Support access to MethodOptions fields at runtime

[arbassett]

Feature Request

Crates

tonic-build

Motivation

the option field in methods can be used to access contextual information. an example of this would required permissions

syntax = "proto3";

package teams;

import "annotations.proto";

service Teams {
  rpc CreateTeam  (CreateTeamReq) returns (CreateTeamRes) {
    option (annotation.policy).resource = "teams";
    option (annotation.policy).action = "teams:create";
  }
}

message CreateTeamReq {
}

message CreateTeamRes {
}

Having access to this information at runtime would allow building a interceptor that can generically authorize the request before build called

Proposal

Add option values to request.

This should probably be hidden behind a option in the Builder. ideally this could also include whitelisting options. (example to not include googles grpc http transcoding annotations)

prost seems to already support getting option values for methods via the options.uninterpreted_option

some potential issues may be dealing with multiple files and tracking imports. with the example above there is 3 files used

• teams.proto
• annotations.proto
• policy.proto

the annotations.proto just defines the MethodData while policy.proto contains the message

// annotations.proto
syntax = "proto3";

package annotation;

import "policy.proto";
import "google/protobuf/descriptor.proto";

extend google.protobuf.MethodOptions {
  policy.PolicyInfo policy = 50001;
}

// policy.proto
syntax = "proto3";

package policy;

message PolicyInfo {
  string resource = 1;
  string action = 2;
};

tonic-build has no issue with building this example with annotations.rs being a empty file and policy.rs containing just 1 struct for the message

edit: originally I said the values should be added into metadata but that wouldn't make sense as metadata is for binary and ascii data. after looking around this request also seems related to #255 as the values would have to be stored in something like anymap or http::extentions