parseHeader static method

ShieldHeader parseHeader(Uint8List encryptedBytes)

Parses the encrypted asset header (V3 only).

Implementation

static ShieldHeader parseHeader(Uint8List encryptedBytes) {
  if (encryptedBytes.lengthInBytes < 28) {
    throw const FormatException('Encrypted asset is too short.');
  }
  for (var i = 0; i < _magic.length; i++) {
    if (encryptedBytes[i] != _magic[i]) {
      throw const FormatException('Invalid asset header.');
    }
  }

  final version = encryptedBytes[4];
  if (version != _version4) {
    throw FormatException('Unsupported asset version: $version.');
  }

  final flags = encryptedBytes[5];
  final algo = encryptedBytes[6];
  final ivLength = encryptedBytes[7];
  if (ivLength != _ivLength) {
    throw const FormatException('Invalid IV length.');
  }

  final chunkSize = _readUint32Le(encryptedBytes, 8);
  final originalLength = _readUint32Le(encryptedBytes, 12);
  final iv = Uint8List.sublistView(encryptedBytes, 16, 16 + _ivLength);

  return ShieldHeader(
    version: version,
    compressed: (flags & 0x01) != 0,
    algorithm: algo,
    chunkSize: chunkSize,
    originalLength: originalLength,
    baseIv: iv,
  );
}