request/cache: bind responses and entries to QCLASS (#8272)

Signed-off-by: houyuwushang <liuluoqianqiu@outlook.com>

plugin/cache/qclass_test.go

@@ -0,0 +1,63 @@
+package cache
+
+import (
+	"context"
+	"slices"
+	"testing"
+
+	"github.com/coredns/coredns/plugin"
+	"github.com/coredns/coredns/plugin/pkg/dnstest"
+	"github.com/coredns/coredns/plugin/test"
+
+	"github.com/miekg/dns"
+)
+
+func TestCacheSeparatesQuestionClasses(t *testing.T) {
+	const qname = "victim.cache-class.test."
+
+	classes := []uint16{}
+	c := New()
+	c.Next = plugin.HandlerFunc(func(_ context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
+		qclass := r.Question[0].Qclass
+		classes = append(classes, qclass)
+
+		m := new(dns.Msg)
+		m.SetReply(r)
+		if qclass == dns.ClassCHAOS {
+			m.Rcode = dns.RcodeNameError
+			m.Ns = []dns.RR{test.SOA("cache-class.test. 60 CH SOA ns.cache-class.test. hostmaster.cache-class.test. 1 60 60 60 60")}
+		} else {
+			m.Answer = []dns.RR{test.A(qname + " 60 IN A 192.0.2.1")}
+		}
+
+		if err := w.WriteMsg(m); err != nil {
+			return dns.RcodeServerFailure, err
+		}
+		return m.Rcode, nil
+	})
+
+	query := func(qclass uint16) *dns.Msg {
+		t.Helper()
+		req := new(dns.Msg)
+		req.SetQuestion(qname, dns.TypeA)
+		req.Question[0].Qclass = qclass
+		rec := dnstest.NewRecorder(&test.ResponseWriter{})
+		if _, err := c.ServeDNS(context.Background(), rec, req); err != nil {
+			t.Fatalf("ServeDNS for class %d failed: %v", qclass, err)
+		}
+		return rec.Msg
+	}
+
+	if got := query(dns.ClassCHAOS).Rcode; got != dns.RcodeNameError {
+		t.Fatalf("CHAOS query rcode = %s, want NXDOMAIN", dns.RcodeToString[got])
+	}
+
+	inet := query(dns.ClassINET)
+	if inet.Rcode != dns.RcodeSuccess || len(inet.Answer) != 1 {
+		t.Fatalf("IN query returned rcode %s with %d answers, want NOERROR with one answer", dns.RcodeToString[inet.Rcode], len(inet.Answer))
+	}
+
+	if want := []uint16{dns.ClassCHAOS, dns.ClassINET}; !slices.Equal(classes, want) {
+		t.Fatalf("upstream query classes = %v, want %v", classes, want)
+	}
+}