how to add static(html,js) files for grpc - go

Question

I have a grpc client and server. I have a protofile. I am using a grpc gateway and I want to use html for the client. There is a path localhost:8081/test, I would like it to be an html file when I go through this path. How can I tell the handler to give the html file in the response?
what should the handler look like?
syntax = "proto3";
option go_package = "/go_proto";
package api;
import "google/api/annotations.proto";
service authorization{
rpc Test(testRequest) returns (testResponse){
option(google.api.http) = {
get: "/test"
};
}
}
message testRequest{
}
message testResponse{
int32 arg1 = 1;
}

Answer 1

If I understand your question correctly, you cannot (directly).
gRPC Gateway is one way (Envoy's gRPC-JSON transcoder is another) to expose gRPC services as (JSON) REST APIs.
In your example, the above solutions will enable you to make HTTP GET calls against /test returning a JSON representation of testResponse ({"arg1":...}).
If you want to serve HTML, see Adding custom routes to the mux this would allow you to write a handler that serves HTML.
NOTE This HTML handler could include JavaScript that uses e.g. fetch to GET the /testendpoint.
Have a look at gRPC-Web too. This requires Node.JS but it provides a gRPC client for JavaScript as an alternative to the REST client described above.
If you want to expose gRPC services with REST APIs, then use gRPC Gateway or Envoy's gRPC-JSON transcoder. This gives you the ability to have clients that use gRPC and REST.
If you want to have only gRPC clients, gRPC-Web gives Node.JS developers access to your gRPC services too.