Method handle

packages/common/http/src/xhr.ts:124–447

* Processes a request and returns a stream of response events. * @param req The request object. * @returns An observable of the response events.

(req: HttpRequest<any>)

   * @returns An observable of the response events.
   */
  handle(req: HttpRequest<any>): Observable<HttpEvent<any>> {
    // Quick check to give a better error message when a user attempts to use
    // HttpClient.jsonp() without installing the HttpClientJsonpModule
    if (req.method === 'JSONP') {
      throw new RuntimeError(
        RuntimeErrorCode.MISSING_JSONP_MODULE,
        (typeof ngDevMode === 'undefined' || ngDevMode) &&
          `Cannot make a JSONP request without JSONP support. To fix the problem, either add the \`withJsonpSupport()\` call (if \`provideHttpClient()\` is used) or import the \`HttpClientJsonpModule\` in the root NgModule.`,
      );
    }

    // Validate that the request is compatible with the XHR backend.
    ngDevMode && validateXhrCompatibility(req);

    // Check whether this factory has a special function to load an XHR implementation
    // for various non-browser environments. We currently limit it to only `ServerXhr`
    // class, which needs to load an XHR implementation.
    const xhrFactory: XhrFactory & {ɵloadImpl?: () => Promise<void>} = this.xhrFactory;
    const source: Observable<void | null> =
      // Note that `ɵloadImpl` is never defined in client bundles and can be
      // safely dropped whenever we're running in the browser.
      // This branching is redundant.
      // The `ngServerMode` guard also enables tree-shaking of the `from()`
      // function from the common bundle, as it's only used in server code.
      typeof ngServerMode !== 'undefined' && ngServerMode && xhrFactory.ɵloadImpl
        ? from(xhrFactory.ɵloadImpl())
        : of(null);

    return source.pipe(
      switchMap(() => {
        // Everything happens on Observable subscription.
        return new Observable((observer: Observer<HttpEvent<any>>) => {
          // Start by setting up the XHR object with request method, URL, and withCredentials
          // flag.
          const xhr = xhrFactory.build();
          xhr.open(req.method, req.urlWithParams);
          if (req.withCredentials) {
            xhr.withCredentials = true;
          }

          // Add all the requested headers.
          req.headers.forEach((name, values) => xhr.setRequestHeader(name, values.join(',')));

          // Add an Accept header if one isn't present already.
          if (!req.headers.has(ACCEPT_HEADER)) {
            xhr.setRequestHeader(ACCEPT_HEADER, ACCEPT_HEADER_VALUE);
          }

          // Auto-detect the Content-Type header if one isn't present already.
          if (!req.headers.has(CONTENT_TYPE_HEADER)) {
            const detectedType = req.detectContentTypeHeader();
            // Sometimes Content-Type detection fails.
            if (detectedType !== null) {
              xhr.setRequestHeader(CONTENT_TYPE_HEADER, detectedType);
            }
          }

          if (req.timeout) {