Angular2 : HTTP error handling

Question

I am trying to reproduce the following behaviour that I successfully implemented using Angular 1.x interceptors and promises, in a Angular2 based Ionic2 app :

Intercept HTTP request errors
If the status code is 401, then

a. make another request to register the client. This will provide some token that I can subsequently attach to each request.

b. Retry the orignal request and provide the result to the caller through the promise / observable
If the error status is anything other than 401 just let the flow normally to the caller

NB: The register process does not need any intervention from the user (no login) so I want it to be completely transparent for the user. I register once when the app is first loaded, but the session will eventually expire and I need to automatically re-register.

This is the original Angular 1 implementation (I include only the responseErrorpart of the interceptor):

responseError : function(rejection){
    if(rejection.status == 401){
        $log.info('Intercepting unauthorized 401 response. Will try to re-register the session and retry the request.');

        var security = $injector.get('SecurityService');
        var $http = $injector.get('$http');

        return security.registerSession().then(function(){
            return $http(rejection.config);
        });

    }else{
        return rejection;
    }
}

Now, I have wrapped Angular2's HTTP service and I can do simple things like adding a header to each request. However I am struggling to reproduce the same behaviour using Angular2 and Observables.

My attempt so far, this is the request method of my HTTP wrapper that my services will call :

request(url: string | Request, options?: RequestOptionsArgs): Observable<Response> {

    let req: Request = this.buildRequest(url, options);

    this.beforeCall(req);

    var observable = this.http
        .request(req)
        .retry(3)
        .catch(res => {
            debugger;
            console.log("ERROR! " + res.status);
            if(res.status == 401){
                this.logger.log('Unauthorized request. Trying to register the session and then retry the request.');
                return this.securityService.registerSession().subscribe(() => {
                    // What to do here so the client gets the result of the original request ??
                });
            }
        })
        .do((res:Response) => { this.afterCall(req, res) });

    return observable;
}

Looks like a dup of stackoverflow.com/questions/33941836/… — Günter Zöchbauer
– Günter Zöchbauer, Commented Apr 14, 2016 at 16:40
@Günter : Related but not a dupe IMO. I want to handle the error inside the wrapper and do something with it, then retry. He wants to return error feedback to the caller. — Pierre Henry
– Pierre Henry, Commented Apr 15, 2016 at 7:25
Has this solution been implemented? I have been trying to do the same but without any success. It would be really helpful if you can post the complete solution. — Abhinandan
– Abhinandan, Commented Sep 23, 2016 at 23:46

Thierry Templier · Accepted Answer · 2016-04-14 17:07:46Z

5

You could execute again the request after initialize the session using the flatMap operator of observables:

    var observable = this.http
        .request(req)
        .retry(3)
        .catch(res => {
            debugger;
            console.log("ERROR! " + res.status);
            if(res.status == 401){
                this.logger.log('Unauthorized request. Trying to register the session and then retry the request.');
                return this.securityService.registerSession().flatMap(() => {
                  return this.http.request(req); // <--------
                });
            }
        })
        .do((res:Response) => { this.afterCall(req, res) });

    return observable;
}

answered Apr 14, 2016 at 17:07

Thierry Templier

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1 Comment

Pardeep Jain Over a year ago

what does this mean retry(3) ? request executed 3 times if failed once ?

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