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The AWS Java SDK for Amazon Glacier module holds the client classes that are used for communicating with Amazon Glacier Service
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/*
 * Copyright 2012-2014 Amazon Technologies, Inc.
 *
 * Licensed 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://aws.amazon.com/apache2.0
 *
 * 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.glacier.internal;

import java.io.IOException;
import java.io.InputStream;
import java.security.DigestInputStream;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import com.amazonaws.internal.SdkDigestInputStream;
import com.amazonaws.internal.SdkFilterInputStream;
import com.amazonaws.services.glacier.TreeHashGenerator;

/**
 * Filter input stream that enables tree hash computation on the bytes that
 * it streams.
 */
public class TreeHashInputStream extends SdkFilterInputStream {

    public TreeHashInputStream(InputStream in) throws NoSuchAlgorithmException {
        super(new SdkDigestInputStream(in, MessageDigest.getInstance("SHA-256")));
        this.digestInputStream = (DigestInputStream) super.in;
    }

    /**
     * The private DigestInputStream we use to wrap the source input stream and
     * compute a client-side checksum for every part of the message.
     */
    private final DigestInputStream digestInputStream;

    /**
     * The checksums of megabyte-sized parts of the bytes streamed.
     */
    private final List checksums = new ArrayList();

    private boolean closed = false;

    /**
     * Returns the list of one-megabyte checksums for this input stream. Only
     * valid once the stream has been closed.
     *
     * @throws IOException
     *             If the stream hasn't been closed.
     */
    public List getChecksums() throws IOException {
        if ( !closed ) {
            throw new IOException("Stream must be closed before getting checksums");
        }
        return Collections.unmodifiableList(checksums);
    }

    public String getTreeHash() throws IOException {
        if ( !closed ) {
            throw new IOException("Stream must be closed before getting the tree hash");
        }
        return TreeHashGenerator.calculateTreeHash(getChecksums());
    }

    private int byteOffset = 0;
    private static final int MB = 1024 * 1024;

    @Override
    public int read() throws IOException {
        int read = super.read();
        if ( read >= 0 )
            byteOffset++;

        digestPart();
        return read;
    }

    @Override
    public int read(byte[] b, int off, int len) throws IOException {
        int totalBytesRead = 0;
        int lastBytesRead = 0;
        while ( totalBytesRead < len && lastBytesRead > -1 ) {
            int bytesToRead = Math.min(MB - byteOffset, len - totalBytesRead);

            lastBytesRead = super.read(b, off + totalBytesRead, bytesToRead);
            if ( lastBytesRead > 0 ) {
                totalBytesRead += lastBytesRead;
                byteOffset += lastBytesRead;
            }

            digestPart();
            
            if (lastBytesRead == -1 && totalBytesRead == 0) return -1;
        }

        return totalBytesRead;
    }

    /**
     * Digests the current part of the message, if necessary, and resets digest
     * state.
     */
    private void digestPart() {
        if ( byteOffset >= MB ) {
            byteOffset = 0;
            checksums.add(digestInputStream.getMessageDigest().digest());
            digestInputStream.getMessageDigest().reset();
        }
    }

    @Override
    public void close() throws IOException {
        super.close();

        closed = true;
        if ( byteOffset > 0 ) {
            checksums.add(digestInputStream.getMessageDigest().digest());
        }
    }
}