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dns.go
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dns.go
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// Copyright (c) 2018 The Decred developers
// Use of this source code is governed by an ISC
// license that can be found in the LICENSE file.
package main
import (
"fmt"
"github.com/karlsen-network/karlsend/app/appmessage"
"net"
"os"
"strings"
"sync/atomic"
"time"
"github.com/karlsen-network/karlsend/domain/consensus/model/externalapi"
"github.com/karlsen-network/karlsend/domain/consensus/utils/subnetworks"
"github.com/karlsen-network/karlsend/infrastructure/network/dnsseed"
"github.com/pkg/errors"
"github.com/miekg/dns"
)
// DNSServer struct
type DNSServer struct {
hostname string
listen string
nameserver string
}
// Start - starts server
func (d *DNSServer) Start() {
defer wg.Done()
rr := fmt.Sprintf("%s 86400 IN NS %s", d.hostname, d.nameserver)
authority, err := dns.NewRR(rr)
if err != nil {
log.Infof("NewRR: %v", err)
return
}
udpAddr, err := net.ResolveUDPAddr("udp4", d.listen)
if err != nil {
log.Infof("ResolveUDPAddr: %v", err)
return
}
udpListen, err := net.ListenUDP("udp", udpAddr)
if err != nil {
log.Infof("ListenUDP: %v", err)
return
}
defer udpListen.Close()
for {
b := make([]byte, 512)
mainLoop:
err := udpListen.SetReadDeadline(time.Now().Add(time.Second))
if err != nil {
log.Infof("SetReadDeadline: %v", err)
os.Exit(1)
}
_, addr, err := udpListen.ReadFromUDP(b)
if err != nil {
var netErr net.Error
if errors.As(err, &netErr) && netErr.Timeout() {
if atomic.LoadInt32(&systemShutdown) == 0 {
// use goto in order to do not re-allocate 'b' buffer
goto mainLoop
}
log.Infof("DNS server shutdown")
return
}
var opErr *net.OpError
if errors.As(err, &opErr) {
log.Infof("Read: %T", opErr.Err)
} else {
log.Errorf("Unknown error: %s", err)
}
continue
}
wg.Add(1)
spawn("DNSServer.Start-DNSServer.handleDNSRequest",
func() { d.handleDNSRequest(addr, authority, udpListen, b) })
}
}
// NewDNSServer - create DNS server
func NewDNSServer(hostname, nameserver, listen string) *DNSServer {
if hostname[len(hostname)-1] != '.' {
hostname = hostname + "."
}
if nameserver[len(nameserver)-1] != '.' {
nameserver = nameserver + "."
}
return &DNSServer{
hostname: hostname,
listen: listen,
nameserver: nameserver,
}
}
func (d *DNSServer) extractSubnetworkID(addr *net.UDPAddr, domainName string) (*externalapi.DomainSubnetworkID, bool, error) {
// Domain name may be in following format:
// [n[subnetwork].]hostname
// where connmgr.SubnetworkIDPrefixChar is a prefix
var subnetworkID *externalapi.DomainSubnetworkID
includeAllSubnetworks := true
if d.hostname != domainName {
labels := dns.SplitDomainName(domainName)
if labels[0][0] == dnsseed.SubnetworkIDPrefixChar {
includeAllSubnetworks = false
if len(labels[0]) > 1 {
subnetworkID, err := subnetworks.FromString(labels[0][1:])
if err != nil {
log.Infof("%s: subnetworkid.NewFromStr: %v", addr, err)
return subnetworkID, includeAllSubnetworks, err
}
}
}
}
return subnetworkID, includeAllSubnetworks, nil
}
func (d *DNSServer) validateDNSRequest(addr *net.UDPAddr, b []byte) (dnsMsg *dns.Msg, domainName string, atype string, err error) {
dnsMsg = new(dns.Msg)
err = dnsMsg.Unpack(b[:])
if err != nil {
log.Infof("%s: invalid dns message: %v", addr, err)
return nil, "", "", err
}
if len(dnsMsg.Question) != 1 {
str := fmt.Sprintf("%s sent more than 1 question: %d", addr, len(dnsMsg.Question))
log.Infof("%s", str)
return nil, "", "", errors.Errorf("%s", str)
}
domainName = strings.ToLower(dnsMsg.Question[0].Name)
ff := strings.LastIndex(domainName, d.hostname)
if ff < 0 {
str := fmt.Sprintf("invalid name: %s", dnsMsg.Question[0].Name)
log.Infof("%s", str)
return nil, "", "", errors.Errorf("%s", str)
}
atype, err = translateDNSQuestion(addr, dnsMsg)
return dnsMsg, domainName, atype, err
}
func translateDNSQuestion(addr *net.UDPAddr, dnsMsg *dns.Msg) (string, error) {
var atype string
qtype := dnsMsg.Question[0].Qtype
switch qtype {
case dns.TypeA:
atype = "A"
case dns.TypeAAAA:
atype = "AAAA"
case dns.TypeNS:
atype = "NS"
default:
str := fmt.Sprintf("%s: invalid qtype: %d", addr, dnsMsg.Question[0].Qtype)
log.Infof("%s", str)
return "", errors.Errorf("%s", str)
}
return atype, nil
}
func (d *DNSServer) buildDNSResponse(addr *net.UDPAddr, authority dns.RR, dnsMsg *dns.Msg, includeAllSubnetworks bool,
subnetworkID *externalapi.DomainSubnetworkID, atype string) ([]byte, error) {
respMsg := dnsMsg.Copy()
respMsg.Authoritative = true
respMsg.Response = true
qtype := dnsMsg.Question[0].Qtype
if qtype != dns.TypeNS {
respMsg.Ns = append(respMsg.Ns, authority)
addrs := amgr.GoodAddresses(qtype, includeAllSubnetworks, subnetworkID)
log.Infof("%s: Sending %d addresses", addr, len(addrs))
if len(addrs) == 0 && qtype == dns.TypeAAAA {
// Musl (Alpine) requires non-empty result (work-around):
addrs = append(addrs, appmessage.NewNetAddressIPPort(net.ParseIP("100::"), uint16(0)))
}
for _, a := range addrs {
rr := fmt.Sprintf("%s 30 IN %s %s", dnsMsg.Question[0].Name, atype, a.IP.String())
newRR, err := dns.NewRR(rr)
if err != nil {
log.Infof("%s: NewRR: %v", addr, err)
return nil, err
}
respMsg.Answer = append(respMsg.Answer, newRR)
}
} else {
rr := fmt.Sprintf("%s 86400 IN NS %s", dnsMsg.Question[0].Name, d.nameserver)
newRR, err := dns.NewRR(rr)
if err != nil {
log.Infof("%s: NewRR: %v", addr, err)
return nil, err
}
respMsg.Answer = append(respMsg.Answer, newRR)
}
sendBytes, err := respMsg.Pack()
if err != nil {
log.Infof("%s: failed to pack response: %v", addr, err)
return nil, err
}
return sendBytes, nil
}
func (d *DNSServer) handleDNSRequest(addr *net.UDPAddr, authority dns.RR, udpListen *net.UDPConn, b []byte) {
defer wg.Done()
dnsMsg, domainName, atype, err := d.validateDNSRequest(addr, b)
if err != nil {
return
}
subnetworkID, includeAllSubnetworks, err := d.extractSubnetworkID(addr, domainName)
if err != nil {
return
}
log.Infof("%s: query %d for subnetwork ID %v",
addr, dnsMsg.Question[0].Qtype, subnetworkID)
sendBytes, err := d.buildDNSResponse(addr, authority, dnsMsg, includeAllSubnetworks, subnetworkID, atype)
if err != nil {
return
}
_, err = udpListen.WriteToUDP(sendBytes, addr)
if err != nil {
log.Infof("%s: failed to write response: %v", addr, err)
return
}
}