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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 2011-2014 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.crypto;

import java.io.IOException;
import java.io.InputStream;

import com.amazonaws.internal.SdkFilterInputStream;

/**
 * FilterInputStream that captures a range of bytes from a wrapped input stream.
 */
public class ByteRangeCapturingInputStream extends SdkFilterInputStream {
	private final long startingPosition;
	private final long endingPosition;

	private long streamPosition;
	private int blockPosition = 0;
	private final byte[] block;

	private long markedStreamPosition;
	private int markedBlockPosition;

	public ByteRangeCapturingInputStream(InputStream in, long startingPosition, long endingPosition) {
		super(in);

		if (startingPosition >= endingPosition) {
			throw new IllegalArgumentException("Invalid byte range specified: the starting position must be less than the ending position");
		}

		this.startingPosition = startingPosition;
		this.endingPosition = endingPosition;
		int blockSize = (int)(endingPosition - startingPosition);
		block = new byte[blockSize];
	}

	public byte[] getBlock() {
		return block;
	}

	@Override
	public int read() throws IOException {
		int data = super.read();
		if (data == -1) return -1;

		if (streamPosition >= startingPosition && streamPosition <= endingPosition) {
			block[blockPosition++] = (byte)data;
		}

		streamPosition++;
		return data;
	}

	@Override
	public synchronized void mark(int readlimit) {
		super.mark(readlimit);
		if (markSupported()) {
			markedStreamPosition = streamPosition;
			markedBlockPosition = blockPosition;
		}
	}

	@Override
	public synchronized void reset() throws IOException {
		super.reset();
		if (markSupported()) {
			streamPosition = markedStreamPosition;
			blockPosition = markedBlockPosition;
		}
	}

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

		if (streamPosition + bytesRead >= startingPosition && streamPosition <= endingPosition) {
			for (int i = 0; i < bytesRead; i++) {
				if (streamPosition + i >= startingPosition && streamPosition + i < endingPosition) {
					block[blockPosition++] = b[off + i];
				}
			}
		}

		streamPosition += bytesRead;
		return bytesRead;
	}
}