97 lines
2.4 KiB
Go
97 lines
2.4 KiB
Go
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package dns
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import (
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"log"
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"strings"
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"time"
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"router7/internal/dhcp4d"
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"golang.org/x/time/rate"
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"github.com/miekg/dns"
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)
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type Server struct {
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*dns.Server
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client *dns.Client
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domain string
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upstream string
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sometimes *rate.Limiter
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hostsByName map[string]string
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hostsByIP map[string]string
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}
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func NewServer(addr, domain string) *Server {
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server := &Server{
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Server: &dns.Server{Addr: addr, Net: "udp"},
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client: &dns.Client{},
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domain: domain,
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upstream: "8.8.8.8:53",
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sometimes: rate.NewLimiter(rate.Every(1*time.Second), 1), // at most once per second
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hostsByName: make(map[string]string),
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hostsByIP: make(map[string]string),
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}
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dns.HandleFunc(".", server.handleRequest)
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return server
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}
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func (s *Server) SetLeases(leases []dhcp4d.Lease) {
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for _, l := range leases {
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s.hostsByName[l.Hostname] = l.Addr.String()
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if rev, err := dns.ReverseAddr(l.Addr.String()); err == nil {
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s.hostsByIP[rev] = l.Hostname
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}
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}
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}
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// TODO: is handleRequest called in more than one goroutine at a time?
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// TODO: require search domains to be present, then use HandleFunc("lan.", internalName)
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func (s *Server) handleRequest(w dns.ResponseWriter, r *dns.Msg) {
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if len(r.Question) == 1 { // TODO: answer all questions we can answer
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q := r.Question[0]
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if q.Qtype == dns.TypeA && q.Qclass == dns.ClassINET {
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name := strings.TrimSuffix(q.Name, ".")
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name = strings.TrimSuffix(name, "."+s.domain)
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if !strings.Contains(name, ".") {
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if host, ok := s.hostsByName[name]; ok {
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rr, err := dns.NewRR(q.Name + " 3600 IN A " + host)
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if err != nil {
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log.Fatal(err)
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}
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m := new(dns.Msg)
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m.SetReply(r)
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m.Answer = append(m.Answer, rr)
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w.WriteMsg(m)
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return
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}
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}
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}
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if q.Qtype == dns.TypePTR && q.Qclass == dns.ClassINET {
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if strings.HasSuffix(q.Name, "168.192.in-addr.arpa.") {
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if host, ok := s.hostsByIP[q.Name]; ok {
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rr, err := dns.NewRR(q.Name + " 3600 IN PTR " + host + "." + s.domain)
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if err != nil {
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log.Fatal(err)
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}
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m := new(dns.Msg)
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m.SetReply(r)
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m.Answer = append(m.Answer, rr)
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w.WriteMsg(m)
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return
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}
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}
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}
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}
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in, _, err := s.client.Exchange(r, s.upstream)
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if err != nil {
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if s.sometimes.Allow() {
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log.Printf("resolving %v failed: %v", r.Question, err)
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}
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return // DNS has no reply for resolving errors
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}
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w.WriteMsg(in)
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}
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