Enable max Ethernet MTU sized packets when the remote PC is on the subnet

src/com/limelight/Game.java

@@ -1,5 +1,12 @@
 package com.limelight;
 
+import java.net.Inet4Address;
+import java.net.InetAddress;
+import java.net.InterfaceAddress;
+import java.net.NetworkInterface;
+import java.net.SocketException;
+import java.util.Enumeration;
+
 import com.limelight.binding.PlatformBinding;
 import com.limelight.binding.input.ControllerHandler;
 import com.limelight.binding.input.KeyboardTranslator;
@@ -19,6 +26,7 @@ import android.content.SharedPreferences;
 import android.graphics.Point;
 import android.media.AudioManager;
 import android.net.ConnectivityManager;
+import android.net.NetworkInfo;
 import android.net.wifi.WifiManager;
 import android.os.Bundle;
 import android.os.Handler;
@@ -161,10 +169,29 @@ public class Game extends Activity implements SurfaceHolder.Callback, OnGenericM
         wifiLock = wifiMgr.createWifiLock(WifiManager.WIFI_MODE_FULL_HIGH_PERF, "Limelight");
 		wifiLock.setReferenceCounted(false);
 		wifiLock.acquire();
+		
+		String host = Game.this.getIntent().getStringExtra("host");
+		InetAddress addr;
+		boolean enableLargePackets;
+		try {
+			// If this does a DNS lookup, it could cause a NetworkOnMainThread exception
+			// Chances are if it has to do this, we're not on the same network anyways
+			addr = InetAddress.getByName(host);
+			
+			// Check if we can enable large packets if we get this far
+			enableLargePackets = shouldEnableLargePackets(addr);
+		} catch (Exception e) {
+			// We don't want to deal with any exceptions here. The user will be notified
+			// when the connection fails
+			enableLargePackets = false;
+		}
+		
+		LimeLog.info("Using large packets? "+enableLargePackets);
         
 		// Start the connection
-		conn = new NvConnection(Game.this.getIntent().getStringExtra("host"), Game.this,
-				new StreamConfiguration(width, height, refreshRate, bitrate * 1000), PlatformBinding.getCryptoProvider(this));
+		conn = new NvConnection(host, Game.this,
+				new StreamConfiguration(width, height, refreshRate, bitrate * 1000,
+						enableLargePackets ? 1460 : 1024), PlatformBinding.getCryptoProvider(this));
 		keybTranslator = new KeyboardTranslator(conn);
 		controllerHandler = new ControllerHandler(conn);
 		
@@ -172,6 +199,89 @@ public class Game extends Activity implements SurfaceHolder.Callback, OnGenericM
 		sh.addCallback(this);
 	}
 	
+	private boolean shouldEnableLargePackets(InetAddress targetAddress) {
+		ConnectivityManager connMgr = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);		
+		NetworkInfo activeNetworkInfo = connMgr.getActiveNetworkInfo();
+		String matchingPrefix;
+		
+		if (activeNetworkInfo == null) {
+			return false;
+		}
+		
+		switch (activeNetworkInfo.getType())
+		{
+		case ConnectivityManager.TYPE_ETHERNET:
+			matchingPrefix = "eth";
+			break;
+		case ConnectivityManager.TYPE_WIFI:
+			matchingPrefix = "wlan";
+			break;
+
+		default:
+			// Must be on Ethernet or Wifi to consider that we can send large packets
+			return false;
+		}
+
+		// Try to find the interface that corresponds to the active network
+		try {
+			Enumeration<NetworkInterface> ifaceList = NetworkInterface.getNetworkInterfaces();
+			while (ifaceList.hasMoreElements()) {
+				NetworkInterface iface = ifaceList.nextElement();
+
+				// Look for an interface that matches the prefix we expect
+				if (iface.isUp() && iface.getName().startsWith(matchingPrefix)) {
+					// Find the IPv4 address for the interface
+					for (InterfaceAddress addr : iface.getInterfaceAddresses()) {
+						if (!(addr.getAddress() instanceof Inet4Address)) {
+							// Skip non-IPv4 addresses
+							continue;
+						}
+						
+						// Found the right address on the right interface
+						return isOnSameSubnet(targetAddress, addr.getAddress(), addr.getNetworkPrefixLength());
+					}
+				}
+			}
+		} catch (SocketException e) {
+			e.printStackTrace();
+		}
+
+		// We didn't find the interface or something else went wrong
+		return false;
+	}
+	
+	private boolean isOnSameSubnet(InetAddress targetAddress, InetAddress localAddress, short networkPrefixLength) {
+		byte[] targetBytes = targetAddress.getAddress();
+		byte[] localBytes = localAddress.getAddress();
+
+		for (int byteIndex = 0; networkPrefixLength > 0; byteIndex++) {
+			byte target = targetBytes[byteIndex];
+			byte local = localBytes[byteIndex];
+			
+			if (networkPrefixLength >= 8) {
+				// Do a full byte comparison
+				if (target != local) {
+					return false;
+				}
+				
+				networkPrefixLength -= 8;
+			}
+			else {
+				target &= (byte)(0xFF << (8 - networkPrefixLength));
+				local &= (byte)(0xFF << (8 - networkPrefixLength));
+				
+				// Do a masked comparison
+				if (target != local) {
+					return false;
+				}
+				
+				networkPrefixLength = 0;
+			}
+		}
+		
+		return true;
+	}
+	
 	private void checkDataConnection()
 	{
 		ConnectivityManager mgr = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);