Custom Validation

framework/controller/controller.gotext

@@ -69,6 +69,19 @@ func ({{$action.Short}} *{{ $.Pascal }}{{$action.Pascal}}Action) handler(httpRes
 			JSON: response.Status(400).Set("Content-Type", "application/json").JSON(map[string]string{"error": err.Error()}),
 		}
 	}
+	// validate input
+	{{- if (index $action.Params 0).HasValidate }}
+	// single input struct has validate method
+	if err := in.Validate(); err != nil {
+		return &response.Format{
+			{{- if ne $action.Method "GET" }}
+			HTML: response.Status(http.StatusSeeOther).RedirectBack(httpRequest.URL.Path),
+			{{- end }}
+			JSON: response.Status(400).Set("Content-Type", "application/json").JSON(map[string]string{"error": err.Error()}),
+		}
+	}
+	{{- end }}
+
 	{{- end }}
 	{{- with $provider := $action.Provider }}
 	controller, err := {{ $provider.Name }}(

framework/controller/controller_test.go

@@ -2792,3 +2792,36 @@ func TestIndexControllerWithRootIndexAction(t *testing.T) {
 	`))
 	is.NoErr(app.Close())
 }
+
+// Asserts the Validate() method is called on single input
+// structs.
+func TestInputValidateMethod(t *testing.T) {
+	is := is.New(t)
+	ctx := context.Background()
+	dir := t.TempDir()
+	td := testdir.New(dir)
+	// root controller with input struct to validate
+	td.Files["controller/controller.go"] = `
+		package controller
+		import "errors"
+		type Controller struct{}
+		type Input struct{}
+		func (in *Input) Validate() error {
+			return errors.New("")
+		}
+		func (c *Controller) Index(in *Input) []string {
+			return []string{}
+		}
+	`
+	is.NoErr(td.Write(ctx))
+	cli := testcli.New(dir)
+	app, err := cli.Start(ctx, "run")
+	is.NoErr(err)
+	defer app.Close()
+	res, err := app.GetJSON("/")
+	is.NoErr(err)
+	is.NoErr(res.DiffHeaders(`
+		HTTP/1.1 400 Bad Request
+		Content-Type: application/json
+	`))
+}

framework/controller/loader.go

@@ -300,6 +300,13 @@ func (l *loader) loadActionParam(param *parser.Param, nth, numParams int) *Actio
 	switch {
 	// Single struct input
 	case numParams == 1 && dec.Kind() == parser.KindStruct:
+		// this should always work because kind is KindStruct
+		stct := dec.Package().Struct(dec.Name())
+		validateMethod := stct.Method("Validate")
+		if validateMethod != nil && len(validateMethod.Results()) == 1 && validateMethod.Results()[0].IsError() {
+			// mark that the action param has Validate() error
+			ap.HasValidate = true
+		}
 		ap.Variable = "in"
 	// Handle context.Context
 	case ap.IsContext():
@@ -342,6 +349,7 @@ func (l *loader) loadType(dt parser.Type, dec parser.Declaration) string {
 
 func (l *loader) loadActionInput(params []*ActionParam) string {
 	if len(params) == 1 && params[0].Kind == string(parser.KindStruct) {
+		// single struct input
 		return params[0].Type
 	}
 	return l.loadActionInputStruct(params)

framework/controller/state.go

@@ -67,13 +67,14 @@ type View struct {
 
 // ActionParam struct
 type ActionParam struct {
-	Name     string
-	Pascal   string
-	Snake    string
-	Type     string
-	Kind     string
-	Variable string
-	Tag      string
+	Name        string
+	Pascal      string
+	Snake       string
+	Type        string
+	Kind        string
+	Variable    string
+	Tag         string
+	HasValidate bool
 }
 
 func (ap *ActionParam) IsContext() bool {