test python socket server by nc or telnet

Question

I have a simple socket server by python

#!/usr/bin/python3           # This is server.py file
import socket                                         

# create a socket object
serversocket = socket.socket(
            socket.AF_INET, socket.SOCK_STREAM) 

# get local machine name
host = socket.gethostname()                           

port = 2115                                           

# bind to the port
serversocket.bind((host, port))                                  

# queue up to 5 requests
serversocket.listen(5)                                           

while True:
    # establish a connection
    clientsocket,addr = serversocket.accept()      

    print("Got a connection from %s" % str(addr))

    msg = serversocket.recv(1024)
    print (msg.decode('ascii'))
    clientsocket.close()

I want to test this server by nc or telnet for example

telnet 127.0.0.1 2115

but causes error but when i try to connect by another socket program written in python. works well

Answer 1

When you do host = socket.gethostname(), your host is assigned to something like "MacBookPro.local". Then you bind your server to it at serversocket.bind((host, port)). Thus your listening socket isn't bound to 127.0.0.1, so the connection attempt from telnet gets refused.

Instead, try serversocket.bind('', port) and re-run your server. This time, it should accept the telnet connection.