plugin/cache: Fix filtering (#4148)

The filtering of DNSSEC records in the cache plugin was not done
correctly. Also the change to introduced this bug didn't take into
account that the cache - by virtue of differentiating between DNSSEC and
no-DNSSEC - relied on not copying the data from the cache.

This change copies and then filters the data and factors the filtering
into a function that is used in two places (albeit with on ugly boolean
parameters to prevent copying things twice).

Add tests, do_test.go is moved to test/cache_test.go because the OPT
handing is done outside of the cache plugin. The core server re-attaches
the correct OPT when replying, so that makes for a better e2e test.

Added small unit test for filterRRslice and an explicit test that asks
for DNSSEC first and then plain, and vice versa to test cache behavior.

Fixes: #4146

Signed-off-by: Miek Gieben <miek@miek.nl>

plugin/cache/dnssec_test.go

@@ -0,0 +1,112 @@
+package cache
+
+import (
+	"context"
+	"testing"
+
+	"github.com/coredns/coredns/plugin"
+	"github.com/coredns/coredns/plugin/pkg/dnstest"
+	"github.com/coredns/coredns/plugin/test"
+
+	"github.com/miekg/dns"
+)
+
+func TestResponseWithDNSSEC(t *testing.T) {
+	// We do 2 queries, one where we want non-dnssec and one with dnssec and check the responses in each of them
+	var tcs = []test.Case{
+		{
+			Qname: "invent.example.org.", Qtype: dns.TypeA,
+			Answer: []dns.RR{
+				test.CNAME("invent.example.org.		1781	IN	CNAME	leptone.example.org."),
+				test.A("leptone.example.org.	1781	IN	A	195.201.182.103"),
+			},
+		},
+		{
+			Qname: "invent.example.org.", Qtype: dns.TypeA,
+			Do: true,
+			Answer: []dns.RR{
+				test.CNAME("invent.example.org.		1781	IN	CNAME	leptone.example.org."),
+				test.RRSIG("invent.example.org.		1781	IN	RRSIG	CNAME 8 3 1800 20201012085750 20200912082613 57411 example.org. ijSv5FmsNjFviBcOFwQgqjt073lttxTTNqkno6oMa3DD3kC+"),
+				test.A("leptone.example.org.	1781	IN	A	195.201.182.103"),
+				test.RRSIG("leptone.example.org.	1781	IN	RRSIG	A 8 3 1800 20201012093630 20200912083827 57411 example.org. eLuSOkLAzm/WIOpaZD3/4TfvKP1HAFzjkis9LIJSRVpQt307dm9WY9"),
+			},
+		},
+	}
+
+	c := New()
+	c.Next = dnssecHandler()
+
+	for i, tc := range tcs {
+		m := tc.Msg()
+		rec := dnstest.NewRecorder(&test.ResponseWriter{})
+		c.ServeDNS(context.TODO(), rec, m)
+		if err := test.Section(tc, test.Answer, rec.Msg.Answer); err != nil {
+			t.Errorf("Test %d, expected no error, got %s", i, err)
+		}
+	}
+
+	// now do the reverse
+	c = New()
+	c.Next = dnssecHandler()
+
+	for i, tc := range []test.Case{tcs[1], tcs[0]} {
+		m := tc.Msg()
+		rec := dnstest.NewRecorder(&test.ResponseWriter{})
+		c.ServeDNS(context.TODO(), rec, m)
+		if err := test.Section(tc, test.Answer, rec.Msg.Answer); err != nil {
+			t.Errorf("Test %d, expected no error, got %s", i, err)
+		}
+	}
+}
+
+func dnssecHandler() plugin.Handler {
+	return plugin.HandlerFunc(func(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
+		m := new(dns.Msg)
+		m.SetQuestion("example.org.", dns.TypeA)
+
+		m.Answer = make([]dns.RR, 4)
+		m.Answer[0] = test.CNAME("invent.example.org.		1781	IN	CNAME	leptone.example.org.")
+		m.Answer[1] = test.RRSIG("invent.example.org.		1781	IN	RRSIG	CNAME 8 3 1800 20201012085750 20200912082613 57411 example.org. ijSv5FmsNjFviBcOFwQgqjt073lttxTTNqkno6oMa3DD3kC+")
+		m.Answer[2] = test.A("leptone.example.org.	1781	IN	A	195.201.182.103")
+		m.Answer[3] = test.RRSIG("leptone.example.org.	1781	IN	RRSIG	A 8 3 1800 20201012093630 20200912083827 57411 example.org. eLuSOkLAzm/WIOpaZD3/4TfvKP1HAFzjkis9LIJSRVpQt307dm9WY9")
+		w.WriteMsg(m)
+		return dns.RcodeSuccess, nil
+	})
+}
+
+func TestFliterRRSlice(t *testing.T) {
+	rrs := []dns.RR{
+		test.CNAME("invent.example.org.		1781	IN	CNAME	leptone.example.org."),
+		test.RRSIG("invent.example.org.		1781	IN	RRSIG	CNAME 8 3 1800 20201012085750 20200912082613 57411 example.org. ijSv5FmsNjFviBcOFwQgqjt073lttxTTNqkno6oMa3DD3kC+"),
+		test.A("leptone.example.org.	1781	IN	A	195.201.182.103"),
+		test.RRSIG("leptone.example.org.	1781	IN	RRSIG	A 8 3 1800 20201012093630 20200912083827 57411 example.org. eLuSOkLAzm/WIOpaZD3/4TfvKP1HAFzjkis9LIJSRVpQt307dm9WY9"),
+	}
+
+	filter1 := filterRRSlice(rrs, 0, true, false)
+	if len(filter1) != 4 {
+		t.Errorf("Expected 4 RRs after filtering, got %d", len(filter1))
+	}
+	rrsig := 0
+	for _, f := range filter1 {
+		if f.Header().Rrtype == dns.TypeRRSIG {
+			rrsig++
+		}
+	}
+	if rrsig != 2 {
+		t.Errorf("Expected 2 RRSIGs after filtering, got %d", rrsig)
+	}
+
+	filter2 := filterRRSlice(rrs, 0, false, false)
+	if len(filter2) != 2 {
+		t.Errorf("Expected 2 RRs after filtering, got %d", len(filter2))
+	}
+	rrsig = 0
+	for _, f := range filter2 {
+		if f.Header().Rrtype == dns.TypeRRSIG {
+			rrsig++
+		}
+	}
+	if rrsig != 0 {
+		t.Errorf("Expected 0 RRSIGs after filtering, got %d", rrsig)
+	}
+}