Allow bind with a map[string]string (#2484)

Co-authored-by: thinkerou <thinkerou@gmail.com>

binding/form_mapping.go

@@ -29,6 +29,21 @@ func mapForm(ptr interface{}, form map[string][]string) error {
 var emptyField = reflect.StructField{}
 
 func mapFormByTag(ptr interface{}, form map[string][]string, tag string) error {
+	// Check if ptr is a map
+	ptrVal := reflect.ValueOf(ptr)
+	var pointed interface{}
+	if ptrVal.Kind() == reflect.Ptr {
+		ptrVal = ptrVal.Elem()
+		pointed = ptrVal.Interface()
+	}
+	if ptrVal.Kind() == reflect.Map &&
+		ptrVal.Type().Key().Kind() == reflect.String {
+		if pointed != nil {
+			ptr = pointed
+		}
+		return setFormMap(ptr, form)
+	}
+
 	return mappingByPtr(ptr, formSource(form), tag)
 }
 
@@ -349,3 +364,29 @@ func head(str, sep string) (head string, tail string) {
 	}
 	return str[:idx], str[idx+len(sep):]
 }
+
+func setFormMap(ptr interface{}, form map[string][]string) error {
+	el := reflect.TypeOf(ptr).Elem()
+
+	if el.Kind() == reflect.Slice {
+		ptrMap, ok := ptr.(map[string][]string)
+		if !ok {
+			return errors.New("cannot convert to map slices of strings")
+		}
+		for k, v := range form {
+			ptrMap[k] = v
+		}
+
+		return nil
+	}
+
+	ptrMap, ok := ptr.(map[string]string)
+	if !ok {
+		return errors.New("cannot convert to map of strings")
+	}
+	for k, v := range form {
+		ptrMap[k] = v[len(v)-1] // pick last
+	}
+
+	return nil
+}