Package Overview

This package provides the capability to send and receive messages by connecting to the RabbitMQ server.

RabbitMQ gives your applications a common platform to send and receive messages and a safe place for your messages to live until received. RabbitMQ is one of the most popular open-source message brokers. It is lightweight and easy to deploy on-premise and in the cloud.

Basic usage

Set up the connection

First, you need to set up the connection with the RabbitMQ server. The following ways can be used to connect to a RabbitMQ server.

1. Connect to a RabbitMQ node with the default host and port:

1    rabbitmq:Client rabbitmqClient = check new(rabbitmq:DEFAULT_HOST, rabbitmq:DEFAULT_PORT);

2. Connect to a RabbitMQ node with a custom host and port:

1    rabbitmq:Client rabbitmqClient = check new("localhost", 5672);

3. Connect to a RabbitMQ node with host, port, and additional configurations:

1    rabbitmq:ConnectionConfiguration config = {
2        username: "ballerina",
3        password: "password"
4    };
5    rabbitmq:Client rabbitmqClient = check new("localhost", 5672, configs);

The rabbitmq:Client can now be used to send and receive messages as described in the subsequent sections.

Exchanges and queues

Client applications work with exchanges and queues, which are the high-level building blocks of the AMQP protocol. These must be declared before they can be used. The following code declares an exchange and a server-named queue and then binds them together.

1    check rabbitmqClient->exchangeDeclare("MyExchange", rabbitmq:DIRECT_EXCHANGE);
2    check rabbitmqClient->queueDeclare("MyQueue");
3    check rabbitmqClient->queueBind("MyQueue", "MyExchange", "routing-key");

This sample code will declare,

• a durable auto-delete exchange of the type rabbitmq:DIRECT_EXCHANGE
• a non-durable, exclusive auto-delete queue with an auto-generated name

Next, the queueBind function is called to bind the queue to the exchange with the given routing key.

1    check rabbitmqClient->exchangeDeclare("MyExchange", rabbitmq:DIRECT_EXCHANGE);
2    check rabbitmqClient->queueDeclare("MyQueue", { durable: true,
3                                                   exclusive: false,
4                                                   autoDelete: false });
5    check rabbitmqClient->queueBind("MyQueue", "MyExchange", "routing-key");

This sample code will declare,

• a durable auto-delete exchange of the type rabbitmq:DIRECT_EXCHANGE
• a durable, non-exclusive, non-auto-delete queue with a well-known name

Delete entities and purge queues

• Delete a queue:

1    check rabbitmqClient->queueDelete("MyQueue");

• Delete a queue only if it is empty:

1    check rabbitmqClient->queueDelete("MyQueue", false, true);

• Delete a queue only if it is unused (does not have any consumers):

1    check rabbitmqClient->queueDelete("MyQueue", true, false);

• Delete an exchange:

1    check rabbitmqClient->exchangeDelete("MyExchange");

• Purge a queue (delete all of its messages):

1    check rabbitmqClient->queuePurge("MyQueue");

Publish messages

To publish a message to an exchange, use the publishMessage() function as follows:

1    string message = "Hello from Ballerina";
2    check rabbitmqClient->publishMessage({ content: message.toBytes(), routingKey: queueName });

Setting other properties of the message such as routing headers can be done by using the BasicProperties record with the appropriate values.

1    rabbitmq:BasicProperties props = {
2       replyTo: "reply-queue"  
3    };
4    string message = "Hello from Ballerina";
5    check rabbitmqClient->publishMessage({ content: message.toBytes(), routingKey: queueName, properties: props });

Consume messages using consumer services

The most efficient way to receive messages is to set up a subscription using a Ballerina RabbitMQ rabbitmq:Listener and any number of consumer services. The messages will then be delivered automatically as they arrive rather than having to be explicitly requested. Multiple consumer services can be bound to one Ballerina RabbitMQ rabbitmq:Listener. The queue to which the service is listening is configured in the rabbitmq:ServiceConfig annotation of the service or else as the name of the service.

1. Listen to incoming messages with the onMessage remote method:

1    listener rabbitmq:Listener channelListener= new(rabbitmq:DEFAULT_HOST, rabbitmq:DEFAULT_PORT);
2    
3    @rabbitmq:ServiceConfig {
4        queueName: "MyQueue"
5    }
6    service rabbitmq:Service on channelListener {
7        remote function onMessage(rabbitmq:Message message) {
8        }
9    }

2. Listen to incoming messages and reply directly with the onRequest remote method:

1    listener rabbitmq:Listener channelListener= new(rabbitmq:DEFAULT_HOST, rabbitmq:DEFAULT_PORT);
2    
3    @rabbitmq:ServiceConfig {
4        queueName: "MyQueue"
5    }
6    service rabbitmq:Service on channelListener {
7        remote function onRequest(rabbitmq:Message message) returns string {
8            return "Hello Back!";
9        }
10    }

The rabbitmq:Message record received can be used to retrieve its contents.

Advanced usage

Client acknowledgements

The message consuming is supported by mainly two types of acknowledgement modes, which are auto acknowledgements and client acknowledgements. Client acknowledgements can further be divided into two different types as positive and negative acknowledgements. The default acknowledgement mode is auto-ack (messages are acknowledged immediately after consuming). The following examples show the usage of positive and negative acknowledgements.

WARNING: To ensure the reliability of receiving messages, use the client-ack mode.

1. Positive client acknowledgement:

1    listener rabbitmq:Listener channelListener= new(rabbitmq:DEFAULT_HOST, rabbitmq:DEFAULT_PORT);
2    
3    @rabbitmq:ServiceConfig {
4        queueName: "MyQueue",
5        autoAck: false
6    }
7    service rabbitmq:Service on channelListener {
8        remote function onMessage(rabbitmq:Message message, rabbitmq:Caller caller) {
9            rabbitmq:Error? result = caller->basicAck();
10        }
11    }

2. Negative client acknowledgement:

1    listener rabbitmq:Listener channelListener= new(rabbitmq:DEFAULT_HOST, rabbitmq:DEFAULT_PORT);
2    
3    @rabbitmq:ServiceConfig {
4        queueName: "MyQueue",
5        autoAck: false
6    }
7    service rabbitmq:Service on channelListener {
8        remote function onMessage(rabbitmq:Message message) {
9            rabbitmq:Error? result = caller->basicNack(true, requeue = false);
10        }
11    }

The negatively-acknowledged (rejected) messages can be re-queued by setting the requeue to true.

Report issues

To report bugs, request new features, start new discussions, view project boards, etc., go to the Ballerina standard library parent repository.

Useful links

• Chat live with us via our Discord server.
• Post all technical questions on Stack Overflow with the #ballerina tag.