Bug #53899 Wrong mysql_stmt_errno() after connection loss with

automatic reconnect

A client with automatic reconnect enabled will see the error
message "Lost connection to MySQL server during query" if the
connection is lost between mysql_stmt_prepare() and
mysql_stmt_execute(). The mysql_stmt_errno() number, however,
is 0 -- not the corresponding value 2013.

This patch checks for the case where the prepared statement
has been pruned due to a connection loss (i.e., stmt->mysql
has been set to NULL) during a call to cli_advanced_command(),
and avoids changing the last_errno to the result of the last
reconnect attempt.

libmysql/libmysql.c

@@ -2495,7 +2495,12 @@ static my_bool execute(MYSQL_STMT *stmt, char *packet, ulong length)
   stmt->insert_id= mysql->insert_id;
   if (res)
   {
-    set_stmt_errmsg(stmt, net);
+    /* 
+      Don't set stmt error if stmt->mysql is NULL, as the error in this case 
+      has already been set by mysql_prune_stmt_list(). 
+    */
+    if (stmt->mysql)
+      set_stmt_errmsg(stmt, net);
     DBUG_RETURN(1);
   }
   DBUG_RETURN(0);
@@ -2706,7 +2711,12 @@ stmt_read_row_from_cursor(MYSQL_STMT *stmt, unsigned char **row)
                                             buff, sizeof(buff), (uchar*) 0, 0,
                                             1, stmt))
     {
-      set_stmt_errmsg(stmt, net);
+      /* 
+        Don't set stmt error if stmt->mysql is NULL, as the error in this case 
+        has already been set by mysql_prune_stmt_list(). 
+      */
+      if (stmt->mysql)
+        set_stmt_errmsg(stmt, net);
       return 1;
     }
     if ((*mysql->methods->read_rows_from_cursor)(stmt))
@@ -3387,7 +3397,12 @@ mysql_stmt_send_long_data(MYSQL_STMT *stmt, uint param_number,
                                             buff, sizeof(buff), (uchar*) data,
                                             length, 1, stmt))
     {
-      set_stmt_errmsg(stmt, &mysql->net);
+      /* 
+        Don't set stmt error if stmt->mysql is NULL, as the error in this case 
+        has already been set by mysql_prune_stmt_list(). 
+      */
+      if (stmt->mysql)
+        set_stmt_errmsg(stmt, &mysql->net);
       DBUG_RETURN(1);
     }
   }
@@ -4823,7 +4838,12 @@ int STDCALL mysql_stmt_store_result(MYSQL_STMT *stmt)
     if (cli_advanced_command(mysql, COM_STMT_FETCH, buff, sizeof(buff),
                              (uchar*) 0, 0, 1, stmt))
     {
-      set_stmt_errmsg(stmt, net);
+      /* 
+        Don't set stmt error if stmt->mysql is NULL, as the error in this case 
+        has already been set by mysql_prune_stmt_list(). 
+      */
+      if (stmt->mysql)
+        set_stmt_errmsg(stmt, net);
       DBUG_RETURN(1);
     }
   }