netbird/client/internal/dns/upstream.go

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package dns
import (
"context"
"errors"
"github.com/miekg/dns"
log "github.com/sirupsen/logrus"
"net"
"time"
)
const defaultUpstreamTimeout = 15 * time.Second
type upstreamResolver struct {
parentCTX context.Context
upstreamClient *dns.Client
upstreamServers []string
upstreamTimeout time.Duration
}
// ServeDNS handles a DNS request
func (u *upstreamResolver) ServeDNS(w dns.ResponseWriter, r *dns.Msg) {
log.Debugf("received an upstream question: %#v", r.Question[0])
select {
case <-u.parentCTX.Done():
return
default:
}
for _, upstream := range u.upstreamServers {
ctx, cancel := context.WithTimeout(u.parentCTX, u.upstreamTimeout)
rm, t, err := u.upstreamClient.ExchangeContext(ctx, r, upstream)
cancel()
if err != nil {
if err == context.DeadlineExceeded || isTimeout(err) {
log.Warnf("got an error while connecting to upstream %s, error: %v", upstream, err)
continue
}
log.Errorf("got an error while querying the upstream %s, error: %v", upstream, err)
return
}
log.Tracef("took %s to query the upstream %s", t, upstream)
err = w.WriteMsg(rm)
if err != nil {
log.Errorf("got an error while writing the upstream resolver response, error: %v", err)
}
return
}
log.Errorf("all queries to the upstream nameservers failed with timeout")
}
// isTimeout returns true if the given error is a network timeout error.
//
// Copied from k8s.io/apimachinery/pkg/util/net.IsTimeout
func isTimeout(err error) bool {
var neterr net.Error
if errors.As(err, &neterr) {
return neterr != nil && neterr.Timeout()
}
return false
}