MDEV-15935 Adding global/session system var redirect_url

Adding a global/session var `redirect_url' of string type. The initial
value is empty. Can be supplied in mysqld with --redirect-url or set
in --init-connect. A valid redirect_url should be of the format

{mysql,mariadb}://host[:port]

where <host> is an arbitrary string not containing colons, and <port>
is a number between 0 and 65535 inclusive.

The variable will be used by the server to notify clients that they
should connect to another server, specified by the value of the
variable, if not empty.

The notification is done by the inclusion of the variable in
session_track_system_variable.

mysql-test/main/mysqld--help.result

@@ -1064,6 +1064,8 @@ The following specify which files/extra groups are read (specified before remain
  --read-rnd-buffer-size=# 
  When reading rows in sorted order after a sort, the rows
  are read through this buffer to avoid a disk seeks
+ --redirect-url=name URL of another server to redirect clients to. Empty
+ string means no redirection
  --relay-log=name    The location and name to use for relay logs.
  --relay-log-index=name 
  The location and name to use for the file that keeps a
@@ -1838,6 +1840,7 @@ read-binlog-speed-limit 0
 read-buffer-size 131072
 read-only FALSE
 read-rnd-buffer-size 262144
+redirect-url 
 relay-log (No default value)
 relay-log-index (No default value)
 relay-log-info-file relay-log.info
@@ -1869,7 +1872,7 @@ secure-timestamp NO
 server-id 1
 session-track-schema TRUE
 session-track-state-change FALSE
-session-track-system-variables autocommit,character_set_client,character_set_connection,character_set_results,time_zone
+session-track-system-variables autocommit,character_set_client,character_set_connection,character_set_results,redirect_url,time_zone
 session-track-transaction-info OFF
 show-slave-auth-info FALSE
 silent-startup FALSE

mysql-test/suite/sys_vars/r/mdev_32254.result

@@ -0,0 +1,13 @@
+#
+# MDEV-32254 Server crashes when adding records to table after setting redirect_url with empty variable
+#
+set @old_redirect_url=@@global.redirect_url;
+set global redirect_url=@empty_value;
+ERROR 42000: Variable 'redirect_url' can't be set to the value of 'NULL'
+CREATE TABLE t (c1 INT) ENGINE=INNODB;
+INSERT INTO t VALUES (1),(1);
+drop table t;
+set global redirect_url=@old_redirect_url;
+#
+# end of test mdev_32254
+#

mysql-test/suite/sys_vars/r/redirect.result

@@ -0,0 +1,81 @@
+#
+# MDEV-15935 Connection Redirection Mechanism in MariaDB Client/Server Protocol
+#
+connect  con,localhost,anyone_but_root;
+select @@redirect_url;
+@@redirect_url
+mysql://foobar
+connection default;
+set @old_global_redirect_url=@@global.redirect_url;
+set @old_session_redirect_url=@@session.redirect_url;
+set @old_session_track_system_variables=@@session_track_system_variables;
+set session_track_system_variables="";
+select @@global.redirect_url;
+@@global.redirect_url
+
+set global redirect_url=default;
+select @@global.redirect_url;
+@@global.redirect_url
+
+set global redirect_url="mariadb.org";
+ERROR 42000: Variable 'redirect_url' can't be set to the value of 'mariadb.org'
+set global redirect_url="https://mariadb.org";
+ERROR 42000: Variable 'redirect_url' can't be set to the value of 'https://mariadb.org'
+set global redirect_url="mysql://mariadb.org:";
+ERROR 42000: Variable 'redirect_url' can't be set to the value of 'mysql://mariadb.org:'
+set global redirect_url="mysql://mariadb.org:hello";
+ERROR 42000: Variable 'redirect_url' can't be set to the value of 'mysql://mariadb.org:hello'
+set global redirect_url="mysql://";
+ERROR 42000: Variable 'redirect_url' can't be set to the value of 'mysql://'
+set global redirect_url="mysql://mariadb.org";
+select @@global.redirect_url;
+@@global.redirect_url
+mysql://mariadb.org
+set global redirect_url="mysql://mariadb.org:12a";
+ERROR 42000: Variable 'redirect_url' can't be set to the value of 'mysql://mariadb.org:12a'
+set global redirect_url="mysql://mariadb.org:66666";
+ERROR 42000: Variable 'redirect_url' can't be set to the value of 'mysql://mariadb.org:66666'
+set global redirect_url="mysql://mariadb.org:12345";
+select @@global.redirect_url;
+@@global.redirect_url
+mysql://mariadb.org:12345
+set global redirect_url="maria";
+ERROR 42000: Variable 'redirect_url' can't be set to the value of 'maria'
+set global redirect_url="mariadb://mariadb.org:";
+ERROR 42000: Variable 'redirect_url' can't be set to the value of 'mariadb://mariadb.org:'
+set global redirect_url="mariadb://mariadb.org:hello";
+ERROR 42000: Variable 'redirect_url' can't be set to the value of 'mariadb://mariadb.org:hello'
+set global redirect_url="mariadb://";
+ERROR 42000: Variable 'redirect_url' can't be set to the value of 'mariadb://'
+set global redirect_url="mariadb://mariadb.org";
+select @@global.redirect_url;
+@@global.redirect_url
+mariadb://mariadb.org
+set global redirect_url="mariadb://mariadb.org:12a";
+ERROR 42000: Variable 'redirect_url' can't be set to the value of 'mariadb://mariadb.org:12a'
+set global redirect_url="mariadb://mariadb.org:66666";
+ERROR 42000: Variable 'redirect_url' can't be set to the value of 'mariadb://mariadb.org:66666'
+set global redirect_url="mariadb://mariadb.org:12345";
+select @@global.redirect_url;
+@@global.redirect_url
+mariadb://mariadb.org:12345
+select @@session.redirect_url;
+@@session.redirect_url
+
+set session redirect_url=default;
+select @@session.redirect_url;
+@@session.redirect_url
+mariadb://mariadb.org:12345
+set session redirect_url="mysql://localhost";
+select @@session.redirect_url;
+@@session.redirect_url
+mysql://localhost
+select @@global.redirect_url;
+@@global.redirect_url
+mariadb://mariadb.org:12345
+set global redirect_url=@old_global_redirect_url;
+set session redirect_url=@old_session_redirect_url;
+set session session_track_system_variables=@old_session_track_system_variables;
+#
+# end of test MDEV-15935
+#

mysql-test/suite/sys_vars/r/session_track_system_variables_basic.result

@@ -5,20 +5,20 @@
 # Global - default
 SELECT @@global.session_track_system_variables;
 @@global.session_track_system_variables
-autocommit,character_set_client,character_set_connection,character_set_results,time_zone
+autocommit,character_set_client,character_set_connection,character_set_results,redirect_url,time_zone
 # Session - default
 SELECT @@session.session_track_system_variables;
 @@session.session_track_system_variables
-autocommit,character_set_client,character_set_connection,character_set_results,time_zone
+autocommit,character_set_client,character_set_connection,character_set_results,redirect_url,time_zone
 
 # via INFORMATION_SCHEMA.GLOBAL_VARIABLES
 SELECT * FROM INFORMATION_SCHEMA.GLOBAL_VARIABLES WHERE VARIABLE_NAME LIKE 'session_track_system_variables' ORDER BY VARIABLE_NAME;
 VARIABLE_NAME	VARIABLE_VALUE
-SESSION_TRACK_SYSTEM_VARIABLES	autocommit,character_set_client,character_set_connection,character_set_results,time_zone
+SESSION_TRACK_SYSTEM_VARIABLES	autocommit,character_set_client,character_set_connection,character_set_results,redirect_url,time_zone
 # via INFORMATION_SCHEMA.SESSION_VARIABLES
 SELECT * FROM INFORMATION_SCHEMA.SESSION_VARIABLES WHERE VARIABLE_NAME LIKE 'session_track_system_variables' ORDER BY VARIABLE_NAME;
 VARIABLE_NAME	VARIABLE_VALUE
-SESSION_TRACK_SYSTEM_VARIABLES	autocommit,character_set_client,character_set_connection,character_set_results,time_zone
+SESSION_TRACK_SYSTEM_VARIABLES	autocommit,character_set_client,character_set_connection,character_set_results,redirect_url,time_zone
 SET @global_saved_tmp =  @@global.session_track_system_variables;
 
 # Altering global variable's value
@@ -28,7 +28,7 @@ SELECT @@global.session_track_system_variables;
 autocommit
 SELECT @@session.session_track_system_variables;
 @@session.session_track_system_variables
-autocommit,character_set_client,character_set_connection,character_set_results,time_zone
+autocommit,character_set_client,character_set_connection,character_set_results,redirect_url,time_zone
 
 # Altering session variable's value
 SET @@session.session_track_system_variables='autocommit';
@@ -66,25 +66,25 @@ SET @@session.session_track_system_variables = DEFAULT;
 
 SELECT @@global.session_track_system_variables;
 @@global.session_track_system_variables
-autocommit,character_set_client,character_set_connection,character_set_results,time_zone
+autocommit,character_set_client,character_set_connection,character_set_results,redirect_url,time_zone
 SELECT @@session.session_track_system_variables;
 @@session.session_track_system_variables
-autocommit,character_set_client,character_set_connection,character_set_results,time_zone
+autocommit,character_set_client,character_set_connection,character_set_results,redirect_url,time_zone
 
 # Variables' values in a new session (con2).
 connect  con2,"127.0.0.1",root,,test,$MASTER_MYPORT,;
 SELECT @@global.session_track_system_variables;
 @@global.session_track_system_variables
-autocommit,character_set_client,character_set_connection,character_set_results,time_zone
+autocommit,character_set_client,character_set_connection,character_set_results,redirect_url,time_zone
 SELECT @@session.session_track_system_variables;
 @@session.session_track_system_variables
-autocommit,character_set_client,character_set_connection,character_set_results,time_zone
+autocommit,character_set_client,character_set_connection,character_set_results,redirect_url,time_zone
 
 # Altering session should not affect global.
 SET @@session.session_track_system_variables = 'sql_mode';
 SELECT @@global.session_track_system_variables;
 @@global.session_track_system_variables
-autocommit,character_set_client,character_set_connection,character_set_results,time_zone
+autocommit,character_set_client,character_set_connection,character_set_results,redirect_url,time_zone
 SELECT @@session.session_track_system_variables;
 @@session.session_track_system_variables
 sql_mode
@@ -98,7 +98,7 @@ SELECT @@global.session_track_system_variables;
 sql_mode
 SELECT @@session.session_track_system_variables;
 @@session.session_track_system_variables
-autocommit,character_set_client,character_set_connection,character_set_results,time_zone
+autocommit,character_set_client,character_set_connection,character_set_results,redirect_url,time_zone
 
 # Switching to the default connection.
 connection default;

mysql-test/suite/sys_vars/r/sysvars_server_notembedded.result

@@ -3412,6 +3412,16 @@ NUMERIC_BLOCK_SIZE	1
 ENUM_VALUE_LIST	NULL
 READ_ONLY	NO
 COMMAND_LINE_ARGUMENT	REQUIRED
+VARIABLE_NAME	REDIRECT_URL
+VARIABLE_SCOPE	SESSION
+VARIABLE_TYPE	VARCHAR
+VARIABLE_COMMENT	URL of another server to redirect clients to. Empty string means no redirection
+NUMERIC_MIN_VALUE	NULL
+NUMERIC_MAX_VALUE	NULL
+NUMERIC_BLOCK_SIZE	NULL
+ENUM_VALUE_LIST	NULL
+READ_ONLY	NO
+COMMAND_LINE_ARGUMENT	REQUIRED
 VARIABLE_NAME	RELAY_LOG
 VARIABLE_SCOPE	GLOBAL
 VARIABLE_TYPE	VARCHAR

mysql-test/suite/sys_vars/t/mdev_32254.test

@@ -0,0 +1,17 @@
+--echo #
+--echo # MDEV-32254 Server crashes when adding records to table after setting redirect_url with empty variable
+--echo #
+--source include/have_innodb.inc
+# redirect_url is undefined in embedded.
+--source include/not_embedded.inc
+set @old_redirect_url=@@global.redirect_url;
+--error ER_WRONG_VALUE_FOR_VAR
+set global redirect_url=@empty_value;
+CREATE TABLE t (c1 INT) ENGINE=INNODB;
+INSERT INTO t VALUES (1),(1);
+drop table t;
+set global redirect_url=@old_redirect_url;
+
+--echo #
+--echo # end of test mdev_32254
+--echo #

mysql-test/suite/sys_vars/t/redirect.opt

@@ -0,0 +1 @@
+--init-connect="set redirect_url='mysql://foobar'"

mysql-test/suite/sys_vars/t/redirect.test

@@ -0,0 +1,74 @@
+--echo #
+--echo # MDEV-15935 Connection Redirection Mechanism in MariaDB Client/Server Protocol
+--echo #
+# redirect_url is undefined in embedded.
+--source include/not_embedded.inc
+
+# We need to connect as a non super user for the init-connect to take
+# effect
+--source include/add_anonymous_users.inc
+connect (con,localhost,anyone_but_root);
+select @@redirect_url;
+
+connection default;
+--source include/delete_anonymous_users.inc
+set @old_global_redirect_url=@@global.redirect_url;
+set @old_session_redirect_url=@@session.redirect_url;
+set @old_session_track_system_variables=@@session_track_system_variables;
+set session_track_system_variables="";
+
+select @@global.redirect_url;
+set global redirect_url=default;
+select @@global.redirect_url;
+--error ER_WRONG_VALUE_FOR_VAR
+set global redirect_url="mariadb.org";
+--error ER_WRONG_VALUE_FOR_VAR
+set global redirect_url="https://mariadb.org";
+
+--error ER_WRONG_VALUE_FOR_VAR
+set global redirect_url="mysql://mariadb.org:";
+--error ER_WRONG_VALUE_FOR_VAR
+set global redirect_url="mysql://mariadb.org:hello";
+--error ER_WRONG_VALUE_FOR_VAR
+set global redirect_url="mysql://";
+set global redirect_url="mysql://mariadb.org";
+select @@global.redirect_url;
+--error ER_WRONG_VALUE_FOR_VAR
+set global redirect_url="mysql://mariadb.org:12a";
+--error ER_WRONG_VALUE_FOR_VAR
+set global redirect_url="mysql://mariadb.org:66666";
+set global redirect_url="mysql://mariadb.org:12345";
+select @@global.redirect_url;
+
+--error ER_WRONG_VALUE_FOR_VAR
+set global redirect_url="maria";
+--error ER_WRONG_VALUE_FOR_VAR
+set global redirect_url="mariadb://mariadb.org:";
+--error ER_WRONG_VALUE_FOR_VAR
+set global redirect_url="mariadb://mariadb.org:hello";
+--error ER_WRONG_VALUE_FOR_VAR
+set global redirect_url="mariadb://";
+set global redirect_url="mariadb://mariadb.org";
+select @@global.redirect_url;
+--error ER_WRONG_VALUE_FOR_VAR
+set global redirect_url="mariadb://mariadb.org:12a";
+--error ER_WRONG_VALUE_FOR_VAR
+set global redirect_url="mariadb://mariadb.org:66666";
+set global redirect_url="mariadb://mariadb.org:12345";
+select @@global.redirect_url;
+
+select @@session.redirect_url;
+# Test that session default is global value
+set session redirect_url=default;
+select @@session.redirect_url;
+set session redirect_url="mysql://localhost";
+select @@session.redirect_url;
+select @@global.redirect_url;
+
+set global redirect_url=@old_global_redirect_url;
+set session redirect_url=@old_session_redirect_url;
+set session session_track_system_variables=@old_session_track_system_variables;
+
+--echo #
+--echo # end of test MDEV-15935
+--echo #

sql/sql_class.h

@@ -883,6 +883,7 @@ typedef struct system_variables
 
   Time_zone *time_zone;
   char *session_track_system_variables;
+  char *redirect_url;
 
   /* Some wsrep variables */
   ulonglong wsrep_trx_fragment_size;

sql/sql_plugin.cc

@@ -3278,6 +3278,8 @@ void plugin_thdvar_init(THD *thd)
   /* This and all other variable cleanups are here for COM_CHANGE_USER :( */
 #ifndef EMBEDDED_LIBRARY
   thd->session_tracker.sysvars.deinit(thd);
+  my_free(thd->variables.redirect_url);
+  thd->variables.redirect_url= 0;
 #endif
   my_free((char*) thd->variables.default_master_connection.str);
   thd->variables.default_master_connection.str= 0;
@@ -3311,7 +3313,12 @@ void plugin_thdvar_init(THD *thd)
                MYF(MY_WME | MY_THREAD_SPECIFIC));
 #ifndef EMBEDDED_LIBRARY
   thd->session_tracker.sysvars.init(thd);
+  thd->variables.redirect_url=
+    my_strdup(key_memory_Sys_var_charptr_value,
+              global_system_variables.redirect_url,
+              MYF(MY_WME | MY_THREAD_SPECIFIC));
 #endif
+
   DBUG_VOID_RETURN;
 }
 
@@ -3379,6 +3386,8 @@ void plugin_thdvar_cleanup(THD *thd)
 
 #ifndef EMBEDDED_LIBRARY
   thd->session_tracker.sysvars.deinit(thd);
+  my_free(thd->variables.redirect_url);
+  thd->variables.redirect_url= 0;
 #endif
   my_free((char*) thd->variables.default_master_connection.str);
   thd->variables.default_master_connection.str= 0;