On Wed, Apr 18, 2001 at 08:05:35PM +1000, Glenn McGrath wrote:
> I recently made some big changes to gunzip, looks like i didnt test it
> well enough.
*gag*
> I will look into it now, i doubt #3 is anything serious, as ive been
> using it a lot with dpkg, dpkg-deb, probably some error messages or
> something are getting mixed up in the output stream.
There are at least two bugs: one is that fseek() doesn't work on
unseekable file handles, like stdin and stdout; the other (that you're
fortunately avoiding) is that the order of evaluation in C of the oeprands
of arithmetic operators like "+" is undefined. That is, code like:
int chars_printed = printf("foo") + printf("bar");
will usually equal 6, but you could get "foobar" printed, "barfoo"
printed, or even conceivably something completely different.
A rough patch which seems to get it working again is:
/* Ignore time stamp(4), extra flags(1), OS type(1) */
- fseek(in_file, 6, SEEK_CUR);
+ { int i = 0; while (i < 6) { fgetc(in_file); i++; } }
+ /* fseek(in_file, 6, SEEK_CUR); -- you can't seek on stdin */
if ((flags & extra_field) != 0) {
- fseek(in_file, (size_t) fgetc(in_file) + ((size_t)fgetc(in_file)
<< 8), SEEK_CUR);
+ int i;
+ i = fgetc(in_file);
+ i += fgetc(in_file) << 8;
+ while (i-- > 0) fgetc(in_file);
+ /* fseek(in_file, (size_t) fgetc(in_file) + ((size_t)fgetc(in_fi
le) << 8), SEEK_CUR);
+ * -- you can't seek on stdin, and the order of function calls
+ * in the above isn't guaranteed */
}
Dicking around with gzip code is just asking for obscure bugs to bite in
you in the bum, though...
Cheers,
aj
--
Anthony Towns <aj@humbug.org.au> <http://azure.humbug.org.au/~aj/>
I don't speak for anyone save myself. GPG signed mail preferred.
``_Any_ increase in interface difficulty, in exchange for a benefit you
do not understand, cannot perceive, or don't care about, is too much.''
-- John S. Novak, III (The Humblest Man on the Net)
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