src/ajax.js

import {config} from './config.js';
import {buildUrl, logError, parseUrl} from 'https://github.com/prebid/Prebid.js/blob/master/src/utils.js';

export const dep = {
  fetch: window.fetch.bind(window),
  makeRequest: (r, o) => new Request(r, o),
  timeout(timeout, resource) {
    const ctl = new AbortController();
    let cancelTimer = setTimeout(() => {
      ctl.abort();
      logError(`Request timeout after ${timeout}ms`, resource);
      cancelTimer = null;
    }, timeout);
    return {
      signal: ctl.signal,
      done() {
        cancelTimer && clearTimeout(cancelTimer)
      }
    }
  }
}

const GET = 'GET';
const POST = 'POST';
const CTYPE = 'Content-Type';

/**
 * transform legacy `ajax` parameters into a fetch request.
 * @returns {Request}
 */
export function toFetchRequest(url, data, options = {}) {
  const method = options.method || (data ? POST : GET);
  if (method === GET && data) {
    const urlInfo = parseUrl(url, options);
    Object.assign(urlInfo.search, data);
    url = buildUrl(urlInfo);
  }
  const headers = new Headers(options.customHeaders);
  headers.set(CTYPE, options.contentType || 'text/plain');
  const rqOpts = {
    method,
    headers
  }
  if (method !== GET && data) {
    rqOpts.body = data;
  }
  if (options.withCredentials) {
    rqOpts.credentials = 'include';
  }
  if (options.browsingTopics && isSecureContext) {
    // the Request constructor will throw an exception if the browser supports topics
    // but we're not in a secure context
    rqOpts.browsingTopics = true;
  }
  return dep.makeRequest(url, rqOpts);
}

/**
 * Return a version of `fetch` that automatically cancels requests after `timeout` milliseconds.
 *
 * If provided, `request` and `done` should be functions accepting a single argument.
 * `request` is invoked at the beginning of each request, and `done` at the end; both are passed its origin.
 *
 * @returns {function(*, {}?): Promise<Response>}
 */
export function fetcherFactory(timeout = 3000, {request, done} = {}) {
  let fetcher = (resource, options) => {
    let to;
    if (timeout != null && options?.signal == null && !config.getConfig('disableAjaxTimeout')) {
      to = dep.timeout(timeout, resource);
      options = Object.assign({signal: to.signal}, options);
    }
    let pm = dep.fetch(resource, options);
    if (to?.done != null) pm = pm.finally(to.done);
    return pm;
  };

  if (request != null || done != null) {
    fetcher = ((fetch) => function (resource, options) {
      const origin = new URL(resource?.url == null ? resource : resource.url, document.location).origin;
      let req = fetch(resource, options);
      request && request(origin);
      if (done) req = req.finally(() => done(origin));
      return req;
    })(fetcher);
  }
  return fetcher;
}

function toXHR({status, statusText = '', headers, url}, responseText) {
  let xml = 0;
  function getXML(onError) {
    if (xml === 0) {
      try {
        xml = new DOMParser().parseFromString(responseText, headers?.get(CTYPE)?.split(';')?.[0])
      } catch (e) {
        xml = null;
        onError && onError(e)
      }
    }
    return xml;
  }
  return {
    readyState: XMLHttpRequest.DONE,
    status,
    statusText,
    responseText,
    response: responseText,
    responseType: '',
    responseURL: url,
    get responseXML() {
      return getXML(logError);
    },
    getResponseHeader: (header) => headers?.has(header) ? headers.get(header) : null,
    toJSON() {
      return Object.assign({responseXML: getXML()}, this)
    },
    timedOut: false
  }
}

/**
 * attach legacy `ajax` callbacks to a fetch promise.
 */
export function attachCallbacks(fetchPm, callback) {
  const {success, error} = typeof callback === 'object' && callback != null ? callback : {
    success: typeof callback === 'function' ? callback : () => null,
    error: (e, x) => logError('Network error', e, x)
  };
  fetchPm.then(response => response.text().then((responseText) => [response, responseText]))
    .then(([response, responseText]) => {
      const xhr = toXHR(response, responseText);
      response.ok || response.status === 304 ? success(responseText, xhr) : error(response.statusText, xhr);
    }, (reason) => error('', Object.assign(
      toXHR({status: 0}, ''),
      {reason, timedOut: reason?.name === 'AbortError'}))
    );
}

export function ajaxBuilder(timeout = 3000, {request, done} = {}) {
  const fetcher = fetcherFactory(timeout, {request, done});
  return function (url, callback, data, options = {}) {
    attachCallbacks(fetcher(toFetchRequest(url, data, options)), callback);
  };
}

export const ajax = ajaxBuilder();
export const fetch = fetcherFactory();