handler checks addressing issue #100 (#101)

* handler checks addressing issue #100

* handler check tests

service/grpc/binding.go

@@ -15,6 +15,9 @@ func (s *Server) AddBindingInvocationHandler(name string, fn func(ctx context.Co
 	if name == "" {
 		return fmt.Errorf("binding name required")
 	}
+	if fn == nil {
+		return fmt.Errorf("binding handler required")
+	}
 	s.bindingHandlers[name] = fn
 	return nil
 }

service/grpc/invoke.go

@@ -15,6 +15,9 @@ func (s *Server) AddServiceInvocationHandler(method string, fn func(ctx context.
 	if method == "" {
 		return fmt.Errorf("servie name required")
 	}
+	if fn == nil {
+		return fmt.Errorf("invocation handler required")
+	}
 	s.invokeHandlers[method] = fn
 	return nil
 }

service/grpc/topic.go

@@ -21,6 +21,9 @@ func (s *Server) AddTopicEventHandler(sub *common.Subscription, fn func(ctx cont
 	if sub.PubsubName == "" {
 		return errors.New("pub/sub name required")
 	}
+	if fn == nil {
+		return fmt.Errorf("topic handler required")
+	}
 	key := fmt.Sprintf("%s-%s", sub.PubsubName, sub.Topic)
 	s.topicSubscriptions[key] = &topicEventHandler{
 		component: sub.PubsubName,

service/http/binding.go

@@ -15,6 +15,9 @@ func (s *Server) AddBindingInvocationHandler(route string, fn func(ctx context.C
 	if route == "" {
 		return fmt.Errorf("binding route required")
 	}
+	if fn == nil {
+		return fmt.Errorf("binding handler required")
+	}
 
 	if !strings.HasPrefix(route, "/") {
 		route = fmt.Sprintf("/%s", route)

service/http/binding_test.go

@@ -12,6 +12,12 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
+func TestBindingHandlerWithoutHandler(t *testing.T) {
+	s := newServer("", nil)
+	err := s.AddBindingInvocationHandler("/", nil)
+	assert.Errorf(t, err, "expected error adding nil binding event handler")
+}
+
 func TestBindingHandlerWithoutData(t *testing.T) {
 	s := newServer("", nil)
 	err := s.AddBindingInvocationHandler("/", func(ctx context.Context, in *common.BindingEvent) (out []byte, err error) {

service/http/invoke.go

@@ -16,6 +16,9 @@ func (s *Server) AddServiceInvocationHandler(route string, fn func(ctx context.C
 	if route == "" {
 		return fmt.Errorf("service route required")
 	}
+	if fn == nil {
+		return fmt.Errorf("invocation handler required")
+	}
 
 	if !strings.HasPrefix(route, "/") {
 		route = fmt.Sprintf("/%s", route)

service/http/invoke_test.go

@@ -14,6 +14,12 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
+func TestInvocationHandlerWithoutHandler(t *testing.T) {
+	s := newServer("", nil)
+	err := s.AddServiceInvocationHandler("/", nil)
+	assert.Errorf(t, err, "expected error adding event handler")
+}
+
 func TestInvocationHandlerWithData(t *testing.T) {
 	data := `{"name": "test", "data": hellow}`
 	s := newServer("", nil)

service/http/topic.go

@@ -48,6 +48,9 @@ func (s *Server) AddTopicEventHandler(sub *common.Subscription, fn func(ctx cont
 	if sub.Route == "" {
 		return errors.New("handler route name")
 	}
+	if fn == nil {
+		return fmt.Errorf("topic handler required")
+	}
 
 	if !strings.HasPrefix(sub.Route, "/") {
 		sub.Route = fmt.Sprintf("/%s", sub.Route)

service/http/topic_test.go

@@ -26,6 +26,18 @@ func testErrorTopicFunc(ctx context.Context, e *common.TopicEvent) (retry bool,
 	return true, errors.New("error to cause a retry")
 }
 
+func TestEventNilHandler(t *testing.T) {
+	s := newServer("", nil)
+	sub := &common.Subscription{
+		PubsubName: "messages",
+		Topic:      "test",
+		Route:      "/",
+		Metadata:   map[string]string{},
+	}
+	err := s.AddTopicEventHandler(sub, nil)
+	assert.Errorf(t, err, "expected error adding event handler")
+}
+
 func TestEventHandler(t *testing.T) {
 	data := `{
 		"specversion" : "1.0",