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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.services.s3.internal;

import java.io.IOException;
import java.io.InputStream;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

import com.amazonaws.internal.SdkFilterInputStream;

/**
 * Simple InputStream wrapper that examines the wrapped stream's contents as
 * they are read and calculates and MD5 digest.
 */
public class MD5DigestCalculatingInputStream extends SdkFilterInputStream {
    
    /** The MD5 message digest being calculated by this input stream */
    private MessageDigest digest;
    
    public MD5DigestCalculatingInputStream(InputStream in) throws NoSuchAlgorithmException {
        super(in);
        
        digest = MessageDigest.getInstance("MD5");
    }

    public byte[] getMd5Digest() {
        return digest.digest();
    }

    /**
     * Resets the wrapped input stream and the in progress message digest.
     * 
     * @see java.io.InputStream#reset()
     */
    @Override
    public synchronized void reset() throws IOException {
        try {
            digest = MessageDigest.getInstance("MD5");
        } catch (NoSuchAlgorithmException e) {
            /*
             * Not much to do here. We know the algorithm existed when we
             * created the initial MessageDigest in the constructor, so we
             * can be reasonably sure that it's still going to exist if the
             * stream gets reset.
             */
        }

        in.reset();
    }

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

}