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: 0.1
Last Updated: 2004-06-16
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Superseded By: None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 and XMPP IM 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. Terminology

The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [2].

3. Requirements

4. Use Cases

4.1 Publishing an SI Request

A stream owner uses the <sipub/> element to announce it can perform a specific SI request. This element can be used with pubsub, or sent directly to potential recipients within a <message/>. The following represents the format of <sipub/>.

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>

The format for sipub is nearly identical to that for SI. The major difference is the lack of the feature negogiation 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 sipub sender. If present, this attribute MUST be the valid JID for the actual sipub sender.

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 SI, 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 SI, 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/> MUST contain an element in the namespace specified by "profile". This is the additional information about the data stream.

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

Example 2. Subscribers informed of the <sipub/>'s availability

  <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/> MUST specify that using the "from" attribute.

The <sipub/> MAY also be used directly within a <message/> [5]:

Example 3. Sending <sipub/> directly

  <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.

4.2 Integrating with Data Forms

One of the goals of sipub is to integrate SI 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, field's value(s) MUST be the <sipub/> identier(s). Also, the submitter MUST provide a <sipub/> 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>
    ...
    <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'/>
  </x>

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

4.3 Triggering the SI Request

A potential receiver starts the SI session by performing an IQ-GET to the sender, using the <start xmlns='http://jabber.org/protocol/sipub'/> element. This element contains the attribute "id" to indicate the published SI to retrieve:

Example 6. Receiver requests the start of SI

  <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 SI identifier to be used:

Example 7. Sender accepts request to start SI

  <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 SI negotiation:

Example 8. Sender starts SI

  <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>

5. Implementation Notes

5.1 Publish ID versus SI ID

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

6. Security Considerations

7. IANA Considerations

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

8. Jabber Registrar Considerations

8.1 Protocol Namespaces

SI Publication uses the following protocol namespaces:

http://jabber.org/protocol/sipub

8.2 Data Form Validation Datatypes

The "sipub" datatype prefix shall be registered with the Jabber Registrar [9].

Normally, each SI profile that wishes to be considered for use with Data Forms MUST register their own datatype qualified by "sipub". 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>

9. 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:import 
      namespace='http://jabber.org/protocol/si'
      schemaLocation='http://jabber.org/protocol/si/si.xsd'/>

  <xs:annotation>
    <xs:documentation>
      The protocol documented by this schema is defined in
      JEP-0xxx: http://www.jabber.org/jeps/jep-0xxx.html
    </xs:documentation>
  </xs:annotation>

  <xs:element name='sipub'>
    <xs:annotation>
      <xs:documentation>This is the root content element for publication.</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 an SI be retrieved.</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 indicating the SI 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/>.