docs: public long writeLogTo(long start, Writer w) throws IOException {
          CountingOutputStream os = new CountingOutputStream(new WriterOutputStream(w));
  
          try (Session f = source.open()) {
              f.skip(start);
  
              if (completed) {
                  // write everything till EOF
                  byte[] buf = new byte[1024];
                  int sz;
                  while ((sz = f.read(buf)) >= 0)
                      os.write(buf, 0, sz);
              } else {
                  ByteBuf buf = new ByteBuf(null, f);
                  HeadMark head = new HeadMark(buf);
                  TailMark tail = new TailMark(buf);
  
                  while (tail.moveToNextLine(f)) {
                      head.moveTo(tail, os);
                  }
                  head.finish(os);
              }
          }
          os.flush();
  
          return os.getCount()+start;
      }