src/test/java/org/apache/commons/codec/digest/XXHash32OverflowTest.java

/*
 * 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.codec.digest;

import org.junit.Assert;
import org.junit.Assume;
import org.junit.Test;

public class XXHash32OverflowTest {

    /**
     * This test hits an edge case where a very large number of bytes is added to the incremental
     * hash. The data is constructed so that an integer counter of unprocessed bytes will
     * overflow. If this is not handled correctly then the code throws an exception when it
     * copies more data into the unprocessed bytes array.
     */
    @Test
    public void testIncrementalHashWithUnprocessedBytesAndHugeLengthArray() {
        // Assert the test precondition that a large array added to unprocessed bytes
        // will overflow an integer counter. We use the smallest hugeLength possible
        // as some VMs cannot allocate maximum length arrays.
        final int bufferSize = 16;
        final int unprocessedSize = bufferSize - 1;
        final int hugeLength = Integer.MAX_VALUE - (unprocessedSize - 1);
        Assert.assertTrue("This should overflow to negative", unprocessedSize + hugeLength < bufferSize);

        // Check the test can be run
        byte[] bytes = null;
        try {
            bytes = new byte[hugeLength];
        } catch (final OutOfMemoryError ignore) {
            // Some VMs cannot allocate an array this large.
            // Some test environments may not have enough available memory for this.
        }
        Assume.assumeTrue("Cannot allocate array of length " + hugeLength, bytes != null);

        final XXHash32 inc = new XXHash32();
        // Add bytes that should be unprocessed
        inc.update(bytes, 0, unprocessedSize);
        // Add a huge number of bytes to overflow an integer counter of unprocessed bytes.
        inc.update(bytes, 0, hugeLength);
    }
}