MDEV-29264: JSON function overflow error based on LONGTEXT field

Analysis: The JSON functions(JSON_ARRAY[OBJECT|ARRAY_APPEND|ARRAY_INSERT|INSERT|SET|REPLACE]) result is truncated when the function is called based on LONGTEXT field. The overflow occurs when computing the result length due to the LONGTEXT max length is same as uint32 max length. It lead to wrong result length.
Fix: Add static_cast<ulonglong> to avoid uint32 overflow and fix the arguments used.

mysql-test/main/func_json.result

@@ -822,7 +822,7 @@ CREATE TABLE t2 SELECT JSON_ARRAY_INSERT(fld, '$.[0]', '0') FROM t1;
 SHOW CREATE TABLE t2;
 Table	Create Table
 t2	CREATE TABLE `t2` (
-  `JSON_ARRAY_INSERT(fld, '$.[0]', '0')` varchar(25) DEFAULT NULL
+  `JSON_ARRAY_INSERT(fld, '$.[0]', '0')` varchar(21) DEFAULT NULL
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1
 DROP TABLE t1, t2;
 SET sql_mode=default;
@@ -1437,5 +1437,20 @@ f
 DROP VIEW v;
 DROP TABLE t;
 #
+# MDEV-29264 JSON functions overflow error based ON LONGTEXT field
+#
+CREATE TABLE t(l1 LONGTEXT, l2 LONGTEXT, l3 LONGTEXT, l4 LONGTEXT);
+INSERT INTO t VALUES('k1', 'v1', 'k2', 'v2');
+SELECT JSON_ARRAY(l1, l2, l3, l4), JSON_OBJECT(l1, l2, l3, l4) from t;
+JSON_ARRAY(l1, l2, l3, l4)	JSON_OBJECT(l1, l2, l3, l4)
+["k1", "v1", "k2", "v2"]	{"k1": "v1", "k2": "v2"}
+SELECT JSON_ARRAY_APPEND(JSON_ARRAY(l1, l2, l3, l4), '$[0]', 'k3'), JSON_ARRAY_INSERT(JSON_ARRAY(l1, l2, l3, l4), '$[0]', 'k3') from t;
+JSON_ARRAY_APPEND(JSON_ARRAY(l1, l2, l3, l4), '$[0]', 'k3')	JSON_ARRAY_INSERT(JSON_ARRAY(l1, l2, l3, l4), '$[0]', 'k3')
+[["k1", "k3"], "v1", "k2", "v2"]	["k3", "k1", "v1", "k2", "v2"]
+SELECT JSON_INSERT(JSON_OBJECT(l1, l2, l3, l4), '$.k3', 'v3'),JSON_SET(JSON_OBJECT(l1, l2, l3, l4), '$.k2', 'new v2'),JSON_REPLACE(JSON_OBJECT(l1, l2, l3, l4), '$.k2', 'new v2') from t;
+JSON_INSERT(JSON_OBJECT(l1, l2, l3, l4), '$.k3', 'v3')	JSON_SET(JSON_OBJECT(l1, l2, l3, l4), '$.k2', 'new v2')	JSON_REPLACE(JSON_OBJECT(l1, l2, l3, l4), '$.k2', 'new v2')
+{"k1": "v1", "k2": "v2", "k3": "v3"}	{"k1": "v1", "k2": "new v2"}	{"k1": "v1", "k2": "new v2"}
+DROP TABLE t;
+#
 # End of 10.5 tests
 #

mysql-test/main/func_json.test

@@ -927,6 +927,17 @@ SELECT JSON_ARRAYAGG(a) AS f FROM v;
 DROP VIEW v;
 DROP TABLE t;
 
+
+--echo #
+--echo # MDEV-29264 JSON functions overflow error based ON LONGTEXT field
+--echo #
+CREATE TABLE t(l1 LONGTEXT, l2 LONGTEXT, l3 LONGTEXT, l4 LONGTEXT);
+INSERT INTO t VALUES('k1', 'v1', 'k2', 'v2');
+SELECT JSON_ARRAY(l1, l2, l3, l4), JSON_OBJECT(l1, l2, l3, l4) from t;
+SELECT JSON_ARRAY_APPEND(JSON_ARRAY(l1, l2, l3, l4), '$[0]', 'k3'), JSON_ARRAY_INSERT(JSON_ARRAY(l1, l2, l3, l4), '$[0]', 'k3') from t;
+SELECT JSON_INSERT(JSON_OBJECT(l1, l2, l3, l4), '$.k3', 'v3'),JSON_SET(JSON_OBJECT(l1, l2, l3, l4), '$.k2', 'new v2'),JSON_REPLACE(JSON_OBJECT(l1, l2, l3, l4), '$.k2', 'new v2') from t;
+DROP TABLE t;
+
 --echo #
 --echo # End of 10.5 tests
 --echo #

sql/item_jsonfunc.cc

@@ -1738,7 +1738,7 @@ bool Item_func_json_array::fix_length_and_dec()
     return TRUE;
 
   for (n_arg=0 ; n_arg < arg_count ; n_arg++)
-    char_length+= args[n_arg]->max_char_length() + 4;
+    char_length+= static_cast<ulonglong>(args[n_arg]->max_char_length()) + 4;
 
   fix_char_length_ulonglong(char_length);
   tmp_val.set_charset(collation.collation);
@@ -1797,7 +1797,8 @@ bool Item_func_json_array_append::fix_length_and_dec()
   for (n_arg= 1; n_arg < arg_count; n_arg+= 2)
   {
     paths[n_arg/2].set_constant_flag(args[n_arg]->const_item());
-    char_length+= args[n_arg/2+1]->max_char_length() + 4;
+    char_length+=
+        static_cast<ulonglong>(args[n_arg+1]->max_char_length()) + 4;
   }
 
   fix_char_length_ulonglong(char_length);
@@ -2959,7 +2960,8 @@ bool Item_func_json_insert::fix_length_and_dec()
   for (n_arg= 1; n_arg < arg_count; n_arg+= 2)
   {
     paths[n_arg/2].set_constant_flag(args[n_arg]->const_item());
-    char_length+= args[n_arg/2+1]->max_char_length() + 4;
+    char_length+=
+        static_cast<ulonglong>(args[n_arg+1]->max_char_length()) + 4;
   }
 
   fix_char_length_ulonglong(char_length);