core: add more transports (#574)

* core: add listening for other protocols

Allow CoreDNS to listen for TLS request coming over port 853. This can
be enabled with `tls://` in the config file.

Implement listening for grps:// as well.

a Corefile like:

~~~
. tls://.:1853 {
    whoami
    tls
}
~~~

Means we listen on 1853 for tls requests, the `tls` config item allows
configuration for TLS parameters. We *might* be tempted to use Caddy's
Let's Encrypt implementation here.

* Refactor coredns/grpc into CoreDNS

This makes gRPC a first class citizen in CoreDNS. Add defines as being
just another server.

* some cleanups

* unexport the servers

* Move protobuf dir

* Hook up TLS properly

* Fix test

* listen for TLS as well. README updates

* disable test, fix package

* fix test

* Fix tests

* Fix remaining test

* Some tests

* Make the test work

* Add grpc test from #580

* fix crash

* Fix tests

* Close conn

* README cleanups

* README

* link RFC

2 files changed, 63 insertions, 1 deletions

diff --git a/test/grpc_test.go b/test/grpc_test.go
new file mode 100644
index 000000000..f7c47b57c
--- /dev/null
+++ b/test/grpc_test.go
@@ -0,0 +1,62 @@
+package test
+
+import (
+	"io/ioutil"
+	"log"
+	"testing"
+	"time"
+
+	"github.com/miekg/dns"
+	"golang.org/x/net/context"
+	"google.golang.org/grpc"
+
+	"github.com/coredns/coredns/pb"
+)
+
+func TestGrpc(t *testing.T) {
+	log.SetOutput(ioutil.Discard)
+
+	corefile := `grpc://.:0 {
+		whoami
+}
+`
+	g, err := CoreDNSServer(corefile)
+	if err != nil {
+		t.Fatalf("Could not get CoreDNS serving instance: %s", err)
+	}
+
+	_, tcp := CoreDNSServerPorts(g, 0)
+	defer g.Stop()
+
+	conn, err := grpc.Dial(tcp, grpc.WithInsecure(), grpc.WithBlock(), grpc.WithTimeout(5*time.Second))
+	if err != nil {
+		t.Fatalf("Expected no error but got: %s", err)
+	}
+	defer conn.Close()
+
+	client := pb.NewDnsServiceClient(conn)
+
+	m := new(dns.Msg)
+	m.SetQuestion("whoami.example.org.", dns.TypeA)
+	msg, _ := m.Pack()
+
+	reply, err := client.Query(context.TODO(), &pb.DnsPacket{Msg: msg})
+	if err != nil {
+		t.Errorf("Expected no error but got: %s", err)
+	}
+
+	d := new(dns.Msg)
+	err = d.Unpack(reply.Msg)
+	if err != nil {
+		t.Errorf("Expected no error but got: %s", err)
+	}
+
+	if d.Rcode != dns.RcodeSuccess {
+		t.Errorf("Expected success but got %s", d.Rcode)
+	}
+
+	if len(d.Extra) != 2 {
+		t.Errorf("Expected 2 RRs in additional section, but got %s", len(d.Extra))
+	}
+	t.Logf("Message %v\n", d)
+}
diff --git a/test/proxy_test.go b/test/proxy_test.go
index 7b96582c5..cb9f1b298 100644
--- a/test/proxy_test.go
+++ b/test/proxy_test.go
@@ -46,7 +46,7 @@ func TestLookupProxy(t *testing.T) {
 	}
 	// expect answer section with A record in it
 	if len(resp.Answer) == 0 {
-		t.Error("Expected to at least one RR in the answer section, got none")
+		t.Fatalf("Expected to at least one RR in the answer section, got none: %s", resp)
 	}
 	if resp.Answer[0].Header().Rrtype != dns.TypeA {
 		t.Errorf("Expected RR to A, got: %d", resp.Answer[0].Header().Rrtype)