Function pvsnprintf

src/common/psprintf.c:105–151

* pvsnprintf * * Attempt to format text data under the control of fmt (an sprintf-style * format string) and insert it into buf (which has length len). * * If successful, return the number of bytes emitted, not counting the * trailing zero byte. This will always be strictly less than len. * * If there's not enough space in buf, return an estimate of the buffer size * needed to succeed (t

 * this lets overflow concerns be handled here rather than in the callers.
 */
size_t
pvsnprintf(char *buf, size_t len, const char *fmt, va_list args)
{
	int			nprinted;

	nprinted = vsnprintf(buf, len, fmt, args);

	/* We assume failure means the fmt is bogus, hence hard failure is OK */
	if (unlikely(nprinted < 0))
	{
#ifndef FRONTEND
		elog(ERROR, "vsnprintf failed: %m with format string \"%s\"", fmt);
#else
		fprintf(stderr, "vsnprintf failed: %s with format string \"%s\"\n",
				strerror(errno), fmt);
		exit(EXIT_FAILURE);
#endif
	}

	if ((size_t) nprinted < len)
	{
		/* Success.  Note nprinted does not include trailing null. */
		return (size_t) nprinted;
	}

	/*
	 * We assume a C99-compliant vsnprintf, so believe its estimate of the
	 * required space, and add one for the trailing null.  (If it's wrong, the
	 * logic will still work, but we may loop multiple times.)
	 *
	 * Choke if the required space would exceed MaxAllocSize.  Note we use
	 * this palloc-oriented overflow limit even when in frontend.
	 */
	if (unlikely((size_t) nprinted > MaxAllocSize - 1))
	{
#ifndef FRONTEND
		ereport(ERROR,
				(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
				 errmsg("out of memory")));
#else
		fprintf(stderr, _("out of memory\n"));
		exit(EXIT_FAILURE);
#endif
	}

	return nprinted + 1;
}