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Including a Reply Subject

The optional reply-to field when publishing a message can be used on the receiving side to respond. The reply-to subject is often called an inbox, and most libraries may provide a method for generating unique inbox subjects. Most libraries also provide for the request-reply pattern with a single call. For example to send a request to the subject time, with no content for the messages, you might:

{% tabs %} {% tab title="Go" %}

nc, err := nats.Connect("demo.nats.io")
if err != nil {
    log.Fatal(err)
}
defer nc.Close()

// Create a unique subject name for replies.
uniqueReplyTo := nats.NewInbox()

// Listen for a single response
sub, err := nc.SubscribeSync(uniqueReplyTo)
if err != nil {
    log.Fatal(err)
}

// Send the request.
// If processing is synchronous, use Request() which returns the response message.
if err := nc.PublishRequest("time", uniqueReplyTo, nil); err != nil {
    log.Fatal(err)
}

// Read the reply
msg, err := sub.NextMsg(time.Second)
if err != nil {
    log.Fatal(err)
}

// Use the response
log.Printf("Reply: %s", msg.Data)

{% endtab %}

{% tab title="Java" %}

Connection nc = Nats.connect("nats://demo.nats.io:4222");

// Create a unique subject name
String uniqueReplyTo = NUID.nextGlobal();

// Listen for a single response
Subscription sub = nc.subscribe(uniqueReplyTo);
sub.unsubscribe(1);

// Send the request
nc.publish("time", uniqueReplyTo, null);

// Read the reply
Message msg = sub.nextMessage(Duration.ofSeconds(1));

// Use the response
System.out.println(new String(msg.getData(), StandardCharsets.UTF_8));

// Close the connection
nc.close();

{% endtab %}

{% tab title="JavaScript" %}

let nc = NATS.connect({url: "nats://demo.nats.io:4222"});
// set up a subscription to process the request
nc.subscribe('time', (msg, reply) => {
    if(reply) {
        nc.publish(reply, new Date().toLocaleTimeString());
    }
});

// create a subscription subject that the responding send replies to
let inbox = NATS.createInbox();
nc.subscribe(inbox, {max: 1}, (msg) => {
    t.log('the time is', msg);
    nc.close();
});

nc.publish('time', "", inbox);

{% endtab %}

{% tab title="Python" %}

nc = NATS()

future = asyncio.Future()

async def sub(msg):
  nonlocal future
  future.set_result(msg)

await nc.connect(servers=["nats://demo.nats.io:4222"])
await nc.subscribe("time", cb=sub)

unique_reply_to = new_inbox()
await nc.publish_request("time", unique_reply_to, b'')

# Use the response
msg = await asyncio.wait_for(future, 1)
print("Reply:", msg)

{% endtab %}

{% tab title="Ruby" %}

require 'nats/client'
require 'fiber'

NATS.start(servers:["nats://127.0.0.1:4222"]) do |nc|
  Fiber.new do
    f = Fiber.current

    nc.subscribe("time") do |msg, reply|
      f.resume msg
    end

    nc.publish("time", 'example', NATS.create_inbox)

    # Use the response
    msg = Fiber.yield
    puts "Reply: #{msg}"

  end.resume
end

{% endtab %}

{% tab title="TypeScript" %}

// set up a subscription to process the request
await nc.subscribe('time', (err, msg) => {
    if (err) {
        // this example is running inside of a promise
        reject();
        return;
    }
    if (msg.reply) {
        nc.publish(msg.reply, new Date().toLocaleTimeString());
    }
});

// create a subscription subject that the responding send replies to
let inbox = createInbox();
await nc.subscribe(inbox, (err, msg) => {
    t.log('the time is', msg.data);
    // this example is running inside of a promise
    nc.close();
    resolve();
}, {max: 1});

nc.publish('time', "", inbox);

{% endtab %} {% endtabs %}