Feature: add dhcp type dns client (#1509)

component/dhcp/conn.go

@@ -0,0 +1,18 @@
+package dhcp
+
+import (
+	"context"
+	"net"
+	"runtime"
+
+	"github.com/Dreamacro/clash/component/dialer"
+)
+
+func ListenDHCPClient(ctx context.Context, ifaceName string) (net.PacketConn, error) {
+	listenAddr := "0.0.0.0:68"
+	if runtime.GOOS == "linux" || runtime.GOOS == "android" {
+		listenAddr = "255.255.255.255:68"
+	}
+
+	return dialer.ListenPacket(ctx, "udp4", listenAddr, dialer.WithInterface(ifaceName), dialer.WithAddrReuse(true))
+}

component/dhcp/dhcp.go

@@ -0,0 +1,94 @@
+package dhcp
+
+import (
+	"context"
+	"errors"
+	"math/rand"
+	"net"
+
+	"github.com/insomniacslk/dhcp/dhcpv4"
+)
+
+var (
+	ErrNotResponding = errors.New("DHCP not responding")
+	ErrNotFound      = errors.New("DNS option not found")
+)
+
+func ResolveDNSFromDHCP(context context.Context, ifaceName string) ([]net.IP, error) {
+	conn, err := ListenDHCPClient(context, ifaceName)
+	if err != nil {
+		return nil, err
+	}
+	defer conn.Close()
+
+	result := make(chan []net.IP, 1)
+
+	discovery, err := dhcpv4.NewDiscovery(randomHardware(), dhcpv4.WithBroadcast(true), dhcpv4.WithRequestedOptions(dhcpv4.OptionDomainNameServer))
+	if err != nil {
+		return nil, err
+	}
+
+	go receiveOffer(conn, discovery.TransactionID, result)
+
+	_, err = conn.WriteTo(discovery.ToBytes(), &net.UDPAddr{IP: net.IPv4bcast, Port: 67})
+	if err != nil {
+		return nil, err
+	}
+
+	select {
+	case r, ok := <-result:
+		if !ok {
+			return nil, ErrNotFound
+		}
+		return r, nil
+	case <-context.Done():
+		return nil, ErrNotResponding
+	}
+}
+
+func receiveOffer(conn net.PacketConn, id dhcpv4.TransactionID, result chan<- []net.IP) {
+	defer close(result)
+
+	buf := make([]byte, dhcpv4.MaxMessageSize)
+
+	for {
+		n, _, err := conn.ReadFrom(buf)
+		if err != nil {
+			return
+		}
+
+		pkt, err := dhcpv4.FromBytes(buf[:n])
+		if err != nil {
+			continue
+		}
+
+		if pkt.MessageType() != dhcpv4.MessageTypeOffer {
+			continue
+		}
+
+		if pkt.TransactionID != id {
+			continue
+		}
+
+		dns := pkt.DNS()
+		if len(dns) == 0 {
+			return
+		}
+
+		result <- dns
+
+		return
+	}
+}
+
+func randomHardware() net.HardwareAddr {
+	addr := make(net.HardwareAddr, 6)
+
+	addr[0] = 0xff
+
+	for i := 1; i < len(addr); i++ {
+		addr[i] = byte(rand.Intn(254) + 1)
+	}
+
+	return addr
+}