electron/lib/browser/api/net-fetch.ts

import { net, IncomingMessage, Session as SessionT } from 'electron/main';
import { Readable, Writable, isReadable } from 'stream';
import { allowAnyProtocol } from '@electron/internal/browser/api/net-client-request';

function createDeferredPromise<T, E extends Error = Error> (): { promise: Promise<T>; resolve: (x: T) => void; reject: (e: E) => void; } {
  let res: (x: T) => void;
  let rej: (e: E) => void;
  const promise = new Promise<T>((resolve, reject) => {
    res = resolve;
    rej = reject;
  });

  return { promise, resolve: res!, reject: rej! };
}

export function fetchWithSession (input: RequestInfo, init: (RequestInit & {bypassCustomProtocolHandlers?: boolean}) | undefined, session: SessionT): Promise<Response> {
  const p = createDeferredPromise<Response>();
  let req: Request;
  try {
    req = new Request(input, init);
  } catch (e: any) {
    p.reject(e);
    return p.promise;
  }

  if (req.signal.aborted) {
    // 1. Abort the fetch() call with p, request, null, and
    //    requestObject’s signal’s abort reason.
    const error = (req.signal as any).reason ?? new DOMException('The operation was aborted.', 'AbortError');
    p.reject(error);

    if (req.body != null && isReadable(req.body as unknown as NodeJS.ReadableStream)) {
      req.body.cancel(error).catch((err) => {
        if (err.code === 'ERR_INVALID_STATE') {
          // Node bug?
          return;
        }
        throw err;
      });
    }

    // 2. Return p.
    return p.promise;
  }

  let locallyAborted = false;
  req.signal.addEventListener(
    'abort',
    () => {
      // 1. Set locallyAborted to true.
      locallyAborted = true;

      // 2. Abort the fetch() call with p, request, responseObject,
      //    and requestObject’s signal’s abort reason.
      const error = (req.signal as any).reason ?? new DOMException('The operation was aborted.', 'AbortError');
      p.reject(error);
      if (req.body != null && isReadable(req.body as unknown as NodeJS.ReadableStream)) {
        req.body.cancel(error).catch((err) => {
          if (err.code === 'ERR_INVALID_STATE') {
            // Node bug?
            return;
          }
          throw err;
        });
      }

      r.abort();
    },
    { once: true }
  );

  const origin = req.headers.get('origin') ?? undefined;
  // We can't set credentials to same-origin unless there's an origin set.
  const credentials = req.credentials === 'same-origin' && !origin ? 'include' : req.credentials;

  const r = net.request(allowAnyProtocol({
    session,
    method: req.method,
    url: req.url,
    origin,
    credentials,
    cache: req.cache,
    referrerPolicy: req.referrerPolicy,
    redirect: req.redirect
  }));

  (r as any)._urlLoaderOptions.bypassCustomProtocolHandlers = !!init?.bypassCustomProtocolHandlers;

  // cors is the default mode, but we can't set mode=cors without an origin.
  if (req.mode && (req.mode !== 'cors' || origin)) {
    r.setHeader('Sec-Fetch-Mode', req.mode);
  }

  for (const [k, v] of req.headers) {
    r.setHeader(k, v);
  }

  r.on('response', (resp: IncomingMessage) => {
    if (locallyAborted) return;
    const headers = new Headers();
    for (const [k, v] of Object.entries(resp.headers)) { headers.set(k, Array.isArray(v) ? v.join(', ') : v); }
    const nullBodyStatus = [101, 204, 205, 304];
    const body = nullBodyStatus.includes(resp.statusCode) || req.method === 'HEAD' ? null : Readable.toWeb(resp as unknown as Readable) as ReadableStream;
    const rResp = new Response(body, {
      headers,
      status: resp.statusCode,
      statusText: resp.statusMessage
    });
    (rResp as any).__original_resp = resp;
    p.resolve(rResp);
  });

  r.on('error', (err) => {
    p.reject(err);
  });

  if (!req.body?.pipeTo(Writable.toWeb(r as unknown as Writable)).then(() => r.end())) { r.end(); }

  return p.promise;
}