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/* ====================================================================
   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.poi.poifs.nio;

import org.apache.poi.util.SuppressForbidden;

import java.io.IOException;
import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandles;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.nio.ByteBuffer;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.Objects;

import static java.lang.invoke.MethodHandles.constant;
import static java.lang.invoke.MethodHandles.dropArguments;
import static java.lang.invoke.MethodHandles.filterReturnValue;
import static java.lang.invoke.MethodHandles.guardWithTest;
import static java.lang.invoke.MethodType.methodType;

/**
 * This is taken from Hadoop at https://issues.apache.org/jira/browse/HADOOP-12760 and
 * https://github.com/apache/hadoop/blob/trunk/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/util/CleanerUtil.java
 * Unfortunately this is not available in some general utility library yet, but hopefully will be at some point.
 *
 * sun.misc.Cleaner has moved in OpenJDK 9 and
 * sun.misc.Unsafe#invokeCleaner(ByteBuffer) is the replacement.
 * This class is a hack to use sun.misc.Cleaner in Java 8 and
 * use the replacement in Java 9+.
 * This implementation is inspired by LUCENE-6989.
 */
public final class CleanerUtil {

    // Prevent instantiation
    private CleanerUtil(){}

    /**
     * true, if this platform supports unmapping mmapped files.
     */
    public static final boolean UNMAP_SUPPORTED;

    /**
     * if {@link #UNMAP_SUPPORTED} is {@code false}, this contains the reason
     * why unmapping is not supported.
     */
    public static final String UNMAP_NOT_SUPPORTED_REASON;


    private static final BufferCleaner CLEANER;

    /**
     * Reference to a BufferCleaner that does unmapping.
     * @return {@code null} if not supported.
     */
    public static BufferCleaner getCleaner() {
        return CLEANER;
    }

    static {
        final Object hack = AccessController.doPrivileged(
                (PrivilegedAction) CleanerUtil::unmapHackImpl);
        if (hack instanceof BufferCleaner) {
            CLEANER = (BufferCleaner) hack;
            UNMAP_SUPPORTED = true;
            UNMAP_NOT_SUPPORTED_REASON = null;
        } else {
            CLEANER = null;
            UNMAP_SUPPORTED = false;
            UNMAP_NOT_SUPPORTED_REASON = hack.toString();
        }
    }

    @SuppressForbidden("Java 9 Jigsaw whitelists access to sun.misc.Cleaner, so setAccessible works")
    private static Object unmapHackImpl() {
        final MethodHandles.Lookup lookup = MethodHandles.lookup();
        try {
            try {
                // *** sun.misc.Unsafe unmapping (Java 9+) ***
                final Class unsafeClass = Class.forName("sun.misc.Unsafe");
                // first check if Unsafe has the right method, otherwise we can
                // give up without doing any security critical stuff:
                final MethodHandle unmapper = lookup.findVirtual(unsafeClass,
                        "invokeCleaner", methodType(void.class, ByteBuffer.class));
                // fetch the unsafe instance and bind it to the virtual MH:
                final Field f = unsafeClass.getDeclaredField("theUnsafe");
                f.setAccessible(true);
                final Object theUnsafe = f.get(null);
                return newBufferCleaner(ByteBuffer.class, unmapper.bindTo(theUnsafe));
            } catch (SecurityException se) {
                // rethrow to report errors correctly (we need to catch it here,
                // as we also catch RuntimeException below!):
                throw se;
            } catch (ReflectiveOperationException | RuntimeException e) {
                // *** sun.misc.Cleaner unmapping (Java 8) ***
                final Class directBufferClass =
                        Class.forName("java.nio.DirectByteBuffer");

                final Method m = directBufferClass.getMethod("cleaner");
                m.setAccessible(true);
                final MethodHandle directBufferCleanerMethod = lookup.unreflect(m);
                final Class cleanerClass =
                        directBufferCleanerMethod.type().returnType();

                /*
                 * "Compile" a MethodHandle that basically is equivalent
                 * to the following code:
                 *
                 * void unmapper(ByteBuffer byteBuffer) {
                 *   sun.misc.Cleaner cleaner =
                 *       ((java.nio.DirectByteBuffer) byteBuffer).cleaner();
                 *   if (Objects.nonNull(cleaner)) {
                 *     cleaner.clean();
                 *   } else {
                 *     // the noop is needed because MethodHandles#guardWithTest
                 *     // always needs ELSE
                 *     noop(cleaner);
                 *   }
                 * }
                 */
                final MethodHandle cleanMethod = lookup.findVirtual(
                        cleanerClass, "clean", methodType(void.class));
                final MethodHandle nonNullTest = lookup.findStatic(Objects.class,
                        "nonNull", methodType(boolean.class, Object.class))
                        .asType(methodType(boolean.class, cleanerClass));
                final MethodHandle noop = dropArguments(
                        constant(Void.class, null).asType(methodType(void.class)),
                        0, cleanerClass);
                final MethodHandle unmapper = filterReturnValue(
                        directBufferCleanerMethod,
                        guardWithTest(nonNullTest, cleanMethod, noop))
                        .asType(methodType(void.class, ByteBuffer.class));
                return newBufferCleaner(directBufferClass, unmapper);
            }
        } catch (SecurityException se) {
            return "Unmapping is not supported, because not all required " +
                    "permissions are given to the Hadoop JAR file: " + se +
                    " [Please grant at least the following permissions: " +
                    "RuntimePermission(\"accessClassInPackage.sun.misc\") " +
                    " and ReflectPermission(\"suppressAccessChecks\")]";
        } catch (ReflectiveOperationException | RuntimeException e) {
            return "Unmapping is not supported on this platform, " +
                    "because internal Java APIs are not compatible with " +
                    "this Hadoop version: " + e;
        }
    }

    private static BufferCleaner newBufferCleaner(
            final Class unmappableBufferClass, final MethodHandle unmapper) {
        assert Objects.equals(
                methodType(void.class, ByteBuffer.class), unmapper.type());
        return buffer -> {
            if (!buffer.isDirect()) {
                throw new IllegalArgumentException(
                        "unmapping only works with direct buffers");
            }
            if (!unmappableBufferClass.isInstance(buffer)) {
                throw new IllegalArgumentException("buffer is not an instance of " +
                        unmappableBufferClass.getName());
            }
            final Throwable error = AccessController.doPrivileged(
                    (PrivilegedAction) () -> {
                        try {
                            unmapper.invokeExact(buffer);
                            return null;
                        } catch (Throwable t) {
                            return t;
                        }
                    });
            if (error != null) {
                throw new IOException("Unable to unmap the mapped buffer", error);
            }
        };
    }

    /**
     * Pass in an implementation of this interface to cleanup ByteBuffers.
     * CleanerUtil implements this to allow unmapping of bytebuffers
     * with private Java APIs.
     */
    @FunctionalInterface
    public interface BufferCleaner {
        void freeBuffer(ByteBuffer b) throws IOException;
    }
}
 















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