From 772ea584cef2de7ae1277779829cd0fb835b0a9b Mon Sep 17 00:00:00 2001
From: Wouter Gritter <wouter@gritter.nl>
Date: Mon, 8 Jun 2026 17:04:08 +0200
Subject: [PATCH] Fix fallback chain skipped when initial server stalls after
 accepting connection

---
 .../connection/client/ConnectedPlayer.java    | 43 +++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/proxy/src/main/java/com/velocitypowered/proxy/connection/client/ConnectedPlayer.java b/proxy/src/main/java/com/velocitypowered/proxy/connection/client/ConnectedPlayer.java
index 47d59a7186..455185fa88 100644
--- a/proxy/src/main/java/com/velocitypowered/proxy/connection/client/ConnectedPlayer.java
+++ b/proxy/src/main/java/com/velocitypowered/proxy/connection/client/ConnectedPlayer.java
@@ -69,6 +69,7 @@
 import com.velocitypowered.proxy.connection.util.ConnectionMessages;
 import com.velocitypowered.proxy.connection.util.ConnectionRequestResults.Impl;
 import com.velocitypowered.proxy.connection.util.VelocityInboundConnection;
+import com.velocitypowered.proxy.network.Connections;
 import com.velocitypowered.proxy.protocol.StateRegistry;
 import com.velocitypowered.proxy.protocol.netty.MinecraftEncoder;
 import com.velocitypowered.proxy.protocol.packet.BundleDelimiterPacket;
@@ -105,6 +106,7 @@
 import com.velocitypowered.proxy.util.collect.CappedSet;
 import io.netty.buffer.ByteBuf;
 import io.netty.buffer.Unpooled;
+import io.netty.handler.timeout.ReadTimeoutHandler;
 import java.net.InetSocketAddress;
 import java.util.Collection;
 import java.util.Collections;
@@ -931,6 +933,12 @@ public void setConnectedServer(@Nullable VelocityServerConnection serverConnecti
     if (serverConnection == connectionInFlight) {
       connectionInFlight = null;
     }
+
+    if (serverConnection != null) {
+      // The player has reached a server; restore the read-timeout that was suspended while we
+      // were establishing their initial connection (see pauseReadTimeout / issue GemstoneGG#938).
+      resumeReadTimeout();
+    }
   }
 
   public void sendLegacyForgeHandshakeResetPacket() {
@@ -1439,6 +1447,33 @@ public BossBarManager getBossBarManager() {
     return bossBarManager;
   }
 
+  /**
+   * Suspends the read-timeout on the player's own (client-facing) connection while we establish
+   * their initial connection. The client legitimately idles on the loading screen during that
+   * window, so its read-timeout must not fire -- otherwise a backend that stalls after accepting
+   * the TCP connection times the idle client out before the backend connection's own timeout can
+   * drive the fallback chain, dropping the player instead of moving them on. Restored by
+   * {@link #resumeReadTimeout()} once a server is reached (issue GemstoneGG#938).
+   */
+  private void pauseReadTimeout() {
+    final var pipeline = connection.getChannel().pipeline();
+    if (pipeline.context(Connections.READ_TIMEOUT) != null) {
+      pipeline.remove(Connections.READ_TIMEOUT);
+    }
+  }
+
+  /**
+   * Restores the read-timeout on the player's own connection after it was suspended by
+   * {@link #pauseReadTimeout()}. Idempotent: does nothing if the handler is already present.
+   */
+  private void resumeReadTimeout() {
+    final var pipeline = connection.getChannel().pipeline();
+    if (pipeline.context(Connections.READ_TIMEOUT) == null && pipeline.context(Connections.FRAME_DECODER) != null) {
+      pipeline.addAfter(Connections.FRAME_DECODER, Connections.READ_TIMEOUT, new ReadTimeoutHandler(
+          server.getConfiguration().getReadTimeout(), TimeUnit.MILLISECONDS));
+    }
+  }
+
   private final class ConnectionRequestBuilderImpl implements ConnectionRequestBuilder {
 
     private final RegisteredServer toConnect;
@@ -1499,6 +1534,14 @@ private CompletableFuture<Impl> internalConnect() {
               new VelocityServerConnection(vrs, previousServer, ConnectedPlayer.this, server);
           connectionInFlight = con;
 
+          if (connectedServer == null) {
+            // Establishing the player's initial connection (or working through the fallback chain
+            // for it): they have no backend yet and are idling on a loading screen. Suspend their
+            // connection's read-timeout so a stalled backend can't time the idle client out before
+            // the backend timeout drives the fallback. Restored in setConnectedServer (issue GemstoneGG#938).
+            pauseReadTimeout();
+          }
+
           return con.connect().whenCompleteAsync((result, exception) -> {
             if (result != null && !result.isSuccessful() && !result.isSafe()) {
               handleConnectionException(result.getAttemptedConnection(),