001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.juneau.commons.utils;
018
019import static org.apache.juneau.commons.utils.Shorts.*;
020
021import java.util.zip.*;
022
023/**
024 * Content-checksum utility methods.
025 */
026public class ChecksumUtils {
027
028   /** Prevents instantiation. */
029   private ChecksumUtils() {}
030
031   /**
032    * Formats a CRC32 checksum of the specified bytes as a zero-padded, lower-case, 8-hex-char content hash.
033    *
034    * <p>
035    * Suitable as a compact, content-sensitive cache-buster for classpath-shipped assets (JS/CSS/images, etc.):
036    * the hash changes the instant the underlying bytes do, without relying on a build/version string alone
037    * (which stays stable across {@code -SNAPSHOT} dev rebuilds and so cannot bust a browser's cache on its own).
038    *
039    * @param bytes The bytes to checksum.  Must not be <jk>null</jk>.
040    * @return The zero-padded 8-hex-char CRC32 checksum (e.g. {@code "1a2b3c4d"}).
041    */
042   public static String hash8(byte[] bytes) {
043      var crc = new CRC32();
044      crc.update(bytes);
045      return f("%08x", crc.getValue());
046   }
047}