Offline Data & the Hostage Scenario

Many iOS apps are used in scenarios when offline usage is expected. Data may be collected on a device, retrieved from a server, manipulated while offline, and submitted to a server at a later date. We'll talk briefly about strategies for managing and syncing offline data. But what happens when bad data inadvertently is trapped on a device? What techniques can you use as workarounds in this scenario? How do you fix bad data with an app update? We'll learn the answers to these important questions through the lens of a buggy implementation resulting in critical data held hostage with users locked out.

Transcript

1. Offline Data the Hostage Scenario & Tue, Mar 11, 14
2. Peter Kananen @pkananen Tue, Mar 11, 14
3. iOS {...} GET /stuff Server Tue, Mar 11, 14
4. Server iOS {...} user/pass 45AB8C GET /stuff POST /stuff Tue, Mar 11, 14
5. Server iOS {...} user/pass 45AB8C GET /stuff + POST /stuff Tue, Mar 11, 14
6. what’s hard? Authentication Core Data Updates Tue, Mar 11, 14
7. Authen- tication Offline Tue, Mar 11, 14
8. NSUserDefaults Not Secure Convenient [[NSUserDefaults standardUserDefaults] setObject:currentUser.email] forKey:CURRENT_USER]; Tue, Mar 11, 14
9. Keychain Sandboxed Secure https://github.com/ldandersen/STUtils [SFHFKeychainUtils storeAuthToken:currentUser.authToken forUsername:currentUser.email]; Tue, Mar 11, 14
10. logout? (never?) when to... Tue, Mar 11, 14
11. revalidate? (always?) when to... Tue, Mar 11, 14
12. expire? (never?) when to... Tue, Mar 11, 14
13. Login Known? No Resume Session No Yes Server Auth Local Auth 24 hrs? Data Load Yes Session? End Session Yes Tue, Mar 11, 14
14. Hostage Scenario User.where(email: params[:email_address]).first || User.authenticate(params[:user_api_key]) Tue, Mar 11, 14
15. Login Online? No Resume Session Yes No Server Auth Local Auth 24 hrs? Data Load Yes Session? End Session Yes Tue, Mar 11, 14
16. Core Data Offline is just fine Tue, Mar 11, 14
17. Core Data Syncing is harder Tue, Mar 11, 14
18. Account User Account Region Region Region Region Site Site Site Site Site Site Report Report Report Report Report Report Tue, Mar 11, 14
19. why? new or update? performance missing parent two way merges orphaned data shared data race conditions UI updates Tue, Mar 11, 14
20. http://www.objc.io/issue-10/ http://nshipster.com/core-data- libraries-and-utilities/ http://daringfireball.net/2013/09/ vesper_whats_new_whats_next others think so too Tue, Mar 11, 14
21. HTTP_IF_MODIFIED_SINCE @item = Product.find(params[:id]) respond_with(@item) if stale?(@item) Conditional GET Tue, Mar 11, 14
22. Hostage Scenario Orphaned User Data Tue, Mar 11, 14
23. Account User Account Region Region Region Region Site Site Site Site Site Site Report Report Report Report Report Report Protect User Data Tue, Mar 11, 14
24. Updating two apps at once Tue, Mar 11, 14
25. iOS 1.0 iOS 1.1 Server 1.1 Server 1.0 expired auth old data expired auth? new data Tue, Mar 11, 14
26. Hostage Scenario Trapped User Data Tue, Mar 11, 14
27. Taking it Offline Sounds Simple Tue, Mar 11, 14
28. Questions? Tue, Mar 11, 14
29. Peter Kananen @pkananen Tue, Mar 11, 14