fix(android): stop a failed download from crashing the app

[BMichaelJ]

Summary

Any failed download crashes the Android app. In RNFSManager.reject, react-native-fs 2.20.0 rejects failed operations with a null error code: promise.reject(null, ex.getMessage()). React Native's Kotlin Promise.reject(code: String, message: String?) does not accept a null code, so the call throws:

NullPointerException: Parameter specified as non-null is null:
  method com.facebook.react.bridge.PromiseImpl.reject, parameter code
  at com.rnfs.RNFSManager.reject(RNFSManager.java:979)
  at com.rnfs.RNFSManager$3.onTaskCompleted(RNFSManager.java:735)
  at com.rnfs.Downloader$1.run(Downloader.java:34)

It is thrown on the download thread, which kills the process. It fires on every generic failure:

• a dropped connection
• no network when the download starts
• a read timeout
• stopDownload, which fix(ios): make sign-in work, and stop failures happening in silence #42's inactivity watchdog calls

Other react-native-fs methods that reach the same helper with a generic exception crash the same way. The current Android field build uses the same library versions, so an interrupted model or pack download there most likely crashes too.

The fix is one line in the existing react-native-fs patch: reject with EUNSPECIFIED and pass the exception. The failure then reaches fileDownloadService's retry logic and the "Download failed" alert.

Type of Change

• Bug fix (non-breaking change that fixes an issue)

Screenshots / Screen Recordings

Android

Before	After
The app closes (crash above)	"Download failed – Could not download the embedding pack: Unable to resolve host …", and the app keeps running

Checklist

General

• My code follows the project's coding style and conventions
• I have performed a self-review of my code
• I have added/updated comments where the logic isn't self-evident
• My changes generate no new warnings or errors

Testing

• I have tested on Android (physical device or emulator)
• I have tested on iOS (physical device or simulator)
• I have tested in light mode and dark mode
• Existing tests pass locally (npm test)
• I have added tests that prove my fix is effective or my feature works

Tested on a Pixel 9a (Android 17), using a debug build with this patch. The build was made from #45's branch, which contains the same react-native-fs sources. I switched on airplane mode at 93% of the pack download:

• Before the patch: FATAL EXCEPTION … RNFSManager.reject, and the app closed.
• With the patch: three attempts are logged, the "Download failed" alert appears, and the app keeps running.
• After Wi-Fi returned: "Update to Latest Pack" downloaded, verified and installed the pack.

The patch applies cleanly on a fresh npm ci (patch-package ✔). No JS changed. The iOS side of the patch is unchanged, so iOS is not affected. No automated test was added, since this is a third-party native module; the device run above is the verification.

CI: android-build, lint and test fail in the Setup Android SDK step, where the macOS runner's cmdline-tools 16.0 stops on unaccepted SDK licences. That is the same failure as on #42 and unrelated to this change; typecheck passes.

Performance & Models

• Large files (models, assets) are not committed to the repository

Security

• No secrets, API keys, or credentials are included in the code

Related Issues

Found while testing #45, which is stacked on #42.

Additional Notes

• How the patch was produced. patch-package 8.0.1 could not regenerate the patch on a Windows / Node 24 host, because it fails to spawn npm. So I produced it the same way patch-package does: a git diff of a pristine react-native-fs 2.20.0 against the patched files. Apart from the new hunk and its index line, the patch is byte-identical to the previous one.
• Follow-ups.
  • Retries give up within about 3 s, so even a short outage ends in the alert.
  • The alert shows the raw exception text.