Re: [PATCH v2 1/1] vreportf: Fix interleaving issues, remove 4096 limitation
- From
Jeff King <peff@peff.net>
- Date
- Oct 25, 2019, 22:11 UTC
- Message-ID
- <20191025221118.GA29213@sigill.intra.peff.net>
- In-Reply-To
- <nycvar.QRO.7.76.6.1910251548560.46@tvgsbejvaqbjf.bet>
On Fri, Oct 25, 2019 at 04:02:36PM +0200, Johannes Schindelin wrote:
Show 25 quoted lines
> ... 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. ;)
Show 7 quoted lines
> > 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.
-Peff