Re: ssl tests fail on windows / slurp_file() offset doesn't work on win

Hi,

On 2021-10-03 10:18:31 -0700, Andres Freund wrote:
> As you can see in the test output, every mismatch prints the whole file,
> despite only intending to show the tail. Which appears to be because the
> windows portion of 3c5b0685b921 doesn't actually work. The reason for that in
> turn is that afaict the setFilePointer doesn't change the file position in a
> way that affects perl.
>
> Consequently, if I force the !win32 path, the tests pass.
>
> At first I assumed the cause of this is that while the setFilePointer() modifies the
> state of the underlying handle, it doesn't actually let perl know about
> that. Due to buffering etc perl likely has its own bookeeping about the
> position in the file. There's some pretty clear hints in
> https://perldoc.perl.org/functions/seek
>
> But the problem turns out to be that it's bogus to pass $fh to
> setFilePointer(). That's a perl handle, not an win32 handle. Fixing that seems
> to make the tests pass.

It does (I only let it run to the ssl test, then pushed a newer revision):
https://cirrus-ci.com/task/5345293928497152?logs=ssl#L5

> Why did 3c5b0685b921 choose to use setFilePointer() in the first place? At
> this point it's a perl filehandle, so we should just use perl seek?
>
>
> Leaving the concrete breakage aside, I'm somewhat unhappy that there's not a
> single comment explaining why TestLib.pm is trying to use native windows
> APIs.
>
> Isn't the code as-is also "leaking" an open IO::Handle? There's a
> CloseHandle($fHandle), but nothing is done to $fh. But perhaps there's some
> perl magic cleaning things up? Even if so, loks like just closing $fh will
> close the handle as well...

I think something roughly like the attached might be a good idea. Runs locally
on linux, and hopefully still on windows

https://cirrus-ci.com/build/4857291573821440

Greetings,

Andres Freund