JEP-0137: Publishing SI Requests

This JEP defines protocol for publishing the availability of a particular Stream Initiation request, such as a file.

WARNING: This Standards-Track JEP is Experimental. Publication as a Jabber Enhancement Proposal does not imply approval of this proposal by the Jabber Software 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.

JEP Information

Status: Experimental
Type: Standards Track
Number: 0137
Version: 0.2
Last Updated: 2004-11-03
JIG: Standards JIG
Approving Body: Jabber Council
Dependencies: XMPP Core, JEP-0030, JEP-0095
Supersedes: None
Superseded By: None
Short Name: sipub

Author Information

Matthew Miller

Thomas Muldowney

Legal Notice

This Jabber Enhancement Proposal is copyright 1999 - 2004 by the Jabber Software Foundation (JSF) and is in full conformance with the JSF's Intellectual Property Rights Policy <http://www.jabber.org/jsf/ipr-policy.php>. This material may be distributed only subject to the terms and conditions set forth in the Open Publication License, v1.0 or later (the latest version is presently available at <http://www.opencontent.org/openpub/>).

Discussion Venue

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 Jabber Software Foundation to the Internet Standards Process, which is managed by the Internet Engineering Task Force in accordance with RFC 2026. Any protocols defined in this JEP have been developed outside the Internet Standards Process and are to be understood as extensions to XMPP rather than as an evolution, development, or modification of XMPP itself.

Conformance Terms

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

1. Introduction

Stream Initiation [1] is a protocol to initiate a data stream within Jabber/XMPP. However, the sender is still responsible for informing receivers about this stream. This JEP provides a standardized way for a sender to announce a stream's availability without initiating the data transfer. The purpose is to provide a "pull" protocol for a receiver to request a transfer from a sender.

2. Requirements

3. Use Cases

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 (JEP-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 JEP-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 normally 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 for 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 a valid mime-type. 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 'profile'. This is the additional information about the data stream.

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

Example 2. Advertising a stream via publish-subscribe

<message to="receiver" from="pubsub.jabber.org">
  <event xmlns="http://jabber.org/protocol/pubsub#event">
    <items node="generic/si-publish">
      <item id="current">
        <sipub xmlns='http://jabber.org/protocol/si-pub'
            from='sender'
            id='publish-0123'
            mime-type='text/plain'
            profile='http://jabber.org/protocol/si/profile/file-transfer'>
          <file xmlns='http://jabber.org/protocol/si/profile/file-transfer'
                name='special.txt'
                size='1024'
                date='2004-01-28T10:07:00-07:00'>
            <desc>The special file</desc>
          </file>
        </sipub>
      </item>
    </items>
  </event>
</message>

Since the announcement did not come directly from the sender, the <sipub/> element MUST specify the stream owner in the 'from' attribute.

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 [4] or via Extended Stanza Addressing [5]). This can be especially useful for informing an offline entity about an available stream.

Example 3. Advertising a stream in a message stanza

<message from='sender' to='receiver'>
  <body>Here is the file you requested...</body>
  <sipub xmlns='http://jabber.org/protocol/si-pub'
         id='publish-0123'
         mime-type='text/plain'
         profile='http://jabber.org/protocol/si/profile/file-transfer'>
    <file xmlns='http://jabber.org/protocol/si/profile/file-transfer'
          name='special.txt'
          size='1024'
          date='2004-01-28T10:07:00-07:00'>
      <desc>The special file</desc>
    </file>
  </sipub>
</message>

Since the announcement came directly from the sender, the 'from' attribute is OPTIONAL.

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 [6]. 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 File Transfer [7]):

Example 4. "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 5. 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/plain'
           profile='http://jabber.org/protocol/si/profile/file-transfer'>
      <file xmlns='http://jabber.org/protocol/si/profile/file-transfer'
            name='special.txt'
            size='1024'
            date='2004-01-28T10:07:00-07:00'/>
    </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 performing 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 6. Receiver requests start of stream

  <iq type='get' id='sipub-request-0' to='sender' from='receiver'>
    <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 7. Sender accepts request to start stream

  <iq type='result' id='sipub-request-0' from='sender' to='receiver'>
    <starting xmlns='http://jabber.org/protocol/sipub'
              sid='session-87651234'/>
  </iq>

Then the sender begins the stream initiation negotiation:

Example 8. Sender starts negotiation

  <iq type='set' id='si-0' from='sender' to='receiver'>
    <si xmlns='http://jabber.org/protocol/si'
        id='session-87651234'
        mime-type='text/plain'
        profile='http://jabber.org/protocol/si/profile/file-transfer'>
      <file xmlns='http://jabber.org/protocol/si/profile/file-transfer'
          name='special.txt'
          size='1024'
          date='2004-01-28T10:07:00-07:00'>
        <desc>The special file</desc>
      </file>
    </si>
  </iq>

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

Example 9. Sender denies because of invalid id

  <iq type='error' id='sipub-requeset-0' from='sender' to='receiver'>
    <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 10. Sender denies because receiver is forbidden

  <iq type='error' id='sipub-requeset-0' from='sender' to='receiver'>
    <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. Implementation Notes

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.

5. Security Considerations

6. IANA Considerations

This JEP requires no interaction with the Internet Assigned Numbers Authority (IANA) [8].

7. Jabber Registrar Considerations

7.1 Protocol Namespaces

The Jabber Registrar [9] shall include 'http://jabber.org/protocol/sipub' in its registry of protocol namespaces.

7.2 Data Form Validation Datatypes

The Jabber Registrar shall include '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 JEP 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>JEP-0096</doc>
</datatype>

8. XML Schema

<?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:element name='sipub'>
    <xs:annotation>
      <xs:documentation>This is the root content element for advertising a stream.</xs:documentation>
    </xs:annotation>
    <xs:complexType>
      <xs:choice>
        <xs:any namespace='##other' minOccurs='1'/>
      </xs:choice>
      <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>

Notes

8. 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/>.

9. The Jabber Registrar maintains a list of reserved Jabber protocol namespaces as well as registries of parameters used in the context of protocols approved by the Jabber Software Foundation. For further information, see <http://www.jabber.org/registrar/>.