git/compat/snprintf.c
Jeff King a9bfbc5b69 compat/snprintf: don't look at va_list twice
If you define SNPRINTF_RETURNS_BOGUS, we use a special
git_vsnprintf wrapper assumes that vsnprintf returns "-1"
instead of the number of characters that you would need to
store the result.

To do this, it invokes vsnprintf multiple times, growing a
heap buffer until we have enough space to hold the result.
However, this means we evaluate the va_list parameter
multiple times, which is generally a bad thing (it may be
modified by calls to vsnprintf, yielding undefined
behavior).

Instead, we must va_copy it and hand the copy to vsnprintf,
so we always have a pristine va_list.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2011-12-12 09:09:35 -08:00

70 lines
1.5 KiB
C

#include "../git-compat-util.h"
/*
* The size parameter specifies the available space, i.e. includes
* the trailing NUL byte; but Windows's vsnprintf uses the entire
* buffer and avoids the trailing NUL, should the buffer be exactly
* big enough for the result. Defining SNPRINTF_SIZE_CORR to 1 will
* therefore remove 1 byte from the reported buffer size, so we
* always have room for a trailing NUL byte.
*/
#ifndef SNPRINTF_SIZE_CORR
#if defined(WIN32) && (!defined(__GNUC__) || __GNUC__ < 4)
#define SNPRINTF_SIZE_CORR 1
#else
#define SNPRINTF_SIZE_CORR 0
#endif
#endif
#undef vsnprintf
int git_vsnprintf(char *str, size_t maxsize, const char *format, va_list ap)
{
va_list cp;
char *s;
int ret = -1;
if (maxsize > 0) {
va_copy(cp, ap);
ret = vsnprintf(str, maxsize-SNPRINTF_SIZE_CORR, format, cp);
va_end(cp);
if (ret == maxsize-1)
ret = -1;
/* Windows does not NUL-terminate if result fills buffer */
str[maxsize-1] = 0;
}
if (ret != -1)
return ret;
s = NULL;
if (maxsize < 128)
maxsize = 128;
while (ret == -1) {
maxsize *= 4;
str = realloc(s, maxsize);
if (! str)
break;
s = str;
va_copy(cp, ap);
ret = vsnprintf(str, maxsize-SNPRINTF_SIZE_CORR, format, cp);
va_end(cp);
if (ret == maxsize-1)
ret = -1;
}
free(s);
return ret;
}
int git_snprintf(char *str, size_t maxsize, const char *format, ...)
{
va_list ap;
int ret;
va_start(ap, format);
ret = git_vsnprintf(str, maxsize, format, ap);
va_end(ap);
return ret;
}