Cache

server/cache.go

@@ -0,0 +1,61 @@
+package server
+
+import (
+	"database/sql"
+	"time"
+	_ "github.com/mattn/go-sqlite3" // SQLite driver
+)
+
+const (
+	createTableQuery = `CREATE TABLE IF NOT EXISTS messages (
+		id VARCHAR(20) PRIMARY KEY,
+		time INT NOT NULL,
+		topic VARCHAR(64) NOT NULL,
+		message VARCHAR(1024) NOT NULL
+	)`
+	insertQuery         = `INSERT INTO messages (id, time, topic, message) VALUES (?, ?, ?, ?)`
+	pruneOlderThanQuery = `DELETE FROM messages WHERE time < ?`
+)
+
+type cache struct {
+	db *sql.DB
+	insert *sql.Stmt
+	prune *sql.Stmt
+}
+
+func newCache(filename string) (*cache, error) {
+	db, err := sql.Open("sqlite3", filename)
+	if err != nil {
+		return nil, err
+	}
+	if _, err := db.Exec(createTableQuery); err != nil {
+		return nil, err
+	}
+	insert, err := db.Prepare(insertQuery)
+	if err != nil {
+		return nil, err
+	}
+	prune, err := db.Prepare(pruneOlderThanQuery)
+	if err != nil {
+		return nil, err
+	}
+	return &cache{
+		db:     db,
+		insert: insert,
+		prune:  prune,
+	}, nil
+}
+
+func (c *cache) Load() (map[string]*topic, error) {
+
+}
+
+func (c *cache) Add(m *message) error {
+	_, err := c.insert.Exec(m.ID, m.Time, m.Topic, m.Message)
+	return err
+}
+
+func (c *cache) Prune(olderThan time.Duration) error {
+	_, err := c.prune.Exec(time.Now().Add(-1 * olderThan).Unix())
+	return err
+}

server/index.html

@@ -191,7 +191,7 @@
 
     <p>
         The web server does not log or otherwise store request paths, remote IP addresses or even topics or messages,
-        aside from a short on-disk cache (up to a day) to support the <tt>since=</tt> feature and service restarts.
+        aside from a short on-disk cache (up to a day) to support service restarts.
     </p>
 
     <center id="ironicCenterTagDontFreakOut"><i>Made with ❤️ by <a href="https://heckel.io">Philipp C. Heckel</a></i></center>

server/server.go

@@ -23,7 +23,6 @@ import (
 )
 
 // TODO add "max messages in a topic" limit
-// TODO implement persistence
 // TODO implement "since=<ID>"
 
 // Server is the main server
@@ -33,6 +32,7 @@ type Server struct {
 	visitors map[string]*visitor
 	firebase subscriber
 	messages int64
+	cache *cache
 	mu       sync.Mutex
 }
 
@@ -78,14 +78,32 @@ func New(conf *config.Config) (*Server, error) {
 			return nil, err
 		}
 	}
+	cache, err := maybeCreateCache(conf)
+	if err != nil {
+		return nil, err
+	}
+	topics := make(map[string]*topic)
+	if cache != nil {
+		if topics, err = cache.Load(); err != nil {
+			return nil, err
+		}
+	}
 	return &Server{
 		config:   conf,
+		cache: cache,
 		firebase: firebaseSubscriber,
-		topics:   make(map[string]*topic),
+		topics:   topics,
 		visitors: make(map[string]*visitor),
 	}, nil
 }
 
+func maybeCreateCache(conf *config.Config) (*cache, error) {
+	if conf.CacheFile == "" {
+		return nil, nil
+	}
+	return newCache(conf.CacheFile)
+}
+
 func createFirebaseSubscriber(conf *config.Config) (subscriber, error) {
 	fb, err := firebase.NewApp(context.Background(), nil, option.WithCredentialsFile(conf.FirebaseKeyFile))
 	if err != nil {
@@ -180,9 +198,13 @@ func (s *Server) handlePublish(w http.ResponseWriter, r *http.Request, v *visito
 	if err != nil {
 		return err
 	}
-	if err := t.Publish(newDefaultMessage(t.id, string(b))); err != nil {
+	m := newDefaultMessage(t.id, string(b))
+	if err := t.Publish(m); err != nil {
 		return err
 	}
+	if s.cache != nil {
+		s.cache.Add(m)
+	}
 	w.Header().Set("Access-Control-Allow-Origin", "*") // CORS, allow cross-origin requests
 	s.mu.Lock()
 	s.messages++
@@ -337,6 +359,13 @@ func (s *Server) updateStatsAndExpire() {
 		}
 	}
 
+	// Prune cache
+	if s.cache != nil {
+		if err := s.cache.Prune(s.config.MessageBufferDuration); err != nil {
+			log.Printf("error pruning cache: %s", err.Error())
+		}
+	}
+
 	// Prune old messages, remove subscriptions without subscribers
 	for _, t := range s.topics {
 		t.Prune(s.config.MessageBufferDuration)

server/topic.go

@@ -29,6 +29,7 @@ func newTopic(id string) *topic {
 	return &topic{
 		id:          id,
 		subscribers: make(map[int]subscriber),
+		messages: make([]*message, 0),
 		last:        time.Now(),
 		ctx:         ctx,
 		cancel:      cancel,