I’m trying to write custom protobuf code generator using C++ (for JSON to gRPC transcoding). I’ve the following example proto file:

syntax = "proto3";

package test;

import "google/api/annotations.proto";

service Test {
  rpc TestCall (Request) returns (Response) {
    option (google.api.http) = {
      post: "/test.Test/TestCall/{query}"
      body: "*"
    };
  }
}

message Request {
  string query = 1;
  string language = 2;
}

message Response {
  float temperature = 2;
  int32 pressure = 3;
  string description = 4;
}

I got a MethodDescriptor and I want to get post and body options value from the descriptor like this (code is simplifyed):

const google::protobuf::FileDescriptor* file;
const google::protobuf::MethodDescriptor* descriptor = file->service(0)->method(0);
auto ext = descriptor->options().GetExtension(...);

Is it correct way at all? And I don’t know how correctly initialize ExtensionIdentifier to pass into GetExtension(...).

So how can I get options values from a generator code?

Thanks!