Fix Android bug on FAT32 time resolution and mtime caching

[lmagyar]

As I wrote in https://github.com/wolpi/prim-ftpd/pull/351#issuecomment-2158001529, Android lies about the lastModifiedTime. Even the specs says, that if the time resolution is lower than what we ask, the next getLastModifiedTime will give back the "truncated" value, this is simply not true (tested on real phone, Android 9.0 and emulator). It gives back the truncated values only when he wants, usually hours later. This is an unpredictable nightmare.

This fix:

• adds a new method to the StorageManagerUtil class that detects SAF filesystems from /proc/mounts, it detects:
  • FAT16, FAT32 -> 2000ms
  • exFAT -> 10ms
  • default 1ms
• moves the fileSystemView property from SafSshFile up to SafFile, so all SAF file can call the new getTimeResolution() from SafFileSystemView

Maybe the default 1ms is overkill, in theory FTP has sub-second resolution, though we can modify StorageManagerUtil to return only 1000 vs 2000 ms, in this case no overload needed in SafSshFileSystemView to limit sub second resolution to the 1s resolution of sftp messages.

[lmagyar]

Not the latest logs, but some proof it works. Emulator:

getFilesystemTimeResolutionForSftp(content://com.android.externalstorage.documents/tree/17FB-0715...
  found mount point /mnt/media_rw/17FB-0715 with type vfat

Real FAT32 card:

getFilesystemTimeResolutionForSftp(content://com.android.externalstorage.documents/tree/80AB-022A...
  found mount point /mnt/media_rw/80AB-022A with type sdfat with option fs=vfat:32

The fs=exfat sample in the code comment is from a real exFAT 64GB card.

[wolpi]

I'm really looking forward to that merge script :smile:

[lmagyar]

I'm really looking forward to that merge script 😄

The Python sync? 😄 It is working, I've added remote management (start/stop, with Automate or HomeAssistant) for Tailscale, pFTPd, Termux/sshd services (the later for inotifywait, to catch the changes on the fly). I need a few hours net to finalize it on to a v0.1 quality level, though with a newborn and a relocation I hardly find time to sleep. 😨

I will work on the tech comments above on next week.

[wolpi]

Happy coding between moving boxes and with new born on arm :smile: