code: func GetRequestContentType(r *http.Request) ContentType {
  	if contentType, ok := r.Context().Value(ContentTypeCtxKey).(ContentType); ok {
  		return contentType
  	}
  	return GetContentType(r.Header.Get("Content-Type"))
  }
docs: // GetRequestContentType is a helper function that returns ContentType based on
  // context or request headers.