title: AFNetworking + Pause/ Resume downloading big files
body: <p>I need to download large .zip files (up to 800 MB) with my iPad app.
  I want to resume the download again if it is canceled or if the app is in the background.</p>
  
  <pre><code>operation = [[AFHTTPRequestOperation alloc] initWithRequest:request];
  operation.outputStream = [NSOutputStream outputStreamToFileAtPath:filePath append:YES];
  
  [operation setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject){
  
  // unzip the .zip
  
  
  }failure:^(AFHTTPRequestOperation *operation, NSError *error){
  
  //Handle the error
  
  }];
  
  
  [operation setDownloadProgressBlock:^(NSInteger bytesWritten, long long totalBytesWritten,long long totalBytesExpectedToWrite) {
  
  //update the progressView
  
  }];
  
  [operation setShouldExecuteAsBackgroundTaskWithExpirationHandler:^{
  
  // What I have to do here?
  
  }];
  
  [operation start];
  [operation waitUntilFinished];
  
  
  -(void)applicationWillResignActive:(UIApplication *)application{
  
  // What I have to do here?
  
  }
  </code></pre>
  
  <p>Thanks for your help.</p>