Kordant/tasks/ios-production/11-background-fetch.md

11. Background Fetch & Sync Optimization

meta: id: ios-production-11 feature: ios-production priority: P2 depends_on: [] tags: [performance, background, production]

objective:

• Optimize background fetch and data sync to keep app data fresh without draining battery

deliverables:

• Background fetch configuration
• Efficient sync strategy
• Battery usage optimization
• Background task handling

steps:

1. Configure background fetch:
   • Enable Background Fetch in Signing & Capabilities
   • Set minimum fetch interval (15 minutes)
   • Implement application(_:performFetchWithCompletionHandler)
   • Or use BGAppRefreshTask for iOS 13+
2. Optimize sync strategy:
   • Sync only changed data (delta sync)
   • Use If-Modified-Since or ETag headers
   • Prioritize critical data (alerts, exposures)
   • Defer non-critical sync (reports, historical data)
3. Implement background tasks:
   • Use BGProcessingTask for heavy operations
   • Schedule periodic dark web scans
   • Schedule spam database updates
   • Handle task expiration gracefully
4. Optimize battery usage:
   • Batch network requests
   • Use cellular data efficiently
   • Defer sync until WiFi available (optional)
   • Respect low power mode
5. Handle push notification sync:
   • Silent push notifications for urgent updates
   • Content-available: 1 for background processing
   • Wake app for critical alerts
6. Add sync status indicators:
   • Last sync timestamp in settings
   • Sync progress for large operations
   • Offline mode indicator

tests:

• Unit: Test background task scheduling
• Integration: Test fetch completion within 30 seconds
• Battery: Verify minimal battery impact over 24 hours

acceptance_criteria:

• Background fetch enabled and configured
• Data syncs every 15 minutes minimum
• Delta sync reducing data transfer by >50%
• Background tasks complete within 30 seconds
• Battery impact <5% per day from background activity
• Silent push notifications trigger data refresh
• Low power mode respected (reduced sync frequency)
• Sync status visible to user in settings
• No background task terminations due to timeouts

validation:

• Simulate background fetch → data refreshed
• Check battery settings → Kordant background activity minimal
• Receive silent push → app updates in background
• Enable low power mode → sync frequency reduced
• Monitor network usage → delta sync working

notes:

• iOS limits background fetch frequency based on app usage patterns
• BGAppRefreshTask is modern replacement for performFetch
• Always call completion handler or setTaskCompleted
• Background processing tasks require specific entitlements