From dc6a44f6d610b1d19e511bf2c9f19f9818eeae6a Mon Sep 17 00:00:00 2001
From: Jean Ribes <jean.ribes@bde-insa-lyon.fr>
Date: Thu, 28 Oct 2021 23:11:51 +0200
Subject: [PATCH] PoC

---
 go.mod  |   5 +++
 main.go | 137 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 142 insertions(+)
 create mode 100644 go.mod
 create mode 100644 main.go

diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..9d3fce7
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,5 @@
+module progdns
+
+go 1.16
+
+require github.com/miekg/dns v1.1.43
diff --git a/main.go b/main.go
new file mode 100644
index 0000000..778d189
--- /dev/null
+++ b/main.go
@@ -0,0 +1,137 @@
+package main
+
+import (
+	"flag"
+	"github.com/miekg/dns"
+	"log"
+	"net"
+	"os"
+	"strings"
+	"time"
+)
+
+var (
+	listen_addr = flag.String("addr", "127.0.0.2:8053", "ip:port")
+)
+
+var domainsToAddresses = map[string]string{
+	"google.com.":       "1.2.3.4",
+	"go.dns.ribes.ovh.": "4.3.2.1",
+}
+var zone = map[string]map[uint16]dns.RR{}
+
+func serve_dns(w dns.ResponseWriter, r *dns.Msg) {
+	msg := dns.Msg{}
+	msg.SetReply(r)
+	msg.Authoritative = true
+	domain := msg.Question[0].Name
+	println(" -> ", msg.Question[0].String(), domain)
+
+	if _, zok := zone[domain]; zok { // serve zone file
+		if rr_resp, rok := zone[domain][msg.Question[0].Qtype]; rok {
+			msg.Answer = []dns.RR{rr_resp}
+			w.WriteMsg(&msg)
+			return
+		}
+	}
+
+	start := strings.SplitN(domain, ".", 2)[0]
+	if start == "reload-zone" { // reload hook
+		msg.Answer = []dns.RR{&dns.TXT{
+			Hdr: dns.RR_Header{Name: domain, Rrtype: dns.TypeTXT, Class: dns.ClassINET, Ttl: 60},
+			Txt: []string{"reloaded"},
+		}}
+		reload_zone()
+		w.WriteMsg(&msg)
+		return
+	}
+
+	if start == "time" { // return local time
+		switch r.Question[0].Qtype {
+		case dns.TypeA:
+			msg.Answer = []dns.RR{&dns.A{
+				Hdr: dns.RR_Header{Name: domain, Rrtype: dns.TypeA, Class: dns.ClassINET, Ttl: 60},
+				A:   time_ip(),
+			}}
+		case dns.TypeTXT:
+			msg.Answer = []dns.RR{&dns.TXT{
+				Hdr: dns.RR_Header{Name: domain, Rrtype: dns.TypeTXT, Class: dns.ClassINET, Ttl: 60},
+				Txt: []string{time.Now().Format("15h04")},
+			}}
+
+		}
+		w.WriteMsg(&msg)
+		return
+	}
+
+	switch r.Question[0].Qtype {
+	case dns.TypeA:
+		address, ok := domainsToAddresses[domain]
+		if ok {
+			msg.Answer = append(msg.Answer, &dns.A{
+				Hdr: dns.RR_Header{Name: domain, Rrtype: dns.TypeA, Class: dns.ClassINET, Ttl: 60},
+				A:   net.ParseIP(address),
+			})
+		} else {
+			msg.Answer = append(msg.Answer, &dns.A{
+				Hdr: dns.RR_Header{Name: domain, Rrtype: dns.TypeA, Class: dns.ClassINET, Ttl: 60},
+				A:   w.RemoteAddr().(*net.UDPAddr).IP,
+			})
+		}
+	case dns.TypeTXT:
+		msg.Answer = append(msg.Answer, &dns.TXT{
+			Hdr: dns.RR_Header{Name: domain, Rrtype: dns.TypeTXT, Class: dns.ClassINET, Ttl: 60},
+			Txt: []string{"hey texte dynamique: " + domain, "lol"},
+		})
+	}
+	w.WriteMsg(&msg)
+
+}
+
+func time_ip() net.IP {
+	now := time.Now()
+	return net.IPv4(byte(now.Hour()), byte(now.Minute()), byte(now.Second()), 0)
+}
+
+func parsezone() {
+	f, ferr := os.Open("zone.db")
+	if ferr != nil {
+		panic(ferr)
+	}
+	zp := dns.NewZoneParser(f, ".", "zone.db")
+	ok := true
+	var rr dns.RR
+	for ok {
+		rr, ok = zp.Next()
+		if ok {
+			hdr := rr.Header()
+			if recs, ok := zone[hdr.Name]; ok {
+				recs[hdr.Rrtype] = hdr
+			} else {
+				zone[hdr.Name] = map[uint16]dns.RR{}
+				zone[hdr.Name][hdr.Rrtype] = rr
+			}
+			println(rr.String())
+		}
+	}
+	if er := zp.Err(); er != nil {
+		println(er.Error())
+	}
+	f.Close()
+}
+
+func reload_zone() {
+	zone = map[string]map[uint16]dns.RR{}
+	parsezone()
+}
+
+func main() {
+	flag.Parse()
+	parsezone()
+	dns.HandleFunc(".", serve_dns)
+	srv := &dns.Server{Addr: *listen_addr, Net: "udp"}
+	if err := srv.ListenAndServe(); err != nil {
+		log.Fatalf("Failed to set udp listener %s\n", err.Error())
+	}
+
+}