Re: PATCH: zasprintf

["Bart Schaefer" <schaefer@xxxxxxxxxxxxxxxxxxxxxxx>]

On Sep 16,  2:53pm, Clint Adams wrote:
} Subject: PATCH: zasprintf
}
} In continuation of the crusade against PATH_MAX, this implements
} zasprintf.  It will break on systems where there is a stdarg or
} varargs implementation but neither asprintf nor vsnprintf.

This seems to me to be the wrong way to approach this issue.  If you
can't provide a non-broken implementation -- and I don't see how you
can, if you don't plan to implement a printf-format-string parser --
then you should try harder to restrict the problem domain to something
for which you CAN provide a working implementation.

In particular, zsh appears to use PATH_MAX in four cases (plus one
special case):

1) Feeping or issuing an error message when a string that might be a
   path name is "too long," even though that string isn't immediately
   going to be copied into a buffer or even used as a pathname.  In
   most of these cases I think we could just drop the test entirely.

2) Copying a string known to be a path name into a temp buffer assumed
   to be large enough to hold it.  A call to dupstring() or ztrdup()
   would suffice.

3) Pasting a string obtained from readdir() onto a known path prefix.
   In this case, it would be sufficient to use NAME_MAX + strlen()
   (and use pathconf() to get NAME_MAX if necessary).

4) Pasting together two partial path names to make one longer path.
   This is the case where the patch in 12814 uses zasprintf() -- but
   it's overkill, it'd be sufficient to call strlen() on each of the
   two parts to preallocate a large enough buffer.  A simple function
   similar to dyncat() or tricat() would work.

None of those require varargs, stdarg, snprintf, etc.

The last, special case is to create a "big enough" buffer for use by
readlink().  In this case I think we could use lstat() to read the size
of the link itself, and use that to allocate a buffer.  Does anyone
know of an operating system where that would fail?

-- 
Bart Schaefer                                 Brass Lantern Enterprises
http://www.well.com/user/barts              http://www.brasslantern.com

Zsh: http://www.zsh.org | PHPerl Project: http://phperl.sourceforge.net