Announce bound instead of configured server port

If a port number of 0 is chosen then bind() will open a random port in
an ephemeral range instead of the provided port number
and this port can then be retrieved using getLocalPort().

This enables starting servers on arbitrary ports instead of
preconfigured ones.

Since only direct connections need to know the port number
connections using the registry or LAN can use an ephemeral port number
and the connection information tab can display the port direct
connections should use.

This requires a router with functioning UPnP instead of port forwarding
though so is not univerally useful.

clientserver/src/main/java/net/rptools/clientserver/simple/server/SocketServer.java

@@ -39,6 +39,9 @@ public SocketServer(int port) {
   @Override
   public void start() throws IOException {
     var serverSocket = new ServerSocket(port);
+    if (serverSocket.getLocalPort() == -1) {
+      throw new AssertionError("Socket not bound yet");
+    }
     // If the above throws, it will be as though we never started.
 
     socket = serverSocket;
@@ -70,6 +73,16 @@ public String getError() {
     return null;
   }
 
+  /** Get the port of the socket the server is running on or -1. */
+  public int getPort() {
+    // NOTE: We do not use this.port because the socket's bound port can be different
+    if (socket == null || socket.isClosed()) {
+      return -1;
+    }
+
+    return socket.getLocalPort();
+  }
+
   ////
   // Threads
   private static class ListeningThread extends Thread {

src/main/java/net/rptools/clientserver/ConnectionFactory.java

@@ -49,6 +49,7 @@ public void onLoginError() {
         });
   }
 
+  @Nonnull
   public Server createServer(@Nullable ServerConfig config) {
     if (config == null) {
       return new NilServer();

src/main/java/net/rptools/maptool/server/MapToolServer.java

@@ -28,9 +28,12 @@
 import net.rptools.clientserver.simple.DisconnectHandler;
 import net.rptools.clientserver.simple.MessageHandler;
 import net.rptools.clientserver.simple.connection.Connection;
+import net.rptools.clientserver.simple.server.NilServer;
 import net.rptools.clientserver.simple.server.Router;
 import net.rptools.clientserver.simple.server.Server;
 import net.rptools.clientserver.simple.server.ServerObserver;
+import net.rptools.clientserver.simple.server.SocketServer;
+import net.rptools.clientserver.simple.server.WebRTCServer;
 import net.rptools.maptool.client.AppConstants;
 import net.rptools.maptool.client.MapTool;
 import net.rptools.maptool.client.MapToolRegistry;
@@ -69,7 +72,7 @@ public enum State {
   }
 
   @Nonnull private final String serviceIdentifier;
-  private final Server server;
+  @Nonnull private final Server server;
   private final MessageHandler messageHandler;
   private final Router router;
   private final ServerConfig config;
@@ -199,7 +202,11 @@ public String getName() {
   }
 
   public int getPort() {
-    return config == null ? -1 : config.getPort();
+    return switch (server) {
+      case NilServer s -> -1;
+      case SocketServer s -> s.getPort();
+      case WebRTCServer s -> -1;
+    };
   }
 
   private void connectionAdded(Connection conn) {
@@ -350,8 +357,8 @@ public void stop() {
     }
 
     // Close UPnP port mapping if used
-    if (useUPnP && config != null) {
-      int port = config.getPort();
+    int port;
+    if (useUPnP && (port = getPort()) != -1) {
       UPnPUtil.closePort(port);
     }
 
@@ -388,12 +395,13 @@ public void start() throws IOException {
     }
 
     // Use UPnP to open port in router
-    if (useUPnP && config != null) {
+    int port = getPort();
+    if (useUPnP && port != -1) {
       MapTool.getFrame()
           .showFilledGlassPane(
               new StaticMessageDialog(I18N.getText("msg.info.server.upnp.discovering")));
       try {
-        UPnPUtil.openPort(config.getPort());
+        UPnPUtil.openPort(port);
       } finally {
         MapTool.getFrame().hideGlassPane();
       }
@@ -404,11 +412,11 @@ public void start() throws IOException {
       try {
         MapToolRegistry.RegisterResponse result =
             MapToolRegistry.getInstance()
-                .registerInstance(config.getServerName(), config.getPort(), config.getUseWebRTC());
+                .registerInstance(config.getServerName(), port, config.getUseWebRTC());
         if (result == MapToolRegistry.RegisterResponse.NAME_EXISTS) {
           MapTool.showError("msg.error.alreadyRegistered");
         } else {
-          heartbeatThread = new HeartbeatThread(config.getPort());
+          heartbeatThread = new HeartbeatThread(port);
           heartbeatThread.start();
         }
         // TODO: I don't like this
@@ -417,8 +425,8 @@ public void start() throws IOException {
       }
     }
 
-    if (serviceIdentifier != null && config != null) {
-      announcer = new ServiceAnnouncer(serviceIdentifier, config.getPort(), AppConstants.SERVICE_GROUP);
+    if (serviceIdentifier != null && port != -1) {
+      announcer = new ServiceAnnouncer(serviceIdentifier, port, AppConstants.SERVICE_GROUP);
       announcer.start();
     }