mox/mox-/forkexec_windows.go

package mox

// Fork and exec as unprivileged user.
//
// Not implemented yet on windows. Would need to understand its security model
// first.
func ForkExecUnprivileged() {
	xlog.Fatal("fork and exec to unprivileged user not yet implemented on windows")
}
make mox compile on windows, without "mox serve" but with working "mox localserve" getting mox to compile required changing code in only a few places where package "syscall" was used: for accessing file access times and for umask handling. an open problem is how to start a process as an unprivileged user on windows. that's why "mox serve" isn't implemented yet. and just finding a way to implement it now may not be good enough in the near future: we may want to starting using a more complete privilege separation approach, with a process handling sensitive tasks (handling private keys, authentication), where we may want to pass file descriptors between processes. how would that work on windows? anyway, getting mox to compile for windows doesn't mean it works properly on windows. the largest issue: mox would normally open a file, rename or remove it, and finally close it. this happens during message delivery. that doesn't work on windows, the rename/remove would fail because the file is still open. so this commit swaps many "remove" and "close" calls. renames are a longer story: message delivery had two ways to deliver: with "consuming" the (temporary) message file (which would rename it to its final destination), and without consuming (by hardlinking the file, falling back to copying). the last delivery to a recipient of a message (and the only one in the common case of a single recipient) would consume the message, and the earlier recipients would not. during delivery, the already open message file was used, to parse the message. we still want to use that open message file, and the caller now stays responsible for closing it, but we no longer try to rename (consume) the file. we always hardlink (or copy) during delivery (this works on windows), and the caller is responsible for closing and removing (in that order) the original temporary file. this does cost one syscall more. but it makes the delivery code (responsibilities) a bit simpler. there is one more obvious issue: the file system path separator. mox already used the "filepath" package to join paths in many places, but not everywhere. and it still used strings with slashes for local file access. with this commit, the code now uses filepath.FromSlash for path strings with slashes, uses "filepath" in a few more places where it previously didn't. also switches from "filepath" to regular "path" package when handling mailbox names in a few places, because those always use forward slashes, regardless of local file system conventions. windows can handle forward slashes when opening files, so test code that passes path strings with forward slashes straight to go stdlib file i/o functions are left unchanged to reduce code churn. the regular non-test code, or test code that uses path strings in places other than standard i/o functions, does have the paths converted for consistent paths (otherwise we would end up with paths with mixed forward/backward slashes in log messages). windows cannot dup a listening socket. for "mox localserve", it isn't important, and we can work around the issue. the current approach for "mox serve" (forking a process and passing file descriptors of listening sockets on "privileged" ports) won't work on windows. perhaps it isn't needed on windows, and any user can listen on "privileged" ports? that would be welcome. on windows, os.Open cannot open a directory, so we cannot call Sync on it after message delivery. a cursory internet search indicates that directories cannot be synced on windows. the story is probably much more nuanced than that, with long deep technical details/discussions/disagreement/confusion, like on unix. for "mox localserve" we can get away with making syncdir a no-op. 2023-10-14 11:54:07 +03:00			`package mox`

			`// Fork and exec as unprivileged user.`
			`//`
			`// Not implemented yet on windows. Would need to understand its security model`
			`// first.`
			`func ForkExecUnprivileged() {`
			`xlog.Fatal("fork and exec to unprivileged user not yet implemented on windows")`
			`}`