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main.go
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main.go
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package main
import (
"flag"
"log"
"net"
"strings"
"sync"
"time"
"github.com/golang/groupcache/singleflight"
"github.com/miekg/dns"
)
func main() {
bind := flag.String("bind", "0.0.0.0:53", "server bind addr")
hostfiless := flag.String("hosts", "/etc/hosts", "hosts file, file1,file2,file3...")
flag.Parse()
log.Println("dns server running at", *bind)
server := &dns.Server{Addr: *bind, Net: "udp"}
handler := NewCacheHandler(strings.Split(*hostfiless, ","))
dns.HandleFunc(".", handler.handleRequest)
log.Fatal(server.ListenAndServe())
}
type DnsQueryer interface {
Query(domain string) *TTLInfo
}
func NewCacheHandler(hostfiles []string) *CachedHandler {
hosts := ParseHostsFiles(hostfiles)
log.Printf("load %d hosts from hosts file", len(hosts))
ch := &CachedHandler{
cache: NewRecordCache(),
backend: NewDnspodCli(time.Second * 3),
group: &singleflight.Group{},
hosts: hosts,
}
return ch
}
type CachedHandler struct {
lock sync.RWMutex
group *singleflight.Group
cache *RecordCache
backend DnsQueryer
hosts Hosts
hostfiless []string
}
func (s *CachedHandler) loopUpdateHosts() {
for {
time.Sleep(time.Second * 5)
hosts := ParseHostsFiles(s.hostfiless)
s.lock.Lock()
s.hosts = hosts
s.lock.Unlock()
}
}
func (s *CachedHandler) GetFromHostFile(domain string) *TTLInfo {
s.lock.RLock()
defer s.lock.RUnlock()
d := domain[:len(domain)-1]
if ipTtl, ok := s.hosts[d]; ok {
return &TTLInfo{
Records: []string{ipTtl.IP.String()},
TTL: ipTtl.TTL,
TTLTo: time.Now().Add(time.Second * time.Duration(ipTtl.TTL+1)),
Domain: domain,
}
}
return nil
}
func (s *CachedHandler) handleRequest(w dns.ResponseWriter, r *dns.Msg) {
if len(r.Question) == 0 {
return
}
var (
info *TTLInfo
start time.Time = time.Now()
domain string = strings.ToLower(r.Question[0].Name)
domain_type uint16 = r.Question[0].Qtype
result_from string
)
defer func() {
if info == nil {
return
}
// limit message less than 512 bytes. https://www.ietf.org/rfc/rfc1035.txt
if len(info.Records) > 10 {
info.Records = info.Records[:10]
}
m := s.genReply(info)
m.SetReply(r)
err := w.WriteMsg(m)
from := strings.Split(w.RemoteAddr().String(), ":")[0]
domain = domain[:len(domain)-1]
if info.Err != nil {
log.Printf("%v\t%d\t%v\t%v\t%d\t%v", from, s.cache.Len(), result_from, domain, domain_type, info.Err)
return
}
if err != nil {
log.Printf("%v\t%d\t%v\t%v\t%d\t%v", from, s.cache.Len(), result_from, domain, domain_type, err)
return
}
log.Printf("%v\t%d\t%v\t%vs\t%.3fms\t%v\t%d\t%v", from, s.cache.Len(), result_from,
info.TTL, time.Since(start).Seconds()*1000, domain, domain_type, info.Records)
}()
if domain == "myip." {
from := strings.Split(w.RemoteAddr().String(), ":")[0]
info = &TTLInfo{
Domain: domain,
Records: []string{from},
TTL: 30,
TTLTo: time.Now().Add(time.Second * 31),
}
return
}
// not support PTR Record
if domain_type == 12 {
info = &TTLInfo{
Domain: domain,
Records: []string{"localhost"},
TTL: 30,
TTLTo: time.Now().Add(time.Second * 31),
}
return
}
result_from = "host"
info = s.GetFromHostFile(domain)
if info != nil {
return
}
result_from = "cache"
info = s.cache.Get(domain)
if info != nil {
return
}
i, _ := s.group.Do(domain, func() (interface{}, error) {
result_from = "httpdns"
info := s.backend.Query(domain)
s.cache.Put(info)
return info, nil
})
info = i.(*TTLInfo)
if len(info.Records) != 0 && len(info.Records[0]) != 0 {
return
}
i, _ = s.group.Do(domain, func() (interface{}, error) {
result_from = "localdns"
info := QueryFromDNSServer(domain)
s.cache.Put(info)
return info, nil
})
info = i.(*TTLInfo)
}
func (s *CachedHandler) genReply(info *TTLInfo) *dns.Msg {
m := new(dns.Msg)
for _, record := range info.Records {
now := time.Now()
if now.Before(info.TTLTo) {
info.TTL = uint32(info.TTLTo.Sub(now).Seconds())
}
rr := &dns.A{
Hdr: dns.RR_Header{
Name: info.Domain,
Rrtype: dns.TypeA,
Class: dns.ClassINET,
Ttl: info.TTL,
},
A: net.ParseIP(record).To4(),
}
m.Answer = append(m.Answer, rr)
}
return m
}