gdbrsp.py

import binascii
from gynvael_challanges import packet_parser

NOT_COMPLETE_SEQUENCE=255
BAD_PACKET=254

def checksum(packet):
    packet_sum=0
    for byte in packet:
        packet_sum+=byte
    return packet_sum % 256

def check_integrity(pkt):
    if checksum(pkt[1:-3]) != int(pkt[-2:],16):
        return False
    return True

def read_packet(packet):
    packet = binascii.unhexlify(packet)
    if(packet[-3] != 35):
        return NOT_COMPLETE_SEQUENCE
    correct_integrity = check_integrity(packet)
    if correct_integrity:
        return True
    else:
        return BAD_PACKET

def readfile(filepath):
    with open(filepath, 'r', encoding='windows-1252') as file:
        data = '\n'.join(file.readlines())
    return data

def decode_data(data):
    #data = data.strip()
    #data = binascii.unhexlify(data)
    data = data.split('\n')
    return data

data = decode_data(readfile(r'<input_file>')) #file should contain raw hex data
partial_packet=""
ignore_packet = False
response=False

with open(r'<output_file>','wb') as of:
    for packet in data:
        if partial_packet != "":
            # The packet contains an escape char
            packet = partial_packet+packet
            partial_packet=""
        if len(packet)>2 or ignore_packet:
            if int(packet[-2:],16) == ord('+'):
                packet=packet[:-1]
                response = False
            if int(packet[-2:],16) == ord('-'):
                next_packet = data.index(packet)+1
                ignore_packet = True
                print("[*] Packet {} was requested to be retransmitted. Ignoring it.".format(next_packet))
                response = False

            ignore_packet = False
            return_value = read_packet(packet)
            if return_value == BAD_PACKET:
                print("[*] Packet {} is corrupted".format(packet))
            elif return_value == NOT_COMPLETE_SEQUENCE:
                partial_packet = packet + '$'
            else:
                packet = packet[1*2:-3*2]
                if not packet == b'': #there is no point in sending an empty packet...
                    parser = packet_parser.parser(packet)
                    parsed_msg = parser.get_parsed_packet()()
                    of.write(parsed_msg + b'\n')