Bug#35924 DEFINER should be stored 'quoted' in I_S

The '@' symbol can not be used in the host name according to rfc952.
The fix:
added function check_host_name(LEX_STRING *str)
which checks that all symbols in host name string are valid and
host name length is not more than max host name length
(just moved check_string_length() function from the parser into check_host_name()).

mysql-test/r/create.result

@@ -1546,6 +1546,8 @@ SHOW INDEX FROM t1;
 Table	Non_unique	Key_name	Seq_in_index	Column_name	Collation	Cardinality	Sub_part	Packed	Null	Index_type	Comment
 t1	1	c1	1	c1	A	NULL	NULL	NULL	YES	BTREE	
 DROP TABLE t1;
+create user mysqltest_1@'test@test';
+ERROR HY000: Malformed hostname (illegal symbol: '@')
 CREATE TABLE t1 (a INTEGER AUTO_INCREMENT PRIMARY KEY, b INTEGER NOT NULL);
 INSERT IGNORE INTO t1 (b) VALUES (5);
 CREATE TABLE IF NOT EXISTS t2 (a INTEGER NOT NULL AUTO_INCREMENT PRIMARY KEY)

mysql-test/t/create.test

@@ -1171,6 +1171,11 @@ CREATE TABLE t1(c1 VARCHAR(33), KEY USING HASH (c1) USING BTREE) ENGINE=MEMORY;
 SHOW INDEX FROM t1;
 DROP TABLE t1;
 
+#
+# Bug#35924 DEFINER should be stored 'quoted' in I_S
+#
+--error ER_UNKNOWN_ERROR
+create user mysqltest_1@'test@test';
 
 #
 # Bug#38821: Assert table->auto_increment_field_not_null failed in open_table()

sql/mysql_priv.h

@@ -614,6 +614,7 @@ LEX_USER *create_definer(THD *thd, LEX_STRING *user_name, LEX_STRING *host_name)
 LEX_USER *get_current_user(THD *thd, LEX_USER *user);
 bool check_string_length(LEX_STRING *str,
                          const char *err_msg, uint max_length);
+bool check_host_name(LEX_STRING *str);
 
 enum enum_mysql_completiontype {
   ROLLBACK_RELEASE=-2, ROLLBACK=1,  ROLLBACK_AND_CHAIN=7,

sql/sql_parse.cc

@@ -7982,3 +7982,35 @@ int test_if_data_home_dir(const char *dir)
 
 C_MODE_END
 
+
+/**
+  Check that host name string is valid.
+
+  @param[in] str string to be checked
+
+  @return             Operation status
+    @retval  FALSE    host name is ok
+    @retval  TRUE     host name string is longer than max_length or
+                      has invalid symbols
+*/
+
+bool check_host_name(LEX_STRING *str)
+{
+  const char *name= str->str;
+  const char *end= str->str + str->length;
+  if (check_string_length(str, ER(ER_HOSTNAME), HOSTNAME_LENGTH))
+    return TRUE;
+
+  while (name != end)
+  {
+    if (*name == '@')
+    {
+      my_printf_error(ER_UNKNOWN_ERROR, 
+                      "Malformed hostname (illegal symbol: '%c')", MYF(0),
+                      *name);
+      return TRUE;
+    }
+    name++;
+  }
+  return FALSE;
+}

sql/sql_yacc.yy

@@ -9269,8 +9269,7 @@ user:
 
 	    if (check_string_length(&$$->user,
                                     ER(ER_USERNAME), USERNAME_LENGTH) ||
-	        check_string_length(&$$->host,
-                                    ER(ER_HOSTNAME), HOSTNAME_LENGTH))
+                check_host_name(&$$->host))
 	      MYSQL_YYABORT;
 	  }
 	| CURRENT_USER optional_braces