DNS is not very helpful in determining the local IP addresses, because a DNS entry is not required to make an IP address work, nor is it required to point to (only) the machine that you happen to run your program on.
Instead, inspect the network interfaces and their configuration:
package main
import (
"fmt"
"log"
"net"
"os"
"text/tabwriter"
)
func main() {
tw := tabwriter.NewWriter(os.Stdout, 0, 0, 1, ' ', 0)
ifaces, err := net.Interfaces()
if err != nil {
log.Fatal(err)
}
for _, iface := range ifaces {
addrs, err := iface.Addrs()
if err != nil {
log.Fatal(err)
}
for _, addr := range addrs {
addr, ok := addr.(*net.IPNet)
if !ok {
// Not an IP interface
continue
}
if addr.IP.To4() != nil {
// Skip IPv4 addresses
continue
}
fmt.Fprintf(tw, "%s\t%s\t%s\t%s
",
iface.Name, addr.String(), addr.IP, addr.Mask)
}
}
tw.Flush()
}
For my local machine the output is:
lo ::1/128 ::1 ffffffffffffffffffffffffffffffff
enp2s0 fe80::52e5:49ff:fe3b:107a/64 fe80::52e5:49ff:fe3b:107a ffffffffffffffff0000000000000000
docker0 fe80::42:afff:fedb:7389/64 fe80::42:afff:fedb:7389 ffffffffffffffff0000000000000000
tun0 fe80::f22c:2d3b:a5a0:1b61/64 fe80::f22c:2d3b:a5a0:1b61 ffffffffffffffff0000000000000000
vethd176f0c fe80::1cc1:65ff:fe39:feff/64 fe80::1cc1:65ff:fe39:feff ffffffffffffffff0000000000000000
Note that these addresses are not necessarily reachable from the Internet. This all depends on how the routing of the hoster works. In any kind of cloud setup, you are almost always better off querying the providers APIs.
To list all /64 subnets in a particular /56 subnet, you have to leave the 56 upper bits of the subnet address as they are and permute the following 64-56 = 8 bits (which happens to be the eigth byte):
package main
import (
"fmt"
"net"
)
func main() {
_, subnet, _ := net.ParseCIDR("2001:db8::/56")
fmt.Println(subnet)
subnet.Mask = net.CIDRMask(64, 128) // change mask to /64
for i := 0; i <= 0xff; i++ {
subnet.IP[7] = byte(i) // permute the 8th byte
fmt.Println("\t", subnet)
}
// Output:
// 2001:db8::/56
// 2001:db8::/64
// 2001:db8:0:1::/64
// 2001:db8:0:2::/64
// 2001:db8:0:3::/64
// 2001:db8:0:4::/64
// 2001:db8:0:5::/64
// 2001:db8:0:6::/64
// 2001:db8:0:7::/64
// 2001:db8:0:8::/64
// [...]
}