adding assignment 1

assignments/src/MV3500Cohort2020JulySeptember/homework1/WhiteTcpExample1Telnet.java

+package MV3500Cohort2020JulySeptember.homework1;
+
+import java.io.*;
+import java.net.*;
+
+/**
+ * The simplest possible TCP network program. It listens for
+ * a connection, from telnet (telnet localhost 2317) or a program
+ * you write, which we will do later. Right now the TcpExample simply
+ * writes a string in response to a connection.
+ * 
+ * Modifying his program is the basis for Assignment 1.
+ * 
+ * Testing the running server program from telnet looks like this:
+ * 
+ * it154916:projects mcgredo$ telnet localhost 2317
+ * Trying ::1...
+ * Connected to localhost.
+ * Escape character is '^]'.
+ * This was written by the server
+ * Connection closed by foreign host.
+ * 
+ * Notice that "This was written by the server" matches 
+ * what is written by the code below, over the output stream.
+ * 
+ * After this first connection the program below drops out
+ * the bottom of the program, and does not repeat itself.
+ * The program exits.
+ * 
+ * @author mcgredo
+ * @author brutzman
+ */
+public class WhiteTcpExample1Telnet 
+{
+    public static void main(String[] args) 
+    {
+        try
+        {
+            System.out.println(WhiteTcpExample1Telnet.class.getName() + " has started and is waiting for a connection.");
+            System.out.println("  help: https://savage.nps.edu/Savage/developers.html#telnet");
+            System.out.println("  enter (telnet localhost 2317) or (nc localhost 2317)..." );
+			
+            // The ServerSocket waits for a connection from a client.
+            // It returns a Socket object when the connection occurs.
+            ServerSocket serverSocket = new ServerSocket(2317);
+            
+            // Use Java io classes to write text (as opposed to
+            // unknown bytes of some sort) to the client
+            
+            // The Socket object represents the connection between
+            // the server and client, including a full duplex connection
+            try (Socket clientConnection = serverSocket.accept()) // wait here for a client to connect
+            {
+                // OK we got something, time to respond!
+                // Use Java io classes to write text (as opposed to
+                // unknown bytes of some sort) to the client
+                OutputStream os = clientConnection.getOutputStream();
+                PrintStream ps = new PrintStream(os);
+                
+                ps.println("This client response is brought to you by Slurm, 'It's highly addictive!', and was written by server" + WhiteTcpExample1Telnet.class.getName()); // to remote clientnc
+                System.out.println("This server response is brought to you by Slurm, 'It's highly addictive!', and was written by server " + WhiteTcpExample1Telnet.class.getName()); // to server console
+
+                // "flush()" in important in that it forces a write
+                // across what is in fact a slow connection
+                ps.flush();
+            }
+            System.out.println(WhiteTcpExample1Telnet.class.getName() + " completed successfully.");
+        }
+        catch(IOException e)
+        {
+            System.err.println("Exception with " + WhiteTcpExample1Telnet.class.getName() + " networking:"); // describe what is happening
+            System.err.println(e);
+            // Provide more helpful information to user if exception occurs due to running twice at one time
+            
+            // brute force exception checking, can be brittle if exception message changes
+            // if (e.getMessage().equals("Address already in use: NET_Bind")) 
+            if (e instanceof java.net.BindException)
+                System.err.println("*** Be sure to stop any other running instances of programs using this port!");
+        }
+    }
+}