ZipFileHeader constructor Null safety

Implementation

ZipFileHeader([InputStreamBase? input, InputStreamBase? bytes,
               String? password]) {
  if (input != null) {
    versionMadeBy = input.readUint16();
    versionNeededToExtract = input.readUint16();
    generalPurposeBitFlag = input.readUint16();
    compressionMethod = input.readUint16();
    lastModifiedFileTime = input.readUint16();
    lastModifiedFileDate = input.readUint16();
    crc32 = input.readUint32();
    compressedSize = input.readUint32();
    uncompressedSize = input.readUint32();
    final fnameLen = input.readUint16();
    final extraLen = input.readUint16();
    final commentLen = input.readUint16();
    diskNumberStart = input.readUint16();
    internalFileAttributes = input.readUint16();
    externalFileAttributes = input.readUint32();
    localHeaderOffset = input.readUint32();

    if (fnameLen > 0) {
      filename = input.readString(size: fnameLen);
    }

    if (extraLen > 0) {
      final extra = input.readBytes(extraLen);
      extraField = extra.toUint8List();
      // Rewind to start of the extra fields to read field by field.
      extra.rewind(extraLen);

      final id = extra.readUint16();
      var size = extra.readUint16();
      if (id == 1) {
        // Zip64 extended information
        // The following is the layout of the zip64 extended
        // information "extra" block. If one of the size or
        // offset fields in the Local or Central directory
        // record is too small to hold the required data,
        // a Zip64 extended information record is created.
        // The order of the fields in the zip64 extended
        // information record is fixed, but the fields MUST
        // only appear if the corresponding Local or Central
        // directory record field is set to 0xFFFF or 0xFFFFFFFF.
        // Original
        // Size       8 bytes    Original uncompressed file size
        // Compressed
        // Size       8 bytes    Size of compressed data
        // Relative Header
        // Offset     8 bytes    Offset of local header record
        // Disk Start
        // Number     4 bytes    Number of the disk on which
        // this file starts
        if (size >= 8 && uncompressedSize == 0xFFFFFFFF) {
          uncompressedSize = extra.readUint64();
          size -= 8;
        }
        if (size >= 8 && compressedSize == 0xFFFFFFFF) {
          compressedSize = extra.readUint64();
          size -= 8;
        }
        if (size >= 8 && localHeaderOffset == 0xFFFFFFFF) {
          localHeaderOffset = extra.readUint64();
          size -= 8;
        }
        if (size >= 4 && diskNumberStart == 0xFFFF) {
          diskNumberStart = extra.readUint32();
          size -= 4;
        }
      }
    }

    if (commentLen > 0) {
      fileComment = input.readString(size: commentLen);
    }

    if (bytes != null) {
      bytes.position = localHeaderOffset!;
      file = ZipFile(bytes, this, password);
    }
  }
}