From 16039244ba25dc22c47f9caf6e27492acaff7bb4 Mon Sep 17 00:00:00 2001
From: Swayam-code <swayam123code@gmail.com>
Date: Tue, 20 Oct 2026 22:09:48 +0530
Subject: [PATCH] MDEV-13718 mysqltest crashes upon --sync_slave_with_master
 without active connection

Report the existing no-active-connection error before querying master
status. Stop sync_slave_with_master before it selects a slave after a
handled error.

Cover disconnected commands, connection preservation and successful
replication before and after the error.
---
 client/mysqltest.cc                           | 12 +++++-
 .../r/rpl_mysqltest_closed_connection.result  | 41 +++++++++++++++++++
 .../t/rpl_mysqltest_closed_connection.test    | 41 +++++++++++++++++++
 3 files changed, 93 insertions(+), 1 deletion(-)
 create mode 100644 mysql-test/suite/rpl/r/rpl_mysqltest_closed_connection.result
 create mode 100644 mysql-test/suite/rpl/t/rpl_mysqltest_closed_connection.test

diff --git a/client/mysqltest.cc b/client/mysqltest.cc
index 0f0ecb37c4166..9229eeecc7885 100644
--- a/client/mysqltest.cc
+++ b/client/mysqltest.cc
@@ -5436,6 +5436,12 @@ int do_save_master_pos()
   const char *query;
   DBUG_ENTER("do_save_master_pos");
 
+  if (!mysql)
+  {
+    handle_no_active_connection(curr_command, cur_con, &ds_res);
+    DBUG_RETURN(1);
+  }
+
   if (mysql_query(mysql, query= "show master status"))
     die("failed in 'show master status': %d %s",
 	mysql_errno(mysql), mysql_error(mysql));
@@ -13570,7 +13576,11 @@ int main(int argc, char **argv)
       case Q_SYNC_WITH_MASTER: do_sync_with_master(command); break;
       case Q_SYNC_SLAVE_WITH_MASTER:
       {
-	do_save_master_pos();
+        if (do_save_master_pos())
+        {
+          command->last_argument= command->end;
+          break;
+        }
 	if (*command->first_argument)
 	  select_connection(command);
 	else
diff --git a/mysql-test/suite/rpl/r/rpl_mysqltest_closed_connection.result b/mysql-test/suite/rpl/r/rpl_mysqltest_closed_connection.result
new file mode 100644
index 0000000000000..f572430a6e7bc
--- /dev/null
+++ b/mysql-test/suite/rpl/r/rpl_mysqltest_closed_connection.result
@@ -0,0 +1,41 @@
+include/master-slave.inc
+[connection master]
+# Connected master-position commands still replicate successfully.
+CREATE TABLE t1 (a INT);
+INSERT INTO t1 VALUES (1);
+connection slave;
+SELECT * FROM t1;
+a
+1
+connection master;
+connect  con1,localhost,root,,;
+disconnect con1;
+# MDEV-13718: report a closed connection without switching to a slave.
+ERROR 000000: MariaDB server has gone away
+2006
+connection="-closed_connection-"
+ERROR 000000: MariaDB server has gone away
+2006
+connection="-closed_connection-"
+ERROR 000000: MariaDB server has gone away
+2006
+connection="-closed_connection-"
+# The errors are consumed, and both sync forms still work.
+connection master;
+INSERT INTO t1 VALUES (2);
+connection slave;
+SELECT * FROM t1 ORDER BY a;
+a
+1
+2
+connection master;
+INSERT INTO t1 VALUES (3);
+connection slave1;
+SELECT * FROM t1 ORDER BY a;
+a
+1
+2
+3
+connection master;
+DROP TABLE t1;
+include/rpl_end.inc
diff --git a/mysql-test/suite/rpl/t/rpl_mysqltest_closed_connection.test b/mysql-test/suite/rpl/t/rpl_mysqltest_closed_connection.test
new file mode 100644
index 0000000000000..e1f5494c463b8
--- /dev/null
+++ b/mysql-test/suite/rpl/t/rpl_mysqltest_closed_connection.test
@@ -0,0 +1,41 @@
+--source include/master-slave.inc
+
+--echo # Connected master-position commands still replicate successfully.
+CREATE TABLE t1 (a INT);
+INSERT INTO t1 VALUES (1);
+--save_master_pos
+--connection slave
+--sync_with_master
+SELECT * FROM t1;
+
+--connection master
+--connect (con1,localhost,root,,)
+--disconnect con1
+
+--echo # MDEV-13718: report a closed connection without switching to a slave.
+--error 2006
+--save_master_pos
+--echo $mysql_errno
+--echo connection="$CURRENT_CONNECTION"
+--error 2006
+--sync_slave_with_master
+--echo $mysql_errno
+--echo connection="$CURRENT_CONNECTION"
+--error 2006
+--sync_slave_with_master slave1
+--echo $mysql_errno
+--echo connection="$CURRENT_CONNECTION"
+
+--echo # The errors are consumed, and both sync forms still work.
+--connection master
+INSERT INTO t1 VALUES (2);
+--sync_slave_with_master
+SELECT * FROM t1 ORDER BY a;
+--connection master
+INSERT INTO t1 VALUES (3);
+--sync_slave_with_master slave1
+SELECT * FROM t1 ORDER BY a;
+
+--connection master
+DROP TABLE t1;
+--source include/rpl_end.inc