/
awldns.go
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/
awldns.go
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package awldns
import (
"net"
"strings"
"sync/atomic"
"time"
"unicode"
"github.com/ipfs/go-log/v2"
"github.com/miekg/dns"
)
const (
defaultTTL = 60 * time.Second
defaultTTLSeconds = uint32(defaultTTL / time.Second)
ptrV4Suffix = ".in-addr.arpa."
)
const (
LocalDomain = "awl"
DNSIp = "127.0.0.66"
DefaultDNSPort = "53"
DNSAddress = "127.0.0.66:53"
DefaultUpstreamDNSAddress = "1.1.1.1:53"
)
type Resolver struct {
udpServer *dns.Server
tcpServer *dns.Server
udpClient *dns.Client
tcpClient *dns.Client
cfg atomic.Pointer[config]
logger *log.ZapEventLogger
udpServerWorking bool
tcpServerWorking bool
dnsAddress string
}
type config struct {
upstreamDNS string
directMapping map[string]string
reverseMapping map[string]string
}
func NewResolver(dnsAddress string) *Resolver {
r := &Resolver{
logger: log.Logger("awl/dns"),
udpClient: &dns.Client{
Net: "udp",
},
tcpClient: &dns.Client{
Net: "tcp",
},
dnsAddress: dnsAddress,
}
r.cfg.Store(&config{})
mux := dns.NewServeMux()
mux.HandleFunc(LocalDomain, r.dnsLocalDomainHandler)
mux.HandleFunc(strings.TrimPrefix(ptrV4Suffix, "."), r.ptrv4Handler)
mux.HandleFunc(".", r.dnsProxyHandler)
r.udpServer = &dns.Server{
Addr: dnsAddress,
Net: "udp",
Handler: mux,
NotifyStartedFunc: func() {
r.logger.Infof("udp server has started on %s", dnsAddress)
r.udpServerWorking = true
},
}
r.tcpServer = &dns.Server{
Addr: dnsAddress,
Net: "tcp",
Handler: mux,
NotifyStartedFunc: func() {
r.logger.Infof("tcp server has started on %s", dnsAddress)
r.tcpServerWorking = true
},
}
go func() {
err := r.udpServer.ListenAndServe()
if err != nil {
r.logger.Errorf("serve udp server: %v", err)
}
r.udpServerWorking = false
}()
go func() {
err := r.tcpServer.ListenAndServe()
if err != nil {
r.logger.Errorf("serve tcp server: %v", err)
}
r.tcpServerWorking = false
}()
return r
}
func (r *Resolver) ReceiveConfiguration(upstreamDNS string, namesMapping map[string]string) {
reverseMapping := make(map[string]string, len(namesMapping))
directMapping := make(map[string]string, len(namesMapping))
for key, ip := range namesMapping {
canonicalName := dns.CanonicalName(key + "." + LocalDomain)
directMapping[canonicalName] = ip
existedName, exists := reverseMapping[ip]
// we always have at least two names for one ip: peerName and peerID
// for consistency we will take the shortest one (usually peerName, which is more human-readable)
if !exists {
reverseMapping[ip] = canonicalName
} else if exists && len(canonicalName) < len(existedName) {
reverseMapping[ip] = canonicalName
}
}
cfg := config{
upstreamDNS: upstreamDNS,
directMapping: directMapping,
reverseMapping: reverseMapping,
}
r.cfg.Store(&cfg)
}
func (r *Resolver) DNSAddress() string {
if !r.tcpServerWorking || !r.udpServerWorking {
return ""
}
return r.dnsAddress
}
func (r *Resolver) Close() {
err := r.udpServer.Shutdown()
if err != nil {
r.logger.Warnf("shutdown udp server: %v", err)
}
err = r.tcpServer.Shutdown()
if err != nil {
r.logger.Warnf("shutdown tcp server: %v", err)
}
}
func (r *Resolver) dnsLocalDomainHandler(resp dns.ResponseWriter, req *dns.Msg) {
if len(req.Question) == 0 {
return
}
cfg := r.loadConfig()
m := new(dns.Msg)
m.SetReply(req)
for _, question := range req.Question {
hostname := question.Name
qtype := question.Qtype
hostnameLower := strings.ToLower(hostname)
mappedIP, found := cfg.directMapping[hostnameLower]
switch qtype {
case dns.TypeA, dns.TypeAAAA, dns.TypeANY:
aRec := &dns.A{
Hdr: dns.RR_Header{
// we should return original name from the request as some clients expect that
Name: hostname,
Rrtype: dns.TypeA,
Class: dns.ClassINET,
Ttl: defaultTTLSeconds,
},
}
if found {
// TODO: support ipv6
aRec.A = net.ParseIP(mappedIP).To4()
} else {
m.SetRcode(req, dns.RcodeNameError)
}
m.Answer = append(m.Answer, aRec)
}
}
processOwnResponse(req, resp, m)
_ = resp.WriteMsg(m)
}
func (r *Resolver) ptrv4Handler(resp dns.ResponseWriter, req *dns.Msg) {
if len(req.Question) == 0 || req.Question[0].Qtype != dns.TypePTR {
r.dnsProxyHandler(resp, req)
return
}
name := req.Question[0].Name
cfg := r.loadConfig()
ip := ptrV4NameToIP(name)
if ip == nil {
r.dnsProxyHandler(resp, req)
return
}
mappedName, found := cfg.reverseMapping[ip.String()]
if !found {
r.dnsProxyHandler(resp, req)
return
}
m := new(dns.Msg)
m.SetReply(req)
ptr := &dns.PTR{
Hdr: dns.RR_Header{
Name: name,
Rrtype: dns.TypePTR,
Class: dns.ClassINET,
Ttl: defaultTTLSeconds,
},
Ptr: mappedName,
}
m.Answer = append(m.Answer, ptr)
processOwnResponse(req, resp, m)
_ = resp.WriteMsg(m)
}
func (r *Resolver) dnsProxyHandler(resp dns.ResponseWriter, req *dns.Msg) {
cfg := r.loadConfig()
dnsClient := r.udpClient
if _, ok := resp.RemoteAddr().(*net.TCPAddr); ok {
dnsClient = r.tcpClient
}
upstreamResp, _, err := dnsClient.Exchange(req, cfg.upstreamDNS)
if err != nil {
r.logger.Warnf("send request to upstream dns: %v", err)
m := new(dns.Msg)
m.SetRcode(req, dns.RcodeServerFailure)
_ = resp.WriteMsg(m)
return
}
_ = resp.WriteMsg(upstreamResp)
}
func (r *Resolver) loadConfig() config {
cfg := r.cfg.Load()
if cfg == nil {
return config{}
}
return *cfg
}
func processOwnResponse(req *dns.Msg, respWriter dns.ResponseWriter, resp *dns.Msg) {
maxSize := dns.MinMsgSize
if respWriter.LocalAddr().Network() == "tcp" {
maxSize = dns.MaxMsgSize
} else {
if optRR := req.IsEdns0(); optRR != nil {
udpsize := int(optRR.UDPSize())
if udpsize > maxSize {
maxSize = udpsize
}
}
}
resp.Truncate(maxSize)
resp.Authoritative = true
resp.RecursionAvailable = true
}
func TrimDomainName(domain string) string {
domain = strings.TrimSpace(domain)
domain = strings.Map(func(r rune) rune {
if unicode.IsSpace(r) {
return '_'
}
return r
}, domain)
return strings.ToLower(domain)
}
func IsValidDomainName(domain string) bool {
_, ok := dns.IsDomainName(domain + "." + LocalDomain)
return ok && domain == TrimDomainName(domain)
}
func ptrV4NameToIP(name string) net.IP {
s := strings.TrimSuffix(name, ptrV4Suffix)
revIp := net.ParseIP(s)
revIp = revIp.To4()
if revIp == nil {
return nil
}
return net.IP{revIp[3], revIp[2], revIp[1], revIp[0]}
}