rabbitmq-queue-stream

rabbitmq-queue-stream

Tests

$ make test

Usage

$ npm i rabbitmq-queue-stream

var RabbitMQStream = require("rabbitmq-queue-stream");
var stream         = require("stream");

var options = {
  connection: {
    url: "amqp://user:[e-mail]"
  },
  queue: {
    name: "myQueue",
    subscribe: {
      /* Any option accepted by https://github.com/postwait/node-amqp#queuesubscribeoptions-listener */
    },
    connection: {
      /* Any option accepted by https://github.com/postwait/node-amqp#connectionqueuename-options-opencallback */
    }
  }
};

/*
 * Initialize two consumer channels to our queue.
*/
RabbitMQStream.init(2, options, function(err, streamifiedQueues) {
  if(err) {
    return console.error(err);
  }

  /*
   * Each consumer channel comes with a .source and .sink property.
   * 
   * .source is a Readable stream that gives us a stream of objects
   * from the specified queue
   *
   * Every job written to .sink is deleted from the queue. Only object
   * originating from .source should be written to .sink
   *
  */

  streamifiedQueues.channels.forEach(function(channel) {

    var myProcessingStream = new stream.Transform({objectMode: true});
    myProcessingStream._transform(function(obj, enc, next) {
      /*
      * Messages received from the source will have their data namespaced
      * in the `obj.payload` property. `payload` will contain a parsed 
      * JSON object if clients specified contentType: application/json
      * when enqueuing the message. Messages enqueued with contentType:
      * application/json but are malformed will be automatically rejected.
      * Add a listener to event `parseError`, which will be emitted by
      * channel.source, to handle errors yourself.
      */

      this.push(obj);
      /*
       * Messages are successfully acked and removed from the queue by default.
       * RabbitMQStream provides methods to requeue and delete messages too.
       *
       * Requeue:
       *     this.push(RabbitMQStream.RequeueMessage(obj));
       *
       * Reject:
       *     this.push(RabbitMQStream.RejectMessage(obj));
      */
      next();
    });

    channel.source
      .pipe(myProcessingStream)
      .pipe(channel.sink);
  });

  /* example graceful shutdown routine */
  var gracefulShutdown = function() {
    //stop fetching messages
    streamifiedQueues.unsubscribeConsumers(function(err) {
      if(err) {
        //handle error
      }
      //Wait some time for queues to flush out before closing consumers.
      streamifiedQueues.closeConsumers(function(err) {
        if(err) {
          //handle error
        }
        streamifiedQueues.disconnect(function(err) {
          if(err) {
            //handle error
          }
          process.exit(0);
        });
      });
    });
  };
});

Emitted Events

.source

• parseError - Emitted when a message specifies contentType: application/json but is malformed JSON.

myQueueStream.source.on("parseError", function(err, message) {
  console.error("Problem JSON parsing message", message);
});

.sink

• acknowledged - Emitted everytime a message is acknowledged
• rejected - Emitted when a message is rejected
• requeued - Emitted when a message is requeued

var totalAcked = 0;
myQueueStream.source.on("acknowledged", function(message) {
  console.log("Acknowledged:", message);
  totalAcked++;
});

• formatError - Sink received a job that does not have the necessary information to be deleted from the queue. Most likely emitted when objects not originating from .source are written to sink.

myQueueStream.sink.on("formatError", function(err, message) {
  console.error("Malformatted message written to .sink. Please check your pipeline configuration", message);
});

TODO

• Add a jsonMode to make automatic parsing of source data optional