Working with incomplete data using NSURLSessionDataTask

Question

I use NSURLSessionDataTaskto load data. I see cases when the connection is interrupted, and yet I still receive the data. How should I deal with these cases?

• Am I guaranteed to get an error?
• Should I compare the length of the data with the response expectedContentLength? Is it reliable? What to do if it is unavailable?
• Something else?

the code:

NSURLSession *session = [NSURLSession sharedSession];
NSURLSessionDataTask *task = [session dataTaskWithURL:url completionHandler:^(NSData *data, NSURLResponse *response, NSError *error)
{
    if (error)
    {
        NSLog(@"Request %@ failed with error %@", url, error);
        return;
    }
    const long long expectedContentLength = response.expectedContentLength;
    if (expectedContentLength > -1)
    {
        const NSUInteger dataLength = data.length;
        if (dataLength < expectedContentLength)
        {
            NSLog(@"Request %@ received %ld out of %ld bytes", url, (long)dataLength, (long)expectedContentLength);
            return;
        }
    }
    else
    {
        // How do I know if data is complete?
    }
}];
[task resume];