Handling Protocol Transformation

server {
  listen 80;
  server_name api.example.com;
  return 301 https://$host$request_uri;
}

service Users {
  rpc GetUser(GetUserRequest) returns (User) {
    option (google.api.http) = {
      get: "/v1/users/{id}"
    };
  }
  rpc CreateUser(User) returns (User) {
    option (google.api.http) = {
      post: "/v1/users"
      body: "*"
    };
  }
}

http_filters:
- name: envoy.filters.http.grpc_json_transcoder
  typed_config:
    "@type": type.googleapis.com/envoy.extensions.filters.http.grpc_json_transcoder.v3.GrpcJsonTranscoder
    proto_descriptor: /etc/proto/api.pb
    services: ["users.UserService"]
    print_options:
      add_whitespace: false
      always_print_primitive_fields: true

#[no_mangle]
pub fn on_http_request_headers(&mut self, _: usize) -> Action {
    if let Some(p) = self.get_http_request_header(":path") {
        if p.starts_with("/legacy/") {
            self.set_http_request_header(":path", Some(&p.replace("/legacy/", "/v2/")));
        }
    }
    Action::Continue
}