I have a knack for finding bugs and edge cases, and my experience adapting to the Mac sandboxing facility over the past few years has been no exception.
The latest issue is something of a conundrum: I’m managed to produce two versions of my app, one of which causes the sandbox container to be apparently unwritable to the other after running! Specifically, preferences are not saved and console messages indicate an attempt to write preferences outside the host app’s sandbox.
I suspect it has something to do with changes I’ve made in anticipation of a bundle identifier change. As with so many of my struggles with sandboxing, I’m trying to smooth out the process of migration from one sandbox container to another. To that end I have added some temporary entitlements for preferences and shared file access, as well as modifying the code signing designated requirement to cover both bundle identifiers.
Long story short: if I run app version 1, then run app version 2, then run app version 1, app version 1 is denied access to the container (which had previously been its own!).
These kinds of issues scare the bejeezus out of me because I really fret my users running into data migration problems after I ship an update, and because the relative opacity of the sandboxing system makes a lot of issues very hard to debug.
I suspect there is some association made between a sandbox container and the owning app’s designated requirement, and that perhaps by changing it I’ve yielded ownership to the later version of the app. The Info.plist file inside a sandbox container has various keys such as “Identity” and “SandboxProfileData” which seem likely to pertain to this issue.
Apple supplies an App Sandbox in Depth which alludes to how ownership is determined, but alas does not go quite as deep as I’d like. Has anybody dived deeply enough into the sandbox to understand this issue well?
Update: I probably should have scratched more than the surface of the Info.plist before posting. There are other interesting keyed values in there such as SandboxProfileDataValidationInfo that includes keyed values such as full paths of various apps that share ownership (?) in the container. In summary: I guess I’m curious if anybody has dealt with issues like the one I’m seeing as has debugging tips to share.