import sys
import struct
import asyncio

@asyncio.coroutine
def tcp_echo_client(server, port, loop):
    try:
        try:
            reader, writer = yield from asyncio.wait_for(
                asyncio.open_connection(server, port, loop=loop),
                30.0,
                loop=loop
            )
        except asyncio.TimeoutError:
            print('Timeout while establishing a connection')
            return
        writer.write(struct.pack('!H', port))
        yield from writer.drain()

        try:
            data = yield from asyncio.wait_for(
                reader.readexactly(6),
                30.0,  # Timeout after 30 seconds
                loop=loop
            )
            res = struct.unpack('!BBBBH', data)
            remote_ip, port_used = res[0:4], res[4]
            print('Connection established on port: {}'.format(port_used))
            print('Egress IP address: {}'.format('.'.join(map(str, remote_ip))))
        except asyncio.TimeoutError:
            print('Timeout waiting for response')
        except asyncio.IncompleteReadError:
            print('Error receiving data')
        finally:
            writer.close()
    except ConnectionError:
        print('Error during connection on port {}'.format(port))

def main():
    server_name = sys.argv[1]
    try:
        port = int(sys.argv[2])
        if port < 1 or port > 65536:
            raise ValueError()
    except ValueError:
        print('Error: invalid port value. Admissible range [0-65536]')
        sys.exit()
    loop = asyncio.get_event_loop()
    loop.run_until_complete(tcp_echo_client(server_name, port, loop))
    loop.close()
    sys.exit()

if __name__ == '__main__':
    main()