feat(mysqlnd): send COM_RESET_CONNECTION in restart_psession

ericnorris · ericnorris · commit 8966f72f0819 · 2026-04-23T15:17:49.000-04:00
Before this commit, persistent MySQL connection reuse relied on
COM_CHANGE_USER to reset server-side session state in mysqli. PDO MySQL
did not reset server-side state at all; it only pinged to check
liveness, leaving user variables, temporary tables, and transaction
state from previous requests intact.

After this commit, both mysqli and PDO MySQL send COM_RESET_CONNECTION
when reusing a persistent connection, which resets all server-side
session state without re-authentication.

We've implemented this by adding a reset_connection command to mysqlnd's
command layer. It's similar to the existing ping command, since there's
no payload. We now call it from restart_psession, which we've also
changed to return enum_func_status so callers can handle failures.

In mysqli, we've replaced the COM_CHANGE_USER call in the persistent
reuse path with a call to restart_psession.

In PDO MySQL, we've replaced the mysql_ping in check_liveness with a
call to restart_psession, which both verifies the connection is alive
and resets session state in a single round trip. We've also removed a
call to restart_psession on unconnected handles during initialization.
diff --git a/ext/mysqli/mysqli_mysqlnd.h b/ext/mysqli/mysqli_mysqlnd.h
@@ -37,6 +37,5 @@
 #define mysqli_stmt_close(c, implicit)	mysqlnd_stmt_close((c), (implicit))
 #define mysqli_free_result(r, implicit)	mysqlnd_free_result((r), (implicit))
 #define mysqli_async_query(c, q, l)		mysqlnd_async_query((c), (q), (l))
-#define mysqli_change_user_silent(c, u, p, d, p_len)   mysqlnd_change_user_ex((c), (u), (p), (d), true, (size_t)(p_len))
 
 #endif
diff --git a/ext/mysqli/mysqli_nonapi.c b/ext/mysqli/mysqli_nonapi.c
@@ -173,14 +173,8 @@ void mysqli_common_connect(INTERNAL_FUNCTION_PARAMETERS, bool is_real_connect, b
 							mysql->mysql = zend_ptr_stack_pop(&plist->free_links);
 
 							MyG(num_inactive_persistent)--;
-							/* reset variables */
 
-#ifndef MYSQLI_NO_CHANGE_USER_ON_PCONNECT
-							if (!mysqli_change_user_silent(mysql->mysql, username, passwd, dbname, passwd_len)) {
-#else
-							if (!mysql_ping(mysql->mysql)) {
-#endif
-								mysqlnd_restart_psession(mysql->mysql);
+							if (!mysqlnd_restart_psession(mysql->mysql)) {
 								MyG(num_active_persistent)++;
 
 								/* clear error */
diff --git a/ext/mysqli/tests/mysqli_pconnect_reset.phpt b/ext/mysqli/tests/mysqli_pconnect_reset.phpt
@@ -0,0 +1,61 @@
+--TEST--
+mysqli_pconnect() - COM_RESET_CONNECTION clears session state
+--EXTENSIONS--
+mysqli
+--SKIPIF--
+<?php
+require_once 'skipifconnectfailure.inc';
+?>
+--FILE--
+<?php
+require_once 'connect.inc';
+
+$host = 'p:' . $host;
+
+$link = my_mysqli_connect($host, $user, $passwd, $db, $port, $socket);
+if (!$link) {
+    printf("[001] Cannot connect\n");
+}
+
+mysqli_query($link, "SET @test_var = 42");
+mysqli_query($link, "CREATE TEMPORARY TABLE test_reset_tmp (id INT)");
+mysqli_query($link, "INSERT INTO test_reset_tmp VALUES (1)");
+
+$res = mysqli_query($link, "SELECT @test_var AS v");
+$row = mysqli_fetch_assoc($res);
+if ($row['v'] !== '42') {
+    printf("[002] Expected 42, got %s\n", $row['v']);
+}
+mysqli_free_result($res);
+
+$thread_id = mysqli_thread_id($link);
+mysqli_close($link);
+
+$link = my_mysqli_connect($host, $user, $passwd, $db, $port, $socket);
+if (!$link) {
+    printf("[003] Cannot reconnect\n");
+}
+
+if (mysqli_thread_id($link) !== $thread_id) {
+    printf("[004] Got a different connection, persistent reuse did not happen\n");
+}
+
+$res = mysqli_query($link, "SELECT @test_var AS v");
+$row = mysqli_fetch_assoc($res);
+if ($row['v'] !== null) {
+    printf("[005] Expected NULL after reset, got %s\n", $row['v']);
+}
+mysqli_free_result($res);
+
+$res = mysqli_query($link, "SHOW TABLES LIKE 'test_reset_tmp'");
+if (mysqli_num_rows($res) !== 0) {
+    printf("[006] Temporary table should not exist after reset\n");
+}
+mysqli_free_result($res);
+
+mysqli_close($link);
+
+echo "done!";
+?>
+--EXPECT--
+done!
diff --git a/ext/mysqlnd/mysqlnd_commands.c b/ext/mysqlnd/mysqlnd_commands.c
@@ -143,6 +143,33 @@ MYSQLND_METHOD(mysqlnd_command, ping)(MYSQLND_CONN_DATA * const conn)
 /* }}} */
 
 
+/* {{{ mysqlnd_command::reset_connection */
+static enum_func_status
+MYSQLND_METHOD(mysqlnd_command, reset_connection)(MYSQLND_CONN_DATA * const conn)
+{
+	const func_mysqlnd_protocol_payload_decoder_factory__send_command send_command = conn->payload_decoder_factory->m.send_command;
+	const func_mysqlnd_protocol_payload_decoder_factory__send_command_handle_response send_command_handle_response = conn->payload_decoder_factory->m.send_command_handle_response;
+	enum_func_status ret = FAIL;
+
+	DBG_ENTER("mysqlnd_command::reset_connection");
+
+	ret = send_command(conn->payload_decoder_factory, COM_RESET_CONNECTION, NULL, 0, FALSE,
+					   &conn->state,
+					   conn->error_info,
+					   conn->upsert_status,
+					   conn->stats,
+					   conn->m->send_close,
+					   conn);
+	if (PASS == ret) {
+		ret = send_command_handle_response(conn->payload_decoder_factory, PROT_OK_PACKET, FALSE, COM_RESET_CONNECTION, FALSE,
+										   conn->error_info, conn->upsert_status, &conn->last_message);
+	}
+
+	DBG_RETURN(ret);
+}
+/* }}} */
+
+
 /* {{{ mysqlnd_command::statistics */
 static enum_func_status
 MYSQLND_METHOD(mysqlnd_command, statistics)(MYSQLND_CONN_DATA * const conn, zend_string ** message)
@@ -659,4 +686,5 @@ MYSQLND_CLASS_METHODS_START(mysqlnd_command)
 	MYSQLND_METHOD(mysqlnd_command, stmt_close),
 	MYSQLND_METHOD(mysqlnd_command, enable_ssl),
 	MYSQLND_METHOD(mysqlnd_command, handshake),
+	MYSQLND_METHOD(mysqlnd_command, reset_connection),
 MYSQLND_CLASS_METHODS_END;
diff --git a/ext/mysqlnd/mysqlnd_connection.c b/ext/mysqlnd/mysqlnd_connection.c
@@ -354,14 +354,19 @@ MYSQLND_METHOD(mysqlnd_conn_data, set_server_option)(MYSQLND_CONN_DATA * const c
 
 
 /* {{{ mysqlnd_conn_data::restart_psession */
-static void
+static enum_func_status
 MYSQLND_METHOD(mysqlnd_conn_data, restart_psession)(MYSQLND_CONN_DATA * conn)
 {
 	DBG_ENTER("mysqlnd_conn_data::restart_psession");
-	MYSQLND_INC_CONN_STATISTIC(conn->stats, STAT_CONNECT_REUSED);
-	conn->current_result = NULL;
-	conn->last_message.s = NULL;
-	DBG_VOID_RETURN;
+
+	enum_func_status ret = conn->command->reset_connection(conn);
+	if (ret == PASS) {
+		MYSQLND_INC_CONN_STATISTIC(conn->stats, STAT_CONNECT_REUSED);
+		conn->current_result = NULL;
+		conn->last_message.s = NULL;
+	}
+
+	DBG_RETURN(ret);
 }
 /* }}} */
 
diff --git a/ext/mysqlnd/mysqlnd_structs.h b/ext/mysqlnd/mysqlnd_structs.h
@@ -306,6 +306,7 @@ typedef enum_func_status (*func_mysqlnd_execute_com_set_option)(MYSQLND_CONN_DAT
 typedef enum_func_status (*func_mysqlnd_execute_com_debug)(MYSQLND_CONN_DATA * const conn);
 typedef enum_func_status (*func_mysqlnd_execute_com_init_db)(MYSQLND_CONN_DATA * const conn, const MYSQLND_CSTRING db);
 typedef enum_func_status (*func_mysqlnd_execute_com_ping)(MYSQLND_CONN_DATA * const conn);
+typedef enum_func_status (*func_mysqlnd_execute_com_reset_connection)(MYSQLND_CONN_DATA * const conn);
 typedef enum_func_status (*func_mysqlnd_execute_com_statistics)(MYSQLND_CONN_DATA * const conn, zend_string ** message);
 typedef enum_func_status (*func_mysqlnd_execute_com_process_kill)(MYSQLND_CONN_DATA * const conn, const unsigned int process_id, const bool read_response);
 typedef enum_func_status (*func_mysqlnd_execute_com_refresh)(MYSQLND_CONN_DATA * const conn, const uint8_t options);
@@ -344,6 +345,7 @@ MYSQLND_CLASS_METHODS_TYPE(mysqlnd_command)
 	func_mysqlnd_execute_com_stmt_close stmt_close;
 	func_mysqlnd_execute_com_enable_ssl enable_ssl;
 	func_mysqlnd_execute_com_handshake handshake;
+	func_mysqlnd_execute_com_reset_connection reset_connection;
 };
 
 
@@ -482,7 +484,7 @@ typedef enum_func_status	(*func_mysqlnd_conn_data__free_reference)(MYSQLND_CONN_
 typedef enum_func_status	(*func_mysqlnd_conn_data__send_command_do_request)(MYSQLND_CONN_DATA * const conn, const enum php_mysqlnd_server_command command, const zend_uchar * const arg, const size_t arg_len, const bool silent, const bool ignore_upsert_status);
 typedef enum_func_status	(*func_mysqlnd_conn_data__send_command_handle_response)(MYSQLND_CONN_DATA * const conn, const enum mysqlnd_packet_type ok_packet, const bool silent, const enum php_mysqlnd_server_command command, const bool ignore_upsert_status);
 
-typedef void				(*func_mysqlnd_conn_data__restart_psession)(MYSQLND_CONN_DATA * conn);
+typedef enum_func_status	(*func_mysqlnd_conn_data__restart_psession)(MYSQLND_CONN_DATA * conn);
 typedef void				(*func_mysqlnd_conn_data__end_psession)(MYSQLND_CONN_DATA * conn);
 typedef enum_func_status	(*func_mysqlnd_conn_data__send_close)(MYSQLND_CONN_DATA * conn);
 
diff --git a/ext/pdo_mysql/mysql_driver.c b/ext/pdo_mysql/mysql_driver.c
@@ -603,9 +603,15 @@ static zend_result pdo_mysql_check_liveness(pdo_dbh_t *dbh)
 	PDO_DBG_ENTER("pdo_mysql_check_liveness");
 	PDO_DBG_INF_FMT("dbh=%p", dbh);
 
+#ifdef PDO_USE_MYSQLND
+	if (mysqlnd_restart_psession(H->server)) {
+		PDO_DBG_RETURN(FAILURE);
+	}
+#else
 	if (mysql_ping(H->server)) {
 		PDO_DBG_RETURN(FAILURE);
 	}
+#endif
 	PDO_DBG_RETURN(SUCCESS);
 }
 /* }}} */
@@ -724,11 +730,6 @@ static int pdo_mysql_handle_factory(pdo_dbh_t *dbh, zval *driver_options)
 		pdo_mysql_error(dbh);
 		goto cleanup;
 	}
-#ifdef PDO_USE_MYSQLND
-	if (dbh->is_persistent) {
-		mysqlnd_restart_psession(H->server);
-	}
-#endif
 
 	dbh->driver_data = H;
 
