amqp-rpc

different RPC-like tools over RabbitMQ for Node.js Provides

• Simple rpc: AMQPRPCClient and AMQPRPCServer
• Remote EventEmitter: AMQPEventsSender AMQPEventsReceiver

Getting Started

RPC

There are two ways to run AMQPRPCServer/Client:

Temporary queue

1. The server starts without any predefined queueName, asserts temporary queue.
2. Generated queueName retrieved from the server instance and passed somehow to the client (one or many). It's supposed, that this transfer isn't covered by amqp-rpc lib and it should be implemented somehow by the developer of code, which uses amqp-rpc.
3. Each client gets this queueName and uses it before initialization.

Permanent queue

1. A queue is created somehow by an external service.
2. server gets the name of the queue before initialization and starts listening.
3. client gets the same name before initialization and uses it for sending requests.

Example with temporary queue:

const amqplib = require('amqplib');
const {AMQPRPCServer, AMQPRPCClient} = require('@elastic.io/amqp-rpc');


async function init() {
  const connection = await amqplib.connect('amqp://localhost');
  
  // server start
  const server = new AMQPRPCServer(connection);
  server.addCommand('hello', (name) => ({message: `Hello, ${name}!`}));  
  await server.start();
  
  // name of temporary queue, has to be passed somehow to client by external service
  const requestsQueue = server.requestsQueue;
  
  // client start
  const client = new AMQPRPCClient(connection, {requestsQueue});
  await client.start();
  const response = await client.sendCommand('hello', ['Alisa']);
  console.log('Alisa got response:', response);
  
  return {server, client};
}

Full working example you could find here.

Example with permanent queue:

const amqplib = require('amqplib');
const {AMQPRPCServer, AMQPRPCClient} = require('@elastic.io/amqp-rpc');


async function init() {
  
  const connection = await amqplib.connect('amqp://localhost');
  
  // initial setup (e.g. should be provided on first launch)
  const requestsQueue = 'predefined-queue-name';
  const channel = await connection.createChannel();
  await channel.assertQueue(requestsQueue);
  
  // server start
  const server = new AMQPRPCServer(connection, { requestsQueue });
  server.addCommand('hello', (name) => ({message: `Hello, ${name}!`}));
  await server.start();
  
  // client start
  const client = new AMQPRPCClient(connection, { requestsQueue });
  await client.start();
  const response = await client.sendCommand('hello', ['Alisa']);
  console.log('Alisa got response:', response);
  
  return {server, client};
}

Full working example you could find here.

Server handlers

To register a new RPC command in the server, use addCommand() method:

server.addCommand('hello', (name) => ({message: `Hello, ${name}!`}));

Handler could also return a promise or async function, e.g.:

server.addCommand('print-hello-world', (name) => Promise.resolve({ message: 'ok' });

To call an RPC command from the client, use sendCommand() method:

const result = await client.sendCommand('print-hello-world', [
  'World'
]);

Event Emitter

Events receiver side code

  const { AMQPEventsReceiver } = require('@elastic.io/amqp-rpc');
  const amqp = require('amqplib')

  .......
  const amqpConnection = await amqp.connect('amqp://localhost');
   
  const receiver = new AMQPEventsReceiver(amqpConnection);
  
  receiver
    .on('end', () => {
      console.log('Sender stops to send events, so nothing to do more, disconnecting'); 
    })
    .on('close', () => {
      console.log('Disconnected'); 
    })
    .on('error', (e) => {
      console.log('Error happens', e);
    })
    .on('data', (msg) => {
      console.log('We\'ve got a message', msg); 
    });

  await receiver.start();
  const queueName = receiver.queueName; 
  
  console.log(`Use ${queueName} as QUEUE_TO_SEND_EVENTS in sender part of code`); 
  ........
  await receiver.disconnect();
  await amqpConnection.close();

Events source side code

  const { AMQPEventsSender } = require('@elastic.io/amqp-rpc');
  const amqp = require('amqplib')

  .......
  const amqpConnection = await amqp.connect('amqp://localhost');
   
  const sender = new AMQPEventsSender(amqpConnection, 'QUEUE_TO_SEND_EVENTS');
  sender
    .on('close', () => {
      console.log('Receiver endpoint has been removed, so sender stop to work'); 
    })
    .on('error', (e) => {
      console.log('Error happens', e);
    });

  const data = {
    key: 'value'
  };

  await sender.start();
  await sender.send(data);
  
  ........
  await sender.disconnect();
  await amqpConnection.close();