content: /*
   * 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.streams.kstream.internals.foreignkeyjoin;
  
  import org.apache.kafka.common.errors.UnsupportedVersionException;
  import org.apache.kafka.common.metrics.Sensor;
  import org.apache.kafka.common.serialization.Serializer;
  import org.apache.kafka.streams.kstream.ValueJoiner;
  import org.apache.kafka.streams.kstream.internals.KTableValueGetter;
  import org.apache.kafka.streams.kstream.internals.KTableValueGetterSupplier;
  import org.apache.kafka.streams.processor.api.ContextualProcessor;
  import org.apache.kafka.streams.processor.api.Processor;
  import org.apache.kafka.streams.processor.api.ProcessorContext;
  import org.apache.kafka.streams.processor.api.ProcessorSupplier;
  import org.apache.kafka.streams.processor.api.Record;
  import org.apache.kafka.streams.processor.internals.InternalProcessorContext;
  import org.apache.kafka.streams.processor.internals.metrics.TaskMetrics;
  import org.apache.kafka.streams.state.ValueAndTimestamp;
  import org.apache.kafka.streams.state.internals.Murmur3;
  
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import java.util.function.Supplier;
  
  /**
   * Receives {@code SubscriptionResponseWrapper<VO>} events and filters out events which do not match the current hash
   * of the primary key. This eliminates race-condition results for rapidly-changing foreign-keys for a given primary key.
   * Applies the join and emits nulls according to LEFT/INNER rules.
   *
   * @param <KLeft> Type of primary keys
   * @param <VLeft> Type of primary values
   * @param <VRight> Type of foreign values
   * @param <VOut> Type of joined result of primary and foreign values
   */
  public class ResponseJoinProcessorSupplier<KLeft, VLeft, VRight, VOut>
      implements ProcessorSupplier<KLeft, SubscriptionResponseWrapper<VRight>, KLeft, VOut> {
  
      private static final Logger LOG = LoggerFactory.getLogger(ResponseJoinProcessorSupplier.class);
      private final KTableValueGetterSupplier<KLeft, VLeft> valueGetterSupplier;
      private final Serializer<VLeft> constructionTimeValueSerializer;
      private final Supplier<String> valueHashSerdePseudoTopicSupplier;
      private final ValueJoiner<? super VLeft, ? super VRight, ? extends VOut> joiner;
      private final boolean leftJoin;
  
      public ResponseJoinProcessorSupplier(final KTableValueGetterSupplier<KLeft, VLeft> valueGetterSupplier,
                                           final Serializer<VLeft> valueSerializer,
                                           final Supplier<String> valueHashSerdePseudoTopicSupplier,
                                           final ValueJoiner<? super VLeft, ? super VRight, ? extends VOut> joiner,
                                           final boolean leftJoin) {
          this.valueGetterSupplier = valueGetterSupplier;
          constructionTimeValueSerializer = valueSerializer;
          this.valueHashSerdePseudoTopicSupplier = valueHashSerdePseudoTopicSupplier;
          this.joiner = joiner;
          this.leftJoin = leftJoin;
      }
  
      @Override
      public Processor<KLeft, SubscriptionResponseWrapper<VRight>, KLeft, VOut> get() {
          return new ContextualProcessor<>() {
              private String valueHashSerdePseudoTopic;
              private Serializer<VLeft> runtimeValueSerializer = constructionTimeValueSerializer;
  
              private KTableValueGetter<KLeft, VLeft> valueGetter;
              private Sensor droppedRecordsSensor;
  
  
              @SuppressWarnings({"unchecked", "resource"})
              @Override
              public void init(final ProcessorContext<KLeft, VOut> context) {
                  super.init(context);
                  valueHashSerdePseudoTopic = valueHashSerdePseudoTopicSupplier.get();
                  valueGetter = valueGetterSupplier.get();
                  valueGetter.init(context);
                  if (runtimeValueSerializer == null) {
                      runtimeValueSerializer = (Serializer<VLeft>) context.valueSerde().serializer();
                  }
  
                  final InternalProcessorContext<?, ?> internalProcessorContext = (InternalProcessorContext<?, ?>) context;
                  droppedRecordsSensor = TaskMetrics.droppedRecordsSensor(
                          Thread.currentThread().getName(),
                          internalProcessorContext.taskId().toString(),
                          internalProcessorContext.metrics()
                  );
              }
  
              @Override
              public void process(final Record<KLeft, SubscriptionResponseWrapper<VRight>> record) {
                  if (record.value().version() != SubscriptionResponseWrapper.CURRENT_VERSION) {
                      //Guard against modifications to SubscriptionResponseWrapper. Need to ensure that there is
                      //compatibility with previous versions to enable rolling upgrades. Must develop a strategy for
                      //upgrading from older SubscriptionWrapper versions to newer versions.
                      throw new UnsupportedVersionException("SubscriptionResponseWrapper is of an incompatible version.");
                  }
                  final ValueAndTimestamp<VLeft> currentValueWithTimestamp = valueGetter.get(record.key());
  
                  final long[] currentHash = currentValueWithTimestamp == null ?
                      null :
                      Murmur3.hash128(runtimeValueSerializer.serialize(valueHashSerdePseudoTopic, currentValueWithTimestamp.value()));
  
                  final long[] messageHash = record.value().originalValueHash();
  
                  //If this value doesn't match the current value from the original table, it is stale and should be discarded.
                  if (java.util.Arrays.equals(messageHash, currentHash)) {
                      final VOut result;
  
                      if (record.value().foreignValue() == null && (!leftJoin || currentValueWithTimestamp == null)) {
                          result = null; //Emit tombstone
                      } else {
                          result = joiner.apply(currentValueWithTimestamp == null ? null : currentValueWithTimestamp.value(), record.value().foreignValue());
                      }
                      context().forward(record.withValue(result));
                  } else {
                      LOG.trace("Dropping FK-join response due to hash mismatch. Expected {}. Actual {}", messageHash, currentHash);
                      droppedRecordsSensor.record();
                  }
              }
          };
      }
  }
  