MDEV-27412: JSON_TABLE doesn't properly unquote strings

Analysis:
The value gets appended as string instead of unescaped json value

Fix:
Append the value of json in a temporary string and then store it in the
field instead of directly storing as string.

mysql-test/main/func_json.result

@@ -1757,5 +1757,14 @@ JSON_INSERT(JSON_OBJECT(l1, l2, l3, l4), '$.k3', 'v3')	JSON_SET(JSON_OBJECT(l1,
 {"k1": "v1", "k2": "v2", "k3": "v3"}	{"k1": "v1", "k2": "new v2"}	{"k1": "v1", "k2": "new v2"}
 DROP TABLE t;
 #
+# MDEV-27412: JSON_TABLE doesn't properly unquote strings
+#
+SET @data = '[{"Data": "<root language=\\"de\\"></root>"}]';
+SELECT
+data
+FROM JSON_TABLE (@data, '$[*]' COLUMNS (data text PATH '$.Data')) AS t;
+data
+<root language="de"></root>
+#
 # End of 10.6 tests
 #

mysql-test/main/func_json.test

@@ -1189,6 +1189,18 @@ SELECT JSON_ARRAY_APPEND(JSON_ARRAY(l1, l2, l3, l4), '$[0]', 'k3'), JSON_ARRAY_I
 SELECT JSON_INSERT(JSON_OBJECT(l1, l2, l3, l4), '$.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 # MDEV-27412: JSON_TABLE doesn't properly unquote strings
+--echo #
+
+
+SET @data = '[{"Data": "<root language=\\"de\\"></root>"}]';
+
+SELECT
+  data
+FROM JSON_TABLE (@data, '$[*]' COLUMNS (data text PATH '$.Data')) AS t;
+
 --echo #
 --echo # End of 10.6 tests
 --echo #

sql/item_func.h

@@ -35,6 +35,8 @@ extern "C"				/* Bug in BSDI include file */
 #include <cmath>
 
 
+extern int st_append_json(String *s,
+             CHARSET_INFO *json_cs, const uchar *js, uint js_len);
 class Item_func :public Item_func_or_sum
 {
   void sync_with_sum_func_and_with_field(List<Item> &list);

sql/item_jsonfunc.cc

@@ -79,7 +79,7 @@ static inline bool append_simple(String *s, const uchar *a, size_t a_len)
   Appends JSON string to the String object taking charsets in
   consideration.
 */
-static int st_append_json(String *s,
+int st_append_json(String *s,
              CHARSET_INFO *json_cs, const uchar *js, uint js_len)
 {
   int str_len= js_len * s->charset()->mbmaxlen;

sql/json_table.cc

@@ -380,6 +380,8 @@ int ha_json_table::rnd_init(bool scan)
 
 static void store_json_in_field(Field *f, const json_engine_t *je)
 {
+  String res_tmp("", 0, je->s.cs);
+
   switch (je->value_type)
   {
   case JSON_VALUE_NULL:
@@ -400,7 +402,8 @@ static void store_json_in_field(Field *f, const json_engine_t *je)
   default:
     break;
   };
-  f->store((const char *) je->value, (uint32) je->value_len, je->s.cs);
+  st_append_json(&res_tmp, je->s.cs, je->value, je->value_len);
+  f->store((const char *) res_tmp.ptr(), (uint32) res_tmp.length(), je->s.cs);
 }