MDEV-18323 Convert MySQL JSON type to MariaDB TEXT in mysql_upgrade

This patch solves two key problems.
1. There is a type number clash between MySQL and MariaDB. The number
   245, used for MariaDB Virtual Fields is the same as MySQL's JSON.
   This leads to corrupt FRM errors if unhandled. The code properly
   checks frm table version number and if it matches 5.7+ (until 10.0+)
   it will assume it is dealing with a MySQL table with the JSON
   datatype.
2. MySQL JSON datatype uses a proprietary format to pack JSON data. The
   patch introduces a datatype plugin which parses the format and convers
   it to its string representation.

The intended conversion path is to only use the JSON datatype within
ALTER TABLE <table> FORCE, to force a table recreate. This happens
during mysql_upgrade or via a direct ALTER TABLE <table> FORCE.

mysql-test/main/mysql_json_table_recreate.opt

+--plugin-load=$TYPE_MYSQL_JSON_SO

mysql-test/main/mysql_json_table_recreate.result

+#
+# The following test takes 2 tables containing a JSON column and attempts
+# to repair them.
+#
+# The tables header is (Description, Expected, Actual), where description
+# shows a brief description what the JSON value is testing in the MariaDB
+# implementation. Expected is the longtext string and actual is the JSON
+# column that needs to be converted to MariaDB's representation of
+# LONGTEXT.
+#
+call mtr.add_suppression("Table rebuild required");
+call mtr.add_suppression("is marked as crashed");
+call mtr.add_suppression("Checking");
+SET NAMES utf8;
+#
+# Check that only ALTER TABLE ... FORCE is allowed on a MySQL 5.7 table
+# with a JSON column.
+#
+show create table tempty;
+ERROR HY000: Table rebuild required. Please do "ALTER TABLE `test.tempty` FORCE" or dump/reload to fix it!
+select * from tempty;
+ERROR HY000: Table rebuild required. Please do "ALTER TABLE `test.tempty` FORCE" or dump/reload to fix it!
+alter table tempty force;
+show create table tempty;
+Table	Create Table
+tempty	CREATE TABLE `tempty` (
+  `t` longtext CHARACTER SET utf8mb4 COLLATE utf8mb4_bin DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+show create table mysql_json_test;
+ERROR HY000: Table rebuild required. Please do "ALTER TABLE `test.mysql_json_test` FORCE" or dump/reload to fix it!
+select * from mysql_json_test;
+ERROR HY000: Table rebuild required. Please do "ALTER TABLE `test.mysql_json_test` FORCE" or dump/reload to fix it!
+LOCK TABLES mysql_json_test WRITE;
+ERROR HY000: Table rebuild required. Please do "ALTER TABLE `test.mysql_json_test` FORCE" or dump/reload to fix it!
+alter table mysql_json_test force;
+select description, expected, actual, expected = actual from mysql_json_test;
+description	expected	actual	expected = actual
+Array LITERALS: 	["prefix", false, "suffix", 1]	["prefix", false, "suffix", 1]	1
+Array LITERALS: 	["prefix", null, "suffix", 1]	["prefix", null, "suffix", 1]	1
+Array LITERALS: 	["prefix", true, "suffix", 1]	["prefix", true, "suffix", 1]	1
+DateTime as Raw Value: 	"2015-01-15 23:24:25.000000"	"2015-01-15 23:24:25.000000"	1
+DateTime as Raw Value: 	"2015-01-15 23:24:25.000000"	"2015-01-15 23:24:25.000000"	1
+DateTime as Raw Value: 	"2015-01-15"	"2015-01-15"	1
+DateTime as Raw Value: 	"23:24:25.000000"	"23:24:25.000000"	1
+Empty JSON Object/Array: 	[]	[]	1
+Empty JSON Object/Array: 	{}	{}	1
+GeoJSON	{"type": "GeometryCollection", "geometries": []}	{"type": "GeometryCollection", "geometries": []}	1
+GeoJSON	{"type": "LineString", "coordinates": [[0, 5], [5, 10], [10, 15]]}	{"type": "LineString", "coordinates": [[0, 5], [5, 10], [10, 15]]}	1
+GeoJSON	{"type": "MultiPoint", "coordinates": [[1, 1], [2, 2], [3, 3]]}	{"type": "MultiPoint", "coordinates": [[1, 1], [2, 2], [3, 3]]}	1
+GeoJSON	{"type": "Point", "coordinates": [11.1111, 12.22222]}	{"type": "Point", "coordinates": [11.1111, 12.22222]}	1
+JSON LITERALS: 	{"val": false}	{"val": false}	1
+JSON LITERALS: 	{"val": null}	{"val": null}	1
+JSON LITERALS: 	{"val": true}	{"val": true}	1
+Opaque Types: opaque_mysql_type_binary	"base64:type254:YWJjAAAAAAAAAA=="	"base64:type254:YWJjAAAAAAAAAA=="	1
+Opaque Types: opaque_mysql_type_bit	"base64:type16:yv4="	"base64:type16:yv4="	1
+Opaque Types: opaque_mysql_type_blob	"base64:type252:yv66vg=="	"base64:type252:yv66vg=="	1
+Opaque Types: opaque_mysql_type_date	"2015-01-15"	"2015-01-15"	1
+Opaque Types: opaque_mysql_type_datetime	"2015-01-15 23:24:25.000000"	"2015-01-15 23:24:25.000000"	1
+Opaque Types: opaque_mysql_type_enum	"b"	"b"	1
+Opaque Types: opaque_mysql_type_geom	{"type": "Point", "coordinates": [1, 1]}	{"type": "Point", "coordinates": [1, 1]}	1
+Opaque Types: opaque_mysql_type_longblob	"base64:type251:yv66vg=="	"base64:type251:yv66vg=="	1
+Opaque Types: opaque_mysql_type_mediumblob	"base64:type250:yv66vg=="	"base64:type250:yv66vg=="	1
+Opaque Types: opaque_mysql_type_set	"b,c"	"b,c"	1
+Opaque Types: opaque_mysql_type_time	"23:24:25.000000"	"23:24:25.000000"	1
+Opaque Types: opaque_mysql_type_tinyblob	"base64:type249:yv66vg=="	"base64:type249:yv66vg=="	1
+Opaque Types: opaque_mysql_type_varbinary	"base64:type15:YWJj"	"base64:type15:YWJj"	1
+Opaque Types: opaque_mysql_type_varchar	"base64:type15:Zm9v"	"base64:type15:Zm9v"	1
+Opaque Types: opaque_mysql_type_year	"base64:type13:MjAxOQ=="	"base64:type13:MjAxOQ=="	1
+Raw LITERALS: 	false	false	1
+Raw LITERALS: 	null	null	1
+Raw LITERALS: 	true	true	1
+Raw doubles as JSON	-2.2250738585072014e-308	-2.2250738585072014e-308	1
+Raw doubles as JSON	-5678.987	-5678.987	1
+Raw doubles as JSON	0.0	0.0	1
+Raw doubles as JSON	2.2250738585072014e-308	2.2250738585072014e-308	1
+Raw doubles as JSON	3.14	3.14	1
+Raw integers as JSON	-127	-127	1
+Raw integers as JSON	-2147483648	-2147483648	1
+Raw integers as JSON	-32768	-32768	1
+Raw integers as JSON	-9223372036854775807	-9223372036854775807	1
+Raw integers as JSON	0	0	1
+Raw integers as JSON	128	128	1
+Raw integers as JSON	18446744073709551615	18446744073709551615	1
+Raw integers as JSON	2147483647	2147483647	1
+Raw integers as JSON	32767	32767	1
+Raw integers as JSON	4294967295	4294967295	1
+Raw integers as JSON	65535	65535	1
+Raw integers as JSON	65536	65536	1
+Raw integers as JSON	9223372036854775807	9223372036854775807	1
+Simple Array as Base Key	[1, 2, 3, 4, 5, [], "a", "b", "c"]	[1, 2, 3, 4, 5, [], "a", "b", "c"]	1
+Simple Array as Value	{"a": [1, 2], "b": ["x", "y"]}	{"a": [1, 2], "b": ["x", "y"]}	1
+Simple JSON test	{"key1": "val1", "key2": "val2"}	{"key1": "val1", "key2": "val2"}	1
+Special Characters: 	""	""	1
+Special Characters: 	"'"	"'"	1
+Special Characters: 	"'"	"'"	1
+Special Characters: 	"'"	"'"	1
+Special Characters: 	"''"	"''"	1
+Special Characters: 	"\""	"\""	1
+Special Characters: 	"\\"	"\\"	1
+Special Characters: 	"\\b"	"\\b"	1
+Special Characters: 	"\b"	"\b"	1
+Special Characters: 	"\f"	"\f"	1
+Special Characters: 	"\n"	"\n"	1
+Special Characters: 	"\r"	"\r"	1
+Special Characters: 	"\t"	"\t"	1
+Special Characters: 	"f"	"f"	1
+Special Characters: 	"key1 - with \" val "	"key1 - with \" val "	1
+Special Characters: 	"q"	"q"	1
+Special Characters: 	"some_string"	"some_string"	1
+Special Characters: 	["a ' b", "c ' d"]	["a ' b", "c ' d"]	1
+Special Characters: 	["a \" b", "c \" d"]	["a \" b", "c \" d"]	1
+Special Characters: 	["a \\ b", "c \\ d"]	["a \\ b", "c \\ d"]	1
+Special Characters: 	["a \b b", "c \b d"]	["a \b b", "c \b d"]	1
+Special Characters: 	["a \f b", "c \f d"]	["a \f b", "c \f d"]	1
+Special Characters: 	["a \r b", "c \r d"]	["a \r b", "c \r d"]	1
+Special Characters: 	["a \t b", "c \t d"]	["a \t b", "c \t d"]	1
+Special Characters: 	{"[": "]"}	{"[": "]"}	1
+Special Characters: 	{"key ' key": "val ' val"}	{"key ' key": "val ' val"}	1
+Special Characters: 	{"key \" key": "val \" val"}	{"key \" key": "val \" val"}	1
+Special Characters: 	{"key \\ key": "val \\ val"}	{"key \\ key": "val \\ val"}	1
+Special Characters: 	{"key \\0 key": "val \n val"}	{"key \\0 key": "val \n val"}	1
+Special Characters: 	{"key \\Z key": "val ' val"}	{"key \\Z key": "val ' val"}	1
+Special Characters: 	{"key \b key": "val \b val"}	{"key \b key": "val \b val"}	1
+Special Characters: 	{"key \f key": "val \f val"}	{"key \f key": "val \f val"}	1
+Special Characters: 	{"key \n key": "val \n val"}	{"key \n key": "val \n val"}	1
+Special Characters: 	{"key \r key": "val \r val"}	{"key \r key": "val \r val"}	1
+Special Characters: 	{"key \t key": "val \t val"}	{"key \t key": "val \t val"}	1
+Special Characters: 	{"key1 and \n\"key2\"": "val1\t val2"}	{"key1 and \n\"key2\"": "val1\t val2"}	1
+Special Characters: 	{"{": "}"}	{"{": "}"}	1
+Special Characters: 	{"{": "}"}	{"{": "}"}	1
+Special String Cases: 	[""]	[""]	1
+Special String Cases: 	{"": ""}	{"": ""}	1
+Timestamp as RawValue	"2019-12-26 19:56:03.000000"	"2019-12-26 19:56:03.000000"	1
+UTF8 Characters: 	"Anel Husaković - test: đžšćč"	"Anel Husaković - test: đžšćč"	1
+UTF8 Characters: 	{"Name": "Anel Husaković - test: đžšćč"}	{"Name": "Anel Husaković - test: đžšćč"}	1
+UTF8 Characters: 	{"Person": "EMP", "details": {"Name": "Anel Husaković - test: đžšćč"}}	{"Person": "EMP", "details": {"Name": "Anel Husaković - test: đžšćč"}}	1
+UTF8 Characters: 	{"details": {"Name": "Anel Husaković - test: đžšćč"}, "\"Anel Husaković - test: đžšćč\"": "EMP"}	{"details": {"Name": "Anel Husaković - test: đžšćč"}, "\"Anel Husaković - test: đžšćč\"": "EMP"}	1
+#
+# A quick check that all rows match from the original MySQL Table.
+#
+select count(*) as 'Total_Number_of_Tests',
+sum(expected = actual) as 'Succesful_Tests'
+from mysql_json_test;
+Total_Number_of_Tests	Succesful_Tests
+100	100
+show create table mysql_json_test;
+Table	Create Table
+mysql_json_test	CREATE TABLE `mysql_json_test` (
+  `description` varchar(100) COLLATE utf8mb4_unicode_ci DEFAULT NULL,
+  `expected` longtext COLLATE utf8mb4_unicode_ci DEFAULT NULL,
+  `actual` longtext CHARACTER SET utf8mb4 COLLATE utf8mb4_bin DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci
+show create table mysql_json_test_big;
+ERROR HY000: Table rebuild required. Please do "ALTER TABLE `test.mysql_json_test_big` FORCE" or dump/reload to fix it!
+select * from mysql_json_test_big;
+ERROR HY000: Table rebuild required. Please do "ALTER TABLE `test.mysql_json_test_big` FORCE" or dump/reload to fix it!
+#
+# This test checks the long format implementation of MySQL's JSON
+# Not printing the actual contents as they are not readable by a human,
+# just compare the strings, make sure they match.
+#
+alter table mysql_json_test_big force;
+select count(*) as 'Total_Number_of_Tests',
+sum(expected = actual) as 'Succesful_Tests',
+sum(JSON_VALID(actual)) as 'String_is_valid_JSON'
+from mysql_json_test_big;
+Total_Number_of_Tests	Succesful_Tests	String_is_valid_JSON
+1	1	1
+drop table tempty;
+drop table mysql_json_test;
+drop table mysql_json_test_big;

mysql-test/main/mysql_json_table_recreate.test

+--source include/have_utf8.inc
+
+--echo #
+--echo # The following test takes 2 tables containing a JSON column and attempts
+--echo # to repair them.
+--echo #
+--echo # The tables header is (Description, Expected, Actual), where description
+--echo # shows a brief description what the JSON value is testing in the MariaDB
+--echo # implementation. Expected is the longtext string and actual is the JSON
+--echo # column that needs to be converted to MariaDB's representation of
+--echo # LONGTEXT.
+--echo #
+
+
+call mtr.add_suppression("Table rebuild required");
+call mtr.add_suppression("is marked as crashed");
+call mtr.add_suppression("Checking");
+
+let $MYSQLD_DATADIR= `select @@datadir`;
+
+SET NAMES utf8;
+
+--copy_file std_data/mysql_json/tempty.frm $MYSQLD_DATADIR/test/tempty.frm
+--copy_file std_data/mysql_json/tempty.MYI $MYSQLD_DATADIR/test/tempty.MYI
+--copy_file std_data/mysql_json/tempty.MYD $MYSQLD_DATADIR/test/tempty.MYD
+
+--copy_file std_data/mysql_json/mysql_json_test.frm $MYSQLD_DATADIR/test/mysql_json_test.frm
+--copy_file std_data/mysql_json/mysql_json_test.MYI $MYSQLD_DATADIR/test/mysql_json_test.MYI
+--copy_file std_data/mysql_json/mysql_json_test.MYD $MYSQLD_DATADIR/test/mysql_json_test.MYD
+
+--copy_file std_data/mysql_json/mysql_json_test_big.frm $MYSQLD_DATADIR/test/mysql_json_test_big.frm
+--copy_file std_data/mysql_json/mysql_json_test_big.MYI $MYSQLD_DATADIR/test/mysql_json_test_big.MYI
+--copy_file std_data/mysql_json/mysql_json_test_big.MYD $MYSQLD_DATADIR/test/mysql_json_test_big.MYD
+
+--echo #
+--echo # Check that only ALTER TABLE ... FORCE is allowed on a MySQL 5.7 table
+--echo # with a JSON column.
+--echo #
+
+--error ER_TABLE_NEEDS_REBUILD
+show create table tempty;
+--error ER_TABLE_NEEDS_REBUILD
+select * from tempty;
+
+alter table tempty force;
+show create table tempty;
+
+--error ER_TABLE_NEEDS_REBUILD
+show create table mysql_json_test;
+--error ER_TABLE_NEEDS_REBUILD
+select * from mysql_json_test;
+
+--error ER_TABLE_NEEDS_REBUILD
+LOCK TABLES mysql_json_test WRITE;
+
+alter table mysql_json_test force;
+
+--sorted_result
+select description, expected, actual, expected = actual from mysql_json_test;
+
+--echo #
+--echo # A quick check that all rows match from the original MySQL Table.
+--echo #
+select count(*) as 'Total_Number_of_Tests',
+       sum(expected = actual) as 'Succesful_Tests'
+from mysql_json_test;
+
+show create table mysql_json_test;
+
+--error ER_TABLE_NEEDS_REBUILD
+show create table mysql_json_test_big;
+--error ER_TABLE_NEEDS_REBUILD
+select * from mysql_json_test_big;
+
+--echo #
+--echo # This test checks the long format implementation of MySQL's JSON
+--echo # Not printing the actual contents as they are not readable by a human,
+--echo # just compare the strings, make sure they match.
+--echo #
+alter table mysql_json_test_big force;
+
+select count(*) as 'Total_Number_of_Tests',
+       sum(expected = actual) as 'Succesful_Tests',
+       sum(JSON_VALID(actual)) as 'String_is_valid_JSON'
+from mysql_json_test_big;
+
+drop table tempty;
+drop table mysql_json_test;
+drop table mysql_json_test_big;

mysql-test/main/mysql_upgrade_mysql_json_datatype.result

+call mtr.add_suppression("Table rebuild required");
+call mtr.add_suppression("is marked as crashed");
+call mtr.add_suppression("Checking");
+SET NAMES utf8;
+set sql_mode="";
+install soname 'type_mysql_json.so';
+show create table tempty;
+ERROR HY000: Table rebuild required. Please do "ALTER TABLE `test.tempty` FORCE" or dump/reload to fix it!
+show create table mysql_json_test;
+ERROR HY000: Table rebuild required. Please do "ALTER TABLE `test.mysql_json_test` FORCE" or dump/reload to fix it!
+show create table mysql_json_test_big;
+ERROR HY000: Table rebuild required. Please do "ALTER TABLE `test.mysql_json_test_big` FORCE" or dump/reload to fix it!
+# Run mysql_upgrade to fix the tables containing JSON.
+Phase 1/7: Checking and upgrading mysql database
+Processing databases
+mysql
+mysql.column_stats                                 OK
+mysql.columns_priv                                 OK
+mysql.db                                           OK
+mysql.event                                        OK
+mysql.func                                         OK
+mysql.global_priv                                  OK
+mysql.gtid_slave_pos                               OK
+mysql.help_category                                OK
+mysql.help_keyword                                 OK
+mysql.help_relation                                OK
+mysql.help_topic                                   OK
+mysql.index_stats                                  OK
+mysql.innodb_index_stats                           OK
+mysql.innodb_table_stats                           OK
+mysql.plugin                                       OK
+mysql.proc                                         OK
+mysql.procs_priv                                   OK
+mysql.proxies_priv                                 OK
+mysql.roles_mapping                                OK
+mysql.servers                                      OK
+mysql.table_stats                                  OK
+mysql.tables_priv                                  OK
+mysql.time_zone                                    OK
+mysql.time_zone_leap_second                        OK
+mysql.time_zone_name                               OK
+mysql.time_zone_transition                         OK
+mysql.time_zone_transition_type                    OK
+mysql.transaction_registry                         OK
+Phase 2/7: Installing used storage engines... Skipped
+Phase 3/7: Fixing views
+mysql.user                                         OK
+Phase 4/7: Running 'mysql_fix_privilege_tables'
+Phase 5/7: Fixing table and database names
+Phase 6/7: Checking and upgrading tables
+Processing databases
+information_schema
+mtr
+mtr.global_suppressions                            OK
+mtr.test_suppressions                              OK
+performance_schema
+test
+test.mysql_json_test                               Needs upgrade
+test.mysql_json_test_big                           Needs upgrade
+test.tempty                                        Needs upgrade
+
+Repairing tables
+test.mysql_json_test                               OK
+test.mysql_json_test_big                           OK
+test.tempty                                        OK
+Phase 7/7: Running 'FLUSH PRIVILEGES'
+OK
+#
+# Now check if the table structure is correct and that the data
+# is still present.
+#
+show create table tempty;
+Table	Create Table
+tempty	CREATE TABLE `tempty` (
+  `t` longtext CHARACTER SET utf8mb4 COLLATE utf8mb4_bin DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+show create table mysql_json_test;
+Table	Create Table
+mysql_json_test	CREATE TABLE `mysql_json_test` (
+  `description` varchar(100) COLLATE utf8mb4_unicode_ci DEFAULT NULL,
+  `expected` longtext COLLATE utf8mb4_unicode_ci DEFAULT NULL,
+  `actual` longtext CHARACTER SET utf8mb4 COLLATE utf8mb4_bin DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci
+show create table mysql_json_test_big;
+Table	Create Table
+mysql_json_test_big	CREATE TABLE `mysql_json_test_big` (
+  `description` varchar(100) COLLATE utf8mb4_unicode_ci DEFAULT NULL,
+  `expected` longtext COLLATE utf8mb4_unicode_ci DEFAULT NULL,
+  `actual` longtext CHARACTER SET utf8mb4 COLLATE utf8mb4_bin DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci
+select count(*) as 'Total_Number_of_Tests',
+sum(expected = actual) as 'Succesful_Tests',
+sum(JSON_VALID(actual)) as 'String_is_valid_JSON'
+from mysql_json_test;
+Total_Number_of_Tests	Succesful_Tests	String_is_valid_JSON
+100	100	100
+select count(*) as 'Total_Number_of_Tests',
+sum(expected = actual) as 'Succesful_Tests',
+sum(JSON_VALID(actual)) as 'String_is_valid_JSON'
+from mysql_json_test_big;
+Total_Number_of_Tests	Succesful_Tests	String_is_valid_JSON
+1	1	1
+drop table tempty;
+drop table mysql_json_test;
+drop table mysql_json_test_big;
+uninstall soname 'type_mysql_json.so';

mysql-test/main/mysql_upgrade_mysql_json_datatype.test

+-- source include/mysql_upgrade_preparation.inc
+-- source include/have_working_dns.inc
+-- source include/have_innodb.inc
+
+call mtr.add_suppression("Table rebuild required");
+call mtr.add_suppression("is marked as crashed");
+call mtr.add_suppression("Checking");
+
+let $MYSQLD_DATADIR= `select @@datadir`;
+SET NAMES utf8;
+
+--copy_file std_data/mysql_json/tempty.frm $MYSQLD_DATADIR/test/tempty.frm
+--copy_file std_data/mysql_json/tempty.MYI $MYSQLD_DATADIR/test/tempty.MYI
+--copy_file std_data/mysql_json/tempty.MYD $MYSQLD_DATADIR/test/tempty.MYD
+
+--copy_file std_data/mysql_json/mysql_json_test.frm $MYSQLD_DATADIR/test/mysql_json_test.frm
+--copy_file std_data/mysql_json/mysql_json_test.MYI $MYSQLD_DATADIR/test/mysql_json_test.MYI
+--copy_file std_data/mysql_json/mysql_json_test.MYD $MYSQLD_DATADIR/test/mysql_json_test.MYD
+
+--copy_file std_data/mysql_json/mysql_json_test_big.frm $MYSQLD_DATADIR/test/mysql_json_test_big.frm
+--copy_file std_data/mysql_json/mysql_json_test_big.MYI $MYSQLD_DATADIR/test/mysql_json_test_big.MYI
+--copy_file std_data/mysql_json/mysql_json_test_big.MYD $MYSQLD_DATADIR/test/mysql_json_test_big.MYD
+
+
+set sql_mode="";
+
+--eval install soname '$TYPE_MYSQL_JSON_SO'
+
+--error ER_TABLE_NEEDS_REBUILD
+show create table tempty;
+--error ER_TABLE_NEEDS_REBUILD
+show create table mysql_json_test;
+--error ER_TABLE_NEEDS_REBUILD
+show create table mysql_json_test_big;
+
+--echo # Run mysql_upgrade to fix the tables containing JSON.
+--exec $MYSQL_UPGRADE --force 2>&1
+
+--echo #
+--echo # Now check if the table structure is correct and that the data
+--echo # is still present.
+--echo #
+
+show create table tempty;
+show create table mysql_json_test;
+show create table mysql_json_test_big;
+
+select count(*) as 'Total_Number_of_Tests',
+sum(expected = actual) as 'Succesful_Tests',
+sum(JSON_VALID(actual)) as 'String_is_valid_JSON'
+from mysql_json_test;
+
+select count(*) as 'Total_Number_of_Tests',
+sum(expected = actual) as 'Succesful_Tests',
+sum(JSON_VALID(actual)) as 'String_is_valid_JSON'
+from mysql_json_test_big;
+
+drop table tempty;
+drop table mysql_json_test;
+drop table mysql_json_test_big;
+
+--eval uninstall soname '$TYPE_MYSQL_JSON_SO'
+--remove_file $MYSQLD_DATADIR/mysql_upgrade_info

plugin/type_mysql_json/CMakeLists.txt

+# Copyright (c) 2020, MariaDB Foundation.
+# 
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; version 2 of the License.
+# 
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+# 
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1335  USA
+
+MYSQL_ADD_PLUGIN(type_mysql_json
+                 mysql_json.cc type.cc
+                 MODULE_ONLY RECOMPILE_FOR_EMBEDDED)

plugin/type_mysql_json/mysql_json.h

+/*
+  Copyright (c) 2015, 2016, Oracle and/or its affiliates. All rights reserved.
+  Copyright (c) 2020 MariaDB Foundation
+
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; version 2 of the License.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1335  USA */
+
+#ifndef MYSQL_JSON_INCLUDED
+#define MYSQL_JSON_INCLUDED
+
+#include "my_global.h"
+#include "sql_string.h"                         // String
+
+enum JSONB_TYPES {
+  JSONB_TYPE_SMALL_OBJECT= 0x0,
+  JSONB_TYPE_LARGE_OBJECT= 0x1,
+  JSONB_TYPE_SMALL_ARRAY=  0x2,
+  JSONB_TYPE_LARGE_ARRAY=  0x3,
+  JSONB_TYPE_LITERAL=      0x4,
+  JSONB_TYPE_INT16=        0x5,
+  JSONB_TYPE_UINT16=       0x6,
+  JSONB_TYPE_INT32=        0x7,
+  JSONB_TYPE_UINT32=       0x8,
+  JSONB_TYPE_INT64=        0x9,
+  JSONB_TYPE_UINT64=       0xA,
+  JSONB_TYPE_DOUBLE=       0xB,
+  JSONB_TYPE_STRING=       0xC,
+  JSONB_TYPE_OPAQUE=       0xF
+};
+
+bool parse_mysql_json_value(String *buffer, JSONB_TYPES type, const uchar *data,
+                            size_t len, size_t depth);
+#endif  /* MYSQL_JSON_INCLUDED */

plugin/type_mysql_json/type.cc

+/*
+   Copyright (c) 2020 MariaDB Foundation
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; version 2 of the License.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1335  USA */
+
+#include <mysql/plugin_data_type.h>
+#include <my_global.h>
+#include <sql_type.h>
+#include <field.h>
+#include <mysqld_error.h>
+#include "mysql_json.h"
+
+static const LEX_CSTRING empty_clex_str= {"", 0};
+
+class Type_handler_mysql_json: public Type_handler_blob
+{
+public:
+  Field *make_conversion_table_field(MEM_ROOT *, TABLE *, uint, const Field *)
+    const override;
+  const Type_collection *type_collection() const override;
+  Field *make_table_field_from_def(TABLE_SHARE *, MEM_ROOT *,
+                                   const LEX_CSTRING *, const Record_addr &,
+                                   const Bit_addr &,
+                                   const Column_definition_attributes *,
+                                   uint32) const override;
+  Field *make_table_field(MEM_ROOT *, const LEX_CSTRING *,
+                          const Record_addr &, const Type_all_attributes &,
+                          TABLE_SHARE *) const override;
+};
+
+Type_handler_mysql_json type_handler_mysql_json;
+
+
+class Field_mysql_json: public Field_blob
+{
+public:
+  Field_mysql_json(uchar *ptr_arg, uchar *null_ptr_arg,
+                   uchar null_bit_arg, enum utype unireg_check_arg,
+                   const LEX_CSTRING *field_name_arg, TABLE_SHARE *share,
+                   uint blob_pack_length, const DTCollation &collation)
+    : Field_blob(ptr_arg, null_ptr_arg, null_bit_arg, unireg_check_arg,
+                 field_name_arg, share, blob_pack_length,
+                 &my_charset_utf8mb4_bin)
+  {}
+
+  String *val_str(String *val_buffer, String *val_str);
+  const Type_handler *type_handler() const { return &type_handler_mysql_json; }
+  bool parse_mysql(String *dest, const char *data, size_t length) const;
+  bool send(Protocol *protocol) { return Field::send(protocol); }
+  void sql_type(String &s) const
+  { s.set_ascii(STRING_WITH_LEN("json /* MySQL 5.7 */")); }
+  /* this will make ALTER TABLE to consider it different from built-in field */
+  Compression_method *compression_method() const { return (Compression_method*)1; }
+};
+
+Field *Type_handler_mysql_json::make_conversion_table_field(MEM_ROOT *root,
+                    TABLE *table, uint metadata, const Field *target) const
+{
+  uint pack_length= metadata & 0x00ff;
+  if (pack_length < 1 || pack_length > 4)
+    return NULL; // Broken binary log?
+  return new (root)
+         Field_mysql_json(NULL, (uchar *) "", 1, Field::NONE, &empty_clex_str,
+                          table->s, pack_length, target->charset());
+}
+
+Field *Type_handler_mysql_json::make_table_field_from_def(TABLE_SHARE *share,
+                 MEM_ROOT *root, const LEX_CSTRING *name,
+                 const Record_addr &addr, const Bit_addr &bit,
+                 const Column_definition_attributes *attr, uint32 flags) const
+{
+  return new (root) Field_mysql_json(addr.ptr(), addr.null_ptr(),
+                 addr.null_bit(), attr->unireg_check, name, share,
+                 attr->pack_flag_to_pack_length(), attr->charset);
+}
+
+
+Field *Type_handler_mysql_json::make_table_field(MEM_ROOT *root,
+                 const LEX_CSTRING *name, const Record_addr &addr,
+                 const Type_all_attributes &attr, TABLE_SHARE *share) const
+{
+  return new (root) Field_mysql_json(addr.ptr(), addr.null_ptr(),
+                 addr.null_bit(), Field::NONE, name, share, 2, attr.collation);
+}
+
+
+String *Field_mysql_json::val_str(String *val_buffer, String *val_ptr)
+{
+  String *raw_value= Field_blob::val_str(val_buffer, val_ptr);
+  String data;
+
+  data.copy(*raw_value);
+
+  val_ptr->length(0);
+  if (parse_mysql(val_ptr, data.ptr(), data.length()))
+  {
+    val_ptr->length(0);
+    my_printf_error(ER_UNKNOWN_ERROR,
+        "Error parsing MySQL JSON format, please dump this table from MySQL "
+        "and then restore it to be able to use it in MariaDB.", MYF(0));
+  }
+  return val_ptr;
+}
+
+bool Field_mysql_json::parse_mysql(String *dest,
+                                   const char *data, size_t length) const
+{
+  if (!data)
+    return false;
+
+  /* Each JSON blob must start with a type specifier. */
+  if (length < 2)
+    return true;
+
+  if (parse_mysql_json_value(dest, static_cast<JSONB_TYPES>(data[0]),
+                             reinterpret_cast<const uchar*>(data) + 1,
+                             length - 1, 0))
+    return true;
+
+  return false;
+}
+
+class Type_collection_mysql_json: public Type_collection
+{
+public:
+  const Type_handler *aggregate_for_result(const Type_handler *a,
+                                           const Type_handler *b)
+                                           const override
+  {
+    if (a == b)
+      return a;
+    return NULL;
+  }
+
+  const Type_handler *aggregate_for_min_max(const Type_handler *a,
+                                            const Type_handler *b)
+                                            const override
+  {
+    return aggregate_for_result(a, b);
+  }
+
+  const Type_handler *aggregate_for_comparison(const Type_handler *a,
+                                               const Type_handler *b)
+                                               const override
+  {
+    return aggregate_for_result(a, b);
+  }
+
+  const Type_handler *aggregate_for_num_op(const Type_handler *a,
+                                           const Type_handler *b)
+                                           const override
+  {
+    return NULL;
+  }
+
+  const Type_handler *handler_by_name(const LEX_CSTRING &name) const override
+  {
+    if (type_handler_mysql_json.name().eq(name))
+      return &type_handler_mysql_json;
+    return NULL;
+  }
+};
+
+const Type_collection *Type_handler_mysql_json::type_collection() const
+{
+  static Type_collection_mysql_json type_collection_mysql_json;
+  return &type_collection_mysql_json;
+}
+
+static struct st_mariadb_data_type plugin_descriptor_type_mysql_json=
+{
+  MariaDB_DATA_TYPE_INTERFACE_VERSION,
+  &type_handler_mysql_json
+};
+
+maria_declare_plugin(type_mysql_json)
+{
+  MariaDB_DATA_TYPE_PLUGIN,
+  &plugin_descriptor_type_mysql_json,
+  "MYSQL_JSON",
+  "Anel Husaković, Vicențiu Ciorbaru",
+  "Data type MYSQL_JSON",
+  PLUGIN_LICENSE_GPL,
+  0,
+  0,
+  0x0001,
+  NULL,
+  NULL,
+  "0.1",
+  MariaDB_PLUGIN_MATURITY_ALPHA
+}
+maria_declare_plugin_end;

sql/table.cc

@@ -2367,7 +2367,8 @@ int TABLE_SHARE::init_from_binary_frm_image(THD *thd, bool write,
 	comment_pos+=   comment_length;
       }
 
-      if ((uchar) strpos[13] == (uchar) MYSQL_TYPE_VIRTUAL)
+      if ((uchar) strpos[13] == (uchar) MYSQL_TYPE_VIRTUAL
+          && likely(share->mysql_version >= 100000))
       {
         /*
           MariaDB version 10.0 version.
@@ -2417,7 +2418,18 @@ int TABLE_SHARE::init_from_binary_frm_image(THD *thd, bool write,
         interval_nr=  (uint) strpos[12];
         enum_field_types field_type= (enum_field_types) strpos[13];
         if (!(handler= Type_handler::get_handler_by_real_type(field_type)))
-          goto err; // Not supported field type
+        {
+          if (field_type == 245 &&
+              share->mysql_version >= 50700) // a.k.a MySQL 5.7 JSON
+          {
+            share->incompatible_version|= HA_CREATE_USED_ENGINE;
+            const LEX_CSTRING mysql_json{STRING_WITH_LEN("MYSQL_JSON")};
+            handler= Type_handler::handler_by_name_or_error(thd, mysql_json);
+          }
+
+          if (!handler)
+            goto err; // Not supported field type
+        }
         handler= handler->type_handler_frm_unpack(strpos);
         if (handler->Column_definition_attributes_frm_unpack(&attr, share,
                                                              strpos,