http and multicast examples, refactored

CourseExamples/src/UdpMulticastHttpExamples/HttpWebPageSource.java

+package UdpMulticastHttpExamples;
+
+import java.io.*;
+import java.net.*;
+
+/**
+ * A very simple http web-page reading example that won't work in some circumstances.
+ * But it will in some others.
+ * 
+ * @author mcgredo
+ */
+public class HttpWebPageSource {
+
+    /**
+     * @param args the command line arguments
+     */
+    public static void main(String[] args) 
+    {
+        try
+        {
+           System.out.println("HttpWebPageSource: create http connection and retrieve default page");
+           System.out.println("Reference:  https://en.wikipedia.org/wiki/Hypertext_Transfer_Protocol");
+           System.out.println("Reference:  https://tools.ietf.org/html/rfc7230");
+           System.out.println();
+           
+           // We request an IP to connect to a web server running on port 80.
+           
+           Socket socket = new Socket("www.MovesInstitute.org", 80); 
+           
+           // we send a command to the web server, asking for what
+           // we want. Note that the format for the command is very
+           // specific and documented.
+           OutputStream os = socket.getOutputStream();
+           PrintStream  ps = new PrintStream(os);
+		   
+		   String message = "GET /index.html HTTP/1.0";
+           ps.print(message);
+           System.out.println(message);
+           System.out.println();
+           
+           // Commands have to terminate with "carriage return/line feed"
+           // twice to end the request. Those are the special characters
+           // to have the control characters printed.  Part of the http protocol!
+           ps.print("\r\n\r\n");
+           ps.flush();
+           
+           // Up until now we have been reading one line only.
+           // But a web server will write an unknown number of lines.
+           // So now we read until the transmisson ends.
+           
+           InputStream        is = socket.getInputStream();
+           InputStreamReader isr = new InputStreamReader(is);
+           BufferedReader     br = new BufferedReader(isr);
+           
+           String line;
+           int count = 0;
+           
+           while((line = br.readLine()) != null) // read from BufferedReader br one line at a time
+           {
+               count++;
+               System.out.println(count + ": " + line);
+           }
+           System.out.println("HttpWebPageSource: response finished");
+        }
+        catch(IOException e)
+        {
+            System.out.println("HttpWebPageSource: problem with client");
+            System.out.println(e);
+        }
+    }
+}

CourseExamples/src/UdpMulticastHttpExamples/MulticastReceiver.java

+package UdpMulticastHttpExamples;
+
+import java.io.*;
+import java.net.*;
+
+/**
+ *
+ * @author mcgredo
+ */
+public class MulticastReceiver {
+
+    public static final String MULTICAST_ADDRESS = "239.1.2.15";
+    public static final int     DESTINATION_PORT = 1718;
+    /** How many routers can be crossed */
+    public static final int TTL = 10; 
+    
+    public static void main(String[] args) 
+    {
+        try
+        {
+            System.out.println("MulticastReceiver started...");
+        
+            // This is a java/IPv6 problem. You should also add it to the
+            // arguments used to start the app, eg -Djava.net.preferIPv4Stack=true
+            // set in the "run" section of preferences. Also, typically
+            // netbeans must be restarted after these settings.
+            // https://stackoverflow.com/questions/18747134/getting-cant-assign-requested-address-java-net-socketexception-using-ehcache
+            System.setProperty("java.net.preferIPv4Stack", "true");
+            
+            MulticastSocket multicastSocket = new MulticastSocket(DESTINATION_PORT);
+            multicastSocket.setTimeToLive(TTL);
+            InetAddress multicastAddress = InetAddress.getByName(MULTICAST_ADDRESS);
+            // Join group useful on receiving side
+            multicastSocket.joinGroup(multicastAddress);
+            // You can join multiple groups here
+            System.out.println("Multicast address/port: " + multicastAddress.getHostAddress() + "/" + DESTINATION_PORT);
+            System.out.println("Multicast packets received log:");
+            
+            int count = 0; // initialize
+            
+            while(true)
+            {
+                byte[] packetArray = new byte[1500]; // note use of typical MTU value
+                DatagramPacket packet = new DatagramPacket(packetArray, packetArray.length);
+                
+                multicastSocket.receive(packet);
+                count++;
+                
+                ByteArrayInputStream bais = new ByteArrayInputStream(packet.getData());
+                DataInputStream dis = new DataInputStream(bais);
+				String firstCharacters = new String();
+				char   nextChar  = ' ';
+				while (nextChar != ';') // read and build string until terminator ; found
+				{
+					nextChar = dis.readChar();
+					firstCharacters += nextChar;
+				}
+				if (firstCharacters.equals("quit;"))
+				{
+					System.out.println("Received \"quit;\" sentinel");
+					break; // exit out of reading loop
+				}
+				int   index       = dis.readInt();
+                float firstFloat  = dis.readFloat();
+                float secondFloat = dis.readFloat();
+                
+				if (count < 10) System.out.print(" "); // prettier output formatting
+                System.out.print(count + ". \"" + firstCharacters + "\" "); // wrap string in quote marks
+                System.out.println("index=" + index + ", firstFloat=" + firstFloat + " secondFloat=" + secondFloat);
+            }
+            System.out.println("MulticastReceiver loop complete.");
+        }
+        catch(IOException e)
+        {
+            System.out.println("Problem with MulticastReceiver, see exception trace:");
+            System.out.println(e);
+        }
+		finally // clean up after exit condition
+		{
+			// socket/database/completion cleanup code can go here, if needed.
+            System.out.println("MulticastReceiver finally block, complete.");
+		}
+    }
+}

CourseExamples/src/UdpMulticastHttpExamples/MulticastSender.java

+package UdpMulticastHttpExamples;
+
+import java.io.*;
+import java.net.*;
+
+/**
+ * Looks a lot like a UDP sender.
+ * 
+ * @author mcgredo
+ */
+public class MulticastSender {
+
+    public static final String MULTICAST_ADDRESS = "239.1.2.15"; // within reserved multicast address range
+    public static final int     DESTINATION_PORT = 1718;
+    /** How many routers can be crossed */
+    public static final int TTL = 10; 
+    
+	@SuppressWarnings("SleepWhileInLoop")
+    public static void main(String[] args) 
+    {
+        try
+        {
+            System.out.println("MulticastSender started...");
+            // This is a java/IPv6 problem. You should also add it to the
+            // arguments used to start the app, eg -Djava.net.preferIPv4Stack=true
+            // set in the "run" section of preferences. Also, typically
+            // netbeans must be restarted after these settings.
+            // https://stackoverflow.com/questions/18747134/getting-cant-assign-requested-address-java-net-socketexception-using-ehcache
+            System.setProperty("java.net.preferIPv4Stack", "true");
+            
+            // multicast group we are sending to--not a single host
+            MulticastSocket multicastSocket = new MulticastSocket(DESTINATION_PORT);
+            multicastSocket.setTimeToLive(TTL); // time to live reduces scope of transmission
+            InetAddress multicastAddress = InetAddress.getByName(MULTICAST_ADDRESS);
+            System.out.println("Multicast address/port: " + multicastAddress.getHostAddress() + "/" + DESTINATION_PORT);
+            // Join group useful on receiving side
+            multicastSocket.joinGroup(multicastAddress);
+            // You can join multiple groups here
+            
+			int loopSize = 20;
+            for (int index = 0; index < loopSize; index++)
+            {
+            
+				// Put together a message with binary content. "ByteArrayOutputStream"
+				// is a java.io utility that lets us put together an array of binary
+				// data, which we put into the UDP packet.
+				ByteArrayOutputStream baos = new ByteArrayOutputStream();
+				DataOutputStream       dos = new DataOutputStream(baos);
+
+				// Put together an updated packet to send
+				if (index < loopSize - 1)
+				{
+				// Put together an updated packet to send
+					 dos.writeChars("MulticastSender packet " + Integer.toString(index) + ";"); // string chars for readability
+					 dos.writeInt  (index); // arbitrary data, needs Java or byte-alignment to read
+					 dos.writeFloat(17.0f); // arbitrary data, needs Java or byte-alignment to read
+					 dos.writeFloat(23.0f); // arbitrary data, needs Java or byte-alignment to read
+				}
+				else dos.writeChars("quit;"); // note string must include ; semicolon as termination sentinel
+					
+				byte[] buffer = baos.toByteArray();
+				DatagramPacket packet = new DatagramPacket(buffer, buffer.length, multicastAddress, DESTINATION_PORT);
+				
+				multicastSocket.send(packet);
+				System.out.println("Sent multicast packet " + index + " of " + loopSize);
+       
+				// How fast does this go? Does UDP try to slow it down, or does
+				// this cause network problems? (hint: yes for an unlimited send
+				// rate, unlike TCP). How do you know on the receiving side
+				// that you haven't received a duplicate UDP packet, out of
+				// order packet, or dropped packet?  Necessary considerations.
+				Thread.sleep(1000); // Send 100, one per second
+            }
+            System.out.println("MulticastSender complete.");
+        }
+        catch(IOException | InterruptedException e)
+        {
+            System.out.println("Problem with MulticastSender, see exception trace:");
+            System.out.println(e);
+        }
+    }
+    
+}

CourseExamples/src/UdpMulticastHttpExamples/MulticastTerminalLog.txt

+Invocation instructions:
+1. run/debug MulticastReceiver.java
+2. run/debug MulticastSender.java
+
+Program responses:
+
+===================================================
+run:
+MulticastSender started...
+Multicast address/port: 239.1.2.15/1718
+Sent multicast packet 0 of 20
+Sent multicast packet 1 of 20
+Sent multicast packet 2 of 20
+Sent multicast packet 3 of 20
+Sent multicast packet 4 of 20
+Sent multicast packet 5 of 20
+Sent multicast packet 6 of 20
+Sent multicast packet 7 of 20
+Sent multicast packet 8 of 20
+Sent multicast packet 9 of 20
+Sent multicast packet 10 of 20
+Sent multicast packet 11 of 20
+Sent multicast packet 12 of 20
+Sent multicast packet 13 of 20
+Sent multicast packet 14 of 20
+Sent multicast packet 15 of 20
+Sent multicast packet 16 of 20
+Sent multicast packet 17 of 20
+Sent multicast packet 18 of 20
+Sent multicast packet 19 of 20
+MulticastSender complete.
+BUILD SUCCESSFUL (total time: 20 seconds)
+
+===================================================
+run:
+MulticastReceiver started...
+Multicast address/port: 239.1.2.15/1718
+Multicast packets received log:
+ 1. "MulticastSender packet 0;" index=0, firstFloat=17.0 secondFloat=23.0
+ 2. "MulticastSender packet 1;" index=1, firstFloat=17.0 secondFloat=23.0
+ 3. "MulticastSender packet 2;" index=2, firstFloat=17.0 secondFloat=23.0
+ 4. "MulticastSender packet 3;" index=3, firstFloat=17.0 secondFloat=23.0
+ 5. "MulticastSender packet 4;" index=4, firstFloat=17.0 secondFloat=23.0
+ 6. "MulticastSender packet 5;" index=5, firstFloat=17.0 secondFloat=23.0
+ 7. "MulticastSender packet 6;" index=6, firstFloat=17.0 secondFloat=23.0
+ 8. "MulticastSender packet 7;" index=7, firstFloat=17.0 secondFloat=23.0
+ 9. "MulticastSender packet 8;" index=8, firstFloat=17.0 secondFloat=23.0
+10. "MulticastSender packet 9;" index=9, firstFloat=17.0 secondFloat=23.0
+11. "MulticastSender packet 10;" index=10, firstFloat=17.0 secondFloat=23.0
+12. "MulticastSender packet 11;" index=11, firstFloat=17.0 secondFloat=23.0
+13. "MulticastSender packet 12;" index=12, firstFloat=17.0 secondFloat=23.0
+14. "MulticastSender packet 13;" index=13, firstFloat=17.0 secondFloat=23.0
+15. "MulticastSender packet 14;" index=14, firstFloat=17.0 secondFloat=23.0
+16. "MulticastSender packet 15;" index=15, firstFloat=17.0 secondFloat=23.0
+17. "MulticastSender packet 16;" index=16, firstFloat=17.0 secondFloat=23.0
+18. "MulticastSender packet 17;" index=17, firstFloat=17.0 secondFloat=23.0
+19. "MulticastSender packet 18;" index=18, firstFloat=17.0 secondFloat=23.0
+Received "quit;" sentinel
+MulticastReceiver loop complete.
+MulticastReceiver finally block, complete.
+BUILD SUCCESSFUL (total time: 31 seconds)
+
+===================================================