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assignments/src/MV3500Cohort2023MarchJune/homework2/Islas/HW2.java

+package MV3500Cohort2023MarchJune.homework2.Islas;
+
+import java.io.*;
+import java.net.*;
+
+/**
+ * An example of receiving UDP packets. Since very often both the
+ * sender and receiver are on the same host we use different ports
+ * for each. This prevents collision complaints from the localhost.
+ * 
+ * Start this before launching UdpSender.
+ *
+ * @see <a href="https://docs.oracle.com/javase/tutorial/networking/datagrams/index.html">https://docs.oracle.com/javase/tutorial/networking/datagrams/index.html</a>
+ * @see <a href="https://docs.oracle.com/javase/tutorial/essential/io/datastreams.html">https://docs.oracle.com/javase/tutorial/essential/io/datastreams.html</a>
+ * @see <a href="https://en.wikipedia.org/wiki/User_Datagram_Protocol">https://en.wikipedia.org/wiki/User_Datagram_Protocol</a>
+ * @author mcgredo
+ * @author brutzman@nps.edu
+ */
+public class UnicastUdpReceiver
+{
+    /** Default constructor */
+    public UnicastUdpReceiver()
+    {
+        // default constructor
+    }
+//  public static final int        SENDING_PORT = 1414;        // port used by UdpSender, unneeded here
+    /** socket value of shared interest */
+    public static final int      UDP_PORT = 1415;        // sharable
+    /** socket value of shared interest */
+    public static final String DESTINATION_HOST = "localhost";
+
+    /**
+     * Program invocation, execution starts here
+     * @param args command-line arguments
+     */
+    public static void main(String[] args)
+    {
+        DatagramSocket udpSocket = null;
+        
+        try
+        {
+            // System.out.println(UnicastUdpReceiver.class.getName() + " started...");
+            System.out.println("What is the airspeed velocity of an unladen Swallow?");
+            
+            // Create a UDP socket
+            udpSocket = new DatagramSocket(UDP_PORT);
+            udpSocket.setReceiveBufferSize(1500); // how many bytes are in buffer?  MTU=1500 is good
+            udpSocket.setBroadcast(false);        // we're just receiving here
+//            udpSocket.setReuseAddress(true);
+            
+            byte[] byteArray = new byte[1500];
+            DatagramPacket receivePacket = new DatagramPacket(byteArray, byteArray.length);
+            
+            ByteArrayInputStream bais = new ByteArrayInputStream(byteArray);
+            DataInputStream dis = new DataInputStream(bais);
+            
+            // boolean       isEvenParity;
+            int           packetCount = 0;
+            int           firstInt;   
+            // float         secondFloat;
+            // String        thirdString;
+            // String        padding;
+            
+            // You need a new receiving packet to read from every packet received
+            while (true)
+            {
+                packetCount++; // good practice to increment counter at start of loop, when possible
+                udpSocket.receive(receivePacket); // blocks until packet is received
+                
+                if (packetCount == 1)
+                {                
+                    if  (udpSocket.getInetAddress() == null)
+                         System.out.println("UdpReceiver address/port: UDP socket address null (loopback)" + "/" + UDP_PORT);
+                    else System.out.println("UdpReceiver address/port: " + udpSocket.getInetAddress().getHostAddress() + "/" + UDP_PORT);
+                }
+
+                // values of interest follow. order and types of what was sent must match what you are reading!
+                firstInt     = dis.readInt();     // packetID
+                // secondFloat  = dis.readFloat();
+                // thirdString  = dis.readUTF();     // string value with guaranteed encoding, matches UTF-8 is 8 bit
+                // isEvenParity = dis.readBoolean(); // ok, we've gotten everything we're looking for.  
+                
+                dis.reset(); // now clear the input stream after reading, in preparation for next loop
+                
+                // if  (isEvenParity) 
+                //      padding = " ";
+                // else padding = "";
+                
+                if (firstInt == 11) {
+                    System.out.println("You may pass");
+                } 
+                else {
+                    System.out.println("Pull the lever!");
+                }
+
+                // System.out.println("[" + UnicastUdpReceiver.class.getName() + "]" + 
+                //                                     " port="   + UDP_PORT +
+                //                                 " packetID="   + firstInt +            // have output message use same name as sender
+                //                      ", second float value="   + secondFloat  + 
+                //                      ", third String value=\"" + thirdString  + "\"" + // note that /" is literal quote character
+                //                     " isPacketIdEvenParity="   + isEvenParity + ","  + padding +
+                //                      " packet counter="        + packetCount);
+            }
+        }
+        catch(IOException e)
+        {
+            System.err.println("Problem with UdpReceiver, see exception trace:");
+            System.err.println(e);
+        } 
+        finally // clean up prior to exit, don't want to leave behind zombie socket
+        {
+            if (udpSocket != null)
+                udpSocket.close();
+            System.out.println(UnicastUdpReceiver.class.getName() + " complete."); // all done
+        }
+    }
+}