Multiple POST Requests Occurring - ios

Question

I am seeing strange behaviour on an iOS app with a Rails/Heroku backend. I'll try to give as much detail as possible. Hopefully someone can point out a few possible areas where the problem could arise.
I wrote an iOS 7 app using XCode 5 where a user can log in and POST new articles and comments. I am using the AFNetworking library to communicate with my backend server (Rails 4, Heroku & Postgres). I am POSTing and GETing in the JSON format so I make use of AFJSONRequsetOperation to handle communication.
All my POST's use this method:
- (void) Post:(void (^)(NSURLRequest *request, NSHTTPURLResponse *response, id JSON))success
:(void (^)(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error, id JSON))failure
// allocate a reachability object
Reachability* reach = [Reachability reachabilityWithHostname:#"www.google.com"];
reach.unreachableBlock = ^(Reachability*reach)
{
dispatch_async(dispatch_get_main_queue(), ^{
UIWindow *window = [[[UIApplication sharedApplication] windows] lastObject];
[HUD flashMessage :#"Whoops" :#"No internet connection" :window];
});
failure(nil, nil, nil, nil);
};
reach.reachableBlock = ^(Reachability*reach)
{
// prepare base URL and calculate signature
// Something like: https://myapp.herokuapp.com
NSURL *url = [NSURL URLWithString:BasePath];
AFHTTPClient *httpClient = [[AFHTTPClient alloc] initWithBaseURL:url];
[httpClient registerHTTPOperationClass:[AFJSONRequestOperation class]];
[httpClient setDefaultHeader:#"Accept" value:#"application/json"];
// Generates the POST URL
// Something like: https://myapp.herokuapp.com/api/v1/articles.json
NSString *basePath = [self GetPostURL];
NSLog(#"Post %# With parameters: %#", basePath, Parameters);
NSMutableURLRequest *request = [httpClient requestWithMethod:#"POST" path:basePath parameters:Parameters];
AFJSONRequestOperation *operation = [AFJSONRequestOperation JSONRequestOperationWithRequest:request success:success failure:failure];
[operation start];
};
[reach startNotifier];
}
I did a bit of testing on my iPhone 5. Viewing the list of articles in a tableview, viewing article details in a detail view and then another tableview to view and add comments. I did a lot of testing and noticed no problem. Eventually I saw that there was 3 of the exact same comments. I thought I must of double-tapped on the 'Add' button so disable the button on-tap. I thought no-more about it as it was near impossible to re-create.
I have since updated my phone to iOS 8 and updated my XCode and SDKs to reflect this.
I put the app on my friends phone (iOS 8 & iPhone 5 C). She used it for a day without seeing any problems. She viewed articles, comments and added her own with no problems.
Today was a different story.
Firstly, a bit of background information. When you open the app - I refresh the list of articles so the app usually appears showing the old list of articles, then a loading icon appears, the tableview flashes and the newest articles appear.
When she opened the app today - it flashed multiple times, it looked like 10 or so. When the tableview appeared, the article she posted yesterday appeared twice. The exact article (title, description ,lat/lng, image) appeared twice but with different timestamps.
I thought the app was playing up on her phone so I checked the backend. It had two separate articles, different ids and timestamps but an exact copy otherwise.
Looking at the logs, there was something like 20/30 GET requests from her account. This seems to correspond with the flashing upon opening. It was updating the tableview multiple times.
Then the logs showed a POST request with all the params she POSTed the day before. Its as if she actually posted the exact same article today - but obviously she didn't.
Has anyone seen this kind of thing before?
The only things I can think of are:
The add article view controller was not destroyed after the initial post and somehow was made active again. I presumed ARC would handle all this?
Perhaps the AFNetworking library doesn't get flushed and thinks it needs to post again? Albeit nearly 24 hours later.
Is there a request batch operation on the library? Maybe this could be a problem?
I use a 'dispatch_get_global_queue' when posting. Is this okay?
On successfully adding an article, I move to the list again using the below code. Maybe there is a problem with it that I am unaware of?
ArticleListViewController *articleList = (ArticleListViewController *)[self.storyboard instantiateInitialViewController];
articleList.modalTransitionStyle = UIModalTransitionStyleCrossDissolve;
[self articleList animated:YES completion:nil];
I am at a loss trying to even replicate it, not to mention fix it.
I assume I am correct in pointing the finger at the app? It doesn't seem to be a problem with heroku/rails.
Any help would be greatly appreciated.
Update
I just had this issue again.
I did some testing yesterday, adding 3 articles. Everything worked as expected. I would occasionally go into the app every few hours to make sure everything is okay. I just opened the app now and it started flashing/flickering. It updated the list with a new article I posted yesterday. I did nothing with and it flickered again, and the same article was added again (so thats 2 duplicates with todays created_at date). I continued doing nothing and in a few seconds the other 2 articles that I added yesterday had been updated. One article was added 3 times, one article 2 times and one article was just duplicated once. This is bizarre behaviour.
Could there be some sort of global variable or something that keeps all the data? Maybe the controllers aren't removed completely?
Brian

Answer 1

After endless testing. I found the problem.
The duplicate POST(s) occurred at random. When it did occur it seemed to only happen 1% of the time, sometimes 5 minutes later, sometimes a day later.
I eventually figured out that it had something to do with switching from 3G to WiFi.
Adding an article on 3G, then changing to WiFi would cause a duplicate.
The problem is with the Reachability blocks in my above code.
I start the reachability notifier and set up two blocks for reachable and unreachable.
These blocks get hit when the phone changes reachability state. So moving from 3G to Wifi hit the reachable block again, resulting in a duplicate POST.
A simple fix is to call the following line at the start of each block to prevent further updates:
[reach stopNotifier];
Or, implement reachability like:
-(BOOL)reachable {
Reachability *r = [Reachability reachabilityWithHostName:#"www.google.com"];
NetworkStatus internetStatus = [r currentReachabilityStatus];
if(internetStatus == NotReachable) {
return NO;
}
return YES;
}
// In POST method
if([self reachable])
{
// Do POST
}else{
// No connection
}