Feature: add dhcp type dns client (#1509)

dns/dhcp.go

@@ -0,0 +1,144 @@
+package dns
+
+import (
+	"bytes"
+	"context"
+	"net"
+	"sync"
+	"time"
+
+	"github.com/Dreamacro/clash/component/dhcp"
+	"github.com/Dreamacro/clash/component/iface"
+	"github.com/Dreamacro/clash/component/resolver"
+
+	D "github.com/miekg/dns"
+)
+
+const (
+	IfaceTTL    = time.Second * 20
+	DHCPTTL     = time.Hour
+	DHCPTimeout = time.Minute
+)
+
+type dhcpClient struct {
+	ifaceName string
+
+	lock            sync.Mutex
+	ifaceInvalidate time.Time
+	dnsInvalidate   time.Time
+
+	ifaceAddr *net.IPNet
+	done      chan struct{}
+	resolver  *Resolver
+	err       error
+}
+
+func (d *dhcpClient) Exchange(m *D.Msg) (msg *D.Msg, err error) {
+	ctx, cancel := context.WithTimeout(context.Background(), resolver.DefaultDNSTimeout)
+	defer cancel()
+
+	return d.ExchangeContext(ctx, m)
+}
+
+func (d *dhcpClient) ExchangeContext(ctx context.Context, m *D.Msg) (msg *D.Msg, err error) {
+	res, err := d.resolve(ctx)
+	if err != nil {
+		return nil, err
+	}
+
+	return res.ExchangeContext(ctx, m)
+}
+
+func (d *dhcpClient) resolve(ctx context.Context) (*Resolver, error) {
+	d.lock.Lock()
+
+	invalidated, err := d.invalidate()
+	if err != nil {
+		d.err = err
+	} else if invalidated {
+		done := make(chan struct{})
+
+		d.done = done
+
+		go func() {
+			ctx, cancel := context.WithTimeout(context.Background(), DHCPTimeout)
+			defer cancel()
+
+			var res *Resolver
+			dns, err := dhcp.ResolveDNSFromDHCP(ctx, d.ifaceName)
+			if err == nil {
+				nameserver := make([]NameServer, 0, len(dns))
+				for _, d := range dns {
+					nameserver = append(nameserver, NameServer{Addr: net.JoinHostPort(d.String(), "53")})
+				}
+
+				res = NewResolver(Config{
+					Main: nameserver,
+				})
+			}
+
+			d.lock.Lock()
+			defer d.lock.Unlock()
+
+			close(done)
+
+			d.done = nil
+			d.resolver = res
+			d.err = err
+		}()
+	}
+
+	d.lock.Unlock()
+
+	for {
+		d.lock.Lock()
+
+		res, err, done := d.resolver, d.err, d.done
+
+		d.lock.Unlock()
+
+		// initializing
+		if res == nil && err == nil {
+			select {
+			case <-done:
+				continue
+			case <-ctx.Done():
+				return nil, ctx.Err()
+			}
+		}
+
+		// dirty return
+		return res, err
+	}
+}
+
+func (d *dhcpClient) invalidate() (bool, error) {
+	if time.Now().Before(d.ifaceInvalidate) {
+		return false, nil
+	}
+
+	d.ifaceInvalidate = time.Now().Add(IfaceTTL)
+
+	ifaceObj, err := iface.ResolveInterface(d.ifaceName)
+	if err != nil {
+		return false, err
+	}
+
+	addr, err := ifaceObj.PickIPv4Addr(nil)
+	if err != nil {
+		return false, err
+	}
+
+	if time.Now().Before(d.dnsInvalidate) && d.ifaceAddr.IP.Equal(addr.IP) && bytes.Equal(d.ifaceAddr.Mask, addr.Mask) {
+		return false, nil
+	}
+
+	d.dnsInvalidate = time.Now().Add(DHCPTTL)
+	d.ifaceAddr = addr
+
+	return d.done == nil, nil
+}
+
+func newDHCPClient(ifaceName string) *dhcpClient {
+	return &dhcpClient{ifaceName: ifaceName}
+}