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node-amqb-bus

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Implements a simple bus client to exchange JSON message on queues using AMQP server.

Install

npm install @chauffeur-prive/node-amqp-bus --save

Use

const bus = require('@chauffeur-prive/node-amqp-bus');

Listener API

bus.createListener(url, [options])

Creates a listener, returns a Listener instance. the options parameter can contain a client that is a node-amqp-bus client.

const listener = bus.createListener(url);

or

const client = yield bus.createClient(url);
const listener = yield bus.createListener(url, { client });

Note: in this case, url is ignored in the createListener call.

listener.addHandler(queue, key, handler, options)

Add a new handler to the listener. If you add two handlers with the same queue and key

options will be passed to client.createQueue.

ATTENTION: If your handler is a generator, then you must wrap it. If not, we assume it's either an async function or a function that returns a Promise.

EventEmitter interface

You can use listener as an EventEmitter. It emits the following events =

  • connect() : emitted once, when the first call to listen() is made
  • handle_error(err, { err, queue, message }) : emitted when a message cannot be consumed correctly by the client (not a JSON, handler failed)

Client API

EventEmitter interface

The client is an EventEmitter`. It emits the following events:

  • close_cleanup: emitted once, when handling a close connection event.
    It provides a timeout (defaut = 200ms) before executing a client.close(forceClose = true),
    for the host app to execute any cleanup operations (such as closing a mongodb client).

bus.createClient(url)

Creates a client. Returns a Promise of the client.

const client = yield bus.createClient(url);

client.close(forceClose = false)

Closes the client. Returns a Promise. When passing a truthy forceClose, close() will also exit(1) the current process, so when handling erroneous case that you can't recover from, one should call close(true).

client.close();

client.publish(exchangeName, messageKey, message)

Publishes an event to the bus.

client.publish('your-exchange', 'the-key', message);

The message needs to be in JSON format otherwise an error will be thrown.

client.listen(exchangeName, queueName, messageKey, handler, options)

DANGER: READ THE CODE TO UNDERSTAND HOW LISTEN WORKS:

messageKey SHOULD ONLY BE USED TO DO AMQP ROUTING, NOT APPLICATION ROUTING.

IF YOU WANT APPLICATION ROUTING, DO IT YOURSELF.

Listens on the bus, on the exchange / queue and to the key specified.

The handler parameter must be a yieldable, called with the following arguments:

  • message: the message received
  • fields: information about the message (primarily used by the amqplib library)

If you use a generator just throw an error to nack the message. Be careful, a throw nack the message. Thus the message is re-inserted in the queue. You need to handle the number of times a message can be queued before being dismissed. For example, a message with a bas format will always throw. So there is a risk to be in a infinite loop.

yield client.listen('your-exchange', 'the-queue', 'the-key', function* (message, fields) {
  yield ...
});

client.connection

Raw connection object.

client.channel

Raw channel object.

Developement system dependencies

To run the tests, you need a local RabbitMQ responding on 'amqp://guest:guest@localhost:5672'.