1 files changed, 116 insertions, 1 deletions
diff --git a/policy-endpoints/src/main/java/org/onap/policy/common/endpoints/event/comm/client/BidirectionalTopicClient.java b/policy-endpoints/src/main/java/org/onap/policy/common/endpoints/event/comm/client/BidirectionalTopicClient.java
index 57a331c1..2a9f1446 100644
--- a/policy-endpoints/src/main/java/org/onap/policy/common/endpoints/event/comm/client/BidirectionalTopicClient.java
+++ b/policy-endpoints/src/main/java/org/onap/policy/common/endpoints/event/comm/client/BidirectionalTopicClient.java
@@ -2,7 +2,7 @@
  * ============LICENSE_START=======================================================
  * ONAP
  * ================================================================================
- * Copyright (C) 2020 AT&T Intellectual Property. All rights reserved.
+ * Copyright (C) 2020-2021 AT&T Intellectual Property. All rights reserved.
  * ================================================================================
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -22,6 +22,9 @@ package org.onap.policy.common.endpoints.event.comm.client;
 
 import java.util.Arrays;
 import java.util.List;
+import java.util.concurrent.BlockingDeque;
+import java.util.concurrent.LinkedBlockingDeque;
+import java.util.concurrent.TimeUnit;
 import lombok.Getter;
 import org.onap.policy.common.endpoints.event.comm.Topic.CommInfrastructure;
 import org.onap.policy.common.endpoints.event.comm.TopicEndpoint;
@@ -29,6 +32,11 @@ import org.onap.policy.common.endpoints.event.comm.TopicEndpointManager;
 import org.onap.policy.common.endpoints.event.comm.TopicListener;
 import org.onap.policy.common.endpoints.event.comm.TopicSink;
 import org.onap.policy.common.endpoints.event.comm.TopicSource;
+import org.onap.policy.common.utils.coder.Coder;
+import org.onap.policy.common.utils.coder.CoderException;
+import org.onap.policy.common.utils.coder.StandardCoder;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 /**
  * A "bidirectional" topic, which is a pair of topics, one of which is used to publish
@@ -36,6 +44,9 @@ import org.onap.policy.common.endpoints.event.comm.TopicSource;
  */
 @Getter
 public class BidirectionalTopicClient {
+    private static final Logger logger = LoggerFactory.getLogger(BidirectionalTopicClient.class);
+    private static final Coder coder = new StandardCoder();
+
     private final String sinkTopic;
     private final String sourceTopic;
     private final TopicSink sink;
@@ -44,6 +55,16 @@ public class BidirectionalTopicClient {
     private final CommInfrastructure sourceTopicCommInfrastructure;
 
     /**
+     * Used when checking whether or not a message sent on the sink topic can be received
+     * on the source topic. When a matching message is received on the incoming topic,
+     * {@code true} is placed on the queue. If {@link #stop()} is called or the waiting
+     * thread is interrupted, then {@code false} is placed on the queue. Whenever a value
+     * is pulled from the queue, it is immediately placed back on the queue.
+     */
+    private final BlockingDeque<Boolean> checkerQueue = new LinkedBlockingDeque<>();
+
+
+    /**
      * Constructs the object.
      *
      * @param sinkTopic sink topic name
@@ -94,9 +115,103 @@ public class BidirectionalTopicClient {
         source.unregister(topicListener);
     }
 
+    /**
+     * Determines whether or not the topic is ready (i.e., {@link #awaitReady(Object)} has
+     * previously returned {@code true}).
+     *
+     * @return {@code true}, if the topic is ready to send and receive
+     */
+    public boolean isReady() {
+        return Boolean.TRUE.equals(checkerQueue.peek());
+    }
+
+    /**
+     * Waits for the bidirectional topic to become "ready" by publishing a message on the
+     * sink topic and awaiting receipt of the message on the source topic. If the message
+     * is not received within a few seconds, then it tries again. This process is
+     * continued until the message is received, {@link #stop()} is called, or this thread
+     * is interrupted. Once this returns, subsequent calls will return immediately, always
+     * with the same value.
+     *
+     * @param message message to be sent to the sink topic. Note: the equals() method must
+     *        return {@code true} if and only if two messages are the same
+     * @param waitMs time to wait, in milliseconds, before re-sending the message
+     * @return {@code true} if the message was received from the source topic,
+     *         {@code false} if this method was stopped or interrupted before receipt of
+     *         the message
+     * @throws CoderException if the message cannot be encoded
+     */
+    public synchronized <T> boolean awaitReady(T message, long waitMs) throws CoderException {
+        // see if we already know the answer
+        if (!checkerQueue.isEmpty()) {
+            return checkerQueue.peek();
+        }
+
+        final String messageText = coder.encode(message);
+
+        // class of message to be decoded
+        @SuppressWarnings("unchecked")
+        final Class<? extends T> clazz = (Class<? extends T>) message.getClass();
+
+        // create a listener to detect when a matching message is received
+        final TopicListener listener = (infra, topic, msg) -> {
+            try {
+                T incoming = decode(msg, clazz);
+
+                if (message.equals(incoming)) {
+                    logger.info("topic {} is ready; found matching message {}", topic, incoming);
+                    checkerQueue.add(Boolean.TRUE);
+                }
+
+            } catch (CoderException e) {
+                logger.warn("cannot decode message from topic {}", topic, e);
+                decodeFailed();
+            }
+        };
+
+        source.register(listener);
+
+        // loop until the message is received
+        try {
+            Boolean result;
+            do {
+                send(messageText);
+            } while ((result = checkerQueue.poll(waitMs, TimeUnit.MILLISECONDS)) == null);
+
+            // put it back on the queue
+            checkerQueue.add(result);
+
+        } catch (InterruptedException e) {
+            logger.error("interrupted waiting for topic sink {} source {}", sink.getTopic(), source.getTopic(), e);
+            Thread.currentThread().interrupt();
+            checkerQueue.add(Boolean.FALSE);
+
+        } finally {
+            source.unregister(listener);
+        }
+
+        return checkerQueue.peek();
+    }
+
+    /**
+     * Stops any listeners that are currently stuck in {@link #awaitReady(Object)} by
+     * adding {@code false} to the queue.
+     */
+    public void stopWaiting() {
+        checkerQueue.add(Boolean.FALSE);
+    }
+
     // these may be overridden by junit tests
 
     protected TopicEndpoint getTopicEndpointManager() {
         return TopicEndpointManager.getManager();
     }
+
+    protected <T> T decode(String msg, Class<? extends T> clazz) throws CoderException {
+        return coder.decode(msg, clazz);
+    }
+
+    protected void decodeFailed() {
+        // already logged - nothing else to do
+    }
 }