Function pqCheckInBufferSpace

src/interfaces/libpq/fe-misc.c:394–480

* Make sure conn's input buffer can hold bytes_needed bytes (caller must * include already-stored data into the value!) * * Returns 0 on success, EOF if failed to enlarge buffer */

 * Returns 0 on success, EOF if failed to enlarge buffer
 */
int
pqCheckInBufferSpace(size_t bytes_needed, PGconn *conn)
{
	int			newsize = conn->inBufSize;
	char	   *newbuf;

	/* Quick exit if we have enough space */
	if (bytes_needed <= (size_t) newsize)
		return 0;

	/*
	 * Before concluding that we need to enlarge the buffer, left-justify
	 * whatever is in it and recheck.  The caller's value of bytes_needed
	 * includes any data to the left of inStart, but we can delete that in
	 * preference to enlarging the buffer.  It's slightly ugly to have this
	 * function do this, but it's better than making callers worry about it.
	 */
	bytes_needed -= conn->inStart;

	if (conn->inStart < conn->inEnd)
	{
		if (conn->inStart > 0)
		{
			memmove(conn->inBuffer, conn->inBuffer + conn->inStart,
					conn->inEnd - conn->inStart);
			conn->inEnd -= conn->inStart;
			conn->inCursor -= conn->inStart;
			conn->inStart = 0;
		}
	}
	else
	{
		/* buffer is logically empty, reset it */
		conn->inStart = conn->inCursor = conn->inEnd = 0;
	}

	/* Recheck whether we have enough space */
	if (bytes_needed <= (size_t) newsize)
		return 0;

	/*
	 * If we need to enlarge the buffer, we first try to double it in size; if
	 * that doesn't work, enlarge in multiples of 8K.  This avoids thrashing
	 * the malloc pool by repeated small enlargements.
	 *
	 * Note: tests for newsize > 0 are to catch integer overflow.
	 */
	do
	{
		newsize *= 2;
	} while (newsize > 0 && bytes_needed > (size_t) newsize);

	if (newsize > 0 && bytes_needed <= (size_t) newsize)
	{
		newbuf = realloc(conn->inBuffer, newsize);
		if (newbuf)
		{
			/* realloc succeeded */