Is there an existing issue for this?

• I have searched the existing issues

Kong version (3.9.0)

3.9.0

Current Behavior

I have grpc-gateway plugin enabled for a grpc backend service with http mappings defined in the proto file.
The error proto3 disallow 'optional' label is shown in kong logs when making an Http request to a rpc method with optional labeled field in the request.

kong-1               | 2025/04/11 17:49:53 [error] 1411#0: *6441 [kong] init.lua:406 [grpc-gateway] /usr/local/share/lua/5.1/protoc.lua:651: /protos/proto/feature-a/v1/feature-a-health.proto:23:12: proto3 disallow 'optional' label, client: 192.168.65.1

I experimented and found that adding this line to function _M.new() in kong/tools/grpc.lua fixes the error

  protoc_instance.proto3_optional = true

Expected Behavior

grpc-gateway should successfully load the proto file and route the http request to the rpc method

Steps To Reproduce

kong.yaml

  - name: feature-a-user
    protocol: grpc
    host: grpc-example
    port: 50051
    routes:
      - name: feature-a-user
        protocols:
          - http
        paths:
          - /v1/feature-a/user/
        strip_path: true
        plugins:
          - name: grpc-gateway
            config:
              proto: feature-a/v1/feature-a-user.proto

feature-a-user.proto

syntax = "proto3";

package feature.user.v1;

import "google/api/annotations.proto";

service User {
  rpc UpdateUser (UpdateUserRequest) returns (UpdateUserResponse) {
    option (google.api.http) = {
      patch: "/v1/feature-a/user/{id}"
      body: "*"
    };
  }
}

message UpdateUserRequest {
  string id = 1;
  optional string name = 2;
  optional string email = 3;
}

Http request

curl -X PATCH 0.0.0.0:8000/v1/feature-a/user/1 -d '{"name": "test"}'

Anything else?

I tried to push a branch to this repo with the change to grpc.lua, however I am getting permission denied. I can make the PR if I'm granted permissions to push branches and create PRs