Simplify the PackWriter.preparePack() API

[jgit.git] / org.spearce.jgit / src / org / spearce / jgit / lib / PackWriter.java

/*
 * Copyright (C) 2008, Marek Zawirski <marek.zawirski@gmail.com>
 *
 * 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 Git Development Community 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
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package org.spearce.jgit.lib;

import java.io.BufferedOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.security.MessageDigest;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.zip.Deflater;

import org.spearce.jgit.errors.IncorrectObjectTypeException;
import org.spearce.jgit.errors.MissingObjectException;
import org.spearce.jgit.revwalk.ObjectWalk;
import org.spearce.jgit.revwalk.RevFlag;
import org.spearce.jgit.revwalk.RevObject;
import org.spearce.jgit.revwalk.RevSort;
import org.spearce.jgit.transport.PackedObjectInfo;
import org.spearce.jgit.util.NB;

/**
 * <p>
 * PackWriter class is responsible for generating pack files from specified set
 * of objects from repository. This implementation produce pack files in format
 * version 2.
 * </p>
 * <p>
 * Source of objects may be specified in two ways:
 * <ul>
 * <li>(usually) by providing sets of interesting and uninteresting objects in
 * repository - all interesting objects and their ancestors except uninteresting
 * objects and their ancestors will be included in pack, or</li>
 * <li>by providing iterator of {@link RevObject} specifying exact list and
 * order of objects in pack</li>
 * </ul>
 * Typical usage consists of creating instance intended for some pack,
 * configuring options, preparing the list of objects by calling
 * {@link #preparePack(Iterator)} or
 * {@link #preparePack(Collection, Collection)}, and finally
 * producing the stream with {@link #writePack(OutputStream)}.
 * </p>
 * <p>
 * Class provide set of configurable options and {@link ProgressMonitor}
 * support, as operations may take a long time for big repositories. Deltas
 * searching algorithm is <b>NOT IMPLEMENTED</b> yet - this implementation
 * relies only on deltas and objects reuse.
 * </p>
 * <p>
 * This class is not thread safe, it is intended to be used in one thread, with
 * one instance per created pack. Subsequent calls to writePack result in
 * undefined behavior.
 * </p>
 */

public class PackWriter {
        /**
         * Title of {@link ProgressMonitor} task used during counting objects to
         * pack.
         *
         * @see #preparePack(Collection, Collection)
         */
        public static final String COUNTING_OBJECTS_PROGRESS = "Counting objects";

        /**
         * Title of {@link ProgressMonitor} task used during searching for objects
         * reuse or delta reuse.
         *
         * @see #writePack(OutputStream)
         */
        public static final String SEARCHING_REUSE_PROGRESS = "Compressing objects";

        /**
         * Title of {@link ProgressMonitor} task used during writing out pack
         * (objects)
         *
         * @see #writePack(OutputStream)
         */
        public static final String WRITING_OBJECTS_PROGRESS = "Writing objects";

        /**
         * Default value of deltas reuse option.
         *
         * @see #setReuseDeltas(boolean)
         */
        public static final boolean DEFAULT_REUSE_DELTAS = true;

        /**
         * Default value of objects reuse option.
         *
         * @see #setReuseObjects(boolean)
         */
        public static final boolean DEFAULT_REUSE_OBJECTS = true;

        /**
         * Default value of delta base as offset option.
         *
         * @see #setDeltaBaseAsOffset(boolean)
         */
        public static final boolean DEFAULT_DELTA_BASE_AS_OFFSET = false;

        /**
         * Default value of maximum delta chain depth.
         *
         * @see #setMaxDeltaDepth(int)
         */
        public static final int DEFAULT_MAX_DELTA_DEPTH = 50;

        private static final int PACK_VERSION_GENERATED = 2;

        @SuppressWarnings("unchecked")
        private final List<ObjectToPack> objectsLists[] = new List[Constants.OBJ_TAG + 1];
        {
                objectsLists[0] = Collections.<ObjectToPack> emptyList();
                objectsLists[Constants.OBJ_COMMIT] = new ArrayList<ObjectToPack>();
                objectsLists[Constants.OBJ_TREE] = new ArrayList<ObjectToPack>();
                objectsLists[Constants.OBJ_BLOB] = new ArrayList<ObjectToPack>();
                objectsLists[Constants.OBJ_TAG] = new ArrayList<ObjectToPack>();
        }

        private final ObjectIdSubclassMap<ObjectToPack> objectsMap = new ObjectIdSubclassMap<ObjectToPack>();

        // edge objects for thin packs
        private final ObjectIdSubclassMap<ObjectId> edgeObjects = new ObjectIdSubclassMap<ObjectId>();

        private final Repository db;

        private PackOutputStream out;

        private final Deflater deflater;

        private ProgressMonitor initMonitor;

        private ProgressMonitor writeMonitor;

        private final byte[] buf = new byte[16384]; // 16 KB

        private final WindowCursor windowCursor = new WindowCursor();

        private List<ObjectToPack> sortedByName;

        private byte packcsum[];

        private boolean reuseDeltas = DEFAULT_REUSE_DELTAS;

        private boolean reuseObjects = DEFAULT_REUSE_OBJECTS;

        private boolean deltaBaseAsOffset = DEFAULT_DELTA_BASE_AS_OFFSET;

        private int maxDeltaDepth = DEFAULT_MAX_DELTA_DEPTH;

        private int outputVersion;

        private boolean thin;

        private boolean ignoreMissingUninteresting = true;

        /**
         * Create writer for specified repository.
         * <p>
         * Objects for packing are specified in {@link #preparePack(Iterator)} or
         * {@link #preparePack(Collection, Collection)}.
         *
         * @param repo
         *            repository where objects are stored.
         * @param monitor
         *            operations progress monitor, used within
         *            {@link #preparePack(Iterator)},
         *            {@link #preparePack(Collection, Collection)}
         *            , or {@link #writePack(OutputStream)}.
         */
        public PackWriter(final Repository repo, final ProgressMonitor monitor) {
                this(repo, monitor, monitor);
        }

        /**
         * Create writer for specified repository.
         * <p>
         * Objects for packing are specified in {@link #preparePack(Iterator)} or
         * {@link #preparePack(Collection, Collection)}.
         *
         * @param repo
         *            repository where objects are stored.
         * @param imonitor
         *            operations progress monitor, used within
         *            {@link #preparePack(Iterator)},
         *            {@link #preparePack(Collection, Collection)}
         * @param wmonitor
         *            operations progress monitor, used within
         *            {@link #writePack(OutputStream)}.
         */
        public PackWriter(final Repository repo, final ProgressMonitor imonitor,
                        final ProgressMonitor wmonitor) {
                this.db = repo;
                initMonitor = imonitor;
                writeMonitor = wmonitor;
                this.deflater = new Deflater(db.getConfig().getCore().getCompression());
                outputVersion = repo.getConfig().getCore().getPackIndexVersion();
        }

        /**
         * Check whether object is configured to reuse deltas existing in
         * repository.
         * <p>
         * Default setting: {@value #DEFAULT_REUSE_DELTAS}
         * </p>
         *
         * @return true if object is configured to reuse deltas; false otherwise.
         */
        public boolean isReuseDeltas() {
                return reuseDeltas;
        }

        /**
         * Set reuse deltas configuration option for this writer. When enabled,
         * writer will search for delta representation of object in repository and
         * use it if possible. Normally, only deltas with base to another object
         * existing in set of objects to pack will be used. Exception is however
         * thin-pack (see
         * {@link #preparePack(Collection, Collection)} and
         * {@link #preparePack(Iterator)}) where base object must exist on other
         * side machine.
         * <p>
         * When raw delta data is directly copied from a pack file, checksum is
         * computed to verify data.
         * </p>
         * <p>
         * Default setting: {@value #DEFAULT_REUSE_DELTAS}
         * </p>
         *
         * @param reuseDeltas
         *            boolean indicating whether or not try to reuse deltas.
         */
        public void setReuseDeltas(boolean reuseDeltas) {
                this.reuseDeltas = reuseDeltas;
        }

        /**
         * Checks whether object is configured to reuse existing objects
         * representation in repository.
         * <p>
         * Default setting: {@value #DEFAULT_REUSE_OBJECTS}
         * </p>
         *
         * @return true if writer is configured to reuse objects representation from
         *         pack; false otherwise.
         */
        public boolean isReuseObjects() {
                return reuseObjects;
        }

        /**
         * Set reuse objects configuration option for this writer. If enabled,
         * writer searches for representation in a pack file. If possible,
         * compressed data is directly copied from such a pack file. Data checksum
         * is verified.
         * <p>
         * Default setting: {@value #DEFAULT_REUSE_OBJECTS}
         * </p>
         *
         * @param reuseObjects
         *            boolean indicating whether or not writer should reuse existing
         *            objects representation.
         */
        public void setReuseObjects(boolean reuseObjects) {
                this.reuseObjects = reuseObjects;
        }

        /**
         * Check whether writer can store delta base as an offset (new style
         * reducing pack size) or should store it as an object id (legacy style,
         * compatible with old readers).
         * <p>
         * Default setting: {@value #DEFAULT_DELTA_BASE_AS_OFFSET}
         * </p>
         *
         * @return true if delta base is stored as an offset; false if it is stored
         *         as an object id.
         */
        public boolean isDeltaBaseAsOffset() {
                return deltaBaseAsOffset;
        }

        /**
         * Set writer delta base format. Delta base can be written as an offset in a
         * pack file (new approach reducing file size) or as an object id (legacy
         * approach, compatible with old readers).
         * <p>
         * Default setting: {@value #DEFAULT_DELTA_BASE_AS_OFFSET}
         * </p>
         *
         * @param deltaBaseAsOffset
         *            boolean indicating whether delta base can be stored as an
         *            offset.
         */
        public void setDeltaBaseAsOffset(boolean deltaBaseAsOffset) {
                this.deltaBaseAsOffset = deltaBaseAsOffset;
        }

        /**
         * Get maximum depth of delta chain set up for this writer. Generated chains
         * are not longer than this value.
         * <p>
         * Default setting: {@value #DEFAULT_MAX_DELTA_DEPTH}
         * </p>
         *
         * @return maximum delta chain depth.
         */
        public int getMaxDeltaDepth() {
                return maxDeltaDepth;
        }

        /**
         * Set up maximum depth of delta chain for this writer. Generated chains are
         * not longer than this value. Too low value causes low compression level,
         * while too big makes unpacking (reading) longer.
         * <p>
         * Default setting: {@value #DEFAULT_MAX_DELTA_DEPTH}
         * </p>
         *
         * @param maxDeltaDepth
         *            maximum delta chain depth.
         */
        public void setMaxDeltaDepth(int maxDeltaDepth) {
                this.maxDeltaDepth = maxDeltaDepth;
        }

        /** @return true if this writer is producing a thin pack. */
        public boolean isThin() {
                return thin;
        }

        /**
         * @param packthin
         *            a boolean indicating whether writer may pack objects with
         *            delta base object not within set of objects to pack, but
         *            belonging to party repository (uninteresting/boundary) as
         *            determined by set; this kind of pack is used only for
         *            transport; true - to produce thin pack, false - otherwise.
         */
        public void setThin(final boolean packthin) {
                thin = packthin;
        }

        /**
         * @return true to ignore objects that are uninteresting and also not found
         *         on local disk; false to throw a {@link MissingObjectException}
         *         out of {@link #preparePack(Collection, Collection)} if an
         *         uninteresting object is not in the source repository. By default,
         *         true, permitting gracefully ignoring of uninteresting objects.
         */
        public boolean isIgnoreMissingUninteresting() {
                return ignoreMissingUninteresting;
        }

        /**
         * @param ignore
         *            true if writer should ignore non existing uninteresting
         *            objects during construction set of objects to pack; false
         *            otherwise - non existing uninteresting objects may cause
         *            {@link MissingObjectException}
         */
        public void setIgnoreMissingUninteresting(final boolean ignore) {
                ignoreMissingUninteresting = ignore;
        }

        /**
         * Set the pack index file format version this instance will create.
         *
         * @param version
         *            the version to write. The special version 0 designates the
         *            oldest (most compatible) format available for the objects.
         * @see PackIndexWriter
         */
        public void setIndexVersion(final int version) {
                outputVersion = version;
        }

        /**
         * Returns objects number in a pack file that was created by this writer.
         *
         * @return number of objects in pack.
         */
        public int getObjectsNumber() {
                return objectsMap.size();
        }

        /**
         * Prepare the list of objects to be written to the pack stream.
         * <p>
         * Iterator <b>exactly</b> determines which objects are included in a pack
         * and order they appear in pack (except that objects order by type is not
         * needed at input). This order should conform general rules of ordering
         * objects in git - by recency and path (type and delta-base first is
         * internally secured) and responsibility for guaranteeing this order is on
         * a caller side. Iterator must return each id of object to write exactly
         * once.
         * </p>
         * <p>
         * When iterator returns object that has {@link RevFlag#UNINTERESTING} flag,
         * this object won't be included in an output pack. Instead, it is recorded
         * as edge-object (known to remote repository) for thin-pack. In such a case
         * writer may pack objects with delta base object not within set of objects
         * to pack, but belonging to party repository - those marked with
         * {@link RevFlag#UNINTERESTING} flag. This type of pack is used only for
         * transport.
         * </p>
         *
         * @param objectsSource
         *            iterator of object to store in a pack; order of objects within
         *            each type is important, ordering by type is not needed;
         *            allowed types for objects are {@link Constants#OBJ_COMMIT},
         *            {@link Constants#OBJ_TREE}, {@link Constants#OBJ_BLOB} and
         *            {@link Constants#OBJ_TAG}; objects returned by iterator may
         *            be later reused by caller as object id and type are internally
         *            copied in each iteration; if object returned by iterator has
         *            {@link RevFlag#UNINTERESTING} flag set, it won't be included
         *            in a pack, but is considered as edge-object for thin-pack.
         * @throws IOException
         *             when some I/O problem occur during reading objects.
         */
        public void preparePack(final Iterator<RevObject> objectsSource)
                        throws IOException {
                while (objectsSource.hasNext()) {
                        addObject(objectsSource.next());
                }
        }

        /**
         * Prepare the list of objects to be written to the pack stream.
         * <p>
         * Basing on these 2 sets, another set of objects to put in a pack file is
         * created: this set consists of all objects reachable (ancestors) from
         * interesting objects, except uninteresting objects and their ancestors.
         * This method uses class {@link ObjectWalk} extensively to find out that
         * appropriate set of output objects and their optimal order in output pack.
         * Order is consistent with general git in-pack rules: sort by object type,
         * recency, path and delta-base first.
         * </p>
         *
         * @param interestingObjects
         *            collection of objects to be marked as interesting (start
         *            points of graph traversal).
         * @param uninterestingObjects
         *            collection of objects to be marked as uninteresting (end
         *            points of graph traversal).
         * @throws IOException
         *             when some I/O problem occur during reading objects.
         */
        public void preparePack(
                        final Collection<? extends ObjectId> interestingObjects,
                        final Collection<? extends ObjectId> uninterestingObjects)
                        throws IOException {
                ObjectWalk walker = setUpWalker(interestingObjects,
                                uninterestingObjects);
                findObjectsToPack(walker);
        }

        /**
         * Determine if the pack file will contain the requested object.
         *
         * @param id
         *            the object to test the existence of.
         * @return true if the object will appear in the output pack file.
         */
        public boolean willInclude(final AnyObjectId id) {
                return objectsMap.get(id) != null;
        }

        /**
         * Computes SHA-1 of lexicographically sorted objects ids written in this
         * pack, as used to name a pack file in repository.
         *
         * @return ObjectId representing SHA-1 name of a pack that was created.
         */
        public ObjectId computeName() {
                final MessageDigest md = Constants.newMessageDigest();
                for (ObjectToPack otp : sortByName()) {
                        otp.copyRawTo(buf, 0);
                        md.update(buf, 0, Constants.OBJECT_ID_LENGTH);
                }
                return ObjectId.fromRaw(md.digest());
        }

        /**
         * Create an index file to match the pack file just written.
         * <p>
         * This method can only be invoked after {@link #preparePack(Iterator)} or
         * {@link #preparePack(Collection, Collection)} has been
         * invoked and completed successfully. Writing a corresponding index is an
         * optional feature that not all pack users may require.
         *
         * @param indexStream
         *            output for the index data. Caller is responsible for closing
         *            this stream.
         * @throws IOException
         *             the index data could not be written to the supplied stream.
         */
        public void writeIndex(final OutputStream indexStream) throws IOException {
                final List<ObjectToPack> list = sortByName();
                final PackIndexWriter iw;
                if (outputVersion <= 0)
                        iw = PackIndexWriter.createOldestPossible(indexStream, list);
                else
                        iw = PackIndexWriter.createVersion(indexStream, outputVersion);
                iw.write(list, packcsum);
        }

        private List<ObjectToPack> sortByName() {
                if (sortedByName == null) {
                        sortedByName = new ArrayList<ObjectToPack>(objectsMap.size());
                        for (List<ObjectToPack> list : objectsLists) {
                                for (ObjectToPack otp : list)
                                        sortedByName.add(otp);
                        }
                        Collections.sort(sortedByName);
                }
                return sortedByName;
        }

        /**
         * Write the prepared pack to the supplied stream.
         * <p>
         * At first, this method collects and sorts objects to pack, then deltas
         * search is performed if set up accordingly, finally pack stream is
         * written. {@link ProgressMonitor} tasks {@value #SEARCHING_REUSE_PROGRESS}
         * (only if reuseDeltas or reuseObjects is enabled) and
         * {@value #WRITING_OBJECTS_PROGRESS} are updated during packing.
         * </p>
         * <p>
         * All reused objects data checksum (Adler32/CRC32) is computed and
         * validated against existing checksum.
         * </p>
         *
         * @param packStream
         *            output stream of pack data. If the stream is not buffered it
         *            will be buffered by the writer. Caller is responsible for
         *            closing the stream.
         * @throws IOException
         *             an error occurred reading a local object's data to include in
         *             the pack, or writing compressed object data to the output
         *             stream.
         */
        public void writePack(OutputStream packStream) throws IOException {
                if (reuseDeltas || reuseObjects)
                        searchForReuse();

                if (!(packStream instanceof BufferedOutputStream))
                        packStream = new BufferedOutputStream(packStream);
                out = new PackOutputStream(packStream);

                writeMonitor.beginTask(WRITING_OBJECTS_PROGRESS, getObjectsNumber());
                writeHeader();
                writeObjects();
                writeChecksum();

                out.flush();
                windowCursor.release();
                writeMonitor.endTask();
        }

        private void searchForReuse() throws IOException {
                initMonitor.beginTask(SEARCHING_REUSE_PROGRESS, getObjectsNumber());
                final Collection<PackedObjectLoader> reuseLoaders = new ArrayList<PackedObjectLoader>();
                for (List<ObjectToPack> list : objectsLists) {
                        for (ObjectToPack otp : list) {
                                if (initMonitor.isCancelled())
                                        throw new IOException(
                                                        "Packing cancelled during objects writing");
                                reuseLoaders.clear();
                                db.openObjectInAllPacks(otp, reuseLoaders, windowCursor);
                                if (reuseDeltas) {
                                        selectDeltaReuseForObject(otp, reuseLoaders);
                                }
                                // delta reuse is preferred over object reuse
                                if (reuseObjects && !otp.hasReuseLoader()) {
                                        selectObjectReuseForObject(otp, reuseLoaders);
                                }
                                initMonitor.update(1);
                        }
                }

                initMonitor.endTask();
        }

        private void selectDeltaReuseForObject(final ObjectToPack otp,
                        final Collection<PackedObjectLoader> loaders) throws IOException {
                PackedObjectLoader bestLoader = null;
                ObjectId bestBase = null;

                for (PackedObjectLoader loader : loaders) {
                        ObjectId idBase = loader.getDeltaBase();
                        if (idBase == null)
                                continue;
                        ObjectToPack otpBase = objectsMap.get(idBase);

                        // only if base is in set of objects to write or thin-pack's edge
                        if ((otpBase != null || (thin && edgeObjects.get(idBase) != null))
                        // select smallest possible delta if > 1 available
                                        && isBetterDeltaReuseLoader(bestLoader, loader)) {
                                bestLoader = loader;
                                bestBase = (otpBase != null ? otpBase : idBase);
                        }
                }

                if (bestLoader != null) {
                        otp.setReuseLoader(bestLoader);
                        otp.setDeltaBase(bestBase);
                }
        }

        private static boolean isBetterDeltaReuseLoader(
                        PackedObjectLoader currentLoader, PackedObjectLoader loader)
                        throws IOException {
                if (currentLoader == null)
                        return true;
                if (loader.getRawSize() < currentLoader.getRawSize())
                        return true;
                return (loader.getRawSize() == currentLoader.getRawSize()
                                && loader.supportsFastCopyRawData() && !currentLoader
                                .supportsFastCopyRawData());
        }

        private void selectObjectReuseForObject(final ObjectToPack otp,
                        final Collection<PackedObjectLoader> loaders) {
                for (final PackedObjectLoader loader : loaders) {
                        if (loader instanceof WholePackedObjectLoader) {
                                otp.setReuseLoader(loader);
                                return;
                        }
                }
        }

        private void writeHeader() throws IOException {
                System.arraycopy(Constants.PACK_SIGNATURE, 0, buf, 0, 4);
                NB.encodeInt32(buf, 4, PACK_VERSION_GENERATED);
                NB.encodeInt32(buf, 8, getObjectsNumber());
                out.write(buf, 0, 12);
        }

        private void writeObjects() throws IOException {
                for (List<ObjectToPack> list : objectsLists) {
                        for (ObjectToPack otp : list) {
                                if (writeMonitor.isCancelled())
                                        throw new IOException(
                                                        "Packing cancelled during objects writing");
                                if (!otp.isWritten())
                                        writeObject(otp);
                        }
                }
        }

        private void writeObject(final ObjectToPack otp) throws IOException {
                otp.markWantWrite();
                if (otp.isDeltaRepresentation()) {
                        ObjectToPack deltaBase = otp.getDeltaBase();
                        assert deltaBase != null || thin;
                        if (deltaBase != null && !deltaBase.isWritten()) {
                                if (deltaBase.wantWrite()) {
                                        otp.clearDeltaBase(); // cycle detected
                                        otp.disposeLoader();
                                } else {
                                        writeObject(deltaBase);
                                }
                        }
                }

                assert !otp.isWritten();

                out.resetCRC32();
                otp.setOffset(out.length());
                if (otp.isDeltaRepresentation())
                        writeDeltaObject(otp);
                else
                        writeWholeObject(otp);
                otp.setCRC(out.getCRC32());

                writeMonitor.update(1);
        }

        private void writeWholeObject(final ObjectToPack otp) throws IOException {
                if (otp.hasReuseLoader()) {
                        final PackedObjectLoader loader = otp.getReuseLoader();
                        writeObjectHeader(otp.getType(), loader.getSize());
                        loader.copyRawData(out, buf);
                        otp.disposeLoader();
                } else {
                        final ObjectLoader loader = db.openObject(windowCursor, otp);
                        final byte[] data = loader.getCachedBytes();
                        writeObjectHeader(otp.getType(), data.length);
                        deflater.reset();
                        deflater.setInput(data, 0, data.length);
                        deflater.finish();
                        do {
                                final int n = deflater.deflate(buf, 0, buf.length);
                                if (n > 0)
                                        out.write(buf, 0, n);
                        } while (!deflater.finished());
                }
        }

        private void writeDeltaObject(final ObjectToPack otp) throws IOException {
                final PackedObjectLoader loader = otp.getReuseLoader();
                if (deltaBaseAsOffset && otp.getDeltaBase() != null) {
                        writeObjectHeader(Constants.OBJ_OFS_DELTA, loader.getRawSize());

                        final ObjectToPack deltaBase = otp.getDeltaBase();
                        long offsetDiff = otp.getOffset() - deltaBase.getOffset();
                        int pos = buf.length - 1;
                        buf[pos] = (byte) (offsetDiff & 0x7F);
                        while ((offsetDiff >>= 7) > 0) {
                                buf[--pos] = (byte) (0x80 | (--offsetDiff & 0x7F));
                        }

                        out.write(buf, pos, buf.length - pos);
                } else {
                        writeObjectHeader(Constants.OBJ_REF_DELTA, loader.getRawSize());
                        otp.getDeltaBaseId().copyRawTo(buf, 0);
                        out.write(buf, 0, Constants.OBJECT_ID_LENGTH);
                }
                loader.copyRawData(out, buf);
                otp.disposeLoader();
        }

        private void writeObjectHeader(final int objectType, long dataLength)
                        throws IOException {
                long nextLength = dataLength >>> 4;
                int size = 0;
                buf[size++] = (byte) ((nextLength > 0 ? 0x80 : 0x00)
                                | (objectType << 4) | (dataLength & 0x0F));
                dataLength = nextLength;
                while (dataLength > 0) {
                        nextLength >>>= 7;
                        buf[size++] = (byte) ((nextLength > 0 ? 0x80 : 0x00) | (dataLength & 0x7F));
                        dataLength = nextLength;
                }
                out.write(buf, 0, size);
        }

        private void writeChecksum() throws IOException {
                packcsum = out.getDigest();
                out.write(packcsum);
        }

        private ObjectWalk setUpWalker(
                        final Collection<? extends ObjectId> interestingObjects,
                        final Collection<? extends ObjectId> uninterestingObjects)
                        throws MissingObjectException, IOException,
                        IncorrectObjectTypeException {
                final ObjectWalk walker = new ObjectWalk(db);
                walker.sort(RevSort.TOPO);
                walker.sort(RevSort.COMMIT_TIME_DESC, true);
                if (thin)
                        walker.sort(RevSort.BOUNDARY, true);

                for (ObjectId id : interestingObjects) {
                        RevObject o = walker.parseAny(id);
                        walker.markStart(o);
                }
                for (ObjectId id : uninterestingObjects) {
                        final RevObject o;
                        try {
                                o = walker.parseAny(id);
                        } catch (MissingObjectException x) {
                                if (ignoreMissingUninteresting)
                                        continue;
                                throw x;
                        }
                        walker.markUninteresting(o);
                }
                return walker;
        }

        private void findObjectsToPack(final ObjectWalk walker)
                        throws MissingObjectException, IncorrectObjectTypeException,
                        IOException {
                initMonitor.beginTask(COUNTING_OBJECTS_PROGRESS,
                                ProgressMonitor.UNKNOWN);
                RevObject o;

                while ((o = walker.next()) != null) {
                        addObject(o);
                        o.dispose();
                        initMonitor.update(1);
                }
                while ((o = walker.nextObject()) != null) {
                        addObject(o);
                        o.dispose();
                        initMonitor.update(1);
                }
                initMonitor.endTask();
        }

        /**
         * Include one object to the output file.
         * <p>
         * Objects are written in the order they are added. If the same object is
         * added twice, it may be written twice, creating a larger than necessary
         * file.
         *
         * @param object
         *            the object to add.
         * @throws IncorrectObjectTypeException
         *             the object is an unsupported type.
         */
        public void addObject(final RevObject object)
                        throws IncorrectObjectTypeException {
                if (object.has(RevFlag.UNINTERESTING)) {
                        edgeObjects.add(object);
                        thin = true;
                        return;
                }

                final ObjectToPack otp = new ObjectToPack(object, object.getType());
                try {
                        objectsLists[object.getType()].add(otp);
                } catch (ArrayIndexOutOfBoundsException x) {
                        throw new IncorrectObjectTypeException(object,
                                        "COMMIT nor TREE nor BLOB nor TAG");
                } catch (UnsupportedOperationException x) {
                        // index pointing to "dummy" empty list
                        throw new IncorrectObjectTypeException(object,
                                        "COMMIT nor TREE nor BLOB nor TAG");
                }
                objectsMap.add(otp);
        }

        /**
         * Class holding information about object that is going to be packed by
         * {@link PackWriter}. Information include object representation in a
         * pack-file and object status.
         *
         */
        static class ObjectToPack extends PackedObjectInfo {
                private ObjectId deltaBase;

                private PackedObjectLoader reuseLoader;

                /**
                 * Bit field, from bit 0 to bit 31:
                 * <ul>
                 * <li>1 bit: wantWrite</li>
                 * <li>3 bits: type</li>
                 * <li>28 bits: deltaDepth</li>
                 * </ul>
                 */
                private int flags;

                /**
                 * Construct object for specified object id. <br/> By default object is
                 * marked as not written and non-delta packed (as a whole object).
                 *
                 * @param src
                 *            object id of object for packing
                 * @param type
                 *            real type code of the object, not its in-pack type.
                 */
                ObjectToPack(AnyObjectId src, final int type) {
                        super(src);
                        flags |= type << 1;
                }

                /**
                 * @return delta base object id if object is going to be packed in delta
                 *         representation; null otherwise - if going to be packed as a
                 *         whole object.
                 */
                ObjectId getDeltaBaseId() {
                        return deltaBase;
                }

                /**
                 * @return delta base object to pack if object is going to be packed in
                 *         delta representation and delta is specified as object to
                 *         pack; null otherwise - if going to be packed as a whole
                 *         object or delta base is specified only as id.
                 */
                ObjectToPack getDeltaBase() {
                        if (deltaBase instanceof ObjectToPack)
                                return (ObjectToPack) deltaBase;
                        return null;
                }

                /**
                 * Set delta base for the object. Delta base set by this method is used
                 * by {@link PackWriter} to write object - determines its representation
                 * in a created pack.
                 *
                 * @param deltaBase
                 *            delta base object or null if object should be packed as a
                 *            whole object.
                 *
                 */
                void setDeltaBase(ObjectId deltaBase) {
                        this.deltaBase = deltaBase;
                }

                void clearDeltaBase() {
                        this.deltaBase = null;
                }

                /**
                 * @return true if object is going to be written as delta; false
                 *         otherwise.
                 */
                boolean isDeltaRepresentation() {
                        return deltaBase != null;
                }

                /**
                 * Check if object is already written in a pack. This information is
                 * used to achieve delta-base precedence in a pack file.
                 *
                 * @return true if object is already written; false otherwise.
                 */
                boolean isWritten() {
                        return getOffset() != 0;
                }

                PackedObjectLoader getReuseLoader() {
                        return reuseLoader;
                }

                boolean hasReuseLoader() {
                        return reuseLoader != null;
                }

                void setReuseLoader(PackedObjectLoader reuseLoader) {
                        this.reuseLoader = reuseLoader;
                }

                void disposeLoader() {
                        this.reuseLoader = null;
                }

                int getType() {
                        return (flags>>1) & 0x7;
                }

                int getDeltaDepth() {
                        return flags >>> 4;
                }

                void updateDeltaDepth() {
                        final int d;
                        if (deltaBase instanceof ObjectToPack)
                                d = ((ObjectToPack) deltaBase).getDeltaDepth() + 1;
                        else if (deltaBase != null)
                                d = 1;
                        else
                                d = 0;
                        flags = (d << 4) | flags & 0x15;
                }

                boolean wantWrite() {
                        return (flags & 1) == 1;
                }

                void markWantWrite() {
                        flags |= 1;
                }
        }
}