[GitHub] [bahir-flink] yuruguo commented on a change in pull request #100: [BAHIR-212] Add MQTT Connector for Flink

[GitBox <gi...@apache.org>]

yuruguo commented on a change in pull request #100:
URL: https://github.com/apache/bahir-flink/pull/100#discussion_r592951546



##########
File path: flink-connector-mqtt/src/main/java/org/apache/flink/streaming/connectors/mqtt/MqttSource.java
##########
@@ -0,0 +1,229 @@
+/*
+ * 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.flink.streaming.connectors.mqtt;
+
+import org.apache.commons.lang3.ArrayUtils;
+import org.apache.flink.api.common.serialization.DeserializationSchema;
+import org.apache.flink.api.common.state.ListState;
+import org.apache.flink.api.common.state.ListStateDescriptor;
+import org.apache.flink.api.common.typeinfo.TypeInformation;
+import org.apache.flink.api.java.typeutils.ResultTypeQueryable;
+import org.apache.flink.configuration.Configuration;
+import org.apache.flink.runtime.state.FunctionInitializationContext;
+import org.apache.flink.runtime.state.FunctionSnapshotContext;
+import org.apache.flink.streaming.api.checkpoint.CheckpointedFunction;
+import org.apache.flink.streaming.api.functions.source.RichSourceFunction;
+import org.eclipse.paho.client.mqttv3.IMqttDeliveryToken;
+import org.eclipse.paho.client.mqttv3.MqttCallbackExtended;
+import org.eclipse.paho.client.mqttv3.MqttClient;
+import org.eclipse.paho.client.mqttv3.MqttConnectOptions;
+import org.eclipse.paho.client.mqttv3.MqttMessage;
+import org.eclipse.paho.client.mqttv3.persist.MemoryPersistence;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+import java.util.Properties;
+import java.util.concurrent.LinkedBlockingQueue;
+
+import static java.util.Collections.singletonList;
+import static org.apache.flink.shaded.guava18.com.google.common.collect.Iterables.getOnlyElement;
+import static org.apache.flink.streaming.connectors.mqtt.MqttConfig.checkProperty;
+
+/**
+ * Source for reading messages from an Mqtt queue.
+ *
+ * @param <OUT> type of output messages
+ */
+public class MqttSource<OUT> extends RichSourceFunction<OUT>
+    implements CheckpointedFunction, ResultTypeQueryable<OUT>, MqttCallbackExtended {
+    private static final Logger LOG = LoggerFactory.getLogger(MqttSource.class);
+
+    // Mqtt subcriber client id
+    private static final String MQTT_CLIENT_ID = MqttClient.generateClientId();
+    // Blocking queue max capacity
+    private static final int MAX_QUEUE_CAPACITY = 10000;
+
+    // Subscribe one or more topics
+    private final String[] topics;
+    // Convert bytes to output message
+    private final DeserializationSchema<OUT> deserializationSchema;
+    // User-supplied properties
+    private final Properties properties;
+    // Queue cache data form mqtt client
+    private final LinkedBlockingQueue<MqttMessage> queue;
+
+    private String serverUrl;
+    private String username;
+    private String password;
+    private String clientId;
+    private boolean cleanSession;
+    private int qos;
+
+    private transient ListState<String> mqttState;
+    private transient MqttClient client;
+
+    private volatile boolean isRunning;
+
+    public MqttSource(String topic, DeserializationSchema<OUT> deserializationSchema, Properties properties) {
+        this(Collections.singletonList(topic), deserializationSchema, properties, MAX_QUEUE_CAPACITY);
+    }
+
+    public MqttSource(List<String> topics, DeserializationSchema<OUT> deserializationSchema, Properties properties) {
+        this(topics, deserializationSchema, properties, MAX_QUEUE_CAPACITY);
+    }
+
+    /**
+     * Creates {@link MqttSource} for Streaming
+     *
+     * @param topics                Subscribe topic list
+     * @param deserializationSchema Convert bytes to output message
+     * @param properties            Mqtt properties
+     * @param capacity              Blocking queue capacity
+     */
+    public MqttSource(List<String> topics,
+                      DeserializationSchema<OUT> deserializationSchema,
+                      Properties properties,
+                      int capacity) {
+        checkProperty(properties, MqttConfig.SERVER_URL);
+        checkProperty(properties, MqttConfig.USERNAME);
+        checkProperty(properties, MqttConfig.PASSWORD);
+
+        this.topics = topics.toArray(new String[topics.size()]);
+        this.deserializationSchema = deserializationSchema;
+        this.properties = properties;
+        this.queue = new LinkedBlockingQueue<>(capacity);
+    }
+
+    @Override
+    public void initializeState(FunctionInitializationContext context) throws Exception {
+        this.mqttState = context.getOperatorStateStore().getListState(
+            new ListStateDescriptor<>("mqttClientId", String.class));
+        this.clientId = context.isRestored() ? getOnlyElement(mqttState.get()) : MQTT_CLIENT_ID;
+        LOG.info("Current mqtt subcriber clientId is: {}", clientId);
+    }
+
+    @Override
+    public void open(Configuration parameters) throws Exception {
+        super.open(parameters);
+        if (connect()) {
+            this.isRunning = true;
+        }
+    }
+
+    private boolean connect() throws Exception {
+        this.serverUrl = properties.getProperty(MqttConfig.SERVER_URL);

Review comment:
       It's ok to use directly where needed, but this values may be used in multiple places, such as `properties.getProperty(MqttConfig.SERVER_URL)`, so saving them separately can ensure the code is concise.




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