[ASNetworkImageNode] Add error handler to ASNetworkImageNodeDelegate

AsyncDisplayKit/ASNetworkImageNode.h

@@ -95,6 +95,16 @@ NS_ASSUME_NONNULL_BEGIN
 
 @optional
 
+/**
+ * Notification that the image node failed to download the image.
+ *
+ * @param imageNode The sender.
+ * @param error The error with details.
+ *
+ * @discussion Called on a background queue.
+ */
+- (void)imageNode:(ASNetworkImageNode *)imageNode didFailWithError:(NSError *)error;
+
 /**
  * Notification that the image node finished decoding an image.
  *

AsyncDisplayKit/ASNetworkImageNode.mm

@@ -168,14 +168,14 @@ - (void)_cancelImageDownload
   _cacheUUID = nil;
 }
 
-- (void)_downloadImageWithCompletion:(void (^)(CGImageRef))finished
+- (void)_downloadImageWithCompletion:(void (^)(CGImageRef, NSError*))finished
 {
   _imageDownload = [_downloader downloadImageWithURL:_URL
                                        callbackQueue:dispatch_get_main_queue()
                                downloadProgressBlock:NULL
                                           completion:^(CGImageRef responseImage, NSError *error) {
                                             if (finished != NULL) {
-                                              finished(responseImage);
+                                              finished(responseImage, error);
                                             }
                                           }];
 }
@@ -210,7 +210,7 @@ - (void)_lazilyLoadImageIfNecessary
       }
     } else {
       __weak __typeof__(self) weakSelf = self;
-      void (^finished)(CGImageRef) = ^(CGImageRef responseImage) {
+      void (^finished)(CGImageRef, NSError *) = ^(CGImageRef responseImage, NSError *error) {
         __typeof__(self) strongSelf = weakSelf;
         if (strongSelf == nil) {
           return;
@@ -232,6 +232,9 @@ - (void)_lazilyLoadImageIfNecessary
         if (responseImage != NULL) {
           [strongSelf->_delegate imageNode:strongSelf didLoadImage:strongSelf.image];
         }
+        else if (error && [strongSelf->_delegate respondsToSelector:@selector(imageNode:didFailWithError:)]) {
+          [strongSelf->_delegate imageNode:strongSelf didFailWithError:error];
+        }
       };
 
       if (_cache != nil) {
@@ -247,7 +250,7 @@ - (void)_lazilyLoadImageIfNecessary
           if (image == NULL && _downloader != nil) {
             [self _downloadImageWithCompletion:finished];
           } else {
-            finished(image);
+            finished(image, NULL);
           }
         };