Multicast na interface Wi‑Fi/cabo preferida para presença na LAN.

Evita anunciar heartbeat por interfaces Docker/WSL; TTL 1 e checklist de descoberta em dois PCs.

Co-authored-by: Cursor <cursoragent@cursor.com>

docs/documentation/appendix_portas_e_multicast.md

@@ -29,10 +29,18 @@ Executar o Pitiupi no WSL e peers no Windows (ou vice-versa) pode falhar em mult
 - todos os peers no mesmo ambiente (Linux nativo ou VMs), ou
 - dois PCs físicos na mesma sub-rede.
 
+## Checklist — dois PCs na mesma Wi‑Fi
+
+1. **Mesma porta no login** (ex.: `5000` nos dois). Portas diferentes isolam a sala.
+2. **Configurações → Sua conexão:** IPs na mesma sub-rede (ex. ambos `192.168.0.x` ou `192.168.1.x`). Se um for `172.x` (WSL/Docker) e outro `192.168.x`, o multicast da aula não cruza.
+3. **Firewall:** liberar **UDP entrada e saída** na porta do login (Windows Defender / `ufw`).
+4. **Roteador:** desativar *isolamento de clientes* / *AP isolation* / Wi‑Fi de visitantes.
+5. Aguardar até **~15 s** após abrir os dois apps (heartbeat a cada 5 s).
+
 ## Sintomas
 
 | Sintoma | Verificar |
 | --- | --- |
-| Lista de usuários vazia | Porta igual entre peers? Mesma sub-rede? Firewall? |
-| Plugin não recebe | Desserialização / SPI / JAR em `plugins/` |
-| TCP falha | Peer ativo no heartbeat? IP correto? |
+| Lista só com **Todos**, sem peers | Porta igual? Mesma sub-rede? Firewall UDP? AP isolation? WSL num dos PCs? |
+| Plugin não recebe | Desserialização / SPI / JAR em `PITIUPI_HOME/plugins` |
+| TCP falha | Peer visível na lista? IP correto? |

pitiupi/src/pitiupi/net/udp/SocketUDP.java

@@ -13,6 +13,7 @@ import java.net.*;
 import java.util.logging.Level;
 import java.util.logging.Logger;
 
+import pitiupi.presentation.shell.LocalNetworkInfo;
 import pitiupi.control.ConnectionManager;
 import pitiupi.control.plugins.PluginManager;
 import pitiupi.models.Messages.GoodbyeMessage;
@@ -39,6 +40,7 @@ public class SocketUDP extends Thread {
     private MulticastSocket multicastSocket;
 
     private InetAddress address;
+    private NetworkInterface multicastInterface;
 
     private final ConnectionManager connectionManager;
     private final PluginManager pluginManager;
@@ -62,11 +64,19 @@ public class SocketUDP extends Thread {
         try {
             this.address = InetAddress.getByName(SocketUDP.INET_ADDR);
 
-            multicastSocket = new MulticastSocket(connectionManager.getPort());
+            int port = connectionManager.getPort();
+            multicastSocket = new MulticastSocket(port);
             multicastSocket.setSendBufferSize(256000);
             multicastSocket.setReceiveBufferSize(256000);
             multicastSocket.setReuseAddress(true);
-            multicastSocket.joinGroup(address);
+            multicastSocket.setTimeToLive(1);
+            multicastInterface = LocalNetworkInfo.preferredNetworkInterface();
+            if (multicastInterface != null) {
+                multicastSocket.setNetworkInterface(multicastInterface);
+                multicastSocket.joinGroup(new InetSocketAddress(address, port), multicastInterface);
+            } else {
+                multicastSocket.joinGroup(address);
+            }
         }
         catch (UnknownHostException ex) {
             System.getLogger(SocketUDP.class.getName()).log(System.Logger.Level.ERROR, (String) null, ex);
@@ -118,7 +128,12 @@ public class SocketUDP extends Thread {
         running = false;
         if (multicastSocket != null) {
             try {
-                multicastSocket.leaveGroup(address);
+                int port = connectionManager.getPort();
+                if (multicastInterface != null) {
+                    multicastSocket.leaveGroup(new InetSocketAddress(address, port), multicastInterface);
+                } else {
+                    multicastSocket.leaveGroup(address);
+                }
             } catch (IOException ex) {
                 System.out.println(ex);
             }

pitiupi/src/pitiupi/presentation/shell/LocalNetworkInfo.java

@@ -4,6 +4,7 @@ import java.net.Inet4Address;
 import java.net.InetAddress;
 import java.net.NetworkInterface;
 import java.util.Enumeration;
+import java.util.Locale;
 
 /**
  * Endereço IPv4 local preferencial para compartilhar com peers.
@@ -13,20 +14,49 @@ public final class LocalNetworkInfo {
     private LocalNetworkInfo() {
     }
 
-    public static String bestLocalIpv4() {
+    /**
+     * Interface preferida para LAN (Wi‑Fi/cabo), ignorando bridges Docker/WSL/VPN virtuais quando possível.
+     */
+    public static NetworkInterface preferredNetworkInterface() {
         try {
+            NetworkInterface fallback = null;
             Enumeration<NetworkInterface> interfaces = NetworkInterface.getNetworkInterfaces();
             while (interfaces.hasMoreElements()) {
                 NetworkInterface ni = interfaces.nextElement();
-                if (!ni.isUp() || ni.isLoopback() || ni.isVirtual()) {
+                if (!isCandidateInterface(ni)) {
                     continue;
                 }
-                Enumeration<InetAddress> addresses = ni.getInetAddresses();
-                while (addresses.hasMoreElements()) {
-                    InetAddress addr = addresses.nextElement();
-                    if (addr instanceof Inet4Address && !addr.isLoopbackAddress()) {
-                        return addr.getHostAddress();
-                    }
+                if (isPreferredLanInterfaceName(ni.getName())) {
+                    return ni;
+                }
+                if (fallback == null) {
+                    fallback = ni;
+                }
+            }
+            return fallback;
+        } catch (Exception ex) {
+            return null;
+        }
+    }
+
+    public static String bestLocalIpv4() {
+        try {
+            NetworkInterface preferred = preferredNetworkInterface();
+            if (preferred != null) {
+                String fromPreferred = firstIpv4OnInterface(preferred);
+                if (fromPreferred != null) {
+                    return fromPreferred;
+                }
+            }
+            Enumeration<NetworkInterface> interfaces = NetworkInterface.getNetworkInterfaces();
+            while (interfaces.hasMoreElements()) {
+                NetworkInterface ni = interfaces.nextElement();
+                if (!isCandidateInterface(ni)) {
+                    continue;
+                }
+                String ip = firstIpv4OnInterface(ni);
+                if (ip != null) {
+                    return ip;
                 }
             }
             InetAddress local = InetAddress.getLocalHost();
@@ -36,6 +66,66 @@ public final class LocalNetworkInfo {
         }
     }
 
+    private static boolean isCandidateInterface(NetworkInterface ni) {
+        if (ni == null) {
+            return false;
+        }
+        try {
+            if (!ni.isUp() || ni.isLoopback()) {
+                return false;
+            }
+        } catch (java.net.SocketException ex) {
+            return false;
+        }
+        if (ni.isVirtual() || isVirtualInterfaceName(ni.getName())) {
+            return false;
+        }
+        return firstIpv4OnInterface(ni) != null;
+    }
+
+    private static boolean isVirtualInterfaceName(String name) {
+        if (name == null) {
+            return true;
+        }
+        String n = name.toLowerCase(Locale.ROOT);
+        return n.equals("lo")
+                || n.startsWith("docker")
+                || n.startsWith("br-")
+                || n.startsWith("veth")
+                || n.startsWith("vir")
+                || n.contains("wsl")
+                || n.startsWith("tailscale");
+    }
+
+    private static boolean isPreferredLanInterfaceName(String name) {
+        if (name == null) {
+            return false;
+        }
+        String n = name.toLowerCase(Locale.ROOT);
+        return n.startsWith("wlan")
+                || n.startsWith("wlp")
+                || n.startsWith("wl")
+                || n.startsWith("eth")
+                || n.startsWith("eno")
+                || n.startsWith("enp")
+                || n.startsWith("ens");
+    }
+
+    private static String firstIpv4OnInterface(NetworkInterface ni) {
+        try {
+            Enumeration<InetAddress> addresses = ni.getInetAddresses();
+            while (addresses.hasMoreElements()) {
+                InetAddress addr = addresses.nextElement();
+                if (addr instanceof Inet4Address && !addr.isLoopbackAddress()) {
+                    return addr.getHostAddress();
+                }
+            }
+        } catch (Exception ignored) {
+            return null;
+        }
+        return null;
+    }
+
     /**
      * {@code true} se o IP informado é deste host (inclui loopback e interfaces ativas).
      */