TCP Server with netcat

import sys
import socket 
import getopt
import threading 
import subprocess 

listen   = False
command   = False
upload    = False
execute   = ""
target    = ""
upload_destination = ""
port    = 0

def usage():
 print "BHP Net Tool"
 print 
 print "Usage: bhpnet.py -t target_host -p port"
 print "-l --listen    - listen on [host]:[port] for incoming connections"
 print "-e --execute=file_to_run  - execute the given file upon receiving a connections"
 print "-c --command   - initialize a command shell"
 print "-u --upload=destination  - upon receiving connection upload a file and write to [destination]"
 print 
 print 
 print "Examples: "
 print "bhpnet.py -t 192.168.0.1 -p 5555 -l -c"
 print "bhpnet.py -t 192.168.0.1 -p 5555 -l -u=c:\\target.exe"
 print "bhpnet.py -t 192.169.0.1 -p 5555 -l -e=\"cat /etc/passwd\""
 print "echo 'ABCDEFGHI' | ./bhpnet.py -t 192.168.11.12 -p 135"
 sys.exit();

def client_sender(buffer):

 client = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
 
 try:
  client.connect((target,port))

  if len(buffer):
   client.send(buffer)
  while True:
   recv_len = 1
   response = ""

   while recv_len: 
    data    = client.recv(4096)
    recv_len   = len(data)
    response  += data 

    if recv_len < 4096:
     break
   print response,

   buffer  = raw_input("")
   buffer += "\n"
   
   client.send(buffer)

 except:
  print "[*] Exception! Exiting."
  
  client.close()

def server_loop():
 global target
 
 if not len(target):
  target = "0.0.0.0"

 server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
 server.bind((target,port))
 server.listen(5)

 while True:
  client_socket, addr = server.accept()

  client_thread = threading.Thread(target=client_handler,
  args = (client_socket,))
  client_thread.start()

def run_command(command):
 command = command.rstrip()

 try:
  output = subprocess.check_output(command,stdrr=subprocess.STDOUT, shell=True)
 except:
  output = "Failed to execute command.\r\n"

 return output

def client_handler(client_socket):
 global upload
 global execute
 global command

 if len(upload_destination):
  file_buffer = ""

  while True:
   data = client_socket.recv(1024)

   if not data:
    break
   else:
    file_buffer += data
  
  try:
   file_descriptor = open(upload_destination,"wb")
   file_descriptor.write(file_buffer)
   file_descriptor.close()

   client_socket.send("Successfully saved file to %s\r\n" % upload_destination)
  except:
   client_socket.send("Failed to save file to %s\r\n" % upload_destination)

 if len(execute):
  output = run_command(execute)

  client_socket.send(output)
 
 if command:

  while True:
   client_socket.send("<BHP:#> ")

   cmd_buffer = ""
   while "\n" not in cmd_buffer:
    cmd_buffer += client_socket.recv(1024)

   response = run_command(cmd_buffer)

   client_socket.send(response)

def main():
 global listen
 global port
 global execute 
 global command
 global upload_destination
 global target
 
 if not len(sys.argv[1:]):
  usage()
 try:
  opts, args = getopt.getopt(sys.argv[1:],"hle:t:p:cu:", ["help","listen","execute","target","port","command","upload"])
 except getopt.GetoptError as err:
  print str(err)
  usage()
 
 for o,a in opts:
  if o in ("-h","--help"):
   usage()
  elif o in ("-l","--listen"):
   listen = True
  elif o in ("-e","--execute"):
   execute = a
  elif o in ("-c","--commandshell"):
   command = True
  elif o in ("-u","--upload"):
   upload_destination = a
  elif o in ("-t","--target"):
   target = a
  elif o in ("-p","--port"):
   port = int(a)
  else:
   assert False,"Unhandled Option"
 
 if not listen and len(target) and port > 0:
  buffer = sys.stdin.read()
  client_sender(buffer)

 if listen:
  server_loop()
main()