code: func StructFieldFromJSONName(v reflect.Value, name string) string {
  	if v.Kind() != reflect.Struct {
  		return ""
  	}
  
  	m := getType2jfm(v.Type())
  	m.lock.Lock()
  	defer m.lock.Unlock()
  
  	s, ok := m.fields[name]
  	if !ok {
  		return ""
  	}
  	return s
  }
docs: // StructFieldFromJSONName returns the struct field name on the
  // given struct value. Empty value means the field is either not
  // public, or does not exist.
  //
  // This can be used to map JSON field names to actual struct fields.