Allow lowercase UTF8 OPTS

[dani-garcia]

The FTP client included in Windows Explorer sends this command in lowercase. Without this patch the server would respond with an invalid command error and the client would refuse to continue.

Wireshark trace for reference:

[hannesdejager]

Nice catch, thanks @dani-garcia

[hannesdejager]

@dani-garcia I was curious whether or not you ran unFTP also on Windows? We're not really testing on Windows, so any feedback would be appreciated.

[dani-garcia]

I've tested the server both in Windows and on Ubuntu, using a custom storage backend based on the provided filesystem storage backend (with some changes for separate folders per user, etc.), and so far it hasn't caused any issues. Everything seems to work correctly on Windows the same way as Ubuntu.

I've noticed only one small quirk on the windows version, and when navigating to subdirectories the Windows \ path separator seems to cause some confusion on the clients. I should mention that it seems to only affect visuals in all the clients I've tested, and the clients work correctly against a Windows-based libunftp server.

On Filezilla, navigating to the directory bar inside the test folder moves you to /test\bar, which the client confuses with a valid folder with name test\bar and so it appears on the tree view.
Left is Windows host, and right is Ubuntu host, both using the same Filezilla client:

On WinSCP, going up a directory, by clicking the .. entry, would just append the \.. to the path instead of deleting the last segment.

I haven't looked into how easy would be to convert the \ separators to / in the response to the PWD command, but it's possible that just changing that would fix it. I'll see if I have some time to check that this weekend.

[hannesdejager]

Super feedback, thanks!