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nameserver.go
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/
nameserver.go
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package server
import (
"context"
"net"
"sync"
"time"
"github.com/miekg/dns"
"v2ray.com/core/app/dispatcher"
"v2ray.com/core/app/log"
"v2ray.com/core/common/buf"
"v2ray.com/core/common/dice"
v2net "v2ray.com/core/common/net"
"v2ray.com/core/transport/internet/udp"
)
const (
DefaultTTL = uint32(3600)
CleanupInterval = time.Second * 120
CleanupThreshold = 512
)
var (
pseudoDestination = v2net.UDPDestination(v2net.LocalHostIP, v2net.Port(53))
)
type ARecord struct {
IPs []net.IP
Expire time.Time
}
type NameServer interface {
QueryA(domain string) <-chan *ARecord
}
type PendingRequest struct {
expire time.Time
response chan<- *ARecord
}
type UDPNameServer struct {
sync.Mutex
address v2net.Destination
requests map[uint16]*PendingRequest
udpServer *udp.Dispatcher
nextCleanup time.Time
}
func NewUDPNameServer(address v2net.Destination, dispatcher dispatcher.Interface) *UDPNameServer {
s := &UDPNameServer{
address: address,
requests: make(map[uint16]*PendingRequest),
udpServer: udp.NewDispatcher(dispatcher),
}
return s
}
// Private: Visible for testing.
func (v *UDPNameServer) Cleanup() {
expiredRequests := make([]uint16, 0, 16)
now := time.Now()
v.Lock()
for id, r := range v.requests {
if r.expire.Before(now) {
expiredRequests = append(expiredRequests, id)
close(r.response)
}
}
for _, id := range expiredRequests {
delete(v.requests, id)
}
v.Unlock()
expiredRequests = nil
}
// Private: Visible for testing.
func (v *UDPNameServer) AssignUnusedID(response chan<- *ARecord) uint16 {
var id uint16
v.Lock()
if len(v.requests) > CleanupThreshold && v.nextCleanup.Before(time.Now()) {
v.nextCleanup = time.Now().Add(CleanupInterval)
go v.Cleanup()
}
for {
id = dice.RollUint16()
if _, found := v.requests[id]; found {
continue
}
log.Trace(newError("add pending request id ", id).AtDebug())
v.requests[id] = &PendingRequest{
expire: time.Now().Add(time.Second * 8),
response: response,
}
break
}
v.Unlock()
return id
}
// Private: Visible for testing.
func (v *UDPNameServer) HandleResponse(payload *buf.Buffer) {
msg := new(dns.Msg)
err := msg.Unpack(payload.Bytes())
if err != nil {
log.Trace(newError("failed to parse DNS response").Base(err).AtWarning())
return
}
record := &ARecord{
IPs: make([]net.IP, 0, 16),
}
id := msg.Id
ttl := DefaultTTL
log.Trace(newError("handling response for id ", id, " content: ", msg.String()).AtDebug())
v.Lock()
request, found := v.requests[id]
if !found {
v.Unlock()
return
}
delete(v.requests, id)
v.Unlock()
for _, rr := range msg.Answer {
switch rr := rr.(type) {
case *dns.A:
record.IPs = append(record.IPs, rr.A)
if rr.Hdr.Ttl < ttl {
ttl = rr.Hdr.Ttl
}
case *dns.AAAA:
record.IPs = append(record.IPs, rr.AAAA)
if rr.Hdr.Ttl < ttl {
ttl = rr.Hdr.Ttl
}
}
}
record.Expire = time.Now().Add(time.Second * time.Duration(ttl))
request.response <- record
close(request.response)
}
func (v *UDPNameServer) BuildQueryA(domain string, id uint16) *buf.Buffer {
msg := new(dns.Msg)
msg.Id = id
msg.RecursionDesired = true
msg.Question = []dns.Question{
{
Name: dns.Fqdn(domain),
Qtype: dns.TypeA,
Qclass: dns.ClassINET,
}}
buffer := buf.New()
buffer.AppendSupplier(func(b []byte) (int, error) {
writtenBuffer, err := msg.PackBuffer(b)
return len(writtenBuffer), err
})
return buffer
}
func (v *UDPNameServer) QueryA(domain string) <-chan *ARecord {
response := make(chan *ARecord, 1)
id := v.AssignUnusedID(response)
ctx, cancel := context.WithTimeout(context.Background(), time.Second*8)
v.udpServer.Dispatch(ctx, v.address, v.BuildQueryA(domain, id), v.HandleResponse)
go func() {
for i := 0; i < 2; i++ {
time.Sleep(time.Second)
v.Lock()
_, found := v.requests[id]
v.Unlock()
if found {
v.udpServer.Dispatch(ctx, v.address, v.BuildQueryA(domain, id), v.HandleResponse)
} else {
break
}
}
cancel()
}()
return response
}
type LocalNameServer struct {
}
func (v *LocalNameServer) QueryA(domain string) <-chan *ARecord {
response := make(chan *ARecord, 1)
go func() {
defer close(response)
ips, err := net.LookupIP(domain)
if err != nil {
log.Trace(newError("failed to lookup IPs for domain ", domain).Base(err))
return
}
response <- &ARecord{
IPs: ips,
Expire: time.Now().Add(time.Second * time.Duration(DefaultTTL)),
}
}()
return response
}