code: func (r *GoHeader) GetKeys() (value []string) {
  	if !r.isResponse {
  		for key := range r.Source.(*GoRequest).Original.Header {
  			value = append(value, key)
  		}
  	} else {
  		for key := range r.Source.(*GoResponse).Original.Header() {
  			value = append(value, key)
  		}
  	}
  	return
  }
docs: // Returns list of header keys