NAME

Catalyst::Engine::Stomp - write message handling apps with Catalyst.

SYNOPSIS

  # In a server script:

  BEGIN {
    $ENV{CATALYST_ENGINE} = 'Stomp';
    require Catalyst::Engine::Stomp;
  }

  MyApp->config(
    Engine::Stomp' = {
       tries_per_server => 3,
      'servers' => [
       {
         'hostname' => 'localhost',
         'port' => '61613'
         connect_headers => {
           login => 'myuser',
           passcode => 'mypassword',
         },
       },
       {
         'hostname' => 'stomp.yourmachine.com',
         'port' => '61613'
       },
       ],
       utf8             => 1,
       subscribe_headers => {
         transformation       => 'jms-to-json',
       }
    },
  );
  MyApp->run();

  # In a controller, or controller base class:
  use base qw/ Catalyst::Controller::MessageDriven /;

  # then create actions, which map as message types
  sub testaction : Local {
      my ($self, $c) = @_;

      # Reply with a minimal response message
      my $response = { type => 'testaction_response' };
      $c->stash->{response} = $response;
  }

DESCRIPTION

Write a Catalyst app connected to a Stomp messagebroker, not HTTP. You need a controller that understands messaging, as well as this engine.

This is single-threaded and single process - you need to run multiple instances of this engine to get concurrency, and configure your broker to load-balance across multiple consumers of the same queue.

Controllers are mapped to Stomp queues or topics, and a controller base class is provided, Catalyst::Controller::MessageDriven, which implements YAML-serialized messages, mapping a top-level YAML "type" key to the action.

QUEUES and TOPICS

The controller namespace (either derived from its name, or defined by its action_namespace attribute) defines what the controller is subscribed to:

queue/foo

subscribes to the queue called foo

topic/foo

subscribes to the topic called foo

foo

subscribes to the queue called foo (for simplicity and backward compatibility)

Connction and Subscription Headers

You can specify custom headers to send with the CONNECT and SUBSCRIBE STOMP messages. You can specify them globally:

  MyApp->config(
    Engine::Stomp' = {
      'servers' => [
       {
         'hostname' => 'localhost',
         'port' => '61613'
       },
       ],
       subscribe_headers => {
         transformation       => 'jms-to-json',
       },
       connect_headers => {
         login => 'myuser',
         passcode => 'mypassword',
       },
    },
  );

per server:

  MyApp->config(
    Engine::Stomp' = {
      'servers' => [
       {
         'hostname' => 'localhost',
         'port' => '61613'
         subscribe_headers => {
           strange_stuff => 'something',
         },
         connect_headers => {
           login => 'myuser',
           passcode => 'mypassword',
         },
       },
       ],
    },
  );

or per-controller (subscribe headers only):

  package MyApp::Controller::Special;
  use Moose;
  BEGIN { extends 'Catalyst::Controller::MessageDriven' };

  has stomp_destination => (
    is => 'ro',
    isa => 'Str',
    default => '/topic/crowded',
  );

  has stomp_subscribe_headers => (
    is => 'ro',
    isa => 'HashRef',
    default => sub { +{
        selector => q{custom_header = '1' or JMSType = 'test_foo'},
    } },
  );

This is very useful to set filters / selectors on the subscription.

There are a few caveats, mostly summarized by "if you do confusing things, the program may not work".

  • you can have the stomp_destination and the action_namespace different in a single controller, but this may become confusing if you have more than one controller subscribed to the same destination; you can remove some of the confusion by restricting the kind of messages that each subscription receives

  • if you filter out some messages, don't be surprised if they are never received by your application

  • you can set persistent topic subscriptions, to prevent message loss during reconnects (the broker will remember your subscription and keep the messages while you are not connected):

      MyApp->config(
        Engine::Stomp' = {
          'servers' => [
           {
             'hostname' => 'localhost',
             'port' => '61613'
           },
           ],
           connect_headers => {
             'client-id' => 'myapp',
           },
        },
      );
    
      package MyApp::Controller::Persistent;
      use Moose;
      BEGIN { extends 'Catalyst::Controller::MessageDriven' };
    
      has stomp_destination => (
        is => 'ro',
        isa => 'Str',
        default => '/topic/important',
      );
    
      has stomp_subscribe_headers => (
        is => 'ro',
        isa => 'HashRef',
        default => sub { +{
          'activemq.subscriptionName' => 'important-subscription',
        } },
      );

    According to the ActiveMQ docs, the client-id must be globally unique, and activemq.subscriptionName must be unique within the client. Non-ActiveMQ brokers may use different headers to specify the subscription name.

FAILOVER

You can specify one or more servers in a list for the apps config. This enables fail over if an error occurs, like the broker or network connection disappears.

It will try to use a server a set number of times, as determined by tries_per_server in the config before failing on to the next server in the list. It cycle through each server in turn, going back to the start of the list if need be.

UTF-8

By default STOMP messages are assumed to be in UTF-8. This module can automatically convert a Perl string into a UTF-8 set of octets to be sent over the wire instead. This is a Good Thing, especially if you use the function Load() from the package YAML::XS to un-serialize it in your client - it assumes it is in UTF-8.

If you do want this behaviour, set 'utf8' to '1' in your config.

Simplified configuration

Instead of using the complete config layout as shown in the synopsis, you can

  • not specify a tries_per_server (defaults to 1)

  • specify a single server:

      server => { hostname => $host, port => $port }
  • use the old-style (pre 0.14) config having hostname and port directly in the Engine::Stomp block, without a server key in between.

METHODS

_see_ya

Set to run when signal USR1 is received. Simply sets the stop flag.

run

App entry point. Starts a loop listening for messages.

If the stop flag is set (see _see_ya above) then no more requests are processed. Keep in mind this is a blocking server and it will wait for a STOMP message forever. Only after handling a request does it check the flag.

prepare_request

Overridden to add the source broker to the request, in place of the client IP address.

finalize_headers

Overridden to dump out any errors encountered, since you won't get a #' "debugging" message as for HTTP.

handle_stomp_frame

Dispatch according to Stomp frame type.

handle_stomp_message

Dispatch a Stomp message into the Catalyst app.

handle_stomp_error

Log any Stomp error frames we receive.

CONFIGURATION

subscribe_header

Add additional header key/value pairs to the subscribe message sent to the message broker.

DEVELOPMENT

The source to Catalyst::Engine::Stomp is in github:

  http://github.com/pmooney/catalyst-engine-stomp

AUTHOR

Chris Andrews <chris@nodnol.org>

CONTRIBUTORS

Tomas Doran (t0m) <bobtfish@bobtfish.net>

Jason Tang

Paul Mooney

LICENCE AND COPYRIGHT

Copyright (C) 2009 Venda Ltd

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.8.8 or, at your option, any later version of Perl 5 you may have available.