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}