Pattern match on channel on stub functions (#354)

Provides a better error for invalid argument

Co-authored-by: Paulo Valente <[email protected]>

lib/grpc/stub.ex

@@ -78,7 +78,7 @@ defmodule GRPC.Stub do
         }
 
         if req_stream do
-          def unquote(String.to_atom(func_name))(channel, opts \\ []) do
+          def unquote(String.to_atom(func_name))(%GRPC.Channel{} = channel, opts \\ []) do
             GRPC.Stub.call(
               unquote(service_mod),
               unquote(Macro.escape(rpc)),
@@ -88,7 +88,7 @@ defmodule GRPC.Stub do
             )
           end
         else
-          def unquote(String.to_atom(func_name))(channel, request, opts \\ []) do
+          def unquote(String.to_atom(func_name))(%GRPC.Channel{} = channel, request, opts \\ []) do
             GRPC.Stub.call(
               unquote(service_mod),
               unquote(Macro.escape(rpc)),

test/grpc/integration/stub_test.exs

@@ -68,6 +68,14 @@ defmodule GRPC.Integration.StubTest do
     end)
   end
 
+  test "invalid channel function clause error" do
+    req = Helloworld.HelloRequest.new(name: "GRPC")
+
+    assert_raise FunctionClauseError, ~r/Helloworld.Greeter.Stub.say_hello/, fn ->
+      Helloworld.Greeter.Stub.say_hello(nil, req)
+    end
+  end
+
   test "returns error when timeout" do
     run_server(SlowServer, fn port ->
       {:ok, channel} = GRPC.Stub.connect("localhost:#{port}")