Unix-like OSes allow mounting disk images to explore their contents. But there's many more file formats where exploring files-inside-files is useful. Compressed archives, for one. Some file managers support those, but (imho) application-level is not the optimal layer to put this functionality.
Could be implemented with a kind of driver-per-filetype.
The only thing standing in the way of this today is that MacOS doesn't expose a user space file system API. You can do this on Linux, Windows, and BSDs today.
(No, file provider extensions don't cut it, Apple devs who read this, please give us a FUSE equivalent, we know it exists).
The fundamental issue is that macOS doesn't provide an API for this natively.
I was wondering what issues you were talking about, and then I found this - https://github.com/macos-fuse-t/fuse-t/issues/45 - data corruption
> The fundamental issue is that macOS doesn't provide an API for this natively.
The API is there, Apple just doesn’t want to give anyone outside of Apple the entitlement that lets them use it. I don’t understand why Apple won’t.
Well, I understand that would require them to document it, ship public headers, and support it for external developers - but why not?
If no one can call it it's not an API, it's an implementation detail. And I don't even think its exposed by headers, just alluded to by people who claim APFS is implemented in user space.
> I was wondering what issues you were talking about, and then I found this
Worse than this, it's possible to DoS a Mac with an NFS server just by refusing to reply to a request. That's unacceptable for a user space file system (although FUSE is only kinda better, in that it can force processes that read from the FS into uninterruptable sleep that prevents them from being killed).
> Well, I understand that would require them to document it, ship public headers, and support it for external developers - but why not?
Because Apple doesn't give a fuck about developers. Every developer will eventually learn this, but for those that haven't - Apple doesn't want you writing software for their platform, unless you're an Apple employee and on an Apple team paid to do it. It's why their docs suck, it's why to learn anything you need to watch ADC videos instead of read manpages, and it's why all the cool stuff is behind protected entitlements that you can't get or will be limited in using.
I wonder if their SMB/CIFS client implementation has these kinds of issues? It probably gets used more heavily
> And I don't even think its exposed by headers
Apple (accidentally?) released some of the private headers for this feature in one of their open source releases: https://github.com/apple-oss-distributions/msdosfs/blob/rel/...
That link is very interesting. It doesn't smell like any other Apple API as they're exposing a vtable with good documentation comments. It would be interesting to hack with this with SIP disabled to see how it works. I'm especially curious about how mount/unmount work and how the plugin registers itself with the OS, or what application is the client/host.
It's much more likely that they want to:
a. Dogfood the API using internal use cases first when they can still make changes to the API without breaking anything. Note that the latest MacOS releases moved some filesystems into userspace using this new API. They probably learned some stuff by doing that.
b. Work out how to protect system stability from crappy userland filesystems. As you point out, bugs in FUSE providers can hang apps.
c. Work out how such an API interacts with their sandboxing system and how to avoid FUSE-style filesystems being used to subvert the sandbox. This is a common source of exploits in FUSE-style systems and is one of the key learnings from GNU/Hurd: UNIX software is written on the assumption that filing systems aren't malicious and invalidating that assumption creates new bug classes.
d. Work out what the most important use cases are and try to ensure those use cases will have a good or at least uniform UX first.
Providing a FUSE-like API is presumably also just not a high priority. By far the most common use case in terms of number of users is the Dropbox use case. FUSE is mostly used for toys and experiments beyond that (like filefs). Those matter and I'm sure there are friendly geeks on the Darwin team who'd like to enable those, but Linux also works for exploration. Certainly Apple management would not be happy about an engineer who decided to enable nerd experimentation but undermined the security system whilst doing so.
And it's worth remembering that you can have root on macOS. It means disabling SIP and adding a kernel boot arg, but that only takes a few minutes and then you can grant apps any entitlements you like:
https://github.com/osy/AMFIExemption
That's no good for people who aren't developers, but most FUSE filesystems are designed for developers anyway.