ARTEMIS-362 Broadcast only filled buffer content.

When publishing server connectors to other cluster members the whole buffer is sent.
This fixes ARTEMIS-362 by extracting the filled part of the buffer for broadcasting.

Added test case that checks that packet size does not exceed 1500 bytes with one connector.

artemis-server/src/main/java/org/apache/activemq/artemis/core/server/cluster/impl/BroadcastGroupImpl.java

@@ -191,7 +191,9 @@ public class BroadcastGroupImpl implements BroadcastGroup, Runnable {
          tcConfig.encode(buff);
       }
 
-      byte[] data = buff.toByteBuffer().array();
+      // Only send as many bytes as we need.
+      byte[] data = new byte[buff.readableBytes()];
+      buff.getBytes(buff.readerIndex(), data);
 
       endpoint.broadcast(data);
    }

artemis-server/src/test/java/org/apache/activemq/artemis/core/server/cluster/impl/BroadcastGroupImplTest.java

@@ -0,0 +1,108 @@
+/*
+ * 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.activemq.artemis.core.server.cluster.impl;
+
+import java.util.concurrent.TimeUnit;
+
+import org.apache.activemq.artemis.api.core.BroadcastEndpoint;
+import org.apache.activemq.artemis.api.core.BroadcastEndpointFactory;
+import org.apache.activemq.artemis.api.core.TransportConfiguration;
+import org.apache.activemq.artemis.core.server.impl.InVMNodeManager;
+import org.apache.activemq.artemis.tests.util.ActiveMQTestBase;
+import org.junit.Test;
+
+/** Test the {@link BroadcastGroupImpl}.<br> */
+public class BroadcastGroupImplTest extends ActiveMQTestBase {
+
+   static class BroadcastEndpointFactoryImpl implements BroadcastEndpointFactory {
+      private static final long serialVersionUID = 1L;
+      int sent = 0;
+
+      @Override
+      public BroadcastEndpoint createBroadcastEndpoint() throws Exception {
+         return new BroadcastEndpointImpl(this);
+      }
+
+   }
+
+   static class BroadcastEndpointImpl implements BroadcastEndpoint {
+      private BroadcastEndpointFactoryImpl factory;
+
+      public BroadcastEndpointImpl(BroadcastEndpointFactoryImpl factory) {
+         this.factory = factory;
+      }
+
+      @Override
+      public void openClient() { }
+
+      @Override
+      public void openBroadcaster() { }
+
+      @Override
+      public void close(boolean isBroadcast) { }
+
+      @Override
+      public void broadcast(byte[] data) throws Exception {
+         if (data == null)
+            fail("Attempted to send datagram with null content");
+         if (data.length == 0)
+            fail("Attempted to send datagram with blank content");
+         if (data.length > 1500) // Common MTU size, not specification!
+            fail("Attempted to send a datagram with " + data.length + " bytes");
+         factory.sent++;
+      }
+
+      @Override
+      public byte[] receiveBroadcast() throws Exception {
+         return null;
+      }
+
+      @Override
+      public byte[] receiveBroadcast(long time, TimeUnit unit) throws Exception {
+         return null;
+      }
+   }
+
+   /**
+    * Test the broadcasted packages length.<br>
+    * Broadcast and MultiCast techniques are commonly limited in size by
+    * underlying hardware. Broadcast and MultiCast protocols are typically not
+    * guaranteed (UDP) and as such large packages may be silently discarded by
+    * underlying hardware.<br>
+    * This test validates that Artemis Server does not broadcast packages above
+    * a size of 1500 bytes. The limit is not derived from any normative
+    * documents, but is rather derived from common MTU for network equipment.
+    */
+   @Test
+   public void testBroadcastDatagramLength() throws Throwable {
+      BroadcastEndpointFactoryImpl befi;
+      befi = new BroadcastEndpointFactoryImpl();
+      InVMNodeManager node;
+      node = new InVMNodeManager(false);
+      String name;
+      name = "BroadcastGroupImplTest";
+      BroadcastGroupImpl test;
+      test = new BroadcastGroupImpl(node, name, 1000, null, befi);
+      TransportConfiguration tcon;
+      tcon = new TransportConfiguration(getClass().getName());
+      test.addConnector(tcon);
+      // Broadcast
+      test.broadcastConnectors();
+      // Make sure we sent one package
+      assertEquals("Incorrect number of sent datagrams", 1, befi.sent);
+   }
+}