Fixed a memory leak when using prepared queries

FredyH · Aug 11, 2021 · 0d0191f · 0d0191f
1 parent e750350
commit 0d0191f
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Showing 3 changed files with 10 additions and 9 deletions.
diff --git a/MySQLOO/include/ResultData.h b/MySQLOO/include/ResultData.h
@@ -25,7 +25,7 @@ class ResultDataRow {
 class ResultData {
 public:
 	ResultData(MYSQL_RES* result);
-	ResultData(MYSQL_STMT* result);
+	ResultData(MYSQL_STMT* result, MYSQL_RES* metaData);
 	ResultData();
 	~ResultData();
 	std::vector<std::string> & getColumns() { return columns; }

diff --git a/MySQLOO/source/PreparedQuery.cpp b/MySQLOO/source/PreparedQuery.cpp
@@ -266,18 +266,22 @@ void PreparedQuery::executeQuery(MYSQL* connection, std::shared_ptr<IQueryData>
 				data->m_insertIds.push_back(mysql_stmt_insert_id(stmt));
 				data->m_resultStatus = QUERY_SUCCESS;
 
-				if (mysql_stmt_result_metadata(stmt) == nullptr) {
+				MYSQL_RES* metaData = mysql_stmt_result_metadata(stmt);
+				if (metaData == nullptr) {
 					//This means the statement does not have a resultset (this apparently happens when calling stored procedures)
 					//We need to skip this result, otherwise it screws up the mysql connection
 					//Add an empty ResultData in that case
+					//This is only necessary due to MariaDB client behaving differently to the Mysql client
+					//otherwise we get a hang in the rest of the code below
 					data->m_results.emplace_back();
 					continue;
 				}
+				auto f = finally([&] { mysql_free_result(metaData); });
 				//There is a potential race condition here. What happens
 				//when the query executes fine but something goes wrong while storing the result?
 				mysqlStmtStoreResult(stmt);
-				data->m_results.emplace_back(stmt);
-				mysql_stmt_free_result(stmt);
+				auto f2 = finally([&] { mysql_stmt_free_result(stmt); });
+				data->m_results.emplace_back(stmt, metaData);
 			} while (mysqlStmtNextResult(stmt));
 		}
 	} catch (const MySQLException& error) {

diff --git a/MySQLOO/source/ResultData.cpp b/MySQLOO/source/ResultData.cpp
@@ -12,7 +12,7 @@ ResultData::ResultData(unsigned int columnCount, unsigned int rows) {
 	this->rows.reserve(rows);
 }
 
-ResultData::ResultData() : ResultData(0, 0) {}
+ResultData::ResultData() : ResultData((unsigned int) 0, (unsigned int) 0) {} //Avoids conflict with pointers
 
 //Stores all of the rows of a result set
 //This is used so the result set can be free'd and doesn't have to be used in
@@ -54,11 +54,8 @@ static void mysqlStmtBindResult(MYSQL_STMT* stmt, MYSQL_BIND* bind) {
 
 //Stores all of the rows of a prepared query
 //This needs to be done because the query shouldn't be accessed from a different thread
-ResultData::ResultData(MYSQL_STMT* result) : ResultData((unsigned int)mysql_stmt_field_count(result), (unsigned int)mysql_stmt_num_rows(result)) {
+ResultData::ResultData(MYSQL_STMT* result, MYSQL_RES* metaData) : ResultData((unsigned int)mysql_stmt_field_count(result), (unsigned int)mysql_stmt_num_rows(result)) {
 	if (this->columnCount == 0) return;
-	MYSQL_RES * metaData = mysql_stmt_result_metadata(result);
-	if (metaData == nullptr) { throw MySQLException(0, "mysql_stmt_result_metadata: Unknown Error"); }
-	auto f = finally([&] { mysql_free_result(metaData); });
 	MYSQL_FIELD* fields = mysql_fetch_fields(metaData);
 	std::vector<MYSQL_BIND> binds(columnCount);
 	std::vector<std::vector<char>> buffers;