Module which deals with records needs to be given as input to unary RPC call. This can be presented as a tuple to the Options list that is passed to grpc_client:unary().

{msgs_as_records,ModuleName}.

And user is expeced to generate records based header file using gpb. This can be out of the scope of grpc_client API.

For example for our route_guide example:

Point = #'Point'{
    latitude = 409146138,
    longitude = -746188906
},
Return = route_guide_client:'GetFeature'(Connection, Point, [{msgs_as_records,route_guide_pb}]).

API Return will also include a record:

{ok,#{grpc_status => 0,
      headers => #{<<":status">> => <<"200">>},
      http_status => 200,
      result =>
          {'Feature',<<"Berkshire Valley Management Area Trail, Jefferson, NJ, USA">>,
                     {'Point',409146138,-746188906}},
      status_message => <<>>,
      trailers => #{<<"grpc-status">> => <<"0">>}}}

Details of this request in "Issue 3".

 With this code, user can create a streaming RPC connection by specifying how messages have to be deliverd.

 {ok, Stream} = grpc_client:new_stream(Connection, 'RouteGuide', 'RouteChat', route_guide, [{async_notification, self()}]).

 And when a notification arrives on the stream, a message of the following form {notification,Response} will be delivered to the calling process.

Specs to reflect message to be of type tuple (records) or map

As per code review comment, update notification sent to registered clients as {grpc_notification,Response}