CI 2.1.2 - Unable to upload XML...

[eluser]Narf[/eluser]
The most recent ones of the mentioned topics would probably have comments saying that MIME-type detection depends on the server environment and it is not 100% guaranteed to be correct - that's just not possible to achieve. What you can do is to check what each of these methods say the type is and add it to config/mimes.php:

Code:

//Method 1:
$finfo = finfo_open(FINFO_MIME);
var_dump(finfo_file($finfo, '/path/to/your/file.xml');
finfo_close($finfo);

// Method 2:
file --mime /path/to/your/file.xml // (run in shell command line, on your host)

// Method 3:
var_dump(mime_content_type('/path/to/your/file.xml'));