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The Amazon Web Services SDK for Java provides Java APIs for building software on AWS' cost-effective, scalable, and reliable infrastructure products. The AWS Java SDK allows developers to code against APIs for all of Amazon's infrastructure web services (Amazon S3, Amazon EC2, Amazon SQS, Amazon Relational Database Service, Amazon AutoScaling, etc).

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/*
 * Copyright 2010-2014 Amazon.com, Inc. or its affiliates. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License").
 * You may not use this file except in compliance with the License.
 * A copy of the License is located at
 *
 *  http://aws.amazon.com/apache2.0
 *
 * or in the "license" file accompanying this file. This file 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 com.amazonaws.util;

import java.io.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.zip.CRC32;

/**
 * Simple InputStream wrapper that examines the wrapped stream's contents as
 * they are read and calculates and CRC32 checksum.
 */
public class CRC32ChecksumCalculatingInputStream extends FilterInputStream {

    /** The CRC32 being calculated by this input stream */
    private CRC32 crc32;

    public CRC32ChecksumCalculatingInputStream(InputStream in) {
        super(in);
        crc32 = new CRC32();
    }

    public long getCRC32Checksum() {
        return crc32.getValue();
    }

    /**
     * Resets the wrapped input stream and the CRC32 computation.
     *
     * @see java.io.InputStream#reset()
     */
    @Override
    public synchronized void reset() throws IOException {
        crc32.reset();
        in.reset();
    }

    /**
     * @see java.io.InputStream#read()
     */
    @Override
    public int read() throws IOException {
        int ch = in.read();
        if (ch != -1) {
            crc32.update(ch);
        }
        return ch;
    }

    /**
     * @see java.io.InputStream#read(byte[], int, int)
     */
    @Override
    public int read(byte[] b, int off, int len) throws IOException {
        int result = in.read(b, off, len);
        if (result != -1) {
            crc32.update(b, off, result);
        }
        return result;
    }

}