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/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.