XEP-xxxx: Push

WARNING: This document has not yet been accepted for consideration or approved in any official manner by the XMPP Standards Foundation, and this document is not yet an XMPP Extension Protocol (XEP). If this document is accepted as a XEP by the XMPP Council, it will be published at <http://xmpp.org/extensions/> and announced on the <standards@xmpp.org> mailing list.

1. Introduction
2. Concepts and Approach
    2.1. General Architecture of a Push Notification Service
    2.2. Mapping the General Architecture to XMPP
3. XMPP Push Service
    3.1. Recommended Defaults
    3.2. Business Rules
4. Discovering Support
    4.1. Account Owner Service Discovery
    4.2. Push Service Discovery
5. Enabling Notifications
6. Disabling Notifications
7. Publishing Notifications
    7.1. Publish Errors
    7.2. Notification Delivery
8. Remote Disabling of Notifications
9. Security Considerations
10. IANA Considerations
11. XMPP Registrar Considerations
    11.1. Protocol Namespaces
    11.2. Protocol Versioning
    11.3. Field Standardization
       11.3.1. urn:xmpp:push:summary FORM_TYPE
    11.4. Service Discovery Category/Type
12. XML Schema

Appendices
    A: Document Information
    B: Author Information
    C: Legal Notices
    D: Relation to XMPP
    E: Discussion Venue
    F: Requirements Conformance
    G: Notes
    H: Revision History

1. Introduction

The purpose of push notifications is to inform users of new messages or other pertinent information even when they have no XMPP clients online.

Typically, these notifications are delivered to a user's mobile device, displaying a notice that can trigger opening an XMPP client to continue a conversation or answer a Jingle session request.

There have been several push noticiations implementations by mobile XMPP client vendors. However, experience has shown that these implementations carried several drawbacks:

The goal for this document is to make the generalized case possible, whereby a user may use their XMPP client of choice with their own server of choice. The requirements are thus:

Note: Any publish-subscribe use cases not described herein are described in XEP-0060. Also, this document does not show error flows related to the generic publish-subscribe use cases referenced herein, since they are exhaustively defined in XEP-0060. The reader is referred to XEP-0060 for all relevant protocol details related to the XMPP publish-subscribe extension. This document merely defines a "subset" or "profile" of XMPP publish-subscribe.

2. Concepts and Approach

XMPP Push works between the user's XMPP server and two push notification services in tandem:

This two-tiered push architecture allows the user's XMPP server to deliver notifications to arbitrary third-pary clients, and in turn allows those clients to use the appropriate delivery mechanism for their platforms without having to share any private keys or other credentials with the XMPP server.

2.1 General Architecture of a Push Notification Service

The current state-of-the-art for a generic push notification service requires four actors:

App Client: The app client is the software installed and ran by the user, and is the final receiver of a push notification.
App Server: The app server is a backend service for the app client. At minimum, the app server exists to trigger push notifications, but it often also performs business logic for the app.
User Agent: The user agent is a service running locally on the user's device which receives push notifications and delivers them to the appropriate application.
Push Service: The push service ferries notifications from the App Server to the User Agent. How it does so is often proprietary and vendor/platform dependent.

Enabling notifications is a five step process:

The App Client asks the User Agent to authorize the delivery of notifications.
The User Agent then requests a token from the Push Service which authorizes delivery of notifications to that User Agent and App Client.
The Push Service issues the token to the User Agent.
The User Agent gives the token to the App Client.
The App Client sends the token to the App Server for later use.

Example 1. The five general steps to enable push notifications

+------------+          +------------+   
|            |    5     |            |   
| App Client +----------> App Server |   
|            |          |            |   
+-+--------^-+          +------------+   
  |1       |4                            
  |        |                             
+-v--------+-+  3       +---------------+
|            <----------+               |
| User Agent |          | Push Service  |
|            +---------->               |
+------------+  2       +---------------+

To send a push notification, the App Server sends the notification data to the Push Service along with the saved token.

Example 2. General delivery of a push notification

+------------+          +------------+   
|            |          |            |   
| App Client |          | App Server |   
|            |          |            |   
+-----^------+          +------+-----+   
      |                        |         
      |                        |         
+-----+------+          +------v--------+
|            |          |               |
| User Agent <----------+ Push Service  |
|            |          |               |
+------------+          +---------------+

2.2 Mapping the General Architecture to XMPP

To build an XMPP Push service on top of a general push service, we perform the following mapping:

The general App Client becomes the XMPP User Agent
The general App Server becomes the XMPP Push Service
The XMPP server is now the new logical "App Server"
The XMPP client portion of the application is the new logical "App Client"

Example 3. Mapping the generic push architecture to use XMPP

+-------------+         +-------------+ 
|             |   5     |             |
| XMPP Client +---------> XMPP Server |
|             |         |             |
+-+--------^--+         +-------------+
  |1       |4
  |        | 
+-v--------+-+  3       +------------+-------------------+
|            <----------+            |                   |
| App Client |          | App Server | XMPP Push Service |
|            +---------->            |                   |
+------------+  2       +------------+-------------------+

3. XMPP Push Service

An XMPP Push Service is a PubSub service as defined by the XMPP Publish-Subscribe [1] extension. The functional difference between a Push Service and a generic pubsub service is that a Push Service will generally summarize and forward published content via non-XMPP mechanisms.

Note: a Push Service is provided by a specific client application as part of the App Server. A user's XMPP server will typically not act as a Push Service itself, but will instead publish to the Push Services for the user's client applications.

3.1 Recommended Defaults

A Push Service MUST:

Support the 'whitelist' access model and set it to the default.
Support the 'publish-only' affiliation.

3.2 Business Rules

Each PubSub node is a delivery target for the Push Service, which could represent multiple devices for a single user.

In order to prevent information leaks, each node SHOULD be configured with a 'whitelist' access model so that only trusted entities are able to view or subscribe to published notifications. Furthermore, the 'publish-only' affiliation SHOULD be used to allow acceptable entities (such as the user's bare JID) to publish to the node to trigger notifications.

Care SHOULD be taken to ensure that publish requests are coming from the user's server and not from other third-party client applications using the full JID of a user. A Push Service MAY opt to only accept or further process publish requests from bare JIDs to ensure that only a user's server is able to publish, but it SHOULD instead use publish options with credentials shared only with the user's server (see Enabling Notifications).

4. Discovering Support

4.1 Account Owner Service Discovery

Before enabling or disabling push services, a client SHOULD determine whether the user's server supports publishing push notifications; to do so, it MUST send a Service Discovery [2] information quest to the user's bare JID:

Example 4. Client queries server regarding protocol support

<iq from='user@example.com/mobile'
    to='user@example.com'
    id='x13'
    type='get'>
  <query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>

If the user's server supports publishing push notifications and the account is provisioned to allow them, the server MUST include the feature 'urn:xmpp:push:0' in its list of supported features.

Example 5. Server communicates protocol support

<iq from='juliet@capulet.lit'
    to='juliet@capulet.lit/balcony'
    id='disco1'
    type='result'>
  <query xmlns='http://jabber.org/protocol/disco#info'>
    <identity category='account' type='registered'/>
    <feature var='urn:xmpp:push:0'/>
    ...
  </query>
</iq>

4.2 Push Service Discovery

If a service supports the XMPP Push Service publish-subscribe profile described herein, it MUST include an identity of "pubsub/push" in "disco#info" results.

Example 6. Service identifies as a Push Services

<iq from='push-5.client.example'
    to='user@example.com/mobile'
    id='x23'
    type='result'>
  <query xmlns='http://jabber.org/protocol/disco#info'>
    <identity category='pubsub' type='push' />
    <feature var='urn:xmpp:push:0'/>
    ...
  </query>
</iq>

5. Enabling Notifications

The full process for enabling notifications requires initializing two separate push services: between the App Client and App Server, and between the App Server and the user's XMPP server.

Note: It is assumed that an App Client is able to perform any registration procedures it requires to bootstrap its own preferred push notification system. Furthermore, it is assumed that the App Client or App Server is able to provision a node on its own XMPP Push Service. It is possible, but not required, to perform these actions over XMPP using In-Band Registration [3].

+-------------+         +-------------+                   
|             |         |             |                   
| XMPP Client +---------> XMPP Server |                   
|             |  5b     |             |                   
+------^------+         +-------------+                   
       |5a                                                
       |                                                  
+------+-----+   4      +--------------+---------------------+
|            <----------+              |                     |
| App Client |          | App Server <-3-> XMPP Push Service |
|            +---------->              |                     |
+--+------^--+   2      +--------------+---------------------+
   |1a    |1d                                             
   |      |                                               
+--v------+--+   1c     +---------------+                 
|            <----------+               |                 
| User Agent |          | Push Service  |                 
|            +---------->               |                 
+------------+   1b     +---------------+

For the last step, the App Client sends an IQ-set to the user's bare JID with an <enable /> element qualified by the 'urn:xmpp:push:0' namespace, which MUST contain a 'jid' attribute of the XMPP Push Service being enabled. It SHOULD contain a 'node' attribute which is set to the provisioned node specified by the App Server.

<iq type='set' id='x42'>
  <enable xmlns='urn:xmpp:push:0' jid='push-5.client.example' node='yxs32uqsflafdk3iuqo' />
</iq>

An App Server MAY require additional information to be provided with each published notification, such as authentication credentials. These parameters are included in the enable request by adding a XEP-0004 data form with a FORM_TYPE of 'http://jabber.org/protocol/pubsub#publish-options'.

<iq type='set' id='x43'>
  <enable xmlns='urn:xmpp:push:0' jid='push-5.client.example' node='yxs32uqsflafdk3iuqo'>
    <x xmlns='jabber:x:data'>
      <field var='FORM_TYPE'><value>http://jabber.org/protocol/pubsub#publish-options</value></field>
      <field var='secret'><value>eruio234vzxc2kla-91<value></field>
    </x>
  </enable>
</iq>

The JID for a Push Service MAY be enabled multiple times for a user only if different node values are provided. If the combination of JID and node has already been enabled, then the server SHOULD use the last received request for any publish options.

6. Disabling Notifications

If the user decides to stop push notifications for a particular client application, the App Client SHOULD send an IQ-set to the user's bare JID with a <disable /> element qualified by the 'urn:xmpp:push:0' namespace, which MUST include a 'jid' attribute of the service to be removed.

<iq type='set' id='x97'>
  <disable xmlns='urn:xmpp:push:0' jid='push-5.client.example' />
</iq>

A 'node' attribute MAY be included to remove a particular JID and node combination if multiple nodes have been enabled for a single service JID.

<iq type='set' id='x97'>
  <disable xmlns='urn:xmpp:push:0' jid='push-5.client.example' node='yxs32uqsflafdk3iuqo' />
</iq>

If a 'node' attribute is provided, then only that combination of JID and node SHOULD be removed from the set of enabled services. Otherwise, the server SHOULD disable all enabled entries for the specified service for the user.

When a service is not enabled, the server MUST NOT attempt publishing notifications to the service.

7. Publishing Notifications

When the user's server detects an event warranting a push notification, it performs a PubSub publish to all XMPP Push Services registered for the user, where the item payload is a <notification /> element in the 'urn:xmpp:push:0' namespace.

A XEP-0004 data form whose FORM_TYPE is 'urn:xmpp:push:summary' MAY be included to provide summarized information such as the number of unread messages or number of pending subscription requests.

<iq type='set'
    from='user@example.com'
    to='push-5.client.example'
    id='n12'>
  <pubsub xmlns='http://jabber.org/protocol/pubsub'>
    <publish node='yxs32uqsflafdk3iuqo'>
      <item>
        <notification xmlns='urn:xmpp:push:0'>
          <x xmlns='jabber:x:data'>
            <field var='FORM_TYPE'><value>urn:xmpp:push:summary</value></field>
            <field var='message-count'><value>1</value></field>
            <field var='last-message-sender'><value>juliet@capulet.example/balcony</value></field>
            <field var='last-message-body'><value>Wherefore art thou, Romeo?</value></field>
          </x>
          <additional xmlns='http://example.com/custom'>Additional custom elements</additional>
        </notification>
      </item>
    </publish>
  </pubsub>
</iq>

If additional data was provided when enabling the service, the publish request SHOULD include the data as publish options.

<iq type='set'
    from='user@example.com'
    to='push-5.client.example'
    id='n12'>
  <pubsub xmlns='http://jabber.org/protocol/pubsub'>
    <publish node='yxs32uqsflafdk3iuqo'>
      <item>
        <notification xmlns='urn:xmpp:push:0'>
          <x xmlns='jabber:x:data'>
            <field var='FORM_TYPE'><value>urn:xmpp:push:summary</value></field>
            <field var='message-count'><value>1</value></field>
            <field var='last-message-sender'><value>juliet@capulet.example/balcony</value></field>
            <field var='last-message-body'><value>Wherefore art thou, Romeo?</value></field>
          </x>
          <additional xmlns='http://example.com/custom'>Additional custom elements</additional>
        </notification>
      </item>
    </publish>
    <publish-options>
      <x xmlns='jabber:x:data'>
        <field var='FORM_TYPE'><value>http://jabber.org/protocol/pubsub#publish-options</value></field>
        <field var='secret'><value>eruio234vzxc2kla-91<value></field>
      </x>
    </publish-options>
  </pubsub>
</iq>

7.1 Publish Errors

If a publish request is returned with an IQ-error, then the server SHOULD consider the particular JID and node combination to be disabled.

However, a server MAY choose to keep a service enabled if the error is deemed recoverable or transient, until a sufficient number of errors have been received in a row.

A server MAY retry an automatically disabled JID and node combination after a period of time (e.g. 1 day).

7.2 Notification Delivery

Once the notification has been published to the XMPP Push Service, it is left to the implementation how to deliver the notification to the user's device. However, the general flow for the process looks like so:

Example 14. The full path of a push notification, from XMPP server to user client

+-------------+         +-------------+ 
|             |         |             | 
| XMPP Client |         | XMPP Server +--------+ 
|             |         |             |        | 
+-----^-------+         +-------------+        | 
      .                                        | 
      .                                        | 
+-----+------+          +------------+---------v---------+
|            |          |            |                   |
| App Client |          | App Server < XMPP Push Service |
|            |          |            |                   |
+-----^------+          +------+-----+-------------------+
      |                        | 
      |                        | 
+-----+------+          +------v--------+
|            |          |               |
| User Agent <----------+ Push Service  |
|            |          |               |
+------------+          +---------------+

8. Remote Disabling of Notifications

It can be desirable for an XMPP Push Service to stop accepting notifications the user's XMPP server. To do so, the XMPP Push Service removes the 'publish-only' (or other publish-enabling affiliation) from the user's JID, and MAY send an affiliation change notice to the user's bare JID:

<message from='push-5.client.example' to='user@example.com'>
  <pubsub xmlns='http://jabber.org/protocol/pubsub' node='yxs32uqsflafdk3iuqo'>
    <affiliation jid='user@example.com' affiliation='none' />
  </pubsub>
</message>

Upon receiving an affiliation change event, the server MAY remove the received JID and node combination from the set of enabled services. If a server does not do so, then the service will be removed from the enabled set through the error handling process.

9. Security Considerations

Push notifications require routing private information, such as message bodies, through third parties. As such, servers SHOULD allow users to limit the information sent via push notifications.

It is NOT RECOMMENDED to allow in-band modification of push notification content settings. Such operations SHOULD be done out-of-band to prevent privilege escalation.

10. IANA Considerations

11. XMPP Registrar Considerations

11.1 Protocol Namespaces

The XMPP Registrar [5] includes 'urn:xmpp:push:0' in its registry of protocol namespaces (see <http://xmpp.org/registrar/namespaces.html>).

urn:xmpp:push:0

11.2 Protocol Versioning

If the protocol defined in this specification undergoes a revision that is not fully backwards-compatible with an older version, the XMPP Registrar shall increment the protocol version number found at the end of the XML namespaces defined herein, as described in Section 4 of XEP-0053.

11.3 Field Standardization

XEP-0068 defines a process for standardizing the fields used within Data Forms scoped by a particular namespace, and the XMPP Registrar maintains a registry of such FORM_TYPES (see <http://xmpp.org/registrar/formtypes.html>).

11.3.1 urn:xmpp:push:summary FORM_TYPE

<form_type>
  <name>urn:xmpp:push:summary</name>
  <doc>XEP-XXXX</doc>
  <desc>Provides summarizing information about a user for use in push notifications.</desc>
  <field
      var='message-count'
      type='text-single'
      label='The number of unread or undelivered messages'/>
  <field
      var='pending-subscription-count'
      type='text-single'
      label='The number of pending incoming presence subscription requests'/>
  <field
      var='last-message-sender'
      type='jid-single'
      label='The sender of the last received message'/>
  <field
      var='last-message-body'
      type='text-single'
      label='The body text of the last received message'/>
</form_type>

11.4 Service Discovery Category/Type

The XMPP Registrar [6] includes a category of "component" in its registry of Service Discovery identities (see <http://xmpp.org/registrar/disco-categories.html>); as a result of this document, the Registrar includes a type of "jidprep" to that category.

The registry submission is as follows:

<category>
  <name>pubsub</name>
  <type>
    <name>push</name>
    <desc>
      A push notification service that supports the publish-subscribe profile defined in XEP-XXXX.
    </desc>
    <doc>XEP-XXXX</doc>
  </type>
</category>

12. XML Schema

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

<xs:schema
    xmlns:xs='http://www.w3.org/2001/XMLSchema'
    targetNamespace='urn:xmpp:push:0'
    xmlns='urn:xmpp:push:0'
    elementFormDefault='qualified'>

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

  <xs:import
      namespace='jabber:x:data'
      schemaLocation='http://xmpp.org/schemas/x-data.xsd' />

  <xs:element name='enable'>
    <xs:complexType>
       <xs:sequence minOccurs='0' maxOccurs='unbounded' xmlns:xdata='jabber:x:data'>
         <xs:element ref='xdata:x' />
       </xs:sequence>
       <xs:attribute name='jid' type='xs:string' use='required' />
       <xs:attribute name='node' type='xs:string' use='required' />
    </xs:complexType>
  </xs:element>

  <xs:element name='disable'>
    <xs:complexType>
       <xs:attribute name='jid' type='xs:string' use='required' />
       <xs:attribute name='node' type='xs:string' use='optional' />
    </xs:complexType>
  </xs:element>

  <xs:element name='notification'>
    <xs:complexType>
       <xs:sequence minOccurs='0' maxOccurs='unbounded' xmlns:xdata='jabber:x:data'>
         <xs:element ref='xdata:x' />
         <xs:any />
       </xs:sequence>
    </xs:complexType>
  </xs:element>

</xs:schema>

Appendices

Appendix A: Document Information

Series: XEP
Number: xxxx
Publisher: XMPP Standards Foundation
Status: ProtoXEP
Type: Standards Track
Version: 0.0.2
Last Updated: 2015-03-10
Approving Body: XMPP Council
Dependencies: XMPP Core, XMPP IM, XEP-0004, XEP-0030, XEP-0060
Supersedes: None
Superseded By: None
Short Name: NOT_YET_ASSIGNED
This document in other formats: XML PDF

Appendix B: Author Information

Lance Stout

Email: lancestout@gmail.com
JabberID: lance@lance.im

Appendix C: Legal Notices

Copyright

Permissions

Permission is hereby granted, free of charge, to any person obtaining a copy of this specification (the "Specification"), to make use of the Specification without restriction, including without limitation the rights to implement the Specification in a software program, deploy the Specification in a network service, and copy, modify, merge, publish, translate, distribute, sublicense, or sell copies of the Specification, and to permit persons to whom the Specification is furnished to do so, subject to the condition that the foregoing copyright notice and this permission notice shall be included in all copies or substantial portions of the Specification. Unless separate permission is granted, modified works that are redistributed shall not contain misleading information regarding the authors, title, number, or publisher of the Specification, and shall not claim endorsement of the modified works by the authors, any organization or project to which the authors belong, or the XMPP Standards Foundation.

Disclaimer of Warranty

## NOTE WELL: This Specification is provided on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, express or implied, including, without limitation, any warranties or conditions of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A PARTICULAR PURPOSE. ##

Limitation of Liability

In no event and under no legal theory, whether in tort (including negligence), contract, or otherwise, unless required by applicable law (such as deliberate and grossly negligent acts) or agreed to in writing, shall the XMPP Standards Foundation or any author of this Specification be liable for damages, including any direct, indirect, special, incidental, or consequential damages of any character arising from, out of, or in connection with the Specification or the implementation, deployment, or other use of the Specification (including but not limited to damages for loss of goodwill, work stoppage, computer failure or malfunction, or any and all other commercial damages or losses), even if the XMPP Standards Foundation or such author has been advised of the possibility of such damages.

IPR Conformance

This XMPP Extension Protocol has been contributed in full conformance with the XSF's Intellectual Property Rights Policy (a copy of which can be found at <http://xmpp.org/about-xmpp/xsf/xsf-ipr-policy/> or obtained by writing to XMPP Standards Foundation, 1899 Wynkoop Street, Suite 600, Denver, CO 80202 USA).

Appendix D: Relation to XMPP

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.

Appendix E: Discussion Venue

The primary venue for discussion of XMPP Extension Protocols is the <standards@xmpp.org> discussion list.

Appendix F: Requirements Conformance

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".

Appendix G: Notes

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

2. XEP-0030: Service Discovery <http://xmpp.org/extensions/xep-0030.html>.

3. XEP-0077: In-Band Registration <http://xmpp.org/extensions/xep-0077.html>.

4. 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/>.

5. 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://xmpp.org/registrar/>.

6. 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://xmpp.org/registrar/>.

Abstract:	This specification defines a way for an XMPP servers to deliver information for use in push notifications to mobile and other devices.
Author:	Lance Stout
Copyright:	© 1999 - 2013 XMPP Standards Foundation. SEE LEGAL NOTICES.
Status:	ProtoXEP
Type:	Standards Track
Version:	0.0.2
Last Updated:	2015-03-10