7 things that lead to f***up

Presented on iFuckup Meetup Kyiv #1 - https://www.facebook.com/events/1363042070378506/

This talk describes 7 thing you should do to not f*ck up. Deep into technology and a bit fun.

Transcript

1. Long time ago in a galaxy far-far-away
2. 7 things that lead to f***up Petro Korienev, iOS Engineer especially for i4☕ ver.1
3. Sponsored by...
4. The problem • UIWebView-based browser application for iOS • After an iteration the regression issue is found • Login to google accounts (mail, drive etc.) is not persisted between app launches on iOS 9
5. Thing #1 Don’t ever work with UIWebView-based browser
6. How to achieve
7. Investigation • UIWebView stores cookies in .binarycookies format on disk • Somehow it’s started to fail to read written cookies • [[NSHTTPCookieStorage sharedCookieStorage] allCookies] is nil
8. The root-cause • We’ve adopted on-the-fly proprietary disk encryption solution • “on-the-fly” means “magic” • We’ve broken cookies storing mechanism
11. Thing #2 With great power comes great responsibility. Don’t rely on magic. Until you understand it.
13. How to achieve pod ‘AwesomeMagicWand.. pod ‘SilverBullet.. pod ‘GoldenHammer
14. Deep investigation • Encryption library hooks UNIX file-system functions. • 200-line function with comparisons to string literals, magic numbers, system imports constants etc. • around 70-80 hooked unix implementations • And todo 17 Jan 2003
15. Meanwhile, - 2 DEBUG DAYS...
16. • System calls atomic write to cookies file • File is written to temp • File is moved to original • Appropriate encryption applied • Hooked move is called on iOS 8 and not on iOS 9 Result
17. • AdHoc for encryption solution - ignore “_tmp_” pattern • Initial vector for encryption is the same for temp/original • Profit Solution
18. Resolution on code- review : rework in next iteration
19. Thing #3 Never break KISS-principle. Doing things well might be expensive. Overly expensive
20. How to achieve
21. • Get the hook working on iOS 9 • symbolic breakpoints on UNIX-functions • debug symbol stubs • compare across different versions of iOS The next iteration
22. • XCode->Debug->Always show disassembly • symbolic breakpoints on UNIX-functions • debug symbol stubs • compare across different versions of iOS Tools
24. Thing #4 If you see use a previous document, you are most-likely doing something wrong.
25. How to achieve Get back to original task and ask PO - probably we should skip it? Ask colleagues.
26. Collective mind has given me a link
27. It didn’t work for this case neither. But trying it first i could save a time. And for sure I could find it myself. The library works exactly as the needed hook code
28. Thing #5 Never skip google.com step...
29. How to achieve
30. Ages of debugging on device, a week spent on implementing this for ARM architecture, offset calculations, reading Mach-O spec and i got the stubs working on iOS 9 I’ve written the solution
31. Used structs
32. Thing #6 Always run on device. Never rely on simulator
33. I did
34. I was inspired by my awkward solution. I’ve reversed a big bunch of a format. I forgot about initial issue with login, cookies, etc... Once upon a time...
35. EXC_BAD_ACCESS (CODESIGN)
36. Thing #7 Always try as a user Without debugger, Carl
37. Under debugger, you can There are also some restrictions, bugs, etc. Try as a user You can’t modify an executable memory
38. There are more things that lead to fuckup…
39. THANKS FOR YOUR ATTENTION