filter cnames, ptr and srv records (close #6 #7 #8)

Signed-off-by: Adphi <philippe.adrien.nousse@gmail.com>

split.go

@@ -10,6 +10,7 @@ import (
 	"github.com/coredns/coredns/plugin"
 	"github.com/coredns/coredns/plugin/metrics"
 	clog "github.com/coredns/coredns/plugin/pkg/log"
+	"github.com/coredns/coredns/plugin/pkg/upstream"
 	"github.com/coredns/coredns/request"
 	"github.com/miekg/dns"
 )
@@ -18,6 +19,18 @@ import (
 // friends to log.
 var log = clog.NewWithPlugin("split")
 
+const noFallback = "split-no-fallback"
+
+func isNoFallback(ctx context.Context) bool {
+	if ctx == nil {
+		return false
+	}
+	if v, ok := ctx.Value(noFallback).(bool); ok {
+		return v
+	}
+	return false
+}
+
 // Split is an example plugin to show how to write a plugin.
 type Split struct {
 	Next plugin.Handler
@@ -48,7 +61,7 @@ func (s Split) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (
 	log.Debug("Received response")
 
 	// Wrap.
-	pw := s.NewResponsePrinter(w, r)
+	pw := s.NewResponsePrinter(ctx, w, r)
 
 	// Export metric with the server label set to the current server handling the request.
 	requestCount.WithLabelValues(metrics.WithServer(ctx)).Inc()
@@ -63,6 +76,7 @@ func (s Split) Name() string { return "split" }
 // ResponsePrinter wrap a dns.ResponseWriter and will write example to standard output when WriteMsg is called.
 type ResponsePrinter struct {
 	dns.ResponseWriter
+	ctx   context.Context
 	state request.Request
 	r     *dns.Msg
 	src   net.IP
@@ -70,30 +84,22 @@ type ResponsePrinter struct {
 }
 
 // NewResponsePrinter returns ResponseWriter.
-func (s Split) NewResponsePrinter(w dns.ResponseWriter, r *dns.Msg) *ResponsePrinter {
+func (s Split) NewResponsePrinter(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) *ResponsePrinter {
 	state := request.Request{W: w, Req: r}
 	ip := net.ParseIP(state.IP())
-	return &ResponsePrinter{ResponseWriter: w, r: r, src: ip, rules: s.Rules, state: state}
+	return &ResponsePrinter{ctx: ctx, ResponseWriter: w, r: r, src: ip, rules: s.Rules, state: state}
 }
 
 // WriteMsg calls the underlying ResponseWriter's WriteMsg method and prints "example" to standard output.
 func (r *ResponsePrinter) WriteMsg(res *dns.Msg) error {
-	var rule Rule
-	for _, v := range r.rules {
-		zone := plugin.Zones(v.Zones).Matches(r.state.Name())
-		if zone == "" {
-			continue
-		}
-		rule = v
-		break
-	}
-	var answers []dns.RR
-	var netAnswers []dns.RR
-	for _, v := range res.Answer {
-		rec, ok := v.(*dns.A)
-		if !ok {
-			answers = append(answers, v)
-			continue
+	filter := func(rec *dns.A) (rule Rule, allowed, match bool) {
+		for _, v := range r.rules {
+			zone := plugin.Zones(v.Zones).Matches(r.state.Name())
+			if zone == "" {
+				continue
+			}
+			rule = v
+			break
 		}
 		var net *Network
 		for _, vv := range rule.Networks {
@@ -103,34 +109,91 @@ func (r *ResponsePrinter) WriteMsg(res *dns.Msg) error {
 			}
 		}
 		if net == nil {
-			answers = append(answers, v)
-			continue
+			return rule, true, false
 		}
-		allowed := false
+
 		for _, vv := range net.Allowed {
 			if vv.Contains(r.src) {
-				allowed = true
-				break
+				return rule, true, true
 			}
 		}
-		if allowed {
+		return rule, false, true
+	}
+	var (
+		rule       Rule
+		answers    []dns.RR
+		netAnswers []dns.RR
+	)
+
+	for _, v := range res.Answer {
+		switch rec := v.(type) {
+		case *dns.A:
+			var allowed, match bool
+			rule, allowed, match = filter(rec)
+			if !match {
+				answers = append(answers, v)
+				continue
+			}
+			if allowed {
+				answers = append(answers, v)
+				netAnswers = append(netAnswers, v)
+				continue
+			}
+			log.Infof("request source %s: %s: filtering %s", r.src.String(), rec.Hdr.Name, rec.A)
+		case *dns.CNAME:
+			res, err := r.query(rec.Target)
+			if err != nil {
+				log.Errorf("error querying %s: %s", rec.Target, err)
+				continue
+			}
+			if res == nil || len(res.Answer) == 0 {
+				log.Debugf("no answers for %s", rec.Target)
+				continue
+			}
 			answers = append(answers, v)
-			netAnswers = append(netAnswers, v)
-			continue
+		case *dns.SRV:
+			res, err := r.query(rec.Target)
+			if err != nil {
+				log.Errorf("error querying %s: %s", rec.Target, err)
+				continue
+			}
+			if res == nil || len(res.Answer) == 0 {
+				log.Debugf("no answers for %s", rec.Target)
+				continue
+			}
+			answers = append(answers, v)
+		case *dns.PTR:
+			a, err := r.query(rec.Ptr)
+			if err != nil {
+				log.Errorf("error querying %s: %s", rec.Ptr, err)
+				continue
+			}
+			if res == nil || len(a.Answer) == 0 {
+				log.Debugf("no answer for %s", rec.Ptr)
+				continue
+			}
+			answers = append(answers, v)
+		default:
+			return r.ResponseWriter.WriteMsg(res)
 		}
-		log.Infof("request source %s: %s: filtering %s", r.src.String(), rec.Hdr.Name, rec.A)
 	}
 	if len(netAnswers) != 0 {
 		res.Answer = netAnswers
 	} else {
 		res.Answer = answers
 	}
-	if len(res.Answer) != 0 {
+	if len(res.Answer) != 0 || len(rule.Zones) == 0 {
+		return r.ResponseWriter.WriteMsg(res)
+	}
+	if isNoFallback(r.ctx) {
+		log.Debugf("no fallback requested for %s", r.state.Name())
 		return r.ResponseWriter.WriteMsg(res)
 	}
 	if rule.Fallback == nil {
-		return nil
+		log.Debugf("no fallback configured for zones %v", rule.Zones)
+		return r.ResponseWriter.WriteMsg(res)
 	}
+	log.Debugf("request source %s: %s: using fallback %s", r.src.String(), r.state.Name(), rule.Fallback)
 	c := new(dns.Client)
 	req := r.state.Req.Copy()
 	req.Id = dns.Id()
@@ -141,3 +204,13 @@ func (r *ResponsePrinter) WriteMsg(res *dns.Msg) error {
 	res.Answer = append(res.Answer, in.Answer...)
 	return r.ResponseWriter.WriteMsg(res)
 }
+
+func (r *ResponsePrinter) query(name string) (*dns.Msg, error) {
+	log.Debugf("internally querying %s", name)
+	ctx := context.WithValue(r.ctx, noFallback, true)
+	res, err := upstream.New().Lookup(ctx, r.state, name, dns.TypeA)
+	if err != nil {
+		return nil, err
+	}
+	return res, nil
+}