diff --git a/_examples/golang-basics/example.gen.go b/_examples/golang-basics/example.gen.go
index af47cad..cf59991 100644
--- a/_examples/golang-basics/example.gen.go
+++ b/_examples/golang-basics/example.gen.go
@@ -1,6 +1,6 @@
 // example v0.0.1 05b7a5c86b98738f4fe6ce9bb1fccd4af064847a
 // --
-// Code generated by webrpc-gen@v0.19.3-11-g71ce490 with ../../../gen-golang generator. DO NOT EDIT.
+// Code generated by webrpc-gen@v0.19.3-14-g44bb43f with ../../../gen-golang generator. DO NOT EDIT.
 //
 // webrpc-gen -schema=example.ridl -target=../../../gen-golang -pkg=main -server -client -legacyErrors -fixEmptyArrays -out=./example.gen.go
 package main
@@ -249,10 +249,6 @@ func (s *exampleServiceServer) ServeHTTP(w http.ResponseWriter, r *http.Request)
 	ctx = context.WithValue(ctx, ServiceNameCtxKey, "ExampleService")
 	ctx = context.WithValue(ctx, MethodAnnotationsCtxKey, methodAnnotations[r.URL.Path])
 
-	if s.OnRequest != nil {
-		s.OnRequest(w, r)
-	}
-
 	var handler func(ctx context.Context, w http.ResponseWriter, r *http.Request)
 	switch r.URL.Path {
 	case "/rpc/ExampleService/Ping":
@@ -288,6 +284,17 @@ func (s *exampleServiceServer) ServeHTTP(w http.ResponseWriter, r *http.Request)
 
 	switch contentType {
 	case "application/json":
+		if s.OnRequest != nil {
+			if err := s.OnRequest(w, r); err != nil {
+				rpcErr, ok := err.(WebRPCError)
+				if !ok {
+					rpcErr = ErrWebrpcEndpoint.WithCause(err)
+				}
+				s.sendErrorJSON(w, r, rpcErr)
+				return
+			}
+		}
+
 		handler(ctx, w, r)
 	default:
 		err := ErrWebrpcBadRequest.WithCause(fmt.Errorf("unsupported Content-Type %q (only application/json is allowed)", r.Header.Get("Content-Type")))
diff --git a/_examples/golang-imports/api.gen.go b/_examples/golang-imports/api.gen.go
index 213d8fe..1a70e82 100644
--- a/_examples/golang-imports/api.gen.go
+++ b/_examples/golang-imports/api.gen.go
@@ -1,6 +1,6 @@
 // example-api-service v1.0.0 cae4e128f4fb4c938bfe1ea312deeea3dfd6b6af
 // --
-// Code generated by webrpc-gen@v0.19.3-11-g71ce490 with ../../../gen-golang generator. DO NOT EDIT.
+// Code generated by webrpc-gen@v0.19.3-14-g44bb43f with ../../../gen-golang generator. DO NOT EDIT.
 //
 // webrpc-gen -schema=./proto/api.ridl -target=../../../gen-golang -out=./api.gen.go -pkg=main -server -client -legacyErrors=true -fmt=false
 package main
@@ -82,7 +82,9 @@ func (x *Location) Is(values ...Location) bool {
 		}
 	}
 	return false
-}var (
+}
+
+var (
 	methodAnnotations = map[string]map[string]string{
     	"/rpc/ExampleAPI/Ping": {},
     	"/rpc/ExampleAPI/Status": {},
@@ -161,10 +163,6 @@ func (s *exampleAPIServer) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	ctx = context.WithValue(ctx, ServiceNameCtxKey, "ExampleAPI")
 	ctx = context.WithValue(ctx, MethodAnnotationsCtxKey, methodAnnotations[r.URL.Path])
 
-    if s.OnRequest != nil {
-        s.OnRequest(w, r)
-    }
-
 	var handler func(ctx context.Context, w http.ResponseWriter, r *http.Request)
 	switch r.URL.Path {
 	case "/rpc/ExampleAPI/Ping":
@@ -194,6 +192,17 @@ func (s *exampleAPIServer) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 
 	switch contentType {
 	case "application/json":
+        if s.OnRequest != nil {
+            if err := s.OnRequest(w, r); err != nil {
+                rpcErr, ok := err.(WebRPCError)
+                if !ok {
+                    rpcErr = ErrWebrpcEndpoint.WithCause(err)
+                }
+                s.sendErrorJSON(w, r, rpcErr)
+                return
+            }
+        }
+
 		handler(ctx, w, r)
 	default:
 		err := ErrWebrpcBadRequest.WithCause(fmt.Errorf("unsupported Content-Type %q (only application/json is allowed)", r.Header.Get("Content-Type")))
diff --git a/server.go.tmpl b/server.go.tmpl
index 87039a1..b528791 100644
--- a/server.go.tmpl
+++ b/server.go.tmpl
@@ -44,10 +44,6 @@ func (s *{{$serviceName}}) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	ctx = context.WithValue(ctx, ServiceNameCtxKey, "{{.Name}}")
 	ctx = context.WithValue(ctx, MethodAnnotationsCtxKey, methodAnnotations[r.URL.Path])
 
-    if s.OnRequest != nil {
-        s.OnRequest(w, r)
-    }
-
 	var handler func(ctx context.Context, w http.ResponseWriter, r *http.Request)
 	switch r.URL.Path {
 	{{- range $_, $method := $service.Methods}}
@@ -75,6 +71,17 @@ func (s *{{$serviceName}}) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 
 	switch contentType {
 	case "application/json":
+        if s.OnRequest != nil {
+            if err := s.OnRequest(w, r); err != nil {
+                rpcErr, ok := err.(WebRPCError)
+                if !ok {
+                    rpcErr = ErrWebrpcEndpoint.WithCause(err)
+                }
+                s.sendErrorJSON(w, r, rpcErr)
+                return
+            }
+        }
+
 		handler(ctx, w, r)
 	default:
 		err := ErrWebrpcBadRequest.WithCause(fmt.Errorf("unsupported Content-Type %q (only application/json is allowed)", r.Header.Get("Content-Type")))
diff --git a/types.go.tmpl b/types.go.tmpl
index 5e0af53..1a1b2dd 100644
--- a/types.go.tmpl
+++ b/types.go.tmpl
@@ -29,7 +29,7 @@
 
 {{- end }}
 
-{{- range $_, $service := $services -}}
+{{ range $_, $service := $services -}}
 var (
 	methodAnnotations = map[string]map[string]string{
     	{{- range $_, $method := $service.Methods }}