Re: race bug !?

[Jean-Jacques Brucker]

Big thanks for all.

Indeed there is no bug, and IMO even nothing to improve in bash.

What put me wrong is that such erroneous command "work down" when first 
"xxd  -r -p | base64" output don't begin with hexadecimals characters. 
This happens most often, and then second "xxd  -r -p" will ignore such 
input.

I should have play with file descriptors and redirections to parallelize 
correctly.


$ echo "dc30a6d79f3b47e310b8b9f5fbadba573DCm1587" | xxd  -r -p | base64
3DCm1587R+MQuLn1+626Vz0Vhw==


$ echo "68b329da9893e34099c7d8ad5cb9c940" |  tee >( head -c 4 ; echo ; 
ls -l /proc/self/fd ) | { tee >(xxd  -r -p | basenc --base64 ) ; ls -l 
/proc/self/fd ; }


Cheers,


Le 29/01/2021 à 14:50, Chet Ramey a écrit :
> On 1/28/21 6:33 PM, Jean-Jacques Brucker wrote:
> > 100 % reproducible on my Debian, package version 5.1-2:
> >
> >
> >
> > $ echo "dc30a6d79f3b47e310b8b9f5fbadba57" | tee >( xxd  -r -p | 
> > base64) | tee >(xxd  -r -p | basenc --base64url )
> > dc30a6d79f3b47e310b8b9f5fbadba57
> > 3DCm1587R+MQuLn1+626Vw==
> > 3DCm1587R-MQuLn1-626Vz0Vhw==
>
> Without looking at this too closely, this is always going to be somewhat
> `racy', for two reasons. First, the process substitutions are executed
> asynchronously, so their execution is non-deterministic. Second, the word
> expansions in pipelines happen after the shell forks, and after piping is
> done, so the standard output of the process substitution is the same as
> the standard output of its parent: the pipe.
>
> You can see this by using `wc' to count the lines the second pipeline 
> element receives:
>
> $ echo "dc30a6d79f3b47e310b8b9f5fbadba57" | tee >( xxd  -r -p | base64 
> ) | wc
>        2       2      58
>
>
>
> > I first thought I missed something about base64url encoding, after 
> > hours or digging and digging documentation I tried :
> >
> > $ echo "dc30a6d79f3b47e310b8b9f5fbadba57" | xxd  -r -p | basenc 
> > --base64url
> > 3DCm1587R-MQuLn1-626Vw==
> >
> >
> > Those 4 extra characters "z0Vh" are quite disturbing :-/
>
> You're not encoding the same data. You've got the original string you
> echoed plus the output of the first encoding process substitution.

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