plugin/grpc: New gRPC plugin (#2667)

* plugin/grpc: New gRPC plugin

* some changes after the first review:

- remove healthcheck. gRPC already has this implicitly implemented
- some naming and stetic changes
- fix some comments
- other minor fixes

* plugin/grpc: New gRPC plugin

* some changes after the first review:

- remove healthcheck. gRPC already has this implicitly implemented
- some naming and stetic changes
- fix some comments
- other minor fixes

* add OWNERS file and change plugin order

* remove Rcode checker

plugin/grpc/setup.go

@@ -0,0 +1,158 @@
+package grpc
+
+import (
+	"crypto/tls"
+	"fmt"
+
+	"github.com/coredns/coredns/core/dnsserver"
+	"github.com/coredns/coredns/plugin"
+	"github.com/coredns/coredns/plugin/metrics"
+	"github.com/coredns/coredns/plugin/pkg/parse"
+	pkgtls "github.com/coredns/coredns/plugin/pkg/tls"
+
+	"github.com/mholt/caddy"
+	"github.com/mholt/caddy/caddyfile"
+)
+
+func init() {
+	caddy.RegisterPlugin("grpc", caddy.Plugin{
+		ServerType: "dns",
+		Action:     setup,
+	})
+}
+
+func setup(c *caddy.Controller) error {
+	g, err := parseGRPC(c)
+	if err != nil {
+		return plugin.Error("grpc", err)
+	}
+
+	if g.len() > max {
+		return plugin.Error("grpc", fmt.Errorf("more than %d TOs configured: %d", max, g.len()))
+	}
+
+	dnsserver.GetConfig(c).AddPlugin(func(next plugin.Handler) plugin.Handler {
+		g.Next = next // Set the Next field, so the plugin chaining works.
+		return g
+	})
+
+	c.OnStartup(func() error {
+		metrics.MustRegister(c, RequestCount, RcodeCount, RequestDuration)
+		return nil
+	})
+
+	return nil
+}
+
+func parseGRPC(c *caddy.Controller) (*GRPC, error) {
+	var (
+		g   *GRPC
+		err error
+		i   int
+	)
+	for c.Next() {
+		if i > 0 {
+			return nil, plugin.ErrOnce
+		}
+		i++
+		g, err = parseGRPCStanza(&c.Dispenser)
+		if err != nil {
+			return nil, err
+		}
+	}
+	return g, nil
+}
+
+func parseGRPCStanza(c *caddyfile.Dispenser) (*GRPC, error) {
+	g := newGRPC()
+
+	if !c.Args(&g.from) {
+		return g, c.ArgErr()
+	}
+	g.from = plugin.Host(g.from).Normalize()
+
+	to := c.RemainingArgs()
+	if len(to) == 0 {
+		return g, c.ArgErr()
+	}
+
+	toHosts, err := parse.HostPortOrFile(to...)
+	if err != nil {
+		return g, err
+	}
+
+	if g.tlsServerName != "" {
+		if g.tlsConfig == nil {
+			g.tlsConfig = new(tls.Config)
+		}
+		g.tlsConfig.ServerName = g.tlsServerName
+	}
+	for _, host := range toHosts {
+		pr, err := newProxy(host, g.tlsConfig)
+		if err != nil {
+			return nil, err
+		}
+		g.proxies = append(g.proxies, pr)
+	}
+
+	for c.NextBlock() {
+		if err := parseBlock(c, g); err != nil {
+			return g, err
+		}
+	}
+
+	return g, nil
+}
+
+func parseBlock(c *caddyfile.Dispenser, g *GRPC) error {
+
+	switch c.Val() {
+	case "except":
+		ignore := c.RemainingArgs()
+		if len(ignore) == 0 {
+			return c.ArgErr()
+		}
+		for i := 0; i < len(ignore); i++ {
+			ignore[i] = plugin.Host(ignore[i]).Normalize()
+		}
+		g.ignored = ignore
+	case "tls":
+		args := c.RemainingArgs()
+		if len(args) > 3 {
+			return c.ArgErr()
+		}
+
+		tlsConfig, err := pkgtls.NewTLSConfigFromArgs(args...)
+		if err != nil {
+			return err
+		}
+		g.tlsConfig = tlsConfig
+	case "tls_servername":
+		if !c.NextArg() {
+			return c.ArgErr()
+		}
+		g.tlsServerName = c.Val()
+	case "policy":
+		if !c.NextArg() {
+			return c.ArgErr()
+		}
+		switch x := c.Val(); x {
+		case "random":
+			g.p = &random{}
+		case "round_robin":
+			g.p = &roundRobin{}
+		case "sequential":
+			g.p = &sequential{}
+		default:
+			return c.Errf("unknown policy '%s'", x)
+		}
+	default:
+		if c.Val() != "}" {
+			return c.Errf("unknown property '%s'", c.Val())
+		}
+	}
+
+	return nil
+}
+
+const max = 15 // Maximum number of upstreams.