Official Seneca AMQP transport plugin

seneca-amqp-transport

This plugin allows seneca listeners and clients to communicate over AMQP.

Important notice: If you are upgrading to 2.1.0 from an older version, please read and follow instructions on this wiki guide to avoid some potential issues.

Install

npm install --save seneca-amqp-transport

This transport supports AMQP 0-9-1, which is what amqplib currently supports. For an AMQP 1.0 compliant transport, take a look at seneca-servicebus-transport

Usage

The following snippets showcase the most basic usage examples.

Listener

require('seneca')()
  .use('seneca-amqp-transport')
  .add('cmd:log,level:*', function(req, done) {
    console[req.level](req.message);
    return done(null, { ok: true, when: Date.now() });
  })
  .listen({
    type: 'amqp',
    pin: 'cmd:log,level:*',
    url: process.env.AMQP_URL
  });

How it works

A listener always creates one and only one queue. The queue name can be provided via the name parameter, but it will be auto-generated from the pin (or pins) if not.

Be careful with name clashing when specifying a name for a listener. Having more than one queue with the same name declared on the AMQP broker will probably behave unexpectedly. It is recommended that you leave the name generation to the plugin in order to avoid problems, unless you know what you are doing.

In the example above, the following things are declared:

• A topic exchange named seneca.topic.
• A queue named seneca.cmd:log.level:any.
• A binding between the queue and the exchange using the routing key cmd.log.level.* (named after the pin).

Queue names are prefixed with a configurable word (seneca., by default). It can be disabled or modified during plugin declaration (read below).

If your intention is to create multiple queues, just declare multiple listeners. Each queue will be bound to an exchange (seneca.topic, by default) using routing keys derived from the pin (or pins).

If your intention is to declare multiple consumers on a single queue, run multiple listeners with the same set of pins. Or just spawn many instances of a single microservice.

Client

var client = require('seneca')()
  .use('seneca-amqp-transport')
  .client({
    type: 'amqp',
    pin: 'cmd:log,level:log',
    url: process.env.AMQP_URL
  });

setInterval(function() {
  client.act('cmd:log,level:log', {
    message: 'Hello World'
  }, (err, res) => {
    if (err) {
      // Handle error in some way
      throw err;
    }
    // Print out the response
    console.log(res);
  });
}, 2000);

How it works

A client creates an exclusive, randomly named response queue (something similar to seneca.act.x42jK0l) and starts consuming from it - much like a listener would do. On every act, the client publishes the message to the seneca.topic exchange using a routing key built from the pin that matches the act pattern. In the simple example above, the pattern is cmd:log,level:log which equals the only declared pin. With that, the routing key cmd.log.level.log is inferred. An AMQP replyTo header is set to the name of the random queue, in an RPC-schema fashion.

Manual queue naming on a client (using the name parameter as seen in the listener configuration) is not supported. Client queues are deleted once the client disconnect and re-created each time.

As you can see, pins play an important role on routing messages on the broker, so in order for a listener to receive messages from a client, their pins must match.

In the example, the following things are declared:

• A topic exchange named seneca.topic.
• An exclusive queue with a random alphanumeric name (like seneca.act.x42jK0l).

Clients do not declare the queue of their listener counterpart. So, if the message does not reach its destination or is discarded by the broker, the seneca instance will fail with a TIMEOUT error on the client side.

Options

The JSON object in defaults.json describes the available options for this transport. These are applicable to both clients and listeners.

To override this settings, pass them to the plugin's .use declaration:

require('seneca')()
  .use('seneca-amqp-transport', {
    amqp: {
      client: {
        queues: {
          options: {
            durable: false
          }
        }
      }
    }
  });

Transport options

AMQP related options may be indicated either by the connection URI or by passing additional parameters to the seneca#client() or seneca#listen() functions.

This,

require('seneca')()
  .use('seneca-amqp-transport')
  .client({
    type: 'amqp',
    url: 'amqp://guest:[email protected]:5672/seneca?locale=es_AR'
  });

will result in the same connection URI as:

require('seneca')()
  .use('seneca-amqp-transport')
  .client({
    type: 'amqp',
    hostname: 'rabbitmq.host',
    port: 5672,
    vhost: 'seneca',
    locale: 'es_AR',
    username: 'guest',
    password: 'guest'
  });

Socket options

Additionally, you may pass in options to the amqp.connect method of amqplib as documented in its API reference, using the socketOptions parameter.

// Example of using a TLS/SSL connection. Note that the server must be
// configured to accept SSL connections; see http://www.rabbitmq.com/ssl.html.

var fs = require('fs');

var opts = {
  cert: fs.readFileSync('../etc/client/cert.pem'),
  key: fs.readFileSync('../etc/client/key.pem'),
  // cert and key or
  // pfx: fs.readFileSync('../etc/client/keycert.p12'),
  passphrase: 'MySecretPassword',
  ca: [fs.readFileSync('../etc/testca/cacert.pem')]
};

require('seneca')()
  .use('seneca-amqp-transport')
  .client({
    type: 'amqp',
    url: 'amqp://guest:[email protected]:5672/seneca?locale=es_AR',
    socketOptions: opts
  });

Snippet above is based on amqplib/examples/ssl.js

Run the examples

There are simple examples under the /examples directory. To run them, just install latest seneca (if you didn't install devDependencies) and execute:

#Install seneca
npm i seneca

# Start listener.js
cd examples
AMQP_URL='amqp://guest:[email protected]:5672' node listener.js
{"kind":"notice","notice":"seneca started","level":"info","when":1476216405556}

# Start client.js
cd examples
AMQP_URL='amqp://guest:[email protected]:5672' node client.js
{"kind":"notice","notice":"seneca started","level":"info","when":1476216473818}
{ id: 93,
  message: 'Hello World!',
  from: { pid: 4150, file: 'examples/listener.js' },
  now: 1476306009801 }
# ...

If you don't export the env variable AMQP_URL the default value of amqp://localhost will be used.

Contributors

• George Haidar ([email protected]) (author of the original version).
• Chris Spiliotopoulos ([email protected])

Roadmap

• [x] :muscle: ~~Mocha unit tests.~~
• [ ] Functional tests.
• [x] :muscle: ~~Setup Travis CI.~~
• [x] :muscle: ~~Support for message TTL and dead-lettering~~ (#59).
• [ ] Better support for work queues.
• [ ] Better support for fanout exchanges.
• [ ] Don't depend on pins for routing (#58).

Contributing

This module follows the general Senecajs.org contribution guidelines and encourages open participation. If you feel you can help in any way, or discover any issues, feel free to create an Issue or a Pull Request. For more information on contribution please see our Contributing guidelines.

License

Licensed under the MIT license.