Add any plugin (#2801)

* Add any plugin

This adds the any plugin, a plain copy of coredns/any documented here
https://coredns.io/explugins/any/ as an external plugin.

Fixes: #2785
Signed-off-by: Miek Gieben <miek@miek.nl>

* Stickler bot nit
Signed-off-by: Miek Gieben <miek@miek.nl>

core/dnsserver/zdirectives.go

@@ -26,6 +26,7 @@ var Directives = []string{
 	"errors",
 	"log",
 	"dnstap",
+	"any",
 	"chaos",
 	"loadbalance",
 	"cache",

core/plugin/zplugin.go

@@ -4,6 +4,7 @@ package plugin
 
 import (
 	// Include all plugins.
+	_ "github.com/coredns/coredns/plugin/any"
 	_ "github.com/coredns/coredns/plugin/auto"
 	_ "github.com/coredns/coredns/plugin/autopath"
 	_ "github.com/coredns/coredns/plugin/bind"

plugin.cfg

@@ -35,6 +35,7 @@ prometheus:metrics
 errors:errors
 log:log
 dnstap:dnstap
+any:any
 chaos:chaos
 loadbalance:loadbalance
 cache:cache

plugin/any/OWNERS

+reviewers:
+  - miekg
+approvers:
+  - miekg

plugin/any/README.md

+
+# any
+
+## Name
+
+*any* - give a minimal response to ANY queries.
+
+## Description
+
+*any* basically blocks ANY queries by responding to them with a short HINFO reply. See [RFC
+8482](https://tools.ietf.org/html/rfc8482) for details.
+
+## Syntax
+
+~~~ txt
+any
+~~~
+
+## Examples
+
+~~~ corefile
+example.org {
+    whoami
+    any
+}
+~~~
+
+A `dig +nocmd ANY example.org +noall +answer` now returns:
+
+~~~ txt
+example.org.  8482	IN	HINFO	"ANY obsoleted" "See RFC 8482"
+~~~
+
+## Also See
+
+[RFC 8482](https://tools.ietf.org/html/rfc8482).

plugin/any/any.go

+package any
+
+import (
+	"context"
+
+	"github.com/coredns/coredns/plugin"
+
+	"github.com/miekg/dns"
+)
+
+// Any is a plugin that returns a HINFO reply to ANY queries.
+type Any struct {
+	Next plugin.Handler
+}
+
+// ServeDNS implements the plugin.Handler interface.
+func (a Any) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
+	if r.Question[0].Qtype != dns.TypeANY {
+		return plugin.NextOrFailure(a.Name(), a.Next, ctx, w, r)
+	}
+
+	m := new(dns.Msg)
+	m.SetReply(r)
+	hdr := dns.RR_Header{Name: r.Question[0].Name, Ttl: 8482, Class: dns.ClassINET, Rrtype: dns.TypeHINFO}
+	m.Answer = []dns.RR{&dns.HINFO{Hdr: hdr, Cpu: "ANY obsoleted", Os: "See RFC 8482"}}
+
+	w.WriteMsg(m)
+	return 0, nil
+}
+
+// Name implements the Handler interface.
+func (a Any) Name() string { return "any" }

plugin/any/any_test.go

+package any
+
+import (
+	"context"
+	"testing"
+
+	"github.com/coredns/coredns/plugin/pkg/dnstest"
+	"github.com/coredns/coredns/plugin/test"
+
+	"github.com/miekg/dns"
+)
+
+func TestAny(t *testing.T) {
+	req := new(dns.Msg)
+	req.SetQuestion("example.org.", dns.TypeANY)
+	a := &Any{}
+
+	rec := dnstest.NewRecorder(&test.ResponseWriter{})
+	_, err := a.ServeDNS(context.TODO(), rec, req)
+
+	if err != nil {
+		t.Errorf("Expected no error, but got %q", err)
+	}
+
+	if rec.Msg.Answer[0].(*dns.HINFO).Cpu != "ANY obsoleted" {
+		t.Errorf("Expected HINFO, but got %q", rec.Msg.Answer[0].(*dns.HINFO).Cpu)
+	}
+}

plugin/any/setup.go

+package any
+
+import (
+	"github.com/coredns/coredns/core/dnsserver"
+	"github.com/coredns/coredns/plugin"
+
+	"github.com/mholt/caddy"
+)
+
+func init() {
+	caddy.RegisterPlugin("any", caddy.Plugin{
+		ServerType: "dns",
+		Action:     setup,
+	})
+}
+
+func setup(c *caddy.Controller) error {
+	a := Any{}
+
+	dnsserver.GetConfig(c).AddPlugin(func(next plugin.Handler) plugin.Handler {
+		a.Next = next
+		return a
+	})
+
+	return nil
+}