PackBitmapIndex.java

/*
 * Copyright (C) 2012, 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.file;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.text.MessageFormat;

import org.eclipse.jgit.errors.CorruptObjectException;
import org.eclipse.jgit.internal.JGitText;
import org.eclipse.jgit.lib.AnyObjectId;
import org.eclipse.jgit.lib.ObjectId;
import org.eclipse.jgit.util.io.SilentFileInputStream;

import com.googlecode.javaewah.EWAHCompressedBitmap;

/**
 * Logical representation of the bitmap data stored in the pack index.
 * {@link org.eclipse.jgit.lib.ObjectId}s are encoded as a single integer in the
 * range [0, {@link #getObjectCount()}). Compressed bitmaps are available at
 * certain {@code ObjectId}s, which represent all of the objects reachable from
 * that {@code ObjectId} (include the {@code ObjectId} itself). The meaning of
 * the positions in the bitmaps can be decoded using {@link #getObject(int)} and
 * {@link #ofObjectType(EWAHCompressedBitmap, int)}. Furthermore,
 * {@link #findPosition(AnyObjectId)} can be used to build other bitmaps that a
 * compatible with the encoded bitmaps available from the index.
 */
public abstract class PackBitmapIndex {
    /** Flag bit denoting the bitmap should be reused during index creation. */
    public static final int FLAG_REUSE = 1;

    /**
     * Read an existing pack bitmap index file from a buffered stream.
     * <p>
     * The format of the file will be automatically detected and a proper access
     * implementation for that format will be constructed and returned to the
     * caller. The file may or may not be held open by the returned instance.
     *
     * @param idxFile
     *            existing pack .bitmap to read.
     * @param packIndex
     *            the pack index for the corresponding pack file.
     * @param reverseIndex
     *            the pack reverse index for the corresponding pack file.
     * @return a copy of the index in-memory.
     * @throws java.io.IOException
     *             the stream cannot be read.
     * @throws CorruptObjectException
     *             the stream does not contain a valid pack bitmap index.
     */
    public static PackBitmapIndex open(
            File idxFile, PackIndex packIndex, PackReverseIndex reverseIndex)
            throws IOException {
        try (SilentFileInputStream fd = new SilentFileInputStream(
                idxFile)) {
            try {
                return read(fd, packIndex, reverseIndex);
            } catch (IOException ioe) {
                throw new IOException(
                        MessageFormat.format(JGitText.get().unreadablePackIndex,
                                idxFile.getAbsolutePath()),
                        ioe);
            }
        }
    }

    /**
     * Read an existing pack bitmap index file from a buffered stream.
     * <p>
     * The format of the file will be automatically detected and a proper access
     * implementation for that format will be constructed and returned to the
     * caller. The file may or may not be held open by the returned instance.
     *
     * @param fd
     *            stream to read the bitmap index file from. The stream must be
     *            buffered as some small IOs are performed against the stream.
     *            The caller is responsible for closing the stream.
     * @param packIndex
     *            the pack index for the corresponding pack file.
     * @param reverseIndex
     *            the pack reverse index for the corresponding pack file.
     * @return a copy of the index in-memory.
     * @throws java.io.IOException
     *             the stream cannot be read.
     * @throws CorruptObjectException
     *             the stream does not contain a valid pack bitmap index.
     */
    public static PackBitmapIndex read(
            InputStream fd, PackIndex packIndex, PackReverseIndex reverseIndex)
            throws IOException {
        return new PackBitmapIndexV1(fd, packIndex, reverseIndex);
    }

    /** Footer checksum applied on the bottom of the pack file. */
    byte[] packChecksum;

    /**
     * Finds the position in the bitmap of the object.
     *
     * @param objectId
     *            the id for which the bitmap position will be found.
     * @return the bitmap id or -1 if the object was not found.
     */
    public abstract int findPosition(AnyObjectId objectId);

    /**
     * Get the object at the bitmap position.
     *
     * @param position
     *            the id for which the object will be found.
     * @return the ObjectId.
     * @throws java.lang.IllegalArgumentException
     *             when the item is not found.
     */
    public abstract ObjectId getObject(int position) throws IllegalArgumentException;

    /**
     * Returns a bitmap containing positions for objects that have the given Git
     * type.
     *
     * @param bitmap
     *            the object bitmap.
     * @param type
     *            the Git type.
     * @return the object bitmap with only objects of the Git type.
     */
    public abstract EWAHCompressedBitmap ofObjectType(
            EWAHCompressedBitmap bitmap, int type);

    /**
     * Returns the previously constructed bitmap for the object.
     *
     * @param objectId
     *            the id for which the bitmap will be found.
     * @return the bitmap or null if the object was not found.
     */
    public abstract EWAHCompressedBitmap getBitmap(AnyObjectId objectId);

    /**
     * Obtain the total number of objects described by this index.
     * {@code getObjectCount() - 1} is the largest bit that will be set in a
     * bitmap.
     *
     * @return number of objects in this index, and likewise in the associated
     *         pack that this index was generated from.
     */
    public abstract int getObjectCount();

    /**
     * Returns the number of bitmaps in this bitmap index.
     *
     * @return the number of bitmaps in this bitmap index.
     */
    public abstract int getBitmapCount();
}