dns: error response from dispatch

So that dispatch can communicate status back to the caller.

agent/dns.go

@@ -3,6 +3,7 @@ package agent
 import (
 	"context"
 	"encoding/hex"
+	"errors"
 	"fmt"
 	"net"
 	"regexp"
@@ -476,7 +477,7 @@ func (d *DNSServer) handleQuery(resp dns.ResponseWriter, req *dns.Msg) {
 	m.Authoritative = true
 	m.RecursionAvailable = (len(cfg.Recursors) > 0)
 
-	ecsGlobal := true
+	var err error
 
 	switch req.Question[0].Qtype {
 	case dns.TypeSOA:
@@ -496,10 +497,10 @@ func (d *DNSServer) handleQuery(resp dns.ResponseWriter, req *dns.Msg) {
 		m.SetRcode(req, dns.RcodeNotImplemented)
 
 	default:
-		ecsGlobal = d.dispatch(network, resp.RemoteAddr(), req, m, maxRecursionLevelDefault)
+		err = d.dispatch(network, resp.RemoteAddr(), req, m, maxRecursionLevelDefault)
 	}
 
-	setEDNS(req, m, ecsGlobal)
+	setEDNS(req, m, !errors.Is(err, errECSNotGlobal))
 
 	// Write out the complete response
 	if err := resp.WriteMsg(m); err != nil {
@@ -601,9 +602,12 @@ func (d *DNSServer) parseDatacenter(labels []string, datacenter *string) bool {
 	}
 }
 
+var errECSNotGlobal = fmt.Errorf("ECS response is not global")
+var errNameNotFound = fmt.Errorf("DNS name not found")
+
 // dispatch is used to parse a request and invoke the correct handler.
 // parameter maxRecursionLevel will handle whether recursive call can be performed
-func (d *DNSServer) dispatch(network string, remoteAddr net.Addr, req, resp *dns.Msg, maxRecursionLevel int) bool {
+func (d *DNSServer) dispatch(network string, remoteAddr net.Addr, req, resp *dns.Msg, maxRecursionLevel int) error {
 	// By default the query is in the default datacenter
 	datacenter := d.agent.config.Datacenter
 
@@ -643,11 +647,11 @@ func (d *DNSServer) dispatch(network string, remoteAddr net.Addr, req, resp *dns
 		}
 	}
 
-	invalid := func() bool {
+	invalid := func() error {
 		d.logger.Warn("QName invalid", "qname", qName)
 		d.addSOA(cfg, resp)
 		resp.SetRcode(req, dns.RcodeNameError)
-		return true
+		return errNameNotFound
 	}
 
 	switch queryKind {
@@ -684,7 +688,7 @@ func (d *DNSServer) dispatch(network string, remoteAddr net.Addr, req, resp *dns
 			lookup.Service = queryParts[0][1:]
 			// _name._tag.service.consul
 			d.serviceLookup(cfg, lookup, req, resp)
-			return true
+			return nil
 		}
 
 		// Consul 0.3 and prior format for SRV queries
@@ -699,7 +703,7 @@ func (d *DNSServer) dispatch(network string, remoteAddr net.Addr, req, resp *dns
 
 		// tag[.tag].name.service.consul
 		d.serviceLookup(cfg, lookup, req, resp)
-		return true
+		return nil
 
 	case "connect":
 		if len(queryParts) < 1 {
@@ -721,7 +725,7 @@ func (d *DNSServer) dispatch(network string, remoteAddr net.Addr, req, resp *dns
 		}
 		// name.connect.consul
 		d.serviceLookup(cfg, lookup, req, resp)
-		return true
+		return nil
 
 	case "ingress":
 		if len(queryParts) < 1 {
@@ -743,7 +747,7 @@ func (d *DNSServer) dispatch(network string, remoteAddr net.Addr, req, resp *dns
 		}
 		// name.ingress.consul
 		d.serviceLookup(cfg, lookup, req, resp)
-		return true
+		return nil
 
 	case "node":
 		if len(queryParts) < 1 {
@@ -757,7 +761,7 @@ func (d *DNSServer) dispatch(network string, remoteAddr net.Addr, req, resp *dns
 		// Allow a "." in the node name, just join all the parts
 		node := strings.Join(queryParts, ".")
 		d.nodeLookup(cfg, datacenter, node, req, resp, maxRecursionLevel)
-		return true
+		return nil
 
 	case "query":
 		// ensure we have a query name
@@ -772,7 +776,7 @@ func (d *DNSServer) dispatch(network string, remoteAddr net.Addr, req, resp *dns
 		// Allow a "." in the query name, just join all the parts.
 		query := strings.Join(queryParts, ".")
 		d.preparedQueryLookup(cfg, network, datacenter, query, remoteAddr, req, resp, maxRecursionLevel)
-		return false
+		return errECSNotGlobal
 
 	case "addr":
 		// <address>.addr.<suffixes>.<domain> - addr must be the second label, datacenter is optional
@@ -825,7 +829,7 @@ func (d *DNSServer) dispatch(network string, remoteAddr net.Addr, req, resp *dns
 				resp.Answer = append(resp.Answer, aaaaRecord)
 			}
 		}
-		return true
+		return nil
 	default:
 		return invalid()
 	}
@@ -1905,6 +1909,7 @@ func (d *DNSServer) resolveCNAME(cfg *dnsConfig, name string, maxRecursionLevel
 		resp := &dns.Msg{}
 
 		req.SetQuestion(name, dns.TypeANY)
+		// TODO: handle error response
 		d.dispatch("udp", nil, req, resp, maxRecursionLevel-1)
 
 		return resp.Answer