Python instant messaging program fails to connect with errno 111

Question

I am trying to implement a simple TCP instant messaging program in Python using the socket module. When I use the value returned by socket.gethostname() in connect(), the client works perfectly fine when connecting to the IM server running on localhost. However, the client returns errno 111 (Connection refused) when I use the value returned by socket.gethostbyname("localhost"). Is there any way to fix this issue?

Answer 1

If you get a 111 when trying to connect, that generally means nothing is listening at that host and port.

It's usually easier to check this with a one-liner using netcat (which you probably have built-in on any platform but Windows, and can get easily if you don't), or telnet if you must:

abarnert$ nc -v localhost 111
nc: connect to localhost port 111 (tcp) failed: Connection refused
nc: connect to localhost port 111 (tcp) failed: Connection refused
nc: connect to localhost port 111 (tcp) failed: Connection refused

Since netcat couldn't connect, the problem isn't your Python client, it really is that there's nothing to connect to.

This means your server isn't listening on localhost:111.

Without knowing anything about your server beyond a brief mention, it's impossible to diagnose, but my first guess would be that you're doing a bind((gethostname(), 111)), which means it ends up listening only on, say, 10.0.0.3:111.

If you want to listen on all hosts and interfaces, there are fancy ways to specify that, but the easiest way is:

serversocket.bind(('', 111))