Electron App Patcher

Patch an Electron app to apply your own changes (macOS only for now)

Setup

Electron App Patcher requires a certificate to sign the app again after it has been patched (see https://stackoverflow.com/a/27474942/1268612).

1. Clone the repo and run pnpm to install the dependencies
2. Open Keychain Access
3. Open the menu item Keychain Access > Certificate Assistant > Create a Certificate...
4. For the name, enter electron-app-patcher-self-signed-cert
5. Under "Certificate Type", select "Code Signing"
6. Create the certificate

Usage

Run pnpm run patch <patch name> in the electron-app-patcher directory, and it will patch your app based on the transforms in the patch file in the patches/ directory. For example, with the included patches/signal.ts patch:

$ pnpm run patch signal
Creating a backup of app.asar...
Processing preload.bundle.js...
Repacking app.asar to enable patch...
Updating hash in Info.plist to bypass asar integrity check...
Signing app with self-signed certificate...
Done!
✨  Done in 6.66s.

You will receive a prompt during the app signing to enter your password, since the codesign command needs access to the self-signed certificate created in Setup above.

After opening the patched app, you may receive a permissions prompt for access to confidential information in your keychain because of the re-signing of the app. Only allow access to information that you believe the app should have access to.

Screenshot of security notification in macOS showing the message Signal wants to use your confidential information stored in "Signal Safe Storage" in your keychain..

Restore app.asar backup

$ pnpm run patch signal restore-backup

Delete app.asar backup

$ pnpm run patch signal delete-backup

How?

Electron App Patcher works by modifying the files inside the asar archive:

1. <app>/Contents/Resources/app.asar is backed up to <app>/Contents/Resources/app.asar.bak
2. <app>/Contents/Resources/app.asar is extracted to <app>/Contents/Resources/app/
3. All transforms in your specified patch file are applied to files in <app>/Contents/Resources/app/
4. The contents of <app>/Contents/Resources/app/ are packed into <app>/Contents/Resources/app.asar
5. The SHA256 hash of the header of the <app>/Contents/Resources/app.asar file is calculated and updated in the <app>/Contents/Info.plist file (to avoid errors from asar integrity check)
6. App is signed with self-signed certificate

Troubleshooting

macOS Security Warning

Newer versions of macOS may prevent the app where you run the script from modifying apps on your computer and require you to allow access manually:

Screenshot of security notification in macOS showing the message "Visual Studio Code" was prevented from modifying apps on your Mac.

Credit

Credit for the original script goes to @degecko:

• https://www.codepicky.com/hacking-electron-restyle-skype
• https://github.com/codepicky/skype-patch