    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 *   https://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 * <p>
    027 * This class avoids making the underlying {@code zstd} classes part of the public or protected API. The underlying implementation is provided through the
    028 * <a href="https://github.com/luben/zstd-jni/">Zstandard JNI</a> library which is based on <a href="https://github.com/facebook/zstd/">zstd</a>.
    029 * </p>
    030 *
    031 * @ThreadSafe
    032 * @see <a href="https://github.com/luben/zstd-jni/">Zstandard JNI</a>
    033 * @see <a href="https://github.com/facebook/zstd/">zstd</a>
    034 * @since 1.16
    035 */
    036public class ZstdUtils {
    037
    038    enum CachedAvailability {
    039        DONT_CACHE, CACHED_AVAILABLE, CACHED_UNAVAILABLE
    040    }
    041
    042    /**
    043     * Zstandard Frame Magic Bytes.
    044     */
    045    private static final byte[] ZSTANDARD_FRAME_MAGIC = { (byte) 0x28, (byte) 0xB5, (byte) 0x2F, (byte) 0xFD };
    046
    047    /**
    048     * Skippable Frame Magic Bytes - the three common bytes.
    049     */
    050    private static final byte[] SKIPPABLE_FRAME_MAGIC = { (byte) 0x2A, (byte) 0x4D, (byte) 0x18 };
    051
    052    private static volatile CachedAvailability cachedZstdAvailability;
    053
    054    static {
    055        cachedZstdAvailability = CachedAvailability.DONT_CACHE;
    056        setCacheZstdAvailablity(!OsgiUtils.isRunningInOsgiEnvironment());
    057    }
    058
    059    // only exists to support unit tests
    060    static CachedAvailability getCachedZstdAvailability() {
    061        return cachedZstdAvailability;
    062    }
    063
    064    private static boolean internalIsZstdCompressionAvailable() {
    065        try {
    066            Class.forName("com.github.luben.zstd.ZstdInputStream");
    067            return true;
    068        } catch (final NoClassDefFoundError | Exception error) { // NOSONAR
    069            return false;
    070        }
    071    }
    072
    073    /**
    074     * Are the classes required to support Zstandard compression available?
    075     *
    076     * @return true if the classes required to support Zstandard compression are available
    077     */
    078    public static boolean isZstdCompressionAvailable() {
    079        final CachedAvailability cachedResult = cachedZstdAvailability;
    080        if (cachedResult != CachedAvailability.DONT_CACHE) {
    081            return cachedResult == CachedAvailability.CACHED_AVAILABLE;
    082        }
    083        return internalIsZstdCompressionAvailable();
    084    }
    085
    086    /**
    087     * Checks if the signature matches what is expected for a Zstandard file.
    088     *
    089     * @param signature the bytes to check
    090     * @param length    the number of bytes to check
    091     * @return true if signature matches the Ztstandard or skippable frame magic bytes, false otherwise
    092     */
    093    public static boolean matches(final byte[] signature, final int length) {
    094        if (length < ZSTANDARD_FRAME_MAGIC.length) {
    095            return false;
    096        }
    097        boolean isZstandard = true;
    098        for (int i = 0; i < ZSTANDARD_FRAME_MAGIC.length; ++i) {
    099            if (signature[i] != ZSTANDARD_FRAME_MAGIC[i]) {
    100                isZstandard = false;
    101                break;
    102            }
    103        }
    104        if (isZstandard) {
    105            return true;
    106        }
    107        if (0x50 == (signature[0] & 0xF0)) {
    108            // skippable frame
    109            for (int i = 0; i < SKIPPABLE_FRAME_MAGIC.length; ++i) {
    110                if (signature[i + 1] != SKIPPABLE_FRAME_MAGIC[i]) {
    111                    return false;
    112                }
    113            }
    114            return true;
    115        }
    116        return false;
    117    }
    118
    119    /**
    120     * Sets whether to cache the result of the Zstandard for Java check.
    121     *
    122     * <p>
    123     * This defaults to {@code false} in an OSGi environment and {@code true} otherwise.
    124     * </p>
    125     *
    126     * @param doCache whether to cache the result
    127     */
    128    public static void setCacheZstdAvailablity(final boolean doCache) {
    129        if (!doCache) {
    130            cachedZstdAvailability = CachedAvailability.DONT_CACHE;
    131        } else if (cachedZstdAvailability == CachedAvailability.DONT_CACHE) {
    132            final boolean hasZstd = internalIsZstdCompressionAvailable();
    133            cachedZstdAvailability = hasZstd ? CachedAvailability.CACHED_AVAILABLE : CachedAvailability.CACHED_UNAVAILABLE;
    134        }
    135    }
    136
    137    /** Private constructor to prevent instantiation of this utility class. */
    138    private ZstdUtils() {
    139    }
    140}