Handling custom headers on the server

[Baryshych]

Hi! I have an issue with my js client sending requests with custom metadata:

commentsClient.getComments(request, metadata, function (err, res) {

I'm using lazy init (as shown in README)

  GRPCWeb.handle(CommentsService::Service) do
    require_relative '../../app/grpc/services/comments_service.rb'
    GetCommentsService.new
  end

and my _call argument is always nil

def get_comments(request, _call = nil)
    return CommentResponse.new(comment: "Hello #{request.resourceId}")

As I have seen in the Golang implementation of GRPC-web, they access headers through the _call argument. I've briefly read sources (so I might be completely wrong, sorry in advance), and its look like

Is it possible to access env or headers is the service implementation?