The virtues of the NATS protocol manifest quickly when you experience how easy it is to use NATS. Because the NATS protocol is text-based, you can use NATS across virtually any platform or language. In the following demo we use Telnet.
On the wire you can publish and subscribe using a simple set of protocol commands.
1. Open a terminal session.
You'll use this terminal as the subscriber.
2. Connect to NATS.
telnet demo.nats.io 4222
Expected result:
$ telnet demo.nats.io 4222
Trying 107.170.221.32...
Connected to demo.nats.io.
Escape character is '^]'.
INFO {"server_id":"NCXMJZYQEWUDJFLYLSTTE745I2WUNCVG3LJJ3NRKSFJXEG6RGK7753DJ","version":"2.0.0","proto":1,"go":"go1.11.10","host":"0.0.0.0","port":4222,"max_payload":1048576,"client_id":5089}
3. Run the subscriber.
Subscribe to the wildcard subject foo.* with subject ID of 90.
sub foo.* 90
Subscriber result: +OK indicating successful interest registration.
sub foo.* 90
+OK
4. Open a second terminal window.
You'll use this terminal for the publisher.
5. Connect to NATS.
telnet demo.nats.io 4222
Expected result:
$ telnet demo.nats.io 4222
Trying 107.170.221.32...
Connected to demo.nats.io.
Escape character is '^]'.
INFO {"server_id":"NCXMJZYQEWUDJFLYLSTTE745I2WUNCVG3LJJ3NRKSFJXEG6RGK7753DJ","version":"2.0.0","proto":1,"go":"go1.11.10","host":"0.0.0.0","port":4222,"max_payload":1048576,"client_id":5089}
6. Publish a message.
The message includes the command (pub), subject (foo.bar), and length of the payload (5). Press enter and provide the payload (hello), then press enter again.
pub foo.bar 5
hello
Publisher result: +OK indicating message publication.
pub foo.bar 5
hello
+OK
Subscriber result: MSG + subject name + subscription ID + message payload size + message payload hello.
sub foo.* 90
+OK
MSG foo.bar 90 5
hello
7. Publish another message with reply subject.
pub foo.bar optional.reply.subject 5
hello
+OK
Subscriber result: MSG indicating message receipt.
MSG foo.bar 90 optional.reply.subject 5
hello
8. Unsubscribe from interest in the subject.
You can use the UNSUB command to unsubscribe from a message.
Run the subscriber to unsubscribe:
unsub 90
Subscriber result: +OK indicating successful deregistration of interest.
unsub 90
+OK
9. Reconnect to server and subscribe.
telnet demo.nats.io 4222
sub foo.* 90
10. Explore the ping/pong interval.
If you leave your telnet session open for a few minutes, you may notice that your clients receives ping requests from the server. If your client is not active, or does not respond to the server pings within the ping/pong interval, the server disconnects the client. The error message is -ERR 'Stale Connection'.
You can send a ping request to the serve and receive a PONG reply. For example:
$ telnet demo.nats.io 4222
Trying 107.170.221.32...
Connected to demo.nats.io.
Escape character is '^]'.
INFO {"server_id":"NCXMJZYQEWUDJFLYLSTTE745I2WUNCVG3LJJ3NRKSFJXEG6RGK7753DJ","version":"2.0.0","proto":1,"go":"go1.11.10","host":"0.0.0.0","port":4222,"max_payload":1048576,"client_id":5089}
ping
PONG