title: How to define a GRPC service method without request parameter?
body: <p>Normally definde a GRPC method as follows which has a request parameter <code>HelloRequest</code>:</p>
  <pre class="lang-java prettyprint-override"><code>// The greeting service definition.
  service Greeter {
    // Sends a greeting
    rpc SayHello (HelloRequest) returns (HelloReply) {}
  }
  
  // The request message containing the user's name.
  message HelloRequest {
    string name = 1;
  }
  
  // The response message containing the greetings
  message HelloReply {
    string message = 1;
  }
  </code></pre>
  <p>But how to define a method without request parameter as following <code>SayHello</code> method:</p>
  <pre class="lang-java prettyprint-override"><code>// The greeting service definition.
  service Greeter {
    // Sends a greeting
    rpc SayHello () returns (HelloReply) {}
  }
  
  
  // The response message containing the greetings
  message HelloReply {
    string message = 1;
  }
  </code></pre>