Magento. Search result stock filter.

mage_serach_result_stock_filter.md

Override _getSearchableProducts function in class Mage_CatalogSearch_Model_Resource_Fulltext so that it always searches in-stock products.

File to modify: app/code/core/Mage/CatalogSearch/Model/Resource/Fulltext.php

/**
 * Retrieve searchable products per store
 *
 * @param int $storeId
 * @param array $staticFields
 * @param array|int $productIds
 * @param int $lastProductId
 * @param int $limit
 * @return array
 */
protected function _getSearchableProducts($storeId, array $staticFields, $productIds = null, $lastProductId = 0, $limit = 100)
{        
    ...

    ->join(
        array('stock_status' => $this->getTable('cataloginventory/stock_status')),
        $writeAdapter->quoteInto(
            'stock_status.product_id=e.entity_id AND stock_status.stock_status = 1 AND stock_status.website_id=?', // add stock_status = 1 condition
            $websiteId
        ),
        array('in_stock' => 'stock_status')
    );

    ....
}

Remember to reindex "Catalog Search Index" afterwards.