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Em::Xmpp

EM::Xmpp is an XMPP client library for EventMachine. It uses Nokogiri as an XML parser and XML builder.

EM::Xmpp provides decorator-style modules in the mean of contexts to easily match and reply to stanzas.

Installation

Standard

gem install em-xmpp

Bundler

Add this line to your application's Gemfile:

gem 'em-xmpp'

And then execute:

$ bundle

Or install it yourself as:

$ gem install em-xmpp

Usage

XMPP is a stateful asynchronous protocol. Hence, to operate an XMPP client, you must be able to receive and send XMPP messages (called stanzas) as well as maintain some sort of states at the same time. For this reason, EventMachine is a good fit to write and XMPP-client in. EM::Xmpp implements a middleware to write XMPP clients on top of EventMachine for the asyncrhonous network, and uses Ruby fibers to encapsulate states. Most of the code could easily be extracted to work with other backends than EventMachine (e.g., TCPSocket) but it would be harder to remove Fibers.

Connecting to an XMPP server

Like many EventMachine libraries, you need to first create a module and pass it to EM::Xmpp::Connection.start

When the connection is ready, EM::Xmpp will call :ready on your connection object. From that point, you can start handling stanzas.

Receiving stanzas

You can setup handlers for message, presence, and iq with on_message, on_presence, and on_iq methods. All these methods take a callback block argument. EM::Xmpp will be call-back the block with a Context object. This context object helps you while reading the content of a stanza and replying to it.

You may have multiple handlers per stanza type and the callback block argument must return the same or another context that will be used for further matching. This layering lets you write stack-like middlewares where every Context handler adds some features/environment-variables to the Context.

You can call #done! on a Context to notify the stack that you are done with this stanza. That is, you do not give a chance to subsequent handlers to match on the stanza.

You can also call #delete_xpath_handler! on a context handler to remove it from the stack for the next stanzas. This let you build temporary handlers quite easily.

Any handler can also throw :halt to interrupt the layering and all the handler removal operations. You should read the code to understand well what you skip by doing so.

Summarizing, when your connection receives a stanza, the stanza is encapsulated in a context object and matched against context handlers. Default handlers exist for the three main stanza types (presence, iq, and message). For example:

on_presence do |ctx|
  some_operation1
  ctx.env['foo'] = 'bar' #passes the 'bar' to the next stanza matcher
  ctx #unmodified context
end

on_presence do |ctx|
  some_operation2
  ctx.env['foo'] #=> 'bar' 
  ctx.done! #next stanza matchers will not receive the context
end

on_presence do |ctx|
  this_code_is_never_called
  ctx
end

You can use on(*xpath_args) to build a matcher for any XPath in the stanza. The arguments are passed verbatim to Nokogiri. A special argument is on(:anything) that will match any stanza (e.g., for logging). This is useful to build new decorators for handling a specific XEP (if you do so, please share with a pull-request).

When an exception occurs in a stanza handler, the stack rescues the error and runs the Context through a set of exception handlers. To handle exception you can use the on_exception(:anything) method.

See the ./samples directory for basic examples.

Interpreting incoming stanzas

Now that you know how to receive contexts, you also want to read content inside the stanza. Contexts have a stanza method to get the Nokogiri representation of the stanza XML node (remember that stanzas are XML nodes of an XML stream). Therefore, you can read any node/attribute in any XML namespace of the original XML node. This way, you have a large control on what to read and you can implement XEPs not covered in this piece of code (please share your code).

EM::Xmpp provides some level of abstraction to handle incoming stanzas that can support multiple XEPs. Since a single stanza can carry lots of different XEPs, single inheritence is not a beautiful option. There are two solutions with a slightly different cost-model (expressive+slow and slightly-verbose+fast).

A first solution is to extend each context with methods (one Ruby module per XEP). Unfortunately, extending Ruby objects is expensive in terms of method cache. Extend lets you write code that clearly expresses your intention at the expense of some slowness.

on_message do |ctx|
  ctx.with(:message) # extends with EM::Xmpp::Context::Contexts::Message
  ctx.with(:mood)    #                                           Mood
  #then lets you write:
  puts ctx.from
  puts ctx.body
  puts ctx.mood
  ctx 
end

This is the "Contexts" method.

A less expensive technique is to create, on demand, some delegators objects for every XEPs. Therefore you must always prepend a method call to name the XEP you use. We call this method the "Bits" method. Because we support XEPs by bits.

on_message do |ctx|
  message = ctx.bit!(:message) # delegate to a EM::Xmpp::Context::Bits::Mood
  mood    = ctx.bit!(:mood)    #                                        Mood 
  #then lets you write:
  puts message.from
  puts message.body
  puts mood.mood
  ctx 
end

My preference now goes for the Bits method. Hence, ctx.with will also generate and cache a Bits object. The reasons why I keep both APIs are (a) backward compatibility (b) forces implementers of XEPs to write the methods for Context::Bits in clean modules. In the future, we might implement ctx.with with Ruby refinements.

Sending stanzas

It is good to receive stanza and interpret them, but sometimes you also want to send data. EM::XMPP for now builds stanzas with Nokogiri::XML::Builder in the form with an explicit block argument. Then you send raw_strings with Connection#send_raw or pre-built stanzas with Connection#send_stanza. Note that if you send malformed XML, your server will disconnect you. Hence, take care when writing XML without and XML builder.

Contexts for message/iq/presence provide a "reply" method that will pre-fill some fields for you. Otherwise, you can use

data = message_stanza('to' => 'someone@somehost') do |xml| 
         xml.body('hello world')
       end
send_stanza data

to send a stanza to someone. Note that since EM:Xmpp sets jabber:client as default namespace of the XML stream, you must not set the XML namespace for body/iq/presence and all the things that sit in jabber:client namespace. For other XEPs, do not forget to set your namespaces.

The XML::Builder uses method_missing and hence this building scheme may be slow if you need a large throughput of outgoing stanzas.

Sometimes, you expect an answer when sending a stanza. For example, an IQ result will come back with the same "id" attribute than the IQ query triggering the result. For this specific use case, send_stanza can take a callback as block parameter. The syntax becomes:

one_time_handler = send_stanza data do |response_ctx|
...
end

Using this syntax will install a one-time handler in the connection handler. Currently, there is no timeout on this timer. Therfore, you should get the value of the one-time handler and you should remove it yourself if the handler never matches any stanza fires.

See the ./samples directory for basic examples.

Features

Entities

XMPP defines entities as something with a JID and with which you can interact with. In EM::Xmpp, each "from" or "to" field encapsulates the JID into an entity object. This lets you write something such as:

on_presence do |ctx|
  pre = ctx.bit!(:presence)
  entity = pre.from #here is your entity object
  if pre.subscription_request?
     send_stanza pre.reply('type' => 'subscribed')
     #here are the nice helper methods
     entity.subscribe                       
     entity.say "hello my new friend"
     entity.add_to_roster
  end
  ctx
end

Stateful Conversations

XMPP is inherently asynchronous. Hence, handling stateful actions (for example, some XEPs have long request/response flow charts) can become tricky. Fortunately, EM::Xmpp proposes an abstraction called Conversation to manage. Under the hood, a Conversation is not much more than a Fiber plus some wiring. So far, EM::Xmpp does not route stanza to the conversations automagically. You must do this by hand.

For short-lived conversations, when you know that an entity should answer to your stanza with a reply stanza (and with same "id" attribute), use the block argument of send_stanza.

Roster management

This library provides helpers to add/remove entities from your roster as well as helpers to get the roster as a list of contacts.

Muc

Good support to join/leave/invite/kick/ban/voice/unvoice/chat with people in MUC rooms.

PubSub

Partial support. You can subscribe/unsubscribe/publish/receive items, configure subscription or node parameters. The missing part is the on accepting PubSub subscriptions.

File Transfer

There is enough to support for IBB file transfers.

Missing

  • anonymous login
  • login as XMPP component
  • obnoxious SASL schemes such as X-GOOGLE-TOKEN (should patch ruby-sasl gem)

FAQ

Ask your questions via GitHub "issues".

Contributing

  1. Fork it
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Added some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create new Pull Request
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