readconfig.go

// ReadConfig reads in a JSON-formatted configuration file, looking for any
// include directives, and recursively reading those files as well. Include directives
// are specified as a list keyed on the "Includes" key.
func ReadConfig(filename string, configuration interface{}) error {

	// grab any path to the config file to add to the include names
	var prefix string
	slashindex := strings.LastIndex(filename, "/")
	if slashindex != -1 {
		prefix = filename[:slashindex+1]
	}
	file, err := os.Open(filename)
	if err != nil {
		log.Println("Can't read", filename)
		return err
	}
	decoder := json.NewDecoder(file)
	if err := decoder.Decode(configuration); err != nil {
		log.Printf("Error in %s\n", filename)
		log.Println(err)
		return err
	}
	v := reflect.ValueOf(configuration).Elem()
	f := v.FieldByName("Includes")
	// make sure that this field is defined, and can be changed.
	if !f.IsValid() {
		// configuration doesn't have an Includes slice
		return nil
	}
	if f.Kind() != reflect.Slice {
		return nil
	}
	myincludes, ok := f.Interface().([]string)
	if !ok {
		// configuration doesn't have an Includes slice
		return nil
	}
	// clear out the slice
	f.Set(reflect.MakeSlice(f.Type(), 0, f.Cap()))

	for _, include := range myincludes {
		var incfilename string
		if slashindex != -1 {
			incfilename = prefix + include
		} else {
			incfilename = include
		}
		if err := ReadConfig(incfilename, configuration); err != nil {
			return err
		}
	}

	return nil
}