golang merge json raw messages / maps

merge.go

package merge

// quick and dirty merge of two json raw messages
// does not merge two json arrays

// MergeJson merges two json raw messages. If key
// exists in both maps, value from first argument will take precendence.
func MergeJson(json1 *json.RawMessage, json2 *json.RawMessage) (*json.RawMessage, error) {
	map1 := map[string]interface{}{}
	map2 := map[string]interface{}{}

	err := json.Unmarshal(*json1, &map1)
	if err != nil {
		return nil, err
	}

	err = json.Unmarshal(*json2, &map2)
	if err != nil {
		return nil, err
	}

	mergedMap, err := MergeStringMaps(map1, map2)
	if err != nil {
		return nil, err
	}

	raw, err := json.Marshal(mergedMap)
	message := json.RawMessage(raw)
	return &message, err
}

// MergeStringMaps merges string maps. If key
// exists in both maps, value from first argument will take precendence.
func MergeStringMaps(map1 map[string]interface{}, map2 map[string]interface{}) (map[string]interface{}, error) {
	mergedMap := map[string]interface{}{}

	for k, v := range map2 {
		mergedMap[k] = v
	}

	for k, v := range map1 {
		mergedMap[k] = v
	}

	return mergedMap, nil
}