.org/protocol/si/profile/file-transfer'>
      <file xmlns='http://jabber.org/protocol/si/profile/file-transfer'
          name='missive.html'
          size='1024'
          date='2005-07-21T11:21Z'>
        <desc>A love letter</desc>
      </file>
    </si>
  </iq>
    

If the requested identifier is not valid, the sender SHOULD respond with a <not-acceptable/> error:

Example 10. Sender denies because of invalid id

  <iq type='error'
      id='sipub-set-1'
      from='romeo@montague.net/pda'
      to='juliet@capulet.com/balcony'>
    <start xmlns='http://jabber.org/protocol/sipub'>publish-0123</start>
    <error code='405' type='modify'>
      <not-acceptable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
    </error>
  </iq>
    

If the receiver does not have permission to request the data stream, the sender SHOULD respond with a <forbidden/> error:

Example 11. Sender denies because receiver is forbidden

  <iq type='error'
      id='sipub-set-1'
      from='romeo@montague.net/pda'
      to='juliet@capulet.com/balcony'>
    <start xmlns='http://jabber.org/protocol/sipub'>publish-0123</start>
    <error code='403' type='auth'>
      <forbidden xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
    </error>
  </iq>
    

4.1 Publish ID versus SI ID

When publishing a stream via the <sipub/> element, the identifier SHOULD NOT be used as-is for the <si/> element, since a single publication will likely result in multiple <si/> requests, possibly from the same receiver.

7.1 Protocol Namespaces

The XMPP Registrar [10] includes 'http://jabber.org/protocol/sipub' in its registry of protocol namespaces.

7.2 Data Form Validation Datatypes

The XMPP Registrar includes 'sipub:' in its registry of Data Forms Validation Datatype Prefixes.

Normally, each SI profile that wishes to be considered for use with Data Forms MUST register its own datatype qualified by the "sipub:" prefix. However, this document provides an initial seed, based on the currently accepted SI profiles. The following datatypes shall be registered for use with Data Forms Validation:

Data Forms Validation Datatypes Registry Submission

<datatype>
  <name>sipub:file-transfer</name>
  <desc>Datatype for publishing an SI using the File Transfer Profile</desc>
  <doc>XEP-0096</doc>
</datatype>
    

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

<xs:schema
    xmlns:xs='http://www.w3.org/2001/XMLSchema'
    targetNamespace='http://jabber.org/protocol/sipub'
    xmlns='http://jabber.org/protocol/sipub'
    elementFormDefault='qualified'>

  <xs:annotation>
    <xs:documentation>
      The protocol documented by this schema is defined in
      XEP-0137: http://www.xmpp.org/extensions/xep-0137.html
    </xs:documentation>
  </xs:annotation>

  <xs:element name='sipub'>
    <xs:annotation>
      <xs:documentation>This is the root content element for advertising a stream.</xs:documentation>
    </xs:annotation>
    <xs:complexType>
      <xs:sequence>
        <xs:any namespace='##other' minOccurs='1' maxOccurs='1'/>
      </xs:sequence>
      <xs:attribute name='id' type='xs:string' use='required'/>
      <xs:attribute name='from' type='xs:string' use='optional'/>
      <xs:attribute name='mime-type' type='xs:string' use='optional'/>
      <xs:attribute name='profile' type='xs:string' use='optional'/>
    </xs:complexType>
  </xs:element>

  <xs:element name='start'>
    <xs:annotation>
      <xs:documentation>This is the element for requesting retrieval of a stream.</xs:documentation>
    </xs:annotation>
    <xs:complexType>
      <xs:attribute name='id' type='xs:string' use='required'/>
    </xs:complexType>
  </xs:element>

  <xs:element name='starting'>
    <xs:annotation>
      <xs:documentation>This is the element for specifying the stream to be retrieved.</xs:documentation>
    </xs:annotation>
    <xs:complexType>
      <xs:attribute name='sid' type='xs:string' use='required'/>
    </xs:complexType>
  </xs:element>

</xs:schema>
  

1. XEP-0095: Stream Initiation <http://www.xmpp.org/extensions/xep-0095.html>.

2. XEP-0096: File Transfer <http://www.xmpp.org/extensions/xep-0096.html>.

3. XEP-0060: Publish-Subscribe <http://www.xmpp.org/extensions/xep-0060.html>.

4. XEP-0004: Data Forms <http://www.xmpp.org/extensions/xep-0004.html>.

5. The IANA registry of content types is located at <http://www.iana.org/assignments/media-types/>.

6. XEP-0045: Multi-User Chat <http://www.xmpp.org/extensions/xep-0045.html>.

7. XEP-0033: Extended Stanza Addressing <http://www.xmpp.org/extensions/xep-0033.html>.

8. XEP-0122: Data Forms Validation <http://www.xmpp.org/extensions/xep-0122.html>.

9. The Internet Assigned Numbers Authority (IANA) is the central coordinator for the assignment of unique parameter values for Internet protocols, such as port numbers and URI schemes. For further information, see <http://www.iana.org/>.

10. The XMPP Registrar maintains a list of reserved protocol namespaces as well as registries of parameters used in the context of XMPP extension protocols approved by the XMPP Standards Foundation. For further information, see <http://www.xmpp.org/registrar/>.

Version 1.0 (2005-08-26)

Version 0.3 (2005-07-21)

Version 0.2 (2004-11-03)

Version 0.1 (2004-06-16)