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

Masahiro Yamada
2023-01-15T03:05:33Z

On Fri, Jan 13, 2023 at 7:06 AM Kees Cook <keescook@chromium.org> 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