Angular 2 REST request HTTP status code 401 changes to 0

If cloudcms.com do to not set the Access-Control-Allow-Origin in 401 response, then nothing much you can do. You properly have to open support ticket with them to confirm if that is normal behavior.

javascript in browsers(FF, Chrome & Safari) I tested won't receive any info if CORS error occur, other than status 0. Angular2 has no control of it.

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I created a simple test and get the same result as yours:

geturl() {
    console.log('geturl() clicked');
    let headers = new Headers({ 'Content-Type': 'application/xhtml+xml' });
    let options = new RequestOptions({ 'headers': headers });
    this.http.get(this.url)
        .catch((error): any => {
            console.log('************* ERROR Response', error);
            let errMsg = (error.message) ? error.message :
                error.status ? `${error.status} - ${error.statusText}` : 'Web Server error';
            return Observable.throw(error);
        })
        .subscribe(
        (i: Response) => { console.log(i); },
        (e: any) => { console.log(e); }
        );
}

After much googling, I found the following(https://github.com/angular/angular.js/issues/3336):

lucassp commented on Aug 19, 2013

I found the issue for a while now but I forgot post here a reply. EVERY response, even Error 500, must have the CORS headers attached. If the server doesn't attach the CORS headers to the Error 500 response then the XHR Object won't parse it, thus the XHR Object won't have any response body, status, or any other response data inside.

Result from Firefox network monitor seems supporting the above reason.

Javascript request will receive empty response.

Plain url request(copy&paste the link in the address bar) will get response body

Javascript use XHRHttpRequest for http communication.

When a XHR reply arrive, the browser will process the header, that's why you will see those 401 network messages. However, if the XHR reply is from a different host then the javascript AND the response header contain no CORS header(eg Access-Control-Allow-Origin: *), the browser will not pass any info back to the XHR layer. As a result, the reply body will be completely empty with no status(0).

I tested with FF 48.0.1, Chrome 52.0.2743.116 and Safari 9.1.2, and they all have the same behavior.

Use browser network monitor to check response header for those 401 Unauthorized entries, it is very likely that there is no Access-Control-Allow-Origin header and causing the issue you are facing. This can be a bug or by design on the service provider side.

Access-Control-Allow-Origin is a response only http header. For more information of https://developer.mozilla.org/en-US/docs/Web/HTTP/Access_control_CORS#The_HTTP_response_headers

The issue is related to CORS requests, see this github issue

No 'Access-Control-Allow-Origin' header is present on the requested resource

means that 'Access-Control-Allow-Origin' is required in the response headers.

Angular is not getting any status codes, that's why it gives you a 0 which is caused by browser not allowing the xml parser to parse the response due to invalid headers.

You need to append correct CORS headers to your error response as well as success.