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package com.netease.cloud.services.nos.internal;

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

/**
 * Simple InputStream wrapper that examines the wrapped stream's contents as
 * they are read and calculates and MD5 digest.
 */
public class MD5DigestCalculatingInputStream extends FilterInputStream {

	/** 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;
	}

}