code: protected static InputStream countingStream(InputStream in, int lookback) throws IOException {
          CountingInputStream cin = new CountingInputStream(in);
          cin.mark(lookback); 
          return cin;
      }
docs: A CountingInputStream is inserted to read compressed-offsets.
  
  @param in stream to wrap
  @param lookback tolerance of initial mark
  @return original stream wrapped in CountingInputStream
  @throws IOException