I have an iOS 5 app that uses NSURLConnection to load some XML via GET. On very rare occasions connections appear to get stuck in a condition where they timeout repeatedly.
An example request:
NSMutableURLRequest *request = [[NSMutableURLRequest alloc] init];
[request setURL:[NSURL URLWithString:url]];
/*
The request is set with a timeout interval of 10 because (due to the nature of
the app and the XML feed) this data is reloaded every 15 seconds.
*/
[request setTimeoutInterval:10];
[request setCachePolicy:NSURLRequestReloadIgnoringCacheData];
[request setHTTPMethod:#"GET"];
self.afOperation = [[AFHTTPRequestOperation alloc] initWithRequest:request];
self.afOperation.successCallbackQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND,0);
self.afOperation.failureCallbackQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND,0);
//snip success/completion block code
[self.afOperation start];
So far I've seen three "recovery" scenarios when the requests begin to hang.
Quit the entire app
Plug the device into a computer (yes, really). Right after the iPhone/iPad acknowledges the connection it will immediately stop timing out.
Leave the app and go do something else for awhile. Quickly leaving and reentering the app is typically insufficient to cause recovery.
As you might imagine, I find this incredibly bizarre. At this time I've replaced my own NSURLConnectionDelegate implementation with AFNetworking (as seen above) and am still running into the same problem. I've added logging to every NSURLConnectionDelegate protocol selector and found that the only selector called (after calling start) is connection:didFailWithError:. I've ensured I'm not piling up multiple requests (the previous request is always canceled and nil'd before starting a new one). Additionally, I've verified that no request is actually being sent via tcpdump on my router. What could cause this type of behavior?
It turns out this problem is caused by the TestFlight SDK v1.0 and below. See Why does NSURLConnection fail to reach the backend?
Until they release a fix there's no way to workaround the problem short of stripping out the SDK entirely.
I started seeing the error after installing the testflight sdk, and removing it helped me get rid of it. However, I think it's caused by the interaction between Testflight and ASIHttpRequest (or whichever rest kit you use). It can also be possibly resolved by the following the solution in the link below (disabling compiler optimization on your ASIHttpRequest and ASIFormDataRequest files in your build phases)
https://groups.google.com/forum/?fromgroups#!topic/asihttprequest/fw7PDcD2wKI%5B1-25%5D
Related
I am having a problem tracking the download progress for ASIFormDataRequest.
I can easily get the upload progress but not the download.
In the example on the ASIHTTPRequest site they use ASIHTTPRequest to show download progress.
So is it possible to get the download progress for the ASIFormDataRequest?
I already checked if I get the Content-Length response from the server, dunno what else I am doing wrong.
My setup.
ASIFormDataRequest *request = [ASIFormDataRequest requestWithURL:url];
request.downloadProgressDelegate = progressIndicator;
[request setShouldAttemptPersistentConnection:NO];
[self performSelectorOnMainThread:#selector(showProgress:) withObject:[NSNumber numberWithInt:0] waitUntilDone:NO];
[request startSynchronous];
The problem with the download progress for ASIFormDataRequest was that I didn't take into consideration the time server is processing the request.
When the ASIFormDataRequest reaches the server it waits until the server responds with the data. If you have to wait for server to perform some kind of calculation this period may take some time.
In my case the upload was super fast as well as the download, hence I could not see the progress, it was always 0 to 100%. The only process that was long and that got me confused was the calculation process the server was performing which in my case is undeterministic.
In short, all was working well, except my understanding... It happens all the time :-)
With work having recently stopped on ASIHTTPRequest, it seems like attention is shifting to AFNetworking.
However, I've not yet found a good comparison of the features of the two libraries, so I don't know what I might lose if/when I switch over.
Major differences I've spotted so far are:
AFNetworking has a much smaller code size (which is good)
AFNetworking is being rapidly improved (so it may not yet be mature, may not have a stable API yet?)
Both seem to have caching, though I've seen hints that because AFNetworking uses NSURLConnection it won't cache objects over 50K
ASIHTTPRequest has very good support for manual & automatic (PAC) http proxies; I can't find any information on what level of support AFNetworking has for proxies
AFNetworking requires iOS 4+, whereas ASIHTTPRequest works right back to iOS 2 (not really an issue for me, but it is an issue for some people)
AFNetworking doesn't (yet) have a built in persistent cache, but there's a persistent cache which has a pending pull request: https://github.com/gowalla/AFNetworking/pull/25
Has anyone seen any good comparisons of the two libraries or any documented experiences of switching from one to the other?
I loved ASIHTTPRequest and I was sad to see it go. However, the developer of ASI was right, ASIHTTPRequest has become so large and bloated that even he couldn't devote time to bring it to par with newest features of iOS and other frameworks. I moved on and now use AFNetworking.
That said, I must say that AFNetworking is much more unstable than ASIHTTP, and for the things I use it for, it needs refinement.
I often need to make HTTP requests to 100 HTTP sources before I display my results on screen, and I have put AFHTTPNetworkOperation into an operation queue. Before all results are downloaded, I want to be able to cancel all operations inside the operation queue and then dismiss the view controller that holds the results.
That doesn't always work.
I get crashes at random times with AFNetworking, while with ASIHTTPRequest, this operations were working flawlessly. I wish I could say which specific part of AFNetworking is crashing, as it keeps crashing at different points (however, most of these times the debugger points to the NSRunLoop that creates an NSURLConnection object). So, AFNetworking needs to mature in order to be considered as complete as ASIHTTPRequest was.
Also, ASIHTTPRequests supports client authentication, which AFNetworking lacks at the moment. The only way to implement it is to subclass AFHTTPRequestOperation and to override NSURLConnection's authentication methods. However, if you start getting involved with NSURLConnection, you will notice that putting NSURLConnection inside an NSOperation wrapper and writing completion blocks isn't so hard as it sounds and you will start thinking what keeps you from dumping 3rd party libraries.
ASI uses a whole different approach, since it uses CFNetworking (lower-level foundation frameworks based on C) to make downloading and file uploading possible, skipping NSURLConnection completely, and touching concepts most of us OS X and iOS developers are too afraid to. Because of this, you get better file uploading and downloading, even web page caches.
Which do i prefer? It's hard to say. If AFNetworking matures enough, I will like it more than ASI. Until then, I can't help but admire ASI, and the way it became one of the most used frameworks of all time for OS X and iOS.
EDIT:
I think it's time to update this answer, as things have changed a bit after this post.
This post was written some time ago, and AFNetworking has matured enough. 1-2 months ago AF posted a small update for POST operations that was my last complaint about the framework (a small line ending fault was the reason that echonest uploads failed with AF but were completed fine with ASI). Authentication is not an issue with AFnetworking, as for complex authentication methods you can subclass the operation and make your own calls and AFHTTPClient makes basic authentication a piece of cake. By subclassing AFHTTPClient you can make an entire service consumer in little time.
Not to mention the absolutely necessary UIImage additions that AFNetworking offers. With blocks and custom completion blocks and some clever algorithm, you can make table views with asynchronous image downloading and cell filling pretty easily, whereas in ASI you had to make operation queues for bandwidth throttling and mind yourself to cancel and resume the operation queue according to table view visibility, and stuff like that. Development time of such operations has been halved.
I also love the success and failure blocks. ASI has only a completion block (which is actually the completion block of NSOperation). You had to check whether you had an error on completion and act accordingly. For complex web services, you could get lost in all the "ifs" and "elses"; In AFNetworking, things are much more simple and intuitive.
ASI was great for its time, but with AF you can change the way you handle web services completely in a good way, and make scalable applications more easily. I really believe that there is no reason whatsoever to stick with ASI anymore, unless you want to target iOS 3 and below.
Just finishing up a project where I'm using AFNetworking instead of ASI. Have used ASI on previous projects; it's been a great help in the past.
Here's what AFNetworking is missing (as of today) that you should know about:
Nothing
ASI is going away. Use AF now. It's small, it works, and it's going to continue to be supported. It's also organized more logically, especially for API clients. It has a number of great classes for oft-used special cases like asynchronous loading of images in table views.
AFNetworking doesn't support clientCertificateIdentity and clientCertificates for TLS client authentication.
We can do that with the - (void)connection:(NSURLConnection *)connection didReceiveAuthenticationChallenge:(NSURLAuthenticationChallenge *)challenge method in a subclass of AFURLConnectionOperation but it's not as easy.
I've been using ASI* for a while now and I absolutely love the fileupload approach of ASI, and though I am excited to jump to AFNetworking, fileupload support in AfNetworking is not as easy to use compared to ASI*.
Until now I couldn't figure out how to set a timeout with AFNetworking when doing a synchronous POST request. UPDATE: I finally figured out: https://stackoverflow.com/a/8774125/601466
Now switching to AFNetworking : ]
==================
Apple overrides the timeout for a POST, setting it to 240 seconds (in case it was set shorter then the 240 seconds), and you can't change it. With ASIHTTP you just set a timeout and it works.
A code example with a synchronous POST request:
NSDictionary *params = [NSDictionary dictionaryWithObjectsAndKeys:
#"doSomething", #"task",
#"foo", #"bar",
nil];
AFHTTPClient *httpClient = [[AFHTTPClient alloc] initWithBaseURL:[NSURL URLWithString:baseURL]];
NSMutableURLRequest *request = [httpClient requestWithMethod:#"POST" path:requestURL parameters:params];
[httpClient release];
AFHTTPRequestOperation *operation = [[[AFHTTPRequestOperation alloc] initWithRequest:request] autorelease];
[operation setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {}
failure:^(AFHTTPRequestOperation *operation, NSError *error) {
NDLog(#"fail! %#", [error localizedDescription]);
}];
NSOperationQueue *queue = [[[NSOperationQueue alloc] init] autorelease];
[[AFNetworkActivityIndicatorManager sharedManager] incrementActivityCount];
[queue addOperation:operation];
[queue waitUntilAllOperationsAreFinished]; // Stuck here for at least 240 seconds!
[[AFNetworkActivityIndicatorManager sharedManager] decrementActivityCount];
if (![[operation responseString] isEqualToString:#""]) {
return [operation responseString];
}
return nil;
I tried to set a timeout here, but nothing worked. This issue keeps me from migrating to AFNetworking.
See also here: How to set a timeout with AFNetworking
AFNetwork lacks the ability to upload large files. It assumes file content is in RAM.
ASI was smart enough to simply stream file content from disk.
In ASIHTTP I loved that I could attach a userinfo dictionary to individual requests. As far as I see there is no direct support for this in AFHTTPRequestOperation. Has anyone come up with an elegant workaround yet? Apart from the trivial subclassing of course.
AFNetworking works with "blocks" which is more natural for me than working with delegates like ASIHTTPRequest does.
Working with blocks it's like working with Anonymous Function in javascript.
I have an app that makes moderate use of NSURLConnection. These async calls eventually finish and release properly (it looks like), but sometimes it takes some time for them to finish.
So, there are times when I exit the app, (note, not just sending it the background), that some of these connections are still active. If I immediately restart the app, the app freezes on startup. (didFinishLaunchingWithOptions never seems to get called).
While I'm not certain these connections are the issue, it would probably be good to terminate or cancel any remaining. Any suggestions on how to do this?
Bonus points on how to debug the restart also. (I'm already saving NSLog statements to a downloadable file)
You can cancel any NSURLConnection by sending it a cancel command.
[connection cancel];
From Apple docs
Cancels an asynchronous load of a
request. Once this method is called,
the receiver’s delegate will no longer
receive any messages for this
NSURLConnection.
Your start up issue could be related but hard to tell without knowing what type of data you're downloading and how you are using it.
Make sure you are calling release on the connection. Maybe it doesn't call shutdown or close on the socket until the last reference is dropped. I do something like this with no issues with references.
NSURLRequest *request = [[NSURLRequest alloc] initWithURL:url];
NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:request delegate:self];
[connection release];
[request release];
For cancel last request : [NSURLConnection cancelPreviousPerformRequestsWithTarget:self];
For cancel any specific request : [request cancel];
Note: Here request is the instance of NSURLConnection
I would like to start a server request, you can cancel.
My idea is to start the request in a thread so that the user interface does not freeze. So you can kill the whole thread including the request with a click on a "Cancel"-button.
With Android it works: the server request gets started in a "AsyncTask" and in the "onReturn()"-method I can react as soon as the server request finish.
How can I implement this using Objective-C on iOS?
My first attempt was a "NSInvocationOperation". You can cancel the operation, but it's difficult to handle when a request is completed and results are available. I think NSInvocationOperation is not the solution for my issue.
The would you recommend to me? Is NSThread the right choice for me?
Thank you very much!
Note!
This extremely old answer is now here only for historic purposes.
The wonderful ASIHttpRequest library no longer exists; technology is totally different now.
It is unbelievably simple to do this with ASIHttpRequest.
(Asynchronous is so simple, there is no reason you would ever do it not-asynchronously.)
Here are some rough extracts that might get you started.
...
ASIFormDataRequest *request;
...
NSURL *url = [NSURL URLWithString:#"https://blah.blah/blah.cgi?blah"];
request = [ASIFormDataRequest requestWithURL:url];
[request setPostValue:#"fred" forKey:#"username"];
[request setPostValue:#"flint" forKey:#"passie"];
[request setPostValue:#"stone" forKey:#"town"];
// send up data...
[request setData:[NSData dataWithBytes:blah length:blah] forKey:#"thefile"];
// or perhaps something like...
[request setData:imageData withFileName:#"blah.png"
andContentType:#"image/jpeg" forKey:#"photoimage"];
[request setDelegate:self];
[request setDidFinishSelector:#selector(postingDone:)];
[request setDidFailSelector:#selector(postingDoneProblem:)];
[request startAsynchronous];
...
-(void) postingDone:(ASIHTTPRequest *)request
{
// it worked
}
-(void) postingDoneProblem:(ASIHTTPRequest *)request
{
// failed
}
Couldn't really be any easier. You're basically just typing out the fields and values.
Per your question, here is how you cancel an "in-flight" request... just set the delegate to nil and then "cancel" it.
[myRequest setDelegate:nil];
[myRequest cancel];
[myRequest release];
ASIHttpRequest is the "miracle library". If you are new to iOS, ASIHttpRequest is simply THE most used 3rd party library. Essentially, every single iPhone app of the 300,000 iPhone apps uses it.
If at all possible BE SURE to donate a few bucks to the guy -- if he stops supporting that library, 100,000 iPhone programmers are buggered!
the documentation is trivial, a child can follow it:
http://allseeing-i.com/ASIHTTPRequest/How-to-use
"Creating an asynchronous request"
it is probably - almost certainly - the most amazingly simple networking library on any platform. It is trivial to do what you describe, happily. Enjoy.
NSURLConnection is async by default and supports cancelation as well as delegate methods when connection has been established, data has been received or whole request has been completed.
Also data transfer takes place in background so that UI stays responsive.
Cocoa's built-in async networking code is not thread-based but works with run loop events, but the result (asynchronous connections) is the same.
Create an NSURLConnection with +[NSURLConnection connectionWithRequest:delegate:]. The delegate you set will be informed about the progress of the connection and can cancel it anytime with -[NSURLConnection cancel].
Check out ASIHTTPRequest, specifically, the ASINetworkQueue subclass, which is described as:
ASINetworkQueue
A subclass of NSOperationQueue that
may be used to track progress across
multiple requests.
I've only used ASIHTTPRequest for a single synchronous request to download directly to disk, which was easy to implement, but I've heard good reports of using queues to manage multiple asynchronous server requests at once.
One thing to note on the recommendations to use +[NSURLConnection connectionWithRequest:delegate:] is that it should only be called from the main thread as of iOS 4.
see http://blog.mugunthkumar.com/coding/ios4-issue-nsurlconnection-and-nsoperation/ for an example of how to deal with this.
I am working on an application where the user at some point must wait for a proper response from a webservice. This might take some time, because it requires a manual confirmation from the webservice. Because of this, the timeoutInterval on the request is set very high to prevent it from terminating too early.
The problem comes when starting the application immediately after the program has returned to the home screen. The application will not start (black screen), and I think it is because the request hasn't been released and is still waiting for a response (I might be wrong though).
I tried the applicationWillTerminate method, but it isn't called when pressing the home button. Again, this might be because the application is still waiting for a response, but a better explanation would be greatly appreciated :)
Also, does someone have any idea on what to do?
code:
NSURLRequest *theRequest=[NSURLRequest requestWithURL:[NSURL URLWithString:urlAdress]
cachePolicy:NSURLRequestUseProtocolCachePolicy
timeoutInterval:10000];
NSHTTPURLResponse* response = nil;
NSError* error = nil;
NSData *responseData = [NSURLConnection sendSynchronousRequest:theRequest
returningResponse:&response
error:&error];
Making a synchronous request on the main thread will block the entire run loop until you receive a response or the request times out. Nothing will get called during this time, including applicationWillTerminate. It is a very bad idea to do this. You should either detach a separate thread for the request or create an asynchronous NSURLConnection.
That being said, the OS will free all memory anyway when it terminates your app so there is little chance that anything from the last launch will be "left over" upon relaunch. Unless your server is blocked because it lost its client when your app terminated. In which case you have to write your server in a way that can handle such a case because it can happen anytime.
If the applicationWillTerminate delegate method is not called,
Then I guess the following delegate method would be getting called.
- (void)applicationWillResignActive:(UIApplication *)application
{
NSLog(#"Application Did Resign Active");
}