#!/usr/bin/env python
# Serial cable sniffer for discrete (single send and single receive style)
# serial communications with hex dump. Note you will need a serial cable
# sniffer (DIY schemes avaiable). 
# HOST -> DEVICE at /dev/ttyUSB0 and DEVICE -> HOST at /dev/ttyUSB1
# 
# NOTE: Use Cheap USB-to-Serial devices else you might run into trouble with
# 'smart' buffering and/or not clearing properly failing devices for example:
# - ID 0557:2008 ATEN International Co., Ltd UC-232A Serial Port [pl2303]
# 
# $Id: serial-sniffer.py 153 2010-07-15 20:21:48Z rick $
# Rick van der Zwet <info@rickvanderzwet.nl>
# license: BSD
import time
import signal
import os
import sys

DEBUG = True

# Stolen from http://snippets.dzone.com/posts/show/7682
# license: MIT License
class Watchdog(Exception):
  def __init__(self, time=5):
    self.time = time
  
  def __enter__(self):
    signal.signal(signal.SIGALRM, self.handler)
    signal.alarm(self.time)
  
  def __exit__(self, type, value, traceback):
    signal.alarm(0)
    
  def handler(self, signum, frame):
    raise self
  
  def __str__(self):
    return "The code you executed took more than %ds to complete" % self.time


send = open('/dev/ttyUSB0','rb', buffering=0)
recv = open('/dev/ttyUSB1','rb', buffering=0)
comment = open('/dev/stdin','r', buffering=0)

def str_to_hex(s):
   """Hexadecimal string representation of 's'"""
   return " ".join(["%02x" % ord(x) for x in s])

def perror(s):
   sys.stderr.write("[ERROR] %s\n" % s)

def pdebug(s):
   if DEBUG:
     sys.stderr.write("[DEBUG] %s\n" % s)

def main():
  while 1:

    # Async USB buffers get all data from sources
    send_buffer = ""
    recv_buffer = ""
    while send_buffer == "" or recv_buffer == "":
      if send_buffer == "":
        pdebug("trying to read send_buffer")
        while 1:
          try:
            with Watchdog(1):
              send_buffer += send.read(1)
          except Watchdog:
            pdebug("trying to read send_buffer")
            break
      else:
         pdebug("send_buffer filled %s" % str_to_hex(send_buffer))
  
      if recv_buffer == "":
        pdebug("trying to read recv_buffer")
        while 1:
          try:
            with Watchdog(5):
              recv_buffer += recv.read(1)
          except Watchdog:
            break
      else:
         pdebug("recv_buffer filled %s" % str_to_hex(recv_buffer))
  
    # Try to fetch comment if we have any
    comment_buffer = ""
    while 1:
      try:
        with Watchdog(1):
          comment_buffer += comment.read(1)
      except Watchdog:
        break
    
    prefix = "[%s] " % time.strftime("%H:%M:%S")
    print prefix + "Send: " + str_to_hex(send_buffer)
    print prefix + "Recv: " + str_to_hex(recv_buffer)
    print prefix + "Comm: " + comment_buffer
  
  send.close()
  recv.close()

if __name__ == "__main__":
  # Little hack to disable output from terminal which will later on be
  # processed and included in variable
  os.system('stty -echo')
  try:
    main()
  except KeyboardInterrupt: 
    pass 
  os.system('stty echo')