iOS - Re-Attempt Failed NSURLRequests In NSURLSession - ios

Question

In my app, 2-4 API calls to my server can be happening at the same time (asynchronously) within my API class's NSURLSession. In order to make API requests to my server, I must supply the authentication token in the HTTPHeaderField of each NSURLRequest. The token is valid for one day, and if it becomes invalid after one day, I need to refresh the token.
I do this in the following code in my API class:
/*!
* #brief sends a request as an NSHTTPURLResponse. This method is private.
* #param request The request to send.
* #param success A block to be called if the request is successful.
* #param error A block to be called if the request fails.
*/
-(void)sendTask:(NSURLRequest*)request successCallback:(void (^)(NSDictionary*))success errorCallback:(void (^)(NSString*))errorCallback
{
NSURLSessionDataTask *task = [self.session dataTaskWithRequest:request completionHandler:^(NSData *data, NSURLResponse *response, NSError *error)
{
[self parseResponse:response data:data fromRequest:request successCallback:success errorCallback:^(NSString *error)
{
//if auth token expired and getting "not authenticated" error (status 401)
NSHTTPURLResponse *httpResp = (NSHTTPURLResponse*) response;
if (httpResp.statusCode == 401) {
[self refreshAuthenticationTokenWithSuccessCallback:^(NSDictionary *response) {
self.authToken = response[#"token"];
//attempt to re-try the request that failed due to token expiration
[self sendTask:request successCallback:success errorCallback:errorCallback];
} errorCallback:^(NSString *error) {
//two weeks have passed and the token is no longer refreshable
NSLog(#"TOKEN NOT REFRESHABLE! HAVE TO LOG IN MANUALLY");
}];
}
}];
}];
[task resume];
}
This sendTask method gets executed with every API request I make in the app, so I just realized this is a bad way of doing it. If 3 API requests fail due to the token being invalid (one day passed), then all 3 of these API requests are going to attempt to make the API call to refresh the authentication token.
Is there a way for me to, in case ONE of the API requests fail, refresh the authentication token only ONCE and then re-attempt the failed API calls?
EDIT
I edited the title of the question to indicate that I'm working with NSURLSession
PROGRESS
So far, to prevent several failed API requests from trying to refresh the authentication token at the same time, I have an NSArray for all the failed requests and an NSNumber that serves as a lock to make sure that the authentication token is only trying to be refreshed once. I do this in the following code:
-(void)sendTask:(NSURLRequest*)request successCallback:(void (^)(NSDictionary*))success errorCallback:(void (^)(NSString*))errorCallback
{
NSURLSessionDataTask *task = [self.session dataTaskWithRequest:request completionHandler:^(NSData *data, NSURLResponse *response, NSError *error)
{
MyAPIInterface *__weak weakSelf = self;
[self parseResponse:response data:data fromRequest:request successCallback:success errorCallback:^(NSString *error)
{
NSHTTPURLResponse *httpResp = (NSHTTPURLResponse*) response;
if (httpResp.statusCode == 401) {
if ([error isEqualToString:#"invalid_credentials"]) {
errorCallback(#"Invalid username and/or password");
}
else if ([error isEqualToString:#"Unknown error"]) {
errorCallback(error);
}
else {
if (!weakSelf.alreadyRefreshingToken.boolValue) {
//lock alreadyRefreshingToken boolean
weakSelf.alreadyRefreshingToken = [NSNumber numberWithBool:YES];
NSLog(#"NOT REFRESHING TOKEN");
// add failed request to failedRequests array
NSMutableArray *mutableFailedRequests = [weakSelf.failedRequests mutableCopy];
[mutableFailedRequests addObject:request];
weakSelf.failedRequests = [mutableFailedRequests copy];
// refresh auth token
[weakSelf refreshAuthenticationTokenWithSuccessCallback:^(NSDictionary *response) {
//store authToken
weakSelf.authToken = response[#"token"];
NSUserDefaults* defaults = [NSUserDefaults standardUserDefaults];
[defaults setObject:weakSelf.authToken forKey:#"authToken"];
[defaults synchronize];
//attempt to re-try all requests that failed due to token expiration
for (NSURLRequest *failedRequest in weakSelf.failedRequests) {
[weakSelf sendTask:failedRequest successCallback:success errorCallback:errorCallback];
}
//clear failedRequests array and unlock alreadyRefreshingToken boolean
[weakSelf clearFailedRequests];
weakSelf.alreadyRefreshingToken = [NSNumber numberWithBool:NO];
NSLog(#"TOKEN REFRESHING SUCCESSFUL THO");
} errorCallback:^(NSString *error) {
NSLog(#"TOKEN NOT REFRESHABLE! HAVE TO LOG IN MANUALLY");
//clear failedRequests array
[weakSelf clearFailedRequests];
errorCallback(#"Your login session has expired");
}];
}
else {
NSLog(#"ALREADY REFRESHING TOKEN. JUST ADD TO FAILED LIST");
NSMutableArray *mutableFailedRequests = [weakSelf.failedRequests mutableCopy];
[mutableFailedRequests addObject:request];
weakSelf.failedRequests = [mutableFailedRequests copy];
}
}
}
else {
NSLog(#"ERROR STRING THO: %#", error);
errorCallback(error);
}
}];
}];
[task resume];
}
#pragma mark Custom Methods
-(void)clearFailedRequests {
NSMutableArray *mutableFailedRequests = [self.failedRequests mutableCopy];
[mutableFailedRequests removeAllObjects];
self.failedRequests = [mutableFailedRequests copy];
}
Am I going about this correctly? One part that I'm paranoid about is that I'm not really calling the success or error callback at certain points. Can this lead to problems?

Answer 1

Instead of using [self sendTask:], try with [weakSelf sendTask]. Check below code:
-(void)sendTask:(NSURLRequest*)request successCallback:(void (^)(NSDictionary*))success errorCallback:(void (^)(NSString*))errorCallback
{
__weak __typeof(self)weakSelf = self;
NSURLSessionDataTask *task = [self.session dataTaskWithRequest:request completionHandler:^(NSData *data, NSURLResponse *response, NSError *error)
{
[self parseResponse:response data:data fromRequest:request successCallback:success errorCallback:^(NSString *error)
{
//if auth token expired and getting "not authenticated" error (status 401)
NSHTTPURLResponse *httpResp = (NSHTTPURLResponse*) response;
if (httpResp.statusCode == 401) {
[self refreshAuthenticationTokenWithSuccessCallback:^(NSDictionary *response) {
self.authToken = response[#"token"];
//attempt to re-try the request that failed due to token expiration
[weakSelf sendTask:request successCallback:success errorCallback:errorCallback];
} errorCallback:^(NSString *error) {
//two weeks have passed and the token is no longer refreshable
NSLog(#"TOKEN NOT REFRESHABLE! HAVE TO LOG IN MANUALLY");
}];
}
}];
}];
[task resume];
}