130 lines
5.1 KiB
Java
130 lines
5.1 KiB
Java
CLChatServer
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import java.net.*;
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import java.io.*;
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public class CLChatServer {
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static final int DEFAULT_PORT = 1728; // Port to listen on,
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// if none is specified
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// on the command line.
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static final String HANDSHAKE = "CLChat"; // Handshake string.
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// Each end of the connection sends this string
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// to the other just after the connection is
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// opened. This is done to confirm that the
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// program on the other side of the connection
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// is a CLChat program.
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static final char MESSAGE = '0'; // This character is prepended
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// to every message that is sent.
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static final char CLOSE = '1'; // This character is sent to
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// the connected program when
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// the user quits.
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public static void main(String[] args) {
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int port; // The port on which the server listens.
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ServerSocket listener; // Listens for a connection request.
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Socket connection; // For communication with the client.
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TextReader incoming; // Stream for receiving data from client.
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PrintWriter outgoing; // Stream for sending data to client.
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String messageOut; // A message to be sent to the client.
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String messageIn; // A message received from the client.
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/* First, get the port number from the command line,
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or use the default port if none is specified. */
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if (args.length == 0)
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port = DEFAULT_PORT;
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else {
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try {
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port= Integer.parseInt(args[0]);
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if (port < 0 || port > 65535)
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throw new NumberFormatException();
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}
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catch (NumberFormatException e) {
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TextIO.putln("Illegal port number, " + args[0]);
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return;
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}
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}
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/* Wait for a connection request. When it arrives, close
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down the listener. Create streams for communication
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and exchange the handshake. */
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try {
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listener = new ServerSocket(port);
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TextIO.putln("Listening on port " + listener.getLocalPort());
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connection = listener.accept();
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listener.close();
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incoming = new TextReader(connection.getInputStream());
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outgoing = new PrintWriter(connection.getOutputStream());
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outgoing.println(HANDSHAKE);
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outgoing.flush();
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messageIn = incoming.getln();
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if (! messageIn.equals(HANDSHAKE) ) {
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throw new IOException("Connected program is not CLChat!");
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}
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TextIO.putln("Connected. Waiting for the first message.
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");
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}
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catch (Exception e) {
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TextIO.putln("An error occurred while opening connection.");
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TextIO.putln(e.toString());
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return;
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}
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/* Exchange messages with the other end of the connection
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until one side or the other closes the connection.
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This server program waits for the first message from
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the client. After that, messages alternate strictly
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back an forth. */
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try {
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while (true) {
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TextIO.putln("WAITING...");
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messageIn = incoming.getln();
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if (messageIn.length() > 0) {
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// The first character of the message is a command.
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// If the command is CLOSE, then the connection
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// is closed. Otherwise, remove the command
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// character from the message and procede.
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if (messageIn.charAt(0) == CLOSE) {
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TextIO.putln("Connection closed at other end.");
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connection.close();
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break;
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}
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messageIn = messageIn.substring(1);
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}
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TextIO.putln("RECEIVED: " + messageIn);
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TextIO.put("SEND: ");
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messageOut = TextIO.getln();
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if (messageOut.equalsIgnoreCase("quit")) {
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// User wants to quit. Inform the other side
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// of the connection, then close the connection.
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outgoing.println(CLOSE);
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outgoing.flush(); // Make sure the data is sent!
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connection.close();
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TextIO.putln("Connection closed.");
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break;
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}
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outgoing.println(MESSAGE + messageOut);
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outgoing.flush(); // Make sure the data is sent!
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if (outgoing.checkError()) {
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throw new IOException("Error ocurred while reading incoming message.");
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}
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}
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}
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catch (Exception e) {
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TextIO.putln("Sorry, an error has occurred. Connection lost.");
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TextIO.putln(e.toString());
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System.exit(1);
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}
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} // end main()
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} //end class CLChatServer
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