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I wanted to make a very simple proxy using python (mostly to understand how it works). I am talking about a generic TCP proxy, not only http. I have built the following code, however, it seems to only work one way : ie the request is sent but I never get the answer. Here is the code : import socket import argparse #Args parser = argparse.ArgumentParser(description='ProxyDescription') parser.add_argument('-l', '--listen', action='store', help='Listening port', default=80, type=int) parser.add_argument('destination', action='store', help='Destination host') parser.add_argument('port', action='store', help='Destination port', type=int) args = parser.parse_args() #Server s1 = socket.socket(socket.AF_INET, socket.SOCK_STREAM) s1.bind(('', args.listen)) s1.listen(1) conn1, addr1 = s1.accept() #Client s2 = socket.socket(socket.AF_INET, socket.SOCK_STREAM) s2.connect((args.destination, args.port)) s2.setblocking(0) print "Connected by ", addr1 while 1: datato = conn1.recv(1024) if not datato: print "breaking to" break s2.send(datato) print "data send : " + datato try: datafrom = s2.recv(1024) print "reveived data : " + datafrom if not datafrom: print "breakinf from" break print "datafrom: " + datafrom conn1.send(datafrom) except socket.error, msg: print "error rcving: " + str(socket.error) + " || " + str(msg) continue print "the end ... closing" conn1.close() s2.close() My test is simply launching this script and telnet through it. If I look with wireshark, I see that the request is fully understood by the server and I do get an answer, however, I never get the answer in the telnet. (testing with simple GET / on google) I feel the problem is related to "blocking" / "non-blocking" socket but I can't really understand where it is.

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