kirktrue commented on code in PR #14364:
URL: https://github.com/apache/kafka/pull/14364#discussion_r1332168444


##########
clients/src/main/java/org/apache/kafka/clients/consumer/internals/HeartbeatRequestManager.java:
##########
@@ -0,0 +1,287 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF 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.apache.kafka.clients.consumer.internals;
+
+import org.apache.kafka.clients.CommonClientConfigs;
+import org.apache.kafka.clients.consumer.ConsumerConfig;
+import org.apache.kafka.common.KafkaException;
+import org.apache.kafka.common.errors.GroupAuthorizationException;
+import org.apache.kafka.common.message.ConsumerGroupHeartbeatRequestData;
+import org.apache.kafka.common.protocol.Errors;
+import org.apache.kafka.common.requests.ConsumerGroupHeartbeatRequest;
+import org.apache.kafka.common.requests.ConsumerGroupHeartbeatResponse;
+import org.apache.kafka.common.utils.LogContext;
+import org.apache.kafka.common.utils.Time;
+import org.apache.kafka.common.utils.Timer;
+import org.slf4j.Logger;
+
+import java.util.ArrayList;
+import java.util.Collections;
+
+/**
+ * Manages the request creation and response handling for the heartbeat. The 
module creates a {@link ConsumerGroupHeartbeatRequest}
+ * using the state stored in the {@link MembershipManager} and enqueue it to 
the network queue to be sent out. Once
+ * the response is received, the module will update the state in the {@link 
MembershipManager} and handle any errors.
+ *
+ * The manager only emits heartbeat when the member is in a group. If the 
member is not in a group, or the
+ * coordinator is lost, the heartbeat won't be sent.
+ *
+ * If the heartbeat request fails, the module will trigger the exponential 
backoff, and resend the request. See
+ * {@link HeartbeatRequestState} for more details.
+ */
+public class HeartbeatRequestManager implements RequestManager {
+    private final Time time;
+    private final Logger logger;
+
+    private final int rebalanceTimeoutMs;
+
+    private final CoordinatorRequestManager coordinatorRequestManager;
+    private final SubscriptionState subscriptions;
+    private final HeartbeatRequestState heartbeatRequestState;
+    private final MembershipManager membershipManager;
+    private final ErrorEventHandler nonRetriableErrorHandler;
+
+    public HeartbeatRequestManager(
+        final Time time,
+        final LogContext logContext,
+        final ConsumerConfig config,
+        final CoordinatorRequestManager coordinatorRequestManager,
+        final SubscriptionState subscriptions,
+        final MembershipManager membershipManager,
+        final ErrorEventHandler nonRetriableErrorHandler) {
+        this.coordinatorRequestManager = coordinatorRequestManager;
+        this.time = time;
+        this.logger = logContext.logger(getClass());
+        this.subscriptions = subscriptions;
+        this.membershipManager = membershipManager;
+        this.nonRetriableErrorHandler = nonRetriableErrorHandler;
+        this.rebalanceTimeoutMs = 
config.getInt(CommonClientConfigs.MAX_POLL_INTERVAL_MS_CONFIG);
+        long retryBackoffMs = 
config.getLong(ConsumerConfig.RETRY_BACKOFF_MS_CONFIG);
+        long retryBackoffMaxMs = 
config.getLong(ConsumerConfig.RETRY_BACKOFF_MAX_MS_CONFIG);
+        this.heartbeatRequestState = new HeartbeatRequestState(logContext, 
time, 0, retryBackoffMs,
+            retryBackoffMaxMs, rebalanceTimeoutMs);
+    }
+
+    // Visible for testing
+    HeartbeatRequestManager(
+        final Time time,
+        final LogContext logContext,
+        final ConsumerConfig config,
+        final CoordinatorRequestManager coordinatorRequestManager,
+        final SubscriptionState subscriptions,
+        final MembershipManager membershipManager,
+        final HeartbeatRequestState heartbeatRequestState,
+        final ErrorEventHandler nonRetriableErrorHandler) {
+        this.time = time;
+        this.logger = logContext.logger(this.getClass());
+        this.subscriptions = subscriptions;
+        this.rebalanceTimeoutMs = 
config.getInt(CommonClientConfigs.MAX_POLL_INTERVAL_MS_CONFIG);
+        this.coordinatorRequestManager = coordinatorRequestManager;
+        this.heartbeatRequestState = heartbeatRequestState;
+        this.membershipManager = membershipManager;
+        this.nonRetriableErrorHandler = nonRetriableErrorHandler;
+    }
+
+    @Override
+    public NetworkClientDelegate.PollResult poll(long currentTimeMs) {
+        if (!coordinatorRequestManager.coordinator().isPresent() || 
!membershipManager.shouldSendHeartbeat()) {
+            return new NetworkClientDelegate.PollResult(
+                Long.MAX_VALUE, Collections.emptyList());
+        }
+
+        if (!heartbeatRequestState.canSendRequest(currentTimeMs)) {
+            return new NetworkClientDelegate.PollResult(
+                heartbeatRequestState.nextHeartbeatMs(currentTimeMs),
+                Collections.emptyList());
+        }
+        this.heartbeatRequestState.onSendAttempt(currentTimeMs);
+        NetworkClientDelegate.UnsentRequest request = makeHeartbeatRequest();
+        // return Long.MAX_VALUE because we will update the timer when the 
response is received
+        return new NetworkClientDelegate.PollResult(Long.MAX_VALUE, 
Collections.singletonList(request));
+    }
+
+    private NetworkClientDelegate.UnsentRequest makeHeartbeatRequest() {
+        ConsumerGroupHeartbeatRequestData data = new 
ConsumerGroupHeartbeatRequestData()
+            .setGroupId(membershipManager.groupId())
+            .setMemberEpoch(membershipManager.memberEpoch())
+            .setMemberId(membershipManager.memberId())
+            .setRebalanceTimeoutMs(rebalanceTimeoutMs);
+
+        membershipManager.groupInstanceId().ifPresent(data::setInstanceId);
+
+        if (this.subscriptions.hasPatternSubscription()) {
+            // We haven't discsussed how Regex is stored in the consumer. We 
could do it in the subscriptionState
+            // , in the memberStateManager, or here.
+            // data.setSubscribedTopicRegex(regex)
+        } else {
+            data.setSubscribedTopicNames(new 
ArrayList<>(this.subscriptions.subscription()));
+        }
+
+        
this.membershipManager.assignorSelection().serverAssignor().ifPresent(data::setServerAssignor);
+
+        NetworkClientDelegate.UnsentRequest request = new 
NetworkClientDelegate.UnsentRequest(
+            new ConsumerGroupHeartbeatRequest.Builder(data),
+            coordinatorRequestManager.coordinator());
+
+        request.future().whenComplete((response, exception) -> {
+            if (exception == null) {
+                onResponse((ConsumerGroupHeartbeatResponse) 
response.responseBody(), response.receivedTimeMs());
+            } else {
+                onFailure(exception, response.receivedTimeMs());
+            }
+        });
+        return request;
+    }
+
+    private void onFailure(final Throwable exception, final long 
responseTimeMs) {
+        this.heartbeatRequestState.onFailedAttempt(responseTimeMs);
+        logger.debug("failed sending heartbeat due to {}", 
exception.getMessage());

Review Comment:
   ```suggestion
           logger.warn("Failed to send heartbeat to coordinator node {} due to 
error: {}", coordinatorRequestManager.coordinator(), exception.getMessage());
   ```



##########
clients/src/main/java/org/apache/kafka/clients/consumer/internals/HeartbeatRequestManager.java:
##########
@@ -0,0 +1,287 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF 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.apache.kafka.clients.consumer.internals;
+
+import org.apache.kafka.clients.CommonClientConfigs;
+import org.apache.kafka.clients.consumer.ConsumerConfig;
+import org.apache.kafka.common.KafkaException;
+import org.apache.kafka.common.errors.GroupAuthorizationException;
+import org.apache.kafka.common.message.ConsumerGroupHeartbeatRequestData;
+import org.apache.kafka.common.protocol.Errors;
+import org.apache.kafka.common.requests.ConsumerGroupHeartbeatRequest;
+import org.apache.kafka.common.requests.ConsumerGroupHeartbeatResponse;
+import org.apache.kafka.common.utils.LogContext;
+import org.apache.kafka.common.utils.Time;
+import org.apache.kafka.common.utils.Timer;
+import org.slf4j.Logger;
+
+import java.util.ArrayList;
+import java.util.Collections;
+
+/**
+ * Manages the request creation and response handling for the heartbeat. The 
module creates a {@link ConsumerGroupHeartbeatRequest}
+ * using the state stored in the {@link MembershipManager} and enqueue it to 
the network queue to be sent out. Once
+ * the response is received, the module will update the state in the {@link 
MembershipManager} and handle any errors.
+ *
+ * The manager only emits heartbeat when the member is in a group. If the 
member is not in a group, or the
+ * coordinator is lost, the heartbeat won't be sent.
+ *
+ * If the heartbeat request fails, the module will trigger the exponential 
backoff, and resend the request. See
+ * {@link HeartbeatRequestState} for more details.
+ */
+public class HeartbeatRequestManager implements RequestManager {
+    private final Time time;
+    private final Logger logger;
+
+    private final int rebalanceTimeoutMs;
+
+    private final CoordinatorRequestManager coordinatorRequestManager;
+    private final SubscriptionState subscriptions;
+    private final HeartbeatRequestState heartbeatRequestState;
+    private final MembershipManager membershipManager;
+    private final ErrorEventHandler nonRetriableErrorHandler;
+
+    public HeartbeatRequestManager(
+        final Time time,
+        final LogContext logContext,
+        final ConsumerConfig config,
+        final CoordinatorRequestManager coordinatorRequestManager,
+        final SubscriptionState subscriptions,
+        final MembershipManager membershipManager,
+        final ErrorEventHandler nonRetriableErrorHandler) {
+        this.coordinatorRequestManager = coordinatorRequestManager;
+        this.time = time;
+        this.logger = logContext.logger(getClass());
+        this.subscriptions = subscriptions;
+        this.membershipManager = membershipManager;
+        this.nonRetriableErrorHandler = nonRetriableErrorHandler;
+        this.rebalanceTimeoutMs = 
config.getInt(CommonClientConfigs.MAX_POLL_INTERVAL_MS_CONFIG);
+        long retryBackoffMs = 
config.getLong(ConsumerConfig.RETRY_BACKOFF_MS_CONFIG);
+        long retryBackoffMaxMs = 
config.getLong(ConsumerConfig.RETRY_BACKOFF_MAX_MS_CONFIG);
+        this.heartbeatRequestState = new HeartbeatRequestState(logContext, 
time, 0, retryBackoffMs,
+            retryBackoffMaxMs, rebalanceTimeoutMs);
+    }
+
+    // Visible for testing
+    HeartbeatRequestManager(
+        final Time time,
+        final LogContext logContext,
+        final ConsumerConfig config,
+        final CoordinatorRequestManager coordinatorRequestManager,
+        final SubscriptionState subscriptions,
+        final MembershipManager membershipManager,
+        final HeartbeatRequestState heartbeatRequestState,
+        final ErrorEventHandler nonRetriableErrorHandler) {
+        this.time = time;
+        this.logger = logContext.logger(this.getClass());
+        this.subscriptions = subscriptions;
+        this.rebalanceTimeoutMs = 
config.getInt(CommonClientConfigs.MAX_POLL_INTERVAL_MS_CONFIG);
+        this.coordinatorRequestManager = coordinatorRequestManager;
+        this.heartbeatRequestState = heartbeatRequestState;
+        this.membershipManager = membershipManager;
+        this.nonRetriableErrorHandler = nonRetriableErrorHandler;
+    }
+
+    @Override
+    public NetworkClientDelegate.PollResult poll(long currentTimeMs) {
+        if (!coordinatorRequestManager.coordinator().isPresent() || 
!membershipManager.shouldSendHeartbeat()) {
+            return new NetworkClientDelegate.PollResult(
+                Long.MAX_VALUE, Collections.emptyList());
+        }
+
+        if (!heartbeatRequestState.canSendRequest(currentTimeMs)) {
+            return new NetworkClientDelegate.PollResult(
+                heartbeatRequestState.nextHeartbeatMs(currentTimeMs),
+                Collections.emptyList());
+        }
+        this.heartbeatRequestState.onSendAttempt(currentTimeMs);
+        NetworkClientDelegate.UnsentRequest request = makeHeartbeatRequest();
+        // return Long.MAX_VALUE because we will update the timer when the 
response is received
+        return new NetworkClientDelegate.PollResult(Long.MAX_VALUE, 
Collections.singletonList(request));
+    }
+
+    private NetworkClientDelegate.UnsentRequest makeHeartbeatRequest() {
+        ConsumerGroupHeartbeatRequestData data = new 
ConsumerGroupHeartbeatRequestData()
+            .setGroupId(membershipManager.groupId())
+            .setMemberEpoch(membershipManager.memberEpoch())
+            .setMemberId(membershipManager.memberId())
+            .setRebalanceTimeoutMs(rebalanceTimeoutMs);
+
+        membershipManager.groupInstanceId().ifPresent(data::setInstanceId);
+
+        if (this.subscriptions.hasPatternSubscription()) {
+            // We haven't discsussed how Regex is stored in the consumer. We 
could do it in the subscriptionState
+            // , in the memberStateManager, or here.
+            // data.setSubscribedTopicRegex(regex)
+        } else {
+            data.setSubscribedTopicNames(new 
ArrayList<>(this.subscriptions.subscription()));
+        }
+
+        
this.membershipManager.assignorSelection().serverAssignor().ifPresent(data::setServerAssignor);
+
+        NetworkClientDelegate.UnsentRequest request = new 
NetworkClientDelegate.UnsentRequest(
+            new ConsumerGroupHeartbeatRequest.Builder(data),
+            coordinatorRequestManager.coordinator());
+
+        request.future().whenComplete((response, exception) -> {
+            if (exception == null) {
+                onResponse((ConsumerGroupHeartbeatResponse) 
response.responseBody(), response.receivedTimeMs());
+            } else {
+                onFailure(exception, response.receivedTimeMs());
+            }
+        });
+        return request;
+    }
+
+    private void onFailure(final Throwable exception, final long 
responseTimeMs) {
+        this.heartbeatRequestState.onFailedAttempt(responseTimeMs);
+        logger.debug("failed sending heartbeat due to {}", 
exception.getMessage());
+    }
+
+    private void onResponse(final ConsumerGroupHeartbeatResponse response, 
long currentTimeMs) {
+        if (response.data().errorCode() == Errors.NONE.code()) {

Review Comment:
   Can we resolve the error code to an `Errors` object via `Errors.forCode()`?



##########
clients/src/main/java/org/apache/kafka/clients/consumer/internals/HeartbeatRequestManager.java:
##########
@@ -0,0 +1,287 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF 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.apache.kafka.clients.consumer.internals;
+
+import org.apache.kafka.clients.CommonClientConfigs;
+import org.apache.kafka.clients.consumer.ConsumerConfig;
+import org.apache.kafka.common.KafkaException;
+import org.apache.kafka.common.errors.GroupAuthorizationException;
+import org.apache.kafka.common.message.ConsumerGroupHeartbeatRequestData;
+import org.apache.kafka.common.protocol.Errors;
+import org.apache.kafka.common.requests.ConsumerGroupHeartbeatRequest;
+import org.apache.kafka.common.requests.ConsumerGroupHeartbeatResponse;
+import org.apache.kafka.common.utils.LogContext;
+import org.apache.kafka.common.utils.Time;
+import org.apache.kafka.common.utils.Timer;
+import org.slf4j.Logger;
+
+import java.util.ArrayList;
+import java.util.Collections;
+
+/**
+ * Manages the request creation and response handling for the heartbeat. The 
module creates a {@link ConsumerGroupHeartbeatRequest}
+ * using the state stored in the {@link MembershipManager} and enqueue it to 
the network queue to be sent out. Once
+ * the response is received, the module will update the state in the {@link 
MembershipManager} and handle any errors.
+ *
+ * The manager only emits heartbeat when the member is in a group. If the 
member is not in a group, or the
+ * coordinator is lost, the heartbeat won't be sent.
+ *
+ * If the heartbeat request fails, the module will trigger the exponential 
backoff, and resend the request. See
+ * {@link HeartbeatRequestState} for more details.
+ */
+public class HeartbeatRequestManager implements RequestManager {
+    private final Time time;
+    private final Logger logger;
+
+    private final int rebalanceTimeoutMs;
+
+    private final CoordinatorRequestManager coordinatorRequestManager;
+    private final SubscriptionState subscriptions;
+    private final HeartbeatRequestState heartbeatRequestState;
+    private final MembershipManager membershipManager;
+    private final ErrorEventHandler nonRetriableErrorHandler;
+
+    public HeartbeatRequestManager(
+        final Time time,
+        final LogContext logContext,
+        final ConsumerConfig config,
+        final CoordinatorRequestManager coordinatorRequestManager,
+        final SubscriptionState subscriptions,
+        final MembershipManager membershipManager,
+        final ErrorEventHandler nonRetriableErrorHandler) {
+        this.coordinatorRequestManager = coordinatorRequestManager;
+        this.time = time;
+        this.logger = logContext.logger(getClass());
+        this.subscriptions = subscriptions;
+        this.membershipManager = membershipManager;
+        this.nonRetriableErrorHandler = nonRetriableErrorHandler;
+        this.rebalanceTimeoutMs = 
config.getInt(CommonClientConfigs.MAX_POLL_INTERVAL_MS_CONFIG);
+        long retryBackoffMs = 
config.getLong(ConsumerConfig.RETRY_BACKOFF_MS_CONFIG);
+        long retryBackoffMaxMs = 
config.getLong(ConsumerConfig.RETRY_BACKOFF_MAX_MS_CONFIG);
+        this.heartbeatRequestState = new HeartbeatRequestState(logContext, 
time, 0, retryBackoffMs,
+            retryBackoffMaxMs, rebalanceTimeoutMs);
+    }
+
+    // Visible for testing
+    HeartbeatRequestManager(
+        final Time time,
+        final LogContext logContext,
+        final ConsumerConfig config,
+        final CoordinatorRequestManager coordinatorRequestManager,
+        final SubscriptionState subscriptions,
+        final MembershipManager membershipManager,
+        final HeartbeatRequestState heartbeatRequestState,
+        final ErrorEventHandler nonRetriableErrorHandler) {
+        this.time = time;
+        this.logger = logContext.logger(this.getClass());
+        this.subscriptions = subscriptions;
+        this.rebalanceTimeoutMs = 
config.getInt(CommonClientConfigs.MAX_POLL_INTERVAL_MS_CONFIG);
+        this.coordinatorRequestManager = coordinatorRequestManager;
+        this.heartbeatRequestState = heartbeatRequestState;
+        this.membershipManager = membershipManager;
+        this.nonRetriableErrorHandler = nonRetriableErrorHandler;
+    }
+
+    @Override
+    public NetworkClientDelegate.PollResult poll(long currentTimeMs) {
+        if (!coordinatorRequestManager.coordinator().isPresent() || 
!membershipManager.shouldSendHeartbeat()) {
+            return new NetworkClientDelegate.PollResult(
+                Long.MAX_VALUE, Collections.emptyList());
+        }
+
+        if (!heartbeatRequestState.canSendRequest(currentTimeMs)) {
+            return new NetworkClientDelegate.PollResult(
+                heartbeatRequestState.nextHeartbeatMs(currentTimeMs),
+                Collections.emptyList());
+        }
+        this.heartbeatRequestState.onSendAttempt(currentTimeMs);
+        NetworkClientDelegate.UnsentRequest request = makeHeartbeatRequest();
+        // return Long.MAX_VALUE because we will update the timer when the 
response is received
+        return new NetworkClientDelegate.PollResult(Long.MAX_VALUE, 
Collections.singletonList(request));
+    }
+
+    private NetworkClientDelegate.UnsentRequest makeHeartbeatRequest() {
+        ConsumerGroupHeartbeatRequestData data = new 
ConsumerGroupHeartbeatRequestData()
+            .setGroupId(membershipManager.groupId())
+            .setMemberEpoch(membershipManager.memberEpoch())
+            .setMemberId(membershipManager.memberId())
+            .setRebalanceTimeoutMs(rebalanceTimeoutMs);
+
+        membershipManager.groupInstanceId().ifPresent(data::setInstanceId);
+
+        if (this.subscriptions.hasPatternSubscription()) {
+            // We haven't discsussed how Regex is stored in the consumer. We 
could do it in the subscriptionState
+            // , in the memberStateManager, or here.
+            // data.setSubscribedTopicRegex(regex)
+        } else {
+            data.setSubscribedTopicNames(new 
ArrayList<>(this.subscriptions.subscription()));
+        }
+
+        
this.membershipManager.assignorSelection().serverAssignor().ifPresent(data::setServerAssignor);
+
+        NetworkClientDelegate.UnsentRequest request = new 
NetworkClientDelegate.UnsentRequest(
+            new ConsumerGroupHeartbeatRequest.Builder(data),
+            coordinatorRequestManager.coordinator());
+
+        request.future().whenComplete((response, exception) -> {
+            if (exception == null) {
+                onResponse((ConsumerGroupHeartbeatResponse) 
response.responseBody(), response.receivedTimeMs());
+            } else {
+                onFailure(exception, response.receivedTimeMs());
+            }
+        });
+        return request;
+    }
+
+    private void onFailure(final Throwable exception, final long 
responseTimeMs) {
+        this.heartbeatRequestState.onFailedAttempt(responseTimeMs);
+        logger.debug("failed sending heartbeat due to {}", 
exception.getMessage());
+    }
+
+    private void onResponse(final ConsumerGroupHeartbeatResponse response, 
long currentTimeMs) {
+        if (response.data().errorCode() == Errors.NONE.code()) {
+            
this.heartbeatRequestState.updateHeartbeatIntervalMs(response.data().heartbeatIntervalMs());
+            this.heartbeatRequestState.onSuccessfulAttempt(currentTimeMs);
+            this.heartbeatRequestState.reset();
+            try {
+                membershipManager.updateState(response.data());
+            } catch (KafkaException e) {
+                logger.error("Received unexpected error in heartbeat response: 
{}", e.getMessage());
+            }
+            return;
+        }
+
+        onErrorResponse(response, currentTimeMs);
+    }
+
+    private void onErrorResponse(final ConsumerGroupHeartbeatResponse response,
+                                 final long currentTimeMs) {
+        this.heartbeatRequestState.onFailedAttempt(currentTimeMs);
+        short errorCode = response.data().errorCode();
+        if (errorCode == Errors.NOT_COORDINATOR.code() || errorCode == 
Errors.COORDINATOR_NOT_AVAILABLE.code()) {
+            logInfo("Coordinator is either not started or not valid. 
Retrying", response, currentTimeMs);

Review Comment:
   ```suggestion
               logInfo("Coordinator node {} is either not started or not valid. 
Retrying", coordinatorRequestManager.coordinator(), response, currentTimeMs);
   ```



##########
clients/src/main/java/org/apache/kafka/clients/consumer/internals/HeartbeatRequestManager.java:
##########
@@ -0,0 +1,287 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF 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.apache.kafka.clients.consumer.internals;
+
+import org.apache.kafka.clients.CommonClientConfigs;
+import org.apache.kafka.clients.consumer.ConsumerConfig;
+import org.apache.kafka.common.KafkaException;
+import org.apache.kafka.common.errors.GroupAuthorizationException;
+import org.apache.kafka.common.message.ConsumerGroupHeartbeatRequestData;
+import org.apache.kafka.common.protocol.Errors;
+import org.apache.kafka.common.requests.ConsumerGroupHeartbeatRequest;
+import org.apache.kafka.common.requests.ConsumerGroupHeartbeatResponse;
+import org.apache.kafka.common.utils.LogContext;
+import org.apache.kafka.common.utils.Time;
+import org.apache.kafka.common.utils.Timer;
+import org.slf4j.Logger;
+
+import java.util.ArrayList;
+import java.util.Collections;
+
+/**
+ * Manages the request creation and response handling for the heartbeat. The 
module creates a {@link ConsumerGroupHeartbeatRequest}
+ * using the state stored in the {@link MembershipManager} and enqueue it to 
the network queue to be sent out. Once
+ * the response is received, the module will update the state in the {@link 
MembershipManager} and handle any errors.
+ *
+ * The manager only emits heartbeat when the member is in a group. If the 
member is not in a group, or the
+ * coordinator is lost, the heartbeat won't be sent.
+ *
+ * If the heartbeat request fails, the module will trigger the exponential 
backoff, and resend the request. See
+ * {@link HeartbeatRequestState} for more details.
+ */
+public class HeartbeatRequestManager implements RequestManager {
+    private final Time time;
+    private final Logger logger;
+
+    private final int rebalanceTimeoutMs;
+
+    private final CoordinatorRequestManager coordinatorRequestManager;
+    private final SubscriptionState subscriptions;
+    private final HeartbeatRequestState heartbeatRequestState;
+    private final MembershipManager membershipManager;
+    private final ErrorEventHandler nonRetriableErrorHandler;
+
+    public HeartbeatRequestManager(
+        final Time time,
+        final LogContext logContext,
+        final ConsumerConfig config,
+        final CoordinatorRequestManager coordinatorRequestManager,
+        final SubscriptionState subscriptions,
+        final MembershipManager membershipManager,
+        final ErrorEventHandler nonRetriableErrorHandler) {
+        this.coordinatorRequestManager = coordinatorRequestManager;
+        this.time = time;
+        this.logger = logContext.logger(getClass());
+        this.subscriptions = subscriptions;
+        this.membershipManager = membershipManager;
+        this.nonRetriableErrorHandler = nonRetriableErrorHandler;
+        this.rebalanceTimeoutMs = 
config.getInt(CommonClientConfigs.MAX_POLL_INTERVAL_MS_CONFIG);
+        long retryBackoffMs = 
config.getLong(ConsumerConfig.RETRY_BACKOFF_MS_CONFIG);
+        long retryBackoffMaxMs = 
config.getLong(ConsumerConfig.RETRY_BACKOFF_MAX_MS_CONFIG);
+        this.heartbeatRequestState = new HeartbeatRequestState(logContext, 
time, 0, retryBackoffMs,
+            retryBackoffMaxMs, rebalanceTimeoutMs);
+    }
+
+    // Visible for testing
+    HeartbeatRequestManager(
+        final Time time,
+        final LogContext logContext,
+        final ConsumerConfig config,
+        final CoordinatorRequestManager coordinatorRequestManager,
+        final SubscriptionState subscriptions,
+        final MembershipManager membershipManager,
+        final HeartbeatRequestState heartbeatRequestState,
+        final ErrorEventHandler nonRetriableErrorHandler) {
+        this.time = time;
+        this.logger = logContext.logger(this.getClass());
+        this.subscriptions = subscriptions;
+        this.rebalanceTimeoutMs = 
config.getInt(CommonClientConfigs.MAX_POLL_INTERVAL_MS_CONFIG);
+        this.coordinatorRequestManager = coordinatorRequestManager;
+        this.heartbeatRequestState = heartbeatRequestState;
+        this.membershipManager = membershipManager;
+        this.nonRetriableErrorHandler = nonRetriableErrorHandler;
+    }
+
+    @Override
+    public NetworkClientDelegate.PollResult poll(long currentTimeMs) {
+        if (!coordinatorRequestManager.coordinator().isPresent() || 
!membershipManager.shouldSendHeartbeat()) {
+            return new NetworkClientDelegate.PollResult(
+                Long.MAX_VALUE, Collections.emptyList());
+        }
+
+        if (!heartbeatRequestState.canSendRequest(currentTimeMs)) {
+            return new NetworkClientDelegate.PollResult(
+                heartbeatRequestState.nextHeartbeatMs(currentTimeMs),
+                Collections.emptyList());
+        }
+        this.heartbeatRequestState.onSendAttempt(currentTimeMs);
+        NetworkClientDelegate.UnsentRequest request = makeHeartbeatRequest();
+        // return Long.MAX_VALUE because we will update the timer when the 
response is received
+        return new NetworkClientDelegate.PollResult(Long.MAX_VALUE, 
Collections.singletonList(request));
+    }
+
+    private NetworkClientDelegate.UnsentRequest makeHeartbeatRequest() {
+        ConsumerGroupHeartbeatRequestData data = new 
ConsumerGroupHeartbeatRequestData()
+            .setGroupId(membershipManager.groupId())
+            .setMemberEpoch(membershipManager.memberEpoch())
+            .setMemberId(membershipManager.memberId())
+            .setRebalanceTimeoutMs(rebalanceTimeoutMs);
+
+        membershipManager.groupInstanceId().ifPresent(data::setInstanceId);
+
+        if (this.subscriptions.hasPatternSubscription()) {
+            // We haven't discsussed how Regex is stored in the consumer. We 
could do it in the subscriptionState
+            // , in the memberStateManager, or here.
+            // data.setSubscribedTopicRegex(regex)
+        } else {
+            data.setSubscribedTopicNames(new 
ArrayList<>(this.subscriptions.subscription()));
+        }
+
+        
this.membershipManager.assignorSelection().serverAssignor().ifPresent(data::setServerAssignor);
+
+        NetworkClientDelegate.UnsentRequest request = new 
NetworkClientDelegate.UnsentRequest(
+            new ConsumerGroupHeartbeatRequest.Builder(data),
+            coordinatorRequestManager.coordinator());
+
+        request.future().whenComplete((response, exception) -> {
+            if (exception == null) {
+                onResponse((ConsumerGroupHeartbeatResponse) 
response.responseBody(), response.receivedTimeMs());
+            } else {
+                onFailure(exception, response.receivedTimeMs());
+            }
+        });
+        return request;
+    }
+
+    private void onFailure(final Throwable exception, final long 
responseTimeMs) {
+        this.heartbeatRequestState.onFailedAttempt(responseTimeMs);
+        logger.debug("failed sending heartbeat due to {}", 
exception.getMessage());
+    }
+
+    private void onResponse(final ConsumerGroupHeartbeatResponse response, 
long currentTimeMs) {
+        if (response.data().errorCode() == Errors.NONE.code()) {
+            
this.heartbeatRequestState.updateHeartbeatIntervalMs(response.data().heartbeatIntervalMs());
+            this.heartbeatRequestState.onSuccessfulAttempt(currentTimeMs);
+            this.heartbeatRequestState.reset();
+            try {
+                membershipManager.updateState(response.data());
+            } catch (KafkaException e) {
+                logger.error("Received unexpected error in heartbeat response: 
{}", e.getMessage());
+            }
+            return;
+        }
+
+        onErrorResponse(response, currentTimeMs);
+    }
+
+    private void onErrorResponse(final ConsumerGroupHeartbeatResponse response,
+                                 final long currentTimeMs) {
+        this.heartbeatRequestState.onFailedAttempt(currentTimeMs);
+        short errorCode = response.data().errorCode();
+        if (errorCode == Errors.NOT_COORDINATOR.code() || errorCode == 
Errors.COORDINATOR_NOT_AVAILABLE.code()) {

Review Comment:
   Same question here, can we use and compare errors based on `Errors` (which 
we can get via `Errors.forCode()`)?



##########
clients/src/main/java/org/apache/kafka/clients/consumer/internals/HeartbeatRequestManager.java:
##########
@@ -0,0 +1,287 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF 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.apache.kafka.clients.consumer.internals;
+
+import org.apache.kafka.clients.CommonClientConfigs;
+import org.apache.kafka.clients.consumer.ConsumerConfig;
+import org.apache.kafka.common.KafkaException;
+import org.apache.kafka.common.errors.GroupAuthorizationException;
+import org.apache.kafka.common.message.ConsumerGroupHeartbeatRequestData;
+import org.apache.kafka.common.protocol.Errors;
+import org.apache.kafka.common.requests.ConsumerGroupHeartbeatRequest;
+import org.apache.kafka.common.requests.ConsumerGroupHeartbeatResponse;
+import org.apache.kafka.common.utils.LogContext;
+import org.apache.kafka.common.utils.Time;
+import org.apache.kafka.common.utils.Timer;
+import org.slf4j.Logger;
+
+import java.util.ArrayList;
+import java.util.Collections;
+
+/**
+ * Manages the request creation and response handling for the heartbeat. The 
module creates a {@link ConsumerGroupHeartbeatRequest}
+ * using the state stored in the {@link MembershipManager} and enqueue it to 
the network queue to be sent out. Once
+ * the response is received, the module will update the state in the {@link 
MembershipManager} and handle any errors.
+ *
+ * The manager only emits heartbeat when the member is in a group. If the 
member is not in a group, or the
+ * coordinator is lost, the heartbeat won't be sent.
+ *
+ * If the heartbeat request fails, the module will trigger the exponential 
backoff, and resend the request. See
+ * {@link HeartbeatRequestState} for more details.
+ */
+public class HeartbeatRequestManager implements RequestManager {
+    private final Time time;
+    private final Logger logger;
+
+    private final int rebalanceTimeoutMs;
+
+    private final CoordinatorRequestManager coordinatorRequestManager;
+    private final SubscriptionState subscriptions;
+    private final HeartbeatRequestState heartbeatRequestState;
+    private final MembershipManager membershipManager;
+    private final ErrorEventHandler nonRetriableErrorHandler;
+
+    public HeartbeatRequestManager(
+        final Time time,
+        final LogContext logContext,
+        final ConsumerConfig config,
+        final CoordinatorRequestManager coordinatorRequestManager,
+        final SubscriptionState subscriptions,
+        final MembershipManager membershipManager,
+        final ErrorEventHandler nonRetriableErrorHandler) {
+        this.coordinatorRequestManager = coordinatorRequestManager;
+        this.time = time;
+        this.logger = logContext.logger(getClass());
+        this.subscriptions = subscriptions;
+        this.membershipManager = membershipManager;
+        this.nonRetriableErrorHandler = nonRetriableErrorHandler;
+        this.rebalanceTimeoutMs = 
config.getInt(CommonClientConfigs.MAX_POLL_INTERVAL_MS_CONFIG);
+        long retryBackoffMs = 
config.getLong(ConsumerConfig.RETRY_BACKOFF_MS_CONFIG);
+        long retryBackoffMaxMs = 
config.getLong(ConsumerConfig.RETRY_BACKOFF_MAX_MS_CONFIG);
+        this.heartbeatRequestState = new HeartbeatRequestState(logContext, 
time, 0, retryBackoffMs,
+            retryBackoffMaxMs, rebalanceTimeoutMs);
+    }
+
+    // Visible for testing
+    HeartbeatRequestManager(
+        final Time time,
+        final LogContext logContext,
+        final ConsumerConfig config,
+        final CoordinatorRequestManager coordinatorRequestManager,
+        final SubscriptionState subscriptions,
+        final MembershipManager membershipManager,
+        final HeartbeatRequestState heartbeatRequestState,
+        final ErrorEventHandler nonRetriableErrorHandler) {
+        this.time = time;
+        this.logger = logContext.logger(this.getClass());
+        this.subscriptions = subscriptions;
+        this.rebalanceTimeoutMs = 
config.getInt(CommonClientConfigs.MAX_POLL_INTERVAL_MS_CONFIG);
+        this.coordinatorRequestManager = coordinatorRequestManager;
+        this.heartbeatRequestState = heartbeatRequestState;
+        this.membershipManager = membershipManager;
+        this.nonRetriableErrorHandler = nonRetriableErrorHandler;
+    }
+
+    @Override
+    public NetworkClientDelegate.PollResult poll(long currentTimeMs) {
+        if (!coordinatorRequestManager.coordinator().isPresent() || 
!membershipManager.shouldSendHeartbeat()) {
+            return new NetworkClientDelegate.PollResult(
+                Long.MAX_VALUE, Collections.emptyList());
+        }
+
+        if (!heartbeatRequestState.canSendRequest(currentTimeMs)) {
+            return new NetworkClientDelegate.PollResult(
+                heartbeatRequestState.nextHeartbeatMs(currentTimeMs),
+                Collections.emptyList());
+        }
+        this.heartbeatRequestState.onSendAttempt(currentTimeMs);
+        NetworkClientDelegate.UnsentRequest request = makeHeartbeatRequest();
+        // return Long.MAX_VALUE because we will update the timer when the 
response is received
+        return new NetworkClientDelegate.PollResult(Long.MAX_VALUE, 
Collections.singletonList(request));
+    }
+
+    private NetworkClientDelegate.UnsentRequest makeHeartbeatRequest() {
+        ConsumerGroupHeartbeatRequestData data = new 
ConsumerGroupHeartbeatRequestData()
+            .setGroupId(membershipManager.groupId())
+            .setMemberEpoch(membershipManager.memberEpoch())
+            .setMemberId(membershipManager.memberId())
+            .setRebalanceTimeoutMs(rebalanceTimeoutMs);
+
+        membershipManager.groupInstanceId().ifPresent(data::setInstanceId);
+
+        if (this.subscriptions.hasPatternSubscription()) {
+            // We haven't discsussed how Regex is stored in the consumer. We 
could do it in the subscriptionState
+            // , in the memberStateManager, or here.
+            // data.setSubscribedTopicRegex(regex)
+        } else {
+            data.setSubscribedTopicNames(new 
ArrayList<>(this.subscriptions.subscription()));
+        }
+
+        
this.membershipManager.assignorSelection().serverAssignor().ifPresent(data::setServerAssignor);
+
+        NetworkClientDelegate.UnsentRequest request = new 
NetworkClientDelegate.UnsentRequest(
+            new ConsumerGroupHeartbeatRequest.Builder(data),
+            coordinatorRequestManager.coordinator());
+
+        request.future().whenComplete((response, exception) -> {
+            if (exception == null) {
+                onResponse((ConsumerGroupHeartbeatResponse) 
response.responseBody(), response.receivedTimeMs());
+            } else {
+                onFailure(exception, response.receivedTimeMs());
+            }
+        });
+        return request;
+    }
+
+    private void onFailure(final Throwable exception, final long 
responseTimeMs) {
+        this.heartbeatRequestState.onFailedAttempt(responseTimeMs);
+        logger.debug("failed sending heartbeat due to {}", 
exception.getMessage());
+    }
+
+    private void onResponse(final ConsumerGroupHeartbeatResponse response, 
long currentTimeMs) {
+        if (response.data().errorCode() == Errors.NONE.code()) {
+            
this.heartbeatRequestState.updateHeartbeatIntervalMs(response.data().heartbeatIntervalMs());
+            this.heartbeatRequestState.onSuccessfulAttempt(currentTimeMs);
+            this.heartbeatRequestState.reset();
+            try {
+                membershipManager.updateState(response.data());
+            } catch (KafkaException e) {
+                logger.error("Received unexpected error in heartbeat response: 
{}", e.getMessage());
+            }
+            return;
+        }
+
+        onErrorResponse(response, currentTimeMs);
+    }
+
+    private void onErrorResponse(final ConsumerGroupHeartbeatResponse response,
+                                 final long currentTimeMs) {
+        this.heartbeatRequestState.onFailedAttempt(currentTimeMs);
+        short errorCode = response.data().errorCode();
+        if (errorCode == Errors.NOT_COORDINATOR.code() || errorCode == 
Errors.COORDINATOR_NOT_AVAILABLE.code()) {
+            logInfo("Coordinator is either not started or not valid. 
Retrying", response, currentTimeMs);
+            
coordinatorRequestManager.markCoordinatorUnknown(response.data().errorMessage(),
 currentTimeMs);
+        } else if (errorCode == Errors.COORDINATOR_LOAD_IN_PROGRESS.code()) {
+            // retry
+            logInfo("Coordinator {} is loading. Retrying", response, 
currentTimeMs);
+        } else {
+            onFatalErrorResponse(response);
+        }
+    }
+
+    private void onFatalErrorResponse(final ConsumerGroupHeartbeatResponse 
response) {
+        final short errorCode = response.data().errorCode();

Review Comment:
   Same request here: use `Errors` to remove unnecessary use of raw error 
`code`.



##########
clients/src/main/java/org/apache/kafka/clients/consumer/internals/MembershipManagerImpl.java:
##########
@@ -115,25 +114,30 @@ public int memberEpoch() {
 
     @Override
     public void updateState(ConsumerGroupHeartbeatResponseData response) {
-        if (response.errorCode() == Errors.NONE.code()) {
-            this.memberId = response.memberId();
-            this.memberEpoch = response.memberEpoch();
-            ConsumerGroupHeartbeatResponseData.Assignment assignment = 
response.assignment();
-            if (assignment != null) {
-                setTargetAssignment(assignment);
-            }
-            maybeTransitionToStable();
-        } else {
-            if (response.errorCode() == Errors.FENCED_MEMBER_EPOCH.code() || 
response.errorCode() == Errors.UNKNOWN_MEMBER_ID.code()) {
-                resetEpoch();
-                transitionTo(MemberState.FENCED);
-            } else if (response.errorCode() == 
Errors.UNRELEASED_INSTANCE_ID.code()) {
-                transitionTo(MemberState.FAILED);
-            }
-            // TODO: handle other errors here to update state accordingly, 
mainly making the
-            //  distinction between the recoverable errors and the fatal ones, 
that should FAILED
-            //  the member
+        this.memberId = response.memberId();
+        this.memberEpoch = response.memberEpoch();
+        ConsumerGroupHeartbeatResponseData.Assignment assignment = 
response.assignment();
+        if (assignment != null) {
+            setTargetAssignment(assignment);
         }
+        maybeTransitionToStable();
+    }
+
+    @Override
+    public void fenceMember() {
+        resetEpoch();
+        transitionTo(MemberState.FENCED);
+    }
+
+    @Override
+    public void failMember() {

Review Comment:
   Per the related comment, can we rename `failMember` something that is more 
descriptive of what action _happened_ vs. that action's _result_?



##########
clients/src/main/java/org/apache/kafka/clients/consumer/internals/HeartbeatRequestManager.java:
##########
@@ -0,0 +1,287 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF 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.apache.kafka.clients.consumer.internals;
+
+import org.apache.kafka.clients.CommonClientConfigs;
+import org.apache.kafka.clients.consumer.ConsumerConfig;
+import org.apache.kafka.common.KafkaException;
+import org.apache.kafka.common.errors.GroupAuthorizationException;
+import org.apache.kafka.common.message.ConsumerGroupHeartbeatRequestData;
+import org.apache.kafka.common.protocol.Errors;
+import org.apache.kafka.common.requests.ConsumerGroupHeartbeatRequest;
+import org.apache.kafka.common.requests.ConsumerGroupHeartbeatResponse;
+import org.apache.kafka.common.utils.LogContext;
+import org.apache.kafka.common.utils.Time;
+import org.apache.kafka.common.utils.Timer;
+import org.slf4j.Logger;
+
+import java.util.ArrayList;
+import java.util.Collections;
+
+/**
+ * Manages the request creation and response handling for the heartbeat. The 
module creates a {@link ConsumerGroupHeartbeatRequest}
+ * using the state stored in the {@link MembershipManager} and enqueue it to 
the network queue to be sent out. Once
+ * the response is received, the module will update the state in the {@link 
MembershipManager} and handle any errors.
+ *
+ * The manager only emits heartbeat when the member is in a group. If the 
member is not in a group, or the
+ * coordinator is lost, the heartbeat won't be sent.
+ *
+ * If the heartbeat request fails, the module will trigger the exponential 
backoff, and resend the request. See
+ * {@link HeartbeatRequestState} for more details.
+ */
+public class HeartbeatRequestManager implements RequestManager {
+    private final Time time;
+    private final Logger logger;
+
+    private final int rebalanceTimeoutMs;
+
+    private final CoordinatorRequestManager coordinatorRequestManager;
+    private final SubscriptionState subscriptions;
+    private final HeartbeatRequestState heartbeatRequestState;
+    private final MembershipManager membershipManager;
+    private final ErrorEventHandler nonRetriableErrorHandler;
+
+    public HeartbeatRequestManager(
+        final Time time,
+        final LogContext logContext,
+        final ConsumerConfig config,
+        final CoordinatorRequestManager coordinatorRequestManager,
+        final SubscriptionState subscriptions,
+        final MembershipManager membershipManager,
+        final ErrorEventHandler nonRetriableErrorHandler) {
+        this.coordinatorRequestManager = coordinatorRequestManager;
+        this.time = time;
+        this.logger = logContext.logger(getClass());
+        this.subscriptions = subscriptions;
+        this.membershipManager = membershipManager;
+        this.nonRetriableErrorHandler = nonRetriableErrorHandler;
+        this.rebalanceTimeoutMs = 
config.getInt(CommonClientConfigs.MAX_POLL_INTERVAL_MS_CONFIG);
+        long retryBackoffMs = 
config.getLong(ConsumerConfig.RETRY_BACKOFF_MS_CONFIG);
+        long retryBackoffMaxMs = 
config.getLong(ConsumerConfig.RETRY_BACKOFF_MAX_MS_CONFIG);
+        this.heartbeatRequestState = new HeartbeatRequestState(logContext, 
time, 0, retryBackoffMs,
+            retryBackoffMaxMs, rebalanceTimeoutMs);
+    }
+
+    // Visible for testing
+    HeartbeatRequestManager(
+        final Time time,
+        final LogContext logContext,
+        final ConsumerConfig config,
+        final CoordinatorRequestManager coordinatorRequestManager,
+        final SubscriptionState subscriptions,
+        final MembershipManager membershipManager,
+        final HeartbeatRequestState heartbeatRequestState,
+        final ErrorEventHandler nonRetriableErrorHandler) {
+        this.time = time;
+        this.logger = logContext.logger(this.getClass());
+        this.subscriptions = subscriptions;
+        this.rebalanceTimeoutMs = 
config.getInt(CommonClientConfigs.MAX_POLL_INTERVAL_MS_CONFIG);
+        this.coordinatorRequestManager = coordinatorRequestManager;
+        this.heartbeatRequestState = heartbeatRequestState;
+        this.membershipManager = membershipManager;
+        this.nonRetriableErrorHandler = nonRetriableErrorHandler;
+    }
+
+    @Override
+    public NetworkClientDelegate.PollResult poll(long currentTimeMs) {
+        if (!coordinatorRequestManager.coordinator().isPresent() || 
!membershipManager.shouldSendHeartbeat()) {
+            return new NetworkClientDelegate.PollResult(
+                Long.MAX_VALUE, Collections.emptyList());
+        }
+
+        if (!heartbeatRequestState.canSendRequest(currentTimeMs)) {
+            return new NetworkClientDelegate.PollResult(
+                heartbeatRequestState.nextHeartbeatMs(currentTimeMs),
+                Collections.emptyList());
+        }
+        this.heartbeatRequestState.onSendAttempt(currentTimeMs);
+        NetworkClientDelegate.UnsentRequest request = makeHeartbeatRequest();
+        // return Long.MAX_VALUE because we will update the timer when the 
response is received
+        return new NetworkClientDelegate.PollResult(Long.MAX_VALUE, 
Collections.singletonList(request));
+    }
+
+    private NetworkClientDelegate.UnsentRequest makeHeartbeatRequest() {
+        ConsumerGroupHeartbeatRequestData data = new 
ConsumerGroupHeartbeatRequestData()
+            .setGroupId(membershipManager.groupId())
+            .setMemberEpoch(membershipManager.memberEpoch())
+            .setMemberId(membershipManager.memberId())
+            .setRebalanceTimeoutMs(rebalanceTimeoutMs);
+
+        membershipManager.groupInstanceId().ifPresent(data::setInstanceId);
+
+        if (this.subscriptions.hasPatternSubscription()) {
+            // We haven't discsussed how Regex is stored in the consumer. We 
could do it in the subscriptionState
+            // , in the memberStateManager, or here.
+            // data.setSubscribedTopicRegex(regex)
+        } else {
+            data.setSubscribedTopicNames(new 
ArrayList<>(this.subscriptions.subscription()));
+        }
+
+        
this.membershipManager.assignorSelection().serverAssignor().ifPresent(data::setServerAssignor);
+
+        NetworkClientDelegate.UnsentRequest request = new 
NetworkClientDelegate.UnsentRequest(
+            new ConsumerGroupHeartbeatRequest.Builder(data),
+            coordinatorRequestManager.coordinator());
+
+        request.future().whenComplete((response, exception) -> {
+            if (exception == null) {
+                onResponse((ConsumerGroupHeartbeatResponse) 
response.responseBody(), response.receivedTimeMs());
+            } else {
+                onFailure(exception, response.receivedTimeMs());
+            }
+        });
+        return request;
+    }
+
+    private void onFailure(final Throwable exception, final long 
responseTimeMs) {
+        this.heartbeatRequestState.onFailedAttempt(responseTimeMs);
+        logger.debug("failed sending heartbeat due to {}", 
exception.getMessage());
+    }
+
+    private void onResponse(final ConsumerGroupHeartbeatResponse response, 
long currentTimeMs) {
+        if (response.data().errorCode() == Errors.NONE.code()) {
+            
this.heartbeatRequestState.updateHeartbeatIntervalMs(response.data().heartbeatIntervalMs());
+            this.heartbeatRequestState.onSuccessfulAttempt(currentTimeMs);
+            this.heartbeatRequestState.reset();
+            try {
+                membershipManager.updateState(response.data());
+            } catch (KafkaException e) {
+                logger.error("Received unexpected error in heartbeat response: 
{}", e.getMessage());
+            }
+            return;
+        }
+
+        onErrorResponse(response, currentTimeMs);
+    }
+
+    private void onErrorResponse(final ConsumerGroupHeartbeatResponse response,
+                                 final long currentTimeMs) {
+        this.heartbeatRequestState.onFailedAttempt(currentTimeMs);
+        short errorCode = response.data().errorCode();
+        if (errorCode == Errors.NOT_COORDINATOR.code() || errorCode == 
Errors.COORDINATOR_NOT_AVAILABLE.code()) {
+            logInfo("Coordinator is either not started or not valid. 
Retrying", response, currentTimeMs);
+            
coordinatorRequestManager.markCoordinatorUnknown(response.data().errorMessage(),
 currentTimeMs);
+        } else if (errorCode == Errors.COORDINATOR_LOAD_IN_PROGRESS.code()) {
+            // retry
+            logInfo("Coordinator {} is loading. Retrying", response, 
currentTimeMs);
+        } else {
+            onFatalErrorResponse(response);
+        }
+    }
+
+    private void onFatalErrorResponse(final ConsumerGroupHeartbeatResponse 
response) {
+        final short errorCode = response.data().errorCode();
+        if (errorCode == Errors.GROUP_AUTHORIZATION_FAILED.code()) {
+            GroupAuthorizationException error = 
GroupAuthorizationException.forGroupId(membershipManager.groupId());
+            logger.error("GroupHeartbeatRequest failed due to group 
authorization failure: {}", error.getMessage());
+            nonRetriableErrorHandler.handle(error);
+        } else if (errorCode == Errors.INVALID_REQUEST.code()) {
+            logger.error("GroupHeartbeatRequest failed due to fatal error: 
{}", response.data().errorMessage());
+            
nonRetriableErrorHandler.handle(Errors.INVALID_REQUEST.exception());
+        } else if (errorCode == Errors.GROUP_MAX_SIZE_REACHED.code()) {
+            logger.error("GroupHeartbeatRequest failed due to the max group 
size limit: {}",
+                response.data().errorMessage());
+            
nonRetriableErrorHandler.handle(Errors.GROUP_MAX_SIZE_REACHED.exception());
+        } else if (errorCode == Errors.UNSUPPORTED_ASSIGNOR.code()) {
+            logger.error("GroupHeartbeatRequest failed due to unsupported 
assignor {}: {}",
+                membershipManager.assignorSelection(), 
response.data().errorMessage());
+            
nonRetriableErrorHandler.handle(Errors.UNSUPPORTED_ASSIGNOR.exception());
+        } else if (errorCode == Errors.UNRELEASED_INSTANCE_ID.code()) {
+            logger.error("GroupHeartbeatRequest failed due to the instance id 
{} was not released: {}",
+                membershipManager.groupInstanceId().orElse("null"),
+                response.data().errorMessage());
+            
nonRetriableErrorHandler.handle(Errors.UNRELEASED_INSTANCE_ID.exception());
+            membershipManager.failMember();

Review Comment:
   Can we rename `failMember` to be more descriptive?



##########
clients/src/main/java/org/apache/kafka/clients/consumer/internals/HeartbeatRequestManager.java:
##########
@@ -0,0 +1,287 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF 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.apache.kafka.clients.consumer.internals;
+
+import org.apache.kafka.clients.CommonClientConfigs;
+import org.apache.kafka.clients.consumer.ConsumerConfig;
+import org.apache.kafka.common.KafkaException;
+import org.apache.kafka.common.errors.GroupAuthorizationException;
+import org.apache.kafka.common.message.ConsumerGroupHeartbeatRequestData;
+import org.apache.kafka.common.protocol.Errors;
+import org.apache.kafka.common.requests.ConsumerGroupHeartbeatRequest;
+import org.apache.kafka.common.requests.ConsumerGroupHeartbeatResponse;
+import org.apache.kafka.common.utils.LogContext;
+import org.apache.kafka.common.utils.Time;
+import org.apache.kafka.common.utils.Timer;
+import org.slf4j.Logger;
+
+import java.util.ArrayList;
+import java.util.Collections;
+
+/**
+ * Manages the request creation and response handling for the heartbeat. The 
module creates a {@link ConsumerGroupHeartbeatRequest}
+ * using the state stored in the {@link MembershipManager} and enqueue it to 
the network queue to be sent out. Once
+ * the response is received, the module will update the state in the {@link 
MembershipManager} and handle any errors.
+ *
+ * The manager only emits heartbeat when the member is in a group. If the 
member is not in a group, or the
+ * coordinator is lost, the heartbeat won't be sent.
+ *
+ * If the heartbeat request fails, the module will trigger the exponential 
backoff, and resend the request. See
+ * {@link HeartbeatRequestState} for more details.
+ */
+public class HeartbeatRequestManager implements RequestManager {
+    private final Time time;
+    private final Logger logger;
+
+    private final int rebalanceTimeoutMs;
+
+    private final CoordinatorRequestManager coordinatorRequestManager;
+    private final SubscriptionState subscriptions;
+    private final HeartbeatRequestState heartbeatRequestState;
+    private final MembershipManager membershipManager;
+    private final ErrorEventHandler nonRetriableErrorHandler;
+
+    public HeartbeatRequestManager(
+        final Time time,
+        final LogContext logContext,
+        final ConsumerConfig config,
+        final CoordinatorRequestManager coordinatorRequestManager,
+        final SubscriptionState subscriptions,
+        final MembershipManager membershipManager,
+        final ErrorEventHandler nonRetriableErrorHandler) {
+        this.coordinatorRequestManager = coordinatorRequestManager;
+        this.time = time;
+        this.logger = logContext.logger(getClass());
+        this.subscriptions = subscriptions;
+        this.membershipManager = membershipManager;
+        this.nonRetriableErrorHandler = nonRetriableErrorHandler;
+        this.rebalanceTimeoutMs = 
config.getInt(CommonClientConfigs.MAX_POLL_INTERVAL_MS_CONFIG);
+        long retryBackoffMs = 
config.getLong(ConsumerConfig.RETRY_BACKOFF_MS_CONFIG);
+        long retryBackoffMaxMs = 
config.getLong(ConsumerConfig.RETRY_BACKOFF_MAX_MS_CONFIG);
+        this.heartbeatRequestState = new HeartbeatRequestState(logContext, 
time, 0, retryBackoffMs,
+            retryBackoffMaxMs, rebalanceTimeoutMs);
+    }
+
+    // Visible for testing
+    HeartbeatRequestManager(
+        final Time time,
+        final LogContext logContext,
+        final ConsumerConfig config,
+        final CoordinatorRequestManager coordinatorRequestManager,
+        final SubscriptionState subscriptions,
+        final MembershipManager membershipManager,
+        final HeartbeatRequestState heartbeatRequestState,
+        final ErrorEventHandler nonRetriableErrorHandler) {
+        this.time = time;
+        this.logger = logContext.logger(this.getClass());
+        this.subscriptions = subscriptions;
+        this.rebalanceTimeoutMs = 
config.getInt(CommonClientConfigs.MAX_POLL_INTERVAL_MS_CONFIG);
+        this.coordinatorRequestManager = coordinatorRequestManager;
+        this.heartbeatRequestState = heartbeatRequestState;
+        this.membershipManager = membershipManager;
+        this.nonRetriableErrorHandler = nonRetriableErrorHandler;
+    }
+
+    @Override
+    public NetworkClientDelegate.PollResult poll(long currentTimeMs) {
+        if (!coordinatorRequestManager.coordinator().isPresent() || 
!membershipManager.shouldSendHeartbeat()) {
+            return new NetworkClientDelegate.PollResult(
+                Long.MAX_VALUE, Collections.emptyList());
+        }
+
+        if (!heartbeatRequestState.canSendRequest(currentTimeMs)) {
+            return new NetworkClientDelegate.PollResult(
+                heartbeatRequestState.nextHeartbeatMs(currentTimeMs),
+                Collections.emptyList());
+        }
+        this.heartbeatRequestState.onSendAttempt(currentTimeMs);
+        NetworkClientDelegate.UnsentRequest request = makeHeartbeatRequest();
+        // return Long.MAX_VALUE because we will update the timer when the 
response is received
+        return new NetworkClientDelegate.PollResult(Long.MAX_VALUE, 
Collections.singletonList(request));
+    }
+
+    private NetworkClientDelegate.UnsentRequest makeHeartbeatRequest() {
+        ConsumerGroupHeartbeatRequestData data = new 
ConsumerGroupHeartbeatRequestData()
+            .setGroupId(membershipManager.groupId())
+            .setMemberEpoch(membershipManager.memberEpoch())
+            .setMemberId(membershipManager.memberId())
+            .setRebalanceTimeoutMs(rebalanceTimeoutMs);
+
+        membershipManager.groupInstanceId().ifPresent(data::setInstanceId);
+
+        if (this.subscriptions.hasPatternSubscription()) {
+            // We haven't discsussed how Regex is stored in the consumer. We 
could do it in the subscriptionState
+            // , in the memberStateManager, or here.
+            // data.setSubscribedTopicRegex(regex)
+        } else {
+            data.setSubscribedTopicNames(new 
ArrayList<>(this.subscriptions.subscription()));
+        }
+
+        
this.membershipManager.assignorSelection().serverAssignor().ifPresent(data::setServerAssignor);
+
+        NetworkClientDelegate.UnsentRequest request = new 
NetworkClientDelegate.UnsentRequest(
+            new ConsumerGroupHeartbeatRequest.Builder(data),
+            coordinatorRequestManager.coordinator());
+
+        request.future().whenComplete((response, exception) -> {
+            if (exception == null) {
+                onResponse((ConsumerGroupHeartbeatResponse) 
response.responseBody(), response.receivedTimeMs());
+            } else {
+                onFailure(exception, response.receivedTimeMs());
+            }
+        });
+        return request;
+    }
+
+    private void onFailure(final Throwable exception, final long 
responseTimeMs) {
+        this.heartbeatRequestState.onFailedAttempt(responseTimeMs);
+        logger.debug("failed sending heartbeat due to {}", 
exception.getMessage());
+    }
+
+    private void onResponse(final ConsumerGroupHeartbeatResponse response, 
long currentTimeMs) {
+        if (response.data().errorCode() == Errors.NONE.code()) {
+            
this.heartbeatRequestState.updateHeartbeatIntervalMs(response.data().heartbeatIntervalMs());
+            this.heartbeatRequestState.onSuccessfulAttempt(currentTimeMs);
+            this.heartbeatRequestState.reset();
+            try {
+                membershipManager.updateState(response.data());
+            } catch (KafkaException e) {
+                logger.error("Received unexpected error in heartbeat response: 
{}", e.getMessage());
+            }
+            return;
+        }
+
+        onErrorResponse(response, currentTimeMs);
+    }
+
+    private void onErrorResponse(final ConsumerGroupHeartbeatResponse response,
+                                 final long currentTimeMs) {
+        this.heartbeatRequestState.onFailedAttempt(currentTimeMs);
+        short errorCode = response.data().errorCode();
+        if (errorCode == Errors.NOT_COORDINATOR.code() || errorCode == 
Errors.COORDINATOR_NOT_AVAILABLE.code()) {
+            logInfo("Coordinator is either not started or not valid. 
Retrying", response, currentTimeMs);
+            
coordinatorRequestManager.markCoordinatorUnknown(response.data().errorMessage(),
 currentTimeMs);
+        } else if (errorCode == Errors.COORDINATOR_LOAD_IN_PROGRESS.code()) {
+            // retry
+            logInfo("Coordinator {} is loading. Retrying", response, 
currentTimeMs);

Review Comment:
   ```suggestion
               logInfo(String.format("Heartbeat was not successful because the 
coordinator node %s is loading. Retrying", 
coordinatorRequestManager.coordinator()), response, currentTimeMs);
   ```



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