Added support for passing <= 1.6.4 clients through

src/main/java/net/raphimc/viaproxy/cli/options/Options.java

@@ -58,6 +58,7 @@ public class Options {
     public static boolean LOCAL_SOCKET_AUTH;
     public static String RESOURCE_PACK_URL; // Example: http://example.com/resourcepack.zip
     public static boolean HAPROXY_PROTOCOL;
+    public static boolean LEGACY_CLIENT_PASSTHROUGH;
 
     public static void parse(final String[] args) throws IOException {
         final OptionParser parser = new OptionParser();
@@ -78,6 +79,7 @@ public class Options {
         final OptionSpec<String> resourcePackUrl = parser.acceptsAll(asList("resource_pack_url", "resource_pack", "rpu", "rp"), "URL of a resource pack which all connecting clients can optionally download").withRequiredArg().ofType(String.class);
         final OptionSpec<String> proxyUrl = parser.acceptsAll(asList("proxy_url", "proxy"), "URL of a SOCKS(4/5)/HTTP(S) proxy which will be used for TCP connections").withRequiredArg().ofType(String.class);
         final OptionSpec<Void> haProxyProtocol = parser.acceptsAll(asList("haproxy-protocol", "haproxy"), "Send HAProxy protocol messages to the backend server");
+        final OptionSpec<Void> legacyClientPassthrough = parser.acceptsAll(asList("legacy_client_passthrough", "legacy_passthrough"), "Allow <= 1.6.4 clients to connect to the backend server instead of being kicked");
         PluginManager.EVENT_MANAGER.call(new PreOptionsParseEvent(parser));
 
         final OptionSet options = parser.parse(args);
@@ -116,6 +118,7 @@ public class Options {
             }
         }
         HAPROXY_PROTOCOL = options.has(haProxyProtocol);
+        LEGACY_CLIENT_PASSTHROUGH = options.has(legacyClientPassthrough);
         PluginManager.EVENT_MANAGER.call(new PostOptionsParseEvent(options));
     }
 

src/main/java/net/raphimc/viaproxy/proxy/client2proxy/Client2ProxyChannelInitializer.java

@@ -22,6 +22,7 @@ import io.netty.channel.ChannelHandler;
 import net.raphimc.netminecraft.constants.MCPipeline;
 import net.raphimc.netminecraft.netty.connection.MinecraftChannelInitializer;
 import net.raphimc.netminecraft.packet.registry.PacketRegistryUtil;
+import net.raphimc.viaproxy.cli.options.Options;
 import net.raphimc.viaproxy.plugins.PluginManager;
 import net.raphimc.viaproxy.plugins.events.Client2ProxyChannelInitializeEvent;
 import net.raphimc.viaproxy.plugins.events.types.ITyped;
@@ -41,6 +42,9 @@ public class Client2ProxyChannelInitializer extends MinecraftChannelInitializer
             return;
         }
 
+        if (Options.LEGACY_CLIENT_PASSTHROUGH) {
+            channel.pipeline().addLast("legacy-passthrough-handler", new LegacyClientPassthroughHandler());
+        }
         super.initChannel(channel);
         channel.attr(MCPipeline.PACKET_REGISTRY_ATTRIBUTE_KEY).set(PacketRegistryUtil.getHandshakeRegistry(false));
 

src/main/java/net/raphimc/viaproxy/proxy/client2proxy/Client2ProxyHandler.java

@@ -121,14 +121,14 @@ public class Client2ProxyHandler extends SimpleChannelInboundHandler<IPacket> {
         switch (this.proxyConnection.getConnectionState()) {
             case HANDSHAKING:
                 if (packet instanceof C2SHandshakePacket) this.handleHandshake((C2SHandshakePacket) packet);
-                else break;
+                else throw new IllegalStateException("Unexpected packet in HANDSHAKING state");
 
                 return;
             case LOGIN:
                 if (packet instanceof C2SLoginHelloPacket1_7) this.handleLoginHello((C2SLoginHelloPacket1_7) packet);
                 else if (packet instanceof C2SLoginKeyPacket1_7) this.handleLoginKey((C2SLoginKeyPacket1_7) packet);
                 else if (packet instanceof C2SLoginCustomPayloadPacket) this.handleLoginCustomPayload((C2SLoginCustomPayloadPacket) packet);
-                else break;
+                else throw new IllegalStateException("Unexpected packet in LOGIN state");
 
                 return;
             case PLAY:

src/main/java/net/raphimc/viaproxy/proxy/client2proxy/LegacyClientPassthroughHandler.java

@@ -0,0 +1,124 @@
+/*
+ * This file is part of ViaProxy - https://github.com/RaphiMC/ViaProxy
+ * Copyright (C) 2023 RK_01/RaphiMC and contributors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+package net.raphimc.viaproxy.proxy.client2proxy;
+
+import io.netty.bootstrap.Bootstrap;
+import io.netty.buffer.ByteBuf;
+import io.netty.channel.*;
+import net.raphimc.netminecraft.netty.connection.NetClient;
+import net.raphimc.netminecraft.util.ServerAddress;
+import net.raphimc.viaproxy.cli.options.Options;
+import net.raphimc.viaproxy.proxy.util.ExceptionUtil;
+import net.raphimc.viaproxy.util.logging.Logger;
+
+public class LegacyClientPassthroughHandler extends SimpleChannelInboundHandler<ByteBuf> {
+
+    private Channel c2pChannel;
+    private NetClient p2sConnection;
+
+    @Override
+    public void channelActive(ChannelHandlerContext ctx) throws Exception {
+        super.channelActive(ctx);
+
+        this.c2pChannel = ctx.channel();
+    }
+
+    @Override
+    public void channelInactive(ChannelHandlerContext ctx) throws Exception {
+        super.channelInactive(ctx);
+
+        try {
+            if (this.p2sConnection != null) {
+                this.p2sConnection.getChannel().close();
+            }
+        } catch (Throwable ignored) {
+        }
+    }
+
+    @Override
+    protected void channelRead0(ChannelHandlerContext ctx, ByteBuf msg) {
+        if (!ctx.channel().isOpen()) return;
+        if (!msg.isReadable()) return;
+
+        if (this.p2sConnection == null) {
+            final int length = msg.getUnsignedByte(0);
+            if (length == 0/*classic*/ || length == 1/*a1.0.15*/ || length == 2/*<= 1.6.4*/ || length == 254/*<= 1.6.4 (ping)*/) {
+                while (ctx.pipeline().last() != this) {
+                    ctx.pipeline().removeLast();
+                }
+
+                this.connectToServer();
+            } else {
+                ctx.pipeline().remove(this);
+                ctx.pipeline().fireChannelRead(msg.retain());
+                return;
+            }
+        }
+
+        this.p2sConnection.getChannel().writeAndFlush(msg.retain()).addListener(ChannelFutureListener.FIRE_EXCEPTION_ON_FAILURE);
+    }
+
+    private void connectToServer() {
+        this.p2sConnection = new NetClient(() -> new SimpleChannelInboundHandler<ByteBuf>() {
+            @Override
+            public void channelInactive(ChannelHandlerContext ctx) throws Exception {
+                super.channelInactive(ctx);
+
+                try {
+                    LegacyClientPassthroughHandler.this.c2pChannel.close();
+                } catch (Throwable ignored) {
+                }
+            }
+
+            @Override
+            protected void channelRead0(ChannelHandlerContext ctx, ByteBuf msg) {
+                LegacyClientPassthroughHandler.this.c2pChannel.writeAndFlush(msg.retain()).addListener(ChannelFutureListener.FIRE_EXCEPTION_ON_FAILURE);
+            }
+
+            @Override
+            public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
+                ExceptionUtil.handleNettyException(ctx, cause, null);
+            }
+        }, s -> new ChannelInitializer<Channel>() {
+            @Override
+            protected void initChannel(Channel channel) {
+                channel.pipeline().addLast(s.get());
+            }
+        }) {
+            @Override
+            public void initialize(Bootstrap bootstrap) {
+                bootstrap.option(ChannelOption.CONNECT_TIMEOUT_MILLIS, 4_000);
+                super.initialize(bootstrap);
+            }
+        };
+
+        try {
+            this.p2sConnection.connect(new ServerAddress(Options.CONNECT_ADDRESS, Options.CONNECT_PORT));
+        } catch (Throwable e) {
+            Logger.LOGGER.error("Failed to connect to target server", e);
+            this.p2sConnection = null;
+            this.c2pChannel.close();
+        }
+    }
+
+    @Override
+    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
+        ExceptionUtil.handleNettyException(ctx, cause, null);
+    }
+
+}

src/main/java/net/raphimc/viaproxy/proxy/util/ExceptionUtil.java

@@ -52,7 +52,9 @@ public class ExceptionUtil {
         }
         Logger.LOGGER.error("Caught unhandled netty exception", cause);
         try {
-            proxyConnection.kickClient("§cAn unhandled error occurred in your connection and it has been closed.\n§aError details for report:§f" + ExceptionUtil.prettyPrint(cause));
+            if (proxyConnection != null) {
+                proxyConnection.kickClient("§cAn unhandled error occurred in your connection and it has been closed.\n§aError details for report:§f" + ExceptionUtil.prettyPrint(cause));
+            }
         } catch (Throwable ignored) {
         }
         ctx.channel().close();