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|
package server
import (
"context"
"log/slog"
"time"
"github.com/miekg/dns"
)
type Server struct {
addr string
logger *slog.Logger
inner *dns.Server
}
func New(addr string, logger *slog.Logger) (*Server, error) {
mux := dns.NewServeMux()
mux.HandleFunc(".", handleQuery)
inner := &dns.Server{
Addr: addr,
Net: "udp",
Handler: mux,
UDPSize: 4096,
ReadTimeout: 5 * time.Second,
WriteTimeout: 5 * time.Second,
}
return &Server{
addr: addr,
logger: logger,
inner: inner,
}, nil
}
func (s *Server) Run(ctx context.Context) error {
errCh := make(chan error, 1)
go func() {
s.logger.Info("udp listener active", "addr", s.addr)
errCh <- s.inner.ListenAndServe()
}()
select {
case <-ctx.Done():
shutdownCtx, cancel := context.WithTimeout(context.Background(), 5 *time.Second)
defer cancel()
if err := s.inner.ShutdownContext(shutdownCtx); err != nil {
s.logger.Error("graceful shutdown failed", "err", err)
return err
}
return ctx.Err()
case err := <-errCh:
return err
}
}
func (s *Server) Close() error {
return s.inner.Shutdown()
}
func handleQuery(w dns.ResponseWriter, req *dns.Msg) {
if len(req.Question) == 0 {
m := new(dns.Msg)
m.SetRcode(req, dns.RcodeFormatError)
_ = w.WriteMsg(m)
return
}
q := req.Question[0]
resp := new(dns.Msg)
resp.SetReply(req)
resp.Authoritative = false
if q.Name == "example.com." && q.Qtype == dns.TypeA {
resp.Answer = []dns.RR{
&dns.A{
Hdr: dns.RR_Header{
Name: q.Name,
Rrtype: dns.TypeA,
Class: dns.ClassINET,
Ttl: 60,
},
A: []byte{127,0,0,1},
},
}
} else {
resp.Rcode = dns.RcodeNameError
}
if err := w.WriteMsg(resp); err != nil {
slog.Error("write response failed",
"err", err,
"qname", q.Name,
"qtype", dns.TypeToString[q.Qtype],
)
return
}
slog.Info("query served",
"qname", q.Name,
"qtype", dns.TypeToString[q.Qtype],
"rcode", dns.RcodeToString[resp.Rcode],
"client", w.RemoteAddr().String(),
)
}
|
