Feature: add dhcp type dns client (#1509)

dns/client.go

@@ -2,6 +2,7 @@ package dns
 
 import (
 	"context"
+	"crypto/tls"
 	"fmt"
 	"net"
 	"strings"
@@ -34,22 +35,16 @@ func (c *client) ExchangeContext(ctx context.Context, m *D.Msg) (msg *D.Msg, err
 		}
 	}
 
-	d, err := dialer.Dialer()
+	network := "udp"
+	if strings.HasPrefix(c.Client.Net, "tcp") {
+		network = "tcp"
+	}
+
+	conn, err := dialer.DialContext(ctx, network, net.JoinHostPort(ip.String(), c.port))
 	if err != nil {
 		return nil, err
 	}
-
-	if ip != nil && ip.IsGlobalUnicast() && dialer.DialHook != nil {
-		network := "udp"
-		if strings.HasPrefix(c.Client.Net, "tcp") {
-			network = "tcp"
-		}
-		if err := dialer.DialHook(d, network, ip); err != nil {
-			return nil, err
-		}
-	}
-
-	c.Client.Dialer = d
+	defer conn.Close()
 
 	// miekg/dns ExchangeContext doesn't respond to context cancel.
 	// this is a workaround
@@ -59,7 +54,17 @@ func (c *client) ExchangeContext(ctx context.Context, m *D.Msg) (msg *D.Msg, err
 	}
 	ch := make(chan result, 1)
 	go func() {
-		msg, _, err := c.Client.Exchange(m, net.JoinHostPort(ip.String(), c.port))
+		if strings.HasSuffix(c.Client.Net, "tls") {
+			conn = tls.Client(conn, c.Client.TLSConfig)
+		}
+
+		msg, _, err = c.Client.ExchangeWithConn(m, &D.Conn{
+			Conn:         conn,
+			UDPSize:      c.Client.UDPSize,
+			TsigSecret:   c.Client.TsigSecret,
+			TsigProvider: c.Client.TsigProvider,
+		})
+
 		ch <- result{msg, err}
 	}()