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Add dns forwarding server library

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This commit is contained in:
Eugene Bujak 2018-11-28 15:40:56 +03:00
parent 39eccc62b1
commit 5a548be16c
8 changed files with 1216 additions and 0 deletions
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225
dnsforward/cache.go Normal file
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package dnsforward
import (
"encoding/binary"
"log"
"math"
"strings"
"sync"
"time"
"github.com/miekg/dns"
)
type item struct {
m *dns.Msg
when time.Time
}
type cache struct {
items map[string]item
sync.RWMutex
}
func (c *cache) Get(request *dns.Msg) (*dns.Msg, bool) {
if request == nil {
return nil, false
}
ok, key := key(request)
if !ok {
log.Printf("Get(): key returned !ok")
return nil, false
}
c.RLock()
item, ok := c.items[key]
c.RUnlock()
if !ok {
return nil, false
}
// get item's TTL
ttl := findLowestTTL(item.m)
// zero TTL? delete and don't serve it
if ttl == 0 {
c.Lock()
delete(c.items, key)
c.Unlock()
return nil, false
}
// too much time has passed? delete and don't serve it
if time.Since(item.when) >= time.Duration(ttl)*time.Second {
c.Lock()
delete(c.items, key)
c.Unlock()
return nil, false
}
response := item.fromItem(request)
return response, true
}
func (c *cache) Set(m *dns.Msg) {
if m == nil {
return // no-op
}
if !isRequestCacheable(m) {
return
}
if !isResponseCacheable(m) {
return
}
ok, key := key(m)
if !ok {
return
}
i := toItem(m)
c.Lock()
if c.items == nil {
c.items = map[string]item{}
}
c.items[key] = i
c.Unlock()
}
// check only request fields
func isRequestCacheable(m *dns.Msg) bool {
// truncated messages aren't valid
if m.Truncated {
log.Printf("Refusing to cache truncated message")
return false
}
// if has wrong number of questions, also don't cache
if len(m.Question) != 1 {
log.Printf("Refusing to cache message with wrong number of questions")
return false
}
// only OK or NXdomain replies are cached
switch m.Rcode {
case dns.RcodeSuccess:
case dns.RcodeNameError: // that's an NXDomain
case dns.RcodeServerFailure:
return false // quietly refuse, don't log
default:
log.Printf("%s: Refusing to cache message with rcode: %s", m.Question[0].Name, dns.RcodeToString[m.Rcode])
return false
}
return true
}
func isResponseCacheable(m *dns.Msg) bool {
ttl := findLowestTTL(m)
if ttl == 0 {
return false
}
return true
}
func findLowestTTL(m *dns.Msg) uint32 {
var ttl uint32 = math.MaxUint32
found := false
if m.Answer != nil {
for _, r := range m.Answer {
if r.Header().Ttl < ttl {
ttl = r.Header().Ttl
found = true
}
}
}
if m.Ns != nil {
for _, r := range m.Ns {
if r.Header().Ttl < ttl {
ttl = r.Header().Ttl
found = true
}
}
}
if m.Extra != nil {
for _, r := range m.Extra {
if r.Header().Rrtype == dns.TypeOPT {
continue // OPT records use TTL for other purposes
}
if r.Header().Ttl < ttl {
ttl = r.Header().Ttl
found = true
}
}
}
if found == false {
return 0
}
return ttl
}
// key is binary little endian in sequence:
// uint16(qtype) then uint16(qclass) then name
func key(m *dns.Msg) (bool, string) {
if len(m.Question) != 1 {
log.Printf("got msg with len(m.Question) != 1: %d", len(m.Question))
return false, ""
}
bb := strings.Builder{}
b := make([]byte, 2)
binary.LittleEndian.PutUint16(b, m.Question[0].Qtype)
bb.Write(b)
binary.LittleEndian.PutUint16(b, m.Question[0].Qclass)
bb.Write(b)
name := strings.ToLower(m.Question[0].Name)
bb.WriteString(name)
return true, bb.String()
}
func toItem(m *dns.Msg) item {
return item{
m: m,
when: time.Now(),
}
}
func (i *item) fromItem(request *dns.Msg) *dns.Msg {
response := &dns.Msg{}
response.SetReply(request)
response.Authoritative = false
response.AuthenticatedData = i.m.AuthenticatedData
response.RecursionAvailable = i.m.RecursionAvailable
response.Rcode = i.m.Rcode
ttl := findLowestTTL(i.m)
timeleft := math.Round(float64(ttl) - time.Since(i.when).Seconds())
var newttl uint32
if timeleft > 0 {
newttl = uint32(timeleft)
}
for _, r := range i.m.Answer {
answer := dns.Copy(r)
answer.Header().Ttl = newttl
response.Answer = append(response.Answer, answer)
}
for _, r := range i.m.Ns {
ns := dns.Copy(r)
ns.Header().Ttl = newttl
response.Ns = append(response.Ns, ns)
}
for _, r := range i.m.Extra {
// don't return OPT records as these are hop-by-hop
if r.Header().Rrtype == dns.TypeOPT {
continue
}
extra := dns.Copy(r)
extra.Header().Ttl = newttl
response.Extra = append(response.Extra, extra)
}
return response
}

144
dnsforward/cache_test.go Normal file
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package dnsforward
import (
"strings"
"testing"
"github.com/go-test/deep"
"github.com/miekg/dns"
)
func RR(rr string) dns.RR {
r, err := dns.NewRR(rr)
if err != nil {
panic(err)
}
return r
}
// deepEqual is same as deep.Equal, except:
// * ignores Id when comparing
// * question names are not case sensetive
func deepEqualMsg(left *dns.Msg, right *dns.Msg) []string {
temp := *left
temp.Id = right.Id
for i := range left.Question {
left.Question[i].Name = strings.ToLower(left.Question[i].Name)
}
for i := range right.Question {
right.Question[i].Name = strings.ToLower(right.Question[i].Name)
}
return deep.Equal(&temp, right)
}
func TestCacheSanity(t *testing.T) {
cache := cache{}
request := dns.Msg{}
request.SetQuestion("google.com.", dns.TypeA)
_, ok := cache.Get(&request)
if ok {
t.Fatal("empty cache replied with positive response")
}
}
type tests struct {
cache []testEntry
cases []testCase
}
type testEntry struct {
q string
t uint16
a []dns.RR
}
type testCase struct {
q string
t uint16
a []dns.RR
ok bool
}
func TestCache(t *testing.T) {
tests := tests{
cache: []testEntry{
{q: "google.com.", t: dns.TypeA, a: []dns.RR{RR("google.com. 3600 IN A 8.8.8.8")}},
},
cases: []testCase{
{q: "google.com.", t: dns.TypeA, a: []dns.RR{RR("google.com. 3600 IN A 8.8.8.8")}, ok: true},
{q: "google.com.", t: dns.TypeMX, ok: false},
},
}
runTests(t, tests)
}
func TestCacheMixedCase(t *testing.T) {
tests := tests{
cache: []testEntry{
{q: "gOOgle.com.", t: dns.TypeA, a: []dns.RR{RR("google.com. 3600 IN A 8.8.8.8")}},
},
cases: []testCase{
{q: "gOOgle.com.", t: dns.TypeA, a: []dns.RR{RR("google.com. 3600 IN A 8.8.8.8")}, ok: true},
{q: "google.com.", t: dns.TypeA, a: []dns.RR{RR("google.com. 3600 IN A 8.8.8.8")}, ok: true},
{q: "GOOGLE.COM.", t: dns.TypeA, a: []dns.RR{RR("google.com. 3600 IN A 8.8.8.8")}, ok: true},
{q: "gOOgle.com.", t: dns.TypeMX, ok: false},
{q: "google.com.", t: dns.TypeMX, ok: false},
{q: "GOOGLE.COM.", t: dns.TypeMX, ok: false},
},
}
runTests(t, tests)
}
func TestZeroTTL(t *testing.T) {
tests := tests{
cache: []testEntry{
{q: "gOOgle.com.", t: dns.TypeA, a: []dns.RR{RR("google.com. 0 IN A 8.8.8.8")}},
},
cases: []testCase{
{q: "google.com.", t: dns.TypeA, ok: false},
{q: "google.com.", t: dns.TypeA, ok: false},
{q: "google.com.", t: dns.TypeA, ok: false},
{q: "google.com.", t: dns.TypeMX, ok: false},
{q: "google.com.", t: dns.TypeMX, ok: false},
{q: "google.com.", t: dns.TypeMX, ok: false},
},
}
runTests(t, tests)
}
func runTests(t *testing.T, tests tests) {
t.Helper()
cache := cache{}
for _, tc := range tests.cache {
reply := dns.Msg{}
reply.SetQuestion(tc.q, tc.t)
reply.Response = true
reply.Answer = tc.a
cache.Set(&reply)
}
for _, tc := range tests.cases {
request := dns.Msg{}
request.SetQuestion(tc.q, tc.t)
val, ok := cache.Get(&request)
if diff := deep.Equal(ok, tc.ok); diff != nil {
t.Error(diff)
}
if tc.a != nil {
if ok == false {
continue
}
reply := dns.Msg{}
reply.SetQuestion(tc.q, tc.t)
reply.Response = true
reply.Answer = tc.a
cache.Set(&reply)
if diff := deepEqualMsg(val, &reply); diff != nil {
t.Error(diff)
} else {
if diff := deep.Equal(val, reply); diff == nil {
t.Error("different message ID were not caught")
}
}
}
}
}

467
dnsforward/dnsforward.go Normal file
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package dnsforward
import (
"fmt"
"log"
"net"
"reflect"
"sync"
"github.com/AdguardTeam/AdGuardHome/dnsfilter"
"github.com/joomcode/errorx"
"github.com/miekg/dns"
)
// Server is the main way to start a DNS server
// Example:
// s := dnsforward.Server{}
// err := s.Start(nil) // will start a DNS server listening on default port 53, in a goroutine
// err := s.Reconfigure(ServerConfig{UDPListenAddr: &net.UDPAddr{Port: 53535}}) // will reconfigure running DNS server to listen on UDP port 53535
// err := s.Stop() // will stop listening on port 53535 and cancel all goroutines
// err := s.Start(nil) // will start listening again, on port 53535, in a goroutine
//
// The zero Server is empty and ready for use.
type Server struct {
udpListen *net.UDPConn
dnsFilter *dnsfilter.Dnsfilter
cache cache
sync.RWMutex
ServerConfig
}
// The zero ServerConfig is empty and ready for use.
type ServerConfig struct {
UDPListenAddr *net.UDPAddr // if nil, then default is is used (port 53 on *)
BlockedTTL uint32 // if 0, then default is used (3600)
Upstreams []Upstream
Filters []Filter
}
var defaultValues = ServerConfig{
UDPListenAddr: &net.UDPAddr{Port: 53},
BlockedTTL: 3600,
Upstreams: []Upstream{
//// dns over HTTPS
// &dnsOverHTTPS{Address: "https://1.1.1.1/dns-query"},
// &dnsOverHTTPS{Address: "https://dns.google.com/experimental"},
// &dnsOverHTTPS{Address: "https://doh.cleanbrowsing.org/doh/security-filter/"},
// &dnsOverHTTPS{Address: "https://dns10.quad9.net/dns-query"},
// &dnsOverHTTPS{Address: "https://doh.powerdns.org"},
// &dnsOverHTTPS{Address: "https://doh.securedns.eu/dns-query"},
//// dns over TLS
// &dnsOverTLS{Address: "tls://8.8.8.8:853"},
// &dnsOverTLS{Address: "tls://8.8.4.4:853"},
&dnsOverTLS{Address: "tls://1.1.1.1:853"},
&dnsOverTLS{Address: "tls://1.0.0.1:853"},
//// plainDNS
// &plainDNS{Address: "8.8.8.8:53"},
// &plainDNS{Address: "8.8.4.4:53"},
// &plainDNS{Address: "1.1.1.1:53"},
// &plainDNS{Address: "1.0.0.1:53"},
},
}
type Filter struct {
ID int64
Rules []string
}
//
// packet loop
//
func (s *Server) packetLoop() {
log.Printf("Entering packet handle loop")
b := make([]byte, dns.MaxMsgSize)
for {
s.RLock()
conn := s.udpListen
s.RUnlock()
if conn == nil {
log.Printf("udp socket has disappeared, exiting loop")
break
}
n, addr, err := conn.ReadFrom(b)
// documentation says to handle the packet even if err occurs, so do that first
if n > 0 {
// make a copy of all bytes because ReadFrom() will overwrite contents of b on next call
// we need the contents to survive the call because we're handling them in goroutine
p := make([]byte, n)
copy(p, b)
go s.handlePacket(p, addr, conn) // ignore errors
}
if err != nil {
if isConnClosed(err) {
log.Printf("ReadFrom() returned because we're reading from a closed connection, exiting loop")
break
}
log.Printf("Got error when reading from udp listen: %s", err)
}
}
}
//
// Control functions
//
func (s *Server) Start(config *ServerConfig) error {
s.Lock()
defer s.Unlock()
if config != nil {
s.ServerConfig = *config
}
// TODO: handle being called Start() second time after Stop()
if s.udpListen == nil {
log.Printf("Creating UDP socket")
var err error
addr := s.UDPListenAddr
if addr == nil {
addr = defaultValues.UDPListenAddr
}
s.udpListen, err = net.ListenUDP("udp", addr)
if err != nil {
return errorx.Decorate(err, "Couldn't listen to UDP socket")
}
log.Println(s.udpListen.LocalAddr(), s.UDPListenAddr)
}
if s.dnsFilter == nil {
log.Printf("Creating dnsfilter")
s.dnsFilter = dnsfilter.New()
}
go s.packetLoop()
return nil
}
func (s *Server) Stop() error {
s.Lock()
defer s.Unlock()
if s.udpListen != nil {
err := s.udpListen.Close()
if err != nil {
return errorx.Decorate(err, "Couldn't close UDP listening socket")
}
s.udpListen = nil
}
return nil
}
//
// Server reconfigure
//
func (s *Server) reconfigureListenAddr(new ServerConfig) error {
oldAddr := s.UDPListenAddr
if oldAddr == nil {
oldAddr = defaultValues.UDPListenAddr
}
newAddr := new.UDPListenAddr
if newAddr == nil {
newAddr = defaultValues.UDPListenAddr
}
if newAddr.Port == 0 {
return errorx.IllegalArgument.New("new port cannot be 0")
}
if reflect.DeepEqual(oldAddr, newAddr) {
// do nothing, the addresses are exactly the same
log.Printf("Not going to rebind because addresses are same: %v -> %v", oldAddr, newAddr)
return nil
}
// rebind, using a strategy:
// * if ports are different, bind new first, then close old
// * if ports are same, close old first, then bind new
var newListen *net.UDPConn
var err error
if oldAddr.Port != newAddr.Port {
log.Printf("Rebinding -- ports are different so bind first then close")
newListen, err = net.ListenUDP("udp", newAddr)
if err != nil {
return errorx.Decorate(err, "Couldn't bind to %v", newAddr)
}
if s.udpListen != nil {
err := s.udpListen.Close()
if err != nil {
return errorx.Decorate(err, "Couldn't close UDP listening socket")
}
}
} else {
log.Printf("Rebinding -- ports are same so close first then bind")
if s.udpListen != nil {
err := s.udpListen.Close()
if err != nil {
return errorx.Decorate(err, "Couldn't close UDP listening socket")
}
}
newListen, err = net.ListenUDP("udp", newAddr)
if err != nil {
return errorx.Decorate(err, "Couldn't bind to %v", newAddr)
}
}
s.Lock()
s.udpListen = newListen
s.UDPListenAddr = new.UDPListenAddr
s.Unlock()
log.Println(s.udpListen.LocalAddr(), s.UDPListenAddr)
go s.packetLoop() // the old one has quit, use new one
return nil
}
func (s *Server) reconfigureBlockedTTL(new ServerConfig) {
newVal := new.BlockedTTL
if newVal == 0 {
newVal = defaultValues.BlockedTTL
}
oldVal := s.BlockedTTL
if oldVal == 0 {
oldVal = defaultValues.BlockedTTL
}
if newVal != oldVal {
s.BlockedTTL = new.BlockedTTL
}
}
func (s *Server) reconfigureUpstreams(new ServerConfig) {
newVal := new.Upstreams
if len(newVal) == 0 {
newVal = defaultValues.Upstreams
}
oldVal := s.Upstreams
if len(oldVal) == 0 {
oldVal = defaultValues.Upstreams
}
if reflect.DeepEqual(newVal, oldVal) {
// they're exactly the same, do nothing
return
}
s.Upstreams = new.Upstreams
}
func (s *Server) reconfigureFilters(new ServerConfig) {
newFilters := new.Filters
if len(newFilters) == 0 {
newFilters = defaultValues.Filters
}
oldFilters := s.Filters
if len(oldFilters) == 0 {
oldFilters = defaultValues.Filters
}
if reflect.DeepEqual(newFilters, oldFilters) {
// they're exactly the same, do nothing
return
}
dnsFilter := dnsfilter.New()
for _, f := range newFilters {
for _, rule := range f.Rules {
err := dnsFilter.AddRule(rule, f.ID)
if err == dnsfilter.ErrAlreadyExists || err == dnsfilter.ErrInvalidSyntax {
continue
}
if err != nil {
log.Printf("Cannot add rule %s: %s", rule, err)
// Just ignore invalid rules
continue
}
}
}
s.Lock()
oldDnsFilter := s.dnsFilter
s.dnsFilter = dnsFilter
s.Unlock()
oldDnsFilter.Destroy()
}
func (s *Server) Reconfigure(new ServerConfig) error {
s.reconfigureBlockedTTL(new)
s.reconfigureUpstreams(new)
s.reconfigureFilters(new)
err := s.reconfigureListenAddr(new)
if err != nil {
return errorx.Decorate(err, "Couldn't reconfigure to new listening address %+v", new.UDPListenAddr)
}
return nil
}
//
// packet handling functions
//
func (s *Server) handlePacket(p []byte, addr net.Addr, conn *net.UDPConn) {
// log.Printf("Got packet %d bytes from %s: %v", len(p), addr, p)
msg := dns.Msg{}
err := msg.Unpack(p)
if err != nil {
log.Printf("failed to unpack DNS packet: %s", err)
return
}
//
// DNS packet byte format is valid
//
// any errors below here require a response to client
// log.Printf("Unpacked: %v", msg.String())
if len(msg.Question) != 1 {
log.Printf("Got invalid number of questions: %v", len(msg.Question))
err := s.respondWithServerFailure(&msg, addr, conn)
if err != nil {
log.Printf("Couldn't respond to UDP packet: %s", err)
return
}
}
{
val, ok := s.cache.Get(&msg)
if ok && val != nil {
err = s.respond(val, addr, conn)
if err != nil {
if isConnClosed(err) {
// ignore this error, the connection was closed and that's ok
return
}
log.Printf("Couldn't respond to UDP packet: %s", err)
return
}
return
}
}
host := msg.Question[0].Name
res, err := s.dnsFilter.CheckHost(host)
if err != nil {
log.Printf("dnsfilter failed to check host '%s': %s", host, err)
err := s.respondWithServerFailure(&msg, addr, conn)
if err != nil {
log.Printf("Couldn't respond to UDP packet: %s", err)
return
}
} else if res.IsFiltered {
log.Printf("Host %s is filtered, reason - '%s', matched rule: '%s'", host, res.Reason, res.Rule)
err := s.respondWithNXDomain(&msg, addr, conn)
if err != nil {
log.Printf("Couldn't respond to UDP packet: %s", err)
return
}
}
// TODO: replace with single-socket implementation
// TODO: replace 8.8.8.8:53 with configurable upstreams
// TODO: support DoH, DoT and TCP
upstream := s.chooseUpstream()
reply, err := upstream.Exchange(&msg)
if err != nil {
log.Printf("talking to upstream failed for host '%s': %s", host, err)
err := s.respondWithServerFailure(&msg, addr, conn)
if err != nil {
if isConnClosed(err) {
// ignore this error, the connection was closed and that's ok
return
}
log.Printf("Couldn't respond to UDP packet with server failure: %s", err)
return
}
return
}
if reply == nil {
log.Printf("SHOULD NOT HAPPEN upstream returned empty message for host '%s'. Request is %v", host, msg.String())
err := s.respondWithServerFailure(&msg, addr, conn)
if err != nil {
log.Printf("Couldn't respond to UDP packet with should not happen: %s", err)
return
}
return
}
err = s.respond(reply, addr, conn)
if err != nil {
if isConnClosed(err) {
// ignore this error, the connection was closed and that's ok
return
}
log.Printf("Couldn't respond to UDP packet: %s", err)
return
}
s.cache.Set(reply)
}
//
// packet sending functions
//
func (s *Server) respond(resp *dns.Msg, addr net.Addr, conn *net.UDPConn) error {
// log.Printf("Replying to %s with %s", addr, resp)
resp.Compress = true
bytes, err := resp.Pack()
if err != nil {
return errorx.Decorate(err, "Couldn't convert message into wire format")
}
n, err := conn.WriteTo(bytes, addr)
if n == 0 && isConnClosed(err) {
return err
}
if n != len(bytes) {
return fmt.Errorf("WriteTo() returned with %d != %d", n, len(bytes))
}
if err != nil {
return errorx.Decorate(err, "WriteTo() returned error")
}
return nil
}
func (s *Server) respondWithServerFailure(request *dns.Msg, addr net.Addr, conn *net.UDPConn) error {
resp := dns.Msg{}
resp.SetRcode(request, dns.RcodeServerFailure)
return s.respond(&resp, addr, conn)
}
func (s *Server) respondWithNXDomain(request *dns.Msg, addr net.Addr, conn *net.UDPConn) error {
resp := dns.Msg{}
resp.SetRcode(request, dns.RcodeNameError)
resp.Ns = s.genSOA(request)
return s.respond(&resp, addr, conn)
}
func (s *Server) genSOA(request *dns.Msg) []dns.RR {
zone := ""
if len(request.Question) > 0 {
zone = request.Question[0].Name
}
soa := dns.SOA{
// values copied from verisign's nonexistent .com domain
// their exact values are not important in our use case because they are used for domain transfers between primary/secondary DNS servers
Refresh: 1800,
Retry: 900,
Expire: 604800,
Minttl: 86400,
// copied from AdGuard DNS
Ns: "fake-for-negative-caching.adguard.com.",
Serial: 100500,
// rest is request-specific
Hdr: dns.RR_Header{
Name: zone,
Rrtype: dns.TypeSOA,
Ttl: s.BlockedTTL,
Class: dns.ClassINET,
},
Mbox: "hostmaster.", // zone will be appended later if it's not empty or "."
}
if soa.Hdr.Ttl == 0 {
soa.Hdr.Ttl = defaultValues.BlockedTTL
}
if len(zone) > 0 && zone[0] != '.' {
soa.Mbox += zone
}
return []dns.RR{&soa}
}

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dnsforward/helpers.go Normal file
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package dnsforward
import (
"fmt"
"net"
"os"
"path"
"runtime"
"strings"
)
func isConnClosed(err error) bool {
if err == nil {
return false
}
nerr, ok := err.(*net.OpError)
if !ok {
return false
}
if strings.Contains(nerr.Err.Error(), "use of closed network connection") {
return true
}
return false
}
// ---------------------
// debug logging helpers
// ---------------------
func trace(format string, args ...interface{}) {
pc := make([]uintptr, 10) // at least 1 entry needed
runtime.Callers(2, pc)
f := runtime.FuncForPC(pc[0])
var buf strings.Builder
buf.WriteString(fmt.Sprintf("%s(): ", path.Base(f.Name())))
text := fmt.Sprintf(format, args...)
buf.WriteString(text)
if len(text) == 0 || text[len(text)-1] != '\n' {
buf.WriteRune('\n')
}
fmt.Fprint(os.Stderr, buf.String())
}

1
dnsforward/standalone/.gitignore vendored Normal file
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/standalone

51
dnsforward/standalone/standalone.go Normal file
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package main
import (
"log"
"net"
"net/http"
_ "net/http/pprof"
"os"
"os/signal"
"runtime"
"syscall"
"time"
"github.com/AdguardTeam/AdGuardHome/dnsforward"
)
//
// main function
//
func main() {
go func() {
log.Println(http.ListenAndServe("localhost:6060", nil))
}()
go func() {
for range time.Tick(time.Second) {
log.Printf("goroutines = %d", runtime.NumGoroutine())
}
}()
s := dnsforward.Server{}
err := s.Start(nil)
if err != nil {
panic(err)
}
time.Sleep(time.Second)
err = s.Stop()
if err != nil {
panic(err)
}
err = s.Start(&dnsforward.ServerConfig{UDPListenAddr: &net.UDPAddr{Port: 53535}})
if err != nil {
panic(err)
}
err = s.Reconfigure(dnsforward.ServerConfig{UDPListenAddr: &net.UDPAddr{Port: 53, IP: net.ParseIP("0.0.0.0")}})
if err != nil {
panic(err)
}
log.Printf("Now serving DNS")
signal_channel := make(chan os.Signal)
signal.Notify(signal_channel, syscall.SIGINT, syscall.SIGTERM)
<-signal_channel
}

187
dnsforward/upstream.go Normal file
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package dnsforward
import (
"bytes"
"crypto/tls"
"fmt"
"io/ioutil"
"log"
"math/rand"
"net/http"
"net/url"
"strings"
"sync"
"time"
"github.com/joomcode/errorx"
"github.com/miekg/dns"
)
const defaultTimeout = time.Second * 10
type Upstream interface {
Exchange(m *dns.Msg) (*dns.Msg, error)
}
//
// plain DNS
//
type plainDNS struct {
Address string
}
var defaultUDPClient = dns.Client{
Timeout: defaultTimeout,
UDPSize: dns.MaxMsgSize,
}
var defaultTCPClient = dns.Client{
Net: "tcp",
UDPSize: dns.MaxMsgSize,
Timeout: defaultTimeout,
}
func (p *plainDNS) Exchange(m *dns.Msg) (*dns.Msg, error) {
reply, _, err := defaultUDPClient.Exchange(m, p.Address)
if err != nil && reply != nil && reply.Truncated {
log.Printf("Truncated message was received, retrying over TCP, question: %s", m.Question[0].String())
reply, _, err = defaultTCPClient.Exchange(m, p.Address)
}
return reply, err
}
//
// DNS-over-TLS
//
type dnsOverTLS struct {
Address string
pool *TLSPool
sync.RWMutex // protects pool
}
var defaultTLSClient = dns.Client{
Net: "tcp-tls",
Timeout: defaultTimeout,
UDPSize: dns.MaxMsgSize,
TLSConfig: &tls.Config{},
}
func (p *dnsOverTLS) Exchange(m *dns.Msg) (*dns.Msg, error) {
var pool *TLSPool
p.RLock()
pool = p.pool
p.RUnlock()
if pool == nil {
p.Lock()
// lazy initialize it
p.pool = &TLSPool{Address: p.Address}
p.Unlock()
}
p.RLock()
poolConn, err := p.pool.Get()
p.RUnlock()
if err != nil {
return nil, errorx.Decorate(err, "Failed to get a connection from TLSPool to %s", p.Address)
}
c := dns.Conn{Conn: poolConn}
err = c.WriteMsg(m)
if err != nil {
poolConn.Close()
return nil, errorx.Decorate(err, "Failed to send a request to %s", p.Address)
}
reply, err := c.ReadMsg()
if err != nil {
poolConn.Close()
return nil, errorx.Decorate(err, "Failed to read a request from %s", p.Address)
}
p.RLock()
p.pool.Put(poolConn)
p.RUnlock()
return reply, nil
}
//
// DNS-over-https
//
type dnsOverHTTPS struct {
Address string
}
var defaultHTTPSTransport = http.Transport{}
var defaultHTTPSClient = http.Client{
Transport: &defaultHTTPSTransport,
Timeout: defaultTimeout,
}
func (p *dnsOverHTTPS) Exchange(m *dns.Msg) (*dns.Msg, error) {
buf, err := m.Pack()
if err != nil {
return nil, errorx.Decorate(err, "Couldn't pack request msg")
}
bb := bytes.NewBuffer(buf)
resp, err := http.Post(p.Address, "application/dns-message", bb)
if resp != nil && resp.Body != nil {
defer resp.Body.Close()
}
if err != nil {
return nil, errorx.Decorate(err, "Couldn't do a POST request to '%s'", p.Address)
}
body, err := ioutil.ReadAll(resp.Body)
if err != nil {
return nil, errorx.Decorate(err, "Couldn't read body contents for '%s'", p.Address)
}
if resp.StatusCode != http.StatusOK {
return nil, fmt.Errorf("Got an unexpected HTTP status code %d from '%s'", resp.StatusCode, p.Address)
}
if len(body) == 0 {
return nil, fmt.Errorf("Got an unexpected empty body from '%s'", p.Address)
}
response := dns.Msg{}
err = response.Unpack(body)
if err != nil {
return nil, errorx.Decorate(err, "Couldn't unpack DNS response from '%s': body is %s", p.Address, string(body))
}
return &response, nil
}
func (s *Server) chooseUpstream() Upstream {
upstreams := s.Upstreams
if upstreams == nil {
upstreams = defaultValues.Upstreams
}
if len(upstreams) == 0 {
panic("SHOULD NOT HAPPEN: no default upstreams specified")
}
if len(upstreams) == 1 {
return upstreams[0]
}
n := rand.Intn(len(upstreams))
upstream := upstreams[n]
return upstream
}
func GetUpstream(address string) (Upstream, error) {
if strings.Contains(address, "://") {
url, err := url.Parse(address)
if err != nil {
return nil, errorx.Decorate(err, "Failed to parse %s", address)
}
switch url.Scheme {
case "dns":
return &plainDNS{Address: address}, nil
case "tls":
return &dnsOverTLS{Address: address}, nil
case "https":
return &dnsOverHTTPS{Address: address}, nil
default:
return &plainDNS{Address: address}, nil
}
}
// we don't have scheme in the url, so it's just a plain DNS host:port
return &plainDNS{Address: address}, nil
}

98
dnsforward/upstream_pool.go Normal file
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package dnsforward
import (
"crypto/tls"
"fmt"
"net"
"net/url"
"sync"
"github.com/joomcode/errorx"
)
// upstream TLS pool.
//
// Example:
// pool := TLSPool{Address: "tls://1.1.1.1:853"}
// netConn, err := pool.Get()
// if err != nil {panic(err)}
// c := dns.Conn{Conn: netConn}
// q := dns.Msg{}
// q.SetQuestion("google.com.", dns.TypeA)
// log.Println(q)
// err = c.WriteMsg(&q)
// if err != nil {panic(err)}
// r, err := c.ReadMsg()
// if err != nil {panic(err)}
// log.Println(r)
// pool.Put(c.Conn)
type TLSPool struct {
Address string
parsedAddress *url.URL
parsedAddressMutex sync.RWMutex
conns []net.Conn
sync.Mutex // protects conns
}
func (n *TLSPool) getHost() (string, error) {
n.parsedAddressMutex.RLock()
if n.parsedAddress != nil {
n.parsedAddressMutex.RUnlock()
return n.parsedAddress.Host, nil
}
n.parsedAddressMutex.RUnlock()
n.parsedAddressMutex.Lock()
defer n.parsedAddressMutex.Unlock()
url, err := url.Parse(n.Address)
if err != nil {
return "", errorx.Decorate(err, "Failed to parse %s", n.Address)
}
if url.Scheme != "tls" {
return "", fmt.Errorf("TLSPool only supports TLS")
}
n.parsedAddress = url
return n.parsedAddress.Host, nil
}
func (n *TLSPool) Get() (net.Conn, error) {
host, err := n.getHost()
if err != nil {
return nil, err
}
// get the connection from the slice inside the lock
var c net.Conn
n.Lock()
num := len(n.conns)
if num > 0 {
last := num - 1
c = n.conns[last]
n.conns = n.conns[:last]
}
n.Unlock()
// if we got connection from the slice, return it
if c != nil {
// log.Printf("Returning existing connection to %s", host)
return c, nil
}
// we'll need a new connection, dial now
// log.Printf("Dialing to %s", host)
conn, err := tls.Dial("tcp", host, nil)
if err != nil {
return nil, errorx.Decorate(err, "Failed to connect to %s", host)
}
return conn, nil
}
func (n *TLSPool) Put(c net.Conn) {
if c == nil {
return
}
n.Lock()
n.conns = append(n.conns, c)
n.Unlock()
}