adopt proto3 optional - explicit field presence

[eric846]

proto3 has restored optional, so for a field

syntax = "proto3";
message X {
  optional bool mybool = 1;
}

we regain the ability to distinguish between

• primitive field unset (has_mybool() false)
• primitive field explicitly set to default value (has_mybool() true, mybool() false)

as in proto2.

optional is optional. If a field is marked optional in proto3, we get the proto2 behavior.

See https://developers.google.com/protocol-buffers/docs/proto3#specifying_field_rules.

We should consider adopting optional, moving away from wrappers like google.protobuf.UInt32Value.

If we created a clean proto, it could just be like:

syntax = "proto3";
message BenchmarkSpec {
  optional uint32 requests_per_second = 1 [(validate.rules).uint32 = {gte: 1, lte: 1000000}];
  optional uint32 connections = 2 [(validate.rules).uint32 = {gte: 1, lte: 1000000}];
  // ...

The gRPC service would be surprisingly easy to update. Maybe:

message StartRequest {
  oneof opts {
    CommandLineOptions options = 1;
    BenchmarkSpec benchmark_spec = 2;
  }
}