You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: sys_unix.go
    path of file: ./repos/goHackTools/vendor/golang.org/x/net/internal/socket
    
    the code of the file until where you have to start completion: // Copyright 2017 The Go Authors. All rights reserved.
// Use of this source code is governed 
    
func addrToSockaddr(a net.Addr) unix.Sockaddr {
	var (
		ip   net.IP
		port int
		zone string
	)
	switch a := a.(type) {
	case *net.TCPAddr:
		ip = a.IP
		port = a.Port
		zone = a.Zone
	case *net.UDPAddr:
		ip = a.IP
		port = a.Port
		zone = a.Zone
	case *net.IPAddr:
		ip = a.IP
		zone = a.Zone
	default:
		return nil
	}

	if ip4 := ip.To4(); ip4 != nil {
		sa := unix.SockaddrInet4{Port: port}
		copy(sa.Addr[:], ip4)
		return &sa
	}

	if ip6 := ip.To16(); ip6 != nil && ip.To4() == nil {
		sa := unix.SockaddrInet6{Port: port}
		copy(sa.Addr[:], ip6)
		if zone != "" {
			sa.ZoneId = uint32(zoneCache.index(zone))
		}
		return &sa
	}

	return nil
}