server/camnetdns: start of camlistore.net DNS server

Updates #722

Change-Id: Ie4c2d6d036f13d7fb6f5545131397f55d1d9a91c

server/camnetdns/main.go

@@ -0,0 +1,122 @@
+/*
+Copyright 2016 The Camlistore Authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// The camnetdns server serves camlistore.net's DNS server and its
+// DNS challenges
+package main
+
+import (
+	"errors"
+	"flag"
+	"log"
+	"net"
+
+	"camlistore.org/pkg/sorted"
+	"github.com/miekg/dns"
+)
+
+// DefaultResponseTTL is the record TTL in seconds
+const DefaultResponseTTL = 300
+
+var ErrRecordNotFound = errors.New("record not found")
+
+// DNSServer implements the dns.Handler interface to serve A and AAAA
+// records using a sorted.KeyValue for the lookups.
+type DNSServer struct {
+	dataSource sorted.KeyValue
+}
+
+func NewDNSServer(src sorted.KeyValue) *DNSServer {
+	return &DNSServer{
+		dataSource: src,
+	}
+}
+
+func (ds *DNSServer) HandleLookup(name string) (string, error) {
+	return ds.dataSource.Get(name)
+}
+
+func (ds *DNSServer) ServeDNS(rw dns.ResponseWriter, mes *dns.Msg) {
+	resp := new(dns.Msg)
+
+	for _, q := range mes.Question {
+		switch q.Qtype {
+		case dns.TypeA, dns.TypeAAAA:
+			val, err := ds.HandleLookup(q.Name)
+			if err != nil {
+				log.Println(err)
+				continue
+			}
+
+			if q.Qclass != dns.ClassINET {
+				log.Printf("error: got invalid DNS question class %d\n", q.Qclass)
+				continue
+			}
+
+			header := dns.RR_Header{
+				Name:   q.Name,
+				Rrtype: q.Qtype,
+				Class:  dns.ClassINET,
+				Ttl:    DefaultResponseTTL,
+			}
+
+			var rr dns.RR
+			// not really super sure why these have to be different types
+			if q.Qtype == dns.TypeA {
+				rr = &dns.A{
+					A:   net.ParseIP(val),
+					Hdr: header,
+				}
+			} else if q.Qtype == dns.TypeAAAA {
+				rr = &dns.AAAA{
+					AAAA: net.ParseIP(val),
+					Hdr:  header,
+				}
+			} else {
+				panic("unreachable")
+			}
+
+			resp.Answer = append(resp.Answer, rr)
+
+		default:
+			log.Printf("unhandled qtype: %d\n", q.Qtype)
+		}
+	}
+
+	resp.Id = mes.Id
+	resp.Response = true
+
+	if err := rw.WriteMsg(resp); err != nil {
+		log.Printf("error responding to DNS query: %s", err)
+	}
+}
+
+func main() {
+	addr := flag.String("addr", "0.0.0.0:5300", "specify address for server to listen on")
+	flag.Parse()
+
+	memkv := sorted.NewMemoryKeyValue()
+	if err := memkv.Set("6401800c.camlistore.net.", "159.203.246.79"); err != nil {
+		panic(err)
+	}
+
+	ds := NewDNSServer(memkv)
+
+	log.Printf("serving DNS on %s\n", *addr)
+	if err := dns.ListenAndServe(*addr, "udp", ds); err != nil {
+		log.Fatal(err)
+	}
+}