[GitHub] [kafka] hachikuji commented on a change in pull request #10275: KAFKA-12434; Admin support for `DescribeProducers` API

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hachikuji commented on a change in pull request #10275:
URL: https://github.com/apache/kafka/pull/10275#discussion_r590025229



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File path: clients/src/main/java/org/apache/kafka/clients/admin/internals/AdminApiDriver.java
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@@ -0,0 +1,464 @@
+/*
+ * 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.admin.internals;
+
+import org.apache.kafka.clients.admin.internals.AdminApiHandler.DynamicKeyMapping;
+import org.apache.kafka.clients.admin.internals.AdminApiHandler.KeyMappings;
+import org.apache.kafka.clients.admin.internals.AdminApiHandler.StaticKeyMapping;
+import org.apache.kafka.clients.admin.internals.AdminApiLookupStrategy.RequestScope;
+import org.apache.kafka.common.errors.DisconnectException;
+import org.apache.kafka.common.internals.KafkaFutureImpl;
+import org.apache.kafka.common.requests.AbstractRequest;
+import org.apache.kafka.common.requests.AbstractResponse;
+import org.apache.kafka.common.utils.LogContext;
+import org.slf4j.Logger;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.OptionalInt;
+import java.util.Set;
+import java.util.function.BiFunction;
+
+/**
+ * The `KafkaAdminClient`'s internal `Call` primitive is not a good fit for multi-stage
+ * request workflows such as we see with the group coordinator APIs or any request which
+ * needs to be sent to a partition leader. Typically these APIs have two concrete stages:
+ *
+ * 1. Lookup: Find the broker that can fulfill the request (e.g. partition leader or group
+ *            coordinator)
+ * 2. Fulfillment: Send the request to the broker found in the first step
+ *
+ * This is complicated by the fact that `Admin` APIs are typically batched, which
+ * means the Lookup stage may result in a set of brokers. For example, take a `ListOffsets`
+ * request for a set of topic partitions. In the Lookup stage, we will find the partition
+ * leaders for this set of partitions; in the Fulfillment stage, we will group together
+ * partition according to the IDs of the discovered leaders.
+ *
+ * Additionally, the flow between these two stages is bi-directional. We may find after
+ * sending a `ListOffsets` request to an expected leader that there was a leader change.
+ * This would result in a topic partition being sent back to the Lookup stage.
+ *
+ * Managing this complexity by chaining together `Call` implementations is challenging
+ * and messy, so instead we use this class to do the bookkeeping. It handles both the
+ * batching aspect as well as the transitions between the Lookup and Fulfillment stages.
+ *
+ * Note that the interpretation of the `retries` configuration becomes ambiguous
+ * for this kind of pipeline. We could treat it as an overall limit on the number
+ * of requests that can be sent, but that is not very useful because each pipeline
+ * has a minimum number of requests that need to be sent in order to satisfy the request.
+ * Instead, we treat this number of retries independently at each stage so that each
+ * stage has at least one opportunity to complete. So if a user sets `retries=1`, then
+ * the full pipeline can still complete as long as there are no request failures.
+ *
+ * @param <K> The key type, which is also the granularity of the request routing (e.g.
+ *            this could be `TopicPartition` in the case of requests intended for a partition
+ *            leader or the `GroupId` in the case of consumer group requests intended for
+ *            the group coordinator)
+ * @param <V> The fulfillment type for each key (e.g. this could be consumer group state
+ *            when the key type is a consumer `GroupId`)
+ */
+public class AdminApiDriver<K, V> {
+    private final Logger log;
+    private final long retryBackoffMs;
+    private final long deadlineMs;
+    private final AdminApiHandler<K, V> handler;
+    private final Optional<StaticKeyMapping<K>> staticMapping;
+    private final Optional<DynamicKeyMapping<K>> dynamicMapping;
+    private final Map<K, KafkaFutureImpl<V>> futures;
+
+    private final BiMultimap<RequestScope, K> lookupMap = new BiMultimap<>();
+    private final BiMultimap<BrokerScope, K> fulfillmentMap = new BiMultimap<>();
+    private final Map<RequestScope, RequestState> requestStates = new HashMap<>();
+
+
+    public AdminApiDriver(
+        AdminApiHandler<K, V> handler,
+        long deadlineMs,
+        long retryBackoffMs,
+        LogContext logContext
+    ) {
+        this.handler = handler;
+        this.deadlineMs = deadlineMs;
+        this.retryBackoffMs = retryBackoffMs;
+        this.log = logContext.logger(AdminApiDriver.class);
+        this.futures = new HashMap<>();
+
+        KeyMappings<K> result = handler.initializeKeys();
+        this.dynamicMapping = result.dynamicMapping;
+        this.staticMapping = result.staticMapping;
+
+        initializeKeys();
+    }
+
+    private void initializeKeys() {
+        staticMapping.ifPresent(mapping -> {
+            for (Map.Entry<K, Integer> staticMapping : mapping.keys.entrySet()) {
+                K key = staticMapping.getKey();
+                Integer brokerId = staticMapping.getValue();
+                futures.put(key, new KafkaFutureImpl<>());
+                map(key, brokerId);
+            }
+        });
+
+        dynamicMapping.ifPresent(mapping -> {
+            for (K key : mapping.keys) {
+                futures.put(key, new KafkaFutureImpl<>());
+                lookupMap.put(mapping.lookupStrategy.lookupScope(key), key);
+            }
+        });
+    }
+
+    /**
+     * Associate a key with a brokerId. This is called after a response in the Lookup
+     * stage reveals the mapping (e.g. when the `FindCoordinator` tells us the the
+     * group coordinator for a specific consumer group).
+     */
+    private void map(K key, Integer brokerId) {
+        lookupMap.remove(key);
+        fulfillmentMap.put(new BrokerScope(brokerId), key);
+
+        // To allow for derived keys, we create futures dynamically if they
+        // do not already exist in the future map
+        futures.computeIfAbsent(key, k -> new KafkaFutureImpl<>());
+    }
+
+    /**
+     * Disassociate a key from the currently mapped brokerId. This will send the key
+     * back to the Lookup stage, which will allow us to attempt lookup again.
+     */
+    private void unmap(K key) {
+        DynamicKeyMapping<K> mapping = dynamicMapping.orElseThrow(() ->
+            new IllegalStateException("Attempt to unmap key " + key + " which is not dynamically mapped")
+        );
+        fulfillmentMap.remove(key);
+        lookupMap.put(mapping.lookupStrategy.lookupScope(key), key);
+    }
+
+    private void clear(K key) {
+        lookupMap.remove(key);
+        fulfillmentMap.remove(key);
+    }
+
+    OptionalInt keyToBrokerId(K key) {

Review comment:
       It was mainly for `remove` that I added it.




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