Protobuf RPC Service method without parameters

Question

I'm trying to describe an RPC service using Google's Protocol Buffers

service WhoamiService {   rpc WhoAreYou() returns (Whoami) {} }  message Whoami {   optional bytes request_id = 1;   optional string hostname = 2;   optional string message = 3; } 

When I try to compile this definition, I get an error Expected type name pointing to the WhoAreYou() piece.

It works fine if I replace WhoAreYou() with WhoAreYou(Whoami), but in this case, the method does not need any parameters.. Is there a way to do this or is it simply not supported?

Answer 1

You have to specify an input type. If you don't want the method to take any parameters, define an empty message type, like:

message WhoAreYouParams {} 

The reason this is required is so that if you later need to add an optional parameter, you can do so without breaking existing code.

Answer 2

You can specify google.protobuf.Empty instead of your own empty message. Example:

rpc WhoAreYou(google.protobuf.Empty) returns (Whoami) { } 

Don't forget to import appropriate proto file:

import "google/protobuf/empty.proto";