Mac only: app becomes unresponsive for a period after downloading the zip file, and the mouse shows a loading icon.

[DamonYu6]

• Electron-Builder Version: 23.3.0

• Node Version: 18.17.1 (integrated within [email protected])

• Electron Version: 27.2.0
• Electron Type (current, beta, nightly): current

• Electron-Updater Version: 6.3.4

• Target: Mac (Apple Silicon / Intel)

Issue: After enabling delta updates for macOS in electron-updater, we observed that once the app downloads the zip file in the background, it becomes unresponsive for a period, and the mouse shows a loading icon. Additionally, our Sentry has captured main process ANR (Application Not Responding) events reported by the app.

Analysis: Upon reviewing the code, I found that in order to implement delta updates, the MacUpdater calls the synchronous copyFileSync Node API to cache the file after the zip file is downloaded locally. This synchronous API blocks the Electron main process, especially when the zip file is large, causing the app to freeze for longer periods (our zip file is around 400MB).

electron-builder/packages/electron-updater/src/MacUpdater.ts

Lines 120 to 129 in 74d98d8

	done: event => {
	if (!downloadUpdateOptions.disableDifferentialDownload) {
	try {
	const cachedUpdateFilePath = path.join(this.downloadedUpdateHelper!.cacheDir, CURRENT_MAC_APP_ZIP_FILE_NAME)
	copyFileSync(event.downloadedFile, cachedUpdateFilePath)
	} catch (error: any) {
	this._logger.warn(`Unable to copy file for caching for future differential downloads: ${error.message}`)
	}
	}
	return this.updateDownloaded(zipFileInfo, event)

Solution: Replace copyFileSync with an asynchronous API, such as the copyFile method provided by the fs-extra module for file copying.

[DamonYu6]

@beyondkmp could you help to check this PR