From 6ce432e4aeea9eddaf7ebbc1158daefe3e53bf5b Mon Sep 17 00:00:00 2001
From: R00tB33rMan <36140389+R00tB33rMan@users.noreply.github.com>
Date: Thu, 9 Apr 2026 10:50:01 -0400
Subject: [PATCH] Handle configuration/transition-phase disconnects as
 connection errors to prevent bricking older client versions (#1753)

---
 .../proxy/connection/backend/ConfigSessionHandler.java     | 7 +++----
 .../proxy/connection/backend/TransitionSessionHandler.java | 5 ++---
 2 files changed, 5 insertions(+), 7 deletions(-)

diff --git a/proxy/src/main/java/com/velocitypowered/proxy/connection/backend/ConfigSessionHandler.java b/proxy/src/main/java/com/velocitypowered/proxy/connection/backend/ConfigSessionHandler.java
index e523f0f71..8cc1bf8cc 100644
--- a/proxy/src/main/java/com/velocitypowered/proxy/connection/backend/ConfigSessionHandler.java
+++ b/proxy/src/main/java/com/velocitypowered/proxy/connection/backend/ConfigSessionHandler.java
@@ -61,7 +61,6 @@ import com.velocitypowered.proxy.protocol.util.PluginMessageUtil;
 import io.netty.buffer.ByteBufUtil;
 import io.netty.buffer.Unpooled;
 import io.netty.channel.Channel;
-import java.io.IOException;
 import java.net.InetSocketAddress;
 import java.util.concurrent.CompletableFuture;
 import net.kyori.adventure.key.Key;
@@ -377,8 +376,8 @@ public class ConfigSessionHandler implements MinecraftSessionHandler {
 
   @Override
   public void disconnected() {
-    resultFuture.completeExceptionally(
-        new IOException("Unexpectedly disconnected from remote server"));
+    resultFuture.complete(ConnectionRequestResults.forDisconnect(
+        ConnectionMessages.INTERNAL_SERVER_CONNECTION_ERROR, serverConn.getServer()));
   }
 
   @Override
@@ -415,4 +414,4 @@ public class ConfigSessionHandler implements MinecraftSessionHandler {
   public enum State {
     START, NEGOTIATING, PLUGIN_MESSAGE_INTERRUPT, RESOURCE_PACK_INTERRUPT, COMPLETE
   }
-}
\ No newline at end of file
+}
diff --git a/proxy/src/main/java/com/velocitypowered/proxy/connection/backend/TransitionSessionHandler.java b/proxy/src/main/java/com/velocitypowered/proxy/connection/backend/TransitionSessionHandler.java
index e713769a6..cfcd8f5e0 100644
--- a/proxy/src/main/java/com/velocitypowered/proxy/connection/backend/TransitionSessionHandler.java
+++ b/proxy/src/main/java/com/velocitypowered/proxy/connection/backend/TransitionSessionHandler.java
@@ -38,7 +38,6 @@ import com.velocitypowered.proxy.protocol.packet.DisconnectPacket;
 import com.velocitypowered.proxy.protocol.packet.JoinGamePacket;
 import com.velocitypowered.proxy.protocol.packet.KeepAlivePacket;
 import com.velocitypowered.proxy.protocol.packet.PluginMessagePacket;
-import java.io.IOException;
 import java.util.concurrent.CompletableFuture;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
@@ -213,7 +212,7 @@ public class TransitionSessionHandler implements MinecraftSessionHandler {
 
   @Override
   public void disconnected() {
-    resultFuture
-        .completeExceptionally(new IOException("Unexpectedly disconnected from remote server"));
+    resultFuture.complete(ConnectionRequestResults.forDisconnect(
+        ConnectionMessages.INTERNAL_SERVER_CONNECTION_ERROR, serverConn.getServer()));
   }
 }