python socket handle keepalive request

Question

I am using python to write a simple web server, and sending requests to it. And I use libevent as my http client. But every time I send a keep-alive request, the http connection have the close callback before the success callback. I think it might be the keep-alive problem. And this is my python(server) code:

import socket

HOST, PORT = '', 8999

listen_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
listen_socket.setsockopt(socket.SOL_SOCKET, socket.SO_KEEPALIVE, 1)
listen_socket.setsockopt(socket.SOL_TCP, socket.TCP_KEEPIDLE, 60)
listen_socket.setsockopt(socket.SOL_TCP, socket.TCP_KEEPCNT, 4)
listen_socket.setsockopt(socket.SOL_TCP, socket.TCP_KEEPINTVL, 15)
listen_socket.bind((HOST, PORT))
listen_socket.listen(1)
print 'Serving HTTP on port %s ...' % PORT
while True:
    client_connection, client_address = listen_socket.accept()
    request = client_connection.recv(1024)
    print request

    http_response = """\
    HTTP/1.1 200 OK

    Hello, World!
    """

    client_connection.sendall(http_response)
    client_connection.close()

Answer 1

But every time I send a keep-alive request, ...

I think you are mixing up the application layer HTTP keep-alive and the transport layer TCP keep-alive.

HTTP keep-alive is used by the client to suggest to the server that the underlying TCP connection should be kept open for further requests from the client. But the server might decline and your server explicitly closes the connection after it handled the clients request,i.e. finished sending the response. Apart from that the way the server sends the response in a way which makes HTTP keep-alive impossible because the length of the response is unknown and thus ends only with the end of the underlying TCP connection. To fix this you would need to specify a Content-length or use chunked transfer encoding.

TCP keep alive instead is used to detect break of connectivity, i.e. one side crashed, router dead or similar. It is not related to HTTP keep-alive at all except for the similar name. It is set with setsockopt and that's what you are doing. But there is no such thing as a keep-alive request which you can explicitly send in case of TCP keep-alive.