@Override
public void onDataAvailable(DataEmitter emitter, ByteBufferList bb) {
if (bb != null) totalRead += bb.remaining();
Util.emitAllData(this, bb);
if (bb != null) totalRead -= bb.remaining();
if (tracker != null && bb != null) tracker.onData(totalRead);
// if there's data after the emitting, and it is paused... the underlying implementation
// is obligated to cache the byte buffer list.
}
