Regression: LOAD DATA INFILE lost BLOB support using utf8 load files

https://github.com/mysql/mysql-server/commit/774e6ffd0897dd763763b69e15028c1fbd44c4e7 changed the way, load data infile parses the data.

The commit starts validating the whole load file using the file character set. BLOBs have always been copied 1:1 (no character set translations - only escape sequences are processed). If the load file is using UTF-8, blob columns can never be encoded in UTF-8, as binary data can contain character sequences, which are invalid UTF-8 and there is no charset conversion.

Starting with this commit, LOAD DATA rejects non-UTF8 sequences in blob fields.

Create a test file:

$ hexdump -C test

00000000  22 25 aa ab ac 22 0a                              |"%ª«¬".|

CREATE TABLE `x` ( `y` mediumblob NOT NULL) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_general_ci;

load data local infile 'test'  into table x charset utf8 FIELDS TERMINATED BY ';' ENCLOSED BY '"' ESCAPED BY '\\' LINES TERMINATED BY '\n';

This will lead to:

ERROR 1300 (HY000): Invalid utf8 character string: '"%'

Older MariaDB 10.0.X releases can load this file.