From bd12e41188c8d85c0acbd713f10f0bd34ea0edca Mon Sep 17 00:00:00 2001
From: wood1986 <5212215+wood1986@users.noreply.github.com>
Date: Thu, 30 Jun 2022 05:13:17 -0700
Subject: [PATCH] fix: fix the race condition when calling readAsDataURL after
 new Blob(blobs) (#34096)

Summary:
```js
async () => {
  let blobs = [];
  for (let i = 0; i < 4; i++) {
    const res = await fetch();
    blobs = [...blobs, await res.blob()]
  }
  const blob = new Blob(blobs); // <<<<<<<<<<<<<<< a
  return await new Promise((resolve, reject) => {
    const fileReader = new FileReader();
    fileReader.onload = async () => {
      await RNFS.writeFile(destPath, (fileReader.result as string).split(',')[1], 'base64');
      resolve(destPath);
    };
    fileReader.onabort = () => {
      reject('');
    };
    fileReader.onerror = (event) => {
      reject('');
    };
    fileReader.readAsDataURL(blob); // <<<<<<<<<<<<<<< b
  });
}
```

Sometime `fileReader.readAsDataURL` is unable to get blob from the dictionary after `new Blob(blobs)` and then reject with `Unable to resolve data for blob: blobId` in iOS or `The specified blob is invalid` in android. Because line `a` and `b` can be run in different thread. `new Blob([])` is in progress and `fileReader.readAsDataURL` accesses the blob dictionary ahead of the blob creation.

The expected behaviour is it should finish new Blob([]) first and then readAsDataURL(blob)

To fix that, there should be a lock inside the method `createFromParts`. For iOS, It needs to be a recursive_mutex to allow same thread to acquire lock

## Changelog

<!-- Help reviewers and the release process by writing your own changelog entry. For an example, see:
https://github.com/facebook/react-native/wiki/Changelog
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[iOS] [Fixed] - fix the race condition when calling readAsDataURL after new Blob(blobs)

Pull Request resolved: https://github.com/facebook/react-native/pull/34096

Reviewed By: cipolleschi

Differential Revision: D37514981

Pulled By: javache

fbshipit-source-id: 4bf84ece99871276ecaa5aa1849b9145ff44dbf4
---
 Libraries/Blob/RCTFileReaderModule.mm | 58 ++++++++++++++-------------
 1 file changed, 31 insertions(+), 27 deletions(-)

diff --git a/Libraries/Blob/RCTFileReaderModule.mm b/Libraries/Blob/RCTFileReaderModule.mm
index e834c61cc7970f..f52a68aba98c19 100644
--- a/Libraries/Blob/RCTFileReaderModule.mm
+++ b/Libraries/Blob/RCTFileReaderModule.mm
@@ -31,24 +31,26 @@ @implementation RCTFileReaderModule
                   reject:(RCTPromiseRejectBlock)reject)
 {
   RCTBlobManager *blobManager = [_moduleRegistry moduleForName:"BlobModule"];
-  NSData *data = [blobManager resolve:blob];
+  dispatch_async(blobManager.methodQueue, ^{
+    NSData *data = [blobManager resolve:blob];
 
-  if (data == nil) {
-    reject(RCTErrorUnspecified,
-           [NSString stringWithFormat:@"Unable to resolve data for blob: %@", [RCTConvert NSString:blob[@"blobId"]]], nil);
-  } else {
-    NSStringEncoding stringEncoding;
-
-    if (encoding == nil) {
-      stringEncoding = NSUTF8StringEncoding;
+    if (data == nil) {
+      reject(RCTErrorUnspecified,
+             [NSString stringWithFormat:@"Unable to resolve data for blob: %@", [RCTConvert NSString:blob[@"blobId"]]], nil);
     } else {
-      stringEncoding = CFStringConvertEncodingToNSStringEncoding(CFStringConvertIANACharSetNameToEncoding((CFStringRef) encoding));
-    }
+      NSStringEncoding stringEncoding;
 
-    NSString *text = [[NSString alloc] initWithData:data encoding:stringEncoding];
+      if (encoding == nil) {
+        stringEncoding = NSUTF8StringEncoding;
+      } else {
+        stringEncoding = CFStringConvertEncodingToNSStringEncoding(CFStringConvertIANACharSetNameToEncoding((CFStringRef) encoding));
+      }
 
-    resolve(text);
-  }
+      NSString *text = [[NSString alloc] initWithData:data encoding:stringEncoding];
+
+      resolve(text);
+    }
+  });
 }
 
 RCT_EXPORT_METHOD(readAsDataURL:(NSDictionary<NSString *, id> *)blob
@@ -56,19 +58,21 @@ @implementation RCTFileReaderModule
                   reject:(RCTPromiseRejectBlock)reject)
 {
   RCTBlobManager *blobManager = [_moduleRegistry moduleForName:"BlobModule"];
-  NSData *data = [blobManager resolve:blob];
-
-  if (data == nil) {
-    reject(RCTErrorUnspecified,
-           [NSString stringWithFormat:@"Unable to resolve data for blob: %@", [RCTConvert NSString:blob[@"blobId"]]], nil);
-  } else {
-    NSString *type = [RCTConvert NSString:blob[@"type"]];
-    NSString *text = [NSString stringWithFormat:@"data:%@;base64,%@",
-                      type != nil && [type length] > 0 ? type : @"application/octet-stream",
-                      [data base64EncodedStringWithOptions:0]];
-
-    resolve(text);
-  }
+  dispatch_async(blobManager.methodQueue, ^{
+    NSData *data = [blobManager resolve:blob];
+
+    if (data == nil) {
+      reject(RCTErrorUnspecified,
+             [NSString stringWithFormat:@"Unable to resolve data for blob: %@", [RCTConvert NSString:blob[@"blobId"]]], nil);
+    } else {
+      NSString *type = [RCTConvert NSString:blob[@"type"]];
+      NSString *text = [NSString stringWithFormat:@"data:%@;base64,%@",
+                        type != nil && [type length] > 0 ? type : @"application/octet-stream",
+                        [data base64EncodedStringWithOptions:0]];
+
+      resolve(text);
+    }
+  });
 }
 
 - (std::shared_ptr<facebook::react::TurboModule>)getTurboModule:(const facebook::react::ObjCTurboModule::InitParams &)params