code: public void backup(OutputStream os) throws IOException {
      int count = 0;
      GzipCompressorOutputStream zipStream = new GzipCompressorOutputStream(os);
      for (Master master : mRegistry.getServers()) {
        Iterator<JournalEntry> it = master.getJournalEntryIterator();
        while (it.hasNext()) {
          it.next().toBuilder().clearSequenceNumber().build().writeDelimitedTo(zipStream);
          count++;
        }
      }
      // finish() instead of close() since close would close os, which is owned by the caller.
      zipStream.finish();
      LOG.info("Created backup with {} entries", count);
    }
docs: Writes a backup to the specified stream.
  
  @param os the stream to write to