Add DNS for container name

If there is no `VIRTUAL_HOST` we add a hostname based on the container
name.

We cannot add more than one name to the same IP, apparently. Otherwise
we could have added both of them.

README.md

@@ -1,7 +1,10 @@
 # Local Docker Development DNS
 
 A systemd service that will monitor your Docker host and provide
-DNS names for containers with a `VIRTUAL_HOST` environment variable.
+DNS names for containers based of the container name.
+
+If a `VIRTUAL_HOST` environment variable is present the DNS we will
+base the DNS of that instead.
 
 The service broadcasts the domain names using multicast DNS
 (a.k.a. mDNS, zeroconf, bounjour, avahi).

container.go

@@ -39,15 +39,15 @@ func handleContainer(
 	}
 
 	hostname := extractHostname(ctx, container)
-	if hostname == "" {
-		return
-	}
-
 	services := extractServices(ctx, container)
 
-	hostname = rewriteHostname(ctx, hostname)
-
-	addToDNS(eg, hostname, ips, services, container.Name[1:])
+	if hostname != "" {
+		hostname = rewriteHostname(hostname)
+		addToDNS(eg, hostname, ips, services, container.Name[1:])
+	} else {
+		containerHostname := rewriteHostname(container.Name[1:] + ".local")
+		addToDNS(eg, containerHostname, ips, services, container.Name[1:])
+	}
 }
 
 // extractIPnumbers from a container.

hostname.go

@@ -1,17 +1,18 @@
 package main
 
 import (
-	"context"
 	"strings"
 
 	"golang.org/x/net/publicsuffix"
 )
 
 // rewriteHostname will make `hostname` suitable for dns-sd.
-func rewriteHostname(_ context.Context, hostname string) string {
+func rewriteHostname(hostname string) string {
 	suffix, _ := publicsuffix.PublicSuffix(hostname)
 	basename := hostname[:len(hostname)-len(suffix)-1]
-	sanitizedHostname := strings.ReplaceAll(basename, ".", "-") + ".local"
+	basename = strings.ReplaceAll(basename, ".", "-")
+	basename = strings.ReplaceAll(basename, "_", "-")
+	sanitizedHostname := basename + ".local"
 
 	if hostname != sanitizedHostname {
 		logf(PriInfo, "Rewrote hostname from %q to %q\n", hostname, sanitizedHostname)