#73 Create Tool for sniffing UDP datagram packets.

src/main/java/org/epics/ca/impl/repeater/UdpMessageSniffer.java

@@ -0,0 +1,134 @@
+/*- Package Declaration ------------------------------------------------------*/
+package org.epics.ca.impl.repeater;
+
+/*- Imported packages --------------------------------------------------------*/
+
+import java.io.IOException;
+import java.net.DatagramPacket;
+import java.net.DatagramSocket;
+import java.net.SocketException;
+import java.util.logging.Logger;
+
+/*- Interface Declaration ----------------------------------------------------*/
+/*- Class Declaration --------------------------------------------------------*/
+
+/**
+ * Provides support for monitoring CA messages associated with UDP broadcasts
+ * sent to some port of interest.
+ *
+ * The CA protocol uses a mixture of broadcast and unicast messages.  For a simple
+ * tool like this which does not leverage off the low-level, OS-specific, libraries
+ * that support the network interface hardware, the unicast messages remain
+ * invisible. This leaves only the following messages available for observation:
+ * <Ul>
+ *    <li>CA Search Messages - sent from the CA Repeater to the IOC's listening
+ *    socket which typically operate on port 5064.</li>
+ *    <li>CA Beacon messages - sent from the IOC Send socket to the CA Repeater
+ *    which typically listens on port 5065.</li>
+ * </Ul>
+ */
+public class UdpMessageSniffer
+{
+
+/*- Public attributes --------------------------------------------------------*/
+/*- Private attributes -------------------------------------------------------*/
+
+private static final Logger logger = Logger.getLogger( UdpMessageSniffer.class.getName () );
+
+static
+{
+   // force only IPv4 sockets, since EPICS does not work right with IPv6 sockets
+   // see http://java.sun.com/j2se/1.5.0/docs/guide/net/properties.html
+   System.setProperty ( "java.net.preferIPv4Stack", "true" );
+   CARepeaterUtils.initializeLogger( logger );
+}
+
+/*- Main ---------------------------------------------------------------------*/
+
+   /**
+    * Starts the UDP Message Sniffer from the command line.
+    *
+    * The first and only argument should specify the port to monitor which
+    * will typically be the ports on which CA messages are broadcast
+    * (usually 5064 or 5065).
+    *
+    * @param argv arguments - should be exactly one.
+    */
+   public static void main( String[] argv )
+   {
+      if ( argv.length != 1 )
+      {
+         System.out.println( "Usage: java -cp <caJarFile> org.epics.ca.impl.repeater.UdpMessageSniffer <port>" );
+         return;
+      }
+
+      int port;
+      try
+      {
+         port = Integer.parseInt( argv[ 0 ] );
+      }
+      catch( NumberFormatException ex)
+      {
+         System.out.println( "The supplied argument ('" + argv[ 0 ] + "') could not be converted to an integer." );
+         return;
+      }
+
+      if ( ( port < 0 ) || (port > 65535 ) )
+      {
+         System.out.println( "The supplied argument ('" + argv[ 0 ] + "') was outside the allowed range (0-65535" );
+         return;
+      }
+
+      sniff( port );
+
+   }
+
+/*- Constructor --------------------------------------------------------------*/
+/*- Public methods -----------------------------------------------------------*/
+/*- Package-level access methods ---------------------------------------------*/
+
+   private static void sniff( int port )
+   {
+      DatagramSocket socket;
+      try
+      {
+         socket = SocketUtilities.createBroadcastAwareListeningSocket(port, true );
+         //socket = new DatagramSocket(port, InetAddress.getByName( "0.0.0.0") );
+         System.out.println ( "Listening for traffic on port " + port);
+      }
+      catch ( SocketException ex )
+      {
+         System.out.println( "ERROR: The listening socket on port " + port + " could not be opened." );
+         return;
+      }
+
+      boolean socketErrors = false;
+      while( ! socketErrors )
+      {
+         DatagramPacket rxPacket = new DatagramPacket( new byte[ 16384 ], 16384 );
+         try
+         {
+            socket.receive(rxPacket);
+         }
+         catch( IOException ex )
+         {
+            System.out.println( "ERROR: The listening socket experienced a problem. This utility will quit." );
+            socketErrors = true;
+            continue;
+         }
+
+         System.out.println( "\nReceived packet from " + rxPacket.getSocketAddress() + " of length " + rxPacket.getLength() + " bytes.");
+         boolean unprocessedMessages = true;
+         while ( unprocessedMessages )
+         {
+            // Note the RX packet data is shortened by the length of the message that is consumed.
+            System.out.println( CARepeaterMessage.extractMessageAsString(rxPacket ) );
+            unprocessedMessages = rxPacket.getLength() > 0;
+         }
+      }
+   }
+
+/*- Private methods ----------------------------------------------------------*/
+/*- Nested Classes -----------------------------------------------------------*/
+
+}