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The AWS SDK for Java with support for OSGi. The AWS 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 2010-2016 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;
    /**
     * The MD5 message digest as at the time when the last {@link #mark(int)}
     * operation was called; always null if mark is not supported.
     */
    private MessageDigest digestLastMarked;

    public MD5DigestCalculatingInputStream(InputStream in) {
        super(in);
        digest = newMD5();
    }

    private MessageDigest newMD5() {
        try {
            return MessageDigest.getInstance("MD5");
        } catch (NoSuchAlgorithmException e) { // should never occur
            throw new IllegalStateException("unexpected", e);
        }
    }
    
    private MessageDigest cloneFrom(MessageDigest from) {
        try {
            return (MessageDigest)from.clone();
        } catch (CloneNotSupportedException e) { // should never occur
            throw new IllegalStateException("unexpected", e);
        }
    }

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

    @Override
    public void mark(int readlimit) {
        if (markSupported()) {
            super.mark(readlimit);
            digestLastMarked = cloneFrom(digest);
        }
    }

    /**
     * Resets the wrapped input stream and the in progress message digest.
     */
    @Override
    public void reset() throws IOException {
        if (markSupported()) {
            super.reset();
            digest = (digestLastMarked == null)
                   // This is necessary so that should there be a reset without a
                   // preceding mark, the MD5 would still be computed correctly.
                   ? newMD5()
                   : cloneFrom(digestLastMarked);
        } else {
            throw new IOException("mark/reset not supported");
        }
    }

    @Override
    public int read() throws IOException {
        int ch = super.read();
        if (ch != -1) {
            digest.update((byte)ch);
        }
        return ch;
    }

    @Override
    public int read(byte[] b, int off, int len) throws IOException {
        int result = super.read(b, off, len);
        if (result != -1) {
            digest.update(b, off, result);
        }
        return result;
    }
}