feat: Simpler custom code error handling

Author: codingconcepts

README.md

@@ -22,7 +22,10 @@ Update your existing handler signatures, by adding an `error` return type and ut
 func addProduct(w http.ResponseWriter, r *http.Request) error {
   var p product
   if err := errhandler.ParseJSON(r, &p); err != nil {
-    return SendError(w, http.StatusUnprocessableEntity, err)
+    return err
+
+    // Or, if you'd prefer to customise the status code:
+    // errhandler.Error(http.StatusUnprocessableEntity, err)
   }
 
   products[p.ID] = p

err.go

@@ -0,0 +1,19 @@
+package errhandler
+
+// HTTPError allows you to return custom status codes.
+type HTTPError struct {
+	status int
+	err    error
+}
+
+// Error returns a new instance of Error.
+func Error(status int, err error) HTTPError {
+	return HTTPError{
+		status: status,
+		err:    err,
+	}
+}
+
+func (err HTTPError) Error() string {
+	return err.err.Error()
+}

errhandler.go

@@ -13,7 +13,11 @@ type Wrap func(w http.ResponseWriter, r *http.Request) error
 // any errors encountered in the ErrHandlerFunc.
 func (fn Wrap) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	if err := fn(w, r); err != nil {
-		http.Error(w, err.Error(), http.StatusInternalServerError)
+		if cerr, ok := err.(HTTPError); ok {
+			http.Error(w, cerr.Error(), cerr.status)
+		} else {
+			http.Error(w, err.Error(), http.StatusInternalServerError)
+		}
 	}
 }
 
@@ -37,16 +41,6 @@ func SendString(w http.ResponseWriter, message string) error {
 	return nil
 }
 
-// SendError returns an error response to the caller, or fails with an error.
-func SendError(w http.ResponseWriter, code int, err error) error {
-	w.Header().Set("Content-Type", "text/plain")
-	w.WriteHeader(code)
-	if _, err := w.Write([]byte(err.Error())); err != nil {
-		return err
-	}
-	return nil
-}
-
 // ParseJSON can be used to parse a string from the body of a request.
 func ParseJSON(r *http.Request, val any) error {
 	return json.NewDecoder(r.Body).Decode(val)

errhandler_test.go

@@ -60,10 +60,10 @@ func TestWrap_ServeHTTP(t *testing.T) {
 		{
 			name: "send error",
 			handler: Wrap(func(w http.ResponseWriter, r *http.Request) error {
-				return SendError(w, http.StatusUnprocessableEntity, fmt.Errorf("error doing stuff: %w", errors.New("database error")))
+				return Error(http.StatusUnprocessableEntity, fmt.Errorf("error doing stuff: %w", errors.New("database error")))
 			}),
 			expectedStatus: http.StatusUnprocessableEntity,
-			expectedBody:   "error doing stuff: database error",
+			expectedBody:   "error doing stuff: database error\n",
 		},
 		{
 			name: "error",