WIP_ Add 'At:'/'Delay:' headers to support scheduled messages

config/config.go

@@ -11,6 +11,7 @@ const (
 	DefaultCacheDuration     = 12 * time.Hour
 	DefaultKeepaliveInterval = 30 * time.Second
 	DefaultManagerInterval   = time.Minute
+	DefaultAtSenderInterval  = 10 * time.Second
 )
 
 // Defines all the limits
@@ -35,6 +36,7 @@ type Config struct {
 	CacheDuration                time.Duration
 	KeepaliveInterval            time.Duration
 	ManagerInterval              time.Duration
+	AtSenderInterval             time.Duration
 	GlobalTopicLimit             int
 	VisitorRequestLimitBurst     int
 	VisitorRequestLimitReplenish time.Duration
@@ -54,6 +56,7 @@ func New(listenHTTP string) *Config {
 		CacheDuration:                DefaultCacheDuration,
 		KeepaliveInterval:            DefaultKeepaliveInterval,
 		ManagerInterval:              DefaultManagerInterval,
+		AtSenderInterval:             DefaultAtSenderInterval,
 		GlobalTopicLimit:             DefaultGlobalTopicLimit,
 		VisitorRequestLimitBurst:     DefaultVisitorRequestLimitBurst,
 		VisitorRequestLimitReplenish: DefaultVisitorRequestLimitReplenish,

server/cache.go

@@ -14,8 +14,10 @@ var (
 // i.e. message structs with the Event messageEvent.
 type cache interface {
 	AddMessage(m *message) error
-	Messages(topic string, since sinceTime) ([]*message, error)
+	Messages(topic string, since sinceTime, scheduled bool) ([]*message, error)
+	MessagesDue() ([]*message, error)
 	MessageCount(topic string) (int, error)
 	Topics() (map[string]*topic, error)
 	Prune(olderThan time.Time) error
+	MarkPublished(m *message) error
 }

server/cache_mem.go

@@ -1,14 +1,16 @@
 package server
 
 import (
+	"sort"
 	"sync"
 	"time"
 )
 
 type memCache struct {
-	messages map[string][]*message
-	nop      bool
-	mu       sync.Mutex
+	messages  map[string][]*message
+	scheduled map[string]*message // Message ID -> message
+	nop       bool
+	mu        sync.Mutex
 }
 
 var _ cache = (*memCache)(nil)
@@ -16,8 +18,9 @@ var _ cache = (*memCache)(nil)
 // newMemCache creates an in-memory cache
 func newMemCache() *memCache {
 	return &memCache{
-		messages: make(map[string][]*message),
-		nop:      false,
+		messages:  make(map[string][]*message),
+		scheduled: make(map[string]*message),
+		nop:       false,
 	}
 }
 
@@ -25,77 +28,109 @@ func newMemCache() *memCache {
 // it is always empty and can be used if caching is entirely disabled
 func newNopCache() *memCache {
 	return &memCache{
-		messages: make(map[string][]*message),
-		nop:      true,
+		messages:  make(map[string][]*message),
+		scheduled: make(map[string]*message),
+		nop:       true,
 	}
 }
 
-func (s *memCache) AddMessage(m *message) error {
-	s.mu.Lock()
-	defer s.mu.Unlock()
-	if s.nop {
+func (c *memCache) AddMessage(m *message) error {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	if c.nop {
 		return nil
 	}
 	if m.Event != messageEvent {
 		return errUnexpectedMessageType
 	}
-	if _, ok := s.messages[m.Topic]; !ok {
-		s.messages[m.Topic] = make([]*message, 0)
+	if _, ok := c.messages[m.Topic]; !ok {
+		c.messages[m.Topic] = make([]*message, 0)
 	}
-	s.messages[m.Topic] = append(s.messages[m.Topic], m)
+	delayed := m.Time > time.Now().Unix()
+	if delayed {
+		c.scheduled[m.ID] = m
+	}
+	c.messages[m.Topic] = append(c.messages[m.Topic], m)
 	return nil
 }
 
-func (s *memCache) Messages(topic string, since sinceTime) ([]*message, error) {
-	s.mu.Lock()
-	defer s.mu.Unlock()
-	if _, ok := s.messages[topic]; !ok || since.IsNone() {
+func (c *memCache) Messages(topic string, since sinceTime, scheduled bool) ([]*message, error) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	if _, ok := c.messages[topic]; !ok || since.IsNone() {
 		return make([]*message, 0), nil
 	}
-	messages := make([]*message, 0) // copy!
-	for _, m := range s.messages[topic] {
-		msgTime := time.Unix(m.Time, 0)
-		if msgTime == since.Time() || msgTime.After(since.Time()) {
+	messages := make([]*message, 0)
+	for _, m := range c.messages[topic] {
+		_, messageScheduled := c.scheduled[m.ID]
+		include := m.Time >= since.Time().Unix() && (!messageScheduled || scheduled)
+		if include {
+			messages = append(messages, m)
+		}
+	}
+	sort.Slice(messages, func(i, j int) bool {
+		return messages[i].Time < messages[j].Time
+	})
+	return messages, nil
+}
+
+func (c *memCache) MessagesDue() ([]*message, error) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	messages := make([]*message, 0)
+	for _, m := range c.scheduled {
+		due := time.Now().Unix() >= m.Time
+		if due {
 			messages = append(messages, m)
 		}
 	}
+	sort.Slice(messages, func(i, j int) bool {
+		return messages[i].Time < messages[j].Time
+	})
 	return messages, nil
 }
 
-func (s *memCache) MessageCount(topic string) (int, error) {
-	s.mu.Lock()
-	defer s.mu.Unlock()
-	if _, ok := s.messages[topic]; !ok {
+func (c *memCache) MarkPublished(m *message) error {
+	c.mu.Lock()
+	delete(c.scheduled, m.ID)
+	c.mu.Unlock()
+	return nil
+}
+
+func (c *memCache) MessageCount(topic string) (int, error) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	if _, ok := c.messages[topic]; !ok {
 		return 0, nil
 	}
-	return len(s.messages[topic]), nil
+	return len(c.messages[topic]), nil
 }
 
-func (s *memCache) Topics() (map[string]*topic, error) {
-	s.mu.Lock()
-	defer s.mu.Unlock()
+func (c *memCache) Topics() (map[string]*topic, error) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
 	topics := make(map[string]*topic)
-	for topic := range s.messages {
+	for topic := range c.messages {
 		topics[topic] = newTopic(topic)
 	}
 	return topics, nil
 }
 
-func (s *memCache) Prune(olderThan time.Time) error {
-	s.mu.Lock()
-	defer s.mu.Unlock()
-	for topic := range s.messages {
-		s.pruneTopic(topic, olderThan)
+func (c *memCache) Prune(olderThan time.Time) error {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	for topic := range c.messages {
+		c.pruneTopic(topic, olderThan)
 	}
 	return nil
 }
 
-func (s *memCache) pruneTopic(topic string, olderThan time.Time) {
+func (c *memCache) pruneTopic(topic string, olderThan time.Time) {
 	messages := make([]*message, 0)
-	for _, m := range s.messages[topic] {
+	for _, m := range c.messages[topic] {
 		if m.Time >= olderThan.Unix() {
 			messages = append(messages, m)
 		}
 	}
-	s.messages[topic] = messages
+	c.messages[topic] = messages
 }

server/cache_mem_test.go

@@ -9,6 +9,10 @@ func TestMemCache_Messages(t *testing.T) {
 	testCacheMessages(t, newMemCache())
 }
 
+func TestMemCache_MessagesScheduled(t *testing.T) {
+	testCacheMessagesScheduled(t, newMemCache())
+}
+
 func TestMemCache_Topics(t *testing.T) {
 	testCacheTopics(t, newMemCache())
 }
@@ -25,7 +29,7 @@ func TestMemCache_NopCache(t *testing.T) {
 	c := newNopCache()
 	assert.Nil(t, c.AddMessage(newDefaultMessage("mytopic", "my message")))
 
-	messages, err := c.Messages("mytopic", sinceAllMessages)
+	messages, err := c.Messages("mytopic", sinceAllMessages, false)
 	assert.Nil(t, err)
 	assert.Empty(t, messages)
 

server/cache_sqlite.go

@@ -21,19 +21,32 @@ const (
 			message VARCHAR(512) NOT NULL,
 			title VARCHAR(256) NOT NULL,
 			priority INT NOT NULL,
-			tags VARCHAR(256) NOT NULL
+			tags VARCHAR(256) NOT NULL,
+			published INT NOT NULL
 		);
 		CREATE INDEX IF NOT EXISTS idx_topic ON messages (topic);
 		COMMIT;
 	`
-	insertMessageQuery           = `INSERT INTO messages (id, time, topic, message, title, priority, tags) VALUES (?, ?, ?, ?, ?, ?, ?)`
+	insertMessageQuery           = `INSERT INTO messages (id, time, topic, message, title, priority, tags, published) VALUES (?, ?, ?, ?, ?, ?, ?, ?)`
 	pruneMessagesQuery           = `DELETE FROM messages WHERE time < ?`
 	selectMessagesSinceTimeQuery = `
-		SELECT id, time, message, title, priority, tags
+		SELECT id, time, topic, message, title, priority, tags
+		FROM messages 
+		WHERE topic = ? AND time >= ? AND published = 1
+		ORDER BY time ASC
+	`
+	selectMessagesSinceTimeIncludeScheduledQuery = `
+		SELECT id, time, topic, message, title, priority, tags
 		FROM messages 
 		WHERE topic = ? AND time >= ?
 		ORDER BY time ASC
 	`
+	selectMessagesDueQuery = `
+		SELECT id, time, topic, message, title, priority, tags
+		FROM messages 
+		WHERE time <= ? AND published = 0
+	`
+	updateMessagePublishedQuery     = `UPDATE messages SET published = 1 WHERE id = ?`
 	selectMessagesCountQuery        = `SELECT COUNT(*) FROM messages`
 	selectMessageCountForTopicQuery = `SELECT COUNT(*) FROM messages WHERE topic = ?`
 	selectTopicsQuery               = `SELECT topic FROM messages GROUP BY topic`
@@ -41,7 +54,7 @@ const (
 
 // Schema management queries
 const (
-	currentSchemaVersion          = 1
+	currentSchemaVersion          = 2
 	createSchemaVersionTableQuery = `
 		CREATE TABLE IF NOT EXISTS schemaVersion (
 			id INT PRIMARY KEY,
@@ -49,6 +62,7 @@ const (
 		);
 	`
 	insertSchemaVersion      = `INSERT INTO schemaVersion VALUES (1, ?)`
+	updateSchemaVersion      = `UPDATE schemaVersion SET version = ? WHERE id = 1`
 	selectSchemaVersionQuery = `SELECT version FROM schemaVersion WHERE id = 1`
 
 	// 0 -> 1
@@ -59,6 +73,13 @@ const (
 		ALTER TABLE messages ADD COLUMN tags VARCHAR(256) NOT NULL DEFAULT('');
 		COMMIT;
 	`
+
+	// 1 -> 2
+	migrate1To2AlterMessagesTableQuery = `
+		BEGIN;
+		ALTER TABLE messages ADD COLUMN published INT NOT NULL DEFAULT(1);
+		COMMIT;
+	`
 )
 
 type sqliteCache struct {
@@ -84,46 +105,39 @@ func (c *sqliteCache) AddMessage(m *message) error {
 	if m.Event != messageEvent {
 		return errUnexpectedMessageType
 	}
-	_, err := c.db.Exec(insertMessageQuery, m.ID, m.Time, m.Topic, m.Message, m.Title, m.Priority, strings.Join(m.Tags, ","))
+	published := m.Time <= time.Now().Unix()
+	_, err := c.db.Exec(insertMessageQuery, m.ID, m.Time, m.Topic, m.Message, m.Title, m.Priority, strings.Join(m.Tags, ","), published)
 	return err
 }
 
-func (c *sqliteCache) Messages(topic string, since sinceTime) ([]*message, error) {
+func (c *sqliteCache) Messages(topic string, since sinceTime, scheduled bool) ([]*message, error) {
 	if since.IsNone() {
 		return make([]*message, 0), nil
 	}
-	rows, err := c.db.Query(selectMessagesSinceTimeQuery, topic, since.Time().Unix())
+	var rows *sql.Rows
+	var err error
+	if scheduled {
+		rows, err = c.db.Query(selectMessagesSinceTimeIncludeScheduledQuery, topic, since.Time().Unix())
+	} else {
+		rows, err = c.db.Query(selectMessagesSinceTimeQuery, topic, since.Time().Unix())
+	}
 	if err != nil {
 		return nil, err
 	}
-	defer rows.Close()
-	messages := make([]*message, 0)
-	for rows.Next() {
-		var timestamp int64
-		var priority int
-		var id, msg, title, tagsStr string
-		if err := rows.Scan(&id, &timestamp, &msg, &title, &priority, &tagsStr); err != nil {
-			return nil, err
-		}
-		var tags []string
-		if tagsStr != "" {
-			tags = strings.Split(tagsStr, ",")
-		}
-		messages = append(messages, &message{
-			ID:       id,
-			Time:     timestamp,
-			Event:    messageEvent,
-			Topic:    topic,
-			Message:  msg,
-			Title:    title,
-			Priority: priority,
-			Tags:     tags,
-		})
-	}
-	if err := rows.Err(); err != nil {
+	return readMessages(rows)
+}
+
+func (c *sqliteCache) MessagesDue() ([]*message, error) {
+	rows, err := c.db.Query(selectMessagesDueQuery, time.Now().Unix())
+	if err != nil {
 		return nil, err
 	}
-	return messages, nil
+	return readMessages(rows)
+}
+
+func (c *sqliteCache) MarkPublished(m *message) error {
+	_, err := c.db.Exec(updateMessagePublishedQuery, m.ID)
+	return err
 }
 
 func (c *sqliteCache) MessageCount(topic string) (int, error) {
@@ -169,6 +183,37 @@ func (c *sqliteCache) Prune(olderThan time.Time) error {
 	return err
 }
 
+func readMessages(rows *sql.Rows) ([]*message, error) {
+	defer rows.Close()
+	messages := make([]*message, 0)
+	for rows.Next() {
+		var timestamp int64
+		var priority int
+		var id, topic, msg, title, tagsStr string
+		if err := rows.Scan(&id, &timestamp, &topic, &msg, &title, &priority, &tagsStr); err != nil {
+			return nil, err
+		}
+		var tags []string
+		if tagsStr != "" {
+			tags = strings.Split(tagsStr, ",")
+		}
+		messages = append(messages, &message{
+			ID:       id,
+			Time:     timestamp,
+			Event:    messageEvent,
+			Topic:    topic,
+			Message:  msg,
+			Title:    title,
+			Priority: priority,
+			Tags:     tags,
+		})
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return messages, nil
+}
+
 func setupDB(db *sql.DB) error {
 	// If 'messages' table does not exist, this must be a new database
 	rowsMC, err := db.Query(selectMessagesCountQuery)
@@ -194,7 +239,9 @@ func setupDB(db *sql.DB) error {
 	if schemaVersion == currentSchemaVersion {
 		return nil
 	} else if schemaVersion == 0 {
-		return migrateFrom0To1(db)
+		return migrateFrom0(db)
+	} else if schemaVersion == 1 {
+		return migrateFrom1(db)
 	}
 	return fmt.Errorf("unexpected schema version found: %d", schemaVersion)
 }
@@ -212,7 +259,7 @@ func setupNewDB(db *sql.DB) error {
 	return nil
 }
 
-func migrateFrom0To1(db *sql.DB) error {
+func migrateFrom0(db *sql.DB) error {
 	log.Print("Migrating cache database schema: from 0 to 1")
 	if _, err := db.Exec(migrate0To1AlterMessagesTableQuery); err != nil {
 		return err
@@ -223,5 +270,16 @@ func migrateFrom0To1(db *sql.DB) error {
 	if _, err := db.Exec(insertSchemaVersion, 1); err != nil {
 		return err
 	}
-	return nil
+	return migrateFrom1(db)
+}
+
+func migrateFrom1(db *sql.DB) error {
+	log.Print("Migrating cache database schema: from 1 to 2")
+	if _, err := db.Exec(migrate1To2AlterMessagesTableQuery); err != nil {
+		return err
+	}
+	if _, err := db.Exec(updateSchemaVersion, 2); err != nil {
+		return err
+	}
+	return nil // Update this when a new version is added
 }

server/cache_sqlite_test.go

@@ -9,10 +9,14 @@ import (
 	"time"
 )
 
-func TestSqliteCache_AddMessage(t *testing.T) {
+func TestSqliteCache_Messages(t *testing.T) {
 	testCacheMessages(t, newSqliteTestCache(t))
 }
 
+func TestSqliteCache_MessagesScheduled(t *testing.T) {
+	testCacheMessagesScheduled(t, newSqliteTestCache(t))
+}
+
 func TestSqliteCache_Topics(t *testing.T) {
 	testCacheTopics(t, newSqliteTestCache(t))
 }
@@ -25,7 +29,7 @@ func TestSqliteCache_Prune(t *testing.T) {
 	testCachePrune(t, newSqliteTestCache(t))
 }
 
-func TestSqliteCache_Migration_0to1(t *testing.T) {
+func TestSqliteCache_Migration_From0(t *testing.T) {
 	filename := newSqliteTestCacheFile(t)
 	db, err := sql.Open("sqlite3", filename)
 	assert.Nil(t, err)
@@ -53,7 +57,7 @@ func TestSqliteCache_Migration_0to1(t *testing.T) {
 
 	// Create cache to trigger migration
 	c := newSqliteTestCacheFromFile(t, filename)
-	messages, err := c.Messages("mytopic", sinceAllMessages)
+	messages, err := c.Messages("mytopic", sinceAllMessages, false)
 	assert.Nil(t, err)
 	assert.Equal(t, 10, len(messages))
 	assert.Equal(t, "some message 5", messages[5].Message)
@@ -67,7 +71,7 @@ func TestSqliteCache_Migration_0to1(t *testing.T) {
 
 	var schemaVersion int
 	assert.Nil(t, rows.Scan(&schemaVersion))
-	assert.Equal(t, 1, schemaVersion)
+	assert.Equal(t, 2, schemaVersion)
 }
 
 func newSqliteTestCache(t *testing.T) *sqliteCache {

server/cache_test.go

@@ -27,7 +27,7 @@ func testCacheMessages(t *testing.T, c cache) {
 	assert.Equal(t, 2, count)
 
 	// mytopic: since all
-	messages, _ := c.Messages("mytopic", sinceAllMessages)
+	messages, _ := c.Messages("mytopic", sinceAllMessages, false)
 	assert.Equal(t, 2, len(messages))
 	assert.Equal(t, "my message", messages[0].Message)
 	assert.Equal(t, "mytopic", messages[0].Topic)
@@ -38,11 +38,11 @@ func testCacheMessages(t *testing.T, c cache) {
 	assert.Equal(t, "my other message", messages[1].Message)
 
 	// mytopic: since none
-	messages, _ = c.Messages("mytopic", sinceNoMessages)
+	messages, _ = c.Messages("mytopic", sinceNoMessages, false)
 	assert.Empty(t, messages)
 
 	// mytopic: since 2
-	messages, _ = c.Messages("mytopic", sinceTime(time.Unix(2, 0)))
+	messages, _ = c.Messages("mytopic", sinceTime(time.Unix(2, 0)), false)
 	assert.Equal(t, 1, len(messages))
 	assert.Equal(t, "my other message", messages[0].Message)
 
@@ -52,7 +52,7 @@ func testCacheMessages(t *testing.T, c cache) {
 	assert.Equal(t, 1, count)
 
 	// example: since all
-	messages, _ = c.Messages("example", sinceAllMessages)
+	messages, _ = c.Messages("example", sinceAllMessages, false)
 	assert.Equal(t, "my example message", messages[0].Message)
 
 	// non-existing: count
@@ -61,7 +61,7 @@ func testCacheMessages(t *testing.T, c cache) {
 	assert.Equal(t, 0, count)
 
 	// non-existing: since all
-	messages, _ = c.Messages("doesnotexist", sinceAllMessages)
+	messages, _ = c.Messages("doesnotexist", sinceAllMessages, false)
 	assert.Empty(t, messages)
 }
 
@@ -103,7 +103,7 @@ func testCachePrune(t *testing.T, c cache) {
 	assert.Nil(t, err)
 	assert.Equal(t, 0, count)
 
-	messages, err := c.Messages("mytopic", sinceAllMessages)
+	messages, err := c.Messages("mytopic", sinceAllMessages, false)
 	assert.Nil(t, err)
 	assert.Equal(t, 1, len(messages))
 	assert.Equal(t, "my other message", messages[0].Message)
@@ -116,8 +116,34 @@ func testCacheMessagesTagsPrioAndTitle(t *testing.T, c cache) {
 	m.Title = "some title"
 	assert.Nil(t, c.AddMessage(m))
 
-	messages, _ := c.Messages("mytopic", sinceAllMessages)
+	messages, _ := c.Messages("mytopic", sinceAllMessages, false)
 	assert.Equal(t, []string{"tag1", "tag2"}, messages[0].Tags)
 	assert.Equal(t, 5, messages[0].Priority)
 	assert.Equal(t, "some title", messages[0].Title)
 }
+
+func testCacheMessagesScheduled(t *testing.T, c cache) {
+	m1 := newDefaultMessage("mytopic", "message 1")
+	m2 := newDefaultMessage("mytopic", "message 2")
+	m2.Time = time.Now().Add(time.Hour).Unix()
+	m3 := newDefaultMessage("mytopic", "message 3")
+	m3.Time = time.Now().Add(time.Minute).Unix() // earlier than m2!
+	m4 := newDefaultMessage("mytopic2", "message 4")
+	m4.Time = time.Now().Add(time.Minute).Unix()
+	assert.Nil(t, c.AddMessage(m1))
+	assert.Nil(t, c.AddMessage(m2))
+	assert.Nil(t, c.AddMessage(m3))
+
+	messages, _ := c.Messages("mytopic", sinceAllMessages, false) // exclude scheduled
+	assert.Equal(t, 1, len(messages))
+	assert.Equal(t, "message 1", messages[0].Message)
+
+	messages, _ = c.Messages("mytopic", sinceAllMessages, true) // include scheduled
+	assert.Equal(t, 3, len(messages))
+	assert.Equal(t, "message 1", messages[0].Message)
+	assert.Equal(t, "message 3", messages[1].Message) // Order!
+	assert.Equal(t, "message 2", messages[2].Message)
+
+	messages, _ = c.MessagesDue()
+	assert.Empty(t, messages)
+}

server/server.go

@@ -73,6 +73,7 @@ var (
 
 const (
 	messageLimit = 512
+	minDelay     = 10 * time.Second
 )
 
 var (
@@ -183,6 +184,15 @@ func (s *Server) Run() error {
 			s.updateStatsAndExpire()
 		}
 	}()
+	go func() {
+		ticker := time.NewTicker(s.config.AtSenderInterval)
+		for {
+			<-ticker.C
+			if err := s.sendDelayedMessages(); err != nil {
+				log.Printf("error sending scheduled messages: %s", err.Error())
+			}
+		}
+	}()
 	listenStr := fmt.Sprintf("%s/http", s.config.ListenHTTP)
 	if s.config.ListenHTTPS != "" {
 		listenStr += fmt.Sprintf(" %s/https", s.config.ListenHTTPS)
@@ -279,14 +289,17 @@ func (s *Server) handlePublish(w http.ResponseWriter, r *http.Request, _ *visito
 	if m.Message == "" {
 		return errHTTPBadRequest
 	}
-	title, priority, tags, cache, firebase := parseHeaders(r.Header)
-	m.Title = title
-	m.Priority = priority
-	m.Tags = tags
-	if err := t.Publish(m); err != nil {
+	cache, firebase, err := parseHeaders(r.Header, m)
+	if err != nil {
 		return err
 	}
-	if s.firebase != nil && firebase {
+	delayed := m.Time > time.Now().Unix()
+	if !delayed {
+		if err := t.Publish(m); err != nil {
+			return err
+		}
+	}
+	if s.firebase != nil && firebase && !delayed {
 		go func() {
 			if err := s.firebase(m); err != nil {
 				log.Printf("Unable to publish to Firebase: %v", err.Error())
@@ -308,35 +321,62 @@ func (s *Server) handlePublish(w http.ResponseWriter, r *http.Request, _ *visito
 	return nil
 }
 
-func parseHeaders(header http.Header) (title string, priority int, tags []string, cache bool, firebase bool) {
-	title = readHeader(header, "x-title", "title", "ti", "t")
+func parseHeaders(header http.Header, m *message) (cache bool, firebase bool, err error) {
+	cache = readHeader(header, "x-cache", "cache") != "no"
+	firebase = readHeader(header, "x-firebase", "firebase") != "no"
+	m.Title = readHeader(header, "x-title", "title", "ti", "t")
 	priorityStr := readHeader(header, "x-priority", "priority", "prio", "p")
 	if priorityStr != "" {
 		switch strings.ToLower(priorityStr) {
 		case "1", "min":
-			priority = 1
+			m.Priority = 1
 		case "2", "low":
-			priority = 2
+			m.Priority = 2
 		case "3", "default":
-			priority = 3
+			m.Priority = 3
 		case "4", "high":
-			priority = 4
+			m.Priority = 4
 		case "5", "max", "urgent":
-			priority = 5
+			m.Priority = 5
 		default:
-			priority = 0
+			return false, false, errHTTPBadRequest
 		}
 	}
 	tagsStr := readHeader(header, "x-tags", "tag", "tags", "ta")
 	if tagsStr != "" {
-		tags = make([]string, 0)
+		m.Tags = make([]string, 0)
 		for _, s := range strings.Split(tagsStr, ",") {
-			tags = append(tags, strings.TrimSpace(s))
+			m.Tags = append(m.Tags, strings.TrimSpace(s))
 		}
 	}
-	cache = readHeader(header, "x-cache", "cache") != "no"
-	firebase = readHeader(header, "x-firebase", "firebase") != "no"
-	return title, priority, tags, cache, firebase
+	atStr := readHeader(header, "x-at", "at", "x-schedule", "schedule", "sched")
+	if atStr != "" {
+		if !cache {
+			return false, false, errHTTPBadRequest
+		}
+		at, err := strconv.Atoi(atStr)
+		if err != nil {
+			return false, false, errHTTPBadRequest
+		} else if int64(at) < time.Now().Add(minDelay).Unix() {
+			return false, false, errHTTPBadRequest
+		}
+		m.Time = int64(at)
+	} else {
+		delayStr := readHeader(header, "x-delay", "delay", "x-in", "in")
+		if delayStr != "" {
+			if !cache {
+				return false, false, errHTTPBadRequest
+			}
+			delay, err := time.ParseDuration(delayStr)
+			if err != nil {
+				return false, false, errHTTPBadRequest
+			} else if delay < minDelay {
+				return false, false, errHTTPBadRequest
+			}
+			m.Time = time.Now().Add(delay).Unix()
+		}
+	}
+	return cache, firebase, nil
 }
 
 func readHeader(header http.Header, names ...string) string {
@@ -401,6 +441,7 @@ func (s *Server) handleSubscribe(w http.ResponseWriter, r *http.Request, v *visi
 	}
 	var wlock sync.Mutex
 	poll := r.URL.Query().Has("poll")
+	scheduled := r.URL.Query().Has("scheduled") || r.URL.Query().Has("sched")
 	sub := func(msg *message) error {
 		wlock.Lock()
 		defer wlock.Unlock()
@@ -419,7 +460,7 @@ func (s *Server) handleSubscribe(w http.ResponseWriter, r *http.Request, v *visi
 	w.Header().Set("Access-Control-Allow-Origin", "*")            // CORS, allow cross-origin requests
 	w.Header().Set("Content-Type", contentType+"; charset=utf-8") // Android/Volley client needs charset!
 	if poll {
-		return s.sendOldMessages(topics, since, sub)
+		return s.sendOldMessages(topics, since, scheduled, sub)
 	}
 	subscriberIDs := make([]int, 0)
 	for _, t := range topics {
@@ -433,7 +474,7 @@ func (s *Server) handleSubscribe(w http.ResponseWriter, r *http.Request, v *visi
 	if err := sub(newOpenMessage(topicsStr)); err != nil { // Send out open message
 		return err
 	}
-	if err := s.sendOldMessages(topics, since, sub); err != nil {
+	if err := s.sendOldMessages(topics, since, scheduled, sub); err != nil {
 		return err
 	}
 	for {
@@ -449,12 +490,12 @@ func (s *Server) handleSubscribe(w http.ResponseWriter, r *http.Request, v *visi
 	}
 }
 
-func (s *Server) sendOldMessages(topics []*topic, since sinceTime, sub subscriber) error {
+func (s *Server) sendOldMessages(topics []*topic, since sinceTime, scheduled bool, sub subscriber) error {
 	if since.IsNone() {
 		return nil
 	}
 	for _, t := range topics {
-		messages, err := s.cache.Messages(t.ID, since)
+		messages, err := s.cache.Messages(t.ID, since, scheduled)
 		if err != nil {
 			return err
 		}
@@ -560,6 +601,32 @@ func (s *Server) updateStatsAndExpire() {
 		s.messages, len(s.topics), subscribers, messages, len(s.visitors))
 }
 
+func (s *Server) sendDelayedMessages() error {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	messages, err := s.cache.MessagesDue()
+	if err != nil {
+		return err
+	}
+	for _, m := range messages {
+		t, ok := s.topics[m.Topic] // If no subscribers, just mark message as published
+		if ok {
+			if err := t.Publish(m); err != nil {
+				log.Printf("unable to publish message %s to topic %s: %v", m.ID, m.Topic, err.Error())
+			}
+			if s.firebase != nil {
+				if err := s.firebase(m); err != nil {
+					log.Printf("unable to publish to Firebase: %v", err.Error())
+				}
+			}
+		}
+		if err := s.cache.MarkPublished(m); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
 func (s *Server) withRateLimit(w http.ResponseWriter, r *http.Request, handler func(w http.ResponseWriter, r *http.Request, v *visitor) error) error {
 	v := s.visitor(r)
 	if err := v.RequestAllowed(); err != nil {