diff --git a/assignments/src/MV3500Cohort2021JulySeptember/homework1/PughTcp2ConnectionCounting b/assignments/src/MV3500Cohort2021JulySeptember/homework1/PughTcp2ConnectionCounting new file mode 100644 index 0000000000000000000000000000000000000000..492e78f857cc84ca5d90e986e9ba2cb65c5b6538 --- /dev/null +++ b/assignments/src/MV3500Cohort2021JulySeptember/homework1/PughTcp2ConnectionCounting @@ -0,0 +1,103 @@ +package MV3500Cohort2021JulySeptember.homework1.Pugh; + +import java.io.*; +import java.net.*; + +/** + * Very slightly more complex than example1. 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. + * + * <code>telnet localhost 2317</code> + * + * If you're sophisticated you can contact the instructor's computer while + * running this program. + * + * <code>telnet ipOfServersLaptop 2317</code> + * + * And have that machine display the socket pairs received. + * + * @author pugh + * @author brutzman + */ +public class PughTcp2ConnectionCounting { + + /** + * Program invocation, execution starts here + * + * @param args command-line arguments + */ + public static void main(String[] args) { + try { + System.out.println("TcpExample2ConnectionCounting has started and is waiting for a connection."); + System.out.println("Get Ready To Network!!!"); + System.out.println(" help: https://savage.nps.edu/Savage/developers.html#telnet"); + System.out.println(" enter (nc localhost 2317) or (telnet localhost 2317)..."); + + // ServerSocket waits for a connection from a client. + // Notice that it is outside the loop; ServerSocket needs to be made only once. + int connectionCount = 0; // state variable + + ServerSocket serverSocket = new ServerSocket(2317); // server decides here what port to listen on. + // of interest: often client doesn't care what port it uses locally when connecting to that server port. + + // Loop, infinitely, waiting for client connections. + // Stop the program somewhere else. + while (true) { + // blocks! then proceeds once a connection is "accept"ed + try ( Socket clientConnection = serverSocket.accept()) { + connectionCount++; // got another one! + + OutputStream os = clientConnection.getOutputStream(); + PrintStream ps = new PrintStream(os); + + ps.println("This client response was written by server " + PughTcp2ConnectionCounting.class.getName()); // to remote client + System.out.println("This server response was written by server " + PughTcp2ConnectionCounting.class.getName() + "\n"); // to server console + if (connectionCount % 2 == 1) { + System.out.println("Go\n"); + } + if (connectionCount % 2 == 0) { + System.out.println("Gators!\n"); + } + if (connectionCount % 3 == 1 && connectionCount != 0) { + System.out.println("O'Doyle Rules!!! \n"); + } + ps.println("You were connection #" + connectionCount + ", by my count"); + + // Print some information locally about the Socket connection. + // This includes the port and IP numbers on both sides (the socket pair.) + InetAddress localAddress = clientConnection.getLocalAddress(); + InetAddress remoteAddress = clientConnection.getInetAddress(); + + int localPort = clientConnection.getLocalPort(); + int remotePort = clientConnection.getPort(); // remember the prior question, why are 2 ports different? + + // 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 )) note IPv6 + // Socket pair: (( /0:0:0:0:0:0:0:1, 2317 ), ( /0:0:0:0:0:0:0:1, 54881 )) + // + // Why is first IP/port the same, while the second set has different ports? + System.out.println("Socket pair: (( " + localAddress.toString() + ", " + localPort + " ), ( " + + remoteAddress.toString() + ", " + remotePort + " ))"); + + System.out.println("got another connection, #" + connectionCount); // report progress + + // Notice the use of flush() and close(). Without + // the close() to Socket object may stay open for + // a while after the client has stopped needing this + // connection. Close() explicitly ends the connection. + ps.flush(); + } + } + } catch (IOException e) { + System.err.println("Problem with " + PughTcp2ConnectionCounting.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!"); + } + } + } +}