Implement TO

Signed-off-by: Miek Gieben <miek@miek.nl>

plugin/traffic/HACKING.md

@@ -33,7 +33,7 @@ Then for CoreDNS, check out the `traffic` branch, create a Corefile:
 
 ~~~ Corefile
 example.org {
-    traffic {
+    traffic grpc://127.0.0.1:18000 {
         id test-id
     }
     debug

plugin/traffic/README.md

@@ -53,7 +53,7 @@ traffic {
 
 ~~~ corefile
 example.org {
-    traffic
+    traffic grpc://127.0.0.1:18000
     debug
     log
 }
@@ -62,6 +62,14 @@ example.org {
 This will add load balancing for domains under example.org; the upstream information comes from
 10.12.13.14; depending on received assignments, replies will be let through as-is or are load balanced.
 
+## Also See
+
+The following documents provide some background on Envoy's control plane.
+
+* https://github.com/envoyproxy/go-control-plane
+* https://blog.christianposta.com/envoy/guidance-for-building-a-control-plane-to-manage-envoy-proxy-based-infrastructure/
+* https://github.com/envoyproxy/envoy/blob/442f9fcf21a5f091cec3fe9913ff309e02288659/api/envoy/api/v2/discovery.proto#L63
+
 ## Bugs
 
 Priority from ClusterLoadAssignments is not used. Locality is also not used. Health status of the
@@ -73,10 +81,4 @@ clients that will use this reply, the responding server (CoreDNS) has no idea ho
 this resolver. So reporting a load of +1 on the CoreDNS side can be anything from 1 to 1000+, making
 the load reporting highly inaccurate.
 
-## Also See
-
-The following documents provide some background on Envoy's control plane.
-
-* https://github.com/envoyproxy/go-control-plane
-* https://blog.christianposta.com/envoy/guidance-for-building-a-control-plane-to-manage-envoy-proxy-based-infrastructure/
-* https://github.com/envoyproxy/envoy/blob/442f9fcf21a5f091cec3fe9913ff309e02288659/api/envoy/api/v2/discovery.proto#L63
+Multiple **TO** addresses is not implemented.

plugin/traffic/setup.go

 package traffic
 
 import (
+	"fmt"
 	"math/rand"
+	"strings"
 	"time"
 
 	"github.com/coredns/coredns/core/dnsserver"
 	"github.com/coredns/coredns/plugin"
 	clog "github.com/coredns/coredns/plugin/pkg/log"
+	"github.com/coredns/coredns/plugin/pkg/parse"
+	"github.com/coredns/coredns/plugin/pkg/transport"
 	"github.com/coredns/coredns/plugin/traffic/xds"
 
 	"github.com/caddyserver/caddy"
@@ -18,7 +22,7 @@ func init() { plugin.Register("traffic", setup) }
 
 func setup(c *caddy.Controller) error {
 	rand.Seed(int64(time.Now().Nanosecond()))
-	t, err := parse(c)
+	t, err := parseTraffic(c)
 	if err != nil {
 		return plugin.Error("traffic", err)
 	}
@@ -48,14 +52,27 @@ func setup(c *caddy.Controller) error {
 	return nil
 }
 
-func parse(c *caddy.Controller) (*Traffic, error) {
+func parseTraffic(c *caddy.Controller) (*Traffic, error) {
 	node := "coredns"
+	toHosts := []string{}
+	var err error
 
 	for c.Next() {
 		args := c.RemainingArgs()
-		if len(args) != 0 {
+		if len(args) < 1 {
 			return nil, c.ArgErr()
-
+		}
+		toHosts, err = parse.HostPortOrFile(args...)
+		if err != nil {
+			return nil, err
+		}
+		for i := range toHosts {
+			if !strings.HasPrefix(toHosts[i], transport.GRPC+"://") {
+				return nil, fmt.Errorf("not a %s scheme: %s", transport.GRPC, toHosts[i])
+			}
+			// now cut the prefix off again, because the dialer needs to see normal address strings. All this
+			// grpc:// stuff is to enfore uniformaty accross plugins and future proofing for other protocols.
+			toHosts[i] = toHosts[i][len(transport.GRPC+"://"):]
 		}
 		for c.NextBlock() {
 			switch c.Val() {
@@ -71,7 +88,8 @@ func parse(c *caddy.Controller) (*Traffic, error) {
 		}
 	}
 
-	x, err := xds.New(":18000", node)
+	// TODO: only the first host is used.
+	x, err := xds.New(toHosts[0], node)
 	if err != nil {
 		return nil, err
 	}

plugin/traffic/setup_test.go

@@ -15,7 +15,7 @@ func TestSetup(t *testing.T) {
 	*/
 }
 
-func TestParse(t *testing.T) {
+func TestParseTraffic(t *testing.T) {
 	tests := []struct {
 		input     string
 		shouldErr bool
@@ -30,7 +30,7 @@ func TestParse(t *testing.T) {
 	}
 	for i, test := range tests {
 		c := caddy.NewTestController("dns", test.input)
-		_, err := parse(c)
+		_, err := parseTraffic(c)
 		if test.shouldErr && err == nil {
 			t.Errorf("Test %v: Expected error but found nil", i)
 			continue