    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    /** Private constructor to prevent instantiation of this utility class. */
    056    private ZstdUtils() {
    057    }
    058
    059    /**
    060     * Are the classes required to support Zstandard compression available?
    061     * @return true if the classes required to support Zstandard compression are available
    062     */
    063    public static boolean isZstdCompressionAvailable() {
    064        final CachedAvailability cachedResult = cachedZstdAvailability;
    065        if (cachedResult != CachedAvailability.DONT_CACHE) {
    066            return cachedResult == CachedAvailability.CACHED_AVAILABLE;
    067        }
    068        return internalIsZstdCompressionAvailable();
    069    }
    070
    071    private static boolean internalIsZstdCompressionAvailable() {
    072        try {
    073            Class.forName("com.github.luben.zstd.ZstdInputStream");
    074            return true;
    075        } catch (final NoClassDefFoundError | Exception error) { // NOSONAR
    076            return false;
    077        }
    078    }
    079
    080    /**
    081     * Whether to cache the result of the Zstandard for Java check.
    082     *
    083     * <p>This defaults to {@code false} in an OSGi environment and {@code true} otherwise.</p>
    084     * @param doCache whether to cache the result
    085     */
    086    public static void setCacheZstdAvailablity(final boolean doCache) {
    087        if (!doCache) {
    088            cachedZstdAvailability = CachedAvailability.DONT_CACHE;
    089        } else if (cachedZstdAvailability == CachedAvailability.DONT_CACHE) {
    090            final boolean hasZstd = internalIsZstdCompressionAvailable();
    091            cachedZstdAvailability = hasZstd ? CachedAvailability.CACHED_AVAILABLE
    092                : CachedAvailability.CACHED_UNAVAILABLE;
    093        }
    094    }
    095
    096    /**
    097     * Checks if the signature matches what is expected for a Zstandard file.
    098     *
    099     * @param   signature     the bytes to check
    100     * @param   length        the number of bytes to check
    101     * @return true if signature matches the Ztstandard or skippable
    102     * frame magic bytes, false otherwise
    103     */
    104    public static boolean matches(final byte[] signature, final int length) {
    105        if (length < ZSTANDARD_FRAME_MAGIC.length) {
    106            return false;
    107        }
    108
    109        boolean isZstandard = true;
    110        for (int i = 0; i < ZSTANDARD_FRAME_MAGIC.length; ++i) {
    111            if (signature[i] != ZSTANDARD_FRAME_MAGIC[i]) {
    112                isZstandard = false;
    113                break;
    114            }
    115        }
    116        if (isZstandard) {
    117            return true;
    118        }
    119
    120        if (0x50 == (signature[0] & 0xF0)) {
    121            // skippable frame
    122            for (int i = 0; i < SKIPPABLE_FRAME_MAGIC.length; ++i) {
    123                if (signature[i + 1] != SKIPPABLE_FRAME_MAGIC[i]) {
    124                    return false;
    125                }
    126            }
    127
    128            return true;
    129        }
    130
    131        return false;
    132    }
    133
    134    // only exists to support unit tests
    135    static CachedAvailability getCachedZstdAvailability() {
    136        return cachedZstdAvailability;
    137    }
    138}