CachedPack.java

/*
 * Copyright (C) 2011, Google Inc. and others
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Distribution License v. 1.0 which is available at
 * https://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

package org.eclipse.jgit.internal.storage.pack;

import java.io.IOException;

/**
 * Describes a pack file
 * {@link org.eclipse.jgit.internal.storage.pack.ObjectReuseAsIs} can append
 * onto a stream.
 */
public abstract class CachedPack {
    /**
     * Get the number of objects in this pack.
     *
     * @return the total object count for the pack.
     * @throws java.io.IOException
     *             if the object count cannot be read.
     */
    public abstract long getObjectCount() throws IOException;

    /**
     * Get the number of delta objects stored in this pack.
     * <p>
     * This is an optional method, not every cached pack storage system knows
     * the precise number of deltas stored within the pack. This number must be
     * smaller than {@link #getObjectCount()} as deltas are not supposed to span
     * across pack files.
     * <p>
     * This method must be fast, if the only way to determine delta counts is to
     * scan the pack file's contents one object at a time, implementors should
     * return 0 and avoid the high cost of the scan.
     *
     * @return the number of deltas; 0 if the number is not known or there are
     *         no deltas.
     * @throws java.io.IOException
     *             if the delta count cannot be read.
     */
    public long getDeltaCount() throws IOException {
        return 0;
    }

    /**
     * Determine if this pack contains the object representation given.
     * <p>
     * PackWriter uses this method during the finding sources phase to prune
     * away any objects from the leading thin-pack that already appear within
     * this pack and should not be sent twice.
     * <p>
     * Implementors are strongly encouraged to rely on looking at {@code rep}
     * only and using its internal state to decide if this object is within this
     * pack. Implementors should ensure a representation from this cached pack
     * is tested as part of
     * {@link org.eclipse.jgit.internal.storage.pack.ObjectReuseAsIs#selectObjectRepresentation(PackWriter, org.eclipse.jgit.lib.ProgressMonitor, Iterable)}
     * , ensuring this method would eventually return true if the object would
     * be included by this cached pack.
     *
     * @param obj
     *            the object being packed. Can be used as an ObjectId.
     * @param rep
     *            representation from the
     *            {@link org.eclipse.jgit.internal.storage.pack.ObjectReuseAsIs}
     *            instance that originally supplied this CachedPack.
     * @return true if this pack contains this object.
     */
    public abstract boolean hasObject(ObjectToPack obj,
            StoredObjectRepresentation rep);
}