add the sanity check back and refactor

server.go

@@ -38,6 +38,7 @@ import (
 	"fmt"
 	"io"
 	"net"
+	"reflect"
 	"strings"
 	"sync"
 
@@ -138,9 +139,17 @@ func NewServer(opt ...ServerOption) *Server {
 // server. Called from the IDL generated code. This must be called before
 // invoking Serve.
 func (s *Server) RegisterService(sd *ServiceDesc, ss interface{}) {
+	ht := reflect.TypeOf(sd.HandlerType).Elem()
+	st := reflect.TypeOf(ss)
+	if !st.Implements(ht) {
+		grpclog.Fatalf("grpc: Server.RegisterService found the handler of type %v that does not satisfy %v", st, ht)
+	}
+	s.register(sd, ss)
+}
+
+func (s *Server) register(sd *ServiceDesc, ss interface{}) {
 	s.mu.Lock()
 	defer s.mu.Unlock()
-	// Does some sanity checks.
 	if _, ok := s.m[sd.ServiceName]; ok {
 		grpclog.Fatalf("grpc: Server.RegisterService found duplicate service registration for %q", sd.ServiceName)
 	}