How to get data from a LONGTEXT to perform string operations

Question

I have some MariaDB code, which I'm fairly new to. I'm a seasoned MSSQL developer, however. I have a script with a variable which I'm setting to what will eventually be the contents of a file. This it is 51k characters long and ends up being a LONGTEXT. I have determined this by putting it into a temp table and checking the resulting datatype. Basically I'm taking the file contents and turning it into lines of data for subsequent processing.

My code looks like this:

    SET @FileData = <51k chars of text>;

    SET @LineIndex = 1;
    SET @FileDataLen = LENGTH(@FileData);
    WHILE @FileDataLen > 0 DO
        SET @Chunk = LEFT(@FileData, 1000);
        SET @Pos = INSTR(@Chunk, "\r\n");
        IF (@Pos = 1) THEN
            SET @LineData = "";
            SET @FileData = SUBSTRING(@FileData, 3); -- skip the CRLF
        ELSE
            SET @LineData = LEFT(@FileData, @Pos);
            SET @FileData = SUBSTRING(@FileData, @Pos+2);
        END IF;
        
        INSERT INTO TextFileLine
            (TextFileID,
            LineIndex,
            LineValue)
        VALUES  (@TextFileID,
            @LineIndex,
            @LineData);
            
        SET @LineIndex = @LineIndex + 1;
        SET @FileDataLen = LENGTH(@FileData);
    END WHILE;

I'm getting the error (that stunningly informative error, which appear to be the only one that MariaDB is capable of generating): "You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near '' at line 2".

Query: WHILE @FileDataLen > 0 DO SET @Chunk = LEFT(@FileData, 1000)

Is it to do with my WHILE loop? Is it to do with using LEFT on LONGTEXT? I've tried fiddling around with both statements to no avail.

Thanks for any help provided.