feat(binding): Support custom BindUnmarshaler for binding. (#3933)

binding/form_mapping.go

@@ -165,6 +165,23 @@ func tryToSetValue(value reflect.Value, field reflect.StructField, setter setter
 	return setter.TrySet(value, field, tagValue, setOpt)
 }
 
+// BindUnmarshaler is the interface used to wrap the UnmarshalParam method.
+type BindUnmarshaler interface {
+	// UnmarshalParam decodes and assigns a value from an form or query param.
+	UnmarshalParam(param string) error
+}
+
+// trySetCustom tries to set a custom type value
+// If the value implements the BindUnmarshaler interface, it will be used to set the value, we will return `true`
+// to skip the default value setting.
+func trySetCustom(val string, value reflect.Value) (isSet bool, err error) {
+	switch v := value.Addr().Interface().(type) {
+	case BindUnmarshaler:
+		return true, v.UnmarshalParam(val)
+	}
+	return false, nil
+}
+
 func setByForm(value reflect.Value, field reflect.StructField, form map[string][]string, tagValue string, opt setOptions) (isSet bool, err error) {
 	vs, ok := form[tagValue]
 	if !ok && !opt.isDefaultExists {
@@ -194,6 +211,9 @@ func setByForm(value reflect.Value, field reflect.StructField, form map[string][
 		if len(vs) > 0 {
 			val = vs[0]
 		}
+		if ok, err := trySetCustom(val, value); ok {
+			return ok, err
+		}
 		return true, setWithProperType(val, value, field)
 	}
 }