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Java idiomatic client for Google Cloud Storage.
There is a newer version: 2.45.0
/*
 * Copyright 2022 Google LLC
 *
 * Licensed 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 com.google.cloud.storage;

import static java.util.Objects.requireNonNull;

import com.google.api.core.ApiFutures;
import com.google.api.core.SettableApiFuture;
import com.google.api.gax.rpc.ServerStreamingCallable;
import com.google.cloud.storage.BufferedReadableByteChannelSession.BufferedReadableByteChannel;
import com.google.cloud.storage.UnbufferedReadableByteChannelSession.UnbufferedReadableByteChannel;
import com.google.common.util.concurrent.MoreExecutors;
import com.google.storage.v2.Object;
import com.google.storage.v2.ReadObjectRequest;
import com.google.storage.v2.ReadObjectResponse;
import java.nio.ByteBuffer;
import java.util.function.BiFunction;
import javax.annotation.concurrent.Immutable;

@Immutable
final class GapicDownloadSessionBuilder {
  private static final GapicDownloadSessionBuilder INSTANCE = new GapicDownloadSessionBuilder();

  private static final int DEFAULT_BUFFER_CAPACITY = ByteSizeConstants._16MiB;

  private GapicDownloadSessionBuilder() {}

  public static GapicDownloadSessionBuilder create() {
    return INSTANCE;
  }

  /**
   * Any retry capability must be defined within the provided ServerStreamingCallable. The
   * ultimately produced channel will not do any retries of its own.
   */
  public ReadableByteChannelSessionBuilder byteChannel(
      ServerStreamingCallable read) {
    return new ReadableByteChannelSessionBuilder(read);
  }

  public static final class ReadableByteChannelSessionBuilder {

    private final ServerStreamingCallable read;
    private boolean autoGzipDecompression;
    private Hasher hasher;

    private ReadableByteChannelSessionBuilder(
        ServerStreamingCallable read) {
      this.read = read;
      this.hasher = Hasher.noop();
      this.autoGzipDecompression = false;
    }

    public BufferedReadableByteChannelSessionBuilder buffered() {
      return buffered(BufferHandle.allocate(DEFAULT_BUFFER_CAPACITY));
    }

    public ReadableByteChannelSessionBuilder setHasher(Hasher hasher) {
      this.hasher = hasher;
      return this;
    }

    public ReadableByteChannelSessionBuilder setAutoGzipDecompression(
        boolean autoGzipDecompression) {
      this.autoGzipDecompression = autoGzipDecompression;
      return this;
    }

    public BufferedReadableByteChannelSessionBuilder buffered(BufferHandle bufferHandle) {
      return new BufferedReadableByteChannelSessionBuilder(bufferHandle, bindFunction());
    }

    public BufferedReadableByteChannelSessionBuilder buffered(ByteBuffer buffer) {
      return buffered(BufferHandle.handleOf(buffer));
    }

    public UnbufferedReadableByteChannelSessionBuilder unbuffered() {
      return new UnbufferedReadableByteChannelSessionBuilder(bindFunction());
    }

    private BiFunction, UnbufferedReadableByteChannel>
        bindFunction() {
      // for any non-final value, create a reference to the value at this point in time
      Hasher hasher = this.hasher;
      boolean autoGzipDecompression = this.autoGzipDecompression;
      return (object, resultFuture) -> {
        if (autoGzipDecompression) {
          return new GzipReadableByteChannel(
              new GapicUnbufferedReadableByteChannel(resultFuture, read, object, hasher),
              ApiFutures.transform(
                  resultFuture, Object::getContentEncoding, MoreExecutors.directExecutor()));
        } else {
          return new GapicUnbufferedReadableByteChannel(resultFuture, read, object, hasher);
        }
      };
    }

    public static final class BufferedReadableByteChannelSessionBuilder {

      private final BiFunction<
              ReadObjectRequest, SettableApiFuture