diff --git a/assignments/src/MV3500Cohort2020JulySeptember/homework1/WhiteTcpExample1Telnet.java b/assignments/src/MV3500Cohort2020JulySeptember/homework1/WhiteTcpExample1Telnet.java new file mode 100644 index 0000000000000000000000000000000000000000..68dc004b03f218ec9f65f4909e9ad7cd3be7fc54 --- /dev/null +++ b/assignments/src/MV3500Cohort2020JulySeptember/homework1/WhiteTcpExample1Telnet.java @@ -0,0 +1,81 @@ +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!"); + } + } +}