[grid] Skip the TCP tunnel read-idle close when reads are paused

java/src/org/openqa/selenium/netty/server/TcpUpgradeTunnelHandler.java

@@ -379,7 +379,7 @@ public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
    * the TCP connection without sending a FIN or RST (common with AWS ALB, k8s ingress-nginx at
    * their default 60 s idle timeout).
    */
-  private static final class IdleCloseHandler extends ChannelInboundHandlerAdapter {
+  static final class IdleCloseHandler extends ChannelInboundHandlerAdapter {
 
     private final Channel peer;
 
@@ -390,6 +390,18 @@ private static final class IdleCloseHandler extends ChannelInboundHandlerAdapter
     @Override
     public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
       if (evt instanceof IdleStateEvent) {
+        // Read-idle while backpressure has paused this channel is expected, not a sign of a
+        // dropped connection: the peer's outbound buffer crossed its high-water mark, the
+        // TcpTunnelHandler set autoRead=false on this side, and bytes will not be read again
+        // until the peer drains. Skip the close so a sustained slow consumer does not get the
+        // tunnel torn down underneath it.
+        if (!ctx.channel().config().isAutoRead()) {
+          LOG.log(
+              Level.FINE,
+              "TCP tunnel read-idle on {0} ignored: reads paused by backpressure",
+              ctx.channel());
+          return;
+        }
         LOG.log(
             Level.FINE,
             "TCP tunnel read-idle timeout on {0}, closing both channels",

java/test/org/openqa/selenium/netty/server/BUILD.bazel

@@ -2,6 +2,7 @@ load("@rules_jvm_external//:defs.bzl", "artifact")
 load("//java:defs.bzl", "JUNIT5_DEPS", "java_library", "java_test_suite")
 
 SMALL_TEST_SRCS = [
+    "IdleCloseHandlerTest.java",
     "MessageInboundConverterTest.java",
     "MessageOutboundConverterTest.java",
     "RequestConverterTest.java",
@@ -20,6 +21,7 @@ java_test_suite(
         artifact("io.netty:netty-buffer"),
         artifact("io.netty:netty-codec-http"),
         artifact("io.netty:netty-common"),
+        artifact("io.netty:netty-handler"),
         artifact("io.netty:netty-transport"),
         artifact("org.junit.jupiter:junit-jupiter-api"),
         artifact("org.assertj:assertj-core"),

java/test/org/openqa/selenium/netty/server/IdleCloseHandlerTest.java

@@ -0,0 +1,56 @@
+// Licensed to the Software Freedom Conservancy (SFC) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The SFC licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+package org.openqa.selenium.netty.server;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import io.netty.channel.embedded.EmbeddedChannel;
+import io.netty.handler.timeout.IdleStateEvent;
+import org.junit.jupiter.api.Test;
+
+class IdleCloseHandlerTest {
+
+  @Test
+  void idleEventClosesBothChannels() {
+    EmbeddedChannel peer = new EmbeddedChannel();
+    EmbeddedChannel self = new EmbeddedChannel(new TcpUpgradeTunnelHandler.IdleCloseHandler(peer));
+
+    assertThat(self.config().isAutoRead()).isTrue();
+    self.pipeline().fireUserEventTriggered(IdleStateEvent.READER_IDLE_STATE_EVENT);
+
+    assertThat(self.isOpen()).isFalse();
+    assertThat(peer.isOpen()).isFalse();
+  }
+
+  @Test
+  void idleEventIsIgnoredWhileBackpressureHasPausedReads() {
+    EmbeddedChannel peer = new EmbeddedChannel();
+    EmbeddedChannel self = new EmbeddedChannel(new TcpUpgradeTunnelHandler.IdleCloseHandler(peer));
+
+    // Simulate backpressure: TcpTunnelHandler would have set autoRead=false on this channel
+    // because the peer's outbound buffer was full.
+    self.config().setAutoRead(false);
+
+    // The read-idle event must NOT tear down the tunnel — no bytes arriving is the expected
+    // consequence of pausing reads, not a sign of a dropped connection.
+    self.pipeline().fireUserEventTriggered(IdleStateEvent.READER_IDLE_STATE_EVENT);
+
+    assertThat(self.isOpen()).isTrue();
+    assertThat(peer.isOpen()).isTrue();
+  }
+}