WebSocket connection keepalive

src/main/java/org/traccar/api/AsyncSocket.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2015 - 2016 Anton Tananaev ([email protected])
+ * Copyright 2015 - 2021 Anton Tananaev ([email protected])
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -63,6 +63,11 @@ public void onWebSocketClose(int statusCode, String reason) {
         Context.getConnectionManager().removeListener(userId, this);
     }
 
+    @Override
+    public void onKeepalive() {
+        sendData(new HashMap<>());
+    }
+
     @Override
     public void onUpdateDevice(Device device) {
         Map<String, Collection<?>> data = new HashMap<>();
@@ -85,7 +90,7 @@ public void onUpdateEvent(Event event) {
     }
 
     private void sendData(Map<String, Collection<?>> data) {
-        if (!data.isEmpty() && isConnected()) {
+        if (isConnected()) {
             try {
                 getRemote().sendString(Context.getObjectMapper().writeValueAsString(data), null);
             } catch (JsonProcessingException e) {

src/main/java/org/traccar/database/ConnectionManager.java

@@ -154,6 +154,14 @@ public Map<Event, Position> updateDeviceState(long deviceId) {
         return result;
     }
 
+    public synchronized void sendKeepalive() {
+        for (Set<UpdateListener> userListeners : listeners.values()) {
+            for (UpdateListener listener : userListeners) {
+                listener.onKeepalive();
+            }
+        }
+    }
+
     public synchronized void updateDevice(Device device) {
         for (long userId : Context.getPermissionsManager().getDeviceUsers(device.getId())) {
             if (listeners.containsKey(userId)) {
@@ -185,6 +193,7 @@ public synchronized void updateEvent(long userId, Event event) {
     }
 
     public interface UpdateListener {
+        void onKeepalive();
         void onUpdateDevice(Device device);
         void onUpdatePosition(Position position);
         void onUpdateEvent(Event event);

src/main/java/org/traccar/schedule/ScheduleManager.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2020 Anton Tananaev ([email protected])
+ * Copyright 2020 - 2021 Anton Tananaev ([email protected])
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -27,6 +27,7 @@ public void start() {
         executor = Executors.newSingleThreadScheduledExecutor();
 
         new TaskDeviceInactivityCheck().schedule(executor);
+        new TaskWebSocketKeepalive().schedule(executor);
 
     }
 

src/main/java/org/traccar/schedule/TaskWebSocketKeepalive.java

@@ -0,0 +1,36 @@
+/*
+ * Copyright 2021 Anton Tananaev ([email protected])
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.traccar.schedule;
+
+import org.traccar.Context;
+
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.TimeUnit;
+
+public class TaskWebSocketKeepalive implements Runnable {
+
+    private static final long PERIOD_SECONDS = 55;
+
+    public void schedule(ScheduledExecutorService executor) {
+        executor.scheduleAtFixedRate(this, PERIOD_SECONDS, PERIOD_SECONDS, TimeUnit.SECONDS);
+    }
+
+    @Override
+    public void run() {
+        Context.getConnectionManager().sendKeepalive();
+    }
+
+}