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The file system driver family for ZIP and related archive file types. Add the JAR artifact of this module to the run time class path to make its file system drivers available for service location in the client API modules.

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/*
 * Copyright (C) 2005-2013 Schlichtherle IT Services.
 * All rights reserved. Use is subject to license terms.
 */
package de.schlichtherle.truezip.crypto;

import de.schlichtherle.truezip.util.Threads;
import javax.annotation.concurrent.Immutable;

/**
 * A utility class for enforcing a suspension penalty of at least
 * {@link #MIN_KEY_RETRY_DELAY} milliseconds between two subsequent key
 * verifications.
 * 
 * @author Christian Schlichtherle
 */
@Immutable
public class SuspensionPenalty {

    /**
     * The minimum delay between subsequent attempts to verify a key
     * in milliseconds.
     */
    public static final int MIN_KEY_RETRY_DELAY = 3 * 1000;

    /* Can't touch this - hammer time! */
    private SuspensionPenalty() { }

    /**
     * Call this method in a key verification loop in order to enforce a
     * suspension penalty for providing a wrong key of at least
     * {@link #MIN_KEY_RETRY_DELAY} milliseconds.
     * Interrupting the current thread does not show any effect on this method.
     * 
     * @param  last the last try time.
     *         This should be zero upon the first call.
     *         Subsequent calls should provide the return value of the last
     *         call.
     * @return The new try time.
     */
    public static long enforce(final long last) {
        final long start = System.currentTimeMillis();
        final long elapsed = start - last;
        final long delay = MIN_KEY_RETRY_DELAY - elapsed;
        if (0 < delay) {
            Threads.pause(delay);
            return start + delay; // ~ System.currentTimeMillis()
        } else {
            return start; // ~ System.currentTimeMillis()
        }
    }
}