Allow adding an alias for the root domain

examples/tailscale-custom-domain-dns.toml

@@ -55,3 +55,8 @@ port = 53
 [fetcher]
 # How frequently the server will fetch the list of devices from your organization.
 interval = "1h"
+
+[aliases]
+# Alias for the root domain without any subdomain
+# Example: root = "machine-one"
+root = ""

server/dns.go

@@ -28,11 +28,19 @@ func buildRR(name string, question dns.Question, address netip.Addr, host string
 	var err error
 
 	if (question.Qtype == dns.TypeA || question.Qtype == dns.TypeANY) && address.Is4() {
-		rr, err = dns.NewRR(fmt.Sprintf("%s.%s A %s", name, host, address.String()))
+		if name == "" {
+			rr, err = dns.NewRR(fmt.Sprintf("%s A %s", host, address.String()))
+		} else {
+			rr, err = dns.NewRR(fmt.Sprintf("%s.%s A %s", name, host, address.String()))
+		}
 	}
 
 	if (question.Qtype == dns.TypeAAAA || question.Qtype == dns.TypeANY) && address.Is6() {
-		rr, err = dns.NewRR(fmt.Sprintf("%s.%s AAAA %s", name, host, address.String()))
+		if name == "" {
+			rr, err = dns.NewRR(fmt.Sprintf("%s AAAA %s", host, address.String()))
+		} else {
+			rr, err = dns.NewRR(fmt.Sprintf("%s.%s AAAA %s", name, host, address.String()))
+		}
 	}
 
 	if err != nil {
@@ -112,9 +120,28 @@ func makeHandler(readDevices chan ReadDevicesOp, host string) DnsHandler {
 		// Get just the subdomain name from the request
 		name := strings.ReplaceAll(question.Name, "."+host, "")
 
-		// Respond if a device with the hostname exists
-		if device, ok := deviceMap[name]; ok {
-			rrs := constructResponses(name, device, question, host)
+		var rrs []dns.RR
+		if question.Name == host {
+			// If the hostname is bare, check for a root alias
+
+			if viper.IsSet("aliases.root") {
+				name := viper.GetString("aliases.root")
+				if device, ok := deviceMap[name]; ok {
+					log.
+						Debug().
+						Str("host", name).
+						Msgf(`Serving root alias for hostname "%s"`, name)
+
+					rrs = constructResponses("", device, question, host)
+					m.Answer = rrs
+				}
+			}
+		} else if device, ok := deviceMap[name]; ok {
+			// Respond if a device with the hostname exists
+			rrs = constructResponses(name, device, question, host)
+		}
+
+		if len(rrs) != 0 {
 			log.Trace().Any("records", rrs).Msg("Sending records to client")
 			m.Answer = rrs
 		}