Fix resolving CNAME with no proxy (#564)

This fixes a crash when we resolve (or try to) an external CNAME
when no proxy is set.

Add test as well.

middleware/proxy/proxy.go

@@ -142,6 +142,10 @@ func (p Proxy) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (
 }
 
 func (p Proxy) match(state request.Request) (u Upstream) {
+	if p.Upstreams == nil {
+		return nil
+	}
+
 	longestMatch := 0
 	for _, upstream := range *p.Upstreams {
 		from := upstream.From()

test/cache_test.go

@@ -18,7 +18,7 @@ func TestLookupCache(t *testing.T) {
 	// Start auth. CoreDNS holding the auth zone.
 	name, rm, err := test.TempFile(".", exampleOrg)
 	if err != nil {
-		t.Fatalf("failed to created zone: %s", err)
+		t.Fatalf("failed to create zone: %s", err)
 	}
 	defer rm()
 

test/ds_file_test.go

@@ -35,7 +35,7 @@ func TestLookupDS(t *testing.T) {
 	t.Parallel()
 	name, rm, err := TempFile(".", miekNL)
 	if err != nil {
-		t.Fatalf("failed to created zone: %s", err)
+		t.Fatalf("failed to create zone: %s", err)
 	}
 	defer rm()
 

test/example_test.go

@@ -8,4 +8,5 @@ example.org.		IN	A	127.0.0.1
 example.org.		IN	A	127.0.0.2
 *.w.example.org.        IN      TXT     "Wildcard"
 a.b.c.w.example.org.    IN      TXT     "Not a wildcard"
+cname.example.org.      IN      CNAME   www.example.net.
 `

test/file_cname_proxy_test.go

+package test
+
+import (
+	"io/ioutil"
+	"log"
+	"testing"
+
+	"github.com/coredns/coredns/middleware/proxy"
+	"github.com/coredns/coredns/middleware/test"
+	"github.com/coredns/coredns/request"
+
+	"github.com/miekg/dns"
+)
+
+func TestZoneExternalCNAMELookup(t *testing.T) {
+	t.Parallel()
+	log.SetOutput(ioutil.Discard)
+
+	name, rm, err := TempFile(".", exampleOrg)
+	if err != nil {
+		t.Fatalf("Failed to create zone: %s", err)
+	}
+	defer rm()
+
+	// Corefile with for example without proxy section.
+	corefile := `example.org:0 {
+       file ` + name + `
+}
+`
+	i, err := CoreDNSServer(corefile)
+	if err != nil {
+		t.Fatalf("Could not get CoreDNS serving instance: %s", err)
+	}
+
+	udp, _ := CoreDNSServerPorts(i, 0)
+	if udp == "" {
+		t.Fatalf("Could not get UDP listening port")
+	}
+	defer i.Stop()
+
+	p := proxy.NewLookup([]string{udp})
+	state := request.Request{W: &test.ResponseWriter{}, Req: new(dns.Msg)}
+
+	resp, err := p.Lookup(state, "cname.example.org.", dns.TypeA)
+	if err != nil {
+		t.Fatalf("Expected to receive reply, but didn't: %s", err)
+	}
+	// There should only be a CNAME in the answer section.
+	if len(resp.Answer) != 1 {
+		t.Fatalf("Expected 1 RR in answer section got %d", len(resp.Answer))
+	}
+}

test/file_reload_test.go

@@ -9,6 +9,7 @@ import (
 	"github.com/coredns/coredns/middleware/proxy"
 	"github.com/coredns/coredns/middleware/test"
 	"github.com/coredns/coredns/request"
+
 	"github.com/miekg/dns"
 )
 
@@ -18,7 +19,7 @@ func TestZoneReload(t *testing.T) {
 
 	name, rm, err := TempFile(".", exampleOrg)
 	if err != nil {
-		t.Fatalf("Failed to created zone: %s", err)
+		t.Fatalf("Failed to create zone: %s", err)
 	}
 	defer rm()
 
@@ -47,7 +48,7 @@ example.net:0 {
 
 	resp, err := p.Lookup(state, "example.org.", dns.TypeA)
 	if err != nil {
-		t.Fatal("Expected to receive reply, but didn't")
+		t.Fatalf("Expected to receive reply, but didn't: %s", err)
 	}
 	if len(resp.Answer) != 2 {
 		t.Fatalf("Expected two RR in answer section got %d", len(resp.Answer))

test/middleware_dnssec_test.go

@@ -15,7 +15,7 @@ func TestLookupBalanceRewriteCacheDnssec(t *testing.T) {
 	t.Parallel()
 	name, rm, err := test.TempFile(".", exampleOrg)
 	if err != nil {
-		t.Fatalf("failed to created zone: %s", err)
+		t.Fatalf("failed to create zone: %s", err)
 	}
 	defer rm()
 	rm1 := createKeyFile(t)

test/middleware_test.go

@@ -14,7 +14,7 @@ func benchmarkLookupBalanceRewriteCache(b *testing.B) {
 	t := new(testing.T)
 	name, rm, err := test.TempFile(".", exampleOrg)
 	if err != nil {
-		t.Fatalf("failed to created zone: %s", err)
+		t.Fatalf("failed to create zone: %s", err)
 	}
 	defer rm()
 

test/proxy_test.go

@@ -16,7 +16,7 @@ func TestLookupProxy(t *testing.T) {
 	t.Parallel()
 	name, rm, err := test.TempFile(".", exampleOrg)
 	if err != nil {
-		t.Fatalf("failed to created zone: %s", err)
+		t.Fatalf("failed to create zone: %s", err)
 	}
 	defer rm()
 

test/reverse_test.go

@@ -16,7 +16,7 @@ func TestReverseFallthrough(t *testing.T) {
 	t.Parallel()
 	name, rm, err := test.TempFile(".", exampleOrg)
 	if err != nil {
-		t.Fatalf("failed to created zone: %s", err)
+		t.Fatalf("failed to create zone: %s", err)
 	}
 	defer rm()
 

test/wildcard_test.go

@@ -16,7 +16,7 @@ func TestLookupWildcard(t *testing.T) {
 	t.Parallel()
 	name, rm, err := test.TempFile(".", exampleOrg)
 	if err != nil {
-		t.Fatalf("failed to created zone: %s", err)
+		t.Fatalf("failed to create zone: %s", err)
 	}
 	defer rm()