Remove the word middleware (#1067)

* Rename middleware to plugin

first pass; mostly used 'sed', few spots where I manually changed
text.

This still builds a coredns binary.

* fmt error

* Rename AddMiddleware to AddPlugin

* Readd AddMiddleware to remain backwards compat

plugin/federation/setup.go

@@ -0,0 +1,89 @@
+package federation
+
+import (
+	"fmt"
+
+	"github.com/coredns/coredns/core/dnsserver"
+	"github.com/coredns/coredns/plugin"
+	"github.com/coredns/coredns/plugin/kubernetes"
+	"github.com/miekg/dns"
+
+	"github.com/mholt/caddy"
+)
+
+func init() {
+	caddy.RegisterPlugin("federation", caddy.Plugin{
+		ServerType: "dns",
+		Action:     setup,
+	})
+}
+
+func setup(c *caddy.Controller) error {
+	fed, err := federationParse(c)
+	if err != nil {
+		return plugin.Error("federation", err)
+	}
+
+	// Do this in OnStartup, so all plugin has been initialized.
+	c.OnStartup(func() error {
+		m := dnsserver.GetConfig(c).Handler("kubernetes")
+		if m == nil {
+			return nil
+		}
+		if x, ok := m.(*kubernetes.Kubernetes); ok {
+			fed.Federations = x.Federations
+		}
+		return nil
+	})
+
+	dnsserver.GetConfig(c).AddPlugin(func(next plugin.Handler) plugin.Handler {
+		fed.Next = next
+		return fed
+	})
+
+	return nil
+}
+
+func federationParse(c *caddy.Controller) (*Federation, error) {
+	fed := New()
+
+	for c.Next() {
+		// federation [zones..]
+		zones := c.RemainingArgs()
+		origins := []string{}
+		if len(zones) > 0 {
+			origins = make([]string, len(zones))
+			copy(origins, zones)
+		} else {
+			origins = make([]string, len(c.ServerBlockKeys))
+			copy(origins, c.ServerBlockKeys)
+		}
+
+		for c.NextBlock() {
+			x := c.Val()
+			switch x {
+			default:
+				args := c.RemainingArgs()
+				if x := len(args); x != 1 {
+					return fed, fmt.Errorf("need two arguments for federation, got %d", x)
+				}
+
+				fed.f[x] = dns.Fqdn(args[0])
+			}
+		}
+
+		for i := range origins {
+			origins[i] = plugin.Host(origins[i]).Normalize()
+		}
+
+		fed.zones = origins
+
+		if len(fed.f) == 0 {
+			return fed, fmt.Errorf("at least one name to zone federation expected")
+		}
+
+		return fed, nil
+	}
+
+	return fed, nil
+}