code: private void writeTrailer(byte[] buf, int offset) throws IOException {
          writeInt((int)crc.getValue(), buf, offset); // CRC-32 of uncompr. data
          writeInt(def.getTotalIn(), buf, offset + 4); // Number of uncompr. bytes
      }
docs: /*
  Writes GZIP member trailer to a byte array, starting at a given
  offset.