Add a delegate method to control the custom logic when blocking the failed url

@@ -142,6 +142,16 @@ typedef NSString * _Nullable (^SDWebImageCacheKeyFilterBlock)(NSURL * _Nullable
 - (BOOL)imageManager:(nonnull SDWebImageManager *)imageManager shouldDownloadImageForURL:(nullable NSURL *)imageURL;
 - (BOOL)imageManager:(nonnull SDWebImageManager *)imageManager shouldDownloadImageForURL:(nullable NSURL *)imageURL;
 
 
 /**
 /**
+ * Controls the complicated logic to mark as failed URLs when download error occur.
+ * If the delegate implement this method, we will not use the built-in way to mark URL as failed based on error code;
+ @param imageManager The current `SDWebImageManager`
+ @param imageURL The url of the image
+ @param error The download error for the url
+ @return Whether to block this url or not. Return YES to mark this URL as failed.
+ */
+- (BOOL)imageManager:(nonnull SDWebImageManager *)imageManager shouldBlockFailedURL:(nonnull NSURL *)imageURL withError:(nonnull NSError *)error;
+
+/**
  * Allows to transform the image immediately after it has been downloaded and just before to cache it on disk and memory.
  * Allows to transform the image immediately after it has been downloaded and just before to cache it on disk and memory.
  * NOTE: This method is called from a global queue in order to not to block the main thread.
  * NOTE: This method is called from a global queue in order to not to block the main thread.
  *
  *

@@ -196,15 +196,22 @@
                     // if we would call the completedBlock, there could be a race condition between this block and another completedBlock for the same object, so if this one is called second, we will overwrite the new data
                     // if we would call the completedBlock, there could be a race condition between this block and another completedBlock for the same object, so if this one is called second, we will overwrite the new data
                 } else if (error) {
                 } else if (error) {
                     [self callCompletionBlockForOperation:strongSubOperation completion:completedBlock error:error url:url];
                     [self callCompletionBlockForOperation:strongSubOperation completion:completedBlock error:error url:url];
-
-                    if (   error.code != NSURLErrorNotConnectedToInternet
-                        && error.code != NSURLErrorCancelled
-                        && error.code != NSURLErrorTimedOut
-                        && error.code != NSURLErrorInternationalRoamingOff
-                        && error.code != NSURLErrorDataNotAllowed
-                        && error.code != NSURLErrorCannotFindHost
-                        && error.code != NSURLErrorCannotConnectToHost
-                        && error.code != NSURLErrorNetworkConnectionLost) {
+                    BOOL shouldBlockFailedURL;
+                    // Check whether we should block failed url
+                    if ([self.delegate respondsToSelector:@selector(imageManager:shouldBlockFailedURL:withError:)]) {
+                        shouldBlockFailedURL = [self.delegate imageManager:self shouldBlockFailedURL:url withError:error];
+                    } else {
+                        shouldBlockFailedURL = (   error.code != NSURLErrorNotConnectedToInternet
+                                                && error.code != NSURLErrorCancelled
+                                                && error.code != NSURLErrorTimedOut
+                                                && error.code != NSURLErrorInternationalRoamingOff
+                                                && error.code != NSURLErrorDataNotAllowed
+                                                && error.code != NSURLErrorCannotFindHost
+                                                && error.code != NSURLErrorCannotConnectToHost
+                                                && error.code != NSURLErrorNetworkConnectionLost);
+                    }
+                    
+                    if (shouldBlockFailedURL) {
                         @synchronized (self.failedURLs) {
                         @synchronized (self.failedURLs) {
                             [self.failedURLs addObject:url];
                             [self.failedURLs addObject:url];
                         }
                         }