code: func isJSONContentType(mediaType string) bool {
  	if mediaType == "application/json" ||
  		strings.HasPrefix(mediaType, vndMediaTypePrefix) ||
  		strings.HasSuffix(mediaType, mediaTypeJSONSuffix) {
  		return true
  	}
  	return false
  }
docs: // isJSONContentType returns whether or not the media type should be expected to
  // contain JSON. Explicit application/json as well as types of the form
  // application/vnd* and *+json are permitted. The simple checks prevent us from
  // running http.DetectContentType on every request or trying to decode things
  // that are clearly not JSON.