MDEV-18281 COM_RESET_CONNECTION changes the connection encoding

Store original charset during client authentication, and restore it for COM_RESET_CONNECTION

Author: vaintroub

client/mysqltest.cc

@@ -5966,6 +5966,7 @@ void do_connect(struct st_command *command)
  int read_timeout= 0;
  int write_timeout= 0;
  int connect_timeout= 0;
+ char *csname=0;
  struct st_connection* con_slot;
 
  static DYNAMIC_STRING ds_connection_name;
@@ -6077,6 +6078,11 @@ void do_connect(struct st_command *command)
  {
  connect_timeout= atoi(con_options + sizeof("connect_timeout=")-1);
  }
+ else if (strncasecmp(con_options, "CHARSET=",
+ sizeof("CHARSET=") - 1) == 0)
+ {
+ csname= strdup(con_options + sizeof("CHARSET=") - 1);
+ }
  else
  die("Illegal option to connect: %.*s", 
  (int) (end - con_options), con_options);
@@ -6114,7 +6120,7 @@ void do_connect(struct st_command *command)
  mysql_options(con_slot->mysql, MYSQL_OPT_COMPRESS, NullS);
  mysql_options(con_slot->mysql, MYSQL_OPT_LOCAL_INFILE, 0);
  mysql_options(con_slot->mysql, MYSQL_SET_CHARSET_NAME,
- charset_info->csname);
+ csname?csname: charset_info->csname);
  if (opt_charsets_dir)
  mysql_options(con_slot->mysql, MYSQL_SET_CHARSET_DIR,
  opt_charsets_dir);
@@ -6225,6 +6231,7 @@ void do_connect(struct st_command *command)
 #ifdef HAVE_SMEM
  dynstr_free(&ds_shm);
 #endif
+ free(csname);
  DBUG_VOID_RETURN;
 }
 

mysql-test/main/reset_connection.result

@@ -5,3 +5,23 @@ Com_select	10
 SHOW local STATUS LIKE 'com_select';
 Variable_name	Value
 Com_select	0
+# Test if charset changes after reset (utf8)
+connect utf8_conn,localhost,root,,,,,CHARSET=utf8;
+connection utf8_conn;
+SELECT IF(@@character_set_client='utf8','OK', 'FAIL') AS RESULT;
+RESULT
+OK
+SELECT IF(@@character_set_client='utf8','OK', 'FAIL') AS RESULT;
+RESULT
+OK
+disconnect utf8_conn;
+# Test if charset changes after reset (latin1)
+connect latin1_conn,localhost,root,,,,,CHARSET=latin1;
+connection latin1_conn;
+SELECT IF(@@character_set_client='latin1','OK', 'FAIL') AS RESULT;
+RESULT
+OK
+SELECT IF(@@character_set_client='latin1','OK', 'FAIL') AS RESULT;
+RESULT
+OK
+disconnect latin1_conn;

mysql-test/main/reset_connection.test

@@ -23,3 +23,18 @@ SHOW local STATUS LIKE 'com_select';
 
 SHOW local STATUS LIKE 'com_select';
 
+--echo # Test if charset changes after reset (utf8)
+connect(utf8_conn,localhost,root,,,,,CHARSET=utf8);
+connection utf8_conn;
+SELECT IF(@@character_set_client='utf8','OK', 'FAIL') AS RESULT;
+--reset_connection
+SELECT IF(@@character_set_client='utf8','OK', 'FAIL') AS RESULT;
+disconnect utf8_conn;
+
+--echo # Test if charset changes after reset (latin1)
+connect(latin1_conn,localhost,root,,,,,CHARSET=latin1);
+connection latin1_conn;
+SELECT IF(@@character_set_client='latin1','OK', 'FAIL') AS RESULT;
+--reset_connection
+SELECT IF(@@character_set_client='latin1','OK', 'FAIL') AS RESULT;
+disconnect latin1_conn;

sql/sql_class.cc

@@ -847,6 +847,7 @@ THD::THD(my_thread_id id, bool is_wsrep_applier, bool skip_global_sys_var_lock)
  prepare_derived_at_open= FALSE;
  create_tmp_table_for_derived= FALSE;
  save_prep_leaf_list= FALSE;
+ org_charset= 0;
  /* Restore THR_THD */
  set_current_thd(old_THR_THD);
  inc_thread_count();

sql/sql_class.h

@@ -2365,6 +2365,9 @@ class THD :public Statement,
  uint dbug_sentry; // watch out for memory corruption
 #endif
  struct st_my_thread_var *mysys_var;
+
+ /* Original charset number from the first client packet, or COM_CHANGE_USER*/
+ CHARSET_INFO *org_charset;
 private:
  /*
  Type of current query: COM_STMT_PREPARE, COM_QUERY, etc. Set from

sql/sql_connect.cc

@@ -796,6 +796,7 @@ bool thd_init_client_charset(THD *thd, uint cs_number)
  cs->csname);
  return true;
  }
+ thd->org_charset= cs;
  thd->update_charset(cs,cs,cs);
  }
  return false;

sql/sql_parse.cc

@@ -1715,6 +1715,9 @@ bool dispatch_command(enum enum_server_command command, THD *thd,
  thd->status_var.com_other++;
  thd->change_user();
  thd->clear_error(); // if errors from rollback
+ /* Restore original charset from client authentication packet.*/
+ if(thd->org_charset)
+ thd->update_charset(thd->org_charset,thd->org_charset,thd->org_charset);
  my_ok(thd, 0, 0, 0);
  break;
  }