- (id)init {
    if ((self = [super init])) {
        _operationClass = [SDWebImageDownloaderOperation class];
        _shouldDecompressImages = YES;
        _executionOrder = SDWebImageDownloaderFIFOExecutionOrder;
        _downloadQueue = [NSOperationQueue new];
        _downloadQueue.maxConcurrentOperationCount = 6;
        _URLCallbacks = [NSMutableDictionary new];

        NSString *userAgent = @"";
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wgnu"
#if defined(__IPHONE_OS_VERSION_MIN_REQUIRED)
        // User-Agent Header; see http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.43
        userAgent = [NSString stringWithFormat:@"%@/%@ (%@; iOS %@; Scale/%0.2f)", [[[NSBundle mainBundle] infoDictionary] objectForKey:(__bridge NSString *)kCFBundleExecutableKey] ?: [[[NSBundle mainBundle] infoDictionary] objectForKey:(__bridge NSString *)kCFBundleIdentifierKey], [[[NSBundle mainBundle] infoDictionary] objectForKey:@"CFBundleShortVersionString"] ?: [[[NSBundle mainBundle] infoDictionary] objectForKey:(__bridge NSString *)kCFBundleVersionKey], [[UIDevice currentDevice] model], [[UIDevice currentDevice] systemVersion], [[UIScreen mainScreen] scale]];
#elif defined(__MAC_OS_X_VERSION_MIN_REQUIRED)
        userAgent = [NSString stringWithFormat:@"%@/%@ (Mac OS X %@)", [[[NSBundle mainBundle] infoDictionary] objectForKey:(__bridge NSString *)kCFBundleExecutableKey] ?: [[[NSBundle mainBundle] infoDictionary] objectForKey:(__bridge NSString *)kCFBundleIdentifierKey], [[[NSBundle mainBundle] infoDictionary] objectForKey:@"CFBundleShortVersionString"] ?: [[[NSBundle mainBundle] infoDictionary] objectForKey:(__bridge NSString *)kCFBundleVersionKey], [[NSProcessInfo processInfo] operatingSystemVersionString]];
#endif
#pragma clang diagnostic pop
        if (userAgent) {
            if (![userAgent canBeConvertedToEncoding:NSASCIIStringEncoding]) {
                NSMutableString *mutableUserAgent = [userAgent mutableCopy];
                if (CFStringTransform((__bridge CFMutableStringRef)(mutableUserAgent), NULL, (__bridge CFStringRef)@"Any-Latin; Latin-ASCII; [:^ASCII:] Remove", false)) {
                    userAgent = mutableUserAgent;
                }
            }
            [self setValue:userAgent forHTTPHeaderField:@"User-Agent"];
        }


#ifdef SD_WEBP
        _HTTPHeaders = [@{@"Accept": @"image/webp,image/*;q=0.8",@"User-Agent":userAgent} mutableCopy];
#else
        _HTTPHeaders = [@{@"Accept": @"image/*;q=0.8",@"User-Agent":userAgent} mutableCopy];
#endif
        _barrierQueue = dispatch_queue_create("com.hackemist.SDWebImageDownloaderBarrierQueue", DISPATCH_QUEUE_CONCURRENT);
        _downloadTimeout = 15.0;
    }
    return self;
}