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}