Add NSID plugin support for CoreDNS (#1273)

* Add NSID plugin support for CoreDNS

This fix adds NSID plugin support for CoreDNS, as was proposed
in 1256.
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Add test cases for NSID plugin
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Generate code for NSID plugin
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Use hostname as the default (as with bind), and remove unneeded copy
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Add README.md
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

core/dnsserver/zdirectives.go

@@ -12,6 +12,7 @@ package dnsserver
 
 var directives = []string{
 	"tls",
+	"nsid",
 	"root",
 	"bind",
 	"debug",

core/zplugin.go

@@ -23,6 +23,7 @@ import (
 	_ "github.com/coredns/coredns/plugin/loadbalance"
 	_ "github.com/coredns/coredns/plugin/log"
 	_ "github.com/coredns/coredns/plugin/metrics"
+	_ "github.com/coredns/coredns/plugin/nsid"
 	_ "github.com/coredns/coredns/plugin/pprof"
 	_ "github.com/coredns/coredns/plugin/proxy"
 	_ "github.com/coredns/coredns/plugin/reverse"

plugin.cfg

@@ -20,6 +20,7 @@
 # log:log
 
 tls:tls
+nsid:nsid
 root:root
 bind:bind
 debug:debug

plugin/nsid/README.md

+# nsid
+
+*nsid* add an identifier of this server to each reply.
+
+This plugin implements RFC 5001 and adds an EDNS0 OPT resource record to replies that uniquely
+identifies the server. This can be useful in anycast setups to see which server was responsible for
+generating the reply and for debugging.
+
+## Syntax
+
+~~ txt
+nsid [DATA]
+~~
+
+**DATA** is the string to use in the nsid record.
+
+If **DATA** is not given, the host's name is used.
+
+## Examples
+
+Enable nsid:
+
+~~ corefile
+. {
+    nsid
+}
+~~

plugin/nsid/nsid.go

+// Package nsid implements NSID protocol
+package nsid
+
+import (
+	"encoding/hex"
+
+	"github.com/coredns/coredns/plugin"
+
+	"github.com/miekg/dns"
+	"golang.org/x/net/context"
+)
+
+// Nsid plugin
+type Nsid struct {
+	Next plugin.Handler
+	Data string
+}
+
+// ResponseWriter is a response writer that adds NSID response
+type ResponseWriter struct {
+	dns.ResponseWriter
+	Data string
+}
+
+// ServeDNS implements the plugin.Handler interface.
+func (n Nsid) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
+	if option := r.IsEdns0(); option != nil {
+		for _, o := range option.Option {
+			if _, ok := o.(*dns.EDNS0_NSID); ok {
+				nw := &ResponseWriter{ResponseWriter: w, Data: n.Data}
+				return plugin.NextOrFailure(n.Name(), n.Next, ctx, nw, r)
+
+			}
+		}
+	}
+	return plugin.NextOrFailure(n.Name(), n.Next, ctx, w, r)
+}
+
+// WriteMsg implements the dns.ResponseWriter interface.
+func (w *ResponseWriter) WriteMsg(res *dns.Msg) error {
+	if option := res.IsEdns0(); option != nil {
+		for _, o := range option.Option {
+			if e, ok := o.(*dns.EDNS0_NSID); ok {
+				e.Code = dns.EDNS0NSID
+				e.Nsid = hex.EncodeToString([]byte(w.Data))
+			}
+		}
+	}
+	returned := w.ResponseWriter.WriteMsg(res)
+	return returned
+}
+
+// Name implements the Handler interface.
+func (n Nsid) Name() string { return "nsid" }

plugin/nsid/nsid_test.go

+package nsid
+
+import (
+	"encoding/hex"
+	"testing"
+
+	"github.com/coredns/coredns/plugin"
+	"github.com/coredns/coredns/plugin/pkg/dnstest"
+	"github.com/coredns/coredns/plugin/test"
+	"github.com/coredns/coredns/plugin/whoami"
+
+	"github.com/miekg/dns"
+	"golang.org/x/net/context"
+)
+
+func TestNsid(t *testing.T) {
+	em := Nsid{
+		Data: "NSID",
+	}
+
+	tests := []struct {
+		next          plugin.Handler
+		qname         string
+		qtype         uint16
+		expectedCode  int
+		expectedReply string
+		expectedErr   error
+	}{
+		{
+			next:          whoami.Whoami{},
+			qname:         ".",
+			expectedCode:  dns.RcodeSuccess,
+			expectedReply: hex.EncodeToString([]byte("NSID")),
+			expectedErr:   nil,
+		},
+	}
+
+	ctx := context.TODO()
+
+	for i, tc := range tests {
+		req := new(dns.Msg)
+		if tc.qtype == 0 {
+			tc.qtype = dns.TypeA
+		}
+		req.SetQuestion(dns.Fqdn(tc.qname), tc.qtype)
+		req.Question[0].Qclass = dns.ClassINET
+
+		req.SetEdns0(4096, false)
+		option := req.Extra[0].(*dns.OPT)
+		option.Option = append(option.Option, &dns.EDNS0_NSID{Code: dns.EDNS0NSID, Nsid: ""})
+		em.Next = tc.next
+
+		rec := dnstest.NewRecorder(&test.ResponseWriter{})
+		code, err := em.ServeDNS(ctx, rec, req)
+
+		if err != tc.expectedErr {
+			t.Errorf("Test %d: Expected error %v, but got %v", i, tc.expectedErr, err)
+		}
+		if code != int(tc.expectedCode) {
+			t.Errorf("Test %d: Expected status code %d, but got %d", i, tc.expectedCode, code)
+		}
+		if tc.expectedReply != "" {
+			for _, extra := range rec.Msg.Extra {
+				if option, ok := extra.(*dns.OPT); ok {
+					e := option.Option[0].(*dns.EDNS0_NSID)
+					if e.Nsid != tc.expectedReply {
+						t.Errorf("Test %d: Expected answer %s, but got %s", i, tc.expectedReply, e.Nsid)
+					}
+				}
+			}
+		}
+	}
+}

plugin/nsid/setup.go

+package nsid
+
+import (
+	"os"
+	"strings"
+
+	"github.com/coredns/coredns/core/dnsserver"
+	"github.com/coredns/coredns/plugin"
+
+	"github.com/mholt/caddy"
+)
+
+func init() {
+	caddy.RegisterPlugin("nsid", caddy.Plugin{
+		ServerType: "dns",
+		Action:     setup,
+	})
+}
+
+func setup(c *caddy.Controller) error {
+	nsid, err := nsidParse(c)
+	if err != nil {
+		return plugin.Error("nsid", err)
+	}
+
+	dnsserver.GetConfig(c).AddPlugin(func(next plugin.Handler) plugin.Handler {
+		return Nsid{Next: next, Data: nsid}
+	})
+
+	return nil
+}
+
+func nsidParse(c *caddy.Controller) (string, error) {
+	// Use hostname as the default
+	nsid, err := os.Hostname()
+	if err != nil {
+		nsid = "localhost"
+	}
+	for c.Next() {
+		args := c.RemainingArgs()
+		if len(args) == 0 {
+			return nsid, nil
+		}
+		nsid = strings.Join(args, " ")
+		return nsid, nil
+	}
+	return nsid, nil
+}

plugin/nsid/setup_test.go

+package nsid
+
+import (
+	"os"
+	"strings"
+	"testing"
+
+	"github.com/mholt/caddy"
+)
+
+func TestSetupNsid(t *testing.T) {
+	defaultNsid, err := os.Hostname()
+	if err != nil {
+		defaultNsid = "localhost"
+	}
+	tests := []struct {
+		input              string
+		shouldErr          bool
+		expectedData       string
+		expectedErrContent string // substring from the expected error. Empty for positive cases.
+	}{
+		{
+			`nsid`, false, defaultNsid, "",
+		},
+		{
+			`nsid "ps0"`, false, "ps0", "",
+		},
+		{
+			`nsid "worker1"`, false, "worker1", "",
+		},
+		{
+			`nsid "tf 2"`, false, "tf 2", "",
+		},
+	}
+
+	for i, test := range tests {
+		c := caddy.NewTestController("dns", test.input)
+		nsid, err := nsidParse(c)
+
+		if test.shouldErr && err == nil {
+			t.Errorf("Test %d: Expected error but found %s for input %s", i, err, test.input)
+		}
+
+		if err != nil {
+			if !test.shouldErr {
+				t.Errorf("Test %d: Expected no error but found one for input %s. Error was: %v", i, test.input, err)
+			}
+
+			if !strings.Contains(err.Error(), test.expectedErrContent) {
+				t.Errorf("Test %d: Expected error to contain: %v, found error: %v, input: %s", i, test.expectedErrContent, err, test.input)
+			}
+		}
+
+		if !test.shouldErr && nsid != test.expectedData {
+			t.Errorf("Nsid not correctly set for input %s. Expected: %s, actual: %s", test.input, test.expectedData, nsid)
+		}
+	}
+}