Reading NSData in parts - ios

Question

I am implementing extensions in ios8. In this import function returns a url. I need to read data from it and save in my app.
Here is the code.
NSFileCoordinator *fileCoordinator = [[NSFileCoordinator alloc] init];
NSError *error;
__block NSData *data;
[fileCoordinator coordinateReadingItemAtURL:url options:0 error:&error byAccessor:^(NSURL *newURL) {
data = [NSData dataWithContentsOfURL:newURL];
//saving in document directory
}];
My question is, if file is too big, dataWithContentsOfURL results in crash due to out of memory.
I wanted a method to read data from that url in parts, save in my documents, then read next part and keep appending. Thus it won't have memory issue.
Can someone help.

Answer 1

Found two solutions.
1- Used NSURLConnection. Using NSFileHandle wrote data in file.
-(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data1{
// [data appendData:data1];
[self.currentFileHandle seekToEndOfFile];
[self.currentFileHandle writeData:data1];
}
-(void)connectionDidFinishLoading:(NSURLConnection *)connection{
[self.currentFileHandle closeFile];
self.currentFileHandle = nil;
}
Instead of converting it in data and then saving. Used following to copy file.
NSFileCoordinator* fileCoordinator = [[NSFileCoordinator alloc] initWithFilePresenter:nil];
[fileCoordinator coordinateReadingItemAtURL:url options:NSFileCoordinatorReadingWithoutChanges error:nil byAccessor:^(NSURL *newURL) {
NSFileManager * fileManager = [[NSFileManager alloc] init];
NSError * error;
NSArray *paths = [[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask];
NSURL *urlDestination = [paths lastObject];
urlDestination = [urlDestination URLByAppendingPathComponent:[url lastPathComponent]];
if([[NSFileManager defaultManager] fileExistsAtPath:[urlDestination relativePath]]){
[[NSFileManager defaultManager] removeItemAtPath:[urlDestination relativePath] error:nil];
}
BOOL success = [fileManager copyItemAtURL:url toURL:urlDestination error:&error];
if (success) {
}
}];
I used 2nd solution. Sorry for wrong alignment. I tried a lot, but not
coming properly.