Because zip compression programs can use different levels of compression
there is certainly no expectation that zipping the same file with different
compression levels will give the the same output. It MIGHT - but it's not
to be expected or relied upon. The only thing that's "guaranteed" is that
unzipping the zipped file (regardless of compression level) will return you
to the original file. If it doesn't then it's obviously a bug. Confusion
can happen because not all zip programs allow varying the compression level
- especially the GUI versions and of course different programs can have
different defaults. Look at the man page for zip and the -Z option or go
to the PKware spec for details.
On Wednesday, August 17, 2016 at 8:40:08 AM UTC-4, Radek Simko wrote:
>
> Hi,
> I read through the 1.7 changelog but didn't spot any change that would
> explain this behaviour.
>
> Basically given a specific slice of bytes archived via "archive/zip" +
> written to a file produces different file when doing so w/ Go 1.6.3 and
> 1.7.0.
>
> See full repro case:
> https://gist.github.com/radeksimko/62aa4b89af6633f7421e45c979523135
> The first example produces different ZIP file, second produces the same
> one.
>
> Is anyone able to explain to me the difference I observed?
>
> I am aware that reproducible ZIP archives are tricky in general due to
> timestamp-based metadata,
> but I don't believe these affect me in the attached example.
>
> Thanks,
> --
> Radek
>
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