plugin/forward: add it (#1447)

* plugin/forward: add it

This moves coredns/forward into CoreDNS. Fixes as a few bugs, adds a
policy option and more tests to the plugin.

Update the documentation, test IPv6 address and add persistent tests.

* Always use random policy when spraying

* include scrub fix here as well

* use correct var name

* Code review

* go vet

* Move logging to metrcs

* Small readme updates

* Fix readme

plugin/forward/setup.go

@@ -0,0 +1,262 @@
+package forward
+
+import (
+	"fmt"
+	"net"
+	"strconv"
+	"time"
+
+	"github.com/coredns/coredns/core/dnsserver"
+	"github.com/coredns/coredns/plugin"
+	"github.com/coredns/coredns/plugin/metrics"
+	"github.com/coredns/coredns/plugin/pkg/dnsutil"
+	pkgtls "github.com/coredns/coredns/plugin/pkg/tls"
+
+	"github.com/mholt/caddy"
+)
+
+func init() {
+	caddy.RegisterPlugin("forward", caddy.Plugin{
+		ServerType: "dns",
+		Action:     setup,
+	})
+}
+
+func setup(c *caddy.Controller) error {
+	f, err := parseForward(c)
+	if err != nil {
+		return plugin.Error("foward", err)
+	}
+	if f.Len() > max {
+		return plugin.Error("forward", fmt.Errorf("more than %d TOs configured: %d", max, f.Len()))
+	}
+
+	dnsserver.GetConfig(c).AddPlugin(func(next plugin.Handler) plugin.Handler {
+		f.Next = next
+		return f
+	})
+
+	c.OnStartup(func() error {
+		once.Do(func() {
+			m := dnsserver.GetConfig(c).Handler("prometheus")
+			if m == nil {
+				return
+			}
+			if x, ok := m.(*metrics.Metrics); ok {
+				x.MustRegister(RequestCount)
+				x.MustRegister(RcodeCount)
+				x.MustRegister(RequestDuration)
+				x.MustRegister(HealthcheckFailureCount)
+				x.MustRegister(SocketGauge)
+			}
+		})
+		return f.OnStartup()
+	})
+
+	c.OnShutdown(func() error {
+		return f.OnShutdown()
+	})
+
+	return nil
+}
+
+// OnStartup starts a goroutines for all proxies.
+func (f *Forward) OnStartup() (err error) {
+	if f.hcInterval == 0 {
+		for _, p := range f.proxies {
+			p.host.fails = 0
+		}
+		return nil
+	}
+
+	for _, p := range f.proxies {
+		go p.healthCheck()
+	}
+	return nil
+}
+
+// OnShutdown stops all configured proxies.
+func (f *Forward) OnShutdown() error {
+	if f.hcInterval == 0 {
+		return nil
+	}
+
+	for _, p := range f.proxies {
+		p.close()
+	}
+	return nil
+}
+
+// Close is a synonym for OnShutdown().
+func (f *Forward) Close() {
+	f.OnShutdown()
+}
+
+func parseForward(c *caddy.Controller) (*Forward, error) {
+	f := New()
+
+	protocols := map[int]int{}
+
+	for c.Next() {
+		if !c.Args(&f.from) {
+			return f, c.ArgErr()
+		}
+		f.from = plugin.Host(f.from).Normalize()
+
+		to := c.RemainingArgs()
+		if len(to) == 0 {
+			return f, c.ArgErr()
+		}
+
+		// A bit fiddly, but first check if we've got protocols and if so add them back in when we create the proxies.
+		protocols = make(map[int]int)
+		for i := range to {
+			protocols[i], to[i] = protocol(to[i])
+		}
+
+		// If parseHostPortOrFile expands a file with a lot of nameserver our accounting in protocols doesn't make
+		// any sense anymore... For now: lets don't care.
+		toHosts, err := dnsutil.ParseHostPortOrFile(to...)
+		if err != nil {
+			return f, err
+		}
+
+		for i, h := range toHosts {
+			// Double check the port, if e.g. is 53 and the transport is TLS make it 853.
+			// This can be somewhat annoying because you *can't* have TLS on port 53 then.
+			switch protocols[i] {
+			case TLS:
+				h1, p, err := net.SplitHostPort(h)
+				if err != nil {
+					break
+				}
+
+				// This is more of a bug in // dnsutil.ParseHostPortOrFile that defaults to
+				// 53 because it doesn't know about the tls:// // and friends (that should be fixed). Hence
+				// Fix the port number here, back to what the user intended.
+				if p == "53" {
+					h = net.JoinHostPort(h1, "853")
+				}
+			}
+
+			// We can't set tlsConfig here, because we haven't parsed it yet.
+			// We set it below at the end of parseBlock.
+			p := NewProxy(h)
+			f.proxies = append(f.proxies, p)
+		}
+
+		for c.NextBlock() {
+			if err := parseBlock(c, f); err != nil {
+				return f, err
+			}
+		}
+	}
+
+	if f.tlsServerName != "" {
+		f.tlsConfig.ServerName = f.tlsServerName
+	}
+	for i := range f.proxies {
+		// Only set this for proxies that need it.
+		if protocols[i] == TLS {
+			f.proxies[i].SetTLSConfig(f.tlsConfig)
+		}
+		f.proxies[i].SetExpire(f.expire)
+	}
+	return f, nil
+}
+
+func parseBlock(c *caddy.Controller, f *Forward) 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()
+		}
+		f.ignored = ignore
+	case "max_fails":
+		if !c.NextArg() {
+			return c.ArgErr()
+		}
+		n, err := strconv.Atoi(c.Val())
+		if err != nil {
+			return err
+		}
+		if n < 0 {
+			return fmt.Errorf("max_fails can't be negative: %d", n)
+		}
+		f.maxfails = uint32(n)
+	case "health_check":
+		if !c.NextArg() {
+			return c.ArgErr()
+		}
+		dur, err := time.ParseDuration(c.Val())
+		if err != nil {
+			return err
+		}
+		if dur < 0 {
+			return fmt.Errorf("health_check can't be negative: %d", dur)
+		}
+		f.hcInterval = dur
+		for i := range f.proxies {
+			f.proxies[i].hcInterval = dur
+		}
+	case "force_tcp":
+		if c.NextArg() {
+			return c.ArgErr()
+		}
+		f.forceTCP = true
+		for i := range f.proxies {
+			f.proxies[i].forceTCP = true
+		}
+	case "tls":
+		args := c.RemainingArgs()
+		if len(args) != 3 {
+			return c.ArgErr()
+		}
+
+		tlsConfig, err := pkgtls.NewTLSConfig(args[0], args[1], args[2])
+		if err != nil {
+			return err
+		}
+		f.tlsConfig = tlsConfig
+	case "tls_servername":
+		if !c.NextArg() {
+			return c.ArgErr()
+		}
+		f.tlsServerName = c.Val()
+	case "expire":
+		if !c.NextArg() {
+			return c.ArgErr()
+		}
+		dur, err := time.ParseDuration(c.Val())
+		if err != nil {
+			return err
+		}
+		if dur < 0 {
+			return fmt.Errorf("expire can't be negative: %s", dur)
+		}
+		f.expire = dur
+	case "policy":
+		if !c.NextArg() {
+			return c.ArgErr()
+		}
+		switch x := c.Val(); x {
+		case "random":
+			f.p = &random{}
+		case "round_robin":
+			f.p = &roundRobin{}
+		default:
+			return c.Errf("unknown policy '%s'", x)
+		}
+
+	default:
+		return c.Errf("unknown property '%s'", c.Val())
+	}
+
+	return nil
+}
+
+const max = 15 // Maximum number of upstreams.