fix(publisher): reuse EntryGroup - reset+(re)commit

avahi/publisher.go

@@ -16,10 +16,11 @@ const (
 )
 
 type Publisher struct {
-	dbusConn    *dbus.Conn
-	avahiServer *avahi.Server
-	fqdn        string
-	rdataField  []byte
+	dbusConn        *dbus.Conn
+	avahiServer     *avahi.Server
+	avahiEntryGroup *avahi.EntryGroup
+	fqdn            string
+	rdataField      []byte
 }
 
 // NewPublisher creates a new service for Publisher.
@@ -39,6 +40,11 @@ func NewPublisher() (*Publisher, error) {
 		return nil, fmt.Errorf("failed to get FQDN from Avahi: %v", err)
 	}
 
+	group, err := server.EntryGroupNew()
+	if err != nil {
+		return nil, fmt.Errorf("failed to create entry group: %v", err)
+	}
+
 	fqdn := dns.Fqdn(avahiFqdn)
 
 	// RDATA: a variable length string of octets that describes the resource. CNAME in our case
@@ -50,10 +56,11 @@ func NewPublisher() (*Publisher, error) {
 	}
 
 	return &Publisher{
-		dbusConn:    conn,
-		avahiServer: server,
-		fqdn:        fqdn,
-		rdataField:  rdataField,
+		dbusConn:        conn,
+		avahiServer:     server,
+		avahiEntryGroup: group,
+		fqdn:            fqdn,
+		rdataField:      rdataField,
 	}, nil
 }
 
@@ -64,13 +71,14 @@ func (p *Publisher) Fqdn() string {
 
 // PublishCNAMES send via Avahi-daemon CNAME records with the provided TTL.
 func (p *Publisher) PublishCNAMES(cnames []string, ttl uint32) error {
-	group, err := p.avahiServer.EntryGroupNew()
-	if err != nil {
-		return fmt.Errorf("failed to create entry group: %v", err)
+	// Reset the entry group to remove all records.
+	// Because we can't update records without it after the `Commit`.
+	if err := p.avahiEntryGroup.Reset(); err != nil {
+		return fmt.Errorf("failed to reset entry group: %v", err)
 	}
 
 	for _, cname := range cnames {
-		err := group.AddRecord(
+		err := p.avahiEntryGroup.AddRecord(
 			avahi.InterfaceUnspec,
 			avahi.ProtoUnspec,
 			uint32(0), // From Avahi Python bindings https://gist.github.com/gdamjan/3168336#file-avahi-alias-py-L42
@@ -85,7 +93,7 @@ func (p *Publisher) PublishCNAMES(cnames []string, ttl uint32) error {
 		}
 	}
 
-	if err := group.Commit(); err != nil {
+	if err := p.avahiEntryGroup.Commit(); err != nil {
 		return fmt.Errorf("failed to commit entry group: %v", err)
 	}
 
@@ -94,5 +102,5 @@ func (p *Publisher) PublishCNAMES(cnames []string, ttl uint32) error {
 
 // Close associated resources.
 func (p *Publisher) Close() {
-	p.avahiServer.Close() // It also close the DBus connection
+	p.avahiServer.Close() // It also closes the DBus connection and free the entry group
 }

cmd/subdomain.go

@@ -117,8 +117,7 @@ func runSubdomain(ctx context.Context, publisher *avahi.Publisher, fqdn string,
 
 		if len(found) > 0 {
 			if err := publisher.PublishCNAMES(found, ttl); err != nil {
-				log.Printf("Failed to publish CNAMEs: %v", err)
-				continue
+				return fmt.Errorf("failed to publish CNAMEs: %w", err)
 			}
 		}
 	}

main.go

@@ -3,8 +3,10 @@ package main
 import (
 	"context"
 	"fmt"
+	"log"
 	"os"
 	"os/signal"
+	"time"
 
 	"github.com/carlmjohnson/versioninfo"
 	"github.com/urfave/cli/v2"
@@ -16,6 +18,15 @@ func main() {
 	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, os.Kill)
 	defer stop()
 
+	// Add a handler for force exiting if we don't exit gracefully (stuck)
+	go func() {
+		<-ctx.Done()
+		time.Sleep(3 * time.Second)
+
+		log.Print("Force exit")
+		os.Exit(1)
+	}()
+
 	app := &cli.App{
 		Name:    "go-avahi-cname",
 		Usage:   "A tool for publishing CNAME records with Avahi",