ethtag.py

#!/usr/bin/env python
import dpkt,sys
import binascii
import json
import caneton

if not len(sys.argv) == 3:
    print("USAGE: "+sys.argv[0]+" candata.cap dbcfile.json")
    print("outputs to stdout")
    sys.exit(1)

capFile = open(sys.argv[1],'r')
with open(sys.argv[2]) as dbc_file:
    dbc_json = json.loads(dbc_file.read())

pcap = dpkt.pcap.Reader(capFile)
for ts, buf in pcap:
    print ts,
    eth = dpkt.sll.SLL(buf)
    ip = eth.data
    udp = ip.data
    if isinstance (udp, dpkt.udp.UDP):
        if udp.sport == 20100:
            packet=''.join(x.encode('hex') for x in str(udp))
            message_id = int(packet[20:24],16)
            message_data = binascii.unhexlify(packet[24:])
            message_length = len(packet[24:]) / 2 # half the number number of hex characters
            try:
                message = caneton.message_decode(message_id, message_length, message_data, dbc_json)
                print(message)
            except:
                print(packet+'    decode failed ID: 0x'+packet[20:24])
        else:
            print "x"
    else:
        print "x"