dns: remove goto INVALID and a naked return

This commit is one small step toward modernizing and making the DNSServer readable.

agent/dns.go

@@ -592,8 +592,7 @@ func (d *DNSServer) parseDatacenter(labels []string, datacenter *string) bool {
 
 // doDispatch is used to parse a request and invoke the correct handler.
 // parameter maxRecursionLevel will handle whether recursive call can be performed
-func (d *DNSServer) doDispatch(network string, remoteAddr net.Addr, req, resp *dns.Msg, maxRecursionLevel int) (ecsGlobal bool) {
-	ecsGlobal = true
+func (d *DNSServer) doDispatch(network string, remoteAddr net.Addr, req, resp *dns.Msg, maxRecursionLevel int) bool {
 	// By default the query is in the default datacenter
 	datacenter := d.agent.config.Datacenter
 
@@ -633,19 +632,26 @@ func (d *DNSServer) doDispatch(network string, remoteAddr net.Addr, req, resp *d
 		}
 	}
 
+	invalid := func() bool {
+		d.logger.Warn("QName invalid", "qname", qName)
+		d.addSOA(cfg, resp)
+		resp.SetRcode(req, dns.RcodeNameError)
+		return true
+	}
+
 	if queryKind == "" {
-		goto INVALID
+		return invalid()
 	}
 
 	switch queryKind {
 	case "service":
 		n := len(queryParts)
 		if n < 1 {
-			goto INVALID
+			return invalid()
 		}
 
 		if !d.parseDatacenterAndEnterpriseMeta(querySuffixes, cfg, &datacenter, &entMeta) {
-			goto INVALID
+			return invalid()
 		}
 
 		lookup := serviceLookup{
@@ -689,11 +695,11 @@ func (d *DNSServer) doDispatch(network string, remoteAddr net.Addr, req, resp *d
 		}
 	case "connect":
 		if len(queryParts) < 1 {
-			goto INVALID
+			return invalid()
 		}
 
 		if !d.parseDatacenterAndEnterpriseMeta(querySuffixes, cfg, &datacenter, &entMeta) {
-			goto INVALID
+			return invalid()
 		}
 
 		lookup := serviceLookup{
@@ -709,11 +715,11 @@ func (d *DNSServer) doDispatch(network string, remoteAddr net.Addr, req, resp *d
 		d.serviceLookup(cfg, lookup, req, resp)
 	case "ingress":
 		if len(queryParts) < 1 {
-			goto INVALID
+			return invalid()
 		}
 
 		if !d.parseDatacenterAndEnterpriseMeta(querySuffixes, cfg, &datacenter, &entMeta) {
-			goto INVALID
+			return invalid()
 		}
 
 		lookup := serviceLookup{
@@ -729,11 +735,11 @@ func (d *DNSServer) doDispatch(network string, remoteAddr net.Addr, req, resp *d
 		d.serviceLookup(cfg, lookup, req, resp)
 	case "node":
 		if len(queryParts) < 1 {
-			goto INVALID
+			return invalid()
 		}
 
 		if !d.parseDatacenter(querySuffixes, &datacenter) {
-			goto INVALID
+			return invalid()
 		}
 
 		// Allow a "." in the node name, just join all the parts
@@ -742,22 +748,22 @@ func (d *DNSServer) doDispatch(network string, remoteAddr net.Addr, req, resp *d
 	case "query":
 		// ensure we have a query name
 		if len(queryParts) < 1 {
-			goto INVALID
+			return invalid()
 		}
 
 		if !d.parseDatacenter(querySuffixes, &datacenter) {
-			goto INVALID
+			return invalid()
 		}
 
 		// Allow a "." in the query name, just join all the parts.
 		query := strings.Join(queryParts, ".")
-		ecsGlobal = false
 		d.preparedQueryLookup(cfg, network, datacenter, query, remoteAddr, req, resp, maxRecursionLevel)
+		return false
 
 	case "addr":
 		// <address>.addr.<suffixes>.<domain> - addr must be the second label, datacenter is optional
 		if len(queryParts) != 1 {
-			goto INVALID
+			return invalid()
 		}
 
 		switch len(queryParts[0]) / 2 {
@@ -765,7 +771,7 @@ func (d *DNSServer) doDispatch(network string, remoteAddr net.Addr, req, resp *d
 		case 4:
 			ip, err := hex.DecodeString(queryParts[0])
 			if err != nil {
-				goto INVALID
+				return invalid()
 			}
 
 			resp.Answer = append(resp.Answer, &dns.A{
@@ -781,7 +787,7 @@ func (d *DNSServer) doDispatch(network string, remoteAddr net.Addr, req, resp *d
 		case 16:
 			ip, err := hex.DecodeString(queryParts[0])
 			if err != nil {
-				goto INVALID
+				return invalid()
 			}
 
 			resp.Answer = append(resp.Answer, &dns.AAAA{
@@ -795,14 +801,7 @@ func (d *DNSServer) doDispatch(network string, remoteAddr net.Addr, req, resp *d
 			})
 		}
 	}
-	// early return without error
-	return
-
-INVALID:
-	d.logger.Warn("QName invalid", "qname", qName)
-	d.addSOA(cfg, resp)
-	resp.SetRcode(req, dns.RcodeNameError)
-	return
+	return true
 }
 
 func (d *DNSServer) trimDomain(query string) string {