title: How to use json as a structure member in protobuf or grpc?
body: <p>When develop with javascript we always need to transport json with rpc. Now I want to use json as structure member of message in grpc. Please see below:</p>
  
  <pre><code>message HelloRequest{
      int32 hello = 1;
      json world = 2
  } 
  </code></pre>
  
  <p>How to do that?</p>