icmp-ping.py 文件源码

def receive_ping(my_socket, ID, timeout):
    """
    receive the ping from the socket
    """
    start_time = timeout
    while True:
        start_select = time.clock()
        # select.select(rlist, wlist, xlist[, timeout])
        # wait until ready for read / write / exceptional condition
        # The return value is a triple of lists
        what_ready = select.select([my_socket], [], [], start_time)
        how_long = (time.clock() - start_select)
        if what_ready[0] == []: #timeout
            return

        time_received = time.clock()
        # socket.recvfrom(bufsize[, flags])
        # The return value is a pair (string, address)
        rec_packet, addr = my_socket.recvfrom(1024)
        icmp_header = rec_packet[20 : 28]
        ip_type, code, checksum, packet_ID, sequence = struct.unpack("bbHHh", icmp_header)
        if ip_type != 8 and packet_ID == ID: # ip_type should be 0
            byte_in_double = struct.calcsize("d")
            time_sent = struct.unpack("d", rec_packet[28 : 28 + byte_in_double])[0]
            return time_received - time_sent

        start_time = start_time - how_long
        if start_time <= 0:
            return