Method handle

packages/common/http/src/jsonp.ts:122–283

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

(req: HttpRequest<never>)

   *
   */
  handle(req: HttpRequest<never>): Observable<HttpEvent<any>> {
    // Firstly, check both the method and response type. If either doesn't match
    // then the request was improperly routed here and cannot be handled.
    if (req.method !== 'JSONP') {
      throw new RuntimeError(
        RuntimeErrorCode.JSONP_WRONG_METHOD,
        ngDevMode && JSONP_ERR_WRONG_METHOD,
      );
    } else if (req.responseType !== 'json') {
      throw new RuntimeError(
        RuntimeErrorCode.JSONP_WRONG_RESPONSE_TYPE,
        ngDevMode && JSONP_ERR_WRONG_RESPONSE_TYPE,
      );
    }

    // Check the request headers. JSONP doesn't support headers and
    // cannot set any that were supplied.
    if (req.headers.keys().length > 0) {
      throw new RuntimeError(
        RuntimeErrorCode.JSONP_HEADERS_NOT_SUPPORTED,
        ngDevMode && JSONP_ERR_HEADERS_NOT_SUPPORTED,
      );
    }

    if (!this.isAllowedJsonpUrl(req.urlWithParams)) {
      throw new RuntimeError(RuntimeErrorCode.JSONP_UNSAFE_URL, ngDevMode && JSONP_ERR_UNSAFE_URL);
    }

    // Everything else happens inside the Observable boundary.
    return new Observable<HttpEvent<any>>((observer: Observer<HttpEvent<any>>) => {
      // The first step to make a request is to generate the callback name, and replace the
      // callback placeholder in the URL with the name. Care has to be taken here to ensure
      // a trailing &, if matched, gets inserted back into the URL in the correct place.
      const callback = this.nextCallback();
      const url = req.urlWithParams.replace(/=JSONP_CALLBACK(&|$)/, `=${callback}$1`);

      // Construct the <script> tag and point it at the URL.
      const node = this.document.createElement('script');
      node.src = url;

      // Set the nonce for Content Security Policy compatibility. Without this,
      // JSONP requests will be blocked by strict-dynamic CSP policies.
      if (this.nonce) {
        node.setAttribute('nonce', this.nonce);
      }

      // A JSONP request requires waiting for multiple callbacks. These variables
      // are closed over and track state across those callbacks.

      // The response object, if one has been received, or null otherwise.
      let body: any | null = null;

      // Whether the response callback has been called.
      let finished: boolean = false;

      // Set the response callback in this.callbackMap (which will be the window
      // object in the browser. The script being loaded via the <script> tag will
      // eventually call this callback.