[ecovacs] Shorten XMPP ping intervals after failure

If a ping failed, subsequent failures are very likely, so a shorter
interval will shorten the time until reconnection while still providing
robustness against single failures.

bundles/org.openhab.binding.ecovacs/src/main/java/org/openhab/binding/ecovacs/internal/api/impl/EcovacsXmppDevice.java

@@ -246,6 +246,8 @@ public void disconnect() {
 
     private class PingHandler {
         private static final long INTERVAL = 30; // seconds
+        // After a failure, use shorter intervals since subsequent further failure is likely
+        private static final long POST_FAILURE_INTERVAL = 5; // seconds
         private static final int MAX_FAILURES = 4;
 
         private final PingManager pingManager;
@@ -278,7 +280,7 @@ public void stop() {
 
         private void sendPing() {
             long timeSinceLastStanza = (System.currentTimeMillis() - connection.getLastStanzaReceived()) / 1000;
-            if (timeSinceLastStanza < INTERVAL) {
+            if (timeSinceLastStanza < currentPingInterval()) {
                 scheduleNextPing(timeSinceLastStanza);
                 return;
             }
@@ -306,9 +308,13 @@ private synchronized void scheduleNextPing(long delta) {
                 oldFuture.cancel(true);
             }
             if (started) {
-                this.nextPing = scheduler.schedule(this::sendPing, INTERVAL - delta, TimeUnit.SECONDS);
+                this.nextPing = scheduler.schedule(this::sendPing, currentPingInterval() - delta, TimeUnit.SECONDS);
             }
         }
+
+        private long currentPingInterval() {
+            return failedPings > 0 ? POST_FAILURE_INTERVAL : INTERVAL;
+        }
     }
 
     private class IncomingMessageHandler extends AbstractIqRequestHandler {