core/src/main/java/org/apache/calcite/runtime/CompressionFunctions.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.calcite.runtime;

import org.apache.calcite.avatica.util.ByteString;

import org.apache.commons.lang3.StringUtils;

import org.checkerframework.checker.nullness.qual.Nullable;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.charset.Charset;
import java.util.zip.DeflaterOutputStream;

/**
 * A collection of functions used in compression and decompression.
 */
public class CompressionFunctions {

  private CompressionFunctions() {
  }

  /**
   * MySql Compression is based on zlib.
   * <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/util/zip/Deflater.html">Deflater</a>
   * is used to implement compression.
   */
  public static @Nullable ByteString compress(@Nullable String data) {
    try {
      if (data == null) {
        return null;
      }
      if (StringUtils.isEmpty(data)) {
        return new ByteString(new byte[0]);
      }
      ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
      ByteBuffer dataLength = ByteBuffer.allocate(4);
      dataLength.order(ByteOrder.LITTLE_ENDIAN);
      dataLength.putInt(data.length());
      outputStream.write(dataLength.array());
      DeflaterOutputStream inflaterStream = new DeflaterOutputStream(outputStream);
      inflaterStream.write(data.getBytes(Charset.defaultCharset()));
      inflaterStream.close();
      return new ByteString(outputStream.toByteArray());
    } catch (IOException e) {
      return null;
    }
  }

}