From b21fc1d0ec252c1ac8c09d98f37db4a3fa2c6112 Mon Sep 17 00:00:00 2001
From: OldDrake <33509198+OldDrake@users.noreply.github.com>
Date: Thu, 24 Nov 2022 16:02:53 +0800
Subject: [PATCH] Add files via upload

---
 echodns.go | 56 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 56 insertions(+)
 create mode 100644 echodns.go

diff --git a/echodns.go b/echodns.go
new file mode 100644
index 0000000..64f1a3e
--- /dev/null
+++ b/echodns.go
@@ -0,0 +1,56 @@
+package main
+
+import (
+	_ "fmt"
+	"net"
+	"strings"
+
+	"github.com/google/gopacket"
+	"github.com/google/gopacket/layers"
+)
+
+func serveDNS(u *net.UDPConn, clientaddr net.Addr, request *layers.DNS) {
+	replyMess := request
+	var dnsAnswer layers.DNSResourceRecord
+	dnsAnswer.Type = layers.DNSTypeA
+	if request == nil || request.Questions == nil || len(request.Questions) == 0 {
+		return
+	} else {
+		dnsAnswer.Name = []byte(request.Questions[0].Name)
+	}
+	//fmt.Println(clientaddr.String())
+	dnsAnswer.Class = layers.DNSClassIN
+	replyMess.QR = true
+	replyMess.ANCount = 1
+	replyMess.OpCode = layers.DNSOpCodeQuery
+	replyMess.AA = true
+	dnsAnswer.IP = net.ParseIP(strings.Split(clientaddr.String(), ":")[0])
+	dnsAnswer.TTL = 1000
+	replyMess.Answers = append(replyMess.Answers, dnsAnswer)
+	replyMess.ResponseCode = layers.DNSResponseCodeNoErr
+	buf := gopacket.NewSerializeBuffer()
+	opts := gopacket.SerializeOptions{}
+	err := replyMess.SerializeTo(buf, opts)
+	if err != nil {
+		panic(err)
+	}
+	u.WriteTo(buf.Bytes(), clientaddr)
+}
+
+func main() {
+	addr := net.UDPAddr{
+		Port: 53,
+		IP:   net.ParseIP("localhost.localdomain"),	//localhost
+	}
+	u, _ := net.ListenUDP("udp", &addr)
+
+	for {
+		tmp := make([]byte, 1024)
+		_, addr, _ := u.ReadFrom(tmp)
+		clientaddr := addr
+		packet := gopacket.NewPacket(tmp, layers.LayerTypeDNS, gopacket.Default)
+		dnsPacket := packet.Layer(layers.LayerTypeDNS)
+		tcp, _ := dnsPacket.(*layers.DNS)
+		serveDNS(u, clientaddr, tcp)
+	}
+}