#!/usr/bin/env python
# -*- coding: utf-8 -*-
import errno
import functools
import tornado.ioloop
import socket
import struct


can_frame_fmt = "=IB3x8s"
can_frame_size = struct.calcsize(can_frame_fmt)

def build_can_frame(can_id, data):
    can_dlc = len(data)
    data = data.ljust(8, b'\x00')
    return struct.pack(can_frame_fmt, can_id, can_dlc, data)

def dissect_can_frame(frame):
    can_id, can_dlc, data = struct.unpack(can_frame_fmt, frame)
    return (can_id, can_dlc, data[:can_dlc])

def connection_ready(sock, fd, events):
    try:
      cf, addr = sock.recvfrom(can_frame_size)
    except BlockingIOError:
      self.logger.debug('Captured no data, socket in non-blocking mode.')
      return None
    except socket.timeout:
      self.logger.debug('Captured no data, socket read timed out.')
      return None

    dissect_can_frame(cf)


if __name__ == '__main__':
    sock = socket.socket(socket.AF_CAN, socket.SOCK_RAW, socket.CAN_RAW)
    sock.bind(('can0',))
    sock.setblocking(0)

    io_loop = tornado.ioloop.IOLoop.current()
    callback = functools.partial(connection_ready, sock)
    io_loop.add_handler(sock.fileno(), callback, io_loop.READ)
    io_loop.start()