core/src/main/java/com/twitter/elephantbird/mapreduce/io/BinaryBlockReader.java
public boolean readNextProtoBytes(BytesWritable writable) throws IOException {
    byte[] blob = readNextProtoBytes();
    if (blob != null) {
      writable.set(blob, 0, blob.length);
      return true;
    }
    return false;
  }
public boolean readNextProtoBytes(BytesWritable writable) throws IOException {
    byte[] blob = readNextProtoBytes();
    if (blob != null) {
      writable.set(blob, 0, blob.length);
      return true;
    }
    return false;
  }
returns true if bytes for next object are written to writable, false
other wise.