Re: [PATCH] scripts: handle BrokenPipeError for python scripts

[Masahiro Yamada]

On Fri, Jan 13, 2023 at 7:06 AM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>
> On Thu, Jan 12, 2023 at 11:30:06AM +0900, Masahiro Yamada wrote:
> >     def main():
> >         try:
> >             # simulate large output (your code replaces this loop)
> >             for x in range(10000):
> >                 print("y")
> >             # flush output here to force SIGPIPE to be triggered
> >             # while inside this try block.
> >             sys.stdout.flush()
> >         except BrokenPipeError:
> >             # Python flushes standard streams on exit; redirect remaining output
> >             # to devnull to avoid another BrokenPipeError at shutdown
> >             devnull = os.open(os.devnull, os.O_WRONLY)
> >             os.dup2(devnull, sys.stdout.fileno())
> >             sys.exit(1)  # Python exits with error code 1 on EPIPE
>
> I still think this is wrong -- they should not continue piping, and
> should just die with SIGPIPE. It should simply be:
>
> signal(SIGPIPE, SIG_DFL);
>
> Nothing else needed. No wasted CPU cycles, shell handling continues as
> per normal.


I prefer try-and-except because it is Python's coding style,
and we can do something before the exit.
(for example, clean up temporary files)


>
> >     if __name__ == '__main__':
> >         main()
> >
> >   Do not set SIGPIPE’s disposition to SIG_DFL in order to avoid
> >   BrokenPipeError. Doing that would cause your program to exit
> >   unexpectedly whenever any socket connection is interrupted while
> >   your program is still writing to it.
>
> This advise is for socket programs, not command-line tools.


I still do not understand what is bad
about using this for command-line tools.


>
> -Kees
>
> --
> Kees Cook



-- 
Best Regards
Masahiro Yamada