    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one
    003 * or more contributor license agreements.  See the NOTICE file
    004 * distributed with this work for additional information
    005 * regarding copyright ownership.  The ASF licenses this file
    006 * to you under the Apache License, Version 2.0 (the
    007 * "License"); you may not use this file except in compliance
    008 * with the License.  You may obtain a copy of the License at
    009 *
    010 * http://www.apache.org/licenses/LICENSE-2.0
    011 *
    012 * Unless required by applicable law or agreed to in writing,
    013 * software distributed under the License is distributed on an
    014 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
    015 * KIND, either express or implied.  See the License for the
    016 * specific language governing permissions and limitations
    017 * under the License.
    018 */
    019package org.apache.commons.compress.compressors.zstandard;
    020
    021import org.apache.commons.compress.utils.OsgiUtils;
    022
    023/**
    024 * Utility code for the Zstandard compression format.
    025 *
    026 * @ThreadSafe
    027 * @since 1.16
    028 */
    029public class ZstdUtils {
    030
    031    enum CachedAvailability {
    032        DONT_CACHE, CACHED_AVAILABLE, CACHED_UNAVAILABLE
    033    }
    034
    035    /**
    036     * Zstandard Frame Magic Bytes.
    037     */
    038    private static final byte[] ZSTANDARD_FRAME_MAGIC = { (byte) 0x28, (byte) 0xB5, (byte) 0x2F, (byte) 0xFD };
    039
    040    /**
    041     * Skippable Frame Magic Bytes - the three common bytes.
    042     */
    043    private static final byte[] SKIPPABLE_FRAME_MAGIC = { (byte) 0x2A, (byte) 0x4D, (byte) 0x18 };
    044
    045    private static volatile CachedAvailability cachedZstdAvailability;
    046
    047    static {
    048        cachedZstdAvailability = CachedAvailability.DONT_CACHE;
    049        setCacheZstdAvailablity(!OsgiUtils.isRunningInOsgiEnvironment());
    050    }
    051
    052    // only exists to support unit tests
    053    static CachedAvailability getCachedZstdAvailability() {
    054        return cachedZstdAvailability;
    055    }
    056
    057    private static boolean internalIsZstdCompressionAvailable() {
    058        try {
    059            Class.forName("com.github.luben.zstd.ZstdInputStream");
    060            return true;
    061        } catch (final NoClassDefFoundError | Exception error) { // NOSONAR
    062            return false;
    063        }
    064    }
    065
    066    /**
    067     * Are the classes required to support Zstandard compression available?
    068     *
    069     * @return true if the classes required to support Zstandard compression are available
    070     */
    071    public static boolean isZstdCompressionAvailable() {
    072        final CachedAvailability cachedResult = cachedZstdAvailability;
    073        if (cachedResult != CachedAvailability.DONT_CACHE) {
    074            return cachedResult == CachedAvailability.CACHED_AVAILABLE;
    075        }
    076        return internalIsZstdCompressionAvailable();
    077    }
    078
    079    /**
    080     * Checks if the signature matches what is expected for a Zstandard file.
    081     *
    082     * @param signature the bytes to check
    083     * @param length    the number of bytes to check
    084     * @return true if signature matches the Ztstandard or skippable frame magic bytes, false otherwise
    085     */
    086    public static boolean matches(final byte[] signature, final int length) {
    087        if (length < ZSTANDARD_FRAME_MAGIC.length) {
    088            return false;
    089        }
    090
    091        boolean isZstandard = true;
    092        for (int i = 0; i < ZSTANDARD_FRAME_MAGIC.length; ++i) {
    093            if (signature[i] != ZSTANDARD_FRAME_MAGIC[i]) {
    094                isZstandard = false;
    095                break;
    096            }
    097        }
    098        if (isZstandard) {
    099            return true;
    100        }
    101
    102        if (0x50 == (signature[0] & 0xF0)) {
    103            // skippable frame
    104            for (int i = 0; i < SKIPPABLE_FRAME_MAGIC.length; ++i) {
    105                if (signature[i + 1] != SKIPPABLE_FRAME_MAGIC[i]) {
    106                    return false;
    107                }
    108            }
    109
    110            return true;
    111        }
    112
    113        return false;
    114    }
    115
    116    /**
    117     * Whether to cache the result of the Zstandard for Java check.
    118     *
    119     * <p>
    120     * This defaults to {@code false} in an OSGi environment and {@code true} otherwise.
    121     * </p>
    122     *
    123     * @param doCache whether to cache the result
    124     */
    125    public static void setCacheZstdAvailablity(final boolean doCache) {
    126        if (!doCache) {
    127            cachedZstdAvailability = CachedAvailability.DONT_CACHE;
    128        } else if (cachedZstdAvailability == CachedAvailability.DONT_CACHE) {
    129            final boolean hasZstd = internalIsZstdCompressionAvailable();
    130            cachedZstdAvailability = hasZstd ? CachedAvailability.CACHED_AVAILABLE : CachedAvailability.CACHED_UNAVAILABLE;
    131        }
    132    }
    133
    134    /** Private constructor to prevent instantiation of this utility class. */
    135    private ZstdUtils() {
    136    }
    137}