android: use WifiManager.MulticastLock to receive broadcast packets

In many cases, broadcast UDP packets can't be received on android unless
a MulticastLock is held.

core/network/naomi_network.cpp

@@ -91,6 +91,7 @@ bool NaomiNetwork::startNetwork()
 
 	if (config::ActAsServer)
 	{
+		enableNetworkBroadcast(true);
 		const auto timeout = seconds(20);
 		NOTICE_LOG(NETWORK, "Waiting for slave connections");
 		steady_clock::time_point start_time = steady_clock::now();
@@ -110,6 +111,7 @@ bool NaomiNetwork::startNetwork()
 				break;
 			std::this_thread::sleep_for(milliseconds(20));
 		}
+		enableNetworkBroadcast(false);
 		if (!slaves.empty())
 		{
 			NOTICE_LOG(NETWORK, "Master starting: %zd slaves", slaves.size());

core/network/naomi_network.h

@@ -50,6 +50,7 @@ public:
 
 	void shutdown()
 	{
+		enableNetworkBroadcast(false);
 		emu.setNetworkState(false);
 		closesocket(sock);
 		sock = INVALID_SOCKET;

core/network/net_platform.h

@@ -125,3 +125,9 @@ static inline const char *inet_ntop(int af, const void* src, char* dst, int cnt)
     	return dst;
 }
 #endif
+
+#ifdef __ANDROID__
+void enableNetworkBroadcast(bool enable);
+#else
+static inline void enableNetworkBroadcast(bool enable) {}
+#endif

core/network/net_serial_maxspeed.h

@@ -90,7 +90,9 @@ struct MaxSpeedNetPipe : public SerialPipe
 		return true;
 	}
 
-	void shutdown() {
+	void shutdown()
+	{
+		enableNetworkBroadcast(false);
 		if (VALID(sock))
 			closesocket(sock);
 		sock = INVALID_SOCKET;
@@ -174,6 +176,7 @@ private:
 			{
 				peerAddress.sin_addr.s_addr = addr.sin_addr.s_addr;
 				peerAddress.sin_port = addr.sin_port;
+				enableNetworkBroadcast(false);
 			}
 		}
 	}
@@ -235,6 +238,8 @@ private:
 				freeaddrinfo(resultAddr);
 			}
 		}
+		else
+			enableNetworkBroadcast(true);
 
 		serial_setPipe(this);
 	}

shell/android-studio/flycast/src/main/AndroidManifest.xml

@@ -15,6 +15,8 @@
     <uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
     <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
     <uses-permission android:name="android.permission.INTERNET" />
+	<uses-permission android:name="android.permission.WAKE_LOCK" />
+	<uses-permission android:name="android.permission.CHANGE_WIFI_MULTICAST_STATE" />
     <uses-permission android:name="android.permission.BLUETOOTH" />
 
     <uses-feature

shell/android-studio/flycast/src/main/java/com/reicast/emulator/Emulator.java

@@ -3,6 +3,7 @@ package com.reicast.emulator;
 import android.app.Application;
 import android.content.Context;
 import android.content.SharedPreferences;
+import android.net.wifi.WifiManager;
 import android.preference.PreferenceManager;
 import android.util.Log;
 
@@ -14,6 +15,8 @@ import com.reicast.emulator.emu.JNIdc;
 public class Emulator extends Application {
     private static Context context;
     private static BaseGLActivity currentActivity;
+    private WifiManager wifiManager = null;
+    private WifiManager.MulticastLock multicastLock = null;
 
     // see MapleDeviceType in hw/maple/maple_devs.h
     public static final int MDT_Microphone = 2;
@@ -92,4 +95,20 @@ public class Emulator extends Application {
     static {
         AppCompatDelegate.setCompatVectorFromResourcesEnabled(true);
     }
+
+    public void enableNetworkBroadcast(boolean enable) {
+        if (enable) {
+            if (wifiManager == null)
+                wifiManager = (WifiManager)Emulator.context.getSystemService(Context.WIFI_SERVICE);
+            if (multicastLock == null)
+                multicastLock = wifiManager.createMulticastLock("Flycast");
+            if (multicastLock != null && !multicastLock.isHeld())
+                multicastLock.acquire();
+        }
+        else
+        {
+            if (multicastLock != null && multicastLock.isHeld())
+                multicastLock.release();
+        }
+    }
 }

shell/android-studio/flycast/src/main/jni/src/Android.cpp

@@ -626,3 +626,10 @@ extern "C" JNIEXPORT void JNICALL Java_com_reicast_emulator_emu_JNIdc_setButtons
     memcpy(DefaultOSDButtons.data(), b, len);
     env->ReleaseByteArrayElements(data, b, JNI_ABORT);
 }
+
+void enableNetworkBroadcast(bool enable)
+{
+    JNIEnv *env = jvm_attacher.getEnv();
+    jmethodID enableNetworkBroadcastMID = env->GetMethodID(env->GetObjectClass(g_emulator), "enableNetworkBroadcast", "(Z)V");
+    env->CallVoidMethod(g_emulator, enableNetworkBroadcastMID, enable);
+}