Files.read/readAllBytes can loop once with zero size buffer

[Martin Buchholz]

I think keeping the status quo is the right outcome.  The /proc filesystem
is intentionally providing incorrect information because providing correct
information is deemed to be too expensive (have to compute contents of file
for stat?).  Reading /proc is sufficiently expensive that the extra realloc
of an empty buffer is noise.  Be thankful that reading files in /proc works
at all!

On Thu, Jul 28, 2016 at 11:28 PM, Fabian Lange <lange.fabian at gmail.com>
wrote:

> Hi,
> yes something like that. I have no strong opinion. After discovering
> this, I switched to a hand rolled implementation with file name
> depended estimated buffer sizes.
> But usually inside the JDK, Edge cases are handled better, usually
> with some Math.min()/Math.max logic.
>
> IMHO that really depends how common it could be that
> SeekableBytesChannel returns a size of 0 while actually containing
> data.
> If the proc files are the only realistic scenario, then maybe my
> concern is not that valid
>
> Fabian
>
> On Fri, Jul 29, 2016 at 8:21 AM,  <ecki at zusammenkunft.net> wrote:
> > Hello,
> >
> >
> >
> > It could always read with a initial buffer of 0.5-16k and return a
> truncated
> > copy if it read less (and a omit truncation by returning shared static 0
> > length array if empty). But this will only optimize the 0 byte case.
> >
> >
> >
> >
> > Gruss
> > Bernd
> > --
> > http://bernd.eckenfels.net
> > From Win 10 Mobile
> >
> >
> >
> > Von: Martin Buchholz
> > Gesendet: Freitag, 29. Juli 2016 03:33
> > An: Fabian Lange
> > Cc: core-libs-dev
> > Betreff: Re: Files.read/readAllBytes can loop once with zero size buffer
> >
> >
> >
> > What do you suggest instead?
> >
> >
> >
> > The extra allocation of a zero-size buffer is not that bad.
> >
> >
> >
> > I think it's best to optimize for files with correct metadata, while
> >
> > tolerating ones with buggy metadata.
> >
> >
> >
> > On Thu, Jul 28, 2016 at 1:13 PM, Fabian Lange <lange.fabian at gmail.com>
> >
> > wrote:
> >
> >
> >
> >> Hi,
> >
> >> I just noticed that when one uses Files.readAllBytes() to read for
> >
> >> example from the Linux proc file system, where file size is claimed to
> >
> >> be 0, Files.read() will allocate a buffer of size 0 before then
> >
> >> adjusting in a second loop (arraycopying the zero size buffer)
> >
> >>
> >
> >> In my opinion an initial size of 0 should not be used.
> >
> >> I admit this might be a regression for files which are really empty
> >
> >> and return an empty byte array, but I think it is actually more common
> >
> >> to read from files which incorrectly report to be zero sized.
> >
> >>
> >
> >> Fabian
> >
> >>
> >
> >
>