Connecting to a simple sockets python server remotely

Question

I am trying to setup a very simply sockets app. My server code is:

import socket

s = socket.socket()
host = socket.gethostname()

port = 1234
s.bind((host,port))

s.listen(5) #Here we wait for a client connection
while True:
    c, addr = s.accept()
    print "Got a connection from: ", addr
    c.send("Thanks for connecting")
    c.close()

I placed this file on my remote Linode server and run it using python server.py. I have checked that the port is open using nap:

PORT     STATE SERVICE
22/tcp   open  ssh
80/tcp   open  http
1234/tcp open  hotline

I now run the client.py on my local machine:

import socket              # Import socket module

s = socket.socket()        # Create a socket object
port = 1234                # Reserve a port for your service.

s.connect(("139.xxx.xx.xx", port))
print s.recv(1024)
s.close                    # Close the socket when done

However I am not getting any kind of activity or report of connection. Could someone give me some pointers to what I might have to do? Do I need to include the hostname in the IP address I specify in the client.py? Any help would be really appreciated!

Solution

I've just summarize our comments, so your problem is this:

When you trying to using the client program connect to the server via the Internet, not LAN. You should configure the port mapping on your router.

And however, you just need configure the port mapping for your server machine.
After you did that, then you can use the client program connect to your server prigram.

Comments

[Remi Guan]

Did you do the port mapping?

[Some programmer dude]

Nothing happens in neither the server nor the client? How long have you waited (because connection attempts can take some time to timeout)?

[Kex]

@KevinGuan haven't done any port mapping, not sure what that is

[Kex]

@JoachimPileborg nothing happens for either. The client script does work though, it actually reports a connection when I run nap (but the connections is itself)

[Remi Guan]

It looks like you're trying to using client connect to the server via the Internet, not LAN. So maybe you need to do port mapping. Please see the wiki: en.wikipedia.org/wiki/Port_forwarding

[Kex]

@KevinGuan yesI'm trying to connect via the internet not LAN.

[dsgdfg]

Friend , use 0.0.0.0 for binding all interface and you need router redirecting for related service !

[Remi Guan]

Yeah, before you try this, please try connect to your computer itself first to check the code can run or not. However I mean: run server program at your computer first, and then run the client program to connect to the server program. And like @dsgdfg said, use 0.0.0.0 or 127.0.0.1 instead 139.xxx.xx.xx.

[Fujiao Liu]

try to change 'host' to linode public ip address on server side, and use the ip on client side to connect.

[Kex]

@KevinGuan yeah checked the client and server on my local machine using 0.0.0.0 and it works fine

[Remi Guan]

So your code is so good, now you can learn about the port mapping :)

[Kex]

@KevinGuan so port mapping is extra code I need to add to my client to pass the connection out over the internet?

[Remi Guan]

Nope. you need to configure it on your router. You can use Google and search How to do port mapping.

[Kex]

@KevinGuan it must be possible to do it by code though right? I want to make a client able to work on any machine without the user having to configure the router first.

[Remi Guan]

However you just need configure the router for your server machine. And then, everyone can connect to it use the client program. For example: if you're configure a web server, you have to mapping the 80 port for your server. But after that, everyone can use they're web browser connect to your web server.

[mhawke]

In the server what is socket.gethostname() returning? It could be that your server is binding to a local interface, not a public interface. Others have suggested using 0.0.0.0 as the host in the server - did you try that? The other thing to check is whether your host allows connections through the firewall to port 1234. If not you need to open port 1234, there is some documentation here: linode.com/docs/security/securing-your-server (see the Firewall section).