/
dns.go
211 lines (172 loc) · 3.79 KB
/
dns.go
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package main
import (
"bytes"
"encoding/json"
"fmt"
"io/ioutil"
"net"
"net/http"
"sync"
"time"
_ "unsafe"
"github.com/golang/groupcache/lru"
)
const (
timeout = 10 * time.Second
)
type answer struct {
Type int `json:"type"`
TTL int `json:"TTL"`
Data string `json:"data"`
ip net.IP
}
type response struct {
Status int `json:"Status"`
Answer []answer `json:"Answer"`
}
type answerCache struct {
ip net.IP
expiredAt time.Time
}
type dnsResolver struct {
waiters []chan answerCache
answer answerCache
finished bool
}
type dns interface {
lookup(host string) (ip net.IP, expriedAt time.Time)
}
type dnsOverHostsFile struct{}
func (d *dnsOverHostsFile) lookup(host string) (ip net.IP, expriedAt time.Time) {
res := goLookupIPFiles(host)
if len(res) == 0 {
return nil, time.Now()
}
return res[0].IP, time.Now()
}
type dnsOverUDP struct{}
func (d *dnsOverUDP) lookup(host string) (ip net.IP, expriedAt time.Time) {
expriedAt = time.Now()
answers, err := net.LookupIP(host)
if err != nil {
return nil, expriedAt
}
return answers[0], expriedAt
}
type dnsOverHTTPS struct {
staticTTL time.Duration
provider string
}
func (d *dnsOverHTTPS) lookup(host string) (ip net.IP, expriedAt time.Time) {
client := &http.Client{
Transport: &http.Transport{
Proxy: nil,
},
}
provider := fmt.Sprintf("%s?name=%s", d.provider, host)
req, _ := http.NewRequest(http.MethodGet, provider, nil)
req.Header.Set("Accept", "application/dns-json")
res, err := client.Do(req)
if res != nil {
defer res.Body.Close()
}
if err != nil {
return nil, time.Now()
}
buf, err := ioutil.ReadAll(res.Body)
if err != nil {
return nil, time.Now()
}
rr := &response{}
json.NewDecoder(bytes.NewBuffer(buf)).Decode(rr)
if rr.Status != 0 {
return nil, time.Now()
}
if len(rr.Answer) == 0 {
return nil, time.Now()
}
var answer *answer
for _, a := range rr.Answer {
if a.Type == typeIPv4 || a.Type == typeIPv6 {
answer = &a
break
}
}
if answer != nil {
ip = net.ParseIP(answer.Data)
expriedAt = time.Now().Add(time.Duration(answer.TTL) * time.Second)
if d.staticTTL != 0 {
expriedAt = time.Now().Add(d.staticTTL)
}
}
return ip, expriedAt
}
type smartDNS struct {
sync.RWMutex
lookups []func(host string) (net.IP, time.Time)
cache *lru.Cache
}
func newSmartDNS(lookups ...func(host string) (net.IP, time.Time)) *smartDNS {
d := &smartDNS{
cache: lru.New(2 << 15),
}
d.lookups = append(d.lookups, lookups...)
return d
}
func (d *smartDNS) lookup(host string) (ip net.IP, expriedAt time.Time) {
d.Lock()
cached, ok := d.cache.Get(host)
var resolver *dnsResolver
if !ok {
resolver = &dnsResolver{}
d.cache.Add(host, resolver)
} else {
resolver = cached.(*dnsResolver)
if resolver.finished && resolver.answer.expiredAt.Before(time.Now()) {
resolver.finished = false
ok = false
}
}
if resolver.finished {
d.Unlock()
return resolver.answer.ip, resolver.answer.expiredAt
}
ch := make(chan answerCache, 1)
resolver.waiters = append(resolver.waiters, ch)
d.Unlock()
if !ok {
go d.do(host)
}
timeout := time.NewTimer(timeout)
defer timeout.Stop()
select {
case answer := <-ch:
return answer.ip, answer.expiredAt
case <-timeout.C:
return nil, time.Now()
}
}
func (d *smartDNS) do(host string) {
var ip net.IP
var expriedAt = time.Now()
for _, lookup := range d.lookups {
ip, expriedAt = lookup(host)
if ip != nil {
break
}
}
d.Lock()
defer d.Unlock()
cache, _ := d.cache.Get(host)
resolver := cache.(*dnsResolver)
resolver.finished = true
resolver.answer.ip = ip
resolver.answer.expiredAt = expriedAt
for _, ch := range resolver.waiters {
ch <- resolver.answer
close(ch)
}
resolver.waiters = nil
}
//go:linkname goLookupIPFiles net.goLookupIPFiles
func goLookupIPFiles(name string) (addrs []net.IPAddr)