Add new plugin: traffic

Traffic is a plugin that communicates via the xDS protocol to an Envoy
control plane. Using the data from this control plane it hands out IP
addresses. This allows you (via controlling the data in the control
plane) to drain or send more traffic to specific endpoints.

The plugin itself only acts upon this data; it doesn't do anything fancy
by itself.

Code used here is copied from grpc-go and other places, this is clearly
marked in the source files.

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

plugin/traffic/setup.go

@@ -0,0 +1,122 @@
+package traffic
+
+import (
+	"crypto/tls"
+	"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"
+	pkgtls "github.com/coredns/coredns/plugin/pkg/tls"
+	"github.com/coredns/coredns/plugin/pkg/transport"
+	"github.com/coredns/coredns/plugin/traffic/xds"
+
+	"github.com/caddyserver/caddy"
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/credentials"
+)
+
+var log = clog.NewWithPlugin("traffic")
+
+func init() { plugin.Register("traffic", setup) }
+
+func setup(c *caddy.Controller) error {
+	rand.Seed(int64(time.Now().Nanosecond()))
+	t, err := parseTraffic(c)
+	if err != nil {
+		return plugin.Error("traffic", err)
+	}
+
+	dnsserver.GetConfig(c).AddPlugin(func(next plugin.Handler) plugin.Handler {
+		t.Next = next
+		return t
+	})
+
+	c.OnStartup(func() error {
+		go t.c.Run()
+		return nil
+	})
+	c.OnShutdown(func() error { return t.c.Stop() })
+	return nil
+}
+
+func parseTraffic(c *caddy.Controller) (*Traffic, error) {
+	node := "coredns"
+	toHosts := []string{}
+	t := &Traffic{}
+	var (
+		err           error
+		tlsConfig     *tls.Config
+		tlsServerName string
+	)
+
+	t.origins = make([]string, len(c.ServerBlockKeys))
+	for i := range c.ServerBlockKeys {
+		t.origins[i] = plugin.Host(c.ServerBlockKeys[i]).Normalize()
+	}
+
+	for c.Next() {
+		args := c.RemainingArgs()
+		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 dialler needs to see normal address strings. All this
+			// grpc:// stuff is to enforce uniform across plugins and future proofing for other protocols.
+			toHosts[i] = toHosts[i][len(transport.GRPC+"://"):]
+		}
+		for c.NextBlock() {
+			switch c.Val() {
+			case "id":
+				args := c.RemainingArgs()
+				if len(args) != 1 {
+					return nil, c.ArgErr()
+				}
+				node = args[0]
+			case "tls":
+				args := c.RemainingArgs()
+				if len(args) > 3 {
+					return nil, c.ArgErr()
+				}
+
+				tlsConfig, err = pkgtls.NewTLSConfigFromArgs(args...)
+				if err != nil {
+					return nil, err
+				}
+			case "tls_servername":
+				if !c.NextArg() {
+					return nil, c.ArgErr()
+				}
+				tlsServerName = c.Val()
+			default:
+				return nil, c.Errf("unknown property '%s'", c.Val())
+			}
+		}
+	}
+
+	opts := []grpc.DialOption{grpc.WithInsecure()}
+	if tlsConfig != nil {
+		if tlsServerName != "" {
+			tlsConfig.ServerName = tlsServerName
+		}
+		opts = []grpc.DialOption{grpc.WithTransportCredentials(credentials.NewTLS(tlsConfig))}
+	}
+
+	// TODO: only the first host is used, need to figure out how to reconcile multiple upstream providers.
+	if t.c, err = xds.New(toHosts[0], node, opts...); err != nil {
+		return nil, err
+	}
+
+	return t, nil
+}