MD5SumEngine.java

/*
  MD5SumEngine.java

  (c) 2015 Edward Swartz

  All rights reserved. This program and the accompanying materials
  are made available under the terms of the Eclipse Public License v1.0
  which accompanies this distribution, and is available at
  http://www.eclipse.org/legal/epl-v10.html
 */
package v9t9.common.files;

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

import v9t9.common.files.IMD5SumFilter.FilterSegment;
import ejs.base.utils.FileUtils;
import ejs.base.utils.TextUtils;

/**
 * This manages generating MD5 sums.
 * @author ejs
 *
 */
public class MD5SumEngine {
	private MD5SumEngine() {
	}

	/**
	 * Create an MD5 of the content with the filter applied.
	 * @param filter
	 * @param content
	 * @return string of hex-encoded MD5
	 */
	public static String createMD5(IMD5SumFilter filter, byte[] content) {
		try {
			return createMD5(filter, new ByteArrayInputStream(content), content.length);
		} catch (IOException e) {
			// shouldn't happen
			return "";
		}
		
	}
	
	/**
	 * Create an MD5 of the input stream's content with the filter applied.
	 * @param filter
	 * @param is stream (closed at end)
	 * @return string of hex-encoded MD5
	 */
	public static String createMD5(IMD5SumFilter filter, InputStream is, int contentLength) throws IOException {
		if (filter == null)
			return "";
			
		MessageDigest digest;
		try {
			digest = MessageDigest.getInstance("MD5");
		} catch (NoSuchAlgorithmException e) {
			throw new IOException(e);
		}

		List<FilterSegment> segments = new ArrayList<FilterSegment>();
		filter.fillSegments(contentLength, segments);
		try {
			long pos = 0;
			for (FilterSegment segment : segments) {
				long toSkip = segment.offset - pos;
				FileUtils.skipFully(is, toSkip);
				pos += toSkip;
				
				byte[] content = FileUtils.readInputStreamContents(is, segment.length);
				pos += content.length;
				
				digest.update(content);
				
				if (content.length < segment.length) {
					digest.update(new byte[segment.length - content.length]);
				}
			}
			return TextUtils.binaryToString(digest.digest());
		} finally {
			is.close();
		}
	}
	
}