Python：socket.recvfrom（）为地址返回none

Question

I am trying to write a Python version of the example here , but for some reason for every call to socket.recvfrom() that I make in both client and server, the address return value is None . The only thing I can think of is that maybe it has something to do with the fact that the sockets are STREAM sockets, however when I tried to change the type to socket.SOCK_DGRAM , I get errors on my call to socket.listen() . How can I fix this problem?

def server(port):
    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    sock.bind(('127.0.0.1', port))
    sock.listen(5)
    clientsocket, address = sock.accept()

    kkp = KnockKnockProtocol(); #Class which implements knock knock
    outputLine = kkp.processInput();
    clientsocket.sendto(outputLine, address)

    inputLine, address = clientsocket.recvfrom(MAX_BYTES)

    while inputLine:
        print inputLine, address
        outputLine = kkp.processInput(inputLine);
        clientsocket.sendto(outputLine, address)
        if outputLine == "Bye.":
            break
        inputLine, address = clientsocket.recvfrom(MAX_BYTES)


def client(port):
    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    sock.connect(("127.0.0.1", port))
    fromServer, address = sock.recvfrom(MAX_BYTES)

    while fromServer:
        print "Server: " + fromServer
        if fromServer == "Bye.":
            break

        fromUser = raw_input()
        if fromUser:
            print "Client: " + fromUser
            sock.sendto(fromUser, ("127.0.0.1", port))
        fromServer, address = sock.recvfrom(MAX_BYTES)


if __name__ == '__main__':
    choices = {'client': client, 'server': server} 
    parser = argparse.ArgumentParser(description='Send and receive UDP locally')
    parser.add_argument('role', choices=choices, help='which role to play')
    parser.add_argument('-p', metavar='PORT', type=int, default=1060, help='UDP port (default 1060)')
    args = parser.parse_args()
    function = choices[args.role]
    function(args.p)

Answer 1

Either use datagram sockets or stream sockets. You are trying to split the difference. Which do you want to use? If you want a connection-based, byte-stream protocol, use stream sockets. If you want a connectionless, datagram protocol, use datagram sockets.

If you want to use stream sockets, don't use recvfrom . It's connection based and the only thing you can receive is bytes from that particular connection.

If you want to use datagram sockets, don't use listen or accept . Since it's connectionless, you can neither listen for nor accept a connection.