Download with NSURLConnection returns empty data?

Question

My app is downloading a file from the internet using NSURLConnection.

Two problems are happening:

1) [connection didReceiveData] is never called

2) When [connection didFinishDownloading] is called, my self.currentData is empty

What am I doing wrong?

My header looks like this:

@interface DIFileDownloader : NSObject <NSURLConnectionDelegate> {

    NSMutableData *currentData;

}

@property (nonatomic, assign) id <DIFileDownloaderDelegate> delegate;

@property (nonatomic, retain) NSMutableArray *supportedFormats;

@property (nonatomic, retain) NSMutableData *currentData;

@property (nonatomic, retain) NSURLConnection *downloadAgent;

@property (nonatomic) long long expectedContentSize;

@property (nonatomic) float currentDownloadProgress;

@property (nonatomic, getter = isRunning) BOOL running;

-(instancetype)initWithSupportedFormats:(NSArray *)extensions;

-(void)downloadFileAtURL:(NSURL *)url;

-(NSString *)documentsDirectoryPath;

@end

And my implementation file:

-(instancetype)initWithSupportedFormats:(NSArray *)extensions {

    self.supportedFormats = [[NSMutableArray alloc] initWithArray:extensions];

    self.running = NO;
}

-(void)downloadFileAtURL:(NSURL *)url {

    NSString *fileExtension = [url pathExtension];

    if ([self.supportedFormats containsObject:fileExtension]) {

        self.downloadAgent = [[NSURLConnection alloc] initWithRequest:[NSURLRequest requestWithURL:url] delegate:self];

        [self.downloadAgent start];

        NSLog(@"Beginning download at URL:%@", url.absoluteString);

    }
    else {

    }

}

-(void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {

    NSLog(@"Connection recieved response with size: %f", (float)[response expectedContentLength]);

    self.expectedContentSize = (float)[response expectedContentLength];

    self.running = YES;

    NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse*)response;

    NSLog(@"%i", [httpResponse statusCode]);

    /*

    if ([httpResponse statusCode] >= 200 && [httpResponse statusCode] <= 299) {

    }

     */

}

-(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {

    NSLog(@"%f", (float)[data length]);

    [currentData appendData:data];

    self.currentDownloadProgress = ((float)[data length] / self.currentDownloadProgress);

    NSLog(@"Connection recieved data. New progress is: %f", self.currentDownloadProgress);

    if ([self.delegate respondsToSelector:@selector(downloader:progressChanged:)]) {
        [self.delegate downloader:self progressChanged:self.currentDownloadProgress];
    }

}

-(void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {

    NSLog(@"Connection failed");

    if ([self.delegate respondsToSelector:@selector(downloader:failedToDownloadFileAtURL:reason:)]) {
        [self.delegate downloader:self failedToDownloadFileAtURL:connection.originalRequest.URL reason:error];
    }

}

-(void)connectionDidFinishDownloading:(NSURLConnection *)connection destinationURL:(NSURL *)destinationURL {

    NSLog(@"Connection finished downloading with size: %f", (float)[currentData length]);

    self.running = NO;

    NSString *filename = [destinationURL.absoluteString lastPathComponent];

    NSString *docPath = [self documentsDirectoryPath];

    NSString *pathToDownloadTo = [NSString stringWithFormat:@"%@/%@", docPath, filename];

    NSError *error = nil;

    [currentData writeToFile:pathToDownloadTo options:NSDataWritingAtomic error:&error];

    if (error != nil) {

        NSLog(@"DIFileDownloader: Failed to save the file because: %@", [error description]);

        if ([self.delegate respondsToSelector:@selector(downloader:failedToDownloadFileAtURL:reason:)]) {
            [self.delegate downloader:self failedToDownloadFileAtURL:connection.originalRequest.URL reason:error];
        }

} 
    else {

        if ([self.delegate respondsToSelector:@selector(downloader:finishedDownloadingFileNamed:atPath:)]) {
            [self.delegate downloader:self finishedDownloadingFileNamed:filename atPath:pathToDownloadTo];
        }

    }

}

- (NSString *)documentsDirectoryPath {
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectoryPath = [paths objectAtIndex:0];
    return documentsDirectoryPath;
}

@end

Answer 1

As mentioned in others and in my comment, there are a few bugs in your code which you need to fix.

But there is also one big misconception - stemming from the former awful documentation of NSURLConnection:

connectionDidFinishDownloading:destinationURL: is NOT a delegate method of the two delegates of NSURLConnection namely, NSURLConnectionDelegate and NSURLConnectionDataDelegate which you are supposed to implement in your case.

The minimal set of delegate methods you need to implement are:

For the NSURLConnectionDelegate:

• (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error;

then for the NSURLConnectionDataDelegate:

• (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response;

• (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data;

• (void)connectionDidFinishLoading:(NSURLConnection*)connection;

If you don't mind, I've put a sample of a minimal implementation on Gist: SimpleGetHTTPRequest which should give you a jump start do implement your own HTTP request class.