JEP-0146: Remote Controlling Clients

This JEP specifies recommended best practices for remote controlling clients using Ad-Hoc Commands.

WARNING: This Informational JEP is Experimental. Publication as a Jabber Enhancement Proposal does not imply approval of this proposal by the Jabber Software Foundation. Implementation of the best practice or protocol profile described herein is encouraged in exploratory implementations, although production systems should not deploy implementations of this protocol until it advances to a status of Draft.

JEP Information

Status: Experimental
Type: Informational
Number: 0146
Version: 0.1
Last Updated: 2004-11-12
JIG: Standards JIG
Approving Body: Jabber Council
Dependencies: None
Supersedes: None
Superseded By: None
Short Name:

Author Information

Remko Troncon

Peter Saint-Andre

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

When one has multiple clients at different locations logged in simultaneously, it is often desirable to control these clients from the client you are currently using. There are a number of common tasks one might want to perform remotely on clients: change the status of the client, forward all received unread messages to this client, and so on. Therefore, it makes sense to define a protocol for performing these tasks.

This JEP describes a protocol to perform a set of common tasks on a remote client, by specifying a profile of Ad-Hoc Commands [1].

2. Terminology

3. Requirements

4. Discovery

A client MUST advertise any remote controlling commands it supports via Service Discovery [3] (as described in JEP-0050: Ad-Hoc Commands). Entity Capabilities [4] can be used to query capability of remote controlling commands in a client.

5. Use Cases

This JEP defines a profile of JEP-0050: Ad-Hoc Commands that enables a user to perform the following tasks on a remote client:

Although this JEP aims to define common use cases for remote controlling clients, an implementation or deployment MAY support any subset and MAY support additional commands not defined herein.

Note: The text that follows assumes that implementors have read and understood JEP-0050: Ad-Hoc Commands.

5.1 Change Status

It is common to forget changing the status of a resource when leaving the client for a longer period. When realizing this while at another location, it might be desirable to change the status from there, to avoid contacts thinking that resource is attended and sending it messages.

Example 1. Local Client Requests to Set the Status of a Remote Client

<iq from='juliet@example.com/chamber'
    to='juliet@example.com/balcony'
    type='set'
    id='set-status-1'
    xml:lang='en'>
  <command xmlns='http://jabber.org/protocol/commands' 
           action='execute'
           node='http://jabber.org/protocol/rc#set-status'/>
</iq>

Unless an error occurs (see the Error Handling section below), the service SHOULD return the appropriate form.

Example 2. Remote Client Replies with a Form to Set its Status

<iq from='juliet@example.com/balcony' 
    to='juliet@example.com/chamber' 
    type='result' 
    id='set-status-1'
    xml:lang='en'>
  <command xmlns='http://jabber.org/protocol/commands'
             node='http://jabber.org/protocol/rc#set-status'
             sessionid='set-status:20040727T0337Z'
             status='executing'>
    <x xmlns='jabber:x:data' type='form'>
      <title>Setting the status</title>
      <instructions>Choose the status and status message</instructions>
      <field type='hidden' var='FORM_TYPE'>
        <value>http://jabber.org/protocol/rc</value>
      </field>
      <field label='Status' 
             type='list-single' 
             var='status'>
        <required/>
        <value>online</value>
        <option label='Chat'> 
            <value>chat</value>
        </option>
        <option label='Online'> 
            <value>online</value>
        </option>
        <option label='Away'> 
            <value>away</value>
        </option>
        <option label='Extended Away'> 
            <value>xa</value>
        </option>
        <option label='Do Not Disturb'> 
            <value>dnd</value>
        </option>
        <option label='Invisible'> 
            <value>invisible</value>
        </option>
        <option label='Offline'> 
            <value>offline</value>
        </option>
      </field>
      <field label='Priority'
             type='text-single'
             var='status-priority'>
        <value>5</value> 
      </field>
      <field label='Message' 
             type='text-multi' 
             var='status-message'/>
    </x>
  </command>
</iq>

Example 3. Local Client Submits Set Status Form to Remote Client

<iq from='juliet@example.com/chamber'
    to='juliet@example.com/balcony'
    type='set'
    id='set-status-2'
    xml:lang='en'>
  <command xmlns='http://jabber.org/protocol/commands' 
           node='http://jabber.org/protocol/rc#set-status'
           sessionid='set-status:20040727T0337Z'>
    <x xmlns='jabber:x:data' type='form' >
      <field type='hidden' var='FORM_TYPE' >
        <value>http://jabber.org/protocol/rc</value>
      </field>
      <field type='list-single' var='status' >
        <value>xa</value>
      </field>
      <field type='text-single' var='status-priority'>
        <value>-1</value>
      </field>
      <field type='text-multi' var='status-message' >
        <value>In my chamber.</value>
      </field>
    </x>
  </command>
</iq>

If the 'status-priority' variable is omitted, the client SHOULD NOT change the priority of the client

Example 4. Remote Client Informs Local Client of Completion

<iq from='juliet@example.com/balcony' 
    to='juliet@example.com/chamber' 
    type='result' 
    id='set-status-2'
    xml:lang='en'>
  <command xmlns='http://jabber.org/protocol/commands'
           node='http://jabber.org/protocol/rc#set-status'
           sessionid='set-status:20040727T0337Z'
           status='completed'/>
</iq>

Notification of completion MAY include the processed data in a data form of type "result".

5.2 Forward Unread Messages Residing at a Remote Client

A user might want to forward all the unread messages residing at the remote client to the local client (e.g. when the remote client was accidentally left on-line, and has received messages in the meantime).

For example, suppose Romeo sends a message to Juliet, thinking she is still on her balcony. The balcony client receives the message:

Example 5. Remote Client Receives Message

<message from="romeo@example.com/orchard" 
         to="juliet@example.com/balcony">
  <subject>Just saying hi</subject>
  <body>Hello Juliet!</body>
</message>

However, Juliet is in her chamber, so she doesn't know about the message (yet). Realizing she left her balcony client unattended, she sends a request to the remote client to forward all unread messages.

Example 6. Local Client Requests to Forward Unread Messages Currently Residing at the Remote Client

<iq from='juliet@example.com/chamber'
    to='juliet@example.com/balcony'
    type='set'
    id='forward-1'
    xml:lang='en'>
  <command xmlns='http://jabber.org/protocol/commands' 
           action='execute'
           node='http://jabber.org/protocol/rc#forward'
           sessionid='forward:20040727T0337Z'/>
</iq>

The client forwards all unread messages to the local client, adding information about the origin of the message (protocol for this to follow). The chamber client receives both these messages and a confirmation that the command was completed.

Example 7. Remote Client Forwards All Unread Messages to Local Client

<message from="juliet@example.com/balcony" 
         to="juliet@example.com/chamber" >
  <subject>Just saying hi</subject>
  <body>Hello Juliet!</body>
  <x xmlns="jabber:x:forward">
    <from jid="romeo@example.com/orchard"/>
  </x>
</message>

Example 8. Remote Client Informs Local Client of Completion

<iq from='juliet@example.com/balcony' 
    to='juliet@example.com/chamber' 
    type='result' 
    id='forward-1'
    xml:lang='en'>
  <command xmlns='http://jabber.org/protocol/commands'
           node='http://jabber.org/protocol/rc#forward'
           sessionid='forward:20040727T0337Z'
           status='completed'/>
</iq>

A client MAY provide a more fine-grained implementation, e.g. by presenting the requester an extra form to select which messages have to be forwarded.

5.3 Change Run-Time Options

It might be desirable to remotely set some run-time options of a client. For example, when neighbours complain about the sounds your client makes while you're at another location, you could turn the sounds off at the remote client.

Protocol to follow.

5.4 Accept Pending File Transfer Requests

Example 9. Local Client Requests to Accept Pending File Transfer Requests on the Remote Client

<iq from='juliet@example.com/chamber'
    to='juliet@example.com/balcony'
    type='set'
    id='accept-files-1'
    xml:lang='en'>
  <command xmlns='http://jabber.org/protocol/commands' 
           action='execute'
           node='http://jabber.org/protocol/rc#accept-files'/>
</iq>

Unless an error occurs (see the Error Handling section below), the service SHOULD return the appropriate form.

Example 10. Remote Client Replies with a Form Containing Pending File Transfers

<iq from='juliet@example.com/balcony' 
    to='juliet@example.com/chamber' 
    type='result' 
    id='accept-files-1'
    xml:lang='en'>
  <command xmlns='http://jabber.org/protocol/commands'
             node='http://jabber.org/protocol/rc#accept-files'
             sessionid='set-status:20040727T0337Z'
             status='executing'>
    <x xmlns='jabber:x:data' type='form'>
      <title>Pending File Transfers</title>
      <instructions>Select the pending file transfers to accept</instructions>
      <field type='hidden' var='FORM_TYPE'>
        <value>http://jabber.org/protocol/rc</value>
      </field>
      <field label='Files' 
             type='list-multi' 
             var='files'>
        <required/>
        <option label='ballad.ogg (romeo@example.com)'> 
          <value>romeo@example.com/orchard:1</value>
        </option>
        <option label='picture.jpg (romeo@example.com)'> 
          <value>romeo@example.com/orchard:2</value>
        </option>
        <option label='challenge.txt (mercutio@example.com)'> 
          <value>mercutio@example.com/orchard:1</value>
        </option>
      </field>
    </x>
  </command>
</iq>

Example 11. Local Client Submits Form to Remote Client

<iq from='juliet@example.com/chamber'
    to='juliet@example.com/balcony'
    type='set'
    id='accept-files-2'
    xml:lang='en'>
  <command xmlns='http://jabber.org/protocol/commands' 
           node='http://jabber.org/protocol/rc#accept-files'
           sessionid='accept-files:20040727T0337Z'>
    <x xmlns="jabber:x:data" type="form" >
      <field type="hidden" var="FORM_TYPE" >
        <value>http://jabber.org/protocol/rc</value>
      </field>
      <field type="list-multi" var="files" >
        <value>romeo@example.com/orchard:2</value>
      </field>
    </x>
  </command>
</iq>

The remote client accepts the selected file transfers, and informs the local client of completion.

Example 12. Remote Client Informs Local Client of Completion

<iq from='juliet@example.com/balcony' 
    to='juliet@example.com/chamber' 
    type='result' 
    id='accept-files-2'
    xml:lang='en'>
  <command xmlns='http://jabber.org/protocol/commands'
           node='http://jabber.org/protocol/rc#accept-files'
           sessionid='accept-files:20040727T0337Z'
           status='completed'/>
</iq>

5.5 Leave Groupchats

Protocol to follow.

6. Error Handling

Several error conditions are possible when an entity sends a command request to the service, as defined in the following table. If one of these errors occurs, the service MUST return an error stanza to the requesting entity.

Condition	Cause
<feature-not-implemented/>	The specific command is not supported (even though the ad-hoc commands protocol is)
<forbidden/>	The requesting entity does not have sufficient privileges to perform the command
<service-unavailable/>	The ad-hoc commands protocol is not supported

For the syntax of these errors, see Error Condition Mappings [5]. Naturally, other errors may be returned as well.

7. Implementation Notes

Implementations of this protocol MAY add or remove fields to forms as they see fit. For example, when setting the status of a remote client that supports multiple accounts, the client may choose to add a boolean field to allow the user to specify whether the status change should be applied globally or only to the receiving account.

Implementations MAY also introduce extra forms for commands. For example, when forwarding unread messages, a client could return a form containing a list of short descriptions of unread messages, allowing the user to select the messages he wants to forward.

8. Security Considerations

The ability to complete the tasks specified herein MUST NOT be granted to users who lack privileges to control a client. A sensible access policy is to only allow remote controlling by other resources of the same account used by the client. If other accounts are to be able to remote control the client, the client needs more complex access right management.

9. IANA Considerations

This JEP requires no interaction with the Internet Assigned Numbers Authority (IANA) [6].

10. Jabber Registrar Considerations

The Jabber Registrar [7] shall include the following information in its registries.

10.1 Protocol Namespaces

The Jabber Registrar shall include 'http://jabber.org/protocol/rc' in its registry of protocol namespaces.

10.2 Field Standardization

Field Standardization for Data Forms [8] defines a process for standardizing the fields used within Data Forms scoped by a particular namespace. The reserved fields for the 'http://jabber.org/protocol/rc' namespace are specified below.

Registry Submission

<form_type>
  <name>http://jabber.org/protocol/rc</name>
  <doc>JEP-??</doc>
  <desc>Forms used for remote controlling clients</desc>
  <field var='status'
         type='list-single'
         var='The list of statuses'/>
  <field var='status-priority'
         type='text-single'
         var='The new priority for the client'/>
  <field var='status-message'
         type='text-multi'
         label='The status message text'/>
</form_type>

11. XML Schema

Because the protocol defined here is a profile of JEP-0050: Ad-Hoc Commands, no schema definition is needed.

Notes

6. 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/>.

7. 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/>.