refactor(iOS): persist bundle as local file on par with Android

packages/react-native/React/Base/RCTBundleManager.h

@@ -72,5 +72,13 @@ typedef NSMutableArray<NSURLQueryItem *> *_Nullable (^RCTPackagerOptionsUpdater)
                     andDefaultGetter:(nullable RCTBridgelessBundleURLGetter)defaultGetter;
 - (void)resetBundleURL;
 @property (nonatomic, nullable) NSURL *bundleURL;
+
+/**
+ * File URL of the most recently downloaded bundle persisted to disk. Only set
+ * when the bundle was fetched from a remote URL (e.g. the packager); nil when
+ * the bundle was loaded from a local file, in which case its location on disk
+ * is the bundleURL itself.
+ */
+@property (nonatomic, nullable) NSURL *downloadedBundleFileURL;
 @property (nonatomic, nonnull) RCTBundleConfiguration *bundleConfig;
 @end

packages/react-native/React/Base/RCTJavaScriptLoader.h

@@ -68,6 +68,14 @@ NS_ENUM(NSInteger){
  */
 @property (nonatomic, readonly) NSInteger filesChangedCount;
 
+/**
+ * File URL of the downloaded bundle persisted to disk, from which self.data is
+ * memory-mapped. Only set when the bundle was fetched from a remote URL (e.g. the
+ * packager); nil when the bundle was loaded from a local file, in which case the
+ * bundle's location on disk is self.url.
+ */
+@property (strong, nonatomic, readonly) NSURL *downloadedBundleFileURL;
+
 @end
 
 typedef void (^RCTSourceLoadProgressBlock)(RCTLoadingProgress *progressData);

packages/react-native/React/Base/RCTJavaScriptLoader.mm

@@ -25,6 +25,7 @@ @interface RCTSource () {
   NSData *_data;
   NSUInteger _length;
   NSInteger _filesChangedCount;
+  NSURL *_downloadedBundleFileURL;
 }
 
 @end
@@ -210,6 +211,15 @@ static void parseHeaders(NSDictionary *headers, RCTSource *source)
   source->_filesChangedCount = [headers[@"X-Metro-Files-Changed-Count"] integerValue];
 }
 
+static NSURL *persistDownloadedBundle(NSData *data, NSError **error)
+{
+  NSString *bundlePath = [NSTemporaryDirectory() stringByAppendingPathComponent:@"ReactNativeDevBundle.js"];
+  if (![data writeToFile:bundlePath options:NSDataWritingAtomic error:error]) {
+    return nil;
+  }
+  return [NSURL fileURLWithPath:bundlePath];
+}
+
 static void attemptAsynchronousLoadOfBundleAtURL(
     NSURL *scriptURL,
     RCTSourceLoadProgressBlock onProgress,
@@ -314,7 +324,24 @@ static void attemptAsynchronousLoadOfBundleAtURL(
           }
         }
 
-        RCTSource *source = RCTSourceCreate(sourceURL, data, data.length);
+        NSError *persistError;
+        NSURL *downloadedBundleFileURL = persistDownloadedBundle(data, &persistError);
+        if (downloadedBundleFileURL == nil) {
+          onComplete(persistError, nil);
+          return;
+        }
+
+        NSError *mappingError;
+        NSData *bundleData = [NSData dataWithContentsOfFile:downloadedBundleFileURL.path
+                                                    options:NSDataReadingMappedIfSafe
+                                                      error:&mappingError];
+        if (bundleData == nil) {
+          onComplete(mappingError, nil);
+          return;
+        }
+
+        RCTSource *source = RCTSourceCreate(sourceURL, bundleData, bundleData.length);
+        source->_downloadedBundleFileURL = downloadedBundleFileURL;
         parseHeaders(headers, source);
         onComplete(nil, source);
       }

packages/react-native/ReactCommon/react/runtime/platform/ios/ReactCommon/RCTHost.mm

@@ -537,10 +537,18 @@ - (void)loadBundleAtURL:(NSURL *)sourceURL
              onProgress:(RCTSourceLoadProgressBlock)onProgress
              onComplete:(RCTSourceLoadBlock)loadCallback
 {
+  __weak RCTHost *weakSelf = self;
+  RCTSourceLoadBlock onComplete = ^(NSError *error, RCTSource *source) {
+    RCTHost *strongSelf = weakSelf;
+    if (strongSelf != nil && source != nil) {
+      strongSelf->_bundleManager.downloadedBundleFileURL = source.downloadedBundleFileURL;
+    }
+    loadCallback(error, source);
+  };
   if ([_hostDelegate respondsToSelector:@selector(loadBundleAtURL:onProgress:onComplete:)]) {
-    [_hostDelegate loadBundleAtURL:sourceURL onProgress:onProgress onComplete:loadCallback];
+    [_hostDelegate loadBundleAtURL:sourceURL onProgress:onProgress onComplete:onComplete];
   } else {
-    [RCTJavaScriptLoader loadBundleAtURL:sourceURL onProgress:onProgress onComplete:loadCallback];
+    [RCTJavaScriptLoader loadBundleAtURL:sourceURL onProgress:onProgress onComplete:onComplete];
   }
 }