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Collaborative editing for Plone

Project description

Introduction

jarn.xmpp.collaboration defines a protocol to do real-time collaborative editing through XMPP and provides:

  • a generic overridable implementation of the server component.

  • a Plone-specific implementation (server component and javascript client).

  • adapters for basic Plone content types (Pages and News Items).

It is part of a suite of packages aiming to provide XMPP services to Plone. The other two packages are

  • jarn.xmpp.twisted, provides XMPP-specific protocol implementation for twisted.

  • jarn.xmpp.core provides facilities for presence, messaging, chatting and microblogging.

Requirements

Please see jarn.xmpp.core for details on setting up your Plone site and XMPP server. If you are not using the recipe included in jarn.xmpp.buildout you will need to configure your ejabberd to allow connections from the collaboration component. For ejabberd this is done by including the following in your config file:

{{5347, {0,0,0,0} }, ejabberd_service, [
  {access, all},
  {shaper_rule, fast},
  {ip, {127, 0, 0, 1}},
  {hosts, ["collaboration.localhost"],
   [{password, "secret"}]
  }
 ]},

The instance that is going to be running the xmpp component should include the component.zcml. You can do this in your buildout:

zcml-additional =
  <configure xmlns="http://namespaces.zope.org/zope">
      <include package="jarn.xmpp.twisted" file="reactor.zcml" />
      <include package="jarn.xmpp.collaboration" file="component.zcml" />
  </configure>

Usage

Using jarn.xmpp.collaboration is easy once you have gotten over setting it up. There are no special views to use when you collaboratively edit content. If an adapter to ICollaborativelyEditable exists for your content then accessing its edit form will allow multiple users to edit simultaneously.

Out of the box there exist adapters for archetypes as well as dexterity-based content types. For AT content types fields that implement IStringField or ITextField will automatically get collaborative editing support. For Dexterity the fields that will be automatically included are those that provide ITextLine, IText or IRichText regardless of the behavior by which they are defined. Note that the javascript client assumes that TinyMCE is used. Collaboration on rich text fields will not work with Kupu.

Protocol specification.

Initialization

In order to initiate a collaborative editing session, the party sends a presence to the server indicating on which node he wishes to work on. The party MUST specify the node attribute in the query element:

<presence from='foo@example.com/work' to='collaboration.example.com'>
    <query xmlns='http://jarn.com/ns/collaborative-editing'
        node='collab-node'/>
</presence>

Upon receipt the server sends a message to the party setting the initial text of the node. If the node is already being edited the initial text is the most current copy on the server:

<message from='collaboration.example.com' to='foo@example.com/work'>
    <x xmlns='http://jarn.com/ns/collaborative-editing'>
        <item action='set' node='collab-node'>Hello world</item>
    </x>
</message>

Editing cycle

When a party edits the text, it notifies the server by sending a message. The message contains one or more item elements which MUST specify the node they apply to, have the attribute action set to patch, and in their body contain the patch created by the Diff-Match-Patch algorithm in text format. For instance if the text changed from “Hello world” to “Hello world, have a nice day!” the message would be:

<message from='foo@example.com/work' to='collaboration.example.com'>
    <x xmlns='http://jarn.com/ns/collaborative-editing'>
        <item node='collab-node' action='patch'>@@ -4,8 +4,26 @@\n lo world\n+, have a nice day!\n</item>
    </x>
</message>

If the server succeeds to apply the patch to its shadow copy, it broadcasts the patch to all other parties who are present on the node. The parties MUST apply it to their text:

<message from='collaboration.example.com' to='bar@example.com/home'>
    <x xmlns='http://jarn.com/ns/collaborative-editing'>
        <item node='collab-node' action='patch'>@@ -4,8 +4,26 @@\n lo world\n+, have a nice day!\n</item>
    </x>
</message>

If the server fails to apply the patch (because for instance there was a network problem and the client fell out of sync, or the diff-match-patch application failed), it SHOULD send a set action to the party with its shadow copy as text.

Focusing

In an environment where multiple nodes are edited in the same time (for instance in a context where the content has more than one collaboratively editable fields) the client CAN send a notification specifying which particular node he is currently editing:

<message from='foo@example.com/work' to='collaboration.example.com'>
    <x xmlns='http://jarn.com/ns/collaborative-editing'>
        <item node='collab-node' action='focus' user='foo@example.com/work'/>
    </x>
</message>

The server MUST propagate the message to all other users that are currently collaborating on the node:

<message from='collaboration.example.com' to='bar@example.com/home'>
    <x xmlns='http://jarn.com/ns/collaborative-editing'>
        <item node='collab-node' action='focus' user='foo@example.com/work'/>
    </x>
</message>

Saving

At any point a party can request a save. This is done by sending a message whose item MUST indicate the node and its action must be set to save:

<message from='foo@example.com/work' to='collaboration.example.com'>
    <x xmlns='http://jarn.com/ns/collaborative-editing'>
        <item node='collab-node' action='save'></item>
    </x>
</message>

It is up to the server component to enforce any security considerations on saving.

Termination

The session is terminated when the party sends an unavailable presence:

<presence from='foo@example.com/work' type='unavailable' />

Credits

  • Most of this work was done using the 10% time available to Jarn AS employees for the development of open-source projects.

  • David Glick (davisagli) for dexterity support and general awesomeness.

  • jarn.xmpp.collaboration relies on the wonderful Diff-Match-Patch from Neil Fraser at Google. It is distributed under the Apache License 2.0.

Changelog

0.1a3

  • Simplified configuration and fixed confusing typos in the registry [ggozad]

0.1a2 - 2010-06-06

  • Configure the component/server password and connection port in p.a.registry. [ggozad]

  • Dexterity content type support. [davisagli, ggozad]

  • Generalized ATContentTypes support. [ggozad]

  • Provide visual feedback when a user updates a node. [ggozad]

  • JS cleanup. [ggozad]

  • Test coverage. [ggozad]

0.1a1 2010-05-09

  • Initial release [ggozad]

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