Let us create a local port forwarding script that will redirect all traffic received at port 8800 to the Google home page (http://www.google.com). We can pass the local and remote host as well as port number to this script. For the sake of simplicity, let's only specify the local port number as we are aware that the web server runs on port 80.

Listing 3.1 shows a port forwarding example, as follows:

#!/usr/bin/env python 
# Python Network Programming Cookbook, Second Edition -- Chapter - 3 
# This program is optimized for Python 2.7.12 and Python 3.5.2. 
# It may run on any other version with/without modifications. 
 
 
import argparse 
 
LOCAL_SERVER_HOST = 'localhost' 
REMOTE_SERVER_HOST = 'www.google.com' 
BUFSIZE = 4096 
 
import asyncore 
import socket 
 
class PortForwarder(asyncore.dispatcher): 
    def __init__(self, ip, port, remoteip,remoteport,backlog=5): 
        asyncore.dispatcher.__init__(self) 
        self.remoteip=remoteip 
        self.remoteport=remoteport 
        self.create_socket(socket.AF_INET,socket.SOCK_STREAM) 
        self.set_reuse_addr() 
        self.bind((ip,port)) 
        self.listen(backlog) 
 
    def handle_accept(self): 
        conn, addr = self.accept() 
        print ("Connected to:",addr) 
        Sender(Receiver(conn),self.remoteip,self.remoteport) 
 
class Receiver(asyncore.dispatcher): 
    def __init__(self,conn): 
        asyncore.dispatcher.__init__(self,conn) 
        self.from_remote_buffer='' 
        self.to_remote_buffer='' 
        self.sender=None 
 
    def handle_connect(self): 
        pass 
 
    def handle_read(self): 
        read = self.recv(BUFSIZE) 
        self.from_remote_buffer += read 
 
    def writable(self): 
        return (len(self.to_remote_buffer) > 0) 
 
    def handle_write(self): 
        sent = self.send(self.to_remote_buffer) 
        self.to_remote_buffer = self.to_remote_buffer[sent:] 
 
    def handle_close(self): 
        self.close() 
        if self.sender: 
            self.sender.close() 
 
class Sender(asyncore.dispatcher): 
    def __init__(self, receiver, remoteaddr,remoteport): 
        asyncore.dispatcher.__init__(self) 
        self.receiver=receiver 
        receiver.sender=self 
        self.create_socket(socket.AF_INET, socket.SOCK_STREAM) 
        self.connect((remoteaddr, remoteport)) 
     
    def handle_connect(self): 
        pass 
     
    def handle_read(self): 
        read = self.recv(BUFSIZE) 
        self.receiver.to_remote_buffer += read 
     
    def writable(self): 
        return (len(self.receiver.from_remote_buffer) > 0) 
     
    def handle_write(self): 
        sent = self.send(self.receiver.from_remote_buffer) 
        self.receiver.from_remote_buffer = self.receiver.
          from_remote_buffer[sent:] 
     
    def handle_close(self): 
        self.close() 
        self.receiver.close() 
 
 
if __name__ == "__main__": 
    parser = argparse.ArgumentParser(description='Stackless
              Socket Server Example') 
    parser.add_argument('--local-host', action="store", 
    dest="local_host", default=LOCAL_SERVER_HOST) 
    parser.add_argument('--local-port', action="store", 
    dest="local_port", type=int, required=True) 
    parser.add_argument('--remote-host', action="store", 
    dest="remote_host",  default=REMOTE_SERVER_HOST) 
    parser.add_argument('--remote-port', action="store", 
    dest="remote_port", type=int, default=80) 
    given_args = parser.parse_args()  
    local_host, remote_host = given_args.local_host, 
    given_args.remote_host 
    local_port, remote_port = given_args.local_port, 
    given_args.remote_port 
     
    print ("Starting port forwarding local %s:%s => remote 
    %s:%s" % (local_host, local_port, remote_host, remote_port)) 
    PortForwarder(local_host, local_port, remote_host, remote_port) 
    asyncore.loop() 

If you run this script, it will show the following output:

$ python 3_1_port_forwarding.py --local-port=8800 
Starting port forwarding local localhost:8800 => remote www.google.com:80 
  

Now, open your browser and visit http://localhost:8800. This will take you to the Google home page and the script will print something similar to the following command:

('Connected to:', ('127.0.0.1', 37236))
  

The following screenshot shows the forwarding of a local port to a remote host: