[issue37834] readlink on Windows cannot read app exec links

[Steve Dower]

Steve Dower <steve.dower at python.org> added the comment:

Thanks Eryk for your valuable response :)

> readlink() and is_link() should be reserved for POSIX symlinks, i.e. only IO_REPARSE_TAG_SYMLINK. 

I'm okay with that reasoning. Honestly, the only real problem I've seen is in applications that use a reimplementation of spawn() rather than the UCRT's version (which handles the reparse point jsut fine).

> they lack an associated filter driver that handles them in normal file operations

Also true, and likely to be a cause of more problems. But not ours to fix :)

> How about adding a separate function such as nt.read_reparse_point() that's able to read reparse points [...]? The internal implementation could be shared with os.readlink.

Maybe it can just return bytes and let the caller do the parsing?

> The current behavior of follow_symlinks in stat() is problematic. It should be limited to symlinks.

This sounds like a good option to me, too. So that would suggest that Modules/posixmodule.c in win32_xstat_impl would verify both FILE_ATTRIBUTE_REPARSE_POINT and IO_REPARSE_TAG_SYMLINK? And if the tag is different it'll return information about the reparse point rather than the target?

> The stat result would gain an st_reparse_tag field (already added by your PR), which would be non-zero whenever a reparse point is opened.

I agree this can stay. We don't need the rest of the logic here - callers who care to follow non-symlink reparse points can use the new nt.read_reparse_point() function to do it.

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<https://bugs.python.org/issue37834>
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