Monitoring the Connection

Managing the interaction with the server is primarily the job of the client library but most of the libraries also provide some insight into what is happening under the covers.

For example, the client library may provide a mechanism to get the connection's current status:

Go

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

getStatusTxt := func(nc *nats.Conn) string {
    switch nc.Status() {
    case nats.CONNECTED:
        return "Connected"
    case nats.CLOSED:
        return "Closed"
    default:
        return "Other"
    }
}
log.Printf("The connection is %v\n", getStatusTxt(nc))

nc.Close()

log.Printf("The connection is %v\n", getStatusTxt(nc))

Java

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

System.out.println("The Connection is: " + nc.getStatus()); // CONNECTED

nc.close();

System.out.println("The Connection is: " + nc.getStatus()); // CLOSED

JavaScript

  // you can find out where you connected:
t.log(`connected to a nats server version ${nc.info.version}`);

// or information about the data in/out of the client:
const stats = nc.stats();
t.log(`client sent ${stats.outMsgs} messages and received ${stats.inMsgs}`);

Python

nc = NATS()

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

# Do something with the connection.

print("The connection is connected?", nc.is_connected)

while True:
  if nc.is_reconnecting:
    print("Reconnecting to NATS...")
    break
  await asyncio.sleep(1)

await nc.close()

print("The connection is closed?", nc.is_closed)

C#

// dotnet add package NATS.Net
using NATS.Net;

await using var client = new NatsClient();

Console.WriteLine($"{client.Connection.ConnectionState}"); // Closed

await client.ConnectAsync();

Console.WriteLine($"{client.Connection.ConnectionState}"); // Open

Ruby

NATS.start(max_reconnect_attempts: 2) do |nc|
  puts "Connect is connected?: #{nc.connected?}"

  timer = EM.add_periodic_timer(1) do
    if nc.closing?
      puts "Connection closed..."
      EM.cancel_timer(timer)
      NATS.stop
    end

    if nc.reconnecting?
      puts "Reconnecting to NATS..."
      next
    end
  end
end