Only allow a single program instance to be run.

Creates a ServerSocket instance on a port (default: 49250).
Credits to marcostudios for the suggestion.

Signed-off-by: Jeffrey Han <itdelatrisu@gmail.com>

src/itdelatrisu/opsu/states/MainMenuExit.java

@@ -131,6 +131,7 @@ public class MainMenuExit extends BasicGameState {
 
 		if (yesButton.contains(x, y)) {
 			Options.saveOptions();
+			Opsu.closeSocket();
 			container.exit();
 		} else if (noButton.contains(x, y))
 			game.enterState(Opsu.STATE_MAINMENU, new EmptyTransition(), new FadeInTransition(Color.black));
@@ -141,6 +142,7 @@ public class MainMenuExit extends BasicGameState {
 		switch (key) {
 		case Input.KEY_1:
 			Options.saveOptions();
+			Opsu.closeSocket();
 			container.exit();
 			break;
 		case Input.KEY_2:

src/itdelatrisu/opsu/states/Options.java

@@ -225,6 +225,11 @@ public class Options extends BasicGameState {
 	 */
 	private static int screenshotFormatIndex = 0;
 
+	/**
+	 * Port binding.
+	 */
+	private static int port = 0;
+
 	/**
 	 * Back button (shared by other states).
 	 */
@@ -673,6 +678,19 @@ public class Options extends BasicGameState {
 	 */
 	public static boolean isComboBurstEnabled() { return showComboBursts; }
 
+	/**
+	 * Returns the port number to bind to.
+	 * @return the port
+	 */
+	public static int getPort() {
+		if (port == 0) {
+			// choose a random port
+			port = 49250;
+			optionsChanged = true;  // force file creation
+		}
+		return port;
+	}
+
 	/**
 	 * Returns the current beatmap directory.
 	 * If invalid, this will attempt to search for the directory,
@@ -761,6 +779,11 @@ public class Options extends BasicGameState {
 				case "ComboBurst":
 					showComboBursts = Boolean.parseBoolean(value);
 					break;
+				case "Port":
+					i = Integer.parseInt(value);
+					if (i > 0 && i <= 65535)
+						port = i;
+					break;
 				}
 			}
 		} catch (IOException e) {
@@ -814,6 +837,8 @@ public class Options extends BasicGameState {
 			writer.newLine();
 			writer.write(String.format("ComboBurst = %b", showComboBursts));
 			writer.newLine();
+			writer.write(String.format("Port = %d", port));
+			writer.newLine();
 			writer.close();
 		} catch (IOException e) {
 			Log.error(String.format("Failed to write to file '%s'.", OPTIONS_FILE), e);