🚀 Improve error handling for net error(s) (gofiber#2421)

* improve error handling for net error(s)
fixes: reverse proxy support gofiber#2419

* Update app.go

Co-authored-by: leonklingele <git@leonklingele.de>

* improve error handling for net error(s)
fixes: reverse proxy support gofiber#2419

* improve error handling for net error(s)
fixes: reverse proxy support gofiber#2419

* improve error handling for net error(s)
fixes: reverse proxy support gofiber#2419

---------

Co-authored-by: leonklingele <git@leonklingele.de>

Author: ReneWerner87

app.go

@@ -1052,13 +1052,18 @@ func (app *App) serverErrorHandler(fctx *fasthttp.RequestCtx, err error) {
 	c := app.AcquireCtx(fctx)
 	defer app.ReleaseCtx(c)
 
-	var errNetOP *net.OpError
+	var (
+		errNetOP *net.OpError
+		netErr   net.Error
+	)
 
 	switch {
 	case errors.As(err, new(*fasthttp.ErrSmallBuffer)):
 		err = ErrRequestHeaderFieldsTooLarge
 	case errors.As(err, &errNetOP) && errNetOP.Timeout():
 		err = ErrRequestTimeout
+	case errors.As(err, &netErr):
+		err = ErrBadGateway
 	case errors.Is(err, fasthttp.ErrBodyTooLarge):
 		err = ErrRequestEntityTooLarge
 	case errors.Is(err, fasthttp.ErrGetOnly):

app_test.go

@@ -268,6 +268,20 @@ func Test_App_serverErrorHandler_Internal_Error(t *testing.T) {
 	utils.AssertEqual(t, c.fasthttp.Response.StatusCode(), StatusBadRequest)
 }
 
+func Test_App_serverErrorHandler_Network_Error(t *testing.T) {
+	t.Parallel()
+	app := New()
+	c := app.AcquireCtx(&fasthttp.RequestCtx{})
+	defer app.ReleaseCtx(c)
+	app.serverErrorHandler(c.fasthttp, &net.DNSError{
+		Err:       "test error",
+		Name:      "test host",
+		IsTimeout: false,
+	})
+	utils.AssertEqual(t, string(c.fasthttp.Response.Body()), utils.StatusMessage(StatusBadGateway))
+	utils.AssertEqual(t, c.fasthttp.Response.StatusCode(), StatusBadGateway)
+}
+
 func Test_App_Nested_Params(t *testing.T) {
 	t.Parallel()
 	app := New()