Function enlargeStringInfo

src/common/stringinfo.c:298–359

* enlargeStringInfo * * Make sure there is enough space for 'needed' more bytes * ('needed' does not include the terminating null). * * External callers usually need not concern themselves with this, since * all stringinfo.c routines do it automatically. However, if a caller * knows that a StringInfo will eventually become X bytes large, it * can save some palloc overhead by enlarging the

 * current.  This is the desired and indeed critical behavior!
 */
void
enlargeStringInfo(StringInfo str, int needed)
{
	int			newlen;

	/*
	 * Guard against out-of-range "needed" values.  Without this, we can get
	 * an overflow or infinite loop in the following.
	 */
	if (needed < 0)				/* should not happen */
	{
#ifndef FRONTEND
		elog(ERROR, "invalid string enlargement request size: %d", needed);
#else
		fprintf(stderr, "invalid string enlargement request size: %d\n", needed);
		exit(EXIT_FAILURE);
#endif
	}
	if (((Size) needed) >= (MaxAllocSize - (Size) str->len))
	{
#ifndef FRONTEND
		ereport(ERROR,
				(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
				 errmsg("out of memory"),
				 errdetail("Cannot enlarge string buffer containing %d bytes by %d more bytes.",
						   str->len, needed)));
#else
		fprintf(stderr,
				_("out of memory\n\nCannot enlarge string buffer containing %d bytes by %d more bytes.\n"),
				str->len, needed);
		exit(EXIT_FAILURE);
#endif
	}

	needed += str->len + 1;		/* total space required now */

	/* Because of the above test, we now have needed <= MaxAllocSize */

	if (needed <= str->maxlen)
		return;					/* got enough space already */

	/*
	 * We don't want to allocate just a little more space with each append;
	 * for efficiency, double the buffer size each time it overflows.
	 * Actually, we might need to more than double it if 'needed' is big...
	 */
	newlen = 2 * str->maxlen;
	while (needed > newlen)
		newlen = 2 * newlen;

	/*
	 * Clamp to MaxAllocSize in case we went past it.  Note we are assuming
	 * here that MaxAllocSize <= INT_MAX/2, else the above loop could
	 * overflow.  We will still have newlen >= needed.
	 */
	if (newlen > (int) MaxAllocSize)
		newlen = (int) MaxAllocSize;