configure: add ipv4 mode

This is difficult since libnet and java/net need to agree on whether
preferIPv4Stack is set, or else libnet will create sockets java/net
can't use. Work around this by setting the launcher vmargs, as libnet is
already loaded by the time we get to main().

src/main/java/net/runelite/launcher/ConfigurationFrame.java

@@ -32,6 +32,8 @@
 import java.awt.event.ActionEvent;
 import java.awt.image.BufferedImage;
 import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
 import javax.annotation.Nullable;
 import javax.imageio.ImageIO;
 import javax.swing.BorderFactory;
@@ -57,6 +59,7 @@ public class ConfigurationFrame extends JFrame
 	private final JCheckBox chkboxSkipTlsVerification;
 	private final JCheckBox chkboxNoUpdates;
 	private final JCheckBox chkboxSafemode;
+	private final JCheckBox chkboxIpv4;
 	private final JTextField txtScale;
 	private final JTextArea txtClientArguments;
 	private final JTextArea txtJvmArguments;
@@ -119,6 +122,12 @@ private ConfigurationFrame(LauncherSettings settings)
 			Boolean.TRUE.equals(settings.safemode)
 		));
 
+		topPanel.add(chkboxIpv4 = checkbox(
+			"IPv4",
+			"Prefer IPv4 over IPv6",
+			Boolean.TRUE.equals(settings.ipv4)
+		));
+
 		pane.add(topPanel);
 
 		var midPanel = new JPanel();
@@ -198,6 +207,7 @@ private void save(ActionEvent l)
 		settings.skipTlsVerification = chkboxSkipTlsVerification.isSelected();
 		settings.noupdates = chkboxNoUpdates.isSelected();
 		settings.safemode = chkboxSafemode.isSelected();
+		settings.ipv4 = chkboxIpv4.isSelected();
 
 		var t = txtScale.getText();
 		settings.scale = null;
@@ -227,6 +237,20 @@ private void save(ActionEvent l)
 
 		LauncherSettings.saveSettings(settings);
 
+		// IPv4 change requires patching packr config
+		PackrConfig.patch(config ->
+		{
+			List<String> vmArgs = (List) config.computeIfAbsent("vmArgs", k -> new ArrayList<>());
+			if (settings.ipv4)
+			{
+				vmArgs.add("-Djava.net.preferIPv4Stack=true");
+			}
+			else
+			{
+				vmArgs.remove("-Djava.net.preferIPv4Stack=true");
+			}
+		});
+
 		log.info("Updated launcher configuration:" + System.lineSeparator() + "{}", settings.configurationStr());
 
 		dispose();

src/main/java/net/runelite/launcher/Launcher.java

@@ -262,7 +262,7 @@ public static void main(String[] args)
 
 			if (postInstall)
 			{
-				postInstall();
+				postInstall(settings);
 				return;
 			}
 
@@ -343,7 +343,7 @@ public static void main(String[] args)
 			}
 
 			// update packr vmargs to the launcher vmargs from bootstrap.
-			PackrConfig.updateLauncherArgs(bootstrap);
+			PackrConfig.updateLauncherArgs(bootstrap, settings);
 
 			// Determine artifacts for this OS
 			List<Artifact> artifacts = Arrays.stream(bootstrap.getArtifacts())
@@ -593,6 +593,11 @@ private static List<String> getJvmArgs(LauncherSettings settings)
 	{
 		var args = new ArrayList<>(settings.jvmArguments);
 
+		if (settings.ipv4)
+		{
+			args.add("-Djava.net.preferIPv4Stack=true");
+		}
+
 		var envArgs = System.getenv("RUNELITE_VMARGS");
 		if (!Strings.isNullOrEmpty(envArgs))
 		{
@@ -921,7 +926,7 @@ static boolean isJava17()
 		return Runtime.version().feature() >= 16;
 	}
 
-	private static void postInstall()
+	private static void postInstall(LauncherSettings settings)
 	{
 		Bootstrap bootstrap;
 		try
@@ -934,7 +939,7 @@ private static void postInstall()
 			return;
 		}
 
-		PackrConfig.updateLauncherArgs(bootstrap);
+		PackrConfig.updateLauncherArgs(bootstrap, settings);
 
 		log.info("Performed postinstall steps");
 	}

src/main/java/net/runelite/launcher/LauncherSettings.java

@@ -66,6 +66,7 @@ class LauncherSettings
 	boolean skipTlsVerification;
 	boolean noupdates;
 	boolean safemode;
+	boolean ipv4;
 	@Nullable
 	Double scale;
 	List<String> clientArguments = Collections.emptyList();
@@ -141,6 +142,7 @@ String configurationStr()
 				" skip tls verification: {}" + System.lineSeparator() +
 				" noupdates: {}" + System.lineSeparator() +
 				" safe mode: {}" + System.lineSeparator() +
+				" ipv4: {}" + System.lineSeparator() +
 				" scale: {}" + System.lineSeparator() +
 				" client arguments: {}" + System.lineSeparator() +
 				" jvm arguments: {}" + System.lineSeparator() +
@@ -152,6 +154,7 @@ String configurationStr()
 				skipTlsVerification,
 				noupdates,
 				safemode,
+				ipv4,
 				scale == null ? "system" : scale,
 				clientArguments.isEmpty() ? "none" : clientArguments,
 				jvmArguments.isEmpty() ? "none" : jvmArguments,

src/main/java/net/runelite/launcher/PackrConfig.java

@@ -39,15 +39,47 @@
 import java.nio.file.AtomicMoveNotSupportedException;
 import java.nio.file.Files;
 import java.nio.file.StandardCopyOption;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
 import java.util.Map;
+import java.util.function.Consumer;
 import lombok.extern.slf4j.Slf4j;
 import net.runelite.launcher.beans.Bootstrap;
 
 @Slf4j
 class PackrConfig
 {
 	// Update the packr config
-	static void updateLauncherArgs(Bootstrap bootstrap)
+	static void updateLauncherArgs(Bootstrap bootstrap, LauncherSettings settings)
+	{
+		String[] bootstrapVmArgs = getVmArgs(bootstrap);
+		if (bootstrapVmArgs == null || bootstrapVmArgs.length == 0)
+		{
+			log.warn("Launcher args are empty");
+			return;
+		}
+
+		List<String> vmArgs = new ArrayList<>(Arrays.asList(bootstrapVmArgs));
+
+		// java.net.preferIPv4Stack needs to be set prior to libnet *loading* (it is read in net_util.c JNI_OnLoad).
+		// Failure to keep preferIPv4Stack consistent between libnet and java/net results in disagreements over
+		// which socket types can be used.
+		if (settings.ipv4)
+		{
+			vmArgs.add("-Djava.net.preferIPv4Stack=true");
+		}
+
+		Map<String, String> env = getEnv(bootstrap);
+
+		patch(config ->
+		{
+			config.put("vmArgs", vmArgs);
+			config.put("env", env);
+		});
+	}
+
+	static void patch(Consumer<Map> configConsumer)
 	{
 		var os = OS.getOs();
 		if (os != OS.OSType.Windows && os != OS.OSType.MacOS)
@@ -71,27 +103,19 @@ static void updateLauncherArgs(Bootstrap bootstrap)
 		}
 		catch (IOException | JsonIOException | JsonSyntaxException e)
 		{
-			log.warn("error deserializing packr vm args!", e);
+			log.warn("error deserializing launcher vm args!", e);
 			return;
 		}
 
 		if (config == null)
 		{
 			// this can't happen when run from the launcher, because an invalid packr config would prevent the launcher itself
 			// from starting. But could happen if the jar launcher was run separately.
-			log.warn("packr config is null!");
-			return;
-		}
-
-		String[] argsArr = getArgs(bootstrap);
-		if (argsArr == null || argsArr.length == 0)
-		{
-			log.warn("Launcher args are empty");
+			log.warn("launcher config is null!");
 			return;
 		}
 
-		config.put("vmArgs", argsArr);
-		config.put("env", getEnv(bootstrap));
+		configConsumer.accept(config);
 
 		try
 		{
@@ -117,14 +141,16 @@ static void updateLauncherArgs(Bootstrap bootstrap)
 				log.debug("atomic move not supported", ex);
 				Files.move(tmpFile.toPath(), configFile.toPath(), StandardCopyOption.REPLACE_EXISTING);
 			}
+
+			log.debug("patched packr config");
 		}
 		catch (IOException e)
 		{
-			log.warn("error updating packr vm args!", e);
+			log.warn("error updating launcher vm args!", e);
 		}
 	}
 
-	private static String[] getArgs(Bootstrap bootstrap)
+	private static String[] getVmArgs(Bootstrap bootstrap)
 	{
 		return Launcher.isJava17() ? getArgsJvm17(bootstrap) : getArgsJvm11(bootstrap);
 	}