middleware/file: Add CNAME chain support (#400)

Up till now we would only chase 1 CNAME. Spec requires we will chase
all. This PR add support for this.  Up to 8 CNAMEs are chased (this
could be longer, by just checking for cycles, but 8 seems enough for
now).

Also add RRSIG of the first CNAME for DNSSEC.

4 files changed, 157 insertions, 16 deletions

diff --git a/middleware/file/cname_test.go b/middleware/file/cname_test.go
new file mode 100644
index 000000000..800020068
--- /dev/null
+++ b/middleware/file/cname_test.go
@@ -0,0 +1,98 @@
+package file
+
+import (
+	"sort"
+	"strings"
+	"testing"
+
+	"github.com/miekg/coredns/middleware/pkg/dnsrecorder"
+	"github.com/miekg/coredns/middleware/test"
+
+	"github.com/miekg/dns"
+	"golang.org/x/net/context"
+)
+
+func TestLookupCNAMEChain(t *testing.T) {
+	name := "example.org."
+	zone, err := Parse(strings.NewReader(dbExampleCNAME), name, "stdin")
+	if err != nil {
+		t.Fatalf("Expected no error when reading zone, got %q", err)
+	}
+
+	fm := File{Next: test.ErrorHandler(), Zones: Zones{Z: map[string]*Zone{name: zone}, Names: []string{name}}}
+	ctx := context.TODO()
+
+	for _, tc := range cnameTestCases {
+		m := tc.Msg()
+
+		rec := dnsrecorder.New(&test.ResponseWriter{})
+		_, err := fm.ServeDNS(ctx, rec, m)
+		if err != nil {
+			t.Errorf("Expected no error, got %v\n", err)
+			return
+		}
+
+		resp := rec.Msg
+		sort.Sort(test.RRSet(resp.Answer))
+		sort.Sort(test.RRSet(resp.Ns))
+		sort.Sort(test.RRSet(resp.Extra))
+
+		if !test.Header(t, tc, resp) {
+			t.Logf("%v\n", resp)
+			continue
+		}
+
+		if !test.Section(t, tc, test.Answer, resp.Answer) {
+			t.Logf("%v\n", resp)
+		}
+		if !test.Section(t, tc, test.Ns, resp.Ns) {
+			t.Logf("%v\n", resp)
+
+		}
+		if !test.Section(t, tc, test.Extra, resp.Extra) {
+			t.Logf("%v\n", resp)
+		}
+	}
+}
+
+var cnameTestCases = []test.Case{
+	{
+		Qname: "a.example.org.", Qtype: dns.TypeA,
+		Answer: []dns.RR{
+			test.A("a.example.org. 1800	IN	A 127.0.0.1"),
+		},
+	},
+	{
+		Qname: "www3.example.org.", Qtype: dns.TypeCNAME,
+		Answer: []dns.RR{
+			test.CNAME("www3.example.org. 1800	IN	CNAME www2.example.org."),
+		},
+	},
+	{
+		Qname: "www3.example.org.", Qtype: dns.TypeA,
+		Answer: []dns.RR{
+			test.A("a.example.org. 1800	IN	A 127.0.0.1"),
+			test.CNAME("www.example.org. 1800	IN	CNAME a.example.org."),
+			test.CNAME("www1.example.org. 1800	IN	CNAME www.example.org."),
+			test.CNAME("www2.example.org. 1800	IN	CNAME www1.example.org."),
+			test.CNAME("www3.example.org. 1800	IN	CNAME www2.example.org."),
+		},
+	},
+}
+
+const dbExampleCNAME = `
+$TTL    30M
+$ORIGIN example.org.
+@       IN      SOA     linode.atoom.net. miek.miek.nl. (
+                             1282630057 ; Serial
+                             4H         ; Refresh
+                             1H         ; Retry
+                             7D         ; Expire
+                             4H )       ; Negative Cache TTL
+
+a               IN      A       127.0.0.1
+www3            IN      CNAME   www2
+www2            IN      CNAME   www1
+www1            IN      CNAME   www
+www             IN      CNAME   a
+dangling        IN      CNAME   foo`
diff --git a/middleware/file/dnssec_test.go b/middleware/file/dnssec_test.go
index 7f4a0916b..40e6429ea 100644
--- a/middleware/file/dnssec_test.go
+++ b/middleware/file/dnssec_test.go
@@ -58,6 +58,7 @@ var dnssecTestCases = []test.Case{
 			test.A("a.miek.nl.	1800	IN	A	139.162.196.78"),
 			test.RRSIG("a.miek.nl.	1800	IN	RRSIG	A 8 3 1800 20160426031301 20160327031301 12051 miek.nl. lxLotCjWZ3kihTxk="),
 			test.CNAME("www.miek.nl.	1800	IN	CNAME	a.miek.nl."),
+			test.RRSIG("www.miek.nl. 1800	RRSIG	CNAME 8 3 1800 20160426031301 20160327031301 12051 miek.nl.  NVZmMJaypS+wDL2Lar4Zw1zF"),
 		},
 
 		Extra: []dns.RR{
@@ -118,7 +119,7 @@ var dnssecTestCases = []test.Case{
 func TestLookupDNSSEC(t *testing.T) {
 	zone, err := Parse(strings.NewReader(dbMiekNLSigned), testzone, "stdin")
 	if err != nil {
-		t.Fatalf("expect no error when reading zone, got %q", err)
+		t.Fatalf("Expected no error when reading zone, got %q", err)
 	}
 
 	fm := File{Next: test.ErrorHandler(), Zones: Zones{Z: map[string]*Zone{testzone: zone}, Names: []string{testzone}}}
@@ -130,7 +131,7 @@ func TestLookupDNSSEC(t *testing.T) {
 		rec := dnsrecorder.New(&test.ResponseWriter{})
 		_, err := fm.ServeDNS(ctx, rec, m)
 		if err != nil {
-			t.Errorf("expected no error, got %v\n", err)
+			t.Errorf("Expected no error, got %v\n", err)
 			return
 		}
 
diff --git a/middleware/file/ds_test.go b/middleware/file/ds_test.go
index a7ba06263..b89c0e15c 100644
--- a/middleware/file/ds_test.go
+++ b/middleware/file/ds_test.go
@@ -54,7 +54,7 @@ var dsTestCases = []test.Case{
 func TestLookupDS(t *testing.T) {
 	zone, err := Parse(strings.NewReader(dbMiekNLDelegation), testzone, "stdin")
 	if err != nil {
-		t.Fatalf("expect no error when reading zone, got %q", err)
+		t.Fatalf("Expected no error when reading zone, got %q", err)
 	}
 
 	fm := File{Next: test.ErrorHandler(), Zones: Zones{Z: map[string]*Zone{testzone: zone}, Names: []string{testzone}}}
@@ -66,7 +66,7 @@ func TestLookupDS(t *testing.T) {
 		rec := dnsrecorder.New(&test.ResponseWriter{})
 		_, err := fm.ServeDNS(ctx, rec, m)
 		if err != nil {
-			t.Errorf("expected no error, got %v\n", err)
+			t.Errorf("Expected no error, got %v\n", err)
 			return
 		}
 
diff --git a/middleware/file/lookup.go b/middleware/file/lookup.go
index 95cd02e73..c47f1f5fa 100644
--- a/middleware/file/lookup.go
+++ b/middleware/file/lookup.go
@@ -118,8 +118,9 @@ func (z *Zone) Lookup(qname string, qtype uint16, do bool) ([]dns.RR, []dns.RR,
 	// Found entire name.
 	if found && shot {
 
-		if rrs := elem.Types(dns.TypeCNAME, qname); len(rrs) > 0 {
-			return z.searchCNAME(rrs, qtype, do)
+		// DNAME...
+		if rrs := elem.Types(dns.TypeCNAME); len(rrs) > 0 && qtype != dns.TypeCNAME {
+			return z.searchCNAME(elem, rrs, qtype, do)
 		}
 
 		rrs := elem.Types(qtype, qname)
@@ -151,7 +152,7 @@ func (z *Zone) Lookup(qname string, qtype uint16, do bool) ([]dns.RR, []dns.RR,
 		auth := []dns.RR{}
 
 		if rrs := wildElem.Types(dns.TypeCNAME, qname); len(rrs) > 0 {
-			return z.searchCNAME(rrs, qtype, do)
+			return z.searchCNAME(wildElem, rrs, qtype, do)
 		}
 
 		rrs := wildElem.Types(qtype, qname)
@@ -250,22 +251,61 @@ func (z *Zone) ns(do bool) []dns.RR {
 	return z.Apex.NS
 }
 
-func (z *Zone) searchCNAME(rrs []dns.RR, qtype uint16, do bool) ([]dns.RR, []dns.RR, []dns.RR, Result) {
-	elem, _ := z.Tree.Search(rrs[0].(*dns.CNAME).Target)
+func (z *Zone) searchCNAME(elem *tree.Elem, rrs []dns.RR, qtype uint16, do bool) ([]dns.RR, []dns.RR, []dns.RR, Result) {
+	if do {
+		sigs := elem.Types(dns.TypeRRSIG)
+		sigs = signatureForSubType(sigs, dns.TypeCNAME)
+		if len(sigs) > 0 {
+			rrs = append(rrs, sigs...)
+		}
+	}
+
+	elem, _ = z.Tree.Search(rrs[0].(*dns.CNAME).Target)
 	if elem == nil {
 		return rrs, nil, nil, Success
 	}
 
-	// RECURSIVE SEARCH, up to 8 deep. Also: tests.
+	i := 0
+
+Redo:
+	cname := elem.Types(dns.TypeCNAME)
+	if len(cname) > 0 {
+		rrs = append(rrs, cname...)
+
+		if do {
+			sigs := elem.Types(dns.TypeRRSIG)
+			sigs = signatureForSubType(sigs, dns.TypeCNAME)
+			if len(sigs) > 0 {
+				rrs = append(rrs, sigs...)
+			}
+		}
+		elem, _ = z.Tree.Search(cname[0].(*dns.CNAME).Target)
+		if elem == nil {
+			return rrs, nil, nil, Success
+		}
+
+		i++
+		if i > maxChain {
+			return rrs, nil, nil, Success
+		}
+
+		goto Redo
+	}
+
 	targets := cnameForType(elem.All(), qtype)
-	if do {
-		sigs := elem.Types(dns.TypeRRSIG)
-		sigs = signatureForSubType(sigs, qtype)
-		if len(sigs) > 0 {
-			targets = append(targets, sigs...)
+	if len(targets) > 0 {
+		rrs = append(rrs, targets...)
+
+		if do {
+			sigs := elem.Types(dns.TypeRRSIG)
+			sigs = signatureForSubType(sigs, qtype)
+			if len(sigs) > 0 {
+				rrs = append(rrs, sigs...)
+			}
 		}
 	}
-	return append(rrs, targets...), nil, nil, Success
+
+	return rrs, nil, nil, Success
 }
 
 func cnameForType(targets []dns.RR, origQtype uint16) []dns.RR {
@@ -317,3 +357,5 @@ func (z *Zone) searchGlue(name string) []dns.RR {
 	}
 	return glue
 }
+
+const maxChain = 8