Synchronous Subscriptions

Synchronous subscriptions require the application to wait for messages. This type of subscription is easy to set-up and use, but requires the application to deal with looping if multiple messages are expected. For situations where a single message is expected, synchronous subscriptions are sometimes easier to manage, depending on the language.
For example, to subscribe to the subject updates and receive a single message you could do:
Go
Java
JavaScript
Python
Ruby
TypeScript
C
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nc, err := nats.Connect("demo.nats.io")
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if err != nil {
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    log.Fatal(err)
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}
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defer nc.Close()
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​
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// Subscribe
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sub, err := nc.SubscribeSync("updates")
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if err != nil {
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    log.Fatal(err)
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}
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​
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// Wait for a message
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msg, err := sub.NextMsg(10 * time.Second)
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if err != nil {
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    log.Fatal(err)
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}
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​
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// Use the response
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log.Printf("Reply: %s", msg.Data)
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Connection nc = Nats.connect("nats://demo.nats.io:4222");
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​
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// Subscribe
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Subscription sub = nc.subscribe("updates");
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​
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// Read a message
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Message msg = sub.nextMessage(Duration.ZERO);
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​
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String str = new String(msg.getData(), StandardCharsets.UTF_8);
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System.out.println(str);
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​
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// Close the connection
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nc.close();
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// node-nats subscriptions are always async.
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# Asyncio NATS client currently does not have a sync subscribe API
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# The Ruby NATS client subscriptions are all async.
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/ Typescript NATS subscriptions are always async.
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natsConnection      *conn      = NULL;
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natsSubscription    *sub       = NULL;
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natsMsg             *msg       = NULL;
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natsStatus          s          = NATS_OK;
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​
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s = natsConnection_ConnectTo(&conn, NATS_DEFAULT_URL);
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​
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// Subscribe
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if (s == NATS_OK)
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    s = natsConnection_SubscribeSync(&sub, conn, "updates");
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​
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// Wait for messages
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if (s == NATS_OK)
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    s = natsSubscription_NextMsg(&msg, sub, 10000);
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​
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if (s == NATS_OK)
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{
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    printf("Received msg: %s - %.*s\n",
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            natsMsg_GetSubject(msg),
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            natsMsg_GetDataLength(msg),
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            natsMsg_GetData(msg));
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​
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    // Destroy message that was received
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    natsMsg_Destroy(msg);
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}
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​
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(...)
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​
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// Destroy objects that were created
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natsSubscription_Destroy(sub);
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natsConnection_Destroy(conn);
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Developing With NATS - Previous

Receiving Messages

Asynchronous Subscriptions

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