Python, why it is errors 10035 (on server) and 10053 (on client) during using TCP sockets?

Question

Almost 2 days I still have the same problem -client and server 'talks' to each other but I don't know why suddenly problem occurs during the communication. I tried really many things and unfortunately still the same problem.

I'm using python 2.7.5 on Windows 7.

My code: cs_common.py

import socket
import os
import sys
import errno
from time import sleep


HOST = 'localhost'
MY_IP = socket.gethostbyname(socket.gethostname())
PORT = 50007
timeout_in_seconds = 2

def createSocket4server(host, port):
    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    s.bind((host, port))
    s.listen(4)
    return s

def createSocket4Client(host, port, timeout_in_seconds=3):
    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

    s.connect( (host, port) )
    print 'connected to %s port %s' % (host, port)
    return s

sent = 0
def sendToSocket(socket_, data): # to debug
    global sent
    print sent, ') Sending:', data
    socket_.send(data)
    sent += 1

received = 0
def recvFromSocket(socket_):
    global received
    print '>>>>>>>>>>Trying to receive'
    data = socket_.recv(1024)
    print received, ') Received:', data
    received += 1
    return data

def sendDataToAllPlayers(data_to_send, connections):
    for c in connections:
        sendToSocket(c[0], data_to_send)

def trySendingAsLongAsNotSent(socket_, data):
    while True:
            try:
                sendToSocket(socket_, data)
                break
            except socket.timeout:
                pass

def tryReceivingAsLongAsNotReceived(socket_):
    while True:
            try:
                data = recvFromSocket(socket_)
                return data
            except socket.timeout:
                pass

server.py:

from cs_common import *


server = createSocket4server(HOST, PORT)
server.setblocking(0) # 1 switch off blocking
server.settimeout(timeout_in_seconds)

connections = []

counter = 0
while counter<3:
    counter += 1
    try:
        c, addr = server.accept()
        print 'Got connection from', addr
        connections.append( [c, addr] )
    except socket.timeout:
        pass

if len(connections) == 0:
    print 'No connections!'
    exit()

number_of_players = len(connections)
print 'Connected with', number_of_players, 'players:'
print [ addr[1] for addr in connections ]

counter = 0
for c in connections:
        counter += 1
        number_of_the_player = counter
        initial_game_data = str(number_of_the_player) + ' rest of initial game data'

        sendToSocket(c[0], initial_game_data) # 2 sending initial game settings

sleep(1)
server.setblocking(1) # 3 switch on blocking

# MAIN LOOP #
while True:
    print 'LOOP___________________________'
    sendDataToAllPlayers('Synchronization data to players', connections) # 4 sending synchronization data to clients

    # doing some stuff

    for c in connections:
        print 'received from player:', recvFromSocket(c[0]) # 5 receiving synchronization data from clients

client.py:

from cs_common import *


server = createSocket4Client(HOST, PORT)
server.setblocking(0) # 1 switch off blocking
server.settimeout(timeout_in_seconds)

initial_game_data = tryReceivingAsLongAsNotReceived(server) # 2 getting initial game settings
print 'received initial_game_data from server:', initial_game_data

sleep(1)
server.setblocking(1) # 3 switch on blocking

# MAIN LOOP #
while True:
    print 'LOOP___________________________'
    sunchronizing_data = recvFromSocket(server) # 4 receive synchronization data from server
    print 'Received from server:', sunchronizing_data

    # doing some stuff

    sendToSocket(server, 'I was doing nothing during the frame')

When I run the codes above:

Output from client:

connected to localhost port 50007
>>>>>>>>>>Trying to receive
>>>>>>>>>>Trying to receive
>>>>>>>>>>Trying to receive
0 ) Received: 1 rest of initial game data
received initial_game_data from server: 1 rest of initial game data
LOOP___________________________
>>>>>>>>>>Trying to receive
1 ) Received: Synchronization data to players
Received from server: Synchronization data to players
0 ) Sending: I was doing nothing during the frame
LOOP___________________________
>>>>>>>>>>Trying to receive
Traceback (most recent call last):
  File ".\client.py", line 19, in <module>
    sunchronizing_data = recvFromSocket(server) # 4 receive synchronization data from server
  File "...\pygame_my\cs_common.py", line 38, in recvFromSocket
    data = socket_.recv(1024)
socket.error: [Errno 10053] An established connection was aborted by the softwar
e in your host machine

Output from server:

Got connection from ('127.0.0.1', 55768)
Connected with 1 players:
[('127.0.0.1', 55768)]
0 ) Sending: 1 rest of initial game data
LOOP___________________________
1 ) Sending: Synchronization data to players
received from player: >>>>>>>>>>Trying to receive
Traceback (most recent call last):
  File ".\server.py", line 49, in <module>
    print 'received from player:', recvFromSocket(c[0]) # 5 receiving synchronization data from clients
  File "...\pygame_my\cs_common.py", line 38, in recvFromSocket
    data = socket_.recv(1024)
socket.error: [Errno 10035] A non-blocking socket operation could not be completed immediately

I tried also the scripts on an another computer -the same problems. I tried also to deactivate not-blocking sockets -still problems

Answer 1

You need to make the child socket blocking. Add this call "c.setblocking(1)" in the server file (server.py) before you append the new connection using "connections.append( [c, addr] )" -- like the following snippet. Looks like the child socket is inheriting the non-blocking option from the parent server socket. With this change, I was able to run your code without any errors.

    c, addr = server.accept()
    print 'Got connection from', addr
    c.setblocking(1) # Make it blocking.
    connections.append( [c, addr] )

The other alternative would be to catch socket.error in the recvFromSocket() function in the cs_common.py -- this is because if the recv() timeouts becuase child sockets are non-blocking, then the recv() call will return with an error. Since your code is not handling it, your application runs into a problem.

And a generic note: If there are clients that would join after the initial list of 3 cliens, then I would recommend using a separate thread to handle incoming connections or to use a select() call to accept read-events for the server fd -- a read event on the server fd means that there is a pending connection and we should call an accept().