McNeely TCP3 Example, HW2

assignments/src/MV3500Cohort2021JulySeptember/homework2/McNeely/McNeelyTCPExample3Client.java

+package MV3500Cohort2021JulySeptember.homework2.McNeely;
+
+import java.io.*;
+import java.net.*;
+
+/**
+ * Before, we always used telnet (netcat) to connect to the server. Here we are 
+ * now writing our own program to do the connection.
+ *
+ * As you will see, when we run this after we start the server we will see the
+ * same string telnet printed, sent by the server. The output at the server will
+ * show different socket pairs for each time the loop iterates.
+ *
+ * @author jrm_u
+ */
+public class McNeelyTCPExample3Client {
+
+    /** IPv6 String constant for localhost address, similarly IPv4 127.0.0.1
+     * @see <a href="https://en.wikipedia.org/wiki/localhost">https://en.wikipedia.org/wiki/localhost</a>
+     * @see <a href="https://en.wikipedia.org/wiki/IPv6_address">https://en.wikipedia.org/wiki/IPv6_address</a> 
+     */
+    public final static String LOCALHOST = "0:0:0:0:0:0:0:1";
+
+    /**
+     * Program invocation, execution starts here
+     * @param args command-line arguments
+     */
+    public static void main(String[] args) throws InterruptedException {
+        
+        // Local variables/fields
+        Socket socket = null;
+        InputStream is;
+        Reader isr;
+        BufferedReader br;
+        String serverMessage;
+        int clientLoopCount = 0;
+        
+        try {
+            while (true)
+            {
+                clientLoopCount++; // increment at beginning of loop for reliability
+                System.out.println(McNeelyTCPExample3Client.class.getName() + "McNeely creating socket...");
+
+                // We request an IP to connect to ("localhost") and
+                // port number at that IP (2317). This establishes
+                // a connection to that IP in the form of a Socket
+                // object; the server uses a ServerSocket to wait for
+                // connections.
+                socket = new Socket(LOCALHOST, 2317); // locohost?
+
+                // Now hook everything up (i.e. set up the streams), Java style:
+                is  = socket.getInputStream();
+                isr = new InputStreamReader(is);
+                br  = new BufferedReader(isr);
+
+                // Read a single line written by the server. We'd
+                // do things a bit differently if there were many lines to be read
+                // from the server instead of one only.
+                serverMessage = br.readLine();
+                System.out.println("==================================================");
+                       
+                System.out.print  ("Client loop " + clientLoopCount + ": ");
+                System.out.println("now we're cooking with diesel fuel!");
+                System.out.println("The message the server sent was: '" + serverMessage + "'");
+                // socket gets closed, either automatically/silently by this code (or possibly by the server)
+                
+                Thread.sleep(500l); // slow things down, for example 500l (long) = 500 msec
+                
+            } // end while(true) // infinite loops are dangerous, be sure to kill this process!
+        } 
+        catch (IOException e)
+        {
+            System.err.println("Problem with " + McNeelyTCPExample3Client.class.getName() + " networking:"); // describe what is happening
+            System.err.println("Error: " + e);
+            
+            // Provide more helpful information to user if exception occurs due to running twice at one time
+            if (e instanceof java.net.BindException) {
+                System.err.println("*** Be sure to stop any other running instances of programs using this port!");
+            }
+        }
+        finally // occurs after any other activity when shutting down
+        {
+            try {
+                if (socket != null)
+                    socket.close();
+            } catch (IOException e) {}
+            
+            // program exit: tell somebody about that happening.  Likely cause: server drops connection.
+            System.out.println();
+            System.out.println(McNeelyTCPExample3Client.class.getName() + " exit");
+        }
+    }
+}

assignments/src/MV3500Cohort2021JulySeptember/homework2/McNeely/McNeelyTCPExample3Server.java

+package MV3500Cohort2021JulySeptember.homework2.McNeely;
+
+import java.io.*;
+import java.net.*;
+
+/**
+ * Very slightly more complex than example1, further modifying example2. The
+ * only thing this does differently is introduce a loop into the response, so
+ * you don't have to restart the program after one response. Also, it prints out
+ * the socket pair the server sees. Run the program via telnet several times and
+ * compare the socket pairs.
+ *
+ * telnet (nc) localhost 2317
+ *
+ * If you're sophisticated you can contact the instructor's computer while
+ * running this program.
+ *
+ *      telnet (nc) [ipNumberOfServerLaptop] 2317
+ *
+ * and have the instructor display the socket pairs received.
+ *
+ * @author jrm_u
+ */
+public class McNeelyTCPExample3Server {
+
+    /**
+     * Program invocation, execution starts here
+     * If already compiled, can run using console in directory ../../build/classes/ by invoking \
+     *      java -classpath . TcpExamples.TcpExample3Server
+     * @param args command-line arguments
+     */
+    public static void main(String[] args) {
+        try {
+            
+            // ServerSocket waits for a connection from a client. 
+            // Notice that it is outside the loop; ServerSocket
+            // needs to be made only once.
+            System.out.println(McNeelyTCPExample3Server.class.getName() + " has started... here we go!"); // it helps debugging to put this on console first
+            
+            ServerSocket serverSocket = new ServerSocket(2317);
+            OutputStream os;
+            PrintStream ps;
+            InetAddress localAddress, remoteAddress;
+            int localPort, remotePort;
+            int serverLoopCount = 0;
+
+            // Server is up and waiting (i.e. "blocked" or paused)
+            // Loop, infinitely, waiting for client connections.
+            // Stop the program somewhere else.
+            while (true) { 
+                
+                // block until connected to a client
+                try (Socket clientConnectionSocket = serverSocket.accept())
+                {
+                    serverLoopCount++; // increment at beginning of loop for reliability
+                    
+                    // Now hook everything up (i.e. set up the streams), Java style:
+                    os = clientConnectionSocket.getOutputStream();
+                    ps = new PrintStream(os);
+                    ps.println("This is response number " + serverLoopCount + " produced by Justin's server."); // this gets sent back to client!
+                    
+                    // Print some information locally about the Socket connection.
+                    // This includes the port and IP numbers on both sides (the socket pair).
+                     localAddress = clientConnectionSocket.getLocalAddress();
+                    remoteAddress = clientConnectionSocket.getInetAddress();
+                        localPort = clientConnectionSocket.getLocalPort();
+                       remotePort = clientConnectionSocket.getPort();
+                       
+                    System.out.print ("Server loop " + serverLoopCount + ": ");
+                    
+                    // My socket pair connection looks like this, to localhost:
+                    // Socket pair: (( /0:0:0:0:0:0:0:1, 2317 ), ( /0:0:0:0:0:0:0:1, 54876 ))
+                    // Socket pair: (( /0:0:0:0:0:0:0:1, 2317 ), ( /0:0:0:0:0:0:0:1, 54881 ))
+                    
+                    // Why is the first IP/port the same, while the second set has different ports?
+                    System.out.println(McNeelyTCPExample3Server.class.getName() + " socket pair showing host name, address, port:");
+                    System.out.println("  (( " + 
+                         localAddress.getHostName() + "=" +  localAddress.getHostAddress() + ", " + localPort + " ), ( " + 
+                        remoteAddress.getHostName() + "=" + remoteAddress.getHostAddress() + ", " + remotePort + " ))");
+                    
+                    if ( localAddress.getHostName().equals( localAddress.getHostAddress()) ||
+                        remoteAddress.getHostName().equals(remoteAddress.getHostAddress()))
+                        System.out.println("  note HostName matches address if host has no DNS name");
+                    
+                    // Notice the use of flush() and try w/ resources. Without
+                    // the try w/ resources the Socket object may stay open for
+                    // a while after the client has stopped needing this
+                    // connection. try w/ resources explicitly ends the connection.
+                    ps.flush();
+                    // like it or not, you're outta here!
+                }
+            }
+        } catch (IOException e) {
+            System.err.println("Problem with " + McNeelyTCPExample3Server.class.getName() + " networking: " + e);
+
+            // Provide more helpful information to user if exception occurs due to running twice at one time
+            if (e instanceof java.net.BindException) {
+                System.err.println("*** Be sure to stop any other running instances of programs using this port!");
+            }
+        }
+    }
+}