Function pqResultAlloc

src/interfaces/libpq/fe-exec.c:562–656

* pqResultAlloc - * Allocate subsidiary storage for a PGresult. * * nBytes is the amount of space needed for the object. * If isBinary is true, we assume that we need to align the object on * a machine allocation boundary. * If isBinary is false, we assume the object is a char string and can * be allocated on any byte boundary. */

 * be allocated on any byte boundary.
 */
void *
pqResultAlloc(PGresult *res, size_t nBytes, bool isBinary)
{
	char	   *space;
	PGresult_data *block;

	if (!res)
		return NULL;

	if (nBytes <= 0)
		return res->null_field;

	/*
	 * If alignment is needed, round up the current position to an alignment
	 * boundary.
	 */
	if (isBinary)
	{
		int			offset = res->curOffset % PGRESULT_ALIGN_BOUNDARY;

		if (offset)
		{
			res->curOffset += PGRESULT_ALIGN_BOUNDARY - offset;
			res->spaceLeft -= PGRESULT_ALIGN_BOUNDARY - offset;
		}
	}

	/* If there's enough space in the current block, no problem. */
	if (nBytes <= (size_t) res->spaceLeft)
	{
		space = res->curBlock->space + res->curOffset;
		res->curOffset += nBytes;
		res->spaceLeft -= nBytes;
		return space;
	}

	/*
	 * If the requested object is very large, give it its own block; this
	 * avoids wasting what might be most of the current block to start a new
	 * block.  (We'd have to special-case requests bigger than the block size
	 * anyway.)  The object is always given binary alignment in this case.
	 */
	if (nBytes >= PGRESULT_SEP_ALLOC_THRESHOLD)
	{
		size_t		alloc_size = nBytes + PGRESULT_BLOCK_OVERHEAD;

		block = (PGresult_data *) malloc(alloc_size);
		if (!block)
			return NULL;
		res->memorySize += alloc_size;
		space = block->space + PGRESULT_BLOCK_OVERHEAD;
		if (res->curBlock)
		{
			/*
			 * Tuck special block below the active block, so that we don't
			 * have to waste the free space in the active block.
			 */
			block->next = res->curBlock->next;