| /* |
| * Licensed to the Apache Software Foundation (ASF) under one |
| * or more contributor license agreements. See the NOTICE file |
| * distributed with this work for additional information |
| * regarding copyright ownership. The ASF licenses this file |
| * to you under the Apache License, Version 2.0 (the |
| * "License"); you may not use this file except in compliance |
| * with the License. You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, |
| * software distributed under the License is distributed on an |
| * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY |
| * KIND, either express or implied. See the License for the |
| * specific language governing permissions and limitations |
| * under the License. |
| */ |
| package org.apache.commons.compress.compressors.zstandard; |
| |
| /** |
| * Utility code for the Zstandard compression format. |
| * @ThreadSafe |
| * @since 1.16 |
| */ |
| public class ZstdUtils { |
| |
| enum CachedAvailability { |
| DONT_CACHE, CACHED_AVAILABLE, CACHED_UNAVAILABLE |
| } |
| |
| /** |
| * Zstandard Frame Magic Bytes. |
| */ |
| private static final byte[] ZSTANDARD_FRAME_MAGIC = { |
| (byte) 0x28, (byte) 0xB5, (byte) 0x2F, (byte) 0xFD |
| }; |
| |
| /** |
| * Skippable Frame Magic Bytes - the three common bytes. |
| */ |
| private static final byte[] SKIPPABLE_FRAME_MAGIC = { |
| (byte) 0x2A, (byte) 0x4D, (byte) 0x18 |
| }; |
| |
| private static volatile CachedAvailability cachedZstdAvailability; |
| |
| static { |
| cachedZstdAvailability = CachedAvailability.DONT_CACHE; |
| try { |
| Class.forName("org.osgi.framework.BundleEvent"); |
| } catch (final Exception ex) { // NOSONAR |
| setCacheZstdAvailablity(true); |
| } |
| } |
| |
| /** Private constructor to prevent instantiation of this utility class. */ |
| private ZstdUtils() { |
| } |
| |
| /** |
| * Are the classes required to support Zstandard compression available? |
| * @return true if the classes required to support Zstandard compression are available |
| */ |
| public static boolean isZstdCompressionAvailable() { |
| final CachedAvailability cachedResult = cachedZstdAvailability; |
| if (cachedResult != CachedAvailability.DONT_CACHE) { |
| return cachedResult == CachedAvailability.CACHED_AVAILABLE; |
| } |
| return internalIsZstdCompressionAvailable(); |
| } |
| |
| private static boolean internalIsZstdCompressionAvailable() { |
| try { |
| Class.forName("com.github.luben.zstd.ZstdInputStream"); |
| return true; |
| } catch (NoClassDefFoundError | Exception error) { // NOSONAR |
| return false; |
| } |
| } |
| |
| /** |
| * Whether to cache the result of the Zstandard for Java check. |
| * |
| * <p>This defaults to {@code false} in an OSGi environment and {@code true} otherwise.</p> |
| * @param doCache whether to cache the result |
| */ |
| public static void setCacheZstdAvailablity(final boolean doCache) { |
| if (!doCache) { |
| cachedZstdAvailability = CachedAvailability.DONT_CACHE; |
| } else if (cachedZstdAvailability == CachedAvailability.DONT_CACHE) { |
| final boolean hasZstd = internalIsZstdCompressionAvailable(); |
| cachedZstdAvailability = hasZstd ? CachedAvailability.CACHED_AVAILABLE |
| : CachedAvailability.CACHED_UNAVAILABLE; |
| } |
| } |
| |
| /** |
| * Checks if the signature matches what is expected for a Zstandard file. |
| * |
| * @param signature the bytes to check |
| * @param length the number of bytes to check |
| * @return true if signature matches the Ztstandard or skippable |
| * frame magic bytes, false otherwise |
| */ |
| public static boolean matches(final byte[] signature, final int length) { |
| if (length < ZSTANDARD_FRAME_MAGIC.length) { |
| return false; |
| } |
| |
| boolean isZstandard = true; |
| for (int i = 0; i < ZSTANDARD_FRAME_MAGIC.length; ++i) { |
| if (signature[i] != ZSTANDARD_FRAME_MAGIC[i]) { |
| isZstandard = false; |
| break; |
| } |
| } |
| if (isZstandard) { |
| return true; |
| } |
| |
| if (0x50 == (signature[0] & 0xF0)) { |
| // skippable frame |
| for (int i = 0; i < SKIPPABLE_FRAME_MAGIC.length; ++i) { |
| if (signature[i + 1] != SKIPPABLE_FRAME_MAGIC[i]) { |
| return false; |
| } |
| } |
| |
| return true; |
| } |
| |
| return false; |
| } |
| |
| // only exists to support unit tests |
| static CachedAvailability getCachedZstdAvailability() { |
| return cachedZstdAvailability; |
| } |
| } |