Communication between two computers using python s

Question

I am using these two programs to communicate between two of my computers, one that I am ssh'd into and I am not returning anything on either side. It just runs without sending anything

client

import sys
from socket import socket, AF_INET, SOCK_DGRAM

SERVER_IP   = '127.0.0.1'
PORT_NUMBER = 5000
SIZE = 1024
print ("Test client sending packets to IP {0}, via port {1}\n".format(SERVER_IP, PORT_NUMBER))

mySocket = socket( AF_INET, SOCK_DGRAM )

while True:
        mySocket.sendto('cool',(SERVER_IP,PORT_NUMBER))
sys.exit()

server

from socket import socket, gethostbyname, AF_INET, SOCK_DGRAM
import sys
PORT_NUMBER = 5000
SIZE = 1024

hostName = gethostbyname( '0.0.0.0' )

mySocket = socket( AF_INET, SOCK_DGRAM )
mySocket.bind( (hostName, PORT_NUMBER) )

print ("Test server listening on port {0}\n".format(PORT_NUMBER))

while True:
        (data,addr) = mySocket.recvfrom(SIZE)
        print data
sys.ext()

What could I be doing wrong?

Answer 1

The problem is in the address of your client:

SERVER_IP   = '127.0.0.1'

You are connecting to the local machine and sending data, while your server is sitting on a different ip. You need to connect to either the servers ip or hostname.

You can verify this by making the client connect first (and fail if it cant)

...

import time

mySocket = socket( AF_INET, SOCK_DGRAM )
mySocket.connect((SERVER_IP,PORT_NUMBER))

while True:
        mySocket.send('cool')
        time.sleep(.5)

Update from comments

Because you are on a wifi connection, that implies that both these machine are on the local network. You need to find the LAN ip address of the server, to specify it as the target.

Command-line approach to finding your IP

• OSX/Linux: ifconfig
• Windows: ipconfig /all

Answer 2

If this does not work even after changing the SERVER_IP to the real server's address, check whether the firewall on your server accepts traffic for UDP on port 5000.

if your server is a linux machine, iptables -L would show you the firewall rules. iptables -F would delete all(!) firewall rules, so you can test if that helps. this is not reboot persistent.

Answer 3

You should see LAN ip address like this: 192.168.1.102 that are usual WiFi router default local address. For example, you will see following in windows command prompt by using ipconfig:

C:\Users\jackc>ipconfig

Windows IP Configuration

Wireless LAN adapter Wireless Network Connection 3:

   Media State . . . . . . . . . . . : Media disconnected
   Connection-specific DNS Suffix  . :

Wireless LAN adapter Wireless Network Connection:

   Connection-specific DNS Suffix  . :
   Link-local IPv6 Address . . . . . : fe80::ed97:91a4:9449:204b%13
   IPv4 Address. . . . . . . . . . . : 192.168.8.106
   Subnet Mask . . . . . . . . . . . : 255.255.255.0
   Default Gateway . . . . . . . . . : 192.168.8.1

I tried the following test code that works for me.

Client:

#!/usr/bin/env python3

import sys
from socket import socket, AF_INET, SOCK_DGRAM

SERVER_IP   = '192.168.8.102'
PORT_NUMBER = 5000
SIZE = 1024
print ("Test client sending packets to IP {0}, via port {1}\n".format(SERVER_IP, PORT_NUMBER))

mySocket = socket( AF_INET, SOCK_DGRAM )
myMessage = "Hello!"
myMessage1 = ""
i = 0
while i < 10:
    mySocket.sendto(myMessage.encode('utf-8'),(SERVER_IP,PORT_NUMBER))
    i = i + 1

mySocket.sendto(myMessage1.encode('utf-8'),(SERVER_IP,PORT_NUMBER))

sys.exit()

Server:

#!/usr/bin/env python3

from socket import socket, gethostbyname, AF_INET, SOCK_DGRAM
import sys
PORT_NUMBER = 5000
SIZE = 1024

hostName = gethostbyname( '0.0.0.0' )

mySocket = socket( AF_INET, SOCK_DGRAM )
mySocket.bind( (hostName, PORT_NUMBER) )

print ("Test server listening on port {0}\n".format(PORT_NUMBER))

while True:
    (data,addr) = mySocket.recvfrom(SIZE)
    print data
sys.exit()