Add HTTP/2 PING-based connection health checks

docs/modules/ROOT/pages/http-client.adoc

@@ -680,6 +680,41 @@ include::{examples-dir}/channeloptions/Application.java[lines=18..54]
 <4> Configures the time between individual `keepalive` probes to 1 minute.
 <5> Configures the maximum number of TCP `keepalive` probes to 8.
 
+=== HTTP/2 Connection Health Check
+For `HTTP/2 connections`, it's recommended to configure `PING` frames for connection maintenance and health monitoring.
+The `HttpClient` uses `PING` frames to detect unresponsive connections when `maxIdleTime` on the connection pool is configured.
+
+Benefits of using `PING` frames:
+
+- Actively probes connection liveness when idle
+- Detects unresponsive connections through timely health checks
+- Closes stale connections automatically
+- Maintains reliable connection pool state
+
+[NOTE]
+====
+`HTTP/2` `PING` frame-based health checks require `maxIdleTime` on the connection pool to be configured as a prerequisite.
+Without idle timeout configuration, PING frames will not be sent and connections may remain open indefinitely,
+preventing proper detection of inactive or unresponsive connections.
+
+The idle timeout and PING settings work together:
+
+1. Connection becomes idle (no activity for `maxIdleTime`)
+2. A PING frame is sent to check if the peer is responsive
+3. If no ACK within `pingAckTimeout`, retry based on `pingAckDropThreshold`
+4. If all attempts fail, the connection is closed
+====
+
+To enable `PING` frames for `HTTP/2` connections, configure the `HttpClient` as follows:
+
+{examples-link}/liveness/Application.java
+----
+include::{examples-dir}/liveness/Application.java[lines=27..52]
+----
+<1> Configure `maxIdleTime` to enable PING-based health checks. When a connection is idle for this duration, a PING frame will be sent.
+<2> Configure `pingAckTimeout` - the maximum time to wait for each PING ACK response. If no ACK is received within this timeout, another PING is sent (up to the threshold).
+<3> Configure `pingAckDropThreshold` - the maximum number of PING frames to send before closing the connection. For example, `2` means send up to 2 PING frames (if first fails, try once more) before closing.
+
 [[ssl-tls-timeout]]
 ==== SSL/TLS Timeout
 `HttpClient` supports the SSL/TLS functionality provided by Netty.

docs/modules/ROOT/pages/http-server.adoc

@@ -789,6 +789,41 @@ include::{examples-dir}/idle/timeout/Application.java[lines=18..35]
 ----
 <1> Configures the default idle timeout to 1 second.
 
+=== HTTP/2 Connection Health Check
+For `HTTP/2 connections`, it's recommended to configure `PING` frames for connection maintenance and health monitoring.
+The `HttpServer` uses `PING` frames to detect unresponsive clients when `idleTimeout` is configured.
+
+Benefits of using `PING` frames:
+
+- Actively probes connection liveness when idle
+- Detects unresponsive clients through timely health checks
+- Closes stale connections automatically
+- Prevents resource exhaustion from dead connections
+
+[NOTE]
+====
+`HTTP/2` `PING` frame-based health checks require `idleTimeout` to be configured as a prerequisite.
+Without idle timeout configuration, PING frames will not be sent and connections may remain open indefinitely,
+preventing proper detection of inactive or unresponsive connections.
+
+The idle timeout and PING settings work together:
+
+1. Connection becomes idle (no activity for `idleTimeout`)
+2. A PING frame is sent to check if the client is responsive
+3. If no ACK within `pingAckTimeout`, retry based on `pingAckDropThreshold`
+4. If all attempts fail, the connection is closed
+====
+
+To enable `PING` frames for `HTTP/2` connections, configure the `HttpServer` as follows:
+
+{examples-link}/liveness/Application.java
+----
+include::{examples-dir}/liveness/Application.java[lines=26..50]
+----
+<1> Configure `idleTimeout` to enable PING-based health checks. When a connection is idle for this duration, a PING frame will be sent.
+<2> Configure `pingAckTimeout` - the maximum time to wait for each PING ACK response. If no ACK is received within this timeout, another PING is sent (up to the threshold).
+<3> Configure `pingAckDropThreshold` - the maximum number of PING frames to send before closing the connection. For example, `2` means send up to 2 PING frames (if first fails, try once more) before closing.
+
 [[http-server-ssl-tls-timeout]]
 === SSL/TLS Timeout
 `HttpServer` supports the SSL/TLS functionality provided by Netty.

reactor-netty-core/src/main/java/reactor/netty/resources/PooledConnectionProvider.java

@@ -644,6 +644,11 @@ public AllocationStrategy<?> allocationStrategy() {
 			return allocationStrategy;
 		}
 
+		@Nullable
+		public BiPredicate<Connection, ConnectionMetadata> evictionPredicate() {
+			return evictionPredicate;
+		}
+
 		public long maxIdleTime() {
 			return this.maxIdleTime;
 		}

reactor-netty-examples/src/main/java/reactor/netty/examples/documentation/http/client/liveness/Application.java

@@ -0,0 +1,52 @@
+/*
+ * Copyright (c) 2025 VMware, Inc. or its affiliates, All Rights Reserved.
+ *
+ * Licensed 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
+ *
+ *   https://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 reactor.netty.examples.documentation.http.client.liveness;
+
+import io.netty.handler.codec.http.HttpHeaders;
+import reactor.core.publisher.Mono;
+import reactor.netty.http.HttpProtocol;
+import reactor.netty.http.client.HttpClient;
+import reactor.netty.resources.ConnectionProvider;
+import reactor.util.function.Tuple2;
+
+import java.time.Duration;
+
+public class Application {
+
+	public static void main(String[] args) {
+		ConnectionProvider provider =
+				ConnectionProvider.builder("liveness")
+				                  .maxIdleTime(Duration.ofSeconds(2))                              //<1>
+				                  .build();
+
+		HttpClient client =
+				HttpClient.create(provider)
+				          .protocol(HttpProtocol.H2)
+				          .secure()
+				          .http2Settings(builder -> builder.pingAckTimeout(Duration.ofMillis(600)) //<2>
+				                                           .pingAckDropThreshold(2));              //<3>
+
+		Tuple2<String, HttpHeaders> response =
+				client.get()
+				      .uri("https://example.com/")
+				      .responseSingle((res, bytes) -> bytes.asString()
+				                                           .zipWith(Mono.just(res.responseHeaders())))
+				      .block();
+
+		System.out.println("Used stream ID: " + response.getT2().get("x-http2-stream-id"));
+		System.out.println("Response: " + response.getT1());
+	}
+}

reactor-netty-examples/src/main/java/reactor/netty/examples/documentation/http/server/liveness/Application.java

@@ -0,0 +1,47 @@
+/*
+ * Copyright (c) 2025 VMware, Inc. or its affiliates, All Rights Reserved.
+ *
+ * Licensed 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
+ *
+ *   https://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 reactor.netty.examples.documentation.http.server.liveness;
+
+import reactor.netty.DisposableServer;
+import reactor.netty.http.Http2SslContextSpec;
+import reactor.netty.http.HttpProtocol;
+import reactor.netty.http.server.HttpServer;
+
+import java.io.File;
+import java.time.Duration;
+
+public class Application {
+
+	public static void main(String[] args) {
+		File cert = new File("certificate.crt");
+		File key = new File("private.key");
+
+		Http2SslContextSpec http2SslContextSpec = Http2SslContextSpec.forServer(cert, key);
+
+		DisposableServer server =
+				HttpServer.create()
+				          .port(8080)
+				          .protocol(HttpProtocol.H2)
+				          .secure(spec -> spec.sslContext(http2SslContextSpec))
+				          .idleTimeout(Duration.ofSeconds(1))                                      //<1>
+				          .http2Settings(builder -> builder.pingAckTimeout(Duration.ofMillis(600)) //<2>
+				                                           .pingAckDropThreshold(2))               //<3>
+				          .bindNow();
+
+		server.onDispose()
+		      .block();
+	}
+}

reactor-netty-http/build.gradle

@@ -144,6 +144,7 @@ dependencies {
 	testImplementation "io.specto:hoverfly-java-junit5:$hoverflyJavaVersion"
 	testImplementation "org.apache.tomcat.embed:tomcat-embed-core:$tomcatVersion"
 	testImplementation "io.projectreactor:reactor-test:$testAddonVersion"
+	testImplementation "io.projectreactor.addons:reactor-extra:$reactorAddonsVersion"
 	testImplementation "org.assertj:assertj-core:$assertJVersion"
 	testImplementation "org.awaitility:awaitility:$awaitilityVersion"
 	testImplementation "org.junit.jupiter:junit-jupiter-api:$junitVersion"