Class FetchBackend

packages/common/http/src/fetch.ts:74–438

 */
@Service()
export class FetchBackend implements HttpBackend {
  // We use an arrow function to always reference the current global implementation of `fetch`.
  // This is helpful for cases when the global `fetch` implementation is modified by external code,
  // see https://github.com/angular/angular/issues/57527.
  private readonly fetchImpl =
    inject(FetchFactory, {optional: true})?.fetch ?? ((...args) => globalThis.fetch(...args));
  private readonly ngZone = inject(NgZone);
  private readonly destroyRef = inject(DestroyRef);
  private readonly maxResponseSize = inject(HTTP_FETCH_MAX_RESPONSE_SIZE);

  handle(request: HttpRequest<any>): Observable<HttpEvent<any>> {
    return new Observable((observer) => {
      const aborter = new AbortController();
      let done = false;
      const wrappedObserver: Observer<HttpEvent<any>> = {
        next: (val) => {
          if (val.type === HttpEventType.Response) {
            done = true;
          }
          observer.next(val);
        },
        error: (err) => {
          done = true;
          observer.error(err);
        },
        complete: () => {
          done = true;
          observer.complete();
        },
      };

      this.doRequest(request, aborter.signal, wrappedObserver).then(noop, (error) =>
        wrappedObserver.error(new HttpErrorResponse({error})),
      );

      let timeoutId: ReturnType<typeof setTimeout> | undefined;
      if (request.timeout) {
        // TODO: Replace with AbortSignal.any([aborter.signal, AbortSignal.timeout(request.timeout)])
        // when AbortSignal.any support is Baseline widely available (NET nov. 2026)
        timeoutId = this.ngZone.runOutsideAngular(() =>
          setTimeout(() => {
            if (!aborter.signal.aborted) {
              aborter.abort(new DOMException('signal timed out', 'TimeoutError'));
            }
          }, request.timeout),
        );
      }

      return () => {
        if (timeoutId !== undefined) {
          clearTimeout(timeoutId);
        }
        if (!done && !aborter.signal.aborted) {
          aborter.abort();
        }
      };
    });
  }