Add files

meshnamed.go

@@ -0,0 +1,115 @@
+package main
+
+import (
+	"encoding/base32"
+	"fmt"
+	"net"
+	"strings"
+	"errors"
+	"os"
+
+	"github.com/miekg/dns"
+)
+
+const domainZone = "mesh.arpa."
+const maxTtl = 4294967295
+
+var _, validSubnet, _ = net.ParseCIDR("::/0")
+
+var srvPortMap = map[string]uint16{
+	"_xmpp-client._tcp": 5222,
+	"_xmpp-server._tcp": 5269,
+	"_submission._tcp": 587, // rfc6186
+	"_imap._tcp": 143,
+	"_imaps._tcp": 993,
+	"_pop3._tcp": 110,
+	"_pop3s._tcp": 995,
+	"_matrix._tcp": 8448, // https://matrix.org/docs/spec/server_server/unstable#server-discovery
+	"_sip._tcp": 5060, // rfc3263
+	"_sip._udp": 5060,
+	"_sips._tcp": 5061,
+}
+
+
+func lookup(domain string) (net.IP, error) {
+	name := strings.ToUpper(domain) + "======"
+	data, err := base32.StdEncoding.DecodeString(name)
+	if err != nil {
+		return net.IP{}, err
+	}
+	if len(data) != 16 {
+		return net.IP{}, errors.New("Invalid subdomain")
+	}
+	ipAddr := net.IP(data)
+	if ipAddr == nil {
+		return net.IP{}, errors.New("Invalid IP address")
+	}
+	if !validSubnet.Contains(ipAddr) {
+		return net.IP{}, errors.New("Address from invalid subnet")
+	}
+	return ipAddr, nil
+}
+
+func handleRequest(w dns.ResponseWriter, r *dns.Msg) {
+	m := new(dns.Msg)
+	m.SetReply(r)
+
+	for _, v := range r.Question {
+		if v.Qclass != dns.ClassINET {
+			continue
+		}
+		labels := dns.SplitDomainName(v.Name)
+		if len(labels) < 3 {
+			continue
+		}
+		subDomain := labels[len(labels)-3]
+
+		resolvedAddr, err := lookup(subDomain)
+		if err != nil {
+			continue
+		}
+		if v.Qtype == dns.TypeAAAA {
+			r := new(dns.AAAA)
+			r.Hdr = dns.RR_Header{Name: v.Name, Rrtype: dns.TypeAAAA, Class: dns.ClassINET, Ttl: maxTtl}
+			r.AAAA = resolvedAddr
+			m.Answer = append(m.Answer, r)
+		} else if v.Qtype == dns.TypeSRV {
+			if len(labels) < 5 {
+				continue
+			}
+
+			if srvRec := labels[0] + "." + labels[1]; srvPortMap[srvRec] != 0 {
+				r := new(dns.SRV)
+				r.Hdr = dns.RR_Header{Name: v.Name, Rrtype: dns.TypeSRV, Class: dns.ClassINET, Ttl: maxTtl}
+				r.Priority = 0
+				r.Weight = 0
+				r.Port = srvPortMap[srvRec]
+				r.Target = subDomain + "." + domainZone
+				m.Answer = append(m.Answer, r)
+			}
+		}
+	}
+
+	w.WriteMsg(m)
+}
+
+func main() {
+	addr := "127.0.0.1:53535"
+	if os.Getenv("LISTEN_ADDR") != "" {
+		addr = os.Getenv("LISTEN_ADDR")
+	}
+
+	if os.Getenv("MESH_SUBNET") != "" {
+		_, meshSubnet, err := net.ParseCIDR(os.Getenv("MESH_SUBNET"))
+		if err != nil {
+			fmt.Println(err)
+			os.Exit(1)
+		}
+		validSubnet = meshSubnet
+	}
+
+	server := &dns.Server{Addr: addr, Net: "udp"}
+	fmt.Println("Started meshnamed on:", addr)
+	dns.HandleFunc(domainZone, handleRequest)
+	server.ListenAndServe()
+}