[iOS] Uploading an image will change the file size of the image

Description

I uploaded a 2M image and the server received a 6M image. After debugging, the form data sent by the RCTNetworking became larger.

Steps to reproduce

1. Clone the reproducer from https://github.com/carverhong/react-native-reproducer-ios-image-upload.git.

2. Install dependency and prepare the ios project.

cd react-native-reproducer-ios-image-upload
npm install
bundle install
cd ios
bundle exec pod install

After the installation is complete, the RCTNetworking log patch is automatically added for debugging.

3. Start Metro.

npm start

4. Open HelloWorld.xcworkspace with XCode and run the APP.
5. Use the RCTNetworking keyword to filter logs.

React Native Version

0.72.15

Affected Platforms

Runtime - iOS

Output of npx react-native info

System:
  OS: macOS 14.4.1
  CPU: (8) arm64 Apple M3
  Memory: 87.55 MB / 16.00 GB
  Shell:
    version: "5.9"
    path: /bin/zsh
Binaries:
  Node:
    version: 18.19.0
    path: ~/tools/nodejs/node-v18.19.0-darwin-arm64/bin/node
  Yarn: Not Found
  npm:
    version: 10.2.3
    path: ~/tools/nodejs/node-v18.19.0-darwin-arm64/bin/npm
  Watchman: Not Found
Managers:
  CocoaPods: Not Found
SDKs:
  iOS SDK:
    Platforms:
      - DriverKit 23.4
      - iOS 17.4
      - macOS 14.4
      - tvOS 17.4
      - visionOS 1.1
      - watchOS 10.4
  Android SDK: Not Found
IDEs:
  Android Studio: 2023.1 AI-231.9392.1.2311.11076708
  Xcode:
    version: 15.3/15E204a
    path: /usr/bin/xcodebuild
Languages:
  Java:
    version: 17.0.11
    path: /usr/bin/javac
  Ruby:
    version: 2.6.10
    path: /usr/bin/ruby
npmPackages:
  "@react-native-community/cli": Not Found
  react:
    installed: 18.2.0
    wanted: 18.2.0
  react-native:
    installed: 0.72.15
    wanted: 0.72.15
  react-native-macos: Not Found
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: true
  newArchEnabled: false
iOS:
  hermesEnabled: true
  newArchEnabled: false

Stacktrace or Logs

[RCTNetworking processDataForHTTPQuery] file:///Users/carverhong/Library/Developer/CoreSimulator/Devices/E094052D-91B7-493F-A39A-72F089B8937D/data/Containers/Bundle/Application/8BFC2E5C-87BD-4295-A8F0-F04272BC374A/HelloWorld.app/20240808144728-0.jpg rawDataSize=2017293
[RCTNetworking handleResult] multipartDataSize=6151776

Reproducer

https://github.com/carverhong/react-native-reproducer-ios-image-upload.git

Screenshots and Videos

No response

从提供的 reproducer 及其 RCTNetworking 日志开始，然后跟踪 processDataForHTTPQuery 和 handleResult 路径。比较 iOS 上传期间的 rawDataSize 与 multipartDataSize，并确定扩展发生的位置。当 server 收到上传的图像且没有报告中的大小增加，并且该情况具有回归测试覆盖时，即视为完成。