ballerinax/nats Ballerina library

Package Overview

This package provides the capability to connect with NATS server and performs the below functionalities.

• Point to point communication (Queues)
• Pub/Sub (Topics)
• Request/Reply

Basic Usage

Setting up the connection

First step is setting up the connection with the NATS Basic server. The following ways can be used to connect to a NATS Basic server.

1. Connect to a server using the default URL

nats:Client natsClient = new(nats:DEFAULT_URL);

2. Connect to a server using the URL

nats:Client natsClient = new("nats://serverone:4222");

3. Connect to one or more servers with custom configurations

nats:ConnectionConfiguration config = {
    connectionName: "my-nats",
    noEcho: true
};
nats:Client natsClient = new(["nats://serverone:4222",  "nats://servertwo:4222"],  config);

Publishing messages

Publishing messages to the NATS basic server

Once connected, publishing is accomplished via one of the below two methods.

1. Publish with the subject and the message content.

string message = "hello world";
nats:Error? result = 
    natsClient->publishMessage({ content: message.toBytes(), subject: "demo.nats.basic"});

2. Publish as a request that expects a reply.

string message = "hello world";
nats:Message|nats:Error reqReply = 
    natsClient->requestMessage({ content: message.toBytes(), subject: "demo.nats.basic"}, 5);

3. Publish messages with a replyTo subject

string message = "hello world";
nats:Error? result = natsClient->publish({ content: message.toBytes(), subject: "demo.nats.basic",
                                                    replyTo: "demo.reply" });

Listening to incoming messages

Listening to messages from a NATS server

// Binds the consumer to listen to the messages published to the 'demo.example.*' subject.
@nats:ServiceConfig {
    subject: "demo.example.*"
}
service nats:Service on new nats:Listener(nats:DEFAULT_URL) {

    remote function onMessage(nats:Message message) {
    }
}

Note: The default thread pool size used in Ballerina is the number of processors available * 2. You can configure the thread pool size by using the BALLERINA_MAX_POOL_SIZE environment variable.

For information on the operations, which you can perform with this package, see the below Functions.

For examples on the usage of the connector, see the following.

• Basic Publisher and Subscriber Example.