mgrpc: mock out workflow for generated code

The server unit test now manually mocks much of the generated code for a
given service, including back registration of the service. We avoid
having a package-level global descriptor in favor of a closures for the
handler dispatch function.

Signed-off-by: Stephen J Day <stephen.day@docker.com>

server_test.go

@@ -4,16 +4,40 @@ import (
 	"context"
 	"fmt"
 	"net"
+	"reflect"
 	"testing"
 
 	"github.com/gogo/protobuf/proto"
 )
 
-// var serverMethods = map[string]Handler{
-// 	"Create": HandlerFunc(func(ctx context.Context, req interface{}) (interface{}, error) {
+const serviceName = "testService"
 
-// 	},
-// }
+// testingService is our prototype service definition for use in testing the full model.
+//
+// Typically, this is generated. We define it here to ensure that that package
+// primitive has what is required for generated code.
+type testingService interface {
+	Test(ctx context.Context, req *testPayload) (*testPayload, error)
+}
+
+type testingClient struct {
+	client *Client
+}
+
+func newTestingClient(client *Client) *testingClient {
+	return &testingClient{
+		client: client,
+	}
+}
+
+func (tc *testingClient) Test(ctx context.Context, req *testPayload) (*testPayload, error) {
+	resp, err := tc.client.Call(ctx, serviceName, "Test", req)
+	if err != nil {
+		return nil, err
+	}
+
+	return resp.(*testPayload), nil
+}
 
 type testPayload struct {
 	Foo string `protobuf:"bytes,1,opt,name=foo,proto3"`
@@ -23,23 +47,40 @@ func (r *testPayload) Reset()         { *r = testPayload{} }
 func (r *testPayload) String() string { return fmt.Sprintf("%+#v", r) }
 func (r *testPayload) ProtoMessage()  {}
 
+// testingServer is what would be implemented by the user of this package.
+type testingServer struct {
+	payload *testPayload
+}
+
+func (s *testingServer) Test(ctx context.Context, req *testPayload) (*testPayload, error) {
+	return s.payload, nil
+}
+
 func init() {
-	proto.RegisterType((*testPayload)(nil), "testpayload")
+	proto.RegisterType((*testPayload)(nil), "testPayload")
 	proto.RegisterType((*Request)(nil), "Request")
 	proto.RegisterType((*Response)(nil), "Response")
 }
 
 func TestServer(t *testing.T) {
-	server := NewServer()
-	ctx := context.Background()
+	var (
+		ctx              = context.Background()
+		server           = NewServer()
+		expectedResponse = &testPayload{Foo: "baz"}
+		testImpl         = &testingServer{payload: expectedResponse}
+	)
 
-	if err := server.Register("test-service", map[string]Handler{
+	// more mocking of what is generated code. Unlike grpc, we register with a
+	// closure so that the descriptor is allocated only on registration.
+	registerTestingService := func(srv *Server, svc testingService) error {
+		return srv.Register(serviceName, map[string]Handler{
 			"Test": HandlerFunc(func(ctx context.Context, req interface{}) (interface{}, error) {
-			fmt.Println(req)
-
-			return &testPayload{Foo: "baz"}, nil
+				return svc.Test(ctx, req.(*testPayload))
 			}),
-	}); err != nil {
+		})
+	}
+
+	if err := registerTestingService(server, testImpl); err != nil {
 		t.Fatal(err)
 	}
 
@@ -58,14 +99,18 @@ func TestServer(t *testing.T) {
 	}
 	defer conn.Close()
 
-	client := NewClient(conn)
+	client := newTestingClient(NewClient(conn))
 
 	tp := &testPayload{
 		Foo: "bar",
 	}
-	resp, err := client.Call(ctx, "test-service", "Test", tp)
+
+	resp, err := client.Test(ctx, tp)
 	if err != nil {
 		t.Fatal(err)
 	}
-	fmt.Println(resp)
+
+	if !reflect.DeepEqual(resp, expectedResponse) {
+		t.Fatalf("unexpected response: %+#v != %+#v", resp, expectedResponse)
+	}
 }