PackFileSnapshot.java

/*
 * Copyright (C) 2019, Matthias Sohn <matthias.sohn@sap.com>
 * and other copyright owners as documented in the project's IP log.
 *
 * This program and the accompanying materials are made available
 * under the terms of the Eclipse Distribution License v1.0 which
 * accompanies this distribution, is reproduced below, and is
 * available at http://www.eclipse.org/org/documents/edl-v10.php
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or
 * without modification, are permitted provided that the following
 * conditions are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 *
 * - Redistributions in binary form must reproduce the above
 *   copyright notice, this list of conditions and the following
 *   disclaimer in the documentation and/or other materials provided
 *   with the distribution.
 *
 * - Neither the name of the Eclipse Foundation, Inc. nor the
 *   names of its contributors may be used to endorse or promote
 *   products derived from this software without specific prior
 *   written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
 * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
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 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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package org.eclipse.jgit.internal.storage.file;

import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;

import org.eclipse.jgit.lib.AnyObjectId;
import org.eclipse.jgit.lib.ObjectId;

class PackFileSnapshot extends FileSnapshot {

    private static final ObjectId MISSING_CHECKSUM = ObjectId.zeroId();

    /**
     * Record a snapshot for a specific packfile path.
     * <p>
     * This method should be invoked before the packfile is accessed.
     *
     * @param path
     *            the path to later remember. The path's current status
     *            information is saved.
     * @return the snapshot.
     */
    public static PackFileSnapshot save(File path) {
        return new PackFileSnapshot(path);
    }

    private AnyObjectId checksum = MISSING_CHECKSUM;

    private boolean wasChecksumChanged;


    PackFileSnapshot(File packFile) {
        super(packFile);
    }

    void setChecksum(AnyObjectId checksum) {
        this.checksum = checksum;
    }

    /** {@inheritDoc} */
    @Override
    public boolean isModified(File packFile) {
        if (!super.isModified(packFile)) {
            return false;
        }
        if (wasSizeChanged() || wasFileKeyChanged()
                || !wasLastModifiedRacilyClean()) {
            return true;
        }
        return isChecksumChanged(packFile);
    }

    boolean isChecksumChanged(File packFile) {
        return wasChecksumChanged = checksum != MISSING_CHECKSUM
                && !checksum.equals(readChecksum(packFile));
    }

    private AnyObjectId readChecksum(File packFile) {
        try (RandomAccessFile fd = new RandomAccessFile(packFile, "r")) { //$NON-NLS-1$
            fd.seek(fd.length() - 20);
            final byte[] buf = new byte[20];
            fd.readFully(buf, 0, 20);
            return ObjectId.fromRaw(buf);
        } catch (IOException e) {
            return MISSING_CHECKSUM;
        }
    }

    boolean wasChecksumChanged() {
        return wasChecksumChanged;
    }

    @SuppressWarnings("nls")
    @Override
    public String toString() {
        return "PackFileSnapshot [checksum=" + checksum + ", "
                + super.toString() + "]";
    }

}