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
Go
nc, err := nats.Connect("demo.nats.io")
if err != nil {
    log.Fatal(err)
}
defer nc.Close()
​
// Subscribe
sub, err := nc.SubscribeSync("updates")
if err != nil {
    log.Fatal(err)
}
​
// Wait for a message
msg, err := sub.NextMsg(10 * time.Second)
if err != nil {
    log.Fatal(err)
}
​
// Use the response
log.Printf("Reply: %s", msg.Data)
Java
Connection nc = Nats.connect("nats://demo.nats.io:4222");
​
// Subscribe
Subscription sub = nc.subscribe("updates");
​
// Read a message
Message msg = sub.nextMessage(Duration.ZERO);
​
String str = new String(msg.getData(), StandardCharsets.UTF_8);
System.out.println(str);
​
// Close the connection
nc.close();
JavaScript
// node-nats subscriptions are always async.
Python
# Asyncio NATS client currently does not have a sync subscribe API
Ruby
# The Ruby NATS client subscriptions are all async.
TypeScript
/ Typescript NATS subscriptions are always async.
C
natsConnection      *conn      = NULL;
natsSubscription    *sub       = NULL;
natsMsg             *msg       = NULL;
natsStatus          s          = NATS_OK;
​
s = natsConnection_ConnectTo(&conn, NATS_DEFAULT_URL);
​
// Subscribe
if (s == NATS_OK)
    s = natsConnection_SubscribeSync(&sub, conn, "updates");
​
// Wait for messages
if (s == NATS_OK)
    s = natsSubscription_NextMsg(&msg, sub, 10000);
​
if (s == NATS_OK)
{
    printf("Received msg: %s - %.*s\n",
            natsMsg_GetSubject(msg),
            natsMsg_GetDataLength(msg),
            natsMsg_GetData(msg));
​
    // Destroy message that was received
    natsMsg_Destroy(msg);
}
​
(...)
​
// Destroy objects that were created
natsSubscription_Destroy(sub);
natsConnection_Destroy(conn);
Developing With NATS - Previous
Receiving Messages
Asynchronous Subscriptions
Last updated 5 months ago