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PONSURLResponse Content-Length mismatch size of actual data when running concurrent downloads
 

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    <p>I have a UITableView, when a cell is selected, I make a service call to asynchronously download a PDF file from a web service. It works great, until you select multiple cells directly after one-another (individually), then things start going south..</p> <p>Here's some (stripped down) code to clarify:</p> <p><strong>Inside MasterViewController.m:</strong></p> <pre><code>- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath { //To uniquely identify this field, I build a simple string using the indexPath. NSString *key = [[NSString alloc]initWithFormat:@"%d.%d",pIndex.section,pIndex.row]; //Use a pre-populated NSDictionary to specify the file I want from the server. NSString *reportID = [reportDictionary valueForKey:key]; NSURL *url = [NSURL URLWithString:[NSString stringWithFormat:@"%@/RequestReportWithID",myConnectionObject.ServiceURL]]; NSMutableDictionary *body = [[NSMutableDictionary alloc] initWithObjectsAndKeys:reportID, @"reportID", nil]; NSData *requestData = [NSJSONSerialization dataWithJSONObject:dic options:0 error:nil]; NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url]; [request setHTTPMethod:@"POST"]; [request setValue:@"application/json" forHTTPHeaderField:@"Content-Type"]; [request setValue:[NSString stringWithFormat:@"%d", [requestData length]] forHTTPHeaderField:@"Content-Length"]; [request setHTTPBody: requestData]; //Create a new object as delegate to receive the data, also add the key to assist with identification. ReportDownloader *newReportDownloader = [[ReportDownloader alloc]initWithDelegate:self andKey:key]; NSURLConnection *connection = [[NSURLConnection alloc]initWithRequest:request delegate:newReportDownloader]; if (connection) { //Nothing to do here, request was made. } } </code></pre> <p><strong>Inside ReportDownloader.m:</strong></p> <pre><code>long long expectedReportSize; NSString *key; NSData *thisReport; -(NSObject*)initWithDelegate:(NSObject*)pDelegate andKey:(NSString*)pKey { myTypedDelegate = (MasterViewController*)pDelegate; Key = pKey; return self; } - (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response { expectedReportSize = [response expectedContentLength]; NSLog(@"Key:%@, Expected Size=%lld bytes",Key, [response expectedContentLength]); thisReport = [[NSMutableData alloc] init]; } - (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data { [thisReport appendData:data]; } - (void)connectionDidFinishLoading:(NSURLConnection *)connection { //Here is where things go wrong... NSLog(@"Key:%@, Actual Size=%ld bytes",Key, (unsigned long)[thisReport length]); } </code></pre> <p>The above code works fine for a single report. And on a fast line, it works fine for 3-4 reports, but try to do more than that and the Expected length starts mismatching the Actual length. And I can't understand whyyyyy....</p> <p>See the output generated by the code above: <em>(Notice that only the report for indexPath 1.1 was downloaded correctly)</em></p> <pre><code>Key:1.0, Expected Size=304006 bytes Key:1.3, Expected Size=124922 bytes Key:1.0, Actual Size=369494 bytes Key:1.3, Actual Size=380030 bytes Key:1.2, Expected Size=179840 bytes Key:1.4, Expected Size=377046 bytes Key:1.2, Actual Size=114376 bytes Key:1.5, Expected Size=175633 bytes Key:1.4, Actual Size=180558 bytes Key:1.5, Actual Size=274549 bytes Key:1.1, Expected Size=443135 bytes Key:1.1, Actual Size=443135 bytes </code></pre> <p>The data corruption is confirmed when trying to open the PDF documents, which fail for all file's who's data size didn't match the expectedContentLength.</p> <p>I am completely baffled by this behaviour, I'm hoping that I'm making an obvious n00b mistake and that someone here spots it.</p> <p>The main reason WHY I made the ReportDownloader class was to avoid problems like this one.</p> <p>Thanks in advance to whoever takes the time to scan my code!</p>
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    1. COI have the answer, just not enough rep to answer my own question within 5 hours.
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    2. COHi, I have the same problem. Can you please let me know how to solve this??
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    3. COHi Apple, I added the answer below.
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