HttpInterceptors are used to modify the Http request. They can be added to HttpInterceptors or passed into Http.call.

class HttpInterceptor {
 RequestInterceptor request;
 Response response;
 RequestErrorInterceptor requestError;
 ResponseError responseError;

 /**
  * All parameters are optional.
  */
 HttpInterceptor({
     this.request, this.response,
     this.requestError, this.responseError});
}