Am I using ioctl correctly?

Question

I'm writing an http server in python3.3, just to learn how to do this sort of thing. In my function that parses a request, I want to use fcntl.ioctl to get the number of bytes that I can read in the socket, and I only do this when I see a kevent in the result of checking a kqueue that says there is stuff to read on the socket. But whenever I try to call fcntl.ioctl, I get OSError: [Errno 14] Bad address. What am I doing wrong? Also, this seems to be happening on the first call. Here is the relevant code:

def client_thread(kq, client_socket, methods):
    while True:
        events = kq.control([], 2, POLLTIME) #we pass an empty list of changes, because we don't have any changes to make to the events we are interested in.
                                #we want a list that is at most two long. We listen for POLLTIME seconds.
        for event in events:
            if event != KILL_KEV: #there are only two events in our kqueue
                handle_client(client_socket, methods)
            else: #KILL_SOCK has a connection
                break
    client_socket.close()
    client_socket.shutdown()

def handle_client(client_socket, methods):
    request = parse_request(client_socket) #parse the request data in the client socket
    handlers = methods[request["request"]["method"]] #retrieve the appropriate list of handlers from the methods dict
    for path_match_pred, handler_func in handlers:
        if path_match_pred(path): #if the path matches whatever path predicate you've created...
            break
    response = handler_func(request) #... then call the appropriate handler function to handle the request
    send_response(client_socket, response) #and finally, send the response.

def parse_request(client_socket):
    """Returns the request data, parsed into a dictionary like this:
    {
        "request": {
            "method": method,
            "path": path,
            "version": HTTP version
            },
        "headers": header dictionary,
        "body": body data as a string
    }
    This should only be called if the client socket is ready for reading!
    """
    client_fd = client_socket.fileno() #get the file descriptor for the socket
    bytes_in_socket = 0
    fcntl.ioctl(client_fd, termios.FIONREAD, bytes_in_socket) #count the bytes in it
    #^^^^^^^^^THIS IS WHERE IT BREAKS
    print(bytes_in_socket, "bytes in socket")
    msg = bytearray() #make empty byte array
    while bytes_in_socket:
        msg.extend(client_socket.recv(bytes_in_socket)) #read the bytes we counted earlier
        fcntl.ioctl(client_fd, termios.FIONREAD, bytes_in_socket) #check for more bytes
        print(bytes_in_socket, "bytes left to read")

Answer 1

Note that in fcntl.ioctl's documentation, they mention the acceptable types for arg (the argument to the ioctl operation). In some cases, (like this), you need to pass a buffer, or an object that supports its interface. In particular, when you want to receive a value back. You're just passing an integer.