From 23788044fc50f4b0208df1e711728cdc10a43ed9 Mon Sep 17 00:00:00 2001
From: AlexProgrammerDE <40795980+AlexProgrammerDE@users.noreply.github.com>
Date: Fri, 29 Nov 2024 12:47:53 +0100
Subject: [PATCH] Fill in arbitrary values for remote address if ipv6 client
 connects to ipv4 server and vice verse

---
 .../network/helper/NettyHelper.java           | 41 +++++++++++++++++--
 1 file changed, 37 insertions(+), 4 deletions(-)

diff --git a/protocol/src/main/java/org/geysermc/mcprotocollib/network/helper/NettyHelper.java b/protocol/src/main/java/org/geysermc/mcprotocollib/network/helper/NettyHelper.java
index fdbee4c73..818ccca71 100644
--- a/protocol/src/main/java/org/geysermc/mcprotocollib/network/helper/NettyHelper.java
+++ b/protocol/src/main/java/org/geysermc/mcprotocollib/network/helper/NettyHelper.java
@@ -30,8 +30,10 @@
 import org.slf4j.LoggerFactory;
 
 import java.net.Inet4Address;
+import java.net.Inet6Address;
 import java.net.InetAddress;
 import java.net.InetSocketAddress;
+import java.net.SocketAddress;
 import java.net.UnknownHostException;
 
 public class NettyHelper {
@@ -102,12 +104,33 @@ public static void initializeHAProxySupport(Session session, Channel channel) {
         channel.pipeline().addLast("proxy-protocol-packet-sender", new ChannelInboundHandlerAdapter() {
             @Override
             public void channelActive(ChannelHandlerContext ctx) throws Exception {
-                InetSocketAddress remoteAddress = (InetSocketAddress) ctx.channel().remoteAddress();
-                HAProxyProxiedProtocol proxiedProtocol = clientAddress.getAddress() instanceof Inet4Address ? HAProxyProxiedProtocol.TCP4 : HAProxyProxiedProtocol.TCP6;
+                HAProxyProxiedProtocol proxiedProtocol = getProxiedProtocol(clientAddress);
+
+                SocketAddress remoteAddress = ctx.channel().remoteAddress();
+                String destinationAddress;
+                int destinationPort;
+                if (remoteAddress instanceof InetSocketAddress inetRemoteAddress && getProxiedProtocol(inetRemoteAddress) == proxiedProtocol) {
+                    destinationAddress = inetRemoteAddress.getAddress().getHostAddress();
+                    destinationPort = inetRemoteAddress.getPort();
+                } else {
+                    // Fill in arbitrary values for the destination address and port if the remote address is not of the same type
+                    switch (proxiedProtocol) {
+                        case TCP4 -> {
+                            destinationAddress = "0.0.0.0";
+                            destinationPort = 0;
+                        }
+                        case TCP6 -> {
+                            destinationAddress = "::";
+                            destinationPort = 0;
+                        }
+                        default -> throw new UnsupportedOperationException("Unsupported proxied protocol: " + proxiedProtocol);
+                    };
+                }
+
                 ctx.channel().writeAndFlush(new HAProxyMessage(
                     HAProxyProtocolVersion.V2, HAProxyCommand.PROXY, proxiedProtocol,
-                    clientAddress.getAddress().getHostAddress(), remoteAddress.getAddress().getHostAddress(),
-                    clientAddress.getPort(), remoteAddress.getPort()
+                    clientAddress.getAddress().getHostAddress(), destinationAddress,
+                    clientAddress.getPort(), destinationPort
                 )).addListener(future -> channel.pipeline().remove("proxy-protocol-encoder"));
                 ctx.pipeline().remove(this);
 
@@ -116,6 +139,16 @@ public void channelActive(ChannelHandlerContext ctx) throws Exception {
         });
     }
 
+    private static HAProxyProxiedProtocol getProxiedProtocol(InetSocketAddress socketAddress) {
+        if (socketAddress.getAddress() instanceof Inet4Address) {
+            return HAProxyProxiedProtocol.TCP4;
+        } else if (socketAddress.getAddress() instanceof Inet6Address) {
+            return HAProxyProxiedProtocol.TCP6;
+        } else {
+            return HAProxyProxiedProtocol.UNKNOWN;
+        }
+    }
+
     public static void addProxy(ProxyInfo proxy, ChannelPipeline pipeline) {
         if (proxy == null) {
             return;