TCP sockets in Python question

[eljonto]

Hey all,
im writing a python program that uses sockets. Im using a tcp connection (SOCK_STREAM) and until now all testing has been done on my computer with the server and client- not on remote computers. Since im new to sockets- i just have this question- i know that the client has to connect to the server with the servers ip address- but does the server need the clients ip address to accept connections from it? because in my client server scripts that work- the client uses a connect() and the server uses a bind(). i read (from google) that binding is just binding to an address which is neccessary for it to listen() for connections from the client. Also- when 'binding' does the server bind itself to whatever- or to the client??
to reiterate- before i test on remote comps- does the server need the clients ip adress?
thanks alot
~ELJONTO

[nathandelane]

No, your server doesn't need to know the client's ip address, but that is part of the information that is sent in a TCP/IP packet anyway, so you could get it from the first time the client tries to connect. The only reason that you might want to get the client's ip address is in order to suppress connections from a particular client (i.e. create a black list) or vise versa, and only allow certain clients to connect to your server (i.e. a white list).

[eljonto]

ahh ok thanks-
for various reasons it wasn't working over remote computers- ive tried binding server to '' and then port, 'localhost', port, ive also tried 'INNADDR_ANY',port - but this along with 'gethostname()',port causes an info error
on my friends comp i think that windows might've been blocking the server accepting connection though- want me to post example code to have a look?

[tgoe]

Post it

[eljonto]

ok, heres the server:

Code: Select all

import socket
import urllib #needed for other features which i didn't include here for brievity

s = socket.socket ( socket.AF_INET, socket.SOCK_STREAM )
s.bind ( ( '', 8642 ) )

s.listen ( 1 )
while True:
   channel, details = s.accept()
   while(1):
       data= channel.recv ( 100 )
       command=data.split(" ")
       if not data:
           break
       else:
           if command[0] == "/terminate":
               channel.send("Client exit")
               channel.close()
               s.close()
               exit(1);
           elif command[0] == "/quit":
               channel.send("Client exit")
           else:
               print data
               str="received: "+data
               channel.send(str)
   channel.close()


and here's the client:

Code: Select all

import socket
import urllib

print "<<CLIENT>>\n\n"
print ">>connecting to server...\n"

print ">>Attempting to connect to Server..."
s = socket.socket ( socket.AF_INET, socket.SOCK_STREAM )
CONNECT = 0
while CONNECT == 0:
    try:
        s.connect ( ( '127.0.0.1', 8642 ) ) 
    except socket.error, msg:
        continue
    CONNECT = 1
   
print "\n>>Connected to server\n"
 
while (1):
    data=raw_input(">> ")
    if not data:
        break
    else:
        if(s.send(data)):
            retdata=s.recv(1000)                 
            if (retdata != "Client exit" ):
                print ">>Server: ",retdata,"\n"
            else:
                print ">>Closing connection"
                s.close()
                print ">>Connection terminated"
                exit(1);
   
s.close()


obviously replace 127.0.0.1 with the servers remote ip address if used remotely, but i think the problem is either with the server binding, or with firewalls etc

[Steve8x]

I am not familiar with python, However I do socket programming in C++ all the time (for windows aka Winsock) At a glance your code seems fine...

Were you running the server from your friends PC and then running the client on your PC and trying to connect to the server? or vice versa?

Which ever computer you make run the server, has to be PORT FORWARDED! What I mean by that is ANY firewalls have to be open on the port your server is "listening" on... thats how servers work, they listen for incoming clients connections and then accept them when they come in. If a firewall is blocking incoming connections on that port, all incoming requests will not make it to your server!

So for example say you want your server to bind on port 6969, and you ran the server on your friends PC...

Your going to have to unblock ALL firewalls, That means logging into the router (if they have one) and setting up port forwarding so that any incoming TCP requests on port 6969 get forwarded to the computer running the server...

For me I only have/use a hardware firewall (built into my router) so to open a port for me that's all I'd have to do... The trend however with many people is using software firewalls too!

At my friends house when I wanted to test some of my client->server apps I had to not only configure his router, but also windows firewall and another firewall with his AV (one that I almost didn't find)

So make sure all firewalls are unblocked, if you don't want to disable the wall completely, then just add an exception

[eljonto]

ahhhh thanks!
one of my friends said on his comp a windows message came up saying something like "do you want to keep blocking server etc"- but i didn't think of the port forwarding- i guess ill have to find out how to add exceptions via software and so on- any ideas or suggestions please post back here, but thanks for your help.

EDIT: o yea- and i did get them to run server first- and even if they didn't with the original client code waits for the server to start if the client was started first anyway

[tgoe]

If you don't want the user of your server to have to enable port forwarding manually, you can try using UPnP. The MiniUPnP C library can be built with an optional python module that you can use. Also, the python Twisted framework does UPnP.

[eljonto]

ah great thanks, will certainly try it out when i have the time