MDEV-11441 Server crashes in String::append /Item_func_json_extract::val_str.

        Wrong 'value_lengh' taken

mysql-test/r/func_json.result

@@ -90,7 +90,7 @@ json_contains_path('{"key1":1, "key2":[2,3]}', "aLl", "$.key1", "$.key2")
 1
 select json_extract('{"key1":"asd", "key2":[2,3]}', "$.key1");
 json_extract('{"key1":"asd", "key2":[2,3]}', "$.key1")
-asd
+"asd"
 select json_extract('{"key1":"asd", "key2":[2,3]}', "$.keyX", "$.keyY");
 json_extract('{"key1":"asd", "key2":[2,3]}', "$.keyX", "$.keyY")
 NULL
@@ -102,7 +102,10 @@ json_extract('{"key1":5, "key2":[2,3]}', "$.key1", "$.key2")
 [5, [2,3]]
 select json_extract('{"key0":true, "key1":"qwe"}', "$.key1");
 json_extract('{"key0":true, "key1":"qwe"}', "$.key1")
-qwe
+"qwe"
+select json_extract(json_object('foo', 'foobar'),'$');
+json_extract(json_object('foo', 'foobar'),'$')
+{"foo": "foobar"}
 select json_insert('{"a":1, "b":{"c":1}, "d":[1, 2]}', '$.b.k1', 'word');
 json_insert('{"a":1, "b":{"c":1}, "d":[1, 2]}', '$.b.k1', 'word')
 {"a":1, "b":{"c":1, "k1":"word"}, "d":[1, 2]}

mysql-test/t/func_json.test

@@ -41,6 +41,7 @@ select json_extract('{"key1":"asd", "key2":[2,3]}', "$.keyX", "$.keyY");
 select json_extract('{"key1":"asd", "key2":[2,3]}', "$.key1", "$.key2");
 select json_extract('{"key1":5, "key2":[2,3]}', "$.key1", "$.key2");
 select json_extract('{"key0":true, "key1":"qwe"}', "$.key1");
+select json_extract(json_object('foo', 'foobar'),'$');
 
 select json_insert('{"a":1, "b":{"c":1}, "d":[1, 2]}', '$.b.k1', 'word');
 select json_insert('{"a":1, "b":{"c":1}, "d":[1, 2]}', '$.d[3]', 3);

sql/item_jsonfunc.cc

@@ -427,8 +427,8 @@ String *Item_func_json_extract::val_str(String *str)
   json_engine_t je;
   bool multiple_values_found= FALSE;
   const uchar *value;
-  const char *first_value= NULL, *first_p_value;
-  uint n_arg, v_len, first_len, first_p_len;
+  const char *first_value= NULL;
+  uint n_arg, v_len, first_len;
   uint array_counters[JSON_DEPTH_LIMIT];
 
   if ((null_value= args[0]->null_value))
@@ -487,13 +487,6 @@ String *Item_func_json_extract::val_str(String *str)
         */
         first_value= (const char *) value;
         first_len= v_len;
-        /*
-         We need this as we have to preserve quotes around string
-          constants if we use the value to create an array. Otherwise
-          we get the value without the quotes.
-        */
-        first_p_value= (const char *) je.value;
-        first_p_len= je.value_len;
         continue;
       }
       else
@@ -519,7 +512,7 @@ String *Item_func_json_extract::val_str(String *str)
 
   if (multiple_values_found ?
         str->append("]") :
-        str->append(first_p_value, first_p_len))
+        str->append(first_value, first_len))
     goto error; /* Out of memory. */
 
   return str;