Python TCP Server & Keyboard Emulation

Using Python 3.2.2 to receive commands over TCP, emulate keypresses, and run commands. Sounds complex but the script is short & not too crazy. I did this on Windows 7 but it should work fine on other versions of Windows or python.

First lets emulate some key presses. This uses a wrapper[ish] for user32.dll, which is a really handy windows library!

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import ctypes
user32 = ctypes.windll.user32

KEY_LEFT_WIN = 0x5B

user32.keybd_event(KEY_LEFT_WIN, 0,0,0) # press
user32.keybd_event(KEY_LEFT_WIN, 0,2,0) # release 

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No sweat! Full key (and mouse) code list at the bottom.

I also wanted keys to be pressed as a result of some incoming network data, so I needed to listen on a TCP socket:

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#!/usr/bin/env python

import socket

LISTEN_ADDRESS = ''
LISTEN_PORT = 12345
BUFFER_SIZE = 512

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.bind((LISTEN_ADDRESS, LISTEN_PORT))
print("Starting server on port", LISTEN_PORT)
s.listen(1)

while True:
    conn, addr = s.accept()
    print('Connection address:', addr)
    while True:
        data = conn.recv(BUFFER_SIZE)
        if not data: break
        if data == b'\x03': break # control+C
        print("received data:", data)
        conn.send(data)  # echo
    print("Client disconnected")
    conn.close()
print("Exit")
 

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Yes I agree, string formatting for python 3 is weird. One note here, the data comming in for me was ASCII text, which python 3.0+ considers to be data (not a string). To make it a string use the function bytes.decode(my_data).

Why use port 23? All of you old-timers reading this may remember a protocol called Telnet, which happens to run on port 23. All Telnet does is create a TCP connection and then send to/from the other host, displaying the data. What this means is you can connect to this python server using Telnet and just type commands! Of course, you could still write your own client if you wanted to.

That's pretty much it though. The script also runs system commands in a new thread (so they don't block) but that part was a one-liner. Here's the script in all it's glory:

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#!/usr/bin/env python

import os
import sys
import socket
import ctypes
from threading import Thread # we'll run commands in a new thread, just in case they block

# Used to listen for connections
LISTEN_ADDRESS = ''
LISTEN_PORT = 12345
BUFFER_SIZE = 512

# Used for emulating key presses.
user32 = ctypes.windll.user32
# Virtual keys
VK_VOLUME_MUTE = 0xAD
VK_VOLUME_DOWN = 0xAE
VK_VOLUME_UP = 0xAF
VK_MEDIA_NEXT_TRACK = 0xB0
VK_MEDIA_PREV_TRACK = 0xB1
VK_MEDIA_STOP = 0xB2
VK_MEDIA_PLAY_PAUSE = 0xB3

# NOTE: bug in python, if using os.system(my_str) where my_str 
#       contains at least 2 sets of quotes, your must prefix "call" (windows only)
# Playlists
playlist_local = "call \"C:\\program files\\Windows Media Player\\wmplayer.exe\" /playlist \"Party - Jan2012\""
playlist_eh = "\"C:\\program files\\Windows Media Player\\wmplayer.exe\" http://scfire-ntc-aa04.stream.aol.com:80/stream/1025"
playlist_dm = "\"C:\\program files\\Windows Media Player\\wmplayer.exe\" http://80.94.69.106:6104/"

# Mapping expected input to actions
bytes_to_keys = {}
bytes_to_keys["1"] = VK_MEDIA_PLAY_PAUSE
bytes_to_keys["2"] = VK_MEDIA_NEXT_TRACK
bytes_to_keys["3"] = VK_MEDIA_PREV_TRACK
bytes_to_keys["4"] = VK_MEDIA_STOP
bytes_to_commands = {}
bytes_to_commands["a"] = playlist_local
bytes_to_commands["b"] = playlist_eh
bytes_to_commands["c"] = playlist_dm



def run_command(cmd):
    os.system(cmd)

def do_action(char):
    '''Takes a 1-character code and executes the action assoliated with it'''
    if char in bytes_to_keys:
        key_code = bytes_to_keys[char]
        user32.keybd_event(key_code, 0, 0, 0) # press
        user32.keybd_event(key_code, 0, 2, 0) # release
    elif char in bytes_to_commands:
        command = bytes_to_commands[char]
        # print("running command:", command)
        Thread(target=run_command, args=(command,)).start()
    else:
        print("unknown instruction:", char)


##########################################
################## Main ##################
##########################################

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.bind((LISTEN_ADDRESS, LISTEN_PORT))
print("Starting server on port", LISTEN_PORT)
s.listen(1)


while True:
    conn, addr = s.accept()
    print('Connection address:', addr)
    try:
        while True:
            data = conn.recv(BUFFER_SIZE)
            if not data: break
            str_data = bytes.decode(data) # data is non-unicode, but all python strings need to be
            print("received data: \"{0}\"".format(str_data))
            for char in str_data: # highly unlikely, but crazier things have happened
                do_action(char)
        print("Client disconnected")
    except socket.error as e:
        print("Socket error:", e)
    except socket.timeout:
        print("Connection timed-out")
    except Exception as e:
        print("Exception:", e)
    finally:
        conn.close()
print("Exit")

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Windows Virtual Key List - http://msdn.microsoft.com/en-us/library/windows/desktop/dd375731(v=vs.85).aspx
Windows Media Player Command Line Arguments - http://msdn.microsoft.com/en-us/library/windows/desktop/dd562624(v=vs.85).aspx
Python strings vs data - http://python.about.com/od/python30/ss/30_strings_3.htm