/
main.go
141 lines (125 loc) · 2.84 KB
/
main.go
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package main
import (
"fmt"
"github.com/pmylund/go-cache"
"net"
"os"
"strings"
"sync/atomic"
"time"
)
type reply struct {
data []byte
addr *net.UDPAddr
}
var (
server *net.UDPAddr
replyCh chan *reply
theCache *cache.Cache
count int32
)
func main() {
theCache = cache.New(time.Hour, time.Minute)
var err error
server, err = net.ResolveUDPAddr("udp", "208.67.220.220:53")
if err != nil {
fmt.Fprintf(os.Stderr, "Can't resolve server address: %v\n", err)
os.Exit(1)
}
addr, err := net.ResolveUDPAddr("udp", "0.0.0.0:53")
if err != nil {
fmt.Fprintf(os.Stderr, "Can't resolve service address: %v\n", err)
os.Exit(1)
}
conn, err := net.ListenUDP("udp", addr)
if err != nil {
fmt.Fprintf(os.Stderr, "Can't listen on udp port: %v\n", err)
os.Exit(1)
}
replyCh = make(chan *reply)
go sendReply(conn)
for {
reqData := make([]byte, 2048)
nr, client, err := conn.ReadFromUDP(reqData)
if err != nil {
fmt.Fprintf(os.Stderr, "Failed to read from client: %v\n", err)
//checkTempErr(err)
continue
}
go proxyClientDNS(reqData[:nr], client)
}
}
func checkTempErr(err error) {
if err2, ok := err.(*net.OpError); ok && !err2.Temporary() {
fmt.Fprintf(os.Stderr, "FATAL network error\n")
os.Exit(1)
}
}
func proxyClientDNS(reqData []byte, client *net.UDPAddr) {
domain := extractDomain(reqData)
c := atomic.AddInt32(&count, 1)
fmt.Printf("(%3d) Receive DNS request from %24v: %v\n", c, client, domain)
item, found := theCache.Get(domain)
var rep []byte
if found {
rep = item.([]byte)
} else {
rep = doProxyClientDNS(reqData, client)
theCache.Add(domain, rep, 0)
}
replyCh <- &reply{rep, client}
atomic.AddInt32(&count, -1)
}
func extractDomain(reqData []byte) string {
var nodes []string
i := byte(12)
for {
l := reqData[i]
if l == 0 {
break
}
nodes = append(nodes, string(reqData[i+1:i+l+1]))
i += l + 1
}
return strings.Join(nodes, ".")
}
func doProxyClientDNS(reqData []byte, client *net.UDPAddr) []byte {
conn, err := net.DialUDP("udp", nil, server)
if err != nil {
fmt.Fprintf(os.Stderr, "Can't dial server: %v\n", err)
os.Exit(1)
}
defer conn.Close()
_, err = conn.Write(reqData)
if err != nil {
fmt.Fprintf(os.Stderr, "Failed to write to server: %v\n", err)
return nil
}
t := time.Now().Add(time.Duration(5) * time.Second)
conn.SetReadDeadline(t)
var rep []byte
for {
repData := make([]byte, 2048)
nr, err := conn.Read(repData)
if err != nil {
err2, ok := err.(*net.OpError)
if ok && err2.Timeout() {
break
}
fmt.Fprintf(os.Stderr, "Failed to read from server: %v\n", err)
break
}
rep = repData[:nr]
}
return rep
}
func sendReply(conn *net.UDPConn) {
for {
aReply := <-replyCh
_, err := conn.WriteToUDP(aReply.data, aReply.addr)
if err != nil {
fmt.Fprintf(os.Stderr, "Failed to write to client: %v\n", err)
//checkTempErr(err)
}
}
}