/ 
Catalyst-Engine-XMPP2-0.4
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/ Catalyst::Engine::XMPP2

NAME

Catalyst::Engine::XMPP2 - AnyEvent::XMPP::Connection Catalyst Engine

SYNOPSIS

MyApp->config->{Engine::XMPP2} =
 {
  username => "abc",
  domain => "jabber.org",
  password => "foo",
  override_host => "myserver",
  override_port => 5722
 };
MyApp->run();

DESCRIPTION

This engine enables you to deploy a Catalyst application that can be accessed using the XMPP protocol. This is done by a mapping of each XMPP stanza to a HTTP Request, using the Catalyst::Engine::Embeddable as a base.

Semantics mapping

One important thing to realise is that the XMPP semantics are considerably different than the HTTP semantics, that way, a set of mappings must be done.

Request-Response

Usually, an HTTP application implements only Request-Response semantics for every action. That is not always true for the XMPP protocol. In fact, the only stanza that implements this semantics is the <iq/> stanza.

That way, when receiving <message/> or <presence/> stanzas, the response will be ignored on success. If the response is a failure (400 or 500), an error response will be sent. If wanting to send an explicit message, that should be done explicitly.

When receiving <iq/> stanzas, the response will be sent back as the action processing returns, independent of the response status.

In any way, the attributes of the stanza root element will be translated as HTTP Headers with the "XMPP_Stanza_" prefix.

SCRIPT_NAME

This is the most relevant aspect of this mapping. As XMPP doesn't have a URI definition for each stanza, that means that there's no proper way of dispatching a message to a given controller action in Catalyst.

What this mapping does is, at the beggining, creating several connections to the server, providing different resource identifiers based on the Path actions registered in the application.

This have two important side-effects to realize:

A Catalyst XMPP application can only use 'Path' actions, because that is the only DispatchType that have a static mapping of the available actions. Other DispatchTypes, like Chained or Index, depends on the current request to find out which action to dispatch. This doesn't forbid the use of the other DispatchTypes for internal forward and dispatch, but the only really public actions will be the ones seen by the 'Path' DispatchType.

You have to keep in mind that the resources will be pre-advertised, and that for each public path action, you will have a public jabber id, and, at least by now, a separated connection to the server, so it's probably a good idea to do a carefull planning of which actions to make public.

Content-Type

XMPP has no support for MIME types. Every message is, by definition, a XML document. So every request will have the "application/xml" MIME type. If the response content-type is also "application/xml", it will be written as raw into the XMPP stream. This will allow SOAP responses, for instance, to be sent as in XEP-0072.

On the other hand, if the content type is of some other type, it will be sent as literal string inside a <body> tag, as described by XMPP RFC3921, this way, interaction with regular IM clients should be natural.

Scalability

At this point, this engine is single-threaded, which means that it will block in each operation, and, therefore it cannot handle more than one request at a time. At the time of this writing, two options are available to solve this problem:

The first would be to turn this engine into a pre-fork server that would keep pipes to every child and dispatch the requests to them, while keeping a single control thread for the XMPP connections.

The other option would be to implement a balancer server that would accept several connections for the same JID and connect only once for each JID, dispatching a message sent to some JID among each of the candidate connections. DJabberd::Plugin::Balancer implements that for the DJabberd server.

Error handling

Error handling in XMPP is also different than from HTTP. While HTTP defines numeric error codes, XMPP defines a set of named conditions. But both provide a way to return a custom text to the requestor. This way, the HTTP error codes will be mapped to the XMPP error conditions, and the content of the response will be set as the error text. The XMPP spec also define the "error-type" concept which indicates what the requestor can do about, and the recommended error-type for each of the known conditions. The user can override this default by sending the XMPP_error-type header in the failure case.

The HTTP-XMPP error code mapping will happen as described in the following table.

bad-request                          400
conflict                             409
feature-not-implemented              501
forbidden                            403
gone                                 410
internal-server-error                500
item-not-found                       404
jid-malformed                        520*
not-acceptable                       406
not-allowed                          420*
not-authorized                       401
payment-required                     402
recipient-unavailable                521*
redirect                             302
registration-required                421*
remote-server-not-found              502
remote-server-timeout                504
resource-constraint                  412
service-unavailable                  503
subscription-required                422*
undefined-condition                  423*
unexpected-request                   424*

The items marked with an * are of codes that are not standard HTTP error codes. Most error codes in this list could be mapped literally.

USAGE

The 'Engine::XMPP2' configuration key expects a hashref that will be sent to AnyEvent::XMPP::Connection->new dereferenced. It's important to notice, however, that setting "jid" or "resource" in this hash has no effect as this values will be set according to the Action-Resource mapping.

SENDING MESSAGES

One of the greater benefits of the XMPP protocol is the hability to chain operations in a more complex choreography. In order to do that, you just need to send new messages while processing other messages, in order to do that, you can access the engine object by using $c->engine and use one of the following methods

$c->engine->send_message($c, $to, $type, $create_cb, %attrs)

This will call send_message on the connection that generated the current request with the parameters as described in AnyEvent::XMPP::Connection.

One important hint: if $create_db is a CODE ref, it will be executed with a XML::Writer object in UNSAFE mode as its first argument, which means you can call "raw" on it to send unencoded data.

As you'll be sending the message with the connection that generated this request, it will have the complete JID, with the resource, as the "from".

$c->engine->send_presence($c, $type, $create_cb, %attrs)

Same as above.

$c->engine->send_iq($c, $type, $create_cb, $result_cb, %attrs)

Same as above.

Hint: $result_cb is a coderef that will be executed once the response for this iq arrives. This method won't block, so you might have to implement a semaphore if the reply for this iq is relevant to the rest of this request.

DIRECT CONNECTION MANIPULATION

This is strongly discouraged, but it might be life-saving for some corner cases.

$c->engine->connection($c)

Access the connection object that generated the current request.

$c->engine->connections()

This returns a hashref identifying all the connections by the resource name.

INTERNAL METHODS

$engine->handle_xmpp_node($app, $resource, $node)

This method is called by the stanza callbacks in the connections.

SEE ALSO

Catalyst::Engine, Catalyst::Engine::CGI, HTTP::Request, HTTP::Reponse, Catalyst, AnyEvent::XMPP::Connection, Catalyst::Engine::Embeddable

AUTHORS

Daniel Ruoso daniel@ruoso.com

BUG REPORTS

Please submit all bugs regarding Catalyst::Engine::XMPP2 to bug-catalyst-engine-xmpp2@rt.cpan.org

LICENSE

This library is free software, you can redistribute it and/or modify it under the same terms as Perl itself.