A mini webserver with FTP support for XXE payloads.
Basic FTP server to receive payloads from instances of XXE. This will record all data received and respond in a manner which ensures the client keeps sending data. This will keep listening until you shut it down, allowing for multiple XXE file retreivals via FTP. Java connections shouldn't hang connecting to this either.
Has a unique "uno port" option, where everything is served from one port. This means you can serve HTTP/HTTPS/FTP over a single port. When a connection is received, the server will work out which protocol was requested, and handle it accordingly. This is not flawless, but works in most cases.