/*
* Syncany, www.syncany.org
* Copyright (C) 2011-2015 Philipp C. Heckel <philipp.heckel@gmail.com>
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
package org.syncany.chunk;
import java.security.NoSuchAlgorithmException;
/**
* A fingerprinter is used in content based {@link Chunker}s to determine at which
* byte to break a file into {@link Chunk}s.
*
* <p>Implementations should make sure that the underlying algorithm is fast, because
* the {@link #roll(byte) roll()}-method is called for each byte of a file. It
* should rely on a rolling checksum algorithm (also: rolling hash) to reach optimal
* performance.
*
* @see <a href="http://en.wikipedia.org/wiki/Rolling_hash">http://en.wikipedia.org/wiki/Rolling_hash</a>
* @author Philipp C. Heckel <philipp.heckel@gmail.com>
*/
public abstract class Fingerprinter {
public static Fingerprinter getInstance(String name) throws NoSuchAlgorithmException {
try {
Class<?> clazz = Class.forName(Fingerprinter.class.getPackage().getName()+"."+name+Fingerprinter.class.getSimpleName());
return (Fingerprinter) clazz.newInstance();
}
catch (Exception e) {
throw new NoSuchAlgorithmException("No such fingerprinting algorithm: "+name, e);
}
}
/**
* Return the value of the currently computed checksum.
* @return The currently computed checksum.
*/
public abstract int getValue();
/**
* Reset the checksum.
*/
public abstract void reset();
/**
* "Roll" the checksum, i.e. update the underlying
* rolling checksum by the given content byte.
*
* @param bt The next byte.
*/
public abstract void roll(byte bt);
/**
* Update the checksum with an entirely different block, and
* potentially a different block length.
*
* @param buf The byte array that holds the new block.
* @param off From whence to begin reading.
* @param len The length of the block to read.
*/
public abstract void check(byte[] buf, int off, int len);
/**
* Returns a string representation of the fingerprinter
* implementation.
*/
public abstract String toString();
}