plugin/view: Advanced routing interface and new 'view' plugin (#5538)

* introduce new interface "dnsserver.Viewer", that allows a plugin implementing it to decide if a query should be routed into its server block.
* add new plugin "view", that uses the new interface to enable a user to define expression based conditions that must be met for a query to be routed to its server block.

Signed-off-by: Chris O'Haver <cohaver@infoblox.com>

plugin/cache/README.md

@@ -85,14 +85,14 @@ Entries with 0 TTL will remain in the cache until randomly evicted when the shar
 
 If monitoring is enabled (via the *prometheus* plugin) then the following metrics are exported:
 
-* `coredns_cache_entries{server, type, zones}` - Total elements in the cache by cache type.
-* `coredns_cache_hits_total{server, type, zones}` - Counter of cache hits by cache type.
-* `coredns_cache_misses_total{server, zones}` - Counter of cache misses. - Deprecated, derive misses from cache hits/requests counters.
-* `coredns_cache_requests_total{server, zones}` - Counter of cache requests.
-* `coredns_cache_prefetch_total{server, zones}` - Counter of times the cache has prefetched a cached item.
-* `coredns_cache_drops_total{server, zones}` - Counter of responses excluded from the cache due to request/response question name mismatch.
-* `coredns_cache_served_stale_total{server, zones}` - Counter of requests served from stale cache entries.
-* `coredns_cache_evictions_total{server, type, zones}` - Counter of cache evictions.
+* `coredns_cache_entries{server, type, zones, view}` - Total elements in the cache by cache type.
+* `coredns_cache_hits_total{server, type, zones, view}` - Counter of cache hits by cache type.
+* `coredns_cache_misses_total{server, zones, view}` - Counter of cache misses. - Deprecated, derive misses from cache hits/requests counters.
+* `coredns_cache_requests_total{server, zones, view}` - Counter of cache requests.
+* `coredns_cache_prefetch_total{server, zones, view}` - Counter of times the cache has prefetched a cached item.
+* `coredns_cache_drops_total{server, zones, view}` - Counter of responses excluded from the cache due to request/response question name mismatch.
+* `coredns_cache_served_stale_total{server, zones, view}` - Counter of requests served from stale cache entries.
+* `coredns_cache_evictions_total{server, type, zones, view}` - Counter of cache evictions.
 
 Cache types are either "denial" or "success". `Server` is the server handling the request, see the
 prometheus plugin for documentation.

plugin/cache/cache.go

@@ -22,6 +22,7 @@ type Cache struct {
 	Zones []string
 
 	zonesMetricLabel string
+	viewMetricLabel  string
 
 	ncache  *cache.Cache
 	ncap    int
@@ -177,11 +178,11 @@ func (w *ResponseWriter) WriteMsg(res *dns.Msg) error {
 	if hasKey && duration > 0 {
 		if w.state.Match(res) {
 			w.set(res, key, mt, duration)
-			cacheSize.WithLabelValues(w.server, Success, w.zonesMetricLabel).Set(float64(w.pcache.Len()))
-			cacheSize.WithLabelValues(w.server, Denial, w.zonesMetricLabel).Set(float64(w.ncache.Len()))
+			cacheSize.WithLabelValues(w.server, Success, w.zonesMetricLabel, w.viewMetricLabel).Set(float64(w.pcache.Len()))
+			cacheSize.WithLabelValues(w.server, Denial, w.zonesMetricLabel, w.viewMetricLabel).Set(float64(w.ncache.Len()))
 		} else {
 			// Don't log it, but increment counter
-			cacheDrops.WithLabelValues(w.server, w.zonesMetricLabel).Inc()
+			cacheDrops.WithLabelValues(w.server, w.zonesMetricLabel, w.viewMetricLabel).Inc()
 		}
 	}
 
@@ -219,7 +220,7 @@ func (w *ResponseWriter) set(m *dns.Msg, key uint64, mt response.Type, duration
 			i.wildcard = w.wildcardFunc()
 		}
 		if w.pcache.Add(key, i) {
-			evictions.WithLabelValues(w.server, Success, w.zonesMetricLabel).Inc()
+			evictions.WithLabelValues(w.server, Success, w.zonesMetricLabel, w.viewMetricLabel).Inc()
 		}
 		// when pre-fetching, remove the negative cache entry if it exists
 		if w.prefetch {
@@ -236,7 +237,7 @@ func (w *ResponseWriter) set(m *dns.Msg, key uint64, mt response.Type, duration
 			i.wildcard = w.wildcardFunc()
 		}
 		if w.ncache.Add(key, i) {
-			evictions.WithLabelValues(w.server, Denial, w.zonesMetricLabel).Inc()
+			evictions.WithLabelValues(w.server, Denial, w.zonesMetricLabel, w.viewMetricLabel).Inc()
 		}
 
 	case response.OtherError:

plugin/cache/handler.go

@@ -60,7 +60,7 @@ func (c *Cache) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg)
 			cw := newPrefetchResponseWriter(server, state, c)
 			go c.doPrefetch(ctx, state, cw, i, now)
 		}
-		servedStale.WithLabelValues(server, c.zonesMetricLabel).Inc()
+		servedStale.WithLabelValues(server, c.zonesMetricLabel, c.viewMetricLabel).Inc()
 	} else if c.shouldPrefetch(i, now) {
 		cw := newPrefetchResponseWriter(server, state, c)
 		go c.doPrefetch(ctx, state, cw, i, now)
@@ -89,7 +89,7 @@ func wildcardFunc(ctx context.Context) func() string {
 }
 
 func (c *Cache) doPrefetch(ctx context.Context, state request.Request, cw *ResponseWriter, i *item, now time.Time) {
-	cachePrefetches.WithLabelValues(cw.server, c.zonesMetricLabel).Inc()
+	cachePrefetches.WithLabelValues(cw.server, c.zonesMetricLabel, c.viewMetricLabel).Inc()
 	c.doRefresh(ctx, state, cw)
 
 	// When prefetching we loose the item i, and with it the frequency
@@ -122,13 +122,13 @@ func (c *Cache) Name() string { return "cache" }
 // getIgnoreTTL unconditionally returns an item if it exists in the cache.
 func (c *Cache) getIgnoreTTL(now time.Time, state request.Request, server string) *item {
 	k := hash(state.Name(), state.QType())
-	cacheRequests.WithLabelValues(server, c.zonesMetricLabel).Inc()
+	cacheRequests.WithLabelValues(server, c.zonesMetricLabel, c.viewMetricLabel).Inc()
 
 	if i, ok := c.ncache.Get(k); ok {
 		itm := i.(*item)
 		ttl := itm.ttl(now)
 		if itm.matches(state) && (ttl > 0 || (c.staleUpTo > 0 && -ttl < int(c.staleUpTo.Seconds()))) {
-			cacheHits.WithLabelValues(server, Denial, c.zonesMetricLabel).Inc()
+			cacheHits.WithLabelValues(server, Denial, c.zonesMetricLabel, c.viewMetricLabel).Inc()
 			return i.(*item)
 		}
 	}
@@ -136,11 +136,11 @@ func (c *Cache) getIgnoreTTL(now time.Time, state request.Request, server string
 		itm := i.(*item)
 		ttl := itm.ttl(now)
 		if itm.matches(state) && (ttl > 0 || (c.staleUpTo > 0 && -ttl < int(c.staleUpTo.Seconds()))) {
-			cacheHits.WithLabelValues(server, Success, c.zonesMetricLabel).Inc()
+			cacheHits.WithLabelValues(server, Success, c.zonesMetricLabel, c.viewMetricLabel).Inc()
 			return i.(*item)
 		}
 	}
-	cacheMisses.WithLabelValues(server, c.zonesMetricLabel).Inc()
+	cacheMisses.WithLabelValues(server, c.zonesMetricLabel, c.viewMetricLabel).Inc()
 	return nil
 }
 

plugin/cache/metrics.go

@@ -14,54 +14,54 @@ var (
 		Subsystem: "cache",
 		Name:      "entries",
 		Help:      "The number of elements in the cache.",
-	}, []string{"server", "type", "zones"})
+	}, []string{"server", "type", "zones", "view"})
 	// cacheRequests is a counter of all requests through the cache.
 	cacheRequests = promauto.NewCounterVec(prometheus.CounterOpts{
 		Namespace: plugin.Namespace,
 		Subsystem: "cache",
 		Name:      "requests_total",
 		Help:      "The count of cache requests.",
-	}, []string{"server", "zones"})
+	}, []string{"server", "zones", "view"})
 	// cacheHits is counter of cache hits by cache type.
 	cacheHits = promauto.NewCounterVec(prometheus.CounterOpts{
 		Namespace: plugin.Namespace,
 		Subsystem: "cache",
 		Name:      "hits_total",
 		Help:      "The count of cache hits.",
-	}, []string{"server", "type", "zones"})
+	}, []string{"server", "type", "zones", "view"})
 	// cacheMisses is the counter of cache misses. - Deprecated
 	cacheMisses = promauto.NewCounterVec(prometheus.CounterOpts{
 		Namespace: plugin.Namespace,
 		Subsystem: "cache",
 		Name:      "misses_total",
 		Help:      "The count of cache misses. Deprecated, derive misses from cache hits/requests counters.",
-	}, []string{"server", "zones"})
+	}, []string{"server", "zones", "view"})
 	// cachePrefetches is the number of time the cache has prefetched a cached item.
 	cachePrefetches = promauto.NewCounterVec(prometheus.CounterOpts{
 		Namespace: plugin.Namespace,
 		Subsystem: "cache",
 		Name:      "prefetch_total",
 		Help:      "The number of times the cache has prefetched a cached item.",
-	}, []string{"server", "zones"})
+	}, []string{"server", "zones", "view"})
 	// cacheDrops is the number responses that are not cached, because the reply is malformed.
 	cacheDrops = promauto.NewCounterVec(prometheus.CounterOpts{
 		Namespace: plugin.Namespace,
 		Subsystem: "cache",
 		Name:      "drops_total",
 		Help:      "The number responses that are not cached, because the reply is malformed.",
-	}, []string{"server", "zones"})
+	}, []string{"server", "zones", "view"})
 	// servedStale is the number of requests served from stale cache entries.
 	servedStale = promauto.NewCounterVec(prometheus.CounterOpts{
 		Namespace: plugin.Namespace,
 		Subsystem: "cache",
 		Name:      "served_stale_total",
 		Help:      "The number of requests served from stale cache entries.",
-	}, []string{"server", "zones"})
+	}, []string{"server", "zones", "view"})
 	// evictions is the counter of cache evictions.
 	evictions = promauto.NewCounterVec(prometheus.CounterOpts{
 		Namespace: plugin.Namespace,
 		Subsystem: "cache",
 		Name:      "evictions_total",
 		Help:      "The count of cache evictions.",
-	}, []string{"server", "type", "zones"})
+	}, []string{"server", "type", "zones", "view"})
 )

plugin/cache/setup.go

@@ -23,6 +23,12 @@ func setup(c *caddy.Controller) error {
 	if err != nil {
 		return plugin.Error("cache", err)
 	}
+
+	c.OnStartup(func() error {
+		ca.viewMetricLabel = dnsserver.GetConfig(c).ViewName
+		return nil
+	})
+
 	dnsserver.GetConfig(c).AddPlugin(func(next plugin.Handler) plugin.Handler {
 		ca.Next = next
 		return ca

plugin/metadata/metadata.go

@@ -27,17 +27,18 @@ func ContextWithMetadata(ctx context.Context) context.Context {
 
 // ServeDNS implements the plugin.Handler interface.
 func (m *Metadata) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
-	ctx = ContextWithMetadata(ctx)
+	rcode, err := plugin.NextOrFailure(m.Name(), m.Next, ctx, w, r)
+	return rcode, err
+}
 
-	state := request.Request{W: w, Req: r}
+// Collect will retrieve metadata functions from each metadata provider and update the context
+func (m *Metadata) Collect(ctx context.Context, state request.Request) context.Context {
+	ctx = ContextWithMetadata(ctx)
 	if plugin.Zones(m.Zones).Matches(state.Name()) != "" {
 		// Go through all Providers and collect metadata.
 		for _, p := range m.Providers {
 			ctx = p.Metadata(ctx, state)
 		}
 	}
-
-	rcode, err := plugin.NextOrFailure(m.Name(), m.Next, ctx, w, r)
-
-	return rcode, err
+	return ctx
 }

plugin/metadata/metadata_test.go

@@ -47,7 +47,10 @@ func TestMetadataServeDNS(t *testing.T) {
 	}
 
 	ctx := context.TODO()
-	m.ServeDNS(ctx, &test.ResponseWriter{}, new(dns.Msg))
+	w := &test.ResponseWriter{}
+	r := new(dns.Msg)
+	ctx = m.Collect(ctx, request.Request{W: w, Req: r})
+	m.ServeDNS(ctx, w, r)
 	nctx := next.ctx
 
 	for _, expected := range expectedMetadata {

plugin/metrics/README.md

@@ -14,12 +14,12 @@ the following metrics are exported:
 
 * `coredns_build_info{version, revision, goversion}` - info about CoreDNS itself.
 * `coredns_panics_total{}` - total number of panics.
-* `coredns_dns_requests_total{server, zone, proto, family, type}` - total query count.
-* `coredns_dns_request_duration_seconds{server, zone, type}` - duration to process each query.
-* `coredns_dns_request_size_bytes{server, zone, proto}` - size of the request in bytes.
-* `coredns_dns_do_requests_total{server, zone}` -  queries that have the DO bit set
-* `coredns_dns_response_size_bytes{server, zone, proto}` - response size in bytes.
-* `coredns_dns_responses_total{server, zone, rcode, plugin}` - response per zone, rcode and plugin.
+* `coredns_dns_requests_total{server, zone, view, proto, family, type}` - total query count.
+* `coredns_dns_request_duration_seconds{server, zone, view, type}` - duration to process each query.
+* `coredns_dns_request_size_bytes{server, zone, view, proto}` - size of the request in bytes.
+* `coredns_dns_do_requests_total{server, view, zone}` -  queries that have the DO bit set
+* `coredns_dns_response_size_bytes{server, zone, view, proto}` - response size in bytes.
+* `coredns_dns_responses_total{server, zone, view, rcode, plugin}` - response per zone, rcode and plugin.
 * `coredns_dns_https_responses_total{server, status}` - responses per server and http status code.
 * `coredns_plugin_enabled{server, zone, name}` - indicates whether a plugin is enabled on per server and zone basis.
 

plugin/metrics/context.go

@@ -22,3 +22,16 @@ func WithServer(ctx context.Context) string {
 	}
 	return srv.(*dnsserver.Server).Addr
 }
+
+// WithView returns the name of the view currently handling the request, if a view is defined.
+//
+// Basic usage with a metric:
+//
+// <metric>.WithLabelValues(metrics.WithView(ctx), labels..).Add(1)
+func WithView(ctx context.Context) string {
+	v := ctx.Value(dnsserver.ViewKey{})
+	if v == nil {
+		return ""
+	}
+	return v.(string)
+}

plugin/metrics/handler.go

@@ -34,7 +34,7 @@ func (m *Metrics) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg
 		rc = status
 	}
 	plugin := m.authoritativePlugin(rw.Caller)
-	vars.Report(WithServer(ctx), state, zone, rcode.ToString(rc), plugin, rw.Len, rw.Start)
+	vars.Report(WithServer(ctx), state, zone, WithView(ctx), rcode.ToString(rc), plugin, rw.Len, rw.Start)
 
 	return status, err
 }

plugin/metrics/vars/report.go

@@ -9,7 +9,7 @@ import (
 // Report reports the metrics data associated with request. This function is exported because it is also
 // called from core/dnsserver to report requests hitting the server that should not be handled and are thus
 // not sent down the plugin chain.
-func Report(server string, req request.Request, zone, rcode, plugin string, size int, start time.Time) {
+func Report(server string, req request.Request, zone, view, rcode, plugin string, size int, start time.Time) {
 	// Proto and Family.
 	net := req.Proto()
 	fam := "1"
@@ -18,16 +18,16 @@ func Report(server string, req request.Request, zone, rcode, plugin string, size
 	}
 
 	if req.Do() {
-		RequestDo.WithLabelValues(server, zone).Inc()
+		RequestDo.WithLabelValues(server, zone, view).Inc()
 	}
 
 	qType := qTypeString(req.QType())
-	RequestCount.WithLabelValues(server, zone, net, fam, qType).Inc()
+	RequestCount.WithLabelValues(server, zone, view, net, fam, qType).Inc()
 
-	RequestDuration.WithLabelValues(server, zone).Observe(time.Since(start).Seconds())
+	RequestDuration.WithLabelValues(server, zone, view).Observe(time.Since(start).Seconds())
 
-	ResponseSize.WithLabelValues(server, zone, net).Observe(float64(size))
-	RequestSize.WithLabelValues(server, zone, net).Observe(float64(req.Len()))
+	ResponseSize.WithLabelValues(server, zone, view, net).Observe(float64(size))
+	RequestSize.WithLabelValues(server, zone, view, net).Observe(float64(req.Len()))
 
-	ResponseRcode.WithLabelValues(server, zone, rcode, plugin).Inc()
+	ResponseRcode.WithLabelValues(server, zone, view, rcode, plugin).Inc()
 }

plugin/metrics/vars/vars.go

@@ -14,7 +14,7 @@ var (
 		Subsystem: subsystem,
 		Name:      "requests_total",
 		Help:      "Counter of DNS requests made per zone, protocol and family.",
-	}, []string{"server", "zone", "proto", "family", "type"})
+	}, []string{"server", "zone", "view", "proto", "family", "type"})
 
 	RequestDuration = promauto.NewHistogramVec(prometheus.HistogramOpts{
 		Namespace: plugin.Namespace,
@@ -22,7 +22,7 @@ var (
 		Name:      "request_duration_seconds",
 		Buckets:   plugin.TimeBuckets,
 		Help:      "Histogram of the time (in seconds) each request took per zone.",
-	}, []string{"server", "zone"})
+	}, []string{"server", "zone", "view"})
 
 	RequestSize = promauto.NewHistogramVec(prometheus.HistogramOpts{
 		Namespace: plugin.Namespace,
@@ -30,14 +30,14 @@ var (
 		Name:      "request_size_bytes",
 		Help:      "Size of the EDNS0 UDP buffer in bytes (64K for TCP) per zone and protocol.",
 		Buckets:   []float64{0, 100, 200, 300, 400, 511, 1023, 2047, 4095, 8291, 16e3, 32e3, 48e3, 64e3},
-	}, []string{"server", "zone", "proto"})
+	}, []string{"server", "zone", "view", "proto"})
 
 	RequestDo = promauto.NewCounterVec(prometheus.CounterOpts{
 		Namespace: plugin.Namespace,
 		Subsystem: subsystem,
 		Name:      "do_requests_total",
 		Help:      "Counter of DNS requests with DO bit set per zone.",
-	}, []string{"server", "zone"})
+	}, []string{"server", "zone", "view"})
 
 	ResponseSize = promauto.NewHistogramVec(prometheus.HistogramOpts{
 		Namespace: plugin.Namespace,
@@ -45,14 +45,14 @@ var (
 		Name:      "response_size_bytes",
 		Help:      "Size of the returned response in bytes.",
 		Buckets:   []float64{0, 100, 200, 300, 400, 511, 1023, 2047, 4095, 8291, 16e3, 32e3, 48e3, 64e3},
-	}, []string{"server", "zone", "proto"})
+	}, []string{"server", "zone", "view", "proto"})
 
 	ResponseRcode = promauto.NewCounterVec(prometheus.CounterOpts{
 		Namespace: plugin.Namespace,
 		Subsystem: subsystem,
 		Name:      "responses_total",
 		Help:      "Counter of response status codes.",
-	}, []string{"server", "zone", "rcode", "plugin"})
+	}, []string{"server", "zone", "view", "rcode", "plugin"})
 
 	Panic = promauto.NewCounter(prometheus.CounterOpts{
 		Namespace: plugin.Namespace,

plugin/pkg/expression/expression.go

@@ -0,0 +1,47 @@
+package expression
+
+import (
+	"context"
+	"errors"
+	"net"
+
+	"github.com/coredns/coredns/plugin/metadata"
+	"github.com/coredns/coredns/request"
+)
+
+// DefaultEnv returns the default set of custom state variables and functions available to for use in expression evaluation.
+func DefaultEnv(ctx context.Context, state *request.Request) map[string]interface{} {
+	return map[string]interface{}{
+		"incidr": func(ipStr, cidrStr string) (bool, error) {
+			ip := net.ParseIP(ipStr)
+			if ip == nil {
+				return false, errors.New("first argument is not an IP address")
+			}
+			_, cidr, err := net.ParseCIDR(cidrStr)
+			if err != nil {
+				return false, err
+			}
+			return cidr.Contains(ip), nil
+		},
+		"metadata": func(label string) string {
+			f := metadata.ValueFunc(ctx, label)
+			if f == nil {
+				return ""
+			}
+			return f()
+		},
+		"type":        state.Type,
+		"name":        state.Name,
+		"class":       state.Class,
+		"proto":       state.Proto,
+		"size":        state.Len,
+		"client_ip":   state.IP,
+		"port":        state.Port,
+		"id":          func() int { return int(state.Req.Id) },
+		"opcode":      func() int { return state.Req.Opcode },
+		"do":          state.Do,
+		"bufsize":     state.Size,
+		"server_ip":   state.LocalIP,
+		"server_port": state.LocalPort,
+	}
+}

plugin/pkg/expression/expression_test.go

@@ -0,0 +1,73 @@
+package expression
+
+import (
+	"context"
+	"testing"
+
+	"github.com/coredns/coredns/plugin/metadata"
+	"github.com/coredns/coredns/request"
+)
+
+func TestInCidr(t *testing.T) {
+	incidr := DefaultEnv(context.Background(), &request.Request{})["incidr"]
+
+	cases := []struct {
+		ip        string
+		cidr      string
+		expected  bool
+		shouldErr bool
+	}{
+		// positive
+		{ip: "1.2.3.4", cidr: "1.2.0.0/16", expected: true, shouldErr: false},
+		{ip: "10.2.3.4", cidr: "1.2.0.0/16", expected: false, shouldErr: false},
+		{ip: "1:2::3:4", cidr: "1:2::/64", expected: true, shouldErr: false},
+		{ip: "A:2::3:4", cidr: "1:2::/64", expected: false, shouldErr: false},
+		// negative
+		{ip: "1.2.3.4", cidr: "invalid", shouldErr: true},
+		{ip: "invalid", cidr: "1.2.0.0/16", shouldErr: true},
+	}
+
+	for i, c := range cases {
+		r, err := incidr.(func(string, string) (bool, error))(c.ip, c.cidr)
+		if err != nil && !c.shouldErr {
+			t.Errorf("Test %d: unexpected error %v", i, err)
+			continue
+		}
+		if err == nil && c.shouldErr {
+			t.Errorf("Test %d: expected error", i)
+			continue
+		}
+		if c.shouldErr {
+			continue
+		}
+		if r != c.expected {
+			t.Errorf("Test %d: expected %v", i, c.expected)
+			continue
+		}
+	}
+}
+
+func TestMetadata(t *testing.T) {
+	ctx := metadata.ContextWithMetadata(context.Background())
+	metadata.SetValueFunc(ctx, "test/metadata", func() string {
+		return "success"
+	})
+	f := DefaultEnv(ctx, &request.Request{})["metadata"]
+
+	cases := []struct {
+		label     string
+		expected  string
+		shouldErr bool
+	}{
+		{label: "test/metadata", expected: "success"},
+		{label: "test/nonexistent", expected: ""},
+	}
+
+	for i, c := range cases {
+		r := f.(func(string) string)(c.label)
+		if r != c.expected {
+			t.Errorf("Test %d: expected %v", i, c.expected)
+			continue
+		}
+	}
+}

plugin/pkg/replacer/replacer_test.go

@@ -340,13 +340,12 @@ func TestMetadataReplacement(t *testing.T) {
 		Next: next,
 	}
 
-	m.ServeDNS(context.TODO(), &test.ResponseWriter{}, new(dns.Msg))
-	ctx := next.ctx // important because the m.ServeDNS has only now populated the context
-
 	w := dnstest.NewRecorder(&test.ResponseWriter{})
 	r := new(dns.Msg)
 	r.SetQuestion("example.org.", dns.TypeHINFO)
 
+	ctx := m.Collect(context.TODO(), request.Request{W: w, Req: r})
+
 	repl := New()
 	state := request.Request{W: w, Req: r}
 

plugin/rewrite/rewrite_test.go

@@ -604,8 +604,8 @@ func TestRewriteEDNS0LocalVariable(t *testing.T) {
 		}
 		rw.Rules = []Rule{r}
 
-		ctx := context.TODO()
 		rec := dnstest.NewRecorder(&test.ResponseWriter{})
+		ctx := meta.Collect(context.TODO(), request.Request{W: rec, Req: m})
 		meta.ServeDNS(ctx, rec, m)
 
 		resp := rec.Msg

plugin/view/README.md

@@ -0,0 +1,135 @@
+# view
+
+## Name
+
+*view* - defines conditions that must be met for a DNS request to be routed to the server block.
+
+## Description
+
+*view* defines an expression that must evaluate to true for a DNS request to be routed to the server block.
+This enables advanced server block routing functions such as split dns.
+
+## Syntax
+```
+view NAME {
+  expr EXPRESSION
+}
+```
+
+* `view` **NAME** - The name of the view used by metrics and exported as metadata for requests that match the
+  view's expression
+* `expr` **EXPRESSION** - CoreDNS will only route incoming queries to the enclosing server block
+  if the **EXPRESSION** evaluates to true. See the **Expressions** section for available variables and functions.
+  If multiple instances of view are defined, all **EXPRESSION** must evaluate to true for CoreDNS will only route
+  incoming queries to the enclosing server block.
+
+For expression syntax and examples, see the Expressions and Examples sections.
+
+## Examples
+
+Implement CIDR based split DNS routing.  This will return a different
+answer for `test.` depending on client's IP address.  It returns ...
+* `test. 3600 IN A 1.1.1.1`, for queries with a source address in 127.0.0.0/24
+* `test. 3600 IN A 2.2.2.2`, for queries with a source address in 192.168.0.0/16
+* `test. 3600 IN A 3.3.3.3`, for all others
+
+```
+. {
+  view example1 {
+    expr incidr(client_ip(), '127.0.0.0/24')
+  }
+  hosts {
+    1.1.1.1 test
+  }
+}
+
+. {
+  view example2 {
+    expr incidr(client_ip(), '192.168.0.0/16')
+  }
+  hosts {
+    2.2.2.2 test
+  }
+}
+
+. {
+  hosts {
+    3.3.3.3 test
+  }
+}
+```
+
+Send all `A` and `AAAA` requests to `10.0.0.6`, and all other requests to `10.0.0.1`.
+
+```
+. {
+  view example {
+    expr type() in ['A', 'AAAA']
+  }
+  forward . 10.0.0.6
+}
+
+. {
+  forward . 10.0.0.1
+}
+```
+
+Send all requests for `abc.*.example.com` (where * can be any number of labels), to `10.0.0.2`, and all other
+requests to `10.0.0.1`.
+Note that the regex pattern is enclosed in single quotes, and backslashes are escaped with backslashes.
+
+```
+. {
+  view example {
+    expr name() matches '^abc\\..*\\.example\\.com\\.$'
+  }
+  forward . 10.0.0.2
+}
+
+. {
+  forward . 10.0.0.1
+}
+```
+
+## Expressions
+
+To evaluate expressions, *view* uses the antonmedv/expr package (https://github.com/antonmedv/expr).
+For example, an expression could look like:
+`(type() == 'A' && name() == 'example.com') || client_ip() == '1.2.3.4'`.
+
+All expressions should be written to evaluate to a boolean value.
+
+See https://github.com/antonmedv/expr/blob/master/docs/Language-Definition.md as a detailed reference for valid syntax.
+
+### Available Expression Functions
+
+In the context of the *view* plugin, expressions can reference DNS query information by using utility
+functions defined below.
+
+#### DNS Query Functions
+
+* `bufsize() int`: the EDNS0 buffer size advertised in the query
+* `class() string`: class of the request (IN, CH, ...)
+* `client_ip() string`: client's IP address, for IPv6 addresses these are enclosed in brackets: `[::1]`
+* `do() bool`: the EDNS0 DO (DNSSEC OK) bit set in the query
+* `id() int`: query ID
+* `name() string`: name of the request (the domain name requested)
+* `opcode() int`: query OPCODE
+* `port() string`: client's port
+* `proto() string`: protocol used (tcp or udp)
+* `server_ip() string`: server's IP address; for IPv6 addresses these are enclosed in brackets: `[::1]`
+* `server_port() string` : client's port
+* `size() int`: request size in bytes
+* `type() string`: type of the request (A, AAAA, TXT, ...)
+
+#### Utility Functions
+
+* `incidr(ip string, cidr string) bool`: returns true if _ip_ is within _cidr_
+* `metadata(label string)` - returns the value for the metadata matching _label_
+
+## Metadata
+
+The view plugin will publish the following metadata, if the *metadata*
+plugin is also enabled:
+
+* `view/name`: the name of the view handling the current request

plugin/view/metadata.go

@@ -0,0 +1,16 @@
+package view
+
+import (
+	"context"
+
+	"github.com/coredns/coredns/plugin/metadata"
+	"github.com/coredns/coredns/request"
+)
+
+// Metadata implements the metadata.Provider interface.
+func (v *View) Metadata(ctx context.Context, state request.Request) context.Context {
+	metadata.SetValueFunc(ctx, "view/name", func() string {
+		return v.viewName
+	})
+	return ctx
+}

plugin/view/setup.go

@@ -0,0 +1,65 @@
+package view
+
+import (
+	"context"
+	"strings"
+
+	"github.com/coredns/caddy"
+	"github.com/coredns/coredns/core/dnsserver"
+	"github.com/coredns/coredns/plugin"
+	"github.com/coredns/coredns/plugin/pkg/expression"
+
+	"github.com/antonmedv/expr"
+)
+
+func init() { plugin.Register("view", setup) }
+
+func setup(c *caddy.Controller) error {
+	cond, err := parse(c)
+	if err != nil {
+		return plugin.Error("view", err)
+	}
+
+	dnsserver.GetConfig(c).AddPlugin(func(next plugin.Handler) plugin.Handler {
+		cond.Next = next
+		return cond
+	})
+
+	return nil
+}
+
+func parse(c *caddy.Controller) (*View, error) {
+	v := new(View)
+
+	i := 0
+	for c.Next() {
+		i++
+		if i > 1 {
+			return nil, plugin.ErrOnce
+		}
+		args := c.RemainingArgs()
+		if len(args) != 1 {
+			return nil, c.ArgErr()
+		}
+		v.viewName = args[0]
+
+		for c.NextBlock() {
+			switch c.Val() {
+			case "expr":
+				args := c.RemainingArgs()
+				prog, err := expr.Compile(strings.Join(args, " "), expr.Env(expression.DefaultEnv(context.Background(), nil)))
+				if err != nil {
+					return v, err
+				}
+				v.progs = append(v.progs, prog)
+				if err != nil {
+					return nil, err
+				}
+				continue
+			default:
+				return nil, c.Errf("unknown property '%s'", c.Val())
+			}
+		}
+	}
+	return v, nil
+}

plugin/view/setup_test.go

@@ -0,0 +1,38 @@
+package view
+
+import (
+	"testing"
+
+	"github.com/coredns/caddy"
+)
+
+func TestSetup(t *testing.T) {
+	tests := []struct {
+		input     string
+		shouldErr bool
+		progCount int
+	}{
+		{"view example {\n expr name() == 'example.com.'\n}", false, 1},
+		{"view example {\n expr incidr(client_ip(), '10.0.0.0/24')\n}", false, 1},
+		{"view example {\n expr name() == 'example.com.'\n expr name() == 'example2.com.'\n}", false, 2},
+		{"view", true, 0},
+		{"view example {\n expr invalid expression\n}", true, 0},
+	}
+
+	for i, test := range tests {
+		v, err := parse(caddy.NewTestController("dns", test.input))
+
+		if test.shouldErr && err == nil {
+			t.Errorf("Test %d: Expected error but found none for input %s", i, test.input)
+		}
+		if err != nil && !test.shouldErr {
+			t.Errorf("Test %d: Expected no error but found one for input %s. Error was: %v", i, test.input, err)
+		}
+		if test.shouldErr {
+			continue
+		}
+		if test.progCount != len(v.progs) {
+			t.Errorf("Test %d: Expected prog length %d, but got %d for %s.", i, test.progCount, len(v.progs), test.input)
+		}
+	}
+}

plugin/view/view.go

@@ -0,0 +1,48 @@
+package view
+
+import (
+	"context"
+
+	"github.com/coredns/coredns/plugin"
+	"github.com/coredns/coredns/plugin/pkg/expression"
+	"github.com/coredns/coredns/request"
+
+	"github.com/antonmedv/expr"
+	"github.com/antonmedv/expr/vm"
+	"github.com/miekg/dns"
+)
+
+// View is a plugin that enables configuring expression based advanced routing
+type View struct {
+	progs    []*vm.Program
+	viewName string
+	Next     plugin.Handler
+}
+
+// Filter implements dnsserver.Viewer.  It returns true if all View rules evaluate to true for the given state.
+func (v *View) Filter(ctx context.Context, state *request.Request) bool {
+	env := expression.DefaultEnv(ctx, state)
+	for _, prog := range v.progs {
+		result, err := expr.Run(prog, env)
+		if err != nil {
+			return false
+		}
+		if b, ok := result.(bool); ok && b {
+			continue
+		}
+		// anything other than a boolean true result is considered false
+		return false
+	}
+	return true
+}
+
+// ViewName implements dnsserver.Viewer. It returns the view name
+func (v *View) ViewName() string { return v.viewName }
+
+// Name implements the Handler interface
+func (*View) Name() string { return "view" }
+
+// ServeDNS implements the Handler interface.
+func (v *View) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
+	return plugin.NextOrFailure(v.Name(), v.Next, ctx, w, r)
+}