GOSSIP-81 Move Jackson and UDP to their own modules

Part of what makes this work is the test implementation of TransportManager.

This PR is pretty straightforward. A few gotchas though:
* A message signing test was moved into `JacksonTests` because that is
  where the signing actually happens.
* A CRDT serializing test was moved there as well. It's the best place
  for now.
* No UDP tests at all. I plan to fix that in a bit. Reasoning is that it is
  difficult to test any TransportManager implementation without bring up
  a full stack. I plan to address this in the future (GOSSIP-83).
* Simple round trip Jackson serialization tests.

gossip-transport-udp/src/main/java/org/apache/gossip/transport/udp/UdpTransportManager.java

@@ -0,0 +1,99 @@
+/*
+ * 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.gossip.transport.udp;
+
+import org.apache.gossip.manager.GossipCore;
+import org.apache.gossip.manager.GossipManager;
+import org.apache.gossip.transport.AbstractTransportManager;
+import org.apache.log4j.Logger;
+
+import java.io.IOException;
+import java.net.DatagramPacket;
+import java.net.DatagramSocket;
+import java.net.InetAddress;
+import java.net.InetSocketAddress;
+import java.net.SocketAddress;
+import java.net.SocketException;
+import java.net.URI;
+
+/**
+ * This class is constructed by reflection in GossipManager.
+ * It manages transport (byte read/write) operations over UDP.
+ */
+public class UdpTransportManager extends AbstractTransportManager {
+  
+  public static final Logger LOGGER = Logger.getLogger(UdpTransportManager.class);
+  
+  /** The socket used for the passive thread of the gossip service. */
+  private final DatagramSocket server;
+  
+  private final int soTimeout;
+  
+  /** required for reflection to work! */
+  public UdpTransportManager(GossipManager gossipManager, GossipCore gossipCore) {
+    super(gossipManager, gossipCore);
+    
+    soTimeout = gossipManager.getSettings().getGossipInterval() * 2;
+    
+    try {
+      SocketAddress socketAddress = new InetSocketAddress(gossipManager.getMyself().getUri().getHost(),
+              gossipManager.getMyself().getUri().getPort());
+      server = new DatagramSocket(socketAddress);
+    } catch (SocketException ex) {
+      LOGGER.warn(ex);
+      throw new RuntimeException(ex);
+    }
+  }
+
+  @Override
+  public void shutdown() {
+    server.close();
+    super.shutdown();
+  }
+
+  /**
+   * blocking read a message.
+   * @return buffer of message contents.
+   * @throws IOException
+   */
+  public byte[] read() throws IOException {
+    byte[] buf = new byte[server.getReceiveBufferSize()];
+    DatagramPacket p = new DatagramPacket(buf, buf.length);
+    server.receive(p);
+    debug(p.getData());
+    return p.getData();
+  }
+
+  @Override
+  public void send(URI endpoint, byte[] buf) throws IOException {
+    DatagramSocket socket = new DatagramSocket();
+    socket.setSoTimeout(soTimeout);
+    InetAddress dest = InetAddress.getByName(endpoint.getHost());
+    DatagramPacket payload = new DatagramPacket(buf, buf.length, dest, endpoint.getPort());
+    socket.send(payload);
+    // todo: investigate UDP socket reuse. It would save a little setup/teardown time wrt to the local socket.
+    socket.close();
+  }
+  
+  private void debug(byte[] jsonBytes) {
+    if (LOGGER.isDebugEnabled()){
+      String receivedMessage = new String(jsonBytes);
+      LOGGER.debug("Received message ( bytes): " + receivedMessage);
+    }
+  }
+}

gossip-transport-udp/src/test/java/org/apache/gossip/transport/udp/UdpTransportIntegrationTest.java

@@ -0,0 +1,65 @@
+/*
+ * 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.gossip.transport.udp;
+
+import org.apache.gossip.GossipSettings;
+import org.junit.Assert;
+import org.junit.Ignore;
+import org.junit.Test;
+
+import java.util.concurrent.Future;
+import java.util.concurrent.TimeUnit;
+
+public class UdpTransportIntegrationTest {
+  
+  // It's currently impossible to create a UdpTransportManager without bringing up an entire stack.
+  // This is because AbstractTransportManager creates a PassiveGossipThread (requires GossipManager, 
+  // GossipCore) and also requires those same things plus a MetricsRegistry to create the 
+  // ActiveGossiper.
+  // TODO: test UDPTransportManger semantics (read and write) in isolation.
+  // I've written this test to indicate the direction I want things to go.
+  // Uncomment/Fix it once the coupling issues are worked out.
+  @Test @Ignore
+  public void testRoundTrip() {
+    /*
+    GossipSettings settings0 = new GossipSettings();
+    GossipSettings settings1 = new GossipSettings();
+    UdpTransportManager mgr0 = new UdpTransportManager(settings0);
+    UdpTransportManager mgr1 = new UdpTransportManager(settings1);
+    
+    mgr0.startEndpoint();
+    mgr1.startEndpoint();
+    mgr0.startActiveGossiper();
+    mgr1.startActiveGossiper();
+    
+    // wait a little while for convergence
+    // perhaps there is a Mockito Whitebox way to foce members
+    
+    byte[] data = new byte[] {0,1,2,3,4,5};
+    Future<byte[]> someData = asyncWaitForData(mgr1);
+    mgr0.send(toURI(settings1), data);
+
+    Assert.assertEquals(data, someData.get(1000, TimeUnit.MILLISECONDS));
+    
+    mgr0.shutdown();
+    mgr1.shutdown();
+    */
+  }
+  
+  
+}