ShowPackDelta.java

/*
 * Copyright (C) 2010, 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.pgm.debug;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.util.Collections;
import java.util.zip.InflaterInputStream;

import org.eclipse.jgit.errors.MissingObjectException;
import org.eclipse.jgit.errors.StoredObjectRepresentationNotAvailableException;
import org.eclipse.jgit.internal.storage.pack.BinaryDelta;
import org.eclipse.jgit.internal.storage.pack.ObjectReuseAsIs;
import org.eclipse.jgit.internal.storage.pack.ObjectToPack;
import org.eclipse.jgit.internal.storage.pack.PackOutputStream;
import org.eclipse.jgit.internal.storage.pack.PackWriter;
import org.eclipse.jgit.internal.storage.pack.StoredObjectRepresentation;
import org.eclipse.jgit.lib.NullProgressMonitor;
import org.eclipse.jgit.lib.ObjectId;
import org.eclipse.jgit.lib.ObjectReader;
import org.eclipse.jgit.pgm.Command;
import org.eclipse.jgit.pgm.TextBuiltin;
import org.eclipse.jgit.revwalk.RevObject;
import org.eclipse.jgit.revwalk.RevWalk;
import org.eclipse.jgit.util.TemporaryBuffer;
import org.kohsuke.args4j.Argument;

@Command(usage = "usage_ShowPackDelta")
class ShowPackDelta extends TextBuiltin {
    @Argument(index = 0)
    private ObjectId objectId;

    /** {@inheritDoc} */
    @Override
    protected void run() throws Exception {
        ObjectReader reader = db.newObjectReader();
        RevObject obj;
        try (RevWalk rw = new RevWalk(reader)) {
            obj = rw.parseAny(objectId);
        }
        byte[] delta = getDelta(reader, obj);

        // We're crossing our fingers that this will be a delta. Double
        // check the size field in the header, it should match.
        //
        long size = reader.getObjectSize(obj, obj.getType());
        try {
            if (BinaryDelta.getResultSize(delta) != size)
                throw die("Object " + obj.name() + " is not a delta"); //$NON-NLS-1$ //$NON-NLS-2$
        } catch (ArrayIndexOutOfBoundsException bad) {
            throw die("Object " + obj.name() + " is not a delta", bad); //$NON-NLS-1$ //$NON-NLS-2$
        }

        outw.println(BinaryDelta.format(delta));
    }

    private static byte[] getDelta(ObjectReader reader, RevObject obj)
            throws IOException, MissingObjectException,
            StoredObjectRepresentationNotAvailableException {
        ObjectReuseAsIs asis = (ObjectReuseAsIs) reader;
        ObjectToPack target = asis.newObjectToPack(obj, obj.getType());

        PackWriter pw = new PackWriter(reader) {
            @Override
            public void select(ObjectToPack otp, StoredObjectRepresentation next) {
                otp.select(next);
            }
        };

        ByteArrayOutputStream buf = new ByteArrayOutputStream();
        asis.selectObjectRepresentation(pw, NullProgressMonitor.INSTANCE,
                Collections.singleton(target));
        asis.copyObjectAsIs(new PackOutputStream(NullProgressMonitor.INSTANCE,
                buf, pw), target, true);

        // At this point the object header has no delta information,
        // because it was output as though it were a whole object.
        // Skip over the header and inflate.
        //
        byte[] bufArray = buf.toByteArray();
        int ptr = 0;
        while ((bufArray[ptr] & 0x80) != 0)
            ptr++;
        ptr++;

        try (TemporaryBuffer.Heap raw = new TemporaryBuffer.Heap(
                bufArray.length);
                InflaterInputStream inf = new InflaterInputStream(
                        new ByteArrayInputStream(bufArray, ptr,
                                bufArray.length))) {
            raw.copy(inf);
            return raw.toByteArray();
        }
    }
}