net

conn, err := DialRCON("localhost:25575", "CORRECT_PASSWORD")
if err != nil {
	panic(err)
}
defer conn.Close()

err = conn.Cmd("TEST COMMAND")
if err != nil {
	panic(err)
}

for {
	// Server may send the result in more(or less) than one packet.
	// See: https://wiki.vg/RCON#Fragmentation
	resp, err := conn.Resp()
	if err != nil {
		fmt.Print(err)
	}
	fmt.Printf("Server response: %q", resp)
	break
}

Output:

l, err := ListenRCON("localhost:25575")
if err != nil {
	panic(err)
}
defer l.Close()

for {
	conn, err := l.Accept()
	if err != nil {
		fmt.Printf("Accept connection error: %v", err)
	}

	go func(conn RCONServerConn) {
		err = conn.AcceptLogin("CORRECT_PASSWORD")
		if err != nil {
			fmt.Printf("Login fail: %v", err)
		}
		defer conn.Close()

		// The client is login, we are accepting its command
		for {
			cmd, err := conn.AcceptCmd()
			if err != nil {
				fmt.Printf("Read command fail: %v", err)
				break
			}

			resp := handleCommand(cmd)

			// Return the result of command.
			// It's allowed to call RespCmd multiple times for one command.
			err = conn.RespCmd(resp)
			if err != nil {
				fmt.Printf("Response command fail: %v", err)
				break
			}
		}
	}(conn)
}

Output: