flink-connectors/flink-connector-gcp-pubsub/src/main/java/org/apache/flink/streaming/connectors/gcp/pubsub/BlockingGrpcPubSubSubscriber.java

/*
 * 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.flink.streaming.connectors.gcp.pubsub;

import org.apache.flink.api.java.tuple.Tuple2;
import org.apache.flink.streaming.connectors.gcp.pubsub.common.PubSubSubscriber;

import com.google.pubsub.v1.AcknowledgeRequest;
import com.google.pubsub.v1.PullRequest;
import com.google.pubsub.v1.ReceivedMessage;
import com.google.pubsub.v1.SubscriberGrpc;
import io.grpc.ManagedChannel;
import io.grpc.StatusRuntimeException;

import java.time.Duration;
import java.util.List;
import java.util.concurrent.TimeUnit;

import static java.util.Collections.emptyList;
import static java.util.concurrent.TimeUnit.SECONDS;

/**
 * Implementation for {@link PubSubSubscriber}. This Grpc PubSubSubscriber allows for flexible
 * timeouts and retries.
 */
public class BlockingGrpcPubSubSubscriber implements PubSubSubscriber {
    private final String projectSubscriptionName;
    private final ManagedChannel channel;
    private final SubscriberGrpc.SubscriberBlockingStub stub;
    private final int retries;
    private final Duration timeout;
    private final PullRequest pullRequest;

    public BlockingGrpcPubSubSubscriber(
            String projectSubscriptionName,
            ManagedChannel channel,
            SubscriberGrpc.SubscriberBlockingStub stub,
            PullRequest pullRequest,
            int retries,
            Duration timeout) {
        this.projectSubscriptionName = projectSubscriptionName;
        this.channel = channel;
        this.stub = stub;
        this.retries = retries;
        this.timeout = timeout;
        this.pullRequest = pullRequest;
    }

    @Override
    public List<ReceivedMessage> pull() {
        return pull(retries);
    }

    private List<ReceivedMessage> pull(int retriesRemaining) {
        try {
            return stub.withDeadlineAfter(timeout.toMillis(), TimeUnit.MILLISECONDS)
                    .pull(pullRequest)
                    .getReceivedMessagesList();
        } catch (StatusRuntimeException e) {
            if (retriesRemaining > 0) {
                return pull(retriesRemaining - 1);
            }

            throw e;
        }
    }

    @Override
    public void acknowledge(List<String> acknowledgementIds) {
        if (acknowledgementIds.isEmpty()) {
            return;
        }

        // grpc servers won't accept acknowledge requests that are too large so we split the ackIds
        Tuple2<List<String>, List<String>> splittedAckIds = splitAckIds(acknowledgementIds);
        while (!splittedAckIds.f0.isEmpty()) {
            AcknowledgeRequest acknowledgeRequest =
                    AcknowledgeRequest.newBuilder()
                            .setSubscription(projectSubscriptionName)
                            .addAllAckIds(splittedAckIds.f0)
                            .build();

            stub.withDeadlineAfter(60, SECONDS).acknowledge(acknowledgeRequest);

            splittedAckIds = splitAckIds(splittedAckIds.f1);
        }
    }

    /* maxPayload is the maximum number of bytes to devote to actual ids in
    * acknowledgement or modifyAckDeadline requests. A serialized
    * AcknowledgeRequest grpc call has a small constant overhead, plus the size of the
    * subscription name, plus 3 bytes per ID (a tag byte and two size bytes). A
    * ModifyAckDeadlineRequest has an additional few bytes for the deadline. We
    * don't know the subscription name here, so we just assume the size exclusive
    * of ids is 100 bytes.

    * With gRPC there is no way for the client to know the server's max message size (it is
    * configurable on the server). We know from experience that it is 512K.
    * @return First list contains no more than 512k bytes, second list contains remaining ids
    */
    private Tuple2<List<String>, List<String>> splitAckIds(List<String> ackIds) {
        final int maxPayload = 500 * 1024; // little below 512k bytes to be on the safe side
        final int fixedOverheadPerCall = 100;
        final int overheadPerId = 3;

        int totalBytes = fixedOverheadPerCall;

        for (int i = 0; i < ackIds.size(); i++) {
            totalBytes += ackIds.get(i).length() + overheadPerId;
            if (totalBytes > maxPayload) {
                return Tuple2.of(ackIds.subList(0, i), ackIds.subList(i, ackIds.size()));
            }
        }

        return Tuple2.of(ackIds, emptyList());
    }

    @Override
    public void close() throws Exception {
        channel.shutdownNow();
        channel.awaitTermination(20, SECONDS);
    }
}