vwtp_tracer.py

#!/usr/bin/env python3

#import tracer
import can
import util
import struct
import sniff.vw

#NOTE: this is designed for tracing *RAW VWTP SESSIONS*.
#there is *NO* higher-level protocol decoding implemented here.
#since VWTP borrows the CAN concept of "Message ID" for addressing,
#there is no easy way to associate multiple connections without seeing the start-up procedures
#or manual correllation with candump or wireshark.
#fortunately, VWTP includes explicit end-of-packet opcodes, so synchonizing recv buffers with the transmitter
#is relatively painless

class VWTPConnection:
  def __init__(self, num):
    self.num = hex(num) #we don't do any math on it, so we can stringify it here.
    self.framebuf = None
    self.framelen = 0
    self.start = True
    self.blksize = None
    self.seq = 0
  def _recv(self, msg):
    buf = msg.data #the raw buffer contents of a CAN frame.
    op = buf[0]
    buf = buf[1:] #drop the opcode from the frame.
    if op == 0xA8: #disconnect
      self.close()
    elif op == 0xA3: #"ping"
      util.log(5,"[{}] Ping!".format(self.num))
    elif op  == 0xA1: #params response, also sent as a "Pong!"
      if self.blksize:
        util.log(6,"[{}] Pong!".format(self.num)) #already configured, so it's a pong.
        #util.log(3,"[{}] Potential connection fault: recieved 'parameter response' when already configured!".format(self.num))
        return
      self.blksize = buf[0] + 1 # 0 is "1 frame" #we don't actually *use* this, other than "config or pong?"
      scale = [ .1, 1, 10, 100]
      acktime = buf[1] >> 6 #scale is 100ms, 10ms, 1ms, .1ms
      acktime = (scale[acktime] * (buf[1] & 0x3F)) * 0.001 #go from ms to s.
      packival = (scale[buf[3] >> 6] * (buf[3] & 0x3F)) * 0.001
      util.log(5,"[{}] Parameter response received.".format(self.num))
      util.log(6,"channel parameters:",
          "\nTimeout in ms:",acktime * 1000,"\nMinimum Interval between frames in ms:",packival * 1000,"\nBlock Size:",self.blksize)
    elif op & 0xf0 == 0xB0 or op & 0xf0 == 0x90:
      util.log(5,"[{}] Acked block".format(self.num))
    else: #assume it's a data packet.
      seq = op & 0x0f
      if op & 0x20 == 0 and seq == self.seq: #expecting ACK
        util.log(5,"[{}] Expecting Ack".format(self.num))
      self.seq += 1
      if self.seq == 0x10:
        self.seq = 0
      if not self.framebuf: #first frame of a transaction
        util.log(5,"[{}] Frame start".format(self.num))
        if op & 0x10 == 0x10:
          util.log(5,"[{}] Short frame".format(self.num))
          self.recv(bytes(buf)) #single-frame short-circuit
          self.framebuf = None
          return
        self.framebuf = bytearray()
        self.framebuf += buf #the length is only a feature of VWTP/KWP, and is not part of VWTP itself.
      else:
        util.log(6,"[{}] Subframe recieved".format(self.num))
        self.framebuf += buf
      if op & 0x10 == 0x10: #final subframe
        util.log(5,"[{}] Received frame finalizer".format(self.num))
#        if self.framelen != len(self.framebuf) and not self.start: #already synchronized
#          util.log(3,"[{}] Frame length mismatch! expected {}, got {}. Attempting to continue...".format(self.num,self.framelen, len(self.framebuf)))
#        elif self.framelen != len(self.framebuf) and self.start: #not synced, may have started in middle of frame
#          util.log(4,"[{}] First frame is partial, now fully synchronized".format(self.num))
        self.start = False
        self.recv(bytes(self.framebuf))
        self.framebuf = None
  def close(self):
    self.blksize = None
    util.log(5,"[{}] Disconnect".format(self.num))
  def recv(self, frame):
    util.log(4,"[{}] Received VWTP Message:".format(self.num),repr(frame))

if __name__ == "__main__":
  sessions = {}

  try:
    with open("config.json", "r") as fd:
      opts = json.loads(fd.read())
  except FileNotFound: #write default config.
    opts = { "channel":"can0", "bustype":"socketcan"}
    with open("config.json", 'w') as fd:
      fd.write(json.dumps(opts))
  sock = can.interface.Bus(**opts)
  while True:
    msg = sock.recv()
    if not msg.arbitration_id in sessions:
      if msg.arbitration_id > 0x660:
        sessions[msg.arbitration_id] = VWTPConnection(msg.arbitration_id)
    if msg.arbitration_id > 0x660:
      sessions[msg.arbitration_id]._recv(msg)
    else:
      if msg.arbitration_id in sniff.vw.models["3C"]:
        util.log(5, sniff.vw.models["3C"].repr(msg))
      else:
        util.log(6,"Untracked frame from address '{}'".format(msg.arbitration_id))