package dhcpd import ( "fmt" "net" "time" "github.com/AdguardTeam/golibs/log" ) // ipVersion is a documentational alias for int. Use it when the integer means // IP version. type ipVersion = int // IP version constants. const ( ipVersion4 ipVersion = 4 ipVersion6 ipVersion = 6 ) // netIface is the interface for network interface methods. type netIface interface { Addrs() ([]net.Addr, error) } // ifaceIPAddrs returns the interface's IP addresses. func ifaceIPAddrs(iface netIface, ipv ipVersion) (ips []net.IP, err error) { addrs, err := iface.Addrs() if err != nil { return nil, err } for _, a := range addrs { var ip net.IP switch a := a.(type) { case *net.IPAddr: ip = a.IP case *net.IPNet: ip = a.IP default: continue } // Assume that net.(*Interface).Addrs can only return valid IPv4 // and IPv6 addresses. Thus, if it isn't an IPv4 address, it // must be an IPv6 one. switch ipv { case ipVersion4: if ip4 := ip.To4(); ip4 != nil { ips = append(ips, ip4) } case ipVersion6: if ip6 := ip.To4(); ip6 == nil { ips = append(ips, ip) } default: return nil, fmt.Errorf("invalid ip version %d", ipv) } } return ips, nil } // Currently used defaults for ifaceDNSAddrs. const ( defaultMaxAttempts int = 10 defaultBackoff time.Duration = 500 * time.Millisecond ) // ifaceDNSIPAddrs returns IP addresses of the interface suitable to send to // clients as DNS addresses. If err is nil, addrs contains either no addresses // or at least two. // // It makes up to maxAttempts attempts to get the addresses if there are none, // each time using the provided backoff. Sometimes an interface needs a few // seconds to really ititialize. // // See https://github.com/AdguardTeam/AdGuardHome/issues/2304. func ifaceDNSIPAddrs( iface netIface, ipv ipVersion, maxAttempts int, backoff time.Duration, ) (addrs []net.IP, err error) { var n int for n = 1; n <= maxAttempts; n++ { addrs, err = ifaceIPAddrs(iface, ipv) if err != nil { return nil, fmt.Errorf("getting ip addrs: %w", err) } if len(addrs) > 0 { break } log.Debug("dhcpv%d: attempt %d: no ip addresses", ipv, n) time.Sleep(backoff) } switch len(addrs) { case 0: // Don't return errors in case the users want to try and enable // the DHCP server later. t := time.Duration(n) * backoff log.Error("dhcpv%d: no ip for iface after %d attempts and %s", ipv, n, t) return nil, nil case 1: // Some Android devices use 8.8.8.8 if there is not a secondary // DNS server. Fix that by setting the secondary DNS address to // the same address. // // See https://github.com/AdguardTeam/AdGuardHome/issues/1708. log.Debug("dhcpv%d: setting secondary dns ip to itself", ipv) addrs = append(addrs, addrs[0]) default: // Go on. } log.Debug("dhcpv%d: got addresses %s after %d attempts", ipv, addrs, n) return addrs, nil }