chore: share RelayDnsPacket function code

component/resolver/relay.go

@@ -0,0 +1,88 @@
+package resolver
+
+import (
+	"context"
+	"encoding/binary"
+	"io"
+	"net"
+	"time"
+
+	"github.com/metacubex/mihomo/common/pool"
+
+	D "github.com/miekg/dns"
+)
+
+const DefaultDnsReadTimeout = time.Second * 10
+const DefaultDnsRelayTimeout = time.Second * 5
+
+const SafeDnsPacketSize = 2 * 1024 // safe size which is 1232 from https://dnsflagday.net/2020/, so 2048 is enough
+
+func RelayDnsConn(ctx context.Context, conn net.Conn) error {
+	buff := pool.Get(pool.UDPBufferSize)
+	defer func() {
+		_ = pool.Put(buff)
+		_ = conn.Close()
+	}()
+	for {
+		if conn.SetReadDeadline(time.Now().Add(DefaultDnsReadTimeout)) != nil {
+			break
+		}
+
+		length := uint16(0)
+		if err := binary.Read(conn, binary.BigEndian, &length); err != nil {
+			break
+		}
+
+		if int(length) > len(buff) {
+			break
+		}
+
+		n, err := io.ReadFull(conn, buff[:length])
+		if err != nil {
+			break
+		}
+
+		err = func() error {
+			ctx, cancel := context.WithTimeout(ctx, DefaultDnsRelayTimeout)
+			defer cancel()
+			inData := buff[:n]
+			msg, err := RelayDnsPacket(ctx, inData, buff)
+			if err != nil {
+				return err
+			}
+
+			err = binary.Write(conn, binary.BigEndian, uint16(len(msg)))
+			if err != nil {
+				return err
+			}
+
+			_, err = conn.Write(msg)
+			if err != nil {
+				return err
+			}
+			return nil
+		}()
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func RelayDnsPacket(ctx context.Context, payload []byte, target []byte) ([]byte, error) {
+	msg := &D.Msg{}
+	if err := msg.Unpack(payload); err != nil {
+		return nil, err
+	}
+
+	r, err := ServeMsg(ctx, msg)
+	if err != nil {
+		m := new(D.Msg)
+		m.SetRcode(msg, D.RcodeServerFailure)
+		return m.PackBuffer(target)
+	}
+
+	r.SetRcode(msg, r.Rcode)
+	r.Compress = true
+	return r.PackBuffer(target)
+}