How to retry a block based URL Request - ios

Question

I am fetching data using iOS7's new URL request methods, like so:
NSMutableURLRequest *request = [NSMutableURLRequest
requestWithURL:[NSURL URLWithString:[self.baseUrl
stringByAppendingString:path]]];
NSURLSessionDataTask *dataTask = [[NSURLSession sharedSession] dataTaskWithRequest:request completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
NSHTTPURLResponse* httpResponse = (NSHTTPURLResponse*)response;
NSUInteger responseStatusCode = [httpResponse statusCode];
if (responseStatusCode != 200) {
// RETRY (??????)
} else
completionBlock(results[#"result"][symbol]);
}];
[dataTask resume];
Unfortunately, from time to time I get HTTP responses indicating the server is not reachable (response code != 200) and need to resend the same request to the server.
How can this be done? How would I need to complete my code snippet above where my comment // RETRY is?
In my example I call the completion block after a successful fetch.
But how can I send the same request again?
Thank you!

Answer 1

It is better to have a retry counter to prevent your method from running forever:
- (void)someMethodWithRetryCounter:(int) retryCounter
{
if (retryCounter == 0) {
return;
}
retryCounter--;
NSMutableURLRequest *request = [NSMutableURLRequest
requestWithURL:[NSURL URLWithString:[self.baseUrl
stringByAppendingString:path]]];
__weak __typeof(self)weakSelf = self;
NSURLSessionDataTask *dataTask = [[NSURLSession sharedSession] dataTaskWithRequest:request completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
NSHTTPURLResponse* httpResponse = (NSHTTPURLResponse*)response;
NSUInteger responseStatusCode = [httpResponse statusCode];
if (responseStatusCode != 200) {
[weakSelf someMethodWithRetryCounter: retryCounter];
} else
completionBlock(results[#"result"][symbol]);
}];
[dataTask resume];
}
It should be called following way:
[self someMethodWithRetryCounter:5];

Answer 2

Put your request code in a method and call it again in a dispatch_async block ;)
- (void)requestMethod {
NSMutableURLRequest *request = [NSMutableURLRequest
requestWithURL:[NSURL URLWithString:[self.baseUrl
stringByAppendingString:path]]];
__weak typeof (self) weakSelf = self;
NSURLSessionDataTask *dataTask = [[NSURLSession sharedSession] dataTaskWithRequest:request completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
NSHTTPURLResponse* httpResponse = (NSHTTPURLResponse*)response;
NSUInteger responseStatusCode = [httpResponse statusCode];
if (responseStatusCode != 200) {
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0ul), ^{
[weakSelf requestMethod];
});
} else
completionBlock(results[#"result"][symbol]);
}];
[dataTask resume];
}