CommandHandler for the STOU command. Handler logic:
- If the user has not logged in, then reply with 530 and terminate
- Create new unique filename within the current directory
- If the current user does not have write access to the named file, if it already exists, or else to its
parent directory, then reply with 553 and terminate
- If the current user does not have execute access to the parent directory, then reply with 553 and terminate
- Send an initial reply of 150
- Read all available bytes from the data connection and write out to the unique file in the server file system
- If file write/store fails, then reply with 553 and terminate
- Send a final reply with 226, along with the new unique filename