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Fork of https://github.com/airlift/aircompressor (zstd only). This module is temporary until we get an official release that includes the ZstdInputStream API (which is already implemented by two different people but neither PR shows any progress).
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/*
 * Licensed 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 ai.vespa.airlift.zstd;

import ai.vespa.airlift.compress.Compressor;

import java.nio.Buffer;
import java.nio.ByteBuffer;

import static ai.vespa.airlift.zstd.Constants.MAX_BLOCK_SIZE;
import static ai.vespa.airlift.zstd.UnsafeUtil.getAddress;
import static java.lang.String.format;
import static java.util.Objects.requireNonNull;
import static sun.misc.Unsafe.ARRAY_BYTE_BASE_OFFSET;

public class ZstdCompressor
        implements Compressor
{
    @Override
    public int maxCompressedLength(int uncompressedSize)
    {
        int result = uncompressedSize + (uncompressedSize >>> 8);

        if (uncompressedSize < MAX_BLOCK_SIZE) {
            result += (MAX_BLOCK_SIZE - uncompressedSize) >>> 11;
        }

        return result;
    }

    @Override
    public int compress(byte[] input, int inputOffset, int inputLength, byte[] output, int outputOffset, int maxOutputLength)
    {
        verifyRange(input, inputOffset, inputLength);
        verifyRange(output, outputOffset, maxOutputLength);

        long inputAddress = ARRAY_BYTE_BASE_OFFSET + inputOffset;
        long outputAddress = ARRAY_BYTE_BASE_OFFSET + outputOffset;

        return ZstdFrameCompressor.compress(input, inputAddress, inputAddress + inputLength, output, outputAddress, outputAddress + maxOutputLength, CompressionParameters.DEFAULT_COMPRESSION_LEVEL);
    }

    @Override
    public void compress(ByteBuffer inputBuffer, ByteBuffer outputBuffer)
    {
        // Java 9+ added an overload of various methods in ByteBuffer. When compiling with Java 11+ and targeting Java 8 bytecode
        // the resulting signatures are invalid for JDK 8, so accesses below result in NoSuchMethodError. Accessing the
        // methods through the interface class works around the problem
        // Sidenote: we can't target "javac --release 8" because Unsafe is not available in the signature data for that profile
        Buffer input = inputBuffer;
        Buffer output = outputBuffer;

        Object inputBase;
        long inputAddress;
        long inputLimit;
        if (input.isDirect()) {
            inputBase = null;
            long address = getAddress(input);
            inputAddress = address + input.position();
            inputLimit = address + input.limit();
        }
        else if (input.hasArray()) {
            inputBase = input.array();
            inputAddress = ARRAY_BYTE_BASE_OFFSET + input.arrayOffset() + input.position();
            inputLimit = ARRAY_BYTE_BASE_OFFSET + input.arrayOffset() + input.limit();
        }
        else {
            throw new IllegalArgumentException("Unsupported input ByteBuffer implementation " + input.getClass().getName());
        }

        Object outputBase;
        long outputAddress;
        long outputLimit;
        if (output.isDirect()) {
            outputBase = null;
            long address = getAddress(output);
            outputAddress = address + output.position();
            outputLimit = address + output.limit();
        }
        else if (output.hasArray()) {
            outputBase = output.array();
            outputAddress = ARRAY_BYTE_BASE_OFFSET + output.arrayOffset() + output.position();
            outputLimit = ARRAY_BYTE_BASE_OFFSET + output.arrayOffset() + output.limit();
        }
        else {
            throw new IllegalArgumentException("Unsupported output ByteBuffer implementation " + output.getClass().getName());
        }

        // HACK: Assure JVM does not collect Slice wrappers while compressing, since the
        // collection may trigger freeing of the underlying memory resulting in a segfault
        // There is no other known way to signal to the JVM that an object should not be
        // collected in a block, and technically, the JVM is allowed to eliminate these locks.
        synchronized (input) {
            synchronized (output) {
                int written = ZstdFrameCompressor.compress(
                        inputBase,
                        inputAddress,
                        inputLimit,
                        outputBase,
                        outputAddress,
                        outputLimit,
                        CompressionParameters.DEFAULT_COMPRESSION_LEVEL);
                output.position(output.position() + written);
            }
        }
    }

    private static void verifyRange(byte[] data, int offset, int length)
    {
        requireNonNull(data, "data is null");
        if (offset < 0 || length < 0 || offset + length > data.length) {
            throw new IllegalArgumentException(format("Invalid offset or length (%s, %s) in array of length %s", offset, length, data.length));
        }
    }
}