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   1 /**
   2  * Copyright (c) 2010-2023 Contributors to the openHAB project
   3  *
   4  * See the NOTICE file(s) distributed with this work for additional
   5  * information.
   6  *
   7  * This program and the accompanying materials are made available under the
   8  * terms of the Eclipse Public License 2.0 which is available at
   9  * http://www.eclipse.org/legal/epl-2.0
  10  *
  11  * SPDX-License-Identifier: EPL-2.0
  12  */
  13 package org.openhab.binding.mqtt.generic.tools;
  14
  15 import java.nio.charset.StandardCharsets;
  16 import java.util.concurrent.CompletableFuture;
  17 import java.util.concurrent.ExecutionException;
  18 import java.util.concurrent.ScheduledExecutorService;
  19 import java.util.concurrent.TimeUnit;
  20 import java.util.concurrent.TimeoutException;
  21
  22 import org.eclipse.jdt.annotation.NonNullByDefault;
  23 import org.eclipse.jdt.annotation.Nullable;
  24 import org.openhab.core.io.transport.mqtt.MqttBrokerConnection;
  25 import org.openhab.core.io.transport.mqtt.MqttMessageSubscriber;
  26
  27 /**
  28  * Waits for a topic value to appear on a MQTT topic. One-time usable only per instance.
  29  *
  30  * @author David Graeff - Initial contribution
  31  */
  32 @NonNullByDefault
  33 public class WaitForTopicValue {
  34     private final CompletableFuture<String> composeFuture;
  35
  36     /**
  37      * Creates an instance.
  38      *
  39      * @param connection A broker connection.
  40      * @param topic The topic
  41      */
  42     public WaitForTopicValue(MqttBrokerConnection connection, String topic) {
  43         final CompletableFuture<String> future = new CompletableFuture<>();
  44         final MqttMessageSubscriber mqttMessageSubscriber = (t, payload) -> {
  45             future.complete(new String(payload, StandardCharsets.UTF_8));
  46         };
  47         future.whenComplete((r, e) -> {
  48             connection.unsubscribe(topic, mqttMessageSubscriber);
  49         });
  50
  51         composeFuture = connection.subscribe(topic, mqttMessageSubscriber).thenCompose(b -> future);
  52     }
  53
  54     /**
  55      * Free any resources
  56      */
  57     public void stop() {
  58         composeFuture.completeExceptionally(new Exception("Stopped"));
  59     }
  60
  61     /**
  62      * Wait for the value to appear on the MQTT broker.
  63      *
  64      * @param timeoutInMS Maximum time in milliseconds to wait for the value.
  65      * @return Return the value or null if timed out.
  66      */
  67     public @Nullable String waitForTopicValue(int timeoutInMS) {
  68         try {
  69             return composeFuture.get(timeoutInMS, TimeUnit.MILLISECONDS);
  70         } catch (InterruptedException | ExecutionException | TimeoutException e) {
  71             return null;
  72         }
  73     }
  74
  75     private void timeout() {
  76         if (!composeFuture.isDone()) {
  77             composeFuture.completeExceptionally(new TimeoutException());
  78         }
  79     }
  80
  81     /**
  82      * Return a future that completes successfully with a topic value or fails exceptionally with a timeout exception.
  83      *
  84      * @param scheduler A scheduler for the timeout
  85      * @param timeoutInMS The timeout in milliseconds
  86      * @return The future
  87      */
  88     public CompletableFuture<String> waitForTopicValueAsync(ScheduledExecutorService scheduler, int timeoutInMS) {
  89         scheduler.schedule(this::timeout, timeoutInMS, TimeUnit.MILLISECONDS);
  90         return composeFuture;
  91     }
  92 }