Github user arunmahadevan commented on a diff in the pull request:
https://github.com/apache/storm/pull/991#discussion_r49161519
--- Diff:
external/storm-mqtt/core/src/main/java/org/apache/storm/mqtt/trident/MqttPublishFunction.java
---
@@ -0,0 +1,84 @@
+/**
+ * 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.storm.mqtt.trident;
+
+import backtype.storm.Config;
+import backtype.storm.task.OutputCollector;
+import backtype.storm.topology.FailedException;
+import org.apache.storm.mqtt.MqttMessage;
+import org.apache.storm.mqtt.common.MqttOptions;
+import org.apache.storm.mqtt.MqttTupleMapper;
+import org.apache.storm.mqtt.common.MqttPublisher;
+import org.apache.storm.mqtt.common.SslUtils;
+import org.apache.storm.mqtt.ssl.KeyStoreLoader;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import storm.trident.operation.BaseFunction;
+import storm.trident.operation.TridentCollector;
+import storm.trident.operation.TridentOperationContext;
+import storm.trident.tuple.TridentTuple;
+
+import java.util.Map;
+
+public class MqttPublishFunction extends BaseFunction {
--- End diff --
Since the function does not emit anything, it cannot be chained with
further operations like normal functions and it appeared more like a sink.
Hence thought it might be more apt for it to be implemented as a state instead
of a function.
Agree that its difficult to do exactly once, but many other state
implementations also does not guarantee exactly once. Leave it to you to decide
the right approach.
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