Retry failed requests with $http interceptor

Question

The API my webapp is talking to sometimes overloads and is sending 500 Internal Server Error if it cannot handle request.

There are 100+ different requests my web application can send, so if I implement retry on each individually, it will cost me hours of typing.

I'm already using $httpProvider interceptor, here it is (simplified)

$httpProvider.interceptors.push(function ($q) {
    return {
        responseError: function (response) {
            switch (response.status) {
                case 401 :
                    window.location = "/";
                    alert('Session has expired. Redirecting to login page');
                    break;
                case 500 :
                    // TODO: retry the request
                    break;
            }
            return $q.reject(response);
        }
    };
});

How could I resend a request after getting 500 response code from the server?

Answer 1

Angular provides reference to the config object which was used by $http service for doing the request in the response (response.config). That means if we can inject $http service in the interceptor we can easily resend the request. Simple injecting of $http service in the interceptor is not possible because of the circular dependency but luckily there is a workaround for that.

This is an example how the implementation of a such interceptor can be done.

$httpProvider.interceptors.push(function ($q, $injector) {
    var incrementalTimeout = 1000;

    function retryRequest (httpConfig) {
        var $timeout = $injector.get('$timeout');
        var thisTimeout = incrementalTimeout;
        incrementalTimeout *= 2;
        return $timeout(function() {
            var $http = $injector.get('$http');
            return $http(httpConfig);
        }, thisTimeout);
    };

    return {
        responseError: function (response) {
            if (response.status === 500) {
                if (incrementalTimeout < 5000) {
                    return retryRequest(response.config);
                }
                else {
                    alert('The remote server seems to be busy at the moment. Please try again in 5 minutes');
                }
            }
            else {
                incrementalTimeout = 1000;
            }
            return $q.reject(response);
        }
    };
});

Note: In this example implementation the interceptor will retry the request until you receive a response with status that is different than 500. Improvement to this can be adding some timeout before retrying and retrying only once.

Answer 2

You can check for any possible server side errors by expanding the status code check a little more. This interceptor will attempt to retry the request multiple times and will do so on any response code 500 or higher. It will wait 1 second before retrying, and give up after 3 tries.

$httpProvider.interceptors.push(function ($q, $injector) {

    var retries = 0,
        waitBetweenErrors = 1000,
        maxRetries = 3;

    function onResponseError(httpConfig) {
        var $http = $injector.get('$http');
        setTimeout(function () {
            return $http(httpConfig);
        }, waitBetweenErrors);
    }

    return {
        responseError: function (response) {
            if (response.status >= 500 && retries < maxRetries) {
                retries++;
                return onResponseError(response.config);
            }
            retries = 0;
            return $q.reject(response);
        }
    };
});

Answer 3

I wanted to retry requests in my response block also, so combining multiple answers from different posts from SO, I've written my interceptor as follows -

app.config(['$httpProvider', function ($httpProvider) {
    $httpProvider.interceptors.push(['$rootScope', '$cookies', '$q', '$injector', function ($rootScope, $cookies, $q, $injector) {
        var retries = 0, maxRetries = 3;

        return {
            request: function (config) {
                var csrf = $cookies.get("CSRF-Token");
                config.headers['X-CSRF-Token'] = csrf;
                if (config.data) config.data['CSRF-Token'] = csrf;
                return config;
            },
            response: function (r) {
                if (r.data.rCode == "000") {
                    $rootScope.serviceError = true;
                    if (retries < maxRetries) {
                        retries++;
                        var $http = $injector.get('$http');
                        return $http(r.config);
                    } else {
                        console.log('The remote server seems to be busy at the moment. Please try again in 5 minutes');
                    }
                }
                return r;
            },
            responseError: function (r) {
                if (r.status === 500) {
                    if (retries < maxRetries) {
                        retries++;
                        var $http = $injector.get('$http');
                        return $http(r.config);
                    } else {
                        console.log('The remote server seems to be busy at the moment. Please try again in 5 minutes');
                    }
                }

                retries = 0;
                return $q.reject(r);
            }
        }
    }]);
}])

credits to @S.Klechkovski, @Cameron & https://stackoverflow.com/a/20915196/5729813