Slightly simplify the queue settings code to help reduce the risk of problems (#12976)

Signed-off-by: Andrew Thornton <art27@cantab.net>

Co-authored-by: techknowlogick <techknowlogick@gitea.io>

modules/queue/helper.go

@@ -9,25 +9,56 @@ import (
 	"reflect"
 )
 
+// Mappable represents an interface that can MapTo another interface
+type Mappable interface {
+	MapTo(v interface{}) error
+}
+
 // toConfig will attempt to convert a given configuration cfg into the provided exemplar type.
 //
 // It will tolerate the cfg being passed as a []byte or string of a json representation of the
 // exemplar or the correct type of the exemplar itself
 func toConfig(exemplar, cfg interface{}) (interface{}, error) {
+
+	// First of all check if we've got the same type as the exemplar - if so it's all fine.
 	if reflect.TypeOf(cfg).AssignableTo(reflect.TypeOf(exemplar)) {
 		return cfg, nil
 	}
 
+	// Now if not - does it provide a MapTo function we can try?
+	if mappable, ok := cfg.(Mappable); ok {
+		newVal := reflect.New(reflect.TypeOf(exemplar))
+		if err := mappable.MapTo(newVal.Interface()); err == nil {
+			return newVal.Elem().Interface(), nil
+		}
+		// MapTo has failed us ... let's try the json route ...
+	}
+
+	// OK we've been passed a byte array right?
 	configBytes, ok := cfg.([]byte)
 	if !ok {
-		configStr, ok := cfg.(string)
-		if !ok {
-			return nil, ErrInvalidConfiguration{cfg: cfg}
-		}
+		// oh ... it's a string then?
+		var configStr string
+
+		configStr, ok = cfg.(string)
 		configBytes = []byte(configStr)
 	}
+	if !ok {
+		// hmm ... can we marshal it to json?
+		var err error
+
+		configBytes, err = json.Marshal(cfg)
+		ok = (err == nil)
+	}
+	if !ok {
+		// no ... we've tried hard enough at this point - throw an error!
+		return nil, ErrInvalidConfiguration{cfg: cfg}
+	}
+
+	// OK unmarshal the byte array into a new copy of the exemplar
 	newVal := reflect.New(reflect.TypeOf(exemplar))
 	if err := json.Unmarshal(configBytes, newVal.Interface()); err != nil {
+		// If we can't unmarshal it then return an error!
 		return nil, ErrInvalidConfiguration{cfg: cfg, err: err}
 	}
 	return newVal.Elem().Interface(), nil