Re: [PATCH v2 1/1] vreportf: Fix interleaving issues, remove 4096 limitation

> On Fri, Oct 25, 2019 at 04:02:36PM +0200, Johannes Schindelin wrote:
>
> > ... and indeed, I verified that this patch fixes the problem:
> >
> > -- snip --
> > diff --git a/usage.c b/usage.c
> > index 2fdb20086bd..7f5bdfb0f40 100644
> > --- a/usage.c
> > +++ b/usage.c
> > @@ -10,13 +10,16 @@ void vreportf(const char *prefix, const char *err, va_list params)
> >  {
> >  	char msg[4096];
> >  	char *p;
> > -
> > -	vsnprintf(msg, sizeof(msg), err, params);
> > +	size_t off = strlcpy(msg, prefix, sizeof(msg));
> > +	int ret = vsnprintf(msg + off, sizeof(msg) - off, err, params);
> >  	for (p = msg; *p; p++) {
> >  		if (iscntrl(*p) && *p != '\t' && *p != '\n')
> >  			*p = '?';
> >  	}
> > -	fprintf(stderr, "%s%s\n", prefix, msg);
> > +	if (ret > 0) {
> > +		msg[off + ret] = '\n'; /* we no longer need a NUL */
> > +		write_in_full(2, msg, off + ret + 1);
> > +	}
> >  }
>
> Heh. This is quite similar to what I posted in:
>
>   https://public-inbox.org/git/20190828145412.GB14432@sigill.intra.peff.net/
>
> though I missed the cleverness with "we no longer need a NUL" to get an
> extra byte. ;)

> > > except truncation to 4096. Then I would expect a patch to increase
> > > buffer size to 8192 in the next couple years. And if you also try to
> > > solve truncation, it will get you very close to my code.
> >
> > My point is: I don't want to "fix" truncation. I actually think of it as
> > a feature. An error message that is longer than the average news article
> > I read is too long, period.
>
> Yeah. As the person responsible for many of the "avoid truncation" works
> referenced in the original patch, I have come to the conclusion that it
> is not worth the complexity. Even when we do manage to produce a
> gigantic error message correctly, it's generally not very readable.
>
> That's basically what I came here to say, and I was pleased to find that
> you had already argued for it quite well. So I'll just add my support
> for the direction you've taken the conversation.

> I _do_ wish we could do the truncation more intelligently. I'd much
> rather see:
>
>   error: unable to open 'absurdly-long-file-name...': permission denied
>
> than:
>
>   error: unable to open 'absurdly-long-file-name-that-goes-on-forever-and-ev
>
> But I don't think it's possible without reimplementing snprintf
> ourselves.