@Override
  public void writeTo(AsyncWritableChannel channel, Callback<Long> callback) {
    // TODO: read from cloud based store and write to AsyncWritableChannel is needed in the future.
    throw new UnsupportedOperationException();
  }
An implementation of {@code MessageReadSet} for cloud based storage
ambry-cloud/src/main/java/com/github/ambry/cloud/CloudMessageReadSet.java