node-amqp

IMPORTANT: This module only works with node v0.4.0 and later.

This is a client for RabbitMQ (and maybe other servers?). It partially implements the 0.9.1 version of the AMQP protocol.

Installation

npm install amqp

Synopsis

An example of connecting to a server and listening on a queue.

var amqp = require('amqp');

var connection = amqp.createConnection({ host: 'dev.rabbitmq.com' });

// Wait for connection to become established.
connection.on('ready', function () {
  // Use the default 'amq.topic' exchange
  connection.queue('my-queue', function(q){
      // Catch all messages
      q.bind('#');
    
      // Receive messages
      q.subscribe(function (message) {
        // Print messages to stdout
        console.log(message);
      });
  });
});

Connection

new amqp.Connection() Instantiates a new connection. Use connection.connect() to connect to a server.

amqp.createConnection() returns an instance of amqp.Connection, which is a subclass of net.Stream. All the event and methods which work on net.Stream can also be used on an amqp.Connection instance. (e.g., the events 'connected' and 'closed'.)

Connection options and URL

amqp.createConnection([options, [implOptions]]) takes two options objects as parameters. The first options object has these defaults:

{ host: 'localhost'
, port: 5672
, login: 'guest'
, password: 'guest'
, vhost: '/'
}

All of these can be passed in a single URL of the form

amqp[s]://[user:password@]hostname[:port][/vhost]

Note that the vhost must be URL-encoded and appear as the only segment of the path, i.e., the only unencoded slash is that leading; leaving the path entirely empty indicates that the vhost /, as above, should be used (it could also be supplied as the path /%2f).

This URL is supplied as the field url in the options; for example

var conn =
  amqp.createConnection({url: "amqp://guest:guest@localhost:5672"});

Options provided as individual fields will override values given in the URL.

The second options are specific to the node AMQP implementation. It has the default values:

{ defaultExchangeName: ''
, reconnect: true
, reconnectBackoffStrategy: 'linear'
, reconnectExponentialLimit: 120000
, reconnectBackoffTime: 1000
}

The defaultExchangeName is the default exchange to which connection.publish will publish. In the past, the default exchange was amq.topic, which is not ideal. To emulate this behaviour, one can create a connection like:

var conn =
  amqp.createConnection({url: "amqp://guest:guest@localhost:5672"},
                        {defaultExchangeName: "amq.topic"});

If the "reconnect" option is true, then the driver will attempt to reconnect using the configured strategy any time the connection becomes unavailable. If this is not appropriate for your application, set this option to false.

If you would like this option, you can set parameters controlling how aggressively the reconnections will be attempted. Valid strategies are "linear" and "exponential".

Backoff times are in milliseconds. Under the "linear" strategy, the driver will pause 'reconnectBackoffTime' ms before the first attempt, and between each subsequent attempt. Under the "exponential" strategy, the driver will pause 'reconnectBackoffTime' ms before the first attempt, and will double the previous pause between each subsequent attempt until a connection is reestablished.

After a connection is established the 'connect' event is fired as it is with any net.Connection instance. AMQP requires a 7-way handshake which must be completed before any communication can begin. net.Connection does the handshake automatically and emits the 'ready' event when the handshaking is complete.

For backward compatability, two additional options are available. Older versions of this library placed the routingKey and deliveryTag for incoming messages into the JSON payload received. This module was changed to leave inbound JSON payloads pristine. Some applications may need the old behaviour. If the key 'routingKeyInPayload' is set to true in the connection options, the messages resulting from a subscribe call will include a 'routingKey' key in the JSON payload. If the key 'devliryTagInPayload' is set to true in the connection options, the deliveryTag of the incoming message will be placed in the JSON payload.

connection.publish(queueName, body)

Publishes a message to the default exchange; if the defaultExchange is left as '', this effectively publishes the message to the queue named.

connection.end()

amqp.Connection is derived from net.Stream and has all the same methods. So use connection.end() to terminate a connection gracefully.

Queue

Events: A queue will call the callback given to the connection.queue() method once it is usable. For example:

var q = connection.queue('my-queue', function (queue) {
  console.log('Queue ' + queue.name + ' is open');
});

Declaring a queue with an empty name will make the server generate a random name.

connection.queue(name, options, openCallback)

Returns a reference to a queue. The options are

• passive: boolean, default false. If set, the server will not create the queue. The client can use this to check whether a queue exists without modifying the server state.
• durable: boolean, default false. Durable queues remain active when a server restarts. Non-durable queues (transient queues) are purged if/when a server restarts. Note that durable queues do not necessarily hold persistent messages, although it does not make sense to send persistent messages to a transient queue.
• exclusive: boolean, default false. Exclusive queues may only be consumed from by the current connection. Setting the 'exclusive' flag always implies 'autoDelete'.
• autoDelete: boolean, default true. If set, the queue is deleted when all consumers have finished using it. Last consumer can be cancelled either explicitly or because its channel is closed. If there was no consumer ever on the queue, it won't be deleted.
• noDeclare: boolean, default false. If set, the queue will not be declared, this will allow a queue to be deleted if you dont know its previous options.
• arguments: a map of additional arguments to pass in when creating a queue.
• closeChannelOnUnsubscribe : a boolean when true the channel will close on unsubscrube, default false.

queue.subscribe([options,] listener)

An easy subscription command. It works like this

q.subscribe(function (message, headers, deliveryInfo) {
  console.log('Got a message with routing key ' + deliveryInfo.routingKey);
});
    

It will automatically acknowledge receipt of each message.

There are several options available. Setting the options argument to { ack: true } (which defaults to false) will make it so that the AMQP server only delivers a single message at a time. When you want the next message, call q.shift(). When ack is false then you will receive messages as fast as they come in.

You can also use the prefetchCount option to increase the window of how many messages the server will send you before you need to ack (quality of service). '{ ack: true, prefetchCount: 1 }' is the default and will only send you one message before you ack. Setting prefetchCount to 0 will make that window unlimited.

The 'routingKeyInPayload' and 'deliveryKeyInPayload' options determine if the reception process will inject the routingKey and deliveryKey, respectively, into the JSON payload received. These default to unset thus adopting the parent connection's values (which default to false). Setting these to true provide backward compability for older applications.

The 'exclusive' option will subscribe to the queue in exclusive mode. Only one subscriber is allowed at a time, and subsequent attempts to subscribe to the same queue will result in an exception. This option differes from the exclusive option passed when creating in a queue in that the queue itself is not exclusive, only the consumers. This means that long lived durable queues can be used as exclusive queues.

This method will emit 'basicQosOk' when ready.

queue.subscribeRaw([options,] listener)

Subscribes to a queue. The listener argument should be a function which receives a message. This is a low-level interface - the message that the listener receives will be a stream of binary data. You probably want to use subscribe instead. For now this low-level interface is left undocumented. Look at the source code if you need to do this.

This method will emit 'basicConsumeOk' when ready.

queue.unsubscribe(consumerTag)

Unsubscribe from a queue, given the consumer tag. The consumer tag is supplied to the promise callback of Queue.subscribeRaw or Queue.subscribe:

connection.queue('foo', function(queue) {
  var ctag;
  queue.subscribe(function(msg) {...})
    .addCallback(function(ok) { ctag = ok.consumerTag; });
  // ... and in some other callback
  queue.unsubscribe(ctag);
});

Note that Queue.unsubscribe will not requeue messages that have not been acknowledged. You need to close the queue or connection for that to happen. You may also receive messages after calling unsubscribe; you will not receive messages from the queue after the unsubscribe promise callback has been invoked, however.

queue.shift()

For use with subscribe({ack: true}, fn). Acknowledges the last message.

queue.bind([exchange,] routing)

This method binds a queue to an exchange. Until a queue is bound it will not receive any messages, unless they are sent through the unnamed exchange (see defaultExchangeName above).

If the exchange argument is left out 'amq.topic' will be used.

This method will emit 'queueBindOk' when complete.

queue.unbind([exchange,] routing)

This method unbinds a queue from an exchange.

If the exchange argument is left out 'amq.topic' will be used.

Ths method will emit 'queueUnbindOk' when complete.

queue.bind_headers([exchange,] routing)

This method binds a queue to an exchange. Until a queue is bound it will not receive any messages.

This method is to be used on an "headers"-type exchange. The routing argument must contain the routing keys and the x-match value (all or any).

If the exchange argument is left out 'amq.headers' will be used.

queue.destroy(options)

Delete the queue. Without options, the queue will be deleted even if it has pending messages or attached consumers. If +options.ifUnused+ is true, then the queue will only be deleted if there are no consumers. If +options.ifEmpty+ is true, the queue will only be deleted if it has no messages.

Exchange

Events: An exchange will call the callback given to the connection.exchange() method once it is usable. For example:

var exc = connection.exchange('my-exchange', function (exchange) {
  console.log('Exchange ' + exchange.name + ' is open');
});

exchange.on('open', callback)

The open event is emitted when the exchange is declared and ready to be used. This interface is considered deprecated.

connection.exchange()

connection.exchange(name, options={}, openCallback)

An exchange can be created using connection.exchange(). The method returns an amqp.Exchange object.

Without any arguments, this method returns the default exchange. Otherwise a string, name, is given as the first argument and an options object for the second. The options are

• type: the type of exchange 'direct', 'fanout', or 'topic' (default).
• passive: boolean, default false. If set, the server will not create the exchange. The client can use this to check whether an exchange exists without modifying the server state.
• durable: boolean, default false. If set when creating a new exchange, the exchange will be marked as durable. Durable exchanges remain active when a server restarts. Non-durable exchanges (transient exchanges) are purged if/when a server restarts.
• confirm: boolean, default false. If set when connecting to a exchange the channel will send acks for publishes. Published tasks will emit 'ack' when it is acked.
• autoDelete: boolean, default true. If set, the exchange is deleted when there are no longer queues bound to it.
• noDeclare: boolean, default false. If set, the exchange will not be declared, this will allow the exchange to be deleted if you dont know its previous options.
• confirm: boolean, default false. If set, the exchange will be in confirm mode, and you will get a 'ack'|'error' event emitted on a publish, or the callback on the publish will be called.

An exchange will emit the 'open' event when it is finally declared.

exchange.publish(routingKey, message, options, callback)

Publishes a message to the exchange. The routingKey argument is a string which helps routing in topic and direct exchanges. The message can be either a Buffer or Object. A Buffer is used for sending raw bytes; an Object is converted to JSON.

options is an object with any of the following

• mandatory: boolean, default false. This flag tells the server how to react if the message cannot be routed to a queue. If this flag is set, the server will return an unroutable message with a Return method. If this flag is false, the server silently drops the message.
• immediate: boolean, default false. This flag tells the server how to react if the message cannot be routed to a queue consumer immediately. If this flag is set, the server will return an undeliverable message with a Return method. If this flag is false, the server will queue the message, but with no guarantee that it will ever be consumed.
• contentType: default 'application/octet-stream'
• contentEncoding: default null.
• headers: default {}. Arbitrary application-specific message headers.
• deliveryMode: Non-persistent (1) or persistent (2)
• priority: The message priority, 0 to 9.
• correlationId: default null. Application correlation identifier
• replyTo: Usually used to name a reply queue for a request message.
• expiration: default null. Message expiration specification
• messageId: default null. Application message identifier
• timestamp: default null. Message timestamp
• type: default null. Message type name
• userId: default null. Creating user id
• appId: default null. Creating application id

callback is a function that will get called if the exchange is in confirm mode, the value sent will be true or false, this is the presense of a error so true, means an error occured and false, means the publish was successfull

exchange.destroy(ifUnused = true)

Deletes an exchange. If the optional boolean second argument is set, the server will only delete the exchange if it has no queue bindings. If the exchange has queue bindings the server does not delete it but raises a channel exception instead.

exchange.bind(srcExchange, routingKey [, callback])

Binds the exchange (destination) to the given source exchange (srcExchange). When one exchange is bound to another, the destination (or receiving) exchange will receive all messages published to the source exchange that match the given routingKey.

This method will emit 'exchangeBindOk' when complete.

Please note that Exchange to Exchange Bindings (E2E) are an extension to the AMQP spec introduced by RabbitMQ, and that by using this feature, you will be reliant on RabbitMQ's AMQP implementation. For more information on E2E Bindings with RabbitMQ see:

http://www.rabbitmq.com/e2e.html

exchange.unbind(srcExchange, routingKey [, callback])

Unbinds the exchange (destination) from the given source exchange (srcExchange). This is the reverse of the exchange.bind method above, and will stop messages from srcExchange/routingKey from being sent to the destination exchange.

This method will emit 'exchangeUnbindOk' when complete.