BackupKit

Kotlin Multiplatform backup into the user's own cloud: iCloud on iOS (CloudKit or iCloud Drive), the Google Drive app-data folder on Android. No server, no account on your side, no OAuth client setup on iOS.

Built for Vocabloot, the photo vocabulary app for iOS and Android. Part of the Vocabloot open-source libraries.

Start here

1. Setup, iOS: one entitlement, and the CloudKit schema step for Production builds.
2. Setup, Android: a Google Cloud OAuth client and the one-time consent dialog.
3. The quickstart on the README, then restore on first launch.

Guides

• Support matrix: the three transports side by side.

• The SyncEngine contract: the ten guarantees.

• Restore on first launch: probe, hold, download, place, resume.
• Android consent, once.
• Errors: the seven CloudError values and the user copy for each.
• Bring your own scheduler.
• Recipes: SQLDelight, Room, a folder of photos, encrypt before upload.
• FAQ and known issues.
• Stability and versions.

Reference

• API reference (Dokka), binary API tracked in backupkit/api.
• Design and publishing, for maintainers.