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