[CABMAN] Fix a problem with creating temp files on some Windows system

[tkreuzer]

See CORE-14431

[HBelusca]

Do we really know what causes this breakage?

[learn-more]

first tmpfile() fails.

[tkreuzer]

For some reason tmpfile() fails. Only happens with GCC builds, only on some Windows 10 systems. This fixes it for me. Everything else is left as an exersize to the reader ;-)

[ColinFinck]

I think merging this PR is still blocked by people not being able to reproduce the problem and not understanding the fix. And frankly spoken, it is hard to believe that tmpnam() always succeeds when tmpfile() fails.

For the record, MinGW builds of cabman.exe link against the OS msvcrt.dll to import tmpfile(). Visual Studio builds on the other hand statically link tmpfile() from their shipped CRT.
This can at least explain why only MinGW builds fail, and only on Windows 10, which may have introduced a bug in its tmpfile() implementation.

A minimal test to reproduce the tmpfile() problem may be the example code at https://msdn.microsoft.com/nl-nl/library/windows/desktop/x8x7sakw.aspx. @tkreuzer, does that trigger the problem for you as well?

Furthermore, the proposed fix does not handle a possible failure of tmpnam().
Additionally, it expects the returned filename to always be in the format "\tempfile123", indicating a temporary file in the current directory, and therefore skips the first slash. This does not hold when calling tmpnam() under Unix though (see http://en.cppreference.com/w/cpp/io/c/tmpnam).

We either need to understand the root cause and try to fix that. Or, if that is not possible or too boring, the code needs to be rewritten to not call tmp* CRT functions at all.
Either way, replacing one buggy tmp* function by another tmp* function is no option due to the aforementioned reasons.

[ColinFinck]

Requesting changes (see my previous comment)

[tkreuzer]

Hmm. Looks like this PR is only blocked by ... @ColinFinck :)
I could now argue that all I claimed is that this fixes build for me, and whoever can't reproduce it, might just not have put enough effort into it, and whoever finds things hard to believe is free to call me a liar, but luckily it seems like MS has fixed the issue with the latest VS update, so this makes this PR obsolete.

[HBelusca]

Interesting! Diffing old VS crt vs new VS crt one could help knowing what happened there 😃

[tkreuzer]

Reopening, since it is still not fixed for me, not sure how and why it succeeded in between.