Léo Le Bouter via Bug reports for GNU Guix 写道：
> Should we explicitly check if we are over an IPv6 connection 
> instead?
> Is that possible?

My FTP knowledge is about two decades out of date: does an IPv6 
server (de facto) have to support EPSV?

The ‘right’ way would be to send the FEAT command, and check 
whether the server actually supports EPSV.  A bit more 
heavy-weight than your heuristic.

Kind regards,

T G-R