mgrpc: initial implementation of server

With this change, we define a simple server and client framework to
start generating code against. We define a simple handler system with
back registration into the server definition.

From here, we can start generating code against the handlers.

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

server_test.go

@@ -0,0 +1,71 @@
+package mgrpc
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"testing"
+
+	"github.com/gogo/protobuf/proto"
+)
+
+// var serverMethods = map[string]Handler{
+// 	"Create": HandlerFunc(func(ctx context.Context, req interface{}) (interface{}, error) {
+
+// 	},
+// }
+
+type testPayload struct {
+	Foo string `protobuf:"bytes,1,opt,name=foo,proto3"`
+}
+
+func (r *testPayload) Reset()         { *r = testPayload{} }
+func (r *testPayload) String() string { return fmt.Sprintf("%+#v", r) }
+func (r *testPayload) ProtoMessage()  {}
+
+func init() {
+	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()
+
+	if err := server.Register("test-service", map[string]Handler{
+		"Test": HandlerFunc(func(ctx context.Context, req interface{}) (interface{}, error) {
+			fmt.Println(req)
+
+			return &testPayload{Foo: "baz"}, nil
+		}),
+	}); err != nil {
+		t.Fatal(err)
+	}
+
+	listener, err := net.Listen("tcp", ":0")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer listener.Close()
+
+	go server.Serve(listener)
+	defer server.Shutdown(ctx)
+
+	conn, err := net.Dial("tcp", listener.Addr().String())
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer conn.Close()
+
+	client := NewClient(conn)
+
+	tp := &testPayload{
+		Foo: "bar",
+	}
+	resp, err := client.Call(ctx, "test-service", "Test", tp)
+	if err != nil {
+		t.Fatal(err)
+	}
+	fmt.Println(resp)
+}