connectors/mqtt/src/main/java/org/apache/edgent/connectors/mqtt/runtime/MqttSubscriber.java

/*
Licensed to the Apache Software Foundation (ASF) under one
or more contributor license agreements.  See the NOTICE file
distributed with this work for additional information
regarding copyright ownership.  The ASF licenses this file
to you 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.apache.edgent.connectors.mqtt.runtime;

import org.apache.edgent.function.BiFunction;
import org.apache.edgent.function.Consumer;
import org.eclipse.paho.client.mqttv3.MqttClient;
import org.eclipse.paho.client.mqttv3.MqttException;
import org.eclipse.paho.client.mqttv3.MqttMessage;
import org.slf4j.Logger;

/**
 * Consumer that subscribes to topics from an MQTT server
 * producing a stream tuple of type {@code T} for each received message.
 *
 * @param <T> stream tuple type
 */
public class MqttSubscriber<T> implements Consumer<Consumer<T>>, AutoCloseable {
    private static final long serialVersionUID = 1L;
    private final Logger logger;
    private transient String id;
    private final MqttConnector connector;
    private final String topicFilter;
    private final int qos;
    private BiFunction<String, byte[], T> message2Tuple;
    private Consumer<T> eventSubmitter;

    public MqttSubscriber(MqttConnector connector, String topicFilter, int qos, BiFunction<String, byte[], T> message2Tuple) {
        this.logger = connector.getLogger();
        this.connector = connector;
        this.topicFilter = topicFilter;
        this.qos = qos;
        this.message2Tuple = message2Tuple;
        connector.setSubscriber(this);
    }
    
    /**
     * To be called on initial connection and reconnects
     * @param client the MqttClient
     * @throws MqttException
     */
    void connected(MqttClient client) throws MqttException {
        logger.info("{} subscribe({}, {})", id(), topicFilter, qos);
        client.subscribe(topicFilter, qos);
    }

    @Override
    public void accept(Consumer<T> eventSubmitter) {
        this.eventSubmitter = eventSubmitter;

        try {
            connector.client();  // induce connecting.
        } catch (Exception e) {
            logger.error("{} setup failed topicFilter:{}", id(), topicFilter, e);
        }
    }

    void messageArrived(String topic, MqttMessage message) throws Exception {
        T tuple = message2Tuple.apply(topic, message.getPayload());
        eventSubmitter.accept(tuple);
    }
    
    protected String id() {
        if (id == null) {
            // use our short object Id (only single subscriber)
            id = connector.id() + " subscriber ";
        }
        return id;
    }

    @Override
    public void close() throws Exception {
        connector.close();
    }
}