Stream Initiation (XEP-0095) [1] defines a protocol to initiate a data stream between two Jabber/XMPP entities (e.g., for the purpose of SI File Transfer (XEP-0096) [2]). However, the sender is still responsible for informing potential receivers about the existence of a given stream. This document provides an automated way for a sender to announce the availability of a stream without initiating the data transfer. The purpose is to provide a "pull" protocol that enables a receiver to then request initiation of the stream from the sender.
This proposal addresses the following requirements:
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:
<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 Stream Initiation (XEP-0095) [1]). 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:
<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/sipub'
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>
<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/sipub'
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 (XEP-0045) [6] or via Extended Stanza Addressing (XEP-0033) [7]). This can be especially useful for informing an offline entity about an available stream.
<message from='romeo@montague.net/pda' to='juliet@capulet.com'>
<sipub xmlns='http://jabber.org/protocol/sipub'
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>
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 (XEP-0122) [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 SI File Transfer (XEP-0096) [2]:
<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:
<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.
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:
<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:
<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:
<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:
<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:
<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>
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.
This document introduces no security concerns beyond those specified in Publish-Subscribe (XEP-0060) [3] and the relevant Stream Initiation profile in use.
This document requires no interaction with the Internet Assigned Numbers Authority (IANA) [9].
The XMPP Registrar [10] includes 'http://jabber.org/protocol/sipub' in its registry of protocol namespaces.
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:
<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>
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The Extensible Messaging and Presence Protocol (XMPP) is defined in the XMPP Core (RFC 6120) and XMPP IM (RFC 6121) 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.
The primary venue for discussion of XMPP Extension Protocols is the <standards@xmpp.org> discussion list.
Discussion on other xmpp.org discussion lists might also be appropriate; see <https://xmpp.org/community/> for a complete list.
Errata can be sent to <editor@xmpp.org>.
The following requirements 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".
1. XEP-0095: Stream Initiation <https://xmpp.org/extensions/xep-0095.html>.
2. XEP-0096: SI File Transfer <https://xmpp.org/extensions/xep-0096.html>.
3. XEP-0060: Publish-Subscribe <https://xmpp.org/extensions/xep-0060.html>.
4. XEP-0004: Data Forms <https://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 <https://xmpp.org/extensions/xep-0045.html>.
7. XEP-0033: Extended Stanza Addressing <https://xmpp.org/extensions/xep-0033.html>.
8. XEP-0122: Data Forms Validation <https://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 <https://xmpp.org/registrar/>.
Note: Older versions of this specification might be available at https://xmpp.org/extensions/attic/
Deprecated per a vote of the XMPP Council.
@report{miller2004sipub,
title = {Publishing Stream Initiation Requests},
author = {Miller, Matthew and Muldowney, Thomas},
type = {XEP},
number = {0137},
version = {1.1},
institution = {XMPP Standards Foundation},
url = {https://xmpp.org/extensions/xep-0137.html},
date = {2004-06-16/2018-02-28},
}END