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

1 files changed, 24 insertions, 3 deletions

diff --git a/middleware/normalize.go b/middleware/normalize.go
index 87f3ce703..77ef97993 100644
--- a/middleware/normalize.go
+++ b/middleware/normalize.go
@@ -7,6 +7,8 @@ import (
 	"github.com/miekg/dns"
 )
 
+// See core/dnsserver/address.go - we should unify these two impls.
+
 // Zones respresents a lists of zone names.
 type Zones []string
 
@@ -56,12 +58,24 @@ type (
 )
 
 // Normalize will return the host portion of host, stripping
-// of any port. The host will also be fully qualified and lowercased.
+// of any port or transport. The host will also be fully qualified and lowercased.
 func (h Host) Normalize() string {
+
+	s := string(h)
+
+	switch {
+	case strings.HasPrefix(s, TransportTLS+"://"):
+		s = s[len(TransportTLS+"://"):]
+	case strings.HasPrefix(s, TransportDNS+"://"):
+		s = s[len(TransportDNS+"://"):]
+	case strings.HasPrefix(s, TransportGRPC+"://"):
+		s = s[len(TransportGRPC+"://"):]
+	}
+
 	// separate host and port
-	host, _, err := net.SplitHostPort(string(h))
+	host, _, err := net.SplitHostPort(s)
 	if err != nil {
-		host, _, _ = net.SplitHostPort(string(h) + ":")
+		host, _, _ = net.SplitHostPort(s + ":")
 	}
 	return Name(host).Normalize()
 }
@@ -77,3 +91,10 @@ func (a Addr) Normalize() string {
 	// TODO(miek): lowercase it?
 	return net.JoinHostPort(addr, port)
 }
+
+// Duplicated from core/dnsserver/address.go !
+const (
+	TransportDNS  = "dns"
+	TransportTLS  = "tls"
+	TransportGRPC = "grpc"
+)