diff --git a/assignments/src/MV3500Cohort2021JulySeptember/homework1/LeckieTcpExample2.java b/assignments/src/MV3500Cohort2021JulySeptember/homework1/LeckieTcpExample2.java new file mode 100644 index 0000000000000000000000000000000000000000..037e875c50c1d270f877119b837a3e2cda1ca00f --- /dev/null +++ b/assignments/src/MV3500Cohort2021JulySeptember/homework1/LeckieTcpExample2.java @@ -0,0 +1,103 @@ +package pkg3500.leckie; + +import java.io.IOException; +import java.io.OutputStream; +import java.io.PrintStream; +import java.net.InetAddress; +import java.net.ServerSocket; +import java.net.Socket; + +/** + * 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 mcgredo + * @author brutzman + * @author leckie + */ +public class LeckieTcpExample2 +{ + public static void main(String[] args) + { + try + { + System.out.println("TcpExample2ConnectionCounting has started and is waiting for a connection."); + 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 + int totalEntrantCount = 31; // spoofed entrants + + 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 " + LeckieTcpExample2.class.getName()); // to remote client + System.out.println("This server response was written by server " + LeckieTcpExample2.class.getName()); // to server console + + ps.println("This is your lottery attempt number #" + connectionCount + ", you are aplicant number " + totalEntrantCount + " to try and win. Keep trying!"); + + totalEntrantCount = (totalEntrantCount + 79); + // 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 " + LeckieTcpExample2.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!"); + } + } + +}