BlockReader constructor

BlockReader(Uint8List buffer, { int offset = 0, int? length, bool verifyChecksum = true, })

Parses a block starting at offset; length defaults to the rest of buffer.

Implementation

factory BlockReader(
  Uint8List buffer, {
  int offset = 0,
  int? length,
  bool verifyChecksum = true,
}) {
  final end = length == null ? buffer.length : offset + length;
  if (end > buffer.length || end - offset < blockHeaderSize) {
    throw VxsFormatException('block shorter than its header', offset: offset);
  }
  if (buffer[offset] != blockMagic) {
    throw VxsFormatException(
      'bad block magic 0x${buffer[offset].toRadixString(16)}',
      offset: offset,
    );
  }
  if (buffer[offset + 1] != blockVersion) {
    throw VxsFormatException(
      'unsupported block version ${buffer[offset + 1]}',
      offset: offset,
    );
  }
  final flags = buffer[offset + 2];
  if (flags & ~blockFlagCrc32c != 0 || buffer[offset + 3] != 0) {
    throw VxsFormatException(
      'reserved block header bits set',
      offset: offset,
    );
  }
  final hasCrc = flags & blockFlagCrc32c != 0;
  final payloadStart = offset + blockHeaderSize;
  final payloadEnd = end - (hasCrc ? 4 : 0);
  if (payloadEnd < payloadStart) {
    throw VxsFormatException('block has no payload', offset: offset);
  }
  if (hasCrc && verifyChecksum) {
    final stored = VxsLe.u32(buffer, payloadEnd);
    final actual = VxsCrc32c.compute(buffer, payloadStart, payloadEnd);
    if (stored != actual) {
      throw VxsFormatException(
        'block checksum mismatch: stored 0x${stored.toRadixString(16)}, '
        'computed 0x${actual.toRadixString(16)}',
        offset: payloadEnd,
      );
    }
  }
  return BlockReader._(buffer, offset, payloadStart, payloadEnd, flags);
}