Severe memory leak affecting fetch(), iOS Release Mode 0.59.0-rc.3, 0.58.6, 0.57.8

🐛 Bug Report

Every call to fetch() uses memory and does not release it. The larger the fetch response, the more memory leaked.

• I’ve confirmed that this is happening in 0.57.8, 0.58.6, and 0.59.0-rc.3.
• I’ve tried this with both node-fetch and whatwg-fetch and it happens using both libraries.
• It is not isolated to response.blob(). It affects all types of responses.
• It happens with both Release and Debug.
• It happens with raw XMLHttpRequest as well as fetch.
• I can confirm that it’s happening on a (real) iPhone X with iOS 12.1.4 and the Simulator for an iPhone 8 with iOS 12.1.

Comparing memory snapshots in Safari found no difference in size even while the Chrome/Xcode memory profiles showed dramatic increases in memory. I’m not great at debugging memory leaks so I could be wrong but I suspect that means it might be on the native side and not on the JS side.

To Reproduce

I’ve created an example repo to reproduce the error in 0.59.0-rc.3: https://github.com/cjroth/react-native-fetch-memory-leak. You can copy the App.js and see that it happens in previous versions as well.

Expected Behavior

After each fetch() call that is no longer referenced, the memory should return to what it was previously.

Code Example

https://github.com/cjroth/react-native-fetch-memory-leak

Environment

  React Native Environment Info:
    System:
      OS: macOS 10.14.1
      CPU: (4) x64 Intel(R) Core(TM) i7-4650U CPU @ 1.70GHz
      Memory: 16.96 MB / 8.00 GB
      Shell: 5.3 - /bin/zsh
    Binaries:
      Node: 11.10.0 - /usr/local/bin/node
      Yarn: 1.13.0 - /usr/local/bin/yarn
      npm: 6.8.0 - /usr/local/bin/npm
      Watchman: 4.9.0 - /usr/local/bin/watchman
    SDKs:
      iOS SDK:
        Platforms: iOS 12.1, macOS 10.14, tvOS 12.1, watchOS 5.1
    IDEs:
      Xcode: 10.1/10B61 - /usr/bin/xcodebuild
    npmPackages:
      react: 16.8.3 => 16.8.3 
      react-native: 0.59.0-rc.3 => 0.59.0-rc.3 
    npmGlobalPackages:
      react-native-cli: 2.0.1
      react-native-git-upgrade: 0.2.7
      react-native-rename: 2.4.0

[timsawtell]

I think I’ve fixed it. Time to make my first PR into RN.

I found that the RCTNetworkTasks were not de-allocating, and that RCTBlobManager.mm was holding onto it’s blobs (NSData) forever after telling the RCTNetworking coordination code about the response.

[noahpryor]

I was able to reproduce using the iOS simulator and a variant of @cjroth s code with a five mb test file here