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

middleware/root/root.go

@@ -5,6 +5,7 @@ import (
 	"os"
 
 	"github.com/coredns/coredns/core/dnsserver"
+	"github.com/coredns/coredns/middleware"
 
 	"github.com/mholt/caddy"
 )
@@ -21,7 +22,7 @@ func setup(c *caddy.Controller) error {
 
 	for c.Next() {
 		if !c.NextArg() {
-			return c.ArgErr()
+			return middleware.Error("root", c.ArgErr())
 		}
 		config.Root = c.Val()
 	}
@@ -34,7 +35,7 @@ func setup(c *caddy.Controller) error {
 			// But make sure the user knows!
 			log.Printf("[WARNING] Root path does not exist: %s", config.Root)
 		} else {
-			return c.Errf("Unable to access root path '%s': %v", config.Root, err)
+			return middleware.Error("root", c.Errf("unable to access root path '%s': %v", config.Root, err))
 		}
 	}
 

middleware/root/root_test.go

@@ -19,7 +19,7 @@ func TestRoot(t *testing.T) {
 
 	// Predefined error substrings
 	parseErrContent := "Parse error:"
-	unableToAccessErrContent := "Unable to access root path"
+	unableToAccessErrContent := "unable to access root path"
 
 	existingDirPath, err := getTempDirPath()
 	if err != nil {