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>

core/dnsserver/address.go

@@ -49,11 +49,23 @@ func newOverlapZone() *zoneOverlap {
 // registerAndCheck adds a new zoneAddr for validation, it returns information about existing or overlapping with already registered
 // we consider that an unbound address is overlapping all bound addresses for same zone, same port
 func (zo *zoneOverlap) registerAndCheck(z zoneAddr) (existingZone *zoneAddr, overlappingZone *zoneAddr) {
+	existingZone, overlappingZone = zo.check(z)
+	if existingZone != nil || overlappingZone != nil {
+		return existingZone, overlappingZone
+	}
+	// there is no overlap, keep the current zoneAddr for future checks
+	zo.registeredAddr[z] = z
+	zo.unboundOverlap[z.unbound()] = z
+	return nil, nil
+}
+
+// check validates a zoneAddr for overlap without registering it
+func (zo *zoneOverlap) check(z zoneAddr) (existingZone *zoneAddr, overlappingZone *zoneAddr) {
 	if exist, ok := zo.registeredAddr[z]; ok {
 		// exact same zone already registered
 		return &exist, nil
 	}
-	uz := zoneAddr{Zone: z.Zone, Address: "", Port: z.Port, Transport: z.Transport}
+	uz := z.unbound()
 	if already, ok := zo.unboundOverlap[uz]; ok {
 		if z.Address == "" {
 			// current is not bound to an address, but there is already another zone with a bind address registered
@@ -64,8 +76,11 @@ func (zo *zoneOverlap) registerAndCheck(z zoneAddr) (existingZone *zoneAddr, ove
 			return nil, &uz
 		}
 	}
-	// there is no overlap, keep the current zoneAddr for future checks
-	zo.registeredAddr[z] = z
-	zo.unboundOverlap[uz] = z
+	// there is no overlap
 	return nil, nil
 }
+
+// unbound returns an unbound version of the zoneAddr
+func (z zoneAddr) unbound() zoneAddr {
+	return zoneAddr{Zone: z.Zone, Address: "", Port: z.Port, Transport: z.Transport}
+}

core/dnsserver/config.go

@@ -1,12 +1,14 @@
 package dnsserver
 
 import (
+	"context"
 	"crypto/tls"
 	"fmt"
 	"net/http"
 
 	"github.com/coredns/caddy"
 	"github.com/coredns/coredns/plugin"
+	"github.com/coredns/coredns/request"
 )
 
 // Config configuration for a single server.
@@ -40,6 +42,14 @@ type Config struct {
 	// may depend on it.
 	HTTPRequestValidateFunc func(*http.Request) bool
 
+	// FilterFuncs is used to further filter access
+	// to this handler. E.g. to limit access to a reverse zone
+	// on a non-octet boundary, i.e. /17
+	FilterFuncs []FilterFunc
+
+	// ViewName is the name of the Viewer PLugin defined in the Config
+	ViewName string
+
 	// TLSConfig when listening for encrypted connections (gRPC, DNS-over-TLS).
 	TLSConfig *tls.Config
 
@@ -60,8 +70,14 @@ type Config struct {
 	// firstConfigInBlock is used to reference the first config in a server block, for the
 	// purpose of sharing single instance of each plugin among all zones in a server block.
 	firstConfigInBlock *Config
+
+	// metaCollector references the first MetadataCollector plugin, if one exists
+	metaCollector MetadataCollector
 }
 
+// FilterFunc is a function that filters requests from the Config
+type FilterFunc func(context.Context, *request.Request) bool
+
 // keyForConfig builds a key for identifying the configs during setup time
 func keyForConfig(blocIndex int, blocKeyIndex int) string {
 	return fmt.Sprintf("%d:%d", blocIndex, blocKeyIndex)

core/dnsserver/onstartup.go

@@ -21,7 +21,7 @@ func checkZoneSyntax(zone string) bool {
 // startUpZones creates the text that we show when starting up:
 // grpc://example.com.:1055
 // example.com.:1053 on 127.0.0.1
-func startUpZones(protocol, addr string, zones map[string]*Config) string {
+func startUpZones(protocol, addr string, zones map[string][]*Config) string {
 	s := ""
 
 	keys := make([]string, len(zones))

core/dnsserver/register.go

@@ -138,13 +138,6 @@ func (h *dnsContext) InspectServerBlocks(sourceFile string, serverBlocks []caddy
 
 // MakeServers uses the newly-created siteConfigs to create and return a list of server instances.
 func (h *dnsContext) MakeServers() ([]caddy.Server, error) {
-	// Now that all Keys and Directives are parsed and initialized
-	// lets verify that there is no overlap on the zones and addresses to listen for
-	errValid := h.validateZonesAndListeningAddresses()
-	if errValid != nil {
-		return nil, errValid
-	}
-
 	// Copy the Plugin, ListenHosts and Debug from first config in the block
 	// to all other config in the same block . Doing this results in zones
 	// sharing the same plugin instances and settings as other zones in
@@ -198,6 +191,27 @@ func (h *dnsContext) MakeServers() ([]caddy.Server, error) {
 		}
 	}
 
+	// For each server config, check for View Filter plugins
+	for _, c := range h.configs {
+		// Add filters in the plugin.cfg order for consistent filter func evaluation order.
+		for _, d := range Directives {
+			if vf, ok := c.registry[d].(Viewer); ok {
+				if c.ViewName != "" {
+					return nil, fmt.Errorf("multiple views defined in server block")
+				}
+				c.ViewName = vf.ViewName()
+				c.FilterFuncs = append(c.FilterFuncs, vf.Filter)
+			}
+		}
+	}
+
+	// Verify that there is no overlap on the zones and listen addresses
+	// for unfiltered server configs
+	errValid := h.validateZonesAndListeningAddresses()
+	if errValid != nil {
+		return nil, errValid
+	}
+
 	return servers, nil
 }
 
@@ -253,7 +267,15 @@ func (h *dnsContext) validateZonesAndListeningAddresses() error {
 		for _, h := range conf.ListenHosts {
 			// Validate the overlapping of ZoneAddr
 			akey := zoneAddr{Transport: conf.Transport, Zone: conf.Zone, Address: h, Port: conf.Port}
-			existZone, overlapZone := checker.registerAndCheck(akey)
+			var existZone, overlapZone *zoneAddr
+			if len(conf.FilterFuncs) > 0 {
+				// This config has filters. Check for overlap with other (unfiltered) configs.
+				existZone, overlapZone = checker.check(akey)
+			} else {
+				// This config has no filters. Check for overlap with other (unfiltered) configs,
+				// and register the zone to prevent subsequent zones from overlapping with it.
+				existZone, overlapZone = checker.registerAndCheck(akey)
+			}
 			if existZone != nil {
 				return fmt.Errorf("cannot serve %s - it is already defined", akey.String())
 			}

core/dnsserver/server.go

@@ -37,23 +37,28 @@ type Server struct {
 	server [2]*dns.Server // 0 is a net.Listener, 1 is a net.PacketConn (a *UDPConn) in our case.
 	m      sync.Mutex     // protects the servers
 
-	zones        map[string]*Config // zones keyed by their address
-	dnsWg        sync.WaitGroup     // used to wait on outstanding connections
-	graceTimeout time.Duration      // the maximum duration of a graceful shutdown
-	trace        trace.Trace        // the trace plugin for the server
-	debug        bool               // disable recover()
-	stacktrace   bool               // enable stacktrace in recover error log
-	classChaos   bool               // allow non-INET class queries
+	zones        map[string][]*Config // zones keyed by their address
+	dnsWg        sync.WaitGroup       // used to wait on outstanding connections
+	graceTimeout time.Duration        // the maximum duration of a graceful shutdown
+	trace        trace.Trace          // the trace plugin for the server
+	debug        bool                 // disable recover()
+	stacktrace   bool                 // enable stacktrace in recover error log
+	classChaos   bool                 // allow non-INET class queries
 
 	tsigSecret map[string]string
 }
 
+// MetadataCollector is a plugin that can retrieve metadata functions from all metadata providing plugins
+type MetadataCollector interface {
+	Collect(context.Context, request.Request) context.Context
+}
+
 // NewServer returns a new CoreDNS server and compiles all plugins in to it. By default CH class
 // queries are blocked unless queries from enableChaos are loaded.
 func NewServer(addr string, group []*Config) (*Server, error) {
 	s := &Server{
 		Addr:         addr,
-		zones:        make(map[string]*Config),
+		zones:        make(map[string][]*Config),
 		graceTimeout: 5 * time.Second,
 		tsigSecret:   make(map[string]string),
 	}
@@ -72,8 +77,9 @@ func NewServer(addr string, group []*Config) (*Server, error) {
 			log.D.Set()
 		}
 		s.stacktrace = site.Stacktrace
-		// set the config per zone
-		s.zones[site.Zone] = site
+
+		// append the config to the zone's configs
+		s.zones[site.Zone] = append(s.zones[site.Zone], site)
 
 		// copy tsig secrets
 		for key, secret := range site.TsigSecret {
@@ -88,6 +94,12 @@ func NewServer(addr string, group []*Config) (*Server, error) {
 			// register the *handler* also
 			site.registerHandler(stack)
 
+			// If the current plugin is a MetadataCollector, bookmark it for later use. This loop traverses the plugin
+			// list backwards, so the first MetadataCollector plugin wins.
+			if mdc, ok := stack.(MetadataCollector); ok {
+				site.metaCollector = mdc
+			}
+
 			if s.trace == nil && stack.Name() == "trace" {
 				// we have to stash away the plugin, not the
 				// Tracer object, because the Tracer won't be initialized yet
@@ -254,24 +266,39 @@ func (s *Server) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg)
 	)
 
 	for {
-		if h, ok := s.zones[q[off:]]; ok {
-			if h.pluginChain == nil { // zone defined, but has not got any plugins
-				errorAndMetricsFunc(s.Addr, w, r, dns.RcodeRefused)
-				return
-			}
-			if r.Question[0].Qtype != dns.TypeDS {
-				rcode, _ := h.pluginChain.ServeDNS(ctx, w, r)
-				if !plugin.ClientWrite(rcode) {
-					errorFunc(s.Addr, w, r, rcode)
+		if z, ok := s.zones[q[off:]]; ok {
+			for _, h := range z {
+				if h.pluginChain == nil { // zone defined, but has not got any plugins
+					errorAndMetricsFunc(s.Addr, w, r, dns.RcodeRefused)
+					return
+				}
+
+				if h.metaCollector != nil {
+					// Collect metadata now, so it can be used before we send a request down the plugin chain.
+					ctx = h.metaCollector.Collect(ctx, request.Request{Req: r, W: w})
+				}
+
+				// If all filter funcs pass, use this config.
+				if passAllFilterFuncs(ctx, h.FilterFuncs, &request.Request{Req: r, W: w}) {
+					if h.ViewName != "" {
+						// if there was a view defined for this Config, set the view name in the context
+						ctx = context.WithValue(ctx, ViewKey{}, h.ViewName)
+					}
+					if r.Question[0].Qtype != dns.TypeDS {
+						rcode, _ := h.pluginChain.ServeDNS(ctx, w, r)
+						if !plugin.ClientWrite(rcode) {
+							errorFunc(s.Addr, w, r, rcode)
+						}
+						return
+					}
+					// The type is DS, keep the handler, but keep on searching as maybe we are serving
+					// the parent as well and the DS should be routed to it - this will probably *misroute* DS
+					// queries to a possibly grand parent, but there is no way for us to know at this point
+					// if there is an actual delegation from grandparent -> parent -> zone.
+					// In all fairness: direct DS queries should not be needed.
+					dshandler = h
 				}
-				return
 			}
-			// The type is DS, keep the handler, but keep on searching as maybe we are serving
-			// the parent as well and the DS should be routed to it - this will probably *misroute* DS
-			// queries to a possibly grand parent, but there is no way for us to know at this point
-			// if there is an actual delegation from grandparent -> parent -> zone.
-			// In all fairness: direct DS queries should not be needed.
-			dshandler = h
 		}
 		off, end = dns.NextLabel(q, off)
 		if end {
@@ -289,18 +316,46 @@ func (s *Server) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg)
 	}
 
 	// Wildcard match, if we have found nothing try the root zone as a last resort.
-	if h, ok := s.zones["."]; ok && h.pluginChain != nil {
-		rcode, _ := h.pluginChain.ServeDNS(ctx, w, r)
-		if !plugin.ClientWrite(rcode) {
-			errorFunc(s.Addr, w, r, rcode)
+	if z, ok := s.zones["."]; ok {
+		for _, h := range z {
+			if h.pluginChain == nil {
+				continue
+			}
+
+			if h.metaCollector != nil {
+				// Collect metadata now, so it can be used before we send a request down the plugin chain.
+				ctx = h.metaCollector.Collect(ctx, request.Request{Req: r, W: w})
+			}
+
+			// If all filter funcs pass, use this config.
+			if passAllFilterFuncs(ctx, h.FilterFuncs, &request.Request{Req: r, W: w}) {
+				if h.ViewName != "" {
+					// if there was a view defined for this Config, set the view name in the context
+					ctx = context.WithValue(ctx, ViewKey{}, h.ViewName)
+				}
+				rcode, _ := h.pluginChain.ServeDNS(ctx, w, r)
+				if !plugin.ClientWrite(rcode) {
+					errorFunc(s.Addr, w, r, rcode)
+				}
+				return
+			}
 		}
-		return
 	}
 
 	// Still here? Error out with REFUSED.
 	errorAndMetricsFunc(s.Addr, w, r, dns.RcodeRefused)
 }
 
+// passAllFilterFuncs returns true if all filter funcs evaluate to true for the given request
+func passAllFilterFuncs(ctx context.Context, filterFuncs []FilterFunc, req *request.Request) bool {
+	for _, ff := range filterFuncs {
+		if !ff(ctx, req) {
+			return false
+		}
+	}
+	return true
+}
+
 // OnStartupComplete lists the sites served by this server
 // and any relevant information, assuming Quiet is false.
 func (s *Server) OnStartupComplete() {
@@ -341,7 +396,7 @@ func errorAndMetricsFunc(server string, w dns.ResponseWriter, r *dns.Msg, rc int
 	answer.SetRcode(r, rc)
 	state.SizeAndDo(answer)
 
-	vars.Report(server, state, vars.Dropped, rcode.ToString(rc), "" /* plugin */, answer.Len(), time.Now())
+	vars.Report(server, state, vars.Dropped, "", rcode.ToString(rc), "" /* plugin */, answer.Len(), time.Now())
 
 	w.WriteMsg(answer)
 }
@@ -357,6 +412,9 @@ type (
 
 	// LoopKey is the context key to detect server wide loops.
 	LoopKey struct{}
+
+	// ViewKey is the context key for the current view, if defined
+	ViewKey struct{}
 )
 
 // EnableChaos is a map with plugin names for which we should open CH class queries as we block these by default.

core/dnsserver/server_grpc.go

@@ -37,9 +37,11 @@ func NewServergRPC(addr string, group []*Config) (*ServergRPC, error) {
 	// The *tls* plugin must make sure that multiple conflicting
 	// TLS configuration returns an error: it can only be specified once.
 	var tlsConfig *tls.Config
-	for _, conf := range s.zones {
-		// Should we error if some configs *don't* have TLS?
-		tlsConfig = conf.TLSConfig
+	for _, z := range s.zones {
+		for _, conf := range z {
+			// Should we error if some configs *don't* have TLS?
+			tlsConfig = conf.TLSConfig
+		}
 	}
 	// http/2 is required when using gRPC. We need to specify it in next protos
 	// or the upgrade won't happen.

core/dnsserver/server_https.go

@@ -50,9 +50,11 @@ func NewServerHTTPS(addr string, group []*Config) (*ServerHTTPS, error) {
 	// The *tls* plugin must make sure that multiple conflicting
 	// TLS configuration returns an error: it can only be specified once.
 	var tlsConfig *tls.Config
-	for _, conf := range s.zones {
-		// Should we error if some configs *don't* have TLS?
-		tlsConfig = conf.TLSConfig
+	for _, z := range s.zones {
+		for _, conf := range z {
+			// Should we error if some configs *don't* have TLS?
+			tlsConfig = conf.TLSConfig
+		}
 	}
 
 	// http/2 is recommended when using DoH. We need to specify it in next protos
@@ -63,8 +65,10 @@ func NewServerHTTPS(addr string, group []*Config) (*ServerHTTPS, error) {
 
 	// Use a custom request validation func or use the standard DoH path check.
 	var validator func(*http.Request) bool
-	for _, conf := range s.zones {
-		validator = conf.HTTPRequestValidateFunc
+	for _, z := range s.zones {
+		for _, conf := range z {
+			validator = conf.HTTPRequestValidateFunc
+		}
 	}
 	if validator == nil {
 		validator = func(r *http.Request) bool { return r.URL.Path == doh.Path }

core/dnsserver/server_tls.go

@@ -28,9 +28,11 @@ func NewServerTLS(addr string, group []*Config) (*ServerTLS, error) {
 	// The *tls* plugin must make sure that multiple conflicting
 	// TLS configuration returns an error: it can only be specified once.
 	var tlsConfig *tls.Config
-	for _, conf := range s.zones {
-		// Should we error if some configs *don't* have TLS?
-		tlsConfig = conf.TLSConfig
+	for _, z := range s.zones {
+		for _, conf := range z {
+			// Should we error if some configs *don't* have TLS?
+			tlsConfig = conf.TLSConfig
+		}
 	}
 
 	return &ServerTLS{Server: s, tlsConfig: tlsConfig}, nil

core/dnsserver/view.go

@@ -0,0 +1,20 @@
+package dnsserver
+
+import (
+	"context"
+
+	"github.com/coredns/coredns/request"
+)
+
+// Viewer - If Viewer is implemented by a plugin in a server block, its Filter()
+// is added to the server block's filter functions when starting the server. When a running server
+// serves a DNS request, it will route the request to the first Config (server block) that passes
+// all its filter functions.
+type Viewer interface {
+	// Filter returns true if the server should use the server block in which the implementing plugin resides, and the
+	// name of the view for metrics logging.
+	Filter(ctx context.Context, req *request.Request) bool
+
+	// ViewName returns the name of the view
+	ViewName() string
+}

core/dnsserver/zdirectives.go

@@ -60,4 +60,5 @@ var Directives = []string{
 	"whoami",
 	"on",
 	"sign",
+	"view",
 }

core/plugin/zplugin.go

@@ -53,5 +53,6 @@ import (
 	_ "github.com/coredns/coredns/plugin/trace"
 	_ "github.com/coredns/coredns/plugin/transfer"
 	_ "github.com/coredns/coredns/plugin/tsig"
+	_ "github.com/coredns/coredns/plugin/view"
 	_ "github.com/coredns/coredns/plugin/whoami"
 )

go.mod

@@ -6,6 +6,7 @@ require (
 	github.com/Azure/azure-sdk-for-go v66.0.0+incompatible
 	github.com/Azure/go-autorest/autorest v0.11.28
 	github.com/Azure/go-autorest/autorest/azure/auth v0.5.11
+	github.com/antonmedv/expr v1.9.0
 	github.com/apparentlymart/go-cidr v1.1.0
 	github.com/aws/aws-sdk-go v1.44.91
 	github.com/coredns/caddy v1.1.1

go.sum

@@ -93,6 +93,7 @@ github.com/Azure/go-autorest/tracing v0.6.0 h1:TYi4+3m5t6K48TGI9AUdb+IzbnSxvnvUM
 github.com/Azure/go-autorest/tracing v0.6.0/go.mod h1:+vhtPC754Xsa23ID7GlGsrdKBpUA79WCAKPPZVC2DeU=
 github.com/BurntSushi/toml v0.3.1/go.mod h1:xHWCNGjB5oqiDr8zfno3MHue2Ht5sIBksp03qcyfWMU=
 github.com/BurntSushi/xgb v0.0.0-20160522181843-27f122750802/go.mod h1:IVnqGOEym/WlBOVXweHU+Q+/VP0lqqI8lqeDx9IjBqo=
+github.com/DATA-DOG/go-sqlmock v1.3.3/go.mod h1:f/Ixk793poVmq4qj/V1dPUg2JEAKC73Q5eFN3EC/SaM=
 github.com/DataDog/datadog-agent/pkg/obfuscate v0.0.0-20211129110424-6491aa3bf583 h1:3nVO1nQyh64IUY6BPZUpMYMZ738Pu+LsMt3E0eqqIYw=
 github.com/DataDog/datadog-agent/pkg/obfuscate v0.0.0-20211129110424-6491aa3bf583/go.mod h1:EP9f4GqaDJyP1F5jTNMtzdIpw3JpNs3rMSJOnYywCiw=
 github.com/DataDog/datadog-go v3.2.0+incompatible/go.mod h1:LButxg5PwREeZtORoXG3tL4fMGNddJ+vMq1mwgfaqoQ=
@@ -132,6 +133,8 @@ github.com/andreyvit/diff v0.0.0-20170406064948-c7f18ee00883/go.mod h1:rCTlJbsFo
 github.com/andybalholm/brotli v1.0.2/go.mod h1:loMXtMfwqflxFJPmdbJO0a3KNoPuLBgiu3qAvBg8x/Y=
 github.com/andybalholm/brotli v1.0.4/go.mod h1:fO7iG3H7G2nSZ7m0zPUDn85XEX2GTukHGRSepvi9Eig=
 github.com/antihax/optional v1.0.0/go.mod h1:uupD/76wgC+ih3iEmQUL+0Ugr19nfwCT1kdvxnR2qWY=
+github.com/antonmedv/expr v1.9.0 h1:j4HI3NHEdgDnN9p6oI6Ndr0G5QryMY0FNxT4ONrFDGU=
+github.com/antonmedv/expr v1.9.0/go.mod h1:5qsM3oLGDND7sDmQGDXHkYfkjYMUX14qsgqmHhwGEk8=
 github.com/apache/thrift v0.12.0/go.mod h1:cp2SuWMxlEZw2r+iP2GNCdIi4C1qmUzdZFSVb+bacwQ=
 github.com/apparentlymart/go-cidr v1.1.0 h1:2mAhrMoF+nhXqxTzSZMUzDHkLjmIHC+Zzn4tdgBZjnU=
 github.com/apparentlymart/go-cidr v1.1.0/go.mod h1:EBcsNrHc3zQeuaeCeCtQruQm+n9/YjEn/vI25Lg7Gwc=
@@ -197,6 +200,7 @@ github.com/cpuguy83/go-md2man/v2 v2.0.0-20190314233015-f79a8a8ca69d/go.mod h1:ma
 github.com/creack/pty v1.1.7/go.mod h1:lj5s0c3V2DBrqTV7llrYr5NG6My20zk30Fl46Y7DoTY=
 github.com/creack/pty v1.1.9/go.mod h1:oKZEueFk5CKHvIhNR5MUki03XCEU+Q6VDXinZuGJ33E=
 github.com/davecgh/go-spew v0.0.0-20151105211317-5215b55f46b2/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/davecgh/go-spew v0.0.0-20161028175848-04cdfd42973b/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
@@ -261,6 +265,8 @@ github.com/frankban/quicktest v1.13.0/go.mod h1:qLE0fzW0VuyUAJgPU19zByoIr0HtCHN/
 github.com/fsnotify/fsnotify v1.4.7/go.mod h1:jwhsz4b93w/PPRr/qN1Yymfu8t87LnFCMoQvtojpjFo=
 github.com/fsnotify/fsnotify v1.4.9/go.mod h1:znqG4EE+3YCdAaPaxE2ZRY/06pZUdp0tY4IgpuI1SZQ=
 github.com/garyburd/redigo v1.6.3/go.mod h1:rTb6epsqigu3kYKBnaF028A7Tf/Aw5s0cqA47doKKqw=
+github.com/gdamore/encoding v1.0.0/go.mod h1:alR0ol34c49FCSBLjhosxzcPHQbf2trDkoo5dl+VrEg=
+github.com/gdamore/tcell v1.3.0/go.mod h1:Hjvr+Ofd+gLglo7RYKxxnzCBmev3BzsS67MebKS4zMM=
 github.com/getkin/kin-openapi v0.76.0/go.mod h1:660oXbgy5JFMKreazJaQTw7o+X00qeSyhcnluiMv+Xg=
 github.com/ghodss/yaml v0.0.0-20150909031657-73d445a93680/go.mod h1:4dBDuWmgqj2HViK6kFavaiC9ZROes6MMH2rRYeMEF04=
 github.com/ghodss/yaml v1.0.0/go.mod h1:4dBDuWmgqj2HViK6kFavaiC9ZROes6MMH2rRYeMEF04=
@@ -623,6 +629,8 @@ github.com/lib/pq v1.2.0/go.mod h1:5WUZQaWbwv1U+lTReE5YruASi9Al49XbQIvNi/34Woo=
 github.com/lib/pq v1.3.0/go.mod h1:5WUZQaWbwv1U+lTReE5YruASi9Al49XbQIvNi/34Woo=
 github.com/lib/pq v1.10.2/go.mod h1:AlVN5x4E4T544tWzH6hKfbfQvm3HdbOxrmggDNAPY9o=
 github.com/logrusorgru/aurora v0.0.0-20200102142835-e9ef32dff381/go.mod h1:7rIyQOR62GCctdiQpZ/zOJlFyk6y+94wXzv6RNZgaR4=
+github.com/lucasb-eyer/go-colorful v1.0.2/go.mod h1:0MS4r+7BZKSJ5mw4/S5MPN+qHFF1fYclkSPilDOKW0s=
+github.com/lucasb-eyer/go-colorful v1.0.3/go.mod h1:R4dSotOR9KMtayYi1e77YzuveK+i7ruzyGqttikkLy0=
 github.com/lyft/protoc-gen-validate v0.0.13/go.mod h1:XbGvPuh87YZc5TdIa2/I4pLk0QoUACkjt2znoq26NVQ=
 github.com/mailru/easyjson v0.0.0-20160728113105-d5b7844b561a/go.mod h1:C1wdFJiN94OJF2b5HbByQZoLdCWB1Yqtg26g4irojpc=
 github.com/mailru/easyjson v0.0.0-20180730094502-03f2033d19d5/go.mod h1:C1wdFJiN94OJF2b5HbByQZoLdCWB1Yqtg26g4irojpc=
@@ -648,6 +656,8 @@ github.com/mattn/go-isatty v0.0.10/go.mod h1:qgIWMr58cqv1PHHyhnkY9lrL7etaEgOFcME
 github.com/mattn/go-isatty v0.0.11/go.mod h1:PhnuNfih5lzO57/f3n+odYbM4JtupLOxQOAqxQCu2WE=
 github.com/mattn/go-isatty v0.0.12/go.mod h1:cbi8OIDigv2wuxKPP5vlRcQ1OAZbq2CE4Kysco4FUpU=
 github.com/mattn/go-isatty v0.0.14/go.mod h1:7GGIvUiUoEMVVmxf/4nioHXj79iQHKdU27kJ6hsGG94=
+github.com/mattn/go-runewidth v0.0.4/go.mod h1:LwmH8dsx7+W8Uxz3IHJYH5QSwggIsqBzpuz5H//U1FU=
+github.com/mattn/go-runewidth v0.0.8/go.mod h1:H031xJmbD/WCDINGzjvQ9THkh0rPKHF+m2gUSrubnMI=
 github.com/mattn/go-sqlite3 v1.9.0/go.mod h1:FPy6KqzDD04eiIsT53CuJW3U88zkxoIYsOqkbpncsNc=
 github.com/mattn/go-sqlite3 v1.10.0/go.mod h1:FPy6KqzDD04eiIsT53CuJW3U88zkxoIYsOqkbpncsNc=
 github.com/mattn/go-sqlite3 v1.14.12/go.mod h1:NyWgC/yNuGj7Q9rpYnZvas74GogHl5/Z4A/KQRfk6bU=
@@ -786,6 +796,8 @@ github.com/prometheus/procfs v0.8.0/go.mod h1:z7EfXMXOkbkqb9IINtpCn86r/to3BnA0ua
 github.com/rabbitmq/amqp091-go v1.1.0/go.mod h1:ogQDLSOACsLPsIq0NpbtiifNZi2YOz0VTJ0kHRghqbM=
 github.com/rcrowley/go-metrics v0.0.0-20181016184325-3113b8401b8a/go.mod h1:bCqnVzQkZxMG4s8nGwiZ5l3QUCyqpo9Y+/ZMZ9VjZe4=
 github.com/rcrowley/go-metrics v0.0.0-20201227073835-cf1acfcdf475/go.mod h1:bCqnVzQkZxMG4s8nGwiZ5l3QUCyqpo9Y+/ZMZ9VjZe4=
+github.com/rivo/tview v0.0.0-20200219210816-cd38d7432498/go.mod h1:6lkG1x+13OShEf0EaOCaTQYyB7d5nSbb181KtjlS+84=
+github.com/rivo/uniseg v0.1.0/go.mod h1:J6wj4VEh+S6ZtnVlnTBMWIodfgj8LQOQFoIToxlJtxc=
 github.com/rogpeppe/fastuuid v1.2.0/go.mod h1:jVj6XXZzXRy/MSR5jhDC/2q6DgLz+nrA6LYCDYWNEvQ=
 github.com/rogpeppe/go-internal v1.3.0/go.mod h1:M8bDsm7K2OlrFYOpmOWEs/qY81heoFRclV5y23lUDJ4=
 github.com/rs/cors v1.6.0/go.mod h1:gFx+x8UowdsKA9AchylcLynDq+nNFfI8FkUZdN/jGCU=
@@ -796,6 +808,7 @@ github.com/russross/blackfriday/v2 v2.0.1/go.mod h1:+Rmxgy9KzJVeS9/2gXHxylqXiyQD
 github.com/ryanuber/columnize v0.0.0-20160712163229-9b3edd62028f/go.mod h1:sm1tb6uqfes/u+d4ooFouqFdy9/2g9QGwK3SQygK0Ts=
 github.com/ryanuber/columnize v2.1.0+incompatible/go.mod h1:sm1tb6uqfes/u+d4ooFouqFdy9/2g9QGwK3SQygK0Ts=
 github.com/ryanuber/go-glob v1.0.0/go.mod h1:807d1WSdnB0XRJzKNil9Om6lcp/3a0v4qIHxIXzX/Yc=
+github.com/sanity-io/litter v1.2.0/go.mod h1:JF6pZUFgu2Q0sBZ+HSV35P8TVPI1TTzEwyu9FXAw2W4=
 github.com/satori/go.uuid v1.2.0/go.mod h1:dA0hQrYB0VpLJoorglMZABFdXlWrHn1NEOzdhQKdks0=
 github.com/sean-/seed v0.0.0-20170313163322-e2103e2c3529/go.mod h1:DxrIzT+xaE7yg65j358z/aeFdxmN0P9QXhEzd20vsDc=
 github.com/segmentio/kafka-go v0.4.29/go.mod h1:m1lXeqJtIFYZayv0shM/tjrAFljvWLTprxBHd+3PnaU=
@@ -825,6 +838,7 @@ github.com/stretchr/objx v0.1.1/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+
 github.com/stretchr/objx v0.2.0 h1:Hbg2NidpLE8veEBkEZTL3CvlkUIVzuU9jDplZO54c48=
 github.com/stretchr/objx v0.2.0/go.mod h1:qt09Ya8vawLte6SNmTgCsAVtYtaKzEcn8ATUoHMkEqE=
 github.com/stretchr/testify v0.0.0-20151208002404-e3a8ff8ce365/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
+github.com/stretchr/testify v0.0.0-20161117074351-18a02ba4a312/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
 github.com/stretchr/testify v1.2.1/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
 github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
 github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=
@@ -1121,6 +1135,7 @@ golang.org/x/sys v0.0.0-20190502145724-3ef323f4f1fd/go.mod h1:h1NjWce9XRLGQEsW7w
 golang.org/x/sys v0.0.0-20190507160741-ecd444e8653b/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20190606165138-5da285871e9c/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20190624142023-c5567b49c5d0/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20190626150813-e07cf5db2756/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20190726091711-fc99dfbffb4e/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20190813064441-fde4db37ae7a/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20190826190057-c7b8b68b1456/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=

plugin.cfg

@@ -69,3 +69,4 @@ erratic:erratic
 whoami:whoami
 on:github.com/coredns/caddy/onevent
 sign:sign
+view:view

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)
+}

test/view_test.go

@@ -0,0 +1,163 @@
+package test
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/coredns/coredns/plugin/test"
+
+	"github.com/miekg/dns"
+)
+
+func TestView(t *testing.T) {
+	// Hack to get an available port - We spin up a temporary dummy coredns on :0 to get the port number, then we re-use
+	// that one port consistently across all server blocks.
+	corefile := `example.org:0 {
+		erratic
+	}`
+	tmp, addr, _, err := CoreDNSServerAndPorts(corefile)
+	if err != nil {
+		t.Fatalf("Could not get CoreDNS serving instance: %s", err)
+	}
+
+	port := addr[strings.LastIndex(addr, ":")+1:]
+
+	// Corefile with test views
+	corefile = `
+      # split-type config: splits quries for A/AAAA into separate views
+      split-type:` + port + ` {
+		view test-view-a {
+          expr type() == 'A'
+	    }
+        hosts {
+          1.2.3.4 test.split-type
+        }
+      }
+      split-type:` + port + ` {
+		view test-view-aaaa {
+          expr type() == 'AAAA'
+	    }
+        hosts {
+          1:2:3::4 test.split-type
+        }
+      }
+
+      # split-name config: splits queries into separate views based on first label in query name ("one", "two")
+      split-name:` + port + ` {
+		view test-view-1 {
+          expr name() matches '^one\\..*\\.split-name\\.$'
+	    }
+        hosts {
+          1.1.1.1 one.test.split-name one.test.test.test.split-name
+        }
+      }
+      split-name:` + port + ` {
+		view test-view-2 {
+          expr name() matches '^two\\..*\\.split-name\\.$'
+	    }
+        hosts {
+          2.2.2.2 two.test.split-name two.test.test.test.split-name
+        }
+      }
+      split-name:` + port + ` {
+        hosts {
+          3.3.3.3 default.test.split-name
+        }
+      }
+
+     # metadata config: verifies that metadata is properly collected by the server,
+     # and that metadata function correctly looks up the value of the metadata.
+     metadata:` + port + ` {
+       metadata
+       view test-view-meta1 {
+         # This is never true
+         expr metadata('view/name') == 'not-the-view-name'
+	   }
+       hosts {
+         1.1.1.1 test.metadata
+       }
+     }
+     metadata:` + port + ` {
+       view test-view-meta2 {
+         # This is never true. The metadata plugin is not enabled in this server block so the metadata function returns
+         # an empty string
+         expr metadata('view/name') == 'test-view-meta2'
+	   }
+       hosts {
+         2.2.2.2 test.metadata
+       }
+     }
+     metadata:` + port + ` {
+       metadata
+       view test-view-meta3 {
+         # This is always true.  Queries in the zone 'metadata.' should always be served using this view.
+         expr metadata('view/name') == 'test-view-meta3'
+	   }
+       hosts {
+         2.2.2.2 test.metadata
+       }
+     }
+     metadata:` + port + ` {
+       # This block should never be reached since the prior view in the same zone is always true
+       hosts {
+         3.3.3.3 test.metadata
+       }
+     }
+    `
+
+	i, addr, _, err := CoreDNSServerAndPorts(corefile)
+	if err != nil {
+		t.Fatalf("Could not get CoreDNS serving instance: %s", err)
+	}
+	// there are multiple sever blocks, but they are all on the same port, so it's a single server instance to stop
+	defer i.Stop()
+	// stop the temporary instance before starting tests.
+	tmp.Stop()
+
+	viewTest(t, "split-type A", addr, "test.split-type.", dns.TypeA, dns.RcodeSuccess,
+		[]dns.RR{test.A("test.split-type.	303	IN	A	1.2.3.4")})
+
+	viewTest(t, "split-type AAAA", addr, "test.split-type.", dns.TypeAAAA, dns.RcodeSuccess,
+		[]dns.RR{test.AAAA("test.split-type.	303	IN	AAAA	1:2:3::4")})
+
+	viewTest(t, "split-name one.test.test.test.split-name", addr, "one.test.test.test.split-name.", dns.TypeA, dns.RcodeSuccess,
+		[]dns.RR{test.A("one.test.test.test.split-name.	303	IN	A	1.1.1.1")})
+
+	viewTest(t, "split-name one.test.split-name", addr, "one.test.split-name.", dns.TypeA, dns.RcodeSuccess,
+		[]dns.RR{test.A("one.test.split-name.	303	IN	A	1.1.1.1")})
+
+	viewTest(t, "split-name two.test.test.test.split-name", addr, "two.test.test.test.split-name.", dns.TypeA, dns.RcodeSuccess,
+		[]dns.RR{test.A("two.test.test.test.split-name.	303	IN	A	2.2.2.2")})
+
+	viewTest(t, "split-name two.test.split-name", addr, "two.test.split-name.", dns.TypeA, dns.RcodeSuccess,
+		[]dns.RR{test.A("two.test.split-name.	303	IN	A	2.2.2.2")})
+
+	viewTest(t, "split-name default.test.split-name", addr, "default.test.split-name.", dns.TypeA, dns.RcodeSuccess,
+		[]dns.RR{test.A("default.test.split-name.	303	IN	A	3.3.3.3")})
+
+	viewTest(t, "metadata test.metadata", addr, "test.metadata.", dns.TypeA, dns.RcodeSuccess,
+		[]dns.RR{test.A("test.metadata.	303	IN	A	2.2.2.2")})
+}
+
+func viewTest(t *testing.T, testName, addr, qname string, qtype uint16, expectRcode int, expectAnswers []dns.RR) {
+	t.Run(testName, func(t *testing.T) {
+		m := new(dns.Msg)
+
+		m.SetQuestion(qname, qtype)
+		resp, err := dns.Exchange(m, addr)
+		if err != nil {
+			t.Fatalf("Expected to receive reply, but didn't: %s", err)
+		}
+
+		tc := test.Case{
+			Qname: qname, Qtype: qtype,
+			Rcode:  expectRcode,
+			Answer: expectAnswers,
+		}
+
+		err = test.SortAndCheck(resp, tc)
+		if err != nil {
+			t.Error(err)
+		}
+	})
+}