Support a handler for checking connection status using Ping frame in HTTP/2

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

@@ -318,6 +318,10 @@ include::{examples-dir}/http2/H2Application.java[lines=18..42]
 ----
 <1> Configures the client to support only `HTTP/2`
 <2> Configures `SSL`
+<3> Sets the interval for sending `HTTP/2` `PING` frames and receiving `ACK` responses
+<4> Sets the execution interval for the scheduler that sends `HTTP/2` `PING frames and periodically checks for `ACK` responses
+<5> Sets the threshold for retrying `HTTP/2` `PING` frame transmissions.
+
 
 The following listing presents a simple `H2C` example:
 

reactor-netty-core/src/main/java/reactor/netty/NettyPipeline.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2011-2024 VMware, Inc. or its affiliates, All Rights Reserved.
+ * Copyright (c) 2011-2025 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.
@@ -111,6 +111,7 @@ public interface NettyPipeline {
 	String OnChannelReadIdle     = LEFT + "onChannelReadIdle";
 	String OnChannelWriteIdle    = LEFT + "onChannelWriteIdle";
 	String ProxyHandler          = LEFT + "proxyHandler";
+	String H2LivenessHandler     = LEFT + "h2LivenessHandler";
 	/**
 	 * Use to register a special handler which ensures that any {@link io.netty.channel.VoidChannelPromise}
 	 * will be converted to "unvoided" promises.

reactor-netty-examples/src/main/java/reactor/netty/examples/documentation/http/client/http2/H2Application.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020-2021 VMware, Inc. or its affiliates, All Rights Reserved.
+ * Copyright (c) 2020-2025 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.
@@ -21,13 +21,20 @@
 import reactor.netty.http.client.HttpClient;
 import reactor.util.function.Tuple2;
 
+import java.time.Duration;
+
 public class H2Application {
 
 	public static void main(String[] args) {
 		HttpClient client =
 				HttpClient.create()
 				          .protocol(HttpProtocol.H2) //<1>
-				          .secure();                 //<2>
+				          .secure()                 //<2>
+						  .http2Settings(
+								  builder -> builder.pingAckTimeout(Duration.ofMillis(600))  // <3>
+										  .pingScheduleInterval(Duration.ofMillis(300))  // <4>
+										  .pingAckDropThreshold(2)  // <5>
+						  );
 
 		Tuple2<String, HttpHeaders> response =
 				client.get()

reactor-netty-http/src/main/java/reactor/netty/http/Http2SettingsSpec.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020-2023 VMware, Inc. or its affiliates, All Rights Reserved.
+ * Copyright (c) 2020-2025 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.
@@ -19,6 +19,7 @@
 import io.netty.handler.codec.http2.Http2Settings;
 import reactor.util.annotation.Nullable;
 
+import java.time.Duration;
 import java.util.Objects;
 
 /**
@@ -93,6 +94,79 @@ public interface Builder {
 		 * @return {@code this}
 		 */
 		//Builder pushEnabled(boolean pushEnabled);
+
+		/**
+		 * Sets the interval for sending HTTP/2 PING frames and receiving ACK responses.
+		 *
+		 * <p>
+		 * This method configures the time interval at which PING frames are sent to the peer.
+		 * The interval should be chosen carefully to balance between detecting connection issues
+		 * and minimizing unnecessary network traffic.
+		 * </p>
+		 *
+		 * <p>
+		 * If the interval is set too short, it may cause excessive network overhead.
+		 * If set too long, connection failures may not be detected in a timely manner.
+		 * </p>
+		 *
+		 * @param pingAckTimeout the interval in between consecutive PING frames
+		 *                       and ACK responses. Must be a positive value.
+		 */
+		default Builder pingAckTimeout(Duration pingAckTimeout) {
+			return this;
+		}
+
+		/**
+		 * Sets the execution interval for the scheduler that sends HTTP/2 PING frames
+		 * and periodically checks for ACK responses.
+		 *
+		 * <p>
+		 * This method configures the time interval at which the scheduler runs
+		 * to send PING frames and verify if ACK responses are received within
+		 * the expected timeframe.
+		 * Proper tuning of this interval helps in detecting connection issues
+		 * while avoiding unnecessary network overhead.
+		 * </p>
+		 *
+		 * <p>
+		 * If the interval is too short, it may increase network and CPU usage.
+		 * Conversely, setting it too long may delay the detection of connection failures.
+		 * </p>
+		 *
+		 * @param pingScheduleInterval the interval in at which the scheduler executes.
+		 *                       Must be a positive value.
+		 */
+		default Builder pingScheduleInterval(Duration pingScheduleInterval) {
+			return this;
+		}
+
+		/**
+		 * Sets the threshold for retrying HTTP/2 PING frame transmissions.
+		 *
+		 * <p>
+		 * This method defines the maximum number of attempts to send a PING frame
+		 * before considering the connection as unresponsive.
+		 * If the threshold is exceeded without receiving an ACK response,
+		 * the connection may be closed or marked as unhealthy.
+		 * </p>
+		 *
+		 * <p>
+		 * A lower threshold can detect connection failures more quickly but may lead
+		 * to premature disconnections. Conversely, a higher threshold allows more retries
+		 * but may delay failure detection.
+		 * </p>
+		 *
+		 * <p>
+		 * If this value is not specified, it defaults to 0, meaning only one attempt to send a PING frame is made without retries.
+		 * </p>
+		 *
+		 * @param pingAckDropThreshold the maximum number of PING transmission attempts.
+		 *                 Must be a positive integer.
+		 *                 The default value is 0, meaning no retries will occur and only one PING frame will be sent.
+		 */
+		default Builder pingAckDropThreshold(Integer pingAckDropThreshold) {
+			return this;
+		}
 	}
 
 	/**
@@ -176,6 +250,36 @@ public Boolean pushEnabled() {
 		return pushEnabled;
 	}
 
+	/**
+	 * Returns the configured {@code pingAckTimeout} value or null.
+	 *
+	 * @return the configured {@code pingAckTimeout} value or null
+	 */
+	@Nullable
+	public Duration pingAckTimeout() {
+		return pingAckTimeout;
+	}
+
+	/**
+	 * Returns the configured {@code pingScheduleInterval} value or null.
+	 *
+	 * @return the configured {@code pingScheduleInterval} value or null
+	 */
+	@Nullable
+	public Duration pingScheduleInterval() {
+		return pingScheduleInterval;
+	}
+
+	/**
+	 * Returns the configured {@code pingAckDropThreshold} value or null.
+	 *
+	 * @return the configured {@code pingAckDropThreshold} value or null
+	 */
+	@Nullable
+	public Integer pingAckDropThreshold() {
+		return pingAckDropThreshold;
+	}
+
 	@Override
 	public boolean equals(Object o) {
 		if (this == o) {
@@ -191,7 +295,10 @@ public boolean equals(Object o) {
 				Objects.equals(maxFrameSize, that.maxFrameSize) &&
 				maxHeaderListSize.equals(that.maxHeaderListSize) &&
 				Objects.equals(maxStreams, that.maxStreams) &&
-				Objects.equals(pushEnabled, that.pushEnabled);
+				Objects.equals(pushEnabled, that.pushEnabled) &&
+				Objects.equals(pingAckTimeout, that.pingAckTimeout) &&
+				Objects.equals(pingScheduleInterval, that.pingScheduleInterval) &&
+				Objects.equals(pingAckDropThreshold, that.pingAckDropThreshold);
 	}
 
 	@Override
@@ -204,6 +311,9 @@ public int hashCode() {
 		result = 31 * result + Long.hashCode(maxHeaderListSize);
 		result = 31 * result + Long.hashCode(maxStreams);
 		result = 31 * result + Boolean.hashCode(pushEnabled);
+		result = 31 * result + Objects.hashCode(pingAckTimeout);
+		result = 31 * result + Objects.hashCode(pingScheduleInterval);
+		result = 31 * result + Objects.hashCode(pingAckDropThreshold);
 		return result;
 	}
 
@@ -214,6 +324,9 @@ public int hashCode() {
 	final Long maxHeaderListSize;
 	final Long maxStreams;
 	final Boolean pushEnabled;
+	final Duration pingAckTimeout;
+	final Duration pingScheduleInterval;
+	final Integer pingAckDropThreshold;
 
 	Http2SettingsSpec(Build build) {
 		Http2Settings settings = build.http2Settings;
@@ -230,10 +343,16 @@ public int hashCode() {
 		maxHeaderListSize = settings.maxHeaderListSize();
 		maxStreams = build.maxStreams;
 		pushEnabled = settings.pushEnabled();
+		pingAckTimeout = build.pingAckTimeout;
+		pingScheduleInterval = build.pingScheduleInterval;
+		pingAckDropThreshold = build.pingAckDropThreshold;
 	}
 
 	static final class Build implements Builder {
 		Long maxStreams;
+		Duration pingAckTimeout;
+		Duration pingScheduleInterval;
+		Integer pingAckDropThreshold;
 		final Http2Settings http2Settings = Http2Settings.defaultSettings();
 
 		@Override
@@ -280,6 +399,24 @@ public Builder maxStreams(long maxStreams) {
 			return this;
 		}
 
+		@Override
+		public Builder pingAckTimeout(Duration pingAckTimeout) {
+			this.pingAckTimeout = pingAckTimeout;
+			return this;
+		}
+
+		@Override
+		public Builder pingScheduleInterval(Duration pingScheduleInterval) {
+			this.pingScheduleInterval = pingScheduleInterval;
+			return this;
+		}
+
+		@Override
+		public Builder pingAckDropThreshold(Integer pingAckDropThreshold) {
+			this.pingAckDropThreshold = pingAckDropThreshold;
+			return this;
+		}
+
 		/*
 		@Override
 		public Builder pushEnabled(boolean pushEnabled) {