naive implementation

Signed-off-by: Adphi <philippe.adrien.nousse@gmail.com>

.gitignore

@@ -1 +1,2 @@
 .idea
+tests

README.md

@@ -6,9 +6,15 @@
 
 ## Description
 
-The split plugin allows filtering DNS Server response Records based on network definitions. That way
+The split plugin allows filtering DNS Server responses Records based on network definitions. That way
 you do not need to run multiple DNS servers to handle split DNS.
 
+If there are multiple A Records in the response, only the records matching the defined network will be returned
+to a matching querier, and the records not matching the network to the other sources.
+
+This plugin is not about security, it is design only to give a better answer to the incoming source IP,
+if you need to apply security filtering rules, please consider using the [**coredns** *acl*](https://coredns.io/plugins/acl/) plugin.
+
 ## Compilation
 
 This package will always be compiled as part of CoreDNS and not in a standalone way. It will require you to use `go get` or as a dependency on [plugin.cfg](https://github.com/coredns/coredns/blob/master/plugin.cfg).
@@ -21,7 +27,7 @@ A simple way to consume this plugin, is by adding the following on [plugin.cfg](
 split:go.linka.cloud/coredns-split
 ~~~
 
-Put this lower in the plugin list, so that *split* is executed after any of the other plugins.
+Put this higher in the plugin list, so that *split* is before after any of the other plugins.
 
 After this you can compile coredns by:
 
@@ -57,22 +63,17 @@ This plugin reports readiness to the ready plugin. It will be immediately ready.
 
 ## Examples
 
-In this configuration, we forward all queries to 9.9.9.9 and print "example" whenever we receive
-a query.
+In this configuration, we forward all queries to 9.9.9.9 and filter out A records pointing to an IP address
+in the 10.10.10.0/24 network except for queries coming from the 192.168.0.0/24 and 192.168.1.0/24 networks.
 
 ~~~ corefile
 . {
+  example {
+    10.10.10.0/24 {
+        net 192.168.0.0/24 192.168.1.0/24
+    }
+  }
   forward . 9.9.9.9
-  example
-}
-~~~
-
-Or without any external connectivity:
-
-~~~ corefile
-. {
-  whoami
-  example
 }
 ~~~
 

ready.go

@@ -2,4 +2,6 @@ package split
 
 // Ready implements the ready.Readiness interface, once this flips to true CoreDNS
 // assumes this plugin is ready for queries; it is not checked again.
-func (e Split) Ready() bool { return true }
+func (s Split) Ready() bool {
+	return true
+}

setup.go

@@ -1,6 +1,8 @@
 package split
 
 import (
+	"net"
+
 	"github.com/coredns/caddy"
 	"github.com/coredns/coredns/core/dnsserver"
 	"github.com/coredns/coredns/plugin"
@@ -12,17 +14,46 @@ func init() { plugin.Register("split", setup) }
 // setup is the function that gets called when the config parser see the token "example". Setup is responsible
 // for parsing any extra options the example plugin may have. The first token this function sees is "example".
 func setup(c *caddy.Controller) error {
-	c.Next() // Ignore "example" and give us the next token.
-	if c.NextArg() {
-		// If there was another token, return an error, because we don't have any configuration.
-		// Any errors returned from this setup function should be wrapped with plugin.Error, so we
-		// can present a slightly nicer error message to the user.
-		return plugin.Error("split", c.ArgErr())
+	s := Split{}
+	for c.Next() {
+		r := rule{}
+		args := c.RemainingArgs()
+		r.zones = plugin.OriginsFromArgsOrServerBlock(args, c.ServerBlockKeys)
+		if c.NextBlock() {
+			n := network{}
+			_, ipnet, err := net.ParseCIDR(c.Val())
+			if err != nil {
+				return err
+			}
+			n.record = ipnet
+			for c.NextBlock() {
+				for c.NextLine() {
+					a := c.Val()
+					_ = a
+				argsLoop:
+					for _, v := range c.RemainingArgs() {
+						_, ipnet, err := net.ParseCIDR(v)
+						if err != nil {
+							return err
+						}
+						for _, vv := range n.allowed {
+							if vv.Contains(ipnet.IP) {
+								continue argsLoop
+							}
+						}
+						n.allowed = append(n.allowed, ipnet)
+					}
+				}
+				r.networks = append(r.networks, n)
+			}
+			s.Rule = append(s.Rule, r)
+		}
 	}
 
 	// Add the Plugin to CoreDNS, so Servers can use it in their plugin chain.
 	dnsserver.GetConfig(c).AddPlugin(func(next plugin.Handler) plugin.Handler {
-		return Split{Next: next}
+		s.Next = next
+		return s
 	})
 
 	// All OK, return a nil error.

setup_test.go

@@ -13,9 +13,4 @@ func TestSetup(t *testing.T) {
 	if err := setup(c); err != nil {
 		t.Fatalf("Expected no errors, but got: %v", err)
 	}
-
-	c = caddy.NewTestController("dns", `split more`)
-	if err := setup(c); err == nil {
-		t.Fatalf("Expected errors, but got: %v", err)
-	}
 }

split.go

@@ -5,11 +5,12 @@ package split
 
 import (
 	"context"
+	"net"
 
 	"github.com/coredns/coredns/plugin"
 	"github.com/coredns/coredns/plugin/metrics"
 	clog "github.com/coredns/coredns/plugin/pkg/log"
-
+	"github.com/coredns/coredns/request"
 	"github.com/miekg/dns"
 )
 
@@ -20,44 +21,108 @@ var log = clog.NewWithPlugin("split")
 // Split is an example plugin to show how to write a plugin.
 type Split struct {
 	Next plugin.Handler
+
+	Rule []rule
+}
+
+type rule struct {
+	zones    []string
+	networks []network
+}
+
+type network struct {
+	record  *net.IPNet
+	allowed []*net.IPNet
 }
 
 // ServeDNS implements the plugin.Handler interface. This method gets called when example is used
 // in a Server.
-func (e Split) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
+func (s Split) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
 	// This function could be simpler. I.e. just fmt.Println("example") here, but we want to show
 	// a slightly more complex example as to make this more interesting.
 	// Here we wrap the dns.ResponseWriter in a new ResponseWriter and call the next plugin, when the
 	// answer comes back, it will print "example".
 
-	// Debug log that we've have seen the query. This will only be shown when the debug plugin is loaded.
+	// Debug log that we've seen the query. This will only be shown when the debug plugin is loaded.
 	log.Debug("Received response")
 
 	// Wrap.
-	pw := NewResponsePrinter(w)
+	pw := s.NewResponsePrinter(w, r)
 
 	// Export metric with the server label set to the current server handling the request.
 	requestCount.WithLabelValues(metrics.WithServer(ctx)).Inc()
 
 	// Call next plugin (if any).
-	return plugin.NextOrFailure(e.Name(), e.Next, ctx, pw, r)
+	return plugin.NextOrFailure(s.Name(), s.Next, ctx, pw, r)
 }
 
 // Name implements the Handler interface.
-func (e Split) Name() string { return "split" }
+func (s Split) Name() string { return "split" }
 
 // ResponsePrinter wrap a dns.ResponseWriter and will write example to standard output when WriteMsg is called.
 type ResponsePrinter struct {
 	dns.ResponseWriter
+	state request.Request
+	r     *dns.Msg
+	src   net.IP
+	rules []rule
 }
 
 // NewResponsePrinter returns ResponseWriter.
-func NewResponsePrinter(w dns.ResponseWriter) *ResponsePrinter {
-	return &ResponsePrinter{ResponseWriter: w}
+func (s Split) NewResponsePrinter(w dns.ResponseWriter, r *dns.Msg) *ResponsePrinter {
+	state := request.Request{W: w, Req: r}
+	ip := net.ParseIP(state.IP())
+	return &ResponsePrinter{ResponseWriter: w, r: r, src: ip, rules: s.Rule, state: state}
 }
 
 // WriteMsg calls the underlying ResponseWriter's WriteMsg method and prints "example" to standard output.
 func (r *ResponsePrinter) WriteMsg(res *dns.Msg) error {
-	log.Info("example")
+	var rule rule
+	for _, v := range r.rules {
+		zone := plugin.Zones(v.zones).Matches(r.state.Name())
+		if zone == "" {
+			continue
+		}
+		rule = v
+		break
+	}
+	var answers []dns.RR
+	var netAnswers []dns.RR
+	for _, v := range res.Answer {
+		rec, ok := v.(*dns.A)
+		if !ok {
+			answers = append(answers, v)
+			continue
+		}
+		var net *network
+		for _, vv := range rule.networks {
+			if vv.record.Contains(rec.A) {
+				net = &vv
+				break
+			}
+		}
+		if net == nil {
+			answers = append(answers, v)
+			continue
+		}
+		allowed := false
+		for _, vv := range net.allowed {
+			if vv.Contains(r.src) {
+				allowed = true
+				break
+			}
+		}
+		if allowed {
+			answers = append(answers, v)
+			netAnswers = append(netAnswers, v)
+			continue
+		}
+		log.Infof("request source %s: %s: filtering %s", r.src.String(), rec.Hdr.Name, rec.A)
+	}
+	if len(netAnswers) != 0 {
+		res.Answer = netAnswers
+	} else {
+		res.Answer = answers
+	}
 	return r.ResponseWriter.WriteMsg(res)
 }

split_test.go

@@ -1,10 +1,7 @@
 package split
 
 import (
-	"bytes"
 	"context"
-	golog "log"
-	"strings"
 	"testing"
 
 	"github.com/coredns/coredns/plugin/pkg/dnstest"
@@ -17,11 +14,6 @@ func TestExample(t *testing.T) {
 	// Create a new Split Plugin. Use the test.ErrorHandler as the next plugin.
 	x := Split{Next: test.ErrorHandler()}
 
-	// Setup a new output buffer that is *not* standard output, so we can check if
-	// example is really being printed.
-	b := &bytes.Buffer{}
-	golog.SetOutput(b)
-
 	ctx := context.TODO()
 	r := new(dns.Msg)
 	r.SetQuestion("example.org.", dns.TypeA)
@@ -31,7 +23,5 @@ func TestExample(t *testing.T) {
 
 	// Call our plugin directly, and check the result.
 	x.ServeDNS(ctx, rec, r)
-	if a := b.String(); !strings.Contains(a, "[INFO] plugin/split: example") {
-		t.Errorf("Failed to print '%s', got %s", "[INFO] plugin/split: example", a)
-	}
+	t.Log(rec.Msg)
 }