default void writeProtobufOutput(OutputStream os) throws IOException {
    // Creating an explicit CodedOutputStream for the following reasons :
    // 1. This avoids the cost of pre-computing the message size
    // 2. This lets us set the buffer size explicitly
    CodedOutputStream cos = CodedOutputStream.newInstance(os, BUFFER_SIZE);
    messageFromObject().writeTo(cos);
    cos.flush();
  }
Writes the protobuf represention of the model to os
hbase-rest/src/main/java/org/apache/hadoop/hbase/rest/ProtobufMessageHandler.java