Re: [PATCH 4/5] log: handle integer overflow in timestamps

From: Jeff King <peff@peff.net>
Date: Feb 24, 2014, 20:37 UTC
Message-ID: <20140224203709.GA25506@sigill.intra.peff.net>
In-Reply-To: <xmqqeh2s8do2.fsf@gitster.dls.corp.google.com>

On Mon, Feb 24, 2014 at 12:21:33PM -0800, Junio C Hamano wrote:

Show 20 quoted lines

> >> > +	if (date_overflows(date))
> >> > +		date = 0;
> >> > +	else {
> >> > +		if (ident->tz_begin && ident->tz_end)
> >> > +			tz = strtol(ident->tz_begin, NULL, 10);
> >> > +		if (tz == LONG_MAX || tz == LONG_MIN)
> >> > +			tz = 0;
> >> > +	}
> >> 
> >> ... don't we want to fix an input having a bogus timestamp and also
> >> a bogus tz recorded in it?
> >
> > If there is a bogus timestamp, then we do not want to look at tz at all.
> > We leave it at "0", so that we get a true sentinel:
> 
> Ah, OK, I missed the initialization to 0 at the beginning.
> 
> It might have been more clear if "int tz" declaration were left
> uninitialized, and the variable were explicitly cleared to 0 in the
> "date-overflows" error codepath, but it is not a big deal.

It might be, but I think it would end up cumbersome. The initialization was already there from the previous version, which was hitting the else for "ident->tz_begin". Without fallback initializations, you end up with:

  if (ident->date_begin && ident->date_end) {
          date = strtoul(ident->date_begin, NULL, 10);
          if (date_overflows(date)) {
                  date = 0;
                  tz = 0;
          } else {
                  if (ident->tz_begin && ident->tz_end) {
                          tz = strtol(ident->tz_begin, NULL, 10);
                          if (tz == LONG_MAX || tz == LONG_MIN)
                                  tz = 0;
                  } else
                          tz = 0;
          }
  } else {
          date = 0;
          tz = 0;
  }

which I think is much more confusing (and hard to verify that the variables are always set). Checking !date as an error condition would make it a little more readable:

  if (ident->date_begin && ident->date_end) {
          date = strtoul(ident->date_begin, NULL, 10);
          if (date_overflows(date))
                  date = 0;
  } else
          date = 0;

  if (date) {
          if (ident->tz_begin && ident->tz_end) {
                  tz = strtol(ident->tz_begin, NULL, 10);
                  if (tz == LONG_MAX || tz == LONG_MIN)
                          tz = 0;
          } else
                  tz = 0;
  } else
          tz = 0;

but then we treat date==0 as a sentinel, and can never correctly parse dates on Jan 1, 1970.

So I'd be in favor of keeping it as-is, but feel free to mark it up if you feel strongly.

-Peff