Unify XCAsset handling logic

Summary: @​public

This diff unifies the logic for detecting when images refer to XCAsset files into a single function (RCTXCAssetNameForURL) and uses it for both +[RCTConvert UIImage:] and RCTImageLoader.

I've also tightened the definition of XCAssets so that it only applies to images inside .car files, not any image inside the main bundle. This avoids using the +[UIImage imageNamed:] when not strictly necessary, which is desirable since that method is not thread-safe, and has undocumented caching behavior that is difficult to reason about.

Reviewed By: @javache

Differential Revision: D2526400

fb-gh-sync-id: 7199c2a44f1d55ff236d2c38a0a9368739b993d5

React/Base/RCTConvert.m

@@ -12,6 +12,7 @@
 #import <objc/message.h>
 
 #import "RCTDefines.h"
+#import "RCTUtils.h"
 
 @implementation RCTConvert
 
@@ -102,7 +103,10 @@ RCT_CUSTOM_CONVERTER(NSData *, NSData, [json dataUsingEncoding:NSUTF8StringEncod
       // Assume it's a resource path
       path = [[NSBundle bundleForClass:[self class]].resourcePath stringByAppendingPathComponent:path];
     }
-    return [NSURL fileURLWithPath:path];
+    if (!(URL = [NSURL fileURLWithPath:path])) {
+      RCTLogConvertError(json, @"a valid URL");
+    }
+    return URL;
   }
   @catch (__unused NSException *e) {
     RCTLogConvertError(json, @"a valid URL");
@@ -417,7 +421,9 @@ RCT_CGSTRUCT_CONVERTER(CGAffineTransform, (@[
   if ([json isKindOfClass:[NSString class]]) {
     path = json;
   } else if ([json isKindOfClass:[NSDictionary class]]) {
-    path = [self NSString:json[@"uri"]];
+    if (!(path = [self NSString:json[@"uri"]])) {
+      return nil;
+    }
     scale = [self CGFloat:json[@"scale"]];
     isPackagerAsset = [self BOOL:json[@"__packager_asset"]];
   } else {
@@ -427,36 +433,21 @@ RCT_CGSTRUCT_CONVERTER(CGAffineTransform, (@[
 
   NSURL *URL = [self NSURL:path];
   NSString *scheme = URL.scheme.lowercaseString;
-  if (URL && [scheme isEqualToString:@"file"]) {
-    if ([URL.path hasPrefix:[NSBundle mainBundle].resourcePath]) {
-      RCTAssertMainThread();
-
+  if ([scheme isEqualToString:@"file"]) {
+    if (RCTIsXCAssetURL(URL)) {
       // Image may reside inside a .car file, in which case we have no choice
       // but to use +[UIImage imageNamed] - but this method isn't thread safe
-      static NSMutableDictionary *XCAssetMap = nil;
-      if (!XCAssetMap) {
-        XCAssetMap = [NSMutableDictionary new];
-      }
-      NSNumber *isAsset = XCAssetMap[path];
-      if (!isAsset || isAsset.boolValue) {
-        image = [UIImage imageNamed:path];
-      }
-      if (!isAsset) {
-        // Avoid calling `+imageNamed` again in future if it's not needed.
-        XCAssetMap[path] = @(image != nil);
-      }
-    }
-
-    if (!image) {
-      NSString *filePath = URL.path;
-
+      RCTAssertMainThread();
+      NSString *assetName = RCTBundlePathForURL(URL);
+      image = [UIImage imageNamed:assetName];
+    } else {
       // Attempt to load from the file system
+      NSString *filePath = URL.path;
       if (filePath.pathExtension.length == 0) {
         filePath = [filePath stringByAppendingPathExtension:@"png"];
       }
       image = [UIImage imageWithContentsOfFile:filePath];
     }
-
   } else if ([scheme isEqualToString:@"data"]) {
     image = [UIImage imageWithData:[NSData dataWithContentsOfURL:URL]];
   } else if ([scheme isEqualToString:@"http"] && isPackagerAsset) {

React/Base/RCTUtils.h

@@ -77,3 +77,10 @@ RCT_EXTERN NSURL *RCTDataURL(NSString *mimeType, NSData *data);
 
 // Gzip functionality - compression level in range 0 - 1 (-1 for default)
 RCT_EXTERN NSData *RCTGzipData(NSData *data, float level);
+
+// Returns the relative path within the main bundle for an absolute URL
+// (or nil, if the URL does not specify a path within the main bundle)
+RCT_EXTERN NSString *RCTBundlePathForURL(NSURL *URL);
+
+// Determines if a given image URL actually refers to an XCAsset
+RCT_EXTERN BOOL RCTIsXCAssetURL(NSURL *imageURL);

React/Base/RCTUtils.m

@@ -458,3 +458,38 @@ NSData *RCTGzipData(NSData *input, float level)
 
   return output;
 }
+
+NSString *RCTBundlePathForURL(NSURL *URL)
+{
+  if (!URL.fileURL) {
+    // Not a file path
+    return nil;
+  }
+  NSString *path = URL.path;
+  NSString *bundlePath = [[NSBundle mainBundle] resourcePath];
+  if (![path hasPrefix:bundlePath]) {
+    // Not a bundle-relative file
+    return nil;
+  }
+  return [path substringFromIndex:bundlePath.length + 1];
+}
+
+BOOL RCTIsXCAssetURL(NSURL *imageURL)
+{
+  NSString *name = RCTBundlePathForURL(imageURL);
+  if (name.pathComponents.count != 1) {
+    // URL is invalid, or is a file path, not an XCAsset identifier
+    return NO;
+  }
+  NSString *extension = [name pathExtension];
+  if (extension.length && ![extension isEqualToString:@"png"]) {
+    // Not a png
+    return NO;
+  }
+  extension = extension.length ? nil : @"png";
+  if ([[NSBundle mainBundle] pathForResource:name ofType:extension]) {
+    // File actually exists in bundle, so is not an XCAsset
+    return NO;
+  }
+  return YES;
+}