code: func Any() Interface {
  	// TODO: attempt to discover whether the local machine has an
  	// Internet-class address. Return ExtIP in this case.
  	return startautodisc("UPnP or NAT-PMP", func() Interface {
  		found := make(chan Interface, 2)
  		go func() { found <- discoverUPnP() }()
  		go func() { found <- discoverPMP() }()
  		for i := 0; i < cap(found); i++ {
  			if c := <-found; c != nil {
  				return c
  			}
  		}
  		return nil
  	})
  }
docs: // Any returns a port mapper that tries to discover any supported
  // mechanism on the local network.