Fix GH-10344: imagettfbbox(): Could not find/open font UNC path

[nielsdos]

libgd uses an incorrect absolute path check in gdft.c. It checks if either the path starts with a '/' (only valid on Posix btw), or whether it contains something of the form C:\ or C:/. However, this overlooks the possibility of using UNC paths on Windows. As we already do PHP-specific stuff with VCWD_ macros, use IS_ABSOLUTE_PATH to check for an absolute path which will take into account UNC paths as well.

[devnexen]

no hope to push it upstream I see :)

[nielsdos]

no hope to push it upstream I see :)

Indeed.
But even if it was upstreamable, the previous fix I did took a long time to merge... libgd feels unmaintained.
Which reminds me that I need to backport that one fix to php, I'll put it on my todo list for this week.

[Girgias]

I don't really know much about paths and Windows, but this looks reasonable?

[devnexen]

Looks good to me, I m surprised there is still a netware code path :)

[nielsdos]

Looks good to me, I m surprised there is still a netware code path :)

Never really heard of it, Wikipedia says "Final release: 6 May 2009; 14 years ago", so perhaps can be removed from the master branch, but 🤷

[cmb69]

Found this while looking into https://bugs.php.net/75656.

no hope to push it upstream I see :)

Hmm, that would certainly be bad, since the goal should still be to unbundle libgd (the only somewhat sensible alternative would be to drop support for external libgd, but that ship probably has sailed long ago).

Anyway, the respective code is now in font_path(), and had been changed long ago to not only cater to absolute paths, but also to relative paths, but see libgd/libgd#952. I think bundled libgd should also handle it this way (does not necessarily work for ZTS, but this is a different issue).

I m surprised there is still a netware code path :)

See #17596.