@aurelia/fetch-client/src/interfaces.ts

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import { HttpClient } from './http-client';

/**
 * Interceptors can process requests before they are sent, and responses
 * before they are returned to callers.
 */
export interface IFetchInterceptor {
  /**
   * Called with the request before it is sent. Request interceptors can modify and
   * return the request, or return a new one to be sent. If desired, the interceptor
   * may return a Response in order to short-circuit the HTTP request itself.
   *
   * @param request - The request to be sent.
   * @returns The existing request, a new request or a response; or a Promise for any of these.
   */
  request?(request: Request): Request | Response | Promise<Request | Response>;

  /**
   * Handles errors generated by previous request interceptors. This function acts
   * as a Promise rejection handler. It may rethrow the error to propagate the
   * failure, or return a new Request or Response to recover.
   *
   * @param error - The rejection value from the previous interceptor.
   * @returns The existing request, a new request or a response; or a Promise for any of these.
   */
  requestError?(error: unknown): Request | Response | Promise<Request | Response>;

  /**
   * Called with the response after it is received. Response interceptors can modify
   * and return the Response, or create a new one to be returned to the caller.
   *
   * If a Request object was returned at the end of a response interceptor chain, it will rerun the request cycle with that Request object.
   *
   * @param response - The response.
   * @returns The response; or a Promise for one.
   */
  response?(response: Response, request?: Request): Request | Response | Promise<Request | Response>;

  /**
   * Handles fetch errors and errors generated by previous interceptors. This
   * function acts as a Promise rejection handler. It may rethrow the error
   * to propagate the failure, or return a new Response to recover.
   *
   * If a Request object was returned at the end of a responseError interceptor chain, it will rerun the request cycle with that Request object.
   *
   * @param error - The rejection value from the fetch request or from a
   * previous interceptor.
   * @returns The response; or a Promise for one.
   */
  responseError?(error: unknown, request?: Request, httpClient?: HttpClient): Response | Promise<Response>;

  /**
   * Optional. Called when the owning http client is disposed for cleanup purposes.
   */
  dispose?(): void;
}