xplnedsf.py

import struct
import os
import hashlib


def read_dsf(filename):
    size = os.stat(filename).st_size
    footer_start = size - 16  # 16 byte (128bit) for md5 hash
    digest = hashlib.md5()
    with open(filename, 'rb') as f:
        # read 8s = 8 byte string, and "i" = 1 32 bit integer (total: 12 bytes)
        raw_header = f.read(12)
        header, version = struct.unpack('<8si', raw_header)
        digest.update(raw_header)
        
        if header != b'XPLNEDSF':
            raise ValueError('Not a valid XPLNEDSF file')
        if version != 1:
            raise ValueError('Only version 1 supported')
        
        while f.tell() < footer_start:
            raw_atom_header = f.read(8)
            digest.update(raw_atom_header)
            # 32bit atom id + 32 bit atom_size.. total: 8 byte
            atom_id, atom_size = struct.unpack('<ii', raw_atom_header)
            #atom_id = struct.pack('>i', atom_id) 'DAEH' -> 'HEAD'
            
            # data size is atom_size excluding the just read 8 byte id+size header
            atom_data = f.read(atom_size - 8)
            digest.update(atom_data)
            yield atom_id, atom_size, atom_data
        
        checksum = f.read()
        if checksum != digest.digest():
            raise ValueError('checksum mismatch!')


for atom_id, atom_size, atom_data in read_dsf('mesh.dsf'):
    print((atom_id, atom_size, atom_data))