Use wifi network's socket factory on API 21+.

bramble-android/src/main/java/org/briarproject/bramble/plugin/tcp/AndroidLanTcpPlugin.java

@@ -4,6 +4,9 @@ import android.content.BroadcastReceiver;
 import android.content.Context;
 import android.content.Intent;
 import android.content.IntentFilter;
+import android.net.ConnectivityManager;
+import android.net.Network;
+import android.net.NetworkInfo;
 import android.net.wifi.WifiInfo;
 import android.net.wifi.WifiManager;
 
@@ -11,16 +14,22 @@ import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.Backoff;
 import org.briarproject.bramble.api.plugin.duplex.DuplexPluginCallback;
 
+import java.io.IOException;
 import java.net.InetAddress;
+import java.net.Socket;
 import java.net.UnknownHostException;
 import java.util.Collection;
 import java.util.concurrent.Executor;
 import java.util.logging.Logger;
 
 import javax.annotation.Nullable;
+import javax.net.SocketFactory;
 
+import static android.content.Context.CONNECTIVITY_SERVICE;
 import static android.content.Context.WIFI_SERVICE;
 import static android.net.ConnectivityManager.CONNECTIVITY_ACTION;
+import static android.net.ConnectivityManager.TYPE_WIFI;
+import static android.os.Build.VERSION.SDK_INT;
 import static java.util.Collections.emptyList;
 import static java.util.Collections.singletonList;
 
@@ -31,19 +40,26 @@ class AndroidLanTcpPlugin extends LanTcpPlugin {
 			Logger.getLogger(AndroidLanTcpPlugin.class.getName());
 
 	private final Context appContext;
+	private final ConnectivityManager connectivityManager;
 	@Nullable
 	private final WifiManager wifiManager;
 
 	@Nullable
 	private volatile BroadcastReceiver networkStateReceiver = null;
+	private volatile SocketFactory socketFactory;
 
 	AndroidLanTcpPlugin(Executor ioExecutor, Backoff backoff,
 			Context appContext, DuplexPluginCallback callback, int maxLatency,
 			int maxIdleTime) {
 		super(ioExecutor, backoff, callback, maxLatency, maxIdleTime);
 		this.appContext = appContext;
+		ConnectivityManager connectivityManager = (ConnectivityManager)
+				appContext.getSystemService(CONNECTIVITY_SERVICE);
+		if (connectivityManager == null) throw new AssertionError();
+		this.connectivityManager = connectivityManager;
 		wifiManager = (WifiManager) appContext.getApplicationContext()
 				.getSystemService(WIFI_SERVICE);
+		socketFactory = getSocketFactory();
 	}
 
 	@Override
@@ -64,6 +80,11 @@ class AndroidLanTcpPlugin extends LanTcpPlugin {
 		tryToClose(socket);
 	}
 
+	@Override
+	protected Socket createSocket() throws IOException {
+		return socketFactory.createSocket();
+	}
+
 	@Override
 	protected Collection<InetAddress> getLocalIpAddresses() {
 		if (wifiManager == null) return emptyList();
@@ -86,6 +107,19 @@ class AndroidLanTcpPlugin extends LanTcpPlugin {
 		}
 	}
 
+	// On API 21 and later, a socket that is not created with the wifi
+	// network's socket factory may try to connect via another network
+	private SocketFactory getSocketFactory() {
+		if (SDK_INT < 21) return SocketFactory.getDefault();
+		for (Network net : connectivityManager.getAllNetworks()) {
+			NetworkInfo info = connectivityManager.getNetworkInfo(net);
+			if (info != null && info.getType() == TYPE_WIFI)
+				return net.getSocketFactory();
+		}
+		LOG.warning("Could not find suitable socket factory");
+		return SocketFactory.getDefault();
+	}
+
 	private class NetworkStateReceiver extends BroadcastReceiver {
 
 		@Override
@@ -94,9 +128,11 @@ class AndroidLanTcpPlugin extends LanTcpPlugin {
 			WifiInfo info = wifiManager.getConnectionInfo();
 			if (info == null || info.getIpAddress() == 0) {
 				LOG.info("Not connected to wifi");
+				socketFactory = SocketFactory.getDefault();
 				tryToClose(socket);
 			} else {
 				LOG.info("Connected to wifi");
+				socketFactory = getSocketFactory();
 				if (socket == null || socket.isClosed()) bind();
 			}
 		}

bramble-core/src/main/java/org/briarproject/bramble/plugin/tcp/LanTcpPlugin.java

@@ -241,10 +241,11 @@ class LanTcpPlugin extends TcpPlugin {
 			}
 			return null;
 		}
-		Socket s = new Socket();
 		try {
 			if (LOG.isLoggable(INFO))
 				LOG.info("Connecting to " + scrubSocketAddress(remote));
+			Socket s = createSocket();
+			s.bind(new InetSocketAddress(socket.getInetAddress(), 0));
 			s.connect(remote);
 			s.setSoTimeout(socketTimeout);
 			if (LOG.isLoggable(INFO))

bramble-core/src/main/java/org/briarproject/bramble/plugin/tcp/TcpPlugin.java

@@ -243,10 +243,11 @@ abstract class TcpPlugin implements DuplexPlugin {
 				}
 				continue;
 			}
-			Socket s = new Socket();
 			try {
 				if (LOG.isLoggable(INFO))
 					LOG.info("Connecting to " + scrubSocketAddress(remote));
+				Socket s = createSocket();
+				s.bind(new InetSocketAddress(socket.getInetAddress(), 0));
 				s.connect(remote);
 				s.setSoTimeout(socketTimeout);
 				if (LOG.isLoggable(INFO))
@@ -261,6 +262,10 @@ abstract class TcpPlugin implements DuplexPlugin {
 		return null;
 	}
 
+	protected Socket createSocket() throws IOException {
+		return new Socket();
+	}
+
 	@Nullable
 	InetSocketAddress parseSocketAddress(String ipPort) {
 		if (StringUtils.isNullOrEmpty(ipPort)) return null;