proxy.py

#!/usr/bin/python2.7
#Black Hat Python Chapter Two: Building a TCP proxy

import sys
import socket
import threading

def server_loop(local_host,local_port,remote_host,remote_port,receive_first):
    
    server=socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    
    try:
        server.bind((local_host,local_port))
    except:
        print "[!!] Failed to listen on %s:%d" % (local_host,local_port)
        print "[!!] Check for other listening sockets or correct permissions"
        sys.exit(0)
    print "[*] Listening on %s:%d" % (local_host,local_port)
    
    server.listen(5)
    
    while True:
        client_socket, addr= server.accept()
        
        #print out the local connection information
        print "[==>] Recieved incoming connection from %s:%d" (addr[0],addr[1])
        
        #start a thread to talk to the remote host
        proxy_thread=threading.Thread(target=proxy_handler, args=(client_socket,remote_host,remote_port,receive_first))
        
        proxy_thread.start()
def main():
    
    #no fancy command line parsing ehre
    if len(sys.argv[1:]) !=5:
        print "Usage: ./proxy.py [localhost] [localport] [remotehost] [remoteport] [recieve_first]"
        print "Example: ./proxy.py 127.0.0.1 9000 10.12.132.1 9000 True"
        sys.exit(0)
    #setup local listening parameters
    local_host = sys.argv[1]
    local_port = int(sys.argv[2])
    
    #set up remote target
    remote_host = sys.argv[3]
    remote_port = sys.argv[4]
    
    #this tells our proxy to connect and receive data
    # before sending to the remote host
    receive_first = sys.argv[5]
    
    if "True" in receive_first:
        receive_first = True
    else:
        receive_first = False
    
    #now spin up our listening port
    server_loop(local_host,local_port,remote_host,remote_port,receive_first)

def proxy_handler(client_socket,remote_host,remote_port, receive_first):
    
    #connect to the remote host
    remote_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    remote_socket.connect((remote_host,remote_port))
    
    #receive the data from the remote end if necessary
    if receive_first:
        
        remote_buffer= receive_from(remote_socket)
        hexdump(remote_buffer)
        
        #send it to our response handler
        remote_buffer= response_handler(remote_buffer)
        
        #if we have data to send to our local client, send it
        if len(remote_buffer):
            print "[<==] Sedning %d bytes to localhost" % len(remote_buffer)
            client_socket.send(remote_buffer)
    # now lets loop and read from local,
    # send to remote, send to local
    # rinse, wash, repeat
    while True:
        #read from localhost
        local_buffer=receive_from(client_socket)
        
        if len(local_buffer):
            print "[==>] Received %d bytes from localhost." % len(local_buffer)
            hexdump(local_buffer)
            
            #send it to our request handler
            local_buffer = request_handler(local_buffer)
            
            #send off the data to the remote host
            remote_socket.send(local_buffer)
            print "[==>] Sent to remote."
        #receive back the response
        remote_buffer = receive_from(remote_socket)
        
        if len(remote_buffer):
            
            print "[<==] Received %d bytes from remote." % len(remote_buffer)
            hexdump(remote_buffer)
            
            #send to our response handler
            remote_buffer = response_handler(remote_buffer)
            
            #seend the response to the local socket
            client_socket.send(remote_buffer)
            
            print "[<==] Sent to localhost."
            
        # if no more data on either side, close the connections.
        if not len(local_buffer) or not len(remote_buffer):
            client_socket.close()
            remote_socket.close()
            print "[*] No more data. Closing connections."
            
            break

# this is a pretty hexdump function taken from the comments here:
# http://code.activestate.com/recipes/142812-hex-dumper/
def hexdump(src, length=16):
    result = []
    digits = 4 if isinstance(src, unicode) else 2
    for i in xrange(0, len(src), length):
        s = src[i:i+length]
        hexa = b' '.join(["%0*X" % (digits, ord(x)) for x in s])
        text = b''.join([x if 0x20 <= ord(x) < 0x7F else b'.' for x in s])
        result.append( b"%04X   %=*s   %s" % (i, length*(digits + 1), hexa, text) )
    print b'\n'.join(result)

def receive_from(connction):
    buffer= ""
    
    # we set a 2 second timeout; depending on target, 
    # this may need to be adjusted 
    connection.settimeout(2)
    try:
        while True:
            data = connection.recv(4096)
            if not data:
                break
            buffer += data
    except:
        pass
    return buffer

# Modify any requests destined for the remote host
def request_handler(buffer):
    #perform packet modifications
    return buffer

# Modify any responses destined for the local host
def response_handler(buffer):
    #perform packet modifications
    return buffer

        

main()