import { getGlobalObject, isNativeFetch, logger, supportsFetch } from '@sentry/utils';

var global = getGlobalObject();
let cachedFetchImpl;

/**
 * A special usecase for incorrectly wrapped Fetch APIs in conjunction with ad-blockers.
 * Whenever someone wraps the Fetch API and returns the wrong promise chain,
 * this chain becomes orphaned and there is no possible way to capture it's rejections
 * other than allowing it bubble up to this very handler. eg.
 *
 * var f = window.fetch;
 * window.fetch = function () {
 *   var p = f.apply(this, arguments);
 *
 *   p.then(function() {
 *     console.log('hi.');
 *   });
 *
 *   return p;
 * }
 *
 * `p.then(function () { ... })` is producing a completely separate promise chain,
 * however, what's returned is `p` - the result of original `fetch` call.
 *
 * This mean, that whenever we use the Fetch API to send our own requests, _and_
 * some ad-blocker blocks it, this orphaned chain will _always_ reject,
 * effectively causing another event to be captured.
 * This makes a whole process become an infinite loop, which we need to somehow
 * deal with, and break it in one way or another.
 *
 * To deal with this issue, we are making sure that we _always_ use the real
 * browser Fetch API, instead of relying on what `window.fetch` exposes.
 * The only downside to this would be missing our own requests as breadcrumbs,
 * but because we are already not doing this, it should be just fine.
 *
 * Possible failed fetch error messages per-browser:
 *
 * Chrome:  Failed to fetch
 * Edge:    Failed to Fetch
 * Firefox: NetworkError when attempting to fetch resource
 * Safari:  resource blocked by content blocker
 */
function getNativeFetchImplementation() {
  if (cachedFetchImpl) {
    return cachedFetchImpl;
  }

  // Fast path to avoid DOM I/O
  if (isNativeFetch(global.fetch)) {
    return (cachedFetchImpl = global.fetch.bind(global));
  }

  var document = global.document;
  let fetchImpl = global.fetch;
    if (document && typeof document.createElement === 'function') {
    try {
      var sandbox = document.createElement('iframe');
      sandbox.hidden = true;
      document.head.appendChild(sandbox);
      var contentWindow = sandbox.contentWindow;
      if (contentWindow && contentWindow.fetch) {
        fetchImpl = contentWindow.fetch;
      }
      document.head.removeChild(sandbox);
    } catch (e) {
      (typeof __SENTRY_DEBUG__ === 'undefined' || __SENTRY_DEBUG__) &&
        logger.warn('Could not create sandbox iframe for pure fetch check, bailing to window.fetch: ', e);
    }
  }

  return (cachedFetchImpl = fetchImpl.bind(global));
  }

/**
 * Sends sdk client report using sendBeacon or fetch as a fallback if available
 *
 * @param url report endpoint
 * @param body report payload
 */
function sendReport(url, body) {
  var isRealNavigator = Object.prototype.toString.call(global && global.navigator) === '[object Navigator]';
  var hasSendBeacon = isRealNavigator && typeof global.navigator.sendBeacon === 'function';

  if (hasSendBeacon) {
    // Prevent illegal invocations - https://xgwang.me/posts/you-may-not-know-beacon/#it-may-throw-error%2C-be-sure-to-catch
    var sendBeacon = global.navigator.sendBeacon.bind(global.navigator);
    sendBeacon(url, body);
  } else if (supportsFetch()) {
    var fetch = getNativeFetchImplementation();
    fetch(url, {
      body,
      method: 'POST',
      credentials: 'omit',
      keepalive: true,
    }).then(null, error => {
      (typeof __SENTRY_DEBUG__ === 'undefined' || __SENTRY_DEBUG__) && logger.error(error);
    });
  }
}

export { getNativeFetchImplementation, sendReport };
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