Providing an API to load assets from a different directory

Differential Revision: D6368586

fbshipit-source-id: 2a79ba45de3d9c95d0b1b296c9e1ae35cbd33c36

Author: Yujie Liu

Libraries/Image/RCTImageLoader.h

@@ -38,6 +38,18 @@ typedef dispatch_block_t RCTImageLoaderCancellationBlock;
 
 @end
 
+/**
+ * If available, RCTImageRedirectProtocol is invoked before loading an asset.
+ * Implementation should return either a new URL or nil when redirection is
+ * not needed.
+ */
+
+@protocol RCTImageRedirectProtocol
+
+- (NSURL *)redirectAssetsURL:(NSURL *)URL;
+
+@end
+
 @interface UIImage (React)
 
 @property (nonatomic, copy) CAKeyframeAnimation *reactKeyframeAnimation;
@@ -71,6 +83,9 @@ typedef dispatch_block_t RCTImageLoaderCancellationBlock;
  */
 @property (nonatomic, assign) NSUInteger maxConcurrentDecodingBytes;
 
+- (instancetype)init;
+- (instancetype)initWithRedirectDelegate:(id<RCTImageRedirectProtocol>)redirectDelegate NS_DESIGNATED_INITIALIZER;
+
 /**
  * Loads the specified image at the highest available resolution.
  * Can be called from any thread, will call back on an unspecified thread.

Libraries/Image/RCTImageLoader.m

@@ -48,12 +48,26 @@ @implementation RCTImageLoader
     NSMutableArray *_pendingDecodes;
     NSInteger _scheduledDecodes;
     NSUInteger _activeBytes;
+  __weak id<RCTImageRedirectProtocol> _redirectDelegate;
 }
 
 @synthesize bridge = _bridge;
 
 RCT_EXPORT_MODULE()
 
+- (instancetype)init
+{
+  return [self initWithRedirectDelegate:nil];
+}
+
+- (instancetype)initWithRedirectDelegate:(id<RCTImageRedirectProtocol>)redirectDelegate
+{
+    if (self = [super init]) {
+        _redirectDelegate = redirectDelegate;
+    }
+    return self;
+}
+
 - (void)setUp
 {
     // Set defaults
@@ -316,6 +330,9 @@ - (RCTImageLoaderCancellationBlock)_loadImageOrDataWithURLRequest:(NSURLRequest
         if (request.URL.fileURL && request.URL.pathExtension.length == 0) {
             mutableRequest.URL = [request.URL URLByAppendingPathExtension:@"png"];
         }
+        if (_redirectDelegate != nil) {
+            mutableRequest.URL = [_redirectDelegate redirectAssetsURL:mutableRequest.URL];
+        }
         request = mutableRequest;
     }