Merge origin/master

assignments/src/MV3500Cohort2019JulySeptember/homework2/Knobeloch/Knobeloch_TCPIP_Client.java

+package MV3500Cohort2019JulySeptember.homework2.Knobeloch;
+
+import java.io.*;
+import java.math.BigDecimal;
+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 mcgredo
+ */
+public class Knobeloch_TCPIP_Client {
+
+    // IPv6 String constant for localhost address, similarly IPv4 127.0.0.1
+    public final static String LOCALHOST = "0:0:0:0:0:0:0:1";
+    public static void main(String[] args) {
+        
+        // Local vars/fields
+        Socket socket;
+        InputStream is;
+        InputStreamReader isr;
+        BufferedReader br;
+        String serverMessage;
+        double n = 2;
+        
+        System.out.println("First approximation of PI: 4");
+        
+        try {
+            while (true) {
+                System.out.println("\n------------------------------------------------------------------------------------\n");
+                System.out.println("More precise :-) ?");
+                System.out.println("Lets try one more term of the Gregory-Leibniz series!");
+                System.out.printf("Terms now: %.0f", n);
+
+                // 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("\nCalculating...");
+                System.out.printf("\nPi with %.0f terms = %s", n, serverMessage);
+                // socket gets closed, either automatically/silently by this code (or possibly by the server)
+                n++;
+                
+            } // end while(true)
+        } catch (IOException e) {
+            System.err.println("Problem with Knobeloch_TCPIP_Client 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 {
+        
+            // program exit: tell somebody about that
+            System.out.println("\nclient exit");
+        }
+    }
+}

assignments/src/MV3500Cohort2019JulySeptember/homework2/Knobeloch/Knobeloch_TCPIP_Server.java

+package MV3500Cohort2019JulySeptember.homework2.Knobeloch;
+
+import java.io.*;
+import java.math.BigDecimal;
+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 mcgredo
+ */
+public class Knobeloch_TCPIP_Server {
+
+    public static void main(String[] args) throws InterruptedException {
+        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("Knobeloch_TCPIP_Server has started..."); // it helps debugging to put this on console first
+            
+            ServerSocket serverSocket = new ServerSocket(2317);
+            OutputStream os;
+            PrintStream ps;
+            
+            double n = 2;
+            double nominator = 4;
+            BigDecimal apprxPi = new BigDecimal("4.0");
+
+            // 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 clientConnection = serverSocket.accept()) {
+                    // Now hook everything up (i.e. set up the streams), Java style:
+                    os = clientConnection.getOutputStream();
+                    ps = new PrintStream(os);
+                    nominator = nominator * (-1);
+                    
+                    BigDecimal toAdd = new BigDecimal((nominator / (n + (n-1)) ) );
+                    apprxPi = apprxPi.add(toAdd);     
+                            
+                    ps.println("" + apprxPi ); // this gets sent back to client!
+                    
+                    // 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!
+                    n++;
+                }
+            }
+        } catch (IOException e) {
+            System.err.println("Problem with Knobeloch_TCPIP_Server 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!");
+            }
+        }
+    }
+}