Background
I'm writing an part of my app that has no UI. It sits in the background watching what you do and timing your work.
There should be no overlapping times, and there should be no breaks in the time data. If there are either of these things, the app has a bug somewhere and I need to be notified.
What I Want
A class called JGDataIntegrityController that does the following:
Check the data store for duplicate times. Scan since the last Duplicate Report Date stored in NSUserDefaults.
If duplicate times are found, build a report.
Send the report.
If the sending isn't successful, then exit. Otherwise continue.
Remove the duplicates
Update the last Duplicate Report Date in NSUserDefaults
Repeat the above for data breaks.
What I've Got
I've made a base class that does all the hard work of sending the report.
Class Diagram http://synapticmishap.co.uk/ReportClasses.jpg
JGReportSender has the following code:
-(void)postReport:(NSString *)report {
NSMutableDictionary *form = // Dictionary Holding Report;
NSURLRequest *request = [NSURLRequest requestWithURL:#"http://postURL" postForm:form];
[NSURLConnection connectionWithRequest:request delegate:self];
}
Where I'm Getting Stuck
What should I do when the report has been sent?
The delegate methods:
-(void)connectionDidFinishLoading:(NSURLConnection *)connection
-(void)connection:(NSURLConnection *)connection didFailWithError:(NSError*)error
are called when the report has been sent. But how should I communicate with JGDataIntegrityController?
My Crap Idea
My idea is to have a reportStatus NSNumber property in JGReportSender. Then when the delegate methods get called, this is updated.
reportStatus = 1 means "report sent OK".
reportStatus = 2 means "problem sending report".
Then I could add an observer for reportStatus for JGDataDuplicateReportSender and JGDataBreakReportSender. This would then handle the report sending error or continue on.
Any Good Ideas?
I get the feeling this is a really messy way of doing this. I also feel like I'm overlooking something really obvious.
Any ideas how to do this in a neat way?
Update
I totally forgot to mention - this will be a 100% opt in feature. It'll be disabled by default. It'll also have 3 levels of privacy - from "a data break occurred" through to "a data break occurred after this application was active with this document path". And the reports will also be anonymous.
I'm conscious of all the privacy concerns - this is so I can make the software better, not so I can spy on people!
Give the report sender a delegate property and protocol, with at least two methods: reportSenderDidSucceed: and reportSender:failedWithError:. The report sender will send the latter message from its connection:didFailWithError: method, passing along the error object it got.
I do hope you'll make this feature optional. Expect lots of angry/curious email from users (not to mention public warnings of “don't use this app because it phones home” on web pages) if you don't.
Just a quick note to say if anyone wants a good tutorial on implementing your own delegates as Peter is suggesting I do, I found this one:
http://cocoadevcentral.com/articles/000075.php
Check it out. It's excellent!
Related
I am working on an OS X (Yosemite) app which downloads two types of csv data (call them type A and type B) from the internet asynchronously using the NSURLSession API .There are multiple requests for each type of csv. Each request is it's own dedicated session wrapped in a custom class. There is one base request class with a subclass for each type. (In hindsight maybe not an ideal design but irrelevant for my issue I think).
The app is constructed such that each type of csv data is downloaded in a sequential queue. Only one request of each type can be active at a time but both types can occur simultaneously and both use the main thread for delegate callbacks. All of this works fine usually.
The issue I am seeing is that sometimes with heavy traffic I get "cross hearing", i.e. I sometimes get a response back to a type B request that is reported as completed successfully but it contains a number of type B cvs lines and then some type A lines tagged on after - so I sometimes (rarely) get type A data in my type B requests. (or the other way around).
Basically it look like the "switching" logic in Apples API gets confused about which incoming packet belongs to what request/session. The two different request types goes to different URLs but they are related and it may be that they both in the end resolve to the same IP, I am not sure about that. I wonder if there may be something related to the packet headers if they come from the same server that makes it difficult to determine what request they belong to (I'm not good enough at the internet protocols to know if this is a sensible guess). If that is the case then the solution must be to ensure all requests are in one queue so that they cannot be active simultaneously, but I do not want to do that large architecture change before I am confident there is no other workaround.
I looked for similar questions and found this old question (Why is my data getting corrupted when I send requests asynchronously in objective c for iOS?) which appears to describe the exact same issue but unfortunately it has no answer. Other than that I found nothing similar so I guess I am doing something stupid here but it would be good to know why this issue occurs before I start changing the architecture to fix it.
Has anyone seen this before and know what the cause and workaround is?
I did not include any code as I felt there was no point given it appears to be an architecture issue and if I added code it would need to be a lot. However I will be happy to add whatever you suggest if that helps understand the question.
Edit:
The relevant (I hope) code added below. Note objects are one shot only. The parameters for the request are injected by the init method and the NSURLSession is used for a single task only. Hence the session is invalidated after launch and the NSMutableData array released after parsing of the data.
-(BOOL)executeRequest {
NSURLSessionConfiguration *theConfig = [NSURLSessionConfiguration ephemeralSessionConfiguration];
NSURLSession *theSession = [NSURLSession sessionWithConfiguration:theConfig delegate:self delegateQueue:[NSOperationQueue mainQueue]];
NSURLRequest *theRequest = [NSURLRequest requestWithURL:self.queryURL cachePolicy: NSURLRequestReloadIgnoringLocalCacheData timeoutInterval:BSTTIMEOUT];
NSURLSessionDataTask *theTask = [theSession dataTaskWithRequest:theRequest];
if(!theTask) {
return NO;
}
[theTask resume];
[theSession finishTasksAndInvalidate];
self.internetData = [NSMutableData dataWithCapacity:0];
return YES;
}
-(void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveData:(NSData *)data {
[self.internetData appendData:data];
return;
}
-(void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error {
if((error)||(![self parseData]))
{
self.internetData = nil;
if(!error) {
NSDictionary *errorDictionary = #{ NSLocalizedDescriptionKey : #"Parsing of internet data failed", NSLocalizedFailureReasonErrorKey : #"Bad data was found in received buffer"};
error = [NSError errorWithDomain:NSCocoaErrorDomain code:EIO userInfo:errorDictionary];
}
NSDictionary* ui = [NSDictionary dictionaryWithObject:error forKey:#"Error"];
[[NSNotificationCenter defaultCenter] postNotificationName:[self failNotification] object:self userInfo:ui];
return;
}
[[NSNotificationCenter defaultCenter] postNotificationName:[self successNotification] object:self];
return;
}
First of all: You should not create a new session for each request. This are no sessions anymore. From the docs:
With the NSURLSession API, your app creates one or more sessions, each of which coordinates a group of related data transfer tasks. For example, if you are writing a web browser, your app might create one session per tab or window, or one session for interactive use and another session for background downloads. Within each session, your app adds a series of tasks, each of which represents a request for a specific URL (following HTTP redirects if necessary).
Second: Where do you store the session et al., so it is not deallocated?
Your main problem: Obviously you start new requests while requests are potentially running. But you have only one NSMutableData instance that receives the data in -URLSession:task:didReceiveData:: Many requests, one storage … Of course that mixes up.
I finally managed to track down my (stupid) error. For future reference the issue was caused by a failure to realise that the data coming back was not zero terminated.
Most of the data requested in my case is XML and the NSXMLParserclass wants a NSDatawithout extra trailing zeros so that works well.
But the requests which occasionally failed uses a CSV format where the data passes over a NSStringwhich is created by [NSString stringWithUTF8String] which expects a zero terminated c style string as input. This was the main culprit. Often it worked as it should. Sometimes it failed outright and sometimes it just did a buffer overrun and got some of the previous request data that was in the same memory area. These were the cases I noticed when posting the question.
Thus the solution is to switch to the use of [[NSString alloc] initWithData: encoding:NSUTF8StringEncoding] which works with non null-terminated NSDatabuffers.
I am trying to set up a Java server talking to a iPhone client using GCDAsyncSocket. For some reason my client code on the iPhone is not reading back all of the data.
I see didReadData gets called the first time, but never again. Ideally, I need to mimic the functionality of the HTTP protocol where it sends a header and then the payload. The size of the payload would be in the header. But that wasn't working, so I simplified my code even further in hopes of finding the issue. Below is the code, and below that the output.
client:
- (BOOL) sendString:(NSString *) string
{
[asyncSocket writeData:[string dataUsingEncoding:NSUTF8StringEncoding]
withTimeout:-1 tag:TAG_PAYLOAD];
[asyncSocket readDataToLength:1 withTimeout:(-1) tag:TAG_HEADER];
}
- (void) socket:(GCDAsyncSocket *) sock didReadData:(NSData *)data
withTag:(long)tag
{
NSString *str = [[NSString alloc] initWithData:data
encoding:NSUTF8StringEncoding];
NSLog(#"Read data %# with tag: %ld", str, tag);
if(tag == TAG_HEADER)
{
//TODO - parse the header, get the fields
[sock readDataToLength:3 withTimeout:-1 tag:TAG_PAYLOAD];
//[sock readDataToData:[GCDAsyncSocket CRLFData] withTimeout:-1
tag:TAG_PAYLOAD];
}
else
{
NSLog(#"Payload... %#", str);
NSLog(#"Tag: %ld", tag);
}
}
Java server:
BufferedReader in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
PrintWriter out = new PrintWriter(new OutputStreamWriter(clientSocket.getOutputStream()));
String clientCommand = in.readLine();
System.out.println("Client Says :" + clientCommand);
out.println("Andrew\r\nAUSTIN\r\n");
out.flush();
However, on the client, the only thing I get back is A. The exact output is:
Read data A with tag: 10
My question is:
How come the didReadData method is never called again? There should be more of "Andrew\r\nAustin" recv'd back on the client. But it just hangs. The readDataToData and readDataToLength both seem to never get the full string.
I noticed the CRLF defined in GCDAsyncSocket.h is not \r\n but instead the hex values. Does this matter? Thats why I tried the readDataToLength method but that still failed. But I would like to know if this matters cross-platform or not.
Thanks.
OK - so I figured it out after pulling out what little hair I have left.
What is happening is that I have client code above in a separate class outside of the view. Practically all of the examples I came across had the GCDAsyncSocket stuff handled inside the view. It works great in there! I really didn't want to do this because on each view I need to send/read data and didn't want to duplicate my work. By placing an NSLog() line in the dealloc method of this helper class, called SocketComm, I was able to see it was getting deallocated before it was firing. So I needed to change the way I was calling my helper class. I declare SocketComm* sockComm a strong property in the viewController.h file and allocated it in the viewDidLoad() method. This means that it stays in scope the whole time. Of course, this means I need to deallocate it manually and do some other housekeeping things.
I still am not sure if this is the best way to handle this situation either, as far as memory management goes. Because now I will have to alloc this on every viewDidLoad method. It seems like it should be simpler than this, but here we are. And I still don't know why it never read the data the first time (my only guess is that the GCDAsyncSocket library or the iphone software detected a dead thread when the parent that spawned it got deallocated and decided to terminate it - but this is only a guess as I have just started objective-c).
This would also explain why sometimes it would work and sometimes it wouldn't. It seemed like it was in a race condition. Not sure if the above code I originally posted resulted in a race condition exactly, but some things I would try would work, and then the next time fail. It never read more than the first time though, and only about half the time would it even read that. Sometimes it wouldn't even send the data out over the socket!
In summation (and for whoever else comes looking for an answer):
Always check your memory management. I had to place an NSLog in dealloc() of the SocketComm helper class to fully see what was happening, and as soon as I did that I knew what the culprit was.
If you get weird results where sometimes it works and sometimes it doesn't, check your memory management. For me, sometimes it would do the first read and sometimes it wouldn't. This lead me to believe the thread was getting terminated.
If I find a better way to do this I will come back and update this answer.
Memory management. Let me repeat: memory management.
I'm investigating using NSURLSessionUploadTasks to manage the background uploading of a few files. The session is created using:
_urlsession = [NSURLSession sessionWithConfiguration:[NSURLSessionConfiguration backgroundSessionConfiguration:identifier] delegate:self delegateQueue:nil];
This is created within a class that conforms to URLSessionDataTaskDelegate, and specifically defines:
– URLSession:dataTask:didReceiveResponse:completionHandler:
– URLSession:dataTask:didBecomeDownloadTask:
– URLSession:dataTask:didReceiveData:
And logs to the console each time one of these delegates is called.
Then, an upload task is created with the following code:
NSString *urlString = [NSString stringWithFormat:#"%#%#?filename=%#", HOST, UPLOAD_PATH, filename];
NSMutableURLRequest *attachmentUploadRequest = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:urlString]];
attachmentUploadRequest.HTTPMethod = #"POST";
[attachmentUploadRequest addValue:#"application/binary" forHTTPHeaderField:#"Content-Type"];
NSURLSessionTask* task = [_urlsession uploadTaskWithRequest:attachmentUploadRequest fromFile:filePath];
task.taskDescription = 'upload';
However, the sequence of delegate callbacks that I get is not as expected:
URLSession:didReceiveChallenge:completionHandler:]:196: Respond with <NSURLCredential: 0x1cf4fe00>:
URLSession:task:didSendBodyData:totalBytesSent:totalBytesExpectedToSend:]:282: Task 'upload' sent 32768 bytes
URLSession:task:didSendBodyData:totalBytesSent:totalBytesExpectedToSend:]:282: Task 'upload' sent 48150 bytes
URLSession:dataTask:didReceiveData:]:222: Task 'upload' got some data:
Notably, the body data is sent, as expected, but then it switches immediately to didReceiveData delegate callbacks, with no didReceiveResponse callback beforehand. This is an unexpected behavior for me: I'd expected to receive information about the response so that I can properly set up data, or better yet, convert the task to a download task to save the response to a file.
If the upload task is submitted in a default URL session, then didReceiveResponse is called, and I can successfully convert the task to a background download task.
I can't find any indications in Apple's documentation for whether or not didReceiveResponse should be called for NSURLSessionUploadTasks that are in the background. It seems that they should: the documentation for NSURLSessionUploadTask indicates that it is a subclass of NSURLSessionDataTask with small modifications in behavior, but neither of the listed differences involves not sending the didReceiveResponse callback. None of the background-session-specific docs mention this limitation.
Is this a bug, or have a missed/misinterpreted some piece of the documentation that explain that upload tasks in the background do not call didReceiveResponse?
I asked Apple engineers about this during recent Tech Talks. They followed up and gave the following response - not entirely satisfactory, and I feel like they should document this behavior if it is different than any other HTTP handling flow. Especially since the foreground behavior does get the didReceiveData, but doesn't get the didReceiveResponse. At the very least they need to document this non-obvious behavior.
"The way things work today is that we don’t send the didReceiveResponse callback for background uploads to avoid waking the app if it’s not already running. The drawback is that the app cannot choose to convert the background upload into a download task when the response is received. Our decision was based on expecting the response data for a file upload would be small and therefore delivering the response data to the client as NSData instead of a downloaded file would be fine."
I am displaying information from a data model on a user interface. My current approach to doing so is by means of delegation as follows:
#protocol DataModelDelegate <NSObject>
- (void)updateUIFromDataModel;
#end
I am implementing the delegate method in my controller class as follows, using GCD to push the UI updating to the main thread:
- (void)updateUIFromDataModel {
dispatch_async(dispatch_get_main_queue(), ^{
// Code to update various UI controllers
// ...
// ...
});
}
What I am concerned about is that in some situations, this method can be called very frequently (~1000 times per second, each updating multiple UI objects), which to me feels very much like I am 'spamming' the main thread with commands.
Is this too much to be sending to the main thread? If so does anyone have any ideas on what would be the best way of approaching this?
I have looked into dispatch_apply, but that appears to be more useful when coalescing data, which is not what I am after - I really just want to skip updates if they are too frequent so only a sane amount of updates are sent to the main thread!
I was considering taking a different approach and implementing a timer instead to constantly poll the data, say every 10 ms, however since the data updating tends to be sporadic I feel that it would be wasteful to do so.
Combining both approaches, another option I have considered would be to wait for an update message and respond by setting the timer to poll the data at a set interval, and then disabling the timer if the data appears to have stopped changing. But would this be over-complicating the issue, and would the sane approach be to simply have a constant timer running?
edit: Added an answer below showing the adaptations using a dispatch source
One option is to use a Dispatch Source with type DISPATCH_SOURCE_TYPE_DATA_OR which lets you post events repeatedly and have libdispatch combine them together for you. When you have something to post, you use dispatch_source_merge_data to let it know there's something new to do. Multiple calls to dispatch_source_merge_data will be coalesced together if the target queue (in your case, the main queue) is busy.
I have been experimenting with dispatch sources and got it working as expected now - Here is how I have adapted my class implementation in case it is of use to anyone who comes across this question:
#implementation AppController {
#private
dispatch_source_t _gcdUpdateUI;
}
- (void)awakeFromNib {
// Added the following code to set up the dispatch source event handler:
_gcdUpdateUI = dispatch_source_create(DISPATCH_SOURCE_TYPE_DATA_ADD, 0, 0,
dispatch_get_main_queue());
dispatch_source_set_event_handler(_gcdUpdateUI, ^{
// For each UI element I want to update, pull data from model object:
// For testing purposes - print out a notification:
printf("Data Received. Messages Passed: %ld\n",
dispatch_source_get_data(_gcdUpdateUI));
});
dispatch_resume(_gcdUpdateUI);
}
And now in the delegate method I have removed the call to dispatch_async, and replaced it with the following:
- (void)updateUIFromDataModel {
dispatch_source_merge_data(_gcdUpdateUI, 1);
}
This is working absolutely fine for me. Now Even during the most intense data updating the UI stays perfectly responsive.
Although the printf() output was a very crude way of checking if the coalescing is working, a quick scrolling back up the console output showed me that the majority of the messages print outs had a value 1 (easily 98% of them), however there were the intermittent jumps to around 10-20, reaching a peak value of just over 100 coalesced messages around a time when the model was sending the most update messages.
Thanks again for the help!
If the app beach-balls under heavy load, then you've blocked the main thread for too long and you need to implement a coalescing strategy for UI updates. If the app remains responsive to clicks, and doesn't beach-ball, then you're fine.
After (eventually) shipping a v2 implementation of the Google Play in-app billing, I've had nothing but problems with it post-launch. Dropped transactions, crashes, unable to restore, crazy errors like "can't download, you already own this item", and all sorts of other ridiculous things. Honestly, I've integrated IAB on iOS, Amazon App Store, Samsung Apps and Blackberry 10 now and the Google Play code has taken more time than all the others combined. Times ten. It's just terrible.
Anywayyyy, I've decided to try and implement v3 into my app. The integration process was much, much simpler, so kudos to Google for that. Also, restoring previous transactions now works as expected so that's great. However, I've got a couple of show-stopping problems:
When the user dismisses the IAB dialog (i.e. tapping outside of the dialog borders), I don't receive any notification of this. I would expect to receive some kind of "user cancelled" failure event, but nothing is fired to onIabPurchaseFinished, onConsumeFinished or onQueryInventoryFinished. As a result my app doesn't respond to this and I'm left with a dirty great unused Activity on the screen. Am I missing some kind of "dialogIsFinished" event?
When the user tries to purchase an item that they already own, the app crashes. Unbelievably it looks like this is the intended behaviour, as there's something alluding to this printed to the console ("In-app billing error: Unable to buy item, Error response: 7:Item Already Owned"). I understand that I'm supposed to query for restorable transactions at launch, but this isn't a solution as it's conceivable the user can navigate to the purchase flow of my UI before the restore operation finishes. Surely this should be a non-hard stop, like a dialog box or something? Am I doing something wrong here? I simply can't understand that somebody at Google thinks that this situation deserves a hard crash...
Thanks very much (in advance) for your help. I'm more than happy to share code if you think it's necessary, although my questions seem to be more about the functional design more than anything else. I'm hoping that I'm doing something wrong here, as it's inconceivable to me that a company as capable as Google would re-write this entire system and still have such massive holes all over the place... :-/
Thanks again,
Ben
Hmm, that was my mistake. When I wrote launchPurchaseFlow(), I ended up missing some cleanup code on failure cases. Not only there, but also on a couple of catch{} clauses after that. Thanks for pointing that out! This has just been fixed in the source repository: http://code.google.com/p/marketbilling
I had the same error, I accidentally forgot to consume the item after I purchased. But when I tried to purchase another of same item App crashed.
I dig through the Google IabHelper class and found out that this statement is not handled correctly. I made some small change and now it works. Instead of crashing send error message back with listener.
Here is the modified part of the code. It's in launchPurchaseFlow() method. I'm not sure that I did something good by changing the code it looked like needed. Hope it helps.
try {
logDebug("Constructing buy intent for " + sku);
Bundle buyIntentBundle = mService.getBuyIntent(3, mContext.getPackageName(), sku, ITEM_TYPE_INAPP, extraData);
int response = getResponseCodeFromBundle(buyIntentBundle);
if (response != BILLING_RESPONSE_RESULT_OK) {
logError("Unable to buy item, Error response: " + getResponseDesc(response));
result = new IabResult(response, "Unable to buy item");
if (listener != null) listener.onIabPurchaseFinished(result, null);
/* Finish Current Async Task*/
flagEndAsync();
} else {
PendingIntent pendingIntent = buyIntentBundle.getParcelable(RESPONSE_BUY_INTENT);
logDebug("Launching buy intent for " + sku + ". Request code: " + requestCode);
mRequestCode = requestCode;
mPurchaseListener = listener;
act.startIntentSenderForResult(pendingIntent.getIntentSender(),
requestCode, new Intent(),
Integer.valueOf(0), Integer.valueOf(0),
Integer.valueOf(0));
}