/
dns.go
398 lines (362 loc) · 8.57 KB
/
dns.go
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package multidns
import (
"bytes"
"encoding/binary"
"errors"
"fmt"
"math/rand"
"net"
"strings"
"time"
"unsafe"
"github.com/pmylund/go-cache"
)
const (
// dnsHeader.flags
_QR = 1 << 15 // query/response (response=1)
_AA = 1 << 10 // authoritative
_TC = 1 << 9 // truncated
_RD = 1 << 8 // recursion desired
_RA = 1 << 7 // recursion available
//question type
qdTypeA = 1
qdTypeCNAME = 5
//question class
qdClassIN = 1
qdClassAny = 255
namePtrFlag uint8 = 0xc0
nameLenMax = 63
dnsRespMax = 1024
dnsBufSize = 2048
//question ptr compress method
qdNormal = 0
qdCompress1 = 1 //for google dns and opendns
qdCompress2 = 2 //google dns only
//timeout
dnsTimeout = time.Second * 1
)
var qdCompressMap = map[string]int{
"8.8.4.4:53": qdCompress2,
"8.8.8.8:53": qdCompress2,
"208.67.222.222:53": qdCompress1,
"208.67.222.222:5353": qdCompress1,
"208.67.220.220:53": qdCompress1,
"208.67.220.220:5353": qdCompress1,
}
//error
var (
nameFomatError = errors.New("Wrong name format")
nameLargeError = errors.New("Name too large")
qdGenError = errors.New("DNS question gen failed")
reqNetworkError = errors.New("DNS question network error")
respNetworkError = errors.New("DNS response network error")
respFormatError = errors.New("DNS response format error")
respNotFoundError = errors.New("DNS resove failed")
dnsTimeoutError = errors.New("DNS resove timeout")
dnsNoServerError = errors.New("DNS server not configure")
dnsServerAddrError = errors.New("DNS server addr format error")
)
type dnsHeader struct {
Id uint16
Flags uint16
QdCount uint16
AnCount uint16
NsCount uint16
ArCount uint16
}
//question
type qdHeader struct {
name []byte
qdType uint16
qdClass uint16
}
var addrs []*net.UDPAddr
var badIPMap map[uint32]bool
var checkBadResp = false
var badIPs = []uint32{
0x76053106, 0x80797e8b, 0x9f6a794b, 0xa9840d67,
0xbc050460, 0xbda31105, 0xc043c606, 0xc504040c,
0xca6a0102, 0xcab50755, 0xcba1e6ab, 0xcb620741,
0xcf0c5862, 0xd0381f2b, 0xd1913632, 0xd1dc1eae,
0xd1244921, 0xd155e58a, 0xd35e4293, 0xd5a9fb23,
0xd8ddbcb6, 0xd8eab30d, 0x1759053c, 0xf3b9bb27,
0xf9812e30, 0xfd9d0ea5, 0x253d369e, 0x042442b2,
0x2e52ae44, 0x31027b38, 0x364c8701, 0x3b1803ad,
0x402158a1, 0x4021632f, 0x4042a3fb, 0x4168cafc,
0x41a0db71, 0x422dfced, 0x480ecd68, 0x480ecd63,
0x4a7d7f66, 0x4a7d9b66, 0x4a7d2766, 0x4a7d2771,
0x4d04075c, 0x4e10310f, 0x0807c62d, 0x5d2e0859,
0xcc0dfa22, 0xcc0dfb22, 0xd04e4622, 0xd04e4722,
}
var dnsCache *cache.Cache
func init() {
rand.Seed(time.Now().Unix())
dnsCache = cache.New(time.Hour, time.Minute)
}
func nameQdTrans(name string) ([]byte, error) {
n := len(name)
ret := make([]byte, n+1, n+2)
pos := -1
count := 0
for i := 0; i < n; i++ {
if name[i] == '.' {
if count == 0 {
return ret, nameFomatError
} else if count > nameLenMax {
return ret, nameLargeError
}
ret[pos+1] = uint8(count)
pos = i
count = 0
} else {
count += 1
ret[i+1] = name[i]
}
}
ret[pos+1] = uint8(count)
if ret[n] != 0 {
ret = append(ret, 0)
}
return ret, nil
}
func dnsQdGen(name, remote string) ([]byte, error) {
nameBytes, err := nameQdTrans(name)
if err != nil {
return []byte{}, err
}
dns := dnsHeader{
Id: uint16(rand.Uint32() & 0xffff),
Flags: _RD, //recursion desired
QdCount: 1,
}
buf := bytes.Buffer{}
err = binary.Write(&buf, binary.BigEndian, dns)
if err != nil {
return []byte{}, qdGenError
}
qd := qdHeader{
name: nameBytes,
qdType: qdTypeA,
qdClass: qdClassIN,
}
compress, _ := qdCompressMap[remote]
switch compress {
case qdCompress1:
n := len(qd.name)
if qd.name[n-1] == 0 {
qd.name[n-1] = 0xc0
rnd := uint8(rand.Intn(4)*2 + 4) //4, 6, 8, 10
qd.name = append(qd.name, rnd)
}
binary.Write(&buf, binary.BigEndian, qd.name)
binary.Write(&buf, binary.BigEndian, qd.qdType)
binary.Write(&buf, binary.BigEndian, qd.qdClass)
break
case qdCompress2:
rnd := uint8(rand.Intn(5) + 4) //4-8
var pos uint8 = 12 + 2 + 2 + 2 + rnd
binary.Write(&buf, binary.BigEndian, namePtrFlag)
binary.Write(&buf, binary.BigEndian, pos)
binary.Write(&buf, binary.BigEndian, qd.qdType)
binary.Write(&buf, binary.BigEndian, qd.qdClass)
for i := 0; uint8(i) < rnd; i++ {
binary.Write(&buf, binary.BigEndian, uint8(rand.Uint32()))
}
binary.Write(&buf, binary.BigEndian, qd.name)
break
default:
binary.Write(&buf, binary.BigEndian, qd.name)
binary.Write(&buf, binary.BigEndian, qd.qdType)
binary.Write(&buf, binary.BigEndian, qd.qdClass)
}
return buf.Bytes(), nil
}
func parseNameSize(buf []byte, pos int) (size int) {
for {
n := int(buf[pos])
if n == 0 {
size += 1
return
} else if n == int(namePtrFlag) {
size += 2
return
} else if n > nameLenMax {
return -1
}
size += (n + 1)
pos += (n + 1)
if pos >= dnsRespMax {
return -1
}
}
return
}
func dnsReqResp(name string, conn *net.UDPConn) (net.IP, error) {
//question
var ret net.IP
remote := conn.RemoteAddr().String()
header, err := dnsQdGen(name, remote)
if err != nil {
return ret, qdGenError
}
_, err = conn.Write(header)
if err != nil {
return ret, reqNetworkError
}
respBuf := make([]byte, dnsBufSize)
nread, _, err := conn.ReadFromUDP(respBuf[:dnsRespMax])
if err != nil {
return ret, respNetworkError
}
//respose
respRd := bytes.NewReader(respBuf)
dns := dnsHeader{}
err = binary.Read(respRd, binary.BigEndian, &dns)
if (dns.Flags&_QR) == 0 || err != nil {
return ret, respFormatError
}
numQd := dns.QdCount
numAn := dns.AnCount
buflen := len(respBuf)
pos := int(unsafe.Sizeof(dns))
for i := 0; i < int(numQd); i++ {
for {
n := int(respBuf[pos])
if n == 0 {
pos += 1
break
}
if n > nameLenMax {
return ret, respFormatError
}
pos += (n + 1)
if pos >= buflen {
return ret, respFormatError
}
}
pos += 4 //skip type and class
}
if pos >= nread {
return ret, respFormatError
}
for i := 0; i < int(numAn); i++ {
size := parseNameSize(respBuf, pos)
if size <= 0 {
return ret, respFormatError
}
pos += size
tp := (respBuf[pos] << 16) + respBuf[pos+1]
pos += 8 //skip type, class ttl
if pos >= nread {
return ret, respFormatError
}
dataLen := (respBuf[pos] << 16) + respBuf[pos+1]
pos += 2 //skip data len
if tp == qdTypeA && dataLen == net.IPv4len {
ret = respBuf[pos : pos+4]
return ret, nil
}
pos += int(dataLen) //skip data
if pos >= nread {
return ret, respFormatError
}
}
return ret, respNotFoundError
}
func resolve(name string, conn *net.UDPConn, chn chan<- []byte) {
ip, err := dnsReqResp(name, conn)
if err != nil {
return
}
chn <- ip
}
func DNSInit(servers []string) error {
if len(addrs) != 0 {
addrs = make([]*net.UDPAddr, 0)
}
n := len(servers)
for i := 0; i < n; i++ {
if strings.Index(servers[i], ":") < 0 {
servers[i] = fmt.Sprintf("%s:%d", servers[i], 53)
}
}
for i := 0; i < n; i++ {
raddr, err := net.ResolveUDPAddr("udp", servers[i])
if err != nil {
continue
}
addrs = append(addrs, raddr)
}
if badIPMap == nil {
badIPMap = make(map[uint32]bool)
for _, ipLong := range badIPs {
badIPMap[ipLong] = true
}
}
if len(addrs) == 0 {
return dnsServerAddrError
}
for _, addr := range addrs {
if _, ok := qdCompressMap[addr.String()]; ok {
checkBadResp = true
}
}
return nil
}
func DNSQuery(name string) (net.IP, error) {
if v, ok := dnsCache.Get(name); ok {
if ip, ok := v.([]byte); ok && len(ip) == net.IPv4len {
return ip, nil
}
}
n := len(addrs)
if n == 0 {
return net.IP{}, dnsNoServerError
}
conns := make([]*net.UDPConn, 0, n)
for i := 0; i < n; i++ {
conn, err := net.DialUDP("udp", nil, addrs[i])
if err != nil {
continue
}
err = conn.SetDeadline(time.Now().Add(dnsTimeout))
if err != nil {
conn.Close()
continue
}
conns = append(conns, conn)
}
defer func(conns []*net.UDPConn) {
for _, conn := range conns {
conn.Close()
}
}(conns)
n = len(conns)
chn := make(chan []byte, n)
for i := 0; i < n; i++ {
go resolve(name, conns[i], chn)
}
timeleft := dnsTimeout
for i := 0; i < n; i++ {
t := time.Now()
select {
case <-time.After(timeleft):
return net.IP{}, dnsTimeoutError
case ip := <-chn:
if checkBadResp {
ipLong := (uint32)(ip[0])<<24 + (uint32)(ip[1])<<16 + (uint32)(ip[2])<<8 + (uint32)(ip[3])
if badIPMap[ipLong] {
timeleft -= time.Now().Sub(t)
//fmt.Println("bad ip, timeleft", timeleft)
if timeleft <= 0 {
return net.IP{}, dnsTimeoutError
}
continue
}
}
dnsCache.Add(name, ip, cache.DefaultExpiration)
return ip, nil
}
}
return net.IP{}, dnsTimeoutError
}