/*
 * Copyright (C) 2008-2011, Google Inc.
 * Copyright (C) 2007-2008, Robin Rosenberg <robin.rosenberg@dewire.com>
 * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org>
 * 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
 * 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.eclipse.jgit.transport;

import java.io.EOFException;
import java.io.IOException;
import java.io.InputStream;
import java.security.MessageDigest;
import java.text.MessageFormat;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
import java.util.concurrent.TimeUnit;
import java.util.zip.DataFormatException;
import java.util.zip.Inflater;

import org.eclipse.jgit.errors.CorruptObjectException;
import org.eclipse.jgit.errors.MissingObjectException;
import org.eclipse.jgit.errors.TooLargeObjectInPackException;
import org.eclipse.jgit.internal.JGitText;
import org.eclipse.jgit.internal.storage.file.PackLock;
import org.eclipse.jgit.internal.storage.pack.BinaryDelta;
import org.eclipse.jgit.lib.AnyObjectId;
import org.eclipse.jgit.lib.BatchingProgressMonitor;
import org.eclipse.jgit.lib.BlobObjectChecker;
import org.eclipse.jgit.lib.Constants;
import org.eclipse.jgit.lib.InflaterCache;
import org.eclipse.jgit.lib.MutableObjectId;
import org.eclipse.jgit.lib.NullProgressMonitor;
import org.eclipse.jgit.lib.ObjectChecker;
import org.eclipse.jgit.lib.ObjectDatabase;
import org.eclipse.jgit.lib.ObjectId;
import org.eclipse.jgit.lib.ObjectIdOwnerMap;
import org.eclipse.jgit.lib.ObjectIdSubclassMap;
import org.eclipse.jgit.lib.ObjectLoader;
import org.eclipse.jgit.lib.ObjectReader;
import org.eclipse.jgit.lib.ObjectStream;
import org.eclipse.jgit.lib.ProgressMonitor;
import org.eclipse.jgit.util.BlockList;
import org.eclipse.jgit.util.IO;
import org.eclipse.jgit.util.LongMap;
import org.eclipse.jgit.util.NB;
import org.eclipse.jgit.util.sha1.SHA1;

Parses a pack stream and imports it for an ObjectInserter. 
 Applications can acquire an instance of a parser from ObjectInserter's ObjectInserter.newPackParser(InputStream) method. 
 Implementations of ObjectInserter should subclass this type and provide their own logic for the various on*() event methods declared to be abstract. /**
 * Parses a pack stream and imports it for an
 * {@link org.eclipse.jgit.lib.ObjectInserter}.
 * <p>
 * Applications can acquire an instance of a parser from ObjectInserter's
 * {@link org.eclipse.jgit.lib.ObjectInserter#newPackParser(InputStream)}
 * method.
 * <p>
 * Implementations of {@link org.eclipse.jgit.lib.ObjectInserter} should
 * subclass this type and provide their own logic for the various {@code on*()}
 * event methods declared to be abstract.
 */
public abstract class PackParser {
	
Size of the internal stream buffer. /** Size of the internal stream buffer. */
	private static final int BUFFER_SIZE = 8192;

	
Location data is being obtained from. /** Location data is being obtained from. */
	public static enum Source {
		
Data is read from the incoming stream. /** Data is read from the incoming stream. */
		INPUT,

		
Data is read back from the database's buffers. /** Data is read back from the database's buffers. */
		DATABASE;
	}

	
Object database used for loading existing objects. /** Object database used for loading existing objects. */
	private final ObjectDatabase objectDatabase;

	private InflaterStream inflater;

	private byte[] tempBuffer;

	private byte[] hdrBuf;

	private final SHA1 objectHasher = SHA1.newInstance();
	private final MutableObjectId tempObjectId;

	private InputStream in;

	byte[] buf;

	
Position in the input stream of buf[0]. /** Position in the input stream of {@code buf[0]}. */
	private long bBase;

	private int bOffset;

	int bAvail;

	private ObjectChecker objCheck;

	private boolean allowThin;

	private boolean checkObjectCollisions;

	private boolean needBaseObjectIds;

	private boolean checkEofAfterPackFooter;

	private boolean expectDataAfterPackFooter;

	private long expectedObjectCount;

	private PackedObjectInfo[] entries;

	
Every object contained within the incoming pack.
 This is a subset of entries, as thin packs can add additional objects to entries by copying already existing objects from the repository onto the end of the thin pack to make it self-contained. /**
	 * Every object contained within the incoming pack.
	 * <p>
	 * This is a subset of {@link #entries}, as thin packs can add additional
	 * objects to {@code entries} by copying already existing objects from the
	 * repository onto the end of the thin pack to make it self-contained.
	 */
	private ObjectIdSubclassMap<ObjectId> newObjectIds;

	private int deltaCount;

	private int entryCount;

	private ObjectIdOwnerMap<DeltaChain> baseById;

	
Objects referenced by their name from deltas, that aren't in this pack.

This is the set of objects that were copied onto the end of this pack to
make it complete. These objects were not transmitted by the remote peer,
but instead were assumed to already exist in the local repository.
/**
	 * Objects referenced by their name from deltas, that aren't in this pack.
	 * <p>
	 * This is the set of objects that were copied onto the end of this pack to
	 * make it complete. These objects were not transmitted by the remote peer,
	 * but instead were assumed to already exist in the local repository.
	 */
	private ObjectIdSubclassMap<ObjectId> baseObjectIds;

	private LongMap<UnresolvedDelta> baseByPos;

	
Objects need to be double-checked for collision after indexing. /** Objects need to be double-checked for collision after indexing. */
	private BlockList<PackedObjectInfo> collisionCheckObjs;

	private MessageDigest packDigest;

	private ObjectReader readCurs;

	
Message to protect the pack data from garbage collection. /** Message to protect the pack data from garbage collection. */
	private String lockMessage;

	
Git object size limit /** Git object size limit */
	private long maxObjectSizeLimit;

	private final ReceivedPackStatistics.Builder stats =
			new ReceivedPackStatistics.Builder();

	
Initialize a pack parser.
Params:
odb – 
           database the parser will write its objects into.
src – 
           the stream the parser will read./**
	 * Initialize a pack parser.
	 *
	 * @param odb
	 *            database the parser will write its objects into.
	 * @param src
	 *            the stream the parser will read.
	 */
	protected PackParser(ObjectDatabase odb, InputStream src) {
		objectDatabase = odb.newCachedDatabase();
		in = src;

		inflater = new InflaterStream();
		readCurs = objectDatabase.newReader();
		buf = new byte[BUFFER_SIZE];
		tempBuffer = new byte[BUFFER_SIZE];
		hdrBuf = new byte[64];
		tempObjectId = new MutableObjectId();
		packDigest = Constants.newMessageDigest();
		checkObjectCollisions = true;
	}

	
Whether a thin pack (missing base objects) is permitted.
Returns:
true if a thin pack (missing base objects) is permitted./**
	 * Whether a thin pack (missing base objects) is permitted.
	 *
	 * @return {@code true} if a thin pack (missing base objects) is permitted.
	 */
	public boolean isAllowThin() {
		return allowThin;
	}

	
Configure this index pack instance to allow a thin pack.

Thin packs are sometimes used during network transfers to allow a delta
to be sent without a base object. Such packs are not permitted on disk.
Params:
allow – 
           true to enable a thin pack./**
	 * Configure this index pack instance to allow a thin pack.
	 * <p>
	 * Thin packs are sometimes used during network transfers to allow a delta
	 * to be sent without a base object. Such packs are not permitted on disk.
	 *
	 * @param allow
	 *            true to enable a thin pack.
	 */
	public void setAllowThin(boolean allow) {
		allowThin = allow;
	}

	
Whether received objects are verified to prevent collisions.
Returns:
if true received objects are verified to prevent collisions.
Since:
4.1/**
	 * Whether received objects are verified to prevent collisions.
	 *
	 * @return if true received objects are verified to prevent collisions.
	 * @since 4.1
	 */
	protected boolean isCheckObjectCollisions() {
		return checkObjectCollisions;
	}

	
Enable checking for collisions with existing objects.

By default PackParser looks for each received object in the repository.
If the object already exists, the existing object is compared
byte-for-byte with the newly received copy to ensure they are identical.
The receive is aborted with an exception if any byte differs. This check
is necessary to prevent an evil attacker from supplying a replacement
object into this repository in the event that a discovery enabling SHA-1
collisions is made.

This check may be very costly to perform, and some repositories may have
other ways to segregate newly received object data. The check is enabled
by default, but can be explicitly disabled if the implementation can
provide the same guarantee, or is willing to accept the risks associated
with bypassing the check.
Params:
check – 
           true to enable collision checking (strongly encouraged).
Since:
4.1/**
	 * Enable checking for collisions with existing objects.
	 * <p>
	 * By default PackParser looks for each received object in the repository.
	 * If the object already exists, the existing object is compared
	 * byte-for-byte with the newly received copy to ensure they are identical.
	 * The receive is aborted with an exception if any byte differs. This check
	 * is necessary to prevent an evil attacker from supplying a replacement
	 * object into this repository in the event that a discovery enabling SHA-1
	 * collisions is made.
	 * <p>
	 * This check may be very costly to perform, and some repositories may have
	 * other ways to segregate newly received object data. The check is enabled
	 * by default, but can be explicitly disabled if the implementation can
	 * provide the same guarantee, or is willing to accept the risks associated
	 * with bypassing the check.
	 *
	 * @param check
	 *            true to enable collision checking (strongly encouraged).
	 * @since 4.1
	 */
	protected void setCheckObjectCollisions(boolean check) {
		checkObjectCollisions = check;
	}

	
Configure this index pack instance to keep track of new objects.
 By default an index pack doesn't save the new objects that were created when it was instantiated. Setting this flag to true allows the caller to use getNewObjectIds() to retrieve that list. 
Params:
b –  true to enable keeping track of new objects./**
	 * Configure this index pack instance to keep track of new objects.
	 * <p>
	 * By default an index pack doesn't save the new objects that were created
	 * when it was instantiated. Setting this flag to {@code true} allows the
	 * caller to use {@link #getNewObjectIds()} to retrieve that list.
	 *
	 * @param b
	 *            {@code true} to enable keeping track of new objects.
	 */
	public void setNeedNewObjectIds(boolean b) {
		if (b)
			newObjectIds = new ObjectIdSubclassMap<>();
		else
			newObjectIds = null;
	}

	private boolean needNewObjectIds() {
		return newObjectIds != null;
	}

	
Configure this index pack instance to keep track of the objects assumed
for delta bases.
 By default an index pack doesn't save the objects that were used as delta bases. Setting this flag to true will allow the caller to use getBaseObjectIds() to retrieve that list. 
Params:
b –  true to enable keeping track of delta bases./**
	 * Configure this index pack instance to keep track of the objects assumed
	 * for delta bases.
	 * <p>
	 * By default an index pack doesn't save the objects that were used as delta
	 * bases. Setting this flag to {@code true} will allow the caller to use
	 * {@link #getBaseObjectIds()} to retrieve that list.
	 *
	 * @param b
	 *            {@code true} to enable keeping track of delta bases.
	 */
	public void setNeedBaseObjectIds(boolean b) {
		this.needBaseObjectIds = b;
	}

	
Whether the EOF should be read from the input after the footer.
Returns:
true if the EOF should be read from the input after the footer./**
	 * Whether the EOF should be read from the input after the footer.
	 *
	 * @return true if the EOF should be read from the input after the footer.
	 */
	public boolean isCheckEofAfterPackFooter() {
		return checkEofAfterPackFooter;
	}

	
Ensure EOF is read from the input stream after the footer.
Params:
b – 
           true if the EOF should be read; false if it is not checked./**
	 * Ensure EOF is read from the input stream after the footer.
	 *
	 * @param b
	 *            true if the EOF should be read; false if it is not checked.
	 */
	public void setCheckEofAfterPackFooter(boolean b) {
		checkEofAfterPackFooter = b;
	}

	
Whether there is data expected after the pack footer.
Returns:
true if there is data expected after the pack footer./**
	 * Whether there is data expected after the pack footer.
	 *
	 * @return true if there is data expected after the pack footer.
	 */
	public boolean isExpectDataAfterPackFooter() {
		return expectDataAfterPackFooter;
	}

	
Set if there is additional data in InputStream after pack.
Params:
e – 
           true if there is additional data in InputStream after pack.
           This requires the InputStream to support the mark and reset
           functions./**
	 * Set if there is additional data in InputStream after pack.
	 *
	 * @param e
	 *            true if there is additional data in InputStream after pack.
	 *            This requires the InputStream to support the mark and reset
	 *            functions.
	 */
	public void setExpectDataAfterPackFooter(boolean e) {
		expectDataAfterPackFooter = e;
	}

	
Get the new objects that were sent by the user
Returns:
the new objects that were sent by the user/**
	 * Get the new objects that were sent by the user
	 *
	 * @return the new objects that were sent by the user
	 */
	public ObjectIdSubclassMap<ObjectId> getNewObjectIds() {
		if (newObjectIds != null)
			return newObjectIds;
		return new ObjectIdSubclassMap<>();
	}

	
Get set of objects the incoming pack assumed for delta purposes
Returns:
set of objects the incoming pack assumed for delta purposes/**
	 * Get set of objects the incoming pack assumed for delta purposes
	 *
	 * @return set of objects the incoming pack assumed for delta purposes
	 */
	public ObjectIdSubclassMap<ObjectId> getBaseObjectIds() {
		if (baseObjectIds != null)
			return baseObjectIds;
		return new ObjectIdSubclassMap<>();
	}

	
Configure the checker used to validate received objects.

Usually object checking isn't necessary, as Git implementations only
create valid objects in pack files. However, additional checking may be
useful if processing data from an untrusted source.
Params:
oc – 
           the checker instance; null to disable object checking./**
	 * Configure the checker used to validate received objects.
	 * <p>
	 * Usually object checking isn't necessary, as Git implementations only
	 * create valid objects in pack files. However, additional checking may be
	 * useful if processing data from an untrusted source.
	 *
	 * @param oc
	 *            the checker instance; null to disable object checking.
	 */
	public void setObjectChecker(ObjectChecker oc) {
		objCheck = oc;
	}

	
Configure the checker used to validate received objects.

Usually object checking isn't necessary, as Git implementations only
create valid objects in pack files. However, additional checking may be
useful if processing data from an untrusted source.

This is shorthand for:
setObjectChecker(on ? new ObjectChecker() : null);

Params:
on – 
           true to enable the default checker; false to disable it./**
	 * Configure the checker used to validate received objects.
	 * <p>
	 * Usually object checking isn't necessary, as Git implementations only
	 * create valid objects in pack files. However, additional checking may be
	 * useful if processing data from an untrusted source.
	 * <p>
	 * This is shorthand for:
	 *
	 * <pre>
	 * setObjectChecker(on ? new ObjectChecker() : null);
	 * </pre>
	 *
	 * @param on
	 *            true to enable the default checker; false to disable it.
	 */
	public void setObjectChecking(boolean on) {
		setObjectChecker(on ? new ObjectChecker() : null);
	}

	
Get the message to record with the pack lock.
Returns:
the message to record with the pack lock./**
	 * Get the message to record with the pack lock.
	 *
	 * @return the message to record with the pack lock.
	 */
	public String getLockMessage() {
		return lockMessage;
	}

	
Set the lock message for the incoming pack data.
Params:
msg – 
           if not null, the message to associate with the incoming data
           while it is locked to prevent garbage collection./**
	 * Set the lock message for the incoming pack data.
	 *
	 * @param msg
	 *            if not null, the message to associate with the incoming data
	 *            while it is locked to prevent garbage collection.
	 */
	public void setLockMessage(String msg) {
		lockMessage = msg;
	}

	
Set the maximum allowed Git object size.

If an object is larger than the given size the pack-parsing will throw an
exception aborting the parsing.
Params:
limit – 
           the Git object size limit. If zero then there is not limit./**
	 * Set the maximum allowed Git object size.
	 * <p>
	 * If an object is larger than the given size the pack-parsing will throw an
	 * exception aborting the parsing.
	 *
	 * @param limit
	 *            the Git object size limit. If zero then there is not limit.
	 */
	public void setMaxObjectSizeLimit(long limit) {
		maxObjectSizeLimit = limit;
	}

	
Get the number of objects in the stream.
 The object count is only available after parse(ProgressMonitor) has returned. The count may have been increased if the stream was a thin pack, and missing bases objects were appending onto it by the subclass. 
Returns:
number of objects parsed out of the stream./**
	 * Get the number of objects in the stream.
	 * <p>
	 * The object count is only available after {@link #parse(ProgressMonitor)}
	 * has returned. The count may have been increased if the stream was a thin
	 * pack, and missing bases objects were appending onto it by the subclass.
	 *
	 * @return number of objects parsed out of the stream.
	 */
	public int getObjectCount() {
		return entryCount;
	}

	
Get the information about the requested object.
 The object information is only available after parse(ProgressMonitor) has returned. 
Params:
nth –  index of the object in the stream. Must be between 0 and getObjectCount()-1.
Returns:
the object information./**
	 * Get the information about the requested object.
	 * <p>
	 * The object information is only available after
	 * {@link #parse(ProgressMonitor)} has returned.
	 *
	 * @param nth
	 *            index of the object in the stream. Must be between 0 and
	 *            {@link #getObjectCount()}-1.
	 * @return the object information.
	 */
	public PackedObjectInfo getObject(int nth) {
		return entries[nth];
	}

	
Get all of the objects, sorted by their name.
 The object information is only available after parse(ProgressMonitor) has returned. 
 To maintain lower memory usage and good runtime performance, this method sorts the objects in-place and therefore impacts the ordering presented by getObject(int). 
Params:
cmp – 
           comparison function, if null objects are stored by ObjectId.
Returns:
sorted list of objects in this pack stream./**
	 * Get all of the objects, sorted by their name.
	 * <p>
	 * The object information is only available after
	 * {@link #parse(ProgressMonitor)} has returned.
	 * <p>
	 * To maintain lower memory usage and good runtime performance, this method
	 * sorts the objects in-place and therefore impacts the ordering presented
	 * by {@link #getObject(int)}.
	 *
	 * @param cmp
	 *            comparison function, if null objects are stored by ObjectId.
	 * @return sorted list of objects in this pack stream.
	 */
	public List<PackedObjectInfo> getSortedObjectList(
			Comparator<PackedObjectInfo> cmp) {
		Arrays.sort(entries, 0, entryCount, cmp);
		List<PackedObjectInfo> list = Arrays.asList(entries);
		if (entryCount < entries.length)
			list = list.subList(0, entryCount);
		return list;
	}

	
Get the size of the newly created pack.

This will also include the pack index size if an index was created. This
method should only be called after pack parsing is finished.
Returns:
the pack size (including the index size) or -1 if the size cannot
        be determined
Since:
3.3/**
	 * Get the size of the newly created pack.
	 * <p>
	 * This will also include the pack index size if an index was created. This
	 * method should only be called after pack parsing is finished.
	 *
	 * @return the pack size (including the index size) or -1 if the size cannot
	 *         be determined
	 * @since 3.3
	 */
	public long getPackSize() {
		return -1;
	}

	
Returns the statistics of the parsed pack.

This should only be called after pack parsing is finished.
Returns:
ReceivedPackStatistics
Since:
4.6/**
	 * Returns the statistics of the parsed pack.
	 * <p>
	 * This should only be called after pack parsing is finished.
	 *
	 * @return {@link org.eclipse.jgit.transport.ReceivedPackStatistics}
	 * @since 4.6
	 */
	public ReceivedPackStatistics getReceivedPackStatistics() {
		return stats.build();
	}

	
Parse the pack stream.
Params:
progress –  callback to provide progress feedback during parsing. If null, NullProgressMonitor will be used.
Throws:
IOException – 
            the stream is malformed, or contains corrupt objects.
Returns:
the pack lock, if one was requested by setting setLockMessage(String).
Since:
3.0/**
	 * Parse the pack stream.
	 *
	 * @param progress
	 *            callback to provide progress feedback during parsing. If null,
	 *            {@link org.eclipse.jgit.lib.NullProgressMonitor} will be used.
	 * @return the pack lock, if one was requested by setting
	 *         {@link #setLockMessage(String)}.
	 * @throws java.io.IOException
	 *             the stream is malformed, or contains corrupt objects.
	 * @since 3.0
	 */
	public final PackLock parse(ProgressMonitor progress) throws IOException {
		return parse(progress, progress);
	}

	
Parse the pack stream.
Params:
receiving –  receives progress feedback during the initial receiving objects phase. If null, NullProgressMonitor will be used.
resolving – 
           receives progress feedback during the resolving objects phase.
Throws:
IOException – 
            the stream is malformed, or contains corrupt objects.
Returns:
the pack lock, if one was requested by setting setLockMessage(String).
Since:
3.0/**
	 * Parse the pack stream.
	 *
	 * @param receiving
	 *            receives progress feedback during the initial receiving
	 *            objects phase. If null,
	 *            {@link org.eclipse.jgit.lib.NullProgressMonitor} will be used.
	 * @param resolving
	 *            receives progress feedback during the resolving objects phase.
	 * @return the pack lock, if one was requested by setting
	 *         {@link #setLockMessage(String)}.
	 * @throws java.io.IOException
	 *             the stream is malformed, or contains corrupt objects.
	 * @since 3.0
	 */
	public PackLock parse(ProgressMonitor receiving, ProgressMonitor resolving)
			throws IOException {
		if (receiving == null)
			receiving = NullProgressMonitor.INSTANCE;
		if (resolving == null)
			resolving = NullProgressMonitor.INSTANCE;

		if (receiving == resolving)
			receiving.start(2 /* tasks */);
		try {
			readPackHeader();

			entries = new PackedObjectInfo[(int) expectedObjectCount];
			baseById = new ObjectIdOwnerMap<>();
			baseByPos = new LongMap<>();
			collisionCheckObjs = new BlockList<>();

			receiving.beginTask(JGitText.get().receivingObjects,
					(int) expectedObjectCount);
			try {
				for (int done = 0; done < expectedObjectCount; done++) {
					indexOneObject();
					receiving.update(1);
					if (receiving.isCancelled())
						throw new IOException(JGitText.get().downloadCancelled);
				}
				readPackFooter();
				endInput();
			} finally {
				receiving.endTask();
			}

			if (!collisionCheckObjs.isEmpty()) {
				checkObjectCollision();
			}

			if (deltaCount > 0) {
				processDeltas(resolving);
			}

			packDigest = null;
			baseById = null;
			baseByPos = null;
		} finally {
			try {
				if (readCurs != null)
					readCurs.close();
			} finally {
				readCurs = null;
			}

			try {
				inflater.release();
			} finally {
				inflater = null;
			}
		}
		return null; // By default there is no locking.
	}

	private void processDeltas(ProgressMonitor resolving) throws IOException {
		if (resolving instanceof BatchingProgressMonitor) {
			((BatchingProgressMonitor) resolving).setDelayStart(1000,
					TimeUnit.MILLISECONDS);
		}
		resolving.beginTask(JGitText.get().resolvingDeltas, deltaCount);
		resolveDeltas(resolving);
		if (entryCount < expectedObjectCount) {
			if (!isAllowThin()) {
				throw new IOException(MessageFormat.format(
						JGitText.get().packHasUnresolvedDeltas,
						Long.valueOf(expectedObjectCount - entryCount)));
			}

			resolveDeltasWithExternalBases(resolving);

			if (entryCount < expectedObjectCount) {
				throw new IOException(MessageFormat.format(
						JGitText.get().packHasUnresolvedDeltas,
						Long.valueOf(expectedObjectCount - entryCount)));
			}
		}
		resolving.endTask();
	}

	private void resolveDeltas(ProgressMonitor progress)
			throws IOException {
		final int last = entryCount;
		for (int i = 0; i < last; i++) {
			resolveDeltas(entries[i], progress);
			if (progress.isCancelled())
				throw new IOException(
						JGitText.get().downloadCancelledDuringIndexing);
		}
	}

	private void resolveDeltas(final PackedObjectInfo oe,
			ProgressMonitor progress) throws IOException {
		UnresolvedDelta children = firstChildOf(oe);
		if (children == null)
			return;

		DeltaVisit visit = new DeltaVisit();
		visit.nextChild = children;

		ObjectTypeAndSize info = openDatabase(oe, new ObjectTypeAndSize());
		switch (info.type) {
		case Constants.OBJ_COMMIT:
		case Constants.OBJ_TREE:
		case Constants.OBJ_BLOB:
		case Constants.OBJ_TAG:
			visit.data = inflateAndReturn(Source.DATABASE, info.size);
			visit.id = oe;
			break;
		default:
			throw new IOException(MessageFormat.format(
					JGitText.get().unknownObjectType,
					Integer.valueOf(info.type)));
		}

		if (!checkCRC(oe.getCRC())) {
			throw new IOException(MessageFormat.format(
					JGitText.get().corruptionDetectedReReadingAt,
					Long.valueOf(oe.getOffset())));
		}

		resolveDeltas(visit.next(), info.type, info, progress);
	}

	private void resolveDeltas(DeltaVisit visit, final int type,
			ObjectTypeAndSize info, ProgressMonitor progress)
			throws IOException {
		stats.addDeltaObject(type);
		do {
			progress.update(1);
			info = openDatabase(visit.delta, info);
			switch (info.type) {
			case Constants.OBJ_OFS_DELTA:
			case Constants.OBJ_REF_DELTA:
				break;

			default:
				throw new IOException(MessageFormat.format(
						JGitText.get().unknownObjectType,
						Integer.valueOf(info.type)));
			}

			byte[] delta = inflateAndReturn(Source.DATABASE, info.size);
			checkIfTooLarge(type, BinaryDelta.getResultSize(delta));

			visit.data = BinaryDelta.apply(visit.parent.data, delta);
			delta = null;

			if (!checkCRC(visit.delta.crc))
				throw new IOException(MessageFormat.format(
						JGitText.get().corruptionDetectedReReadingAt,
						Long.valueOf(visit.delta.position)));

			SHA1 objectDigest = objectHasher.reset();
			objectDigest.update(Constants.encodedTypeString(type));
			objectDigest.update((byte) ' ');
			objectDigest.update(Constants.encodeASCII(visit.data.length));
			objectDigest.update((byte) 0);
			objectDigest.update(visit.data);
			objectDigest.digest(tempObjectId);

			verifySafeObject(tempObjectId, type, visit.data);
			if (isCheckObjectCollisions() && readCurs.has(tempObjectId)) {
				checkObjectCollision(tempObjectId, type, visit.data);
			}

			PackedObjectInfo oe;
			oe = newInfo(tempObjectId, visit.delta, visit.parent.id);
			oe.setOffset(visit.delta.position);
			oe.setType(type);
			onInflatedObjectData(oe, type, visit.data);
			addObjectAndTrack(oe);
			visit.id = oe;

			visit.nextChild = firstChildOf(oe);
			visit = visit.next();
		} while (visit != null);
	}

	private final void checkIfTooLarge(int typeCode, long size)
			throws IOException {
		if (0 < maxObjectSizeLimit && maxObjectSizeLimit < size) {
			switch (typeCode) {
			case Constants.OBJ_COMMIT:
			case Constants.OBJ_TREE:
			case Constants.OBJ_BLOB:
			case Constants.OBJ_TAG:
				throw new TooLargeObjectInPackException(size, maxObjectSizeLimit);

			case Constants.OBJ_OFS_DELTA:
			case Constants.OBJ_REF_DELTA:
				throw new TooLargeObjectInPackException(size, maxObjectSizeLimit);

			default:
				throw new IOException(MessageFormat.format(
						JGitText.get().unknownObjectType,
						Integer.valueOf(typeCode)));
			}
		}
		if (size > Integer.MAX_VALUE - 8) {
			throw new TooLargeObjectInPackException(size, Integer.MAX_VALUE - 8);
		}
	}

	
Read the header of the current object.
 After the header has been parsed, this method automatically invokes onObjectHeader(Source, byte[], int, int) to allow the implementation to update its internal checksums for the bytes read. 

When this method returns the database will be positioned on the first
byte of the deflated data stream.
Params:
info – 
           the info object to populate.
Throws:
IOException – 
            the size cannot be read.
Returns:
info, after populating./**
	 * Read the header of the current object.
	 * <p>
	 * After the header has been parsed, this method automatically invokes
	 * {@link #onObjectHeader(Source, byte[], int, int)} to allow the
	 * implementation to update its internal checksums for the bytes read.
	 * <p>
	 * When this method returns the database will be positioned on the first
	 * byte of the deflated data stream.
	 *
	 * @param info
	 *            the info object to populate.
	 * @return {@code info}, after populating.
	 * @throws java.io.IOException
	 *             the size cannot be read.
	 */
	protected ObjectTypeAndSize readObjectHeader(ObjectTypeAndSize info)
			throws IOException {
		int hdrPtr = 0;
		int c = readFrom(Source.DATABASE);
		hdrBuf[hdrPtr++] = (byte) c;

		info.type = (c >> 4) & 7;
		long sz = c & 15;
		int shift = 4;
		while ((c & 0x80) != 0) {
			c = readFrom(Source.DATABASE);
			hdrBuf[hdrPtr++] = (byte) c;
			sz += ((long) (c & 0x7f)) << shift;
			shift += 7;
		}
		info.size = sz;

		switch (info.type) {
		case Constants.OBJ_COMMIT:
		case Constants.OBJ_TREE:
		case Constants.OBJ_BLOB:
		case Constants.OBJ_TAG:
			onObjectHeader(Source.DATABASE, hdrBuf, 0, hdrPtr);
			break;

		case Constants.OBJ_OFS_DELTA:
			c = readFrom(Source.DATABASE);
			hdrBuf[hdrPtr++] = (byte) c;
			while ((c & 128) != 0) {
				c = readFrom(Source.DATABASE);
				hdrBuf[hdrPtr++] = (byte) c;
			}
			onObjectHeader(Source.DATABASE, hdrBuf, 0, hdrPtr);
			break;

		case Constants.OBJ_REF_DELTA:
			System.arraycopy(buf, fill(Source.DATABASE, 20), hdrBuf, hdrPtr, 20);
			hdrPtr += 20;
			use(20);
			onObjectHeader(Source.DATABASE, hdrBuf, 0, hdrPtr);
			break;

		default:
			throw new IOException(MessageFormat.format(
					JGitText.get().unknownObjectType,
					Integer.valueOf(info.type)));
		}
		return info;
	}

	private UnresolvedDelta removeBaseById(AnyObjectId id) {
		final DeltaChain d = baseById.get(id);
		return d != null ? d.remove() : null;
	}

	private static UnresolvedDelta reverse(UnresolvedDelta c) {
		UnresolvedDelta tail = null;
		while (c != null) {
			final UnresolvedDelta n = c.next;
			c.next = tail;
			tail = c;
			c = n;
		}
		return tail;
	}

	private UnresolvedDelta firstChildOf(PackedObjectInfo oe) {
		UnresolvedDelta a = reverse(removeBaseById(oe));
		UnresolvedDelta b = reverse(baseByPos.remove(oe.getOffset()));

		if (a == null)
			return b;
		if (b == null)
			return a;

		UnresolvedDelta first = null;
		UnresolvedDelta last = null;
		while (a != null || b != null) {
			UnresolvedDelta curr;
			if (b == null || (a != null && a.position < b.position)) {
				curr = a;
				a = a.next;
			} else {
				curr = b;
				b = b.next;
			}
			if (last != null)
				last.next = curr;
			else
				first = curr;
			last = curr;
			curr.next = null;
		}
		return first;
	}

	private void resolveDeltasWithExternalBases(ProgressMonitor progress)
			throws IOException {
		growEntries(baseById.size());

		if (needBaseObjectIds)
			baseObjectIds = new ObjectIdSubclassMap<>();

		final List<DeltaChain> missing = new ArrayList<>(64);
		for (DeltaChain baseId : baseById) {
			if (baseId.head == null)
				continue;

			if (needBaseObjectIds)
				baseObjectIds.add(baseId);

			final ObjectLoader ldr;
			try {
				ldr = readCurs.open(baseId);
			} catch (MissingObjectException notFound) {
				missing.add(baseId);
				continue;
			}

			final DeltaVisit visit = new DeltaVisit();
			visit.data = ldr.getCachedBytes(Integer.MAX_VALUE);
			visit.id = baseId;
			final int typeCode = ldr.getType();
			final PackedObjectInfo oe = newInfo(baseId, null, null);
			oe.setType(typeCode);
			if (onAppendBase(typeCode, visit.data, oe))
				entries[entryCount++] = oe;
			visit.nextChild = firstChildOf(oe);
			resolveDeltas(visit.next(), typeCode,
					new ObjectTypeAndSize(), progress);

			if (progress.isCancelled())
				throw new IOException(
						JGitText.get().downloadCancelledDuringIndexing);
		}

		for (DeltaChain base : missing) {
			if (base.head != null)
				throw new MissingObjectException(base, "delta base"); //$NON-NLS-1$
		}

		onEndThinPack();
	}

	private void growEntries(int extraObjects) {
		final PackedObjectInfo[] ne;

		ne = new PackedObjectInfo[(int) expectedObjectCount + extraObjects];
		System.arraycopy(entries, 0, ne, 0, entryCount);
		entries = ne;
	}

	private void readPackHeader() throws IOException {
		if (expectDataAfterPackFooter) {
			if (!in.markSupported())
				throw new IOException(
						JGitText.get().inputStreamMustSupportMark);
			in.mark(buf.length);
		}

		final int hdrln = Constants.PACK_SIGNATURE.length + 4 + 4;
		final int p = fill(Source.INPUT, hdrln);
		for (int k = 0; k < Constants.PACK_SIGNATURE.length; k++)
			if (buf[p + k] != Constants.PACK_SIGNATURE[k])
				throw new IOException(JGitText.get().notAPACKFile);

		final long vers = NB.decodeUInt32(buf, p + 4);
		if (vers != 2 && vers != 3)
			throw new IOException(MessageFormat.format(
					JGitText.get().unsupportedPackVersion, Long.valueOf(vers)));
		final long objectCount = NB.decodeUInt32(buf, p + 8);
		use(hdrln);
		setExpectedObjectCount(objectCount);
		onPackHeader(objectCount);
	}

	private void readPackFooter() throws IOException {
		sync();
		final byte[] actHash = packDigest.digest();

		final int c = fill(Source.INPUT, 20);
		final byte[] srcHash = new byte[20];
		System.arraycopy(buf, c, srcHash, 0, 20);
		use(20);

		if (bAvail != 0 && !expectDataAfterPackFooter)
			throw new CorruptObjectException(MessageFormat.format(
					JGitText.get().expectedEOFReceived,
					"\\x" + Integer.toHexString(buf[bOffset] & 0xff))); //$NON-NLS-1$
		if (isCheckEofAfterPackFooter()) {
			int eof = in.read();
			if (0 <= eof)
				throw new CorruptObjectException(MessageFormat.format(
						JGitText.get().expectedEOFReceived,
						"\\x" + Integer.toHexString(eof))); //$NON-NLS-1$
		} else if (bAvail > 0 && expectDataAfterPackFooter) {
			in.reset();
			IO.skipFully(in, bOffset);
		}

		if (!Arrays.equals(actHash, srcHash))
			throw new CorruptObjectException(
					JGitText.get().corruptObjectPackfileChecksumIncorrect);

		onPackFooter(srcHash);
	}

	// Cleanup all resources associated with our input parsing.
	private void endInput() {
		stats.setNumBytesRead(streamPosition());
		in = null;
	}

	// Read one entire object or delta from the input.
	private void indexOneObject() throws IOException {
		final long streamPosition = streamPosition();

		int hdrPtr = 0;
		int c = readFrom(Source.INPUT);
		hdrBuf[hdrPtr++] = (byte) c;

		final int typeCode = (c >> 4) & 7;
		long sz = c & 15;
		int shift = 4;
		while ((c & 0x80) != 0) {
			c = readFrom(Source.INPUT);
			hdrBuf[hdrPtr++] = (byte) c;
			sz += ((long) (c & 0x7f)) << shift;
			shift += 7;
		}

		checkIfTooLarge(typeCode, sz);

		switch (typeCode) {
		case Constants.OBJ_COMMIT:
		case Constants.OBJ_TREE:
		case Constants.OBJ_BLOB:
		case Constants.OBJ_TAG:
			stats.addWholeObject(typeCode);
			onBeginWholeObject(streamPosition, typeCode, sz);
			onObjectHeader(Source.INPUT, hdrBuf, 0, hdrPtr);
			whole(streamPosition, typeCode, sz);
			break;

		case Constants.OBJ_OFS_DELTA: {
			stats.addOffsetDelta();
			c = readFrom(Source.INPUT);
			hdrBuf[hdrPtr++] = (byte) c;
			long ofs = c & 127;
			while ((c & 128) != 0) {
				ofs += 1;
				c = readFrom(Source.INPUT);
				hdrBuf[hdrPtr++] = (byte) c;
				ofs <<= 7;
				ofs += (c & 127);
			}
			final long base = streamPosition - ofs;
			onBeginOfsDelta(streamPosition, base, sz);
			onObjectHeader(Source.INPUT, hdrBuf, 0, hdrPtr);
			inflateAndSkip(Source.INPUT, sz);
			UnresolvedDelta n = onEndDelta();
			n.position = streamPosition;
			n.next = baseByPos.put(base, n);
			deltaCount++;
			break;
		}

		case Constants.OBJ_REF_DELTA: {
			stats.addRefDelta();
			c = fill(Source.INPUT, 20);
			final ObjectId base = ObjectId.fromRaw(buf, c);
			System.arraycopy(buf, c, hdrBuf, hdrPtr, 20);
			hdrPtr += 20;
			use(20);
			DeltaChain r = baseById.get(base);
			if (r == null) {
				r = new DeltaChain(base);
				baseById.add(r);
			}
			onBeginRefDelta(streamPosition, base, sz);
			onObjectHeader(Source.INPUT, hdrBuf, 0, hdrPtr);
			inflateAndSkip(Source.INPUT, sz);
			UnresolvedDelta n = onEndDelta();
			n.position = streamPosition;
			r.add(n);
			deltaCount++;
			break;
		}

		default:
			throw new IOException(
					MessageFormat.format(JGitText.get().unknownObjectType,
							Integer.valueOf(typeCode)));
		}
	}

	private void whole(long pos, int type, long sz)
			throws IOException {
		SHA1 objectDigest = objectHasher.reset();
		objectDigest.update(Constants.encodedTypeString(type));
		objectDigest.update((byte) ' ');
		objectDigest.update(Constants.encodeASCII(sz));
		objectDigest.update((byte) 0);

		final byte[] data;
		if (type == Constants.OBJ_BLOB) {
			byte[] readBuffer = buffer();
			BlobObjectChecker checker = null;
			if (objCheck != null) {
				checker = objCheck.newBlobObjectChecker();
			}
			if (checker == null) {
				checker = BlobObjectChecker.NULL_CHECKER;
			}
			long cnt = 0;
			try (InputStream inf = inflate(Source.INPUT, sz)) {
				while (cnt < sz) {
					int r = inf.read(readBuffer);
					if (r <= 0)
						break;
					objectDigest.update(readBuffer, 0, r);
					checker.update(readBuffer, 0, r);
					cnt += r;
				}
			}
			objectDigest.digest(tempObjectId);
			checker.endBlob(tempObjectId);
			data = null;
		} else {
			data = inflateAndReturn(Source.INPUT, sz);
			objectDigest.update(data);
			objectDigest.digest(tempObjectId);
			verifySafeObject(tempObjectId, type, data);
		}

		PackedObjectInfo obj = newInfo(tempObjectId, null, null);
		obj.setOffset(pos);
		obj.setType(type);
		onEndWholeObject(obj);
		if (data != null)
			onInflatedObjectData(obj, type, data);
		addObjectAndTrack(obj);

		if (isCheckObjectCollisions()) {
			collisionCheckObjs.add(obj);
		}
	}

	
Verify the integrity of the object.
Params:
id – 
           identity of the object to be checked.
type – 
           the type of the object.
data – 
           raw content of the object.
Throws:
CorruptObjectException – 
Since:
4.9/**
	 * Verify the integrity of the object.
	 *
	 * @param id
	 *            identity of the object to be checked.
	 * @param type
	 *            the type of the object.
	 * @param data
	 *            raw content of the object.
	 * @throws org.eclipse.jgit.errors.CorruptObjectException
	 * @since 4.9
	 */
	protected void verifySafeObject(final AnyObjectId id, final int type,
			final byte[] data) throws CorruptObjectException {
		if (objCheck != null) {
			try {
				objCheck.check(id, type, data);
			} catch (CorruptObjectException e) {
				if (e.getErrorType() != null) {
					throw e;
				}
				throw new CorruptObjectException(
						MessageFormat.format(JGitText.get().invalidObject,
								Constants.typeString(type), id.name(),
								e.getMessage()),
						e);
			}
		}
	}

	private void checkObjectCollision() throws IOException {
		for (PackedObjectInfo obj : collisionCheckObjs) {
			if (!readCurs.has(obj)) {
				continue;
			}
			checkObjectCollision(obj);
		}
	}

	private void checkObjectCollision(PackedObjectInfo obj)
			throws IOException {
		ObjectTypeAndSize info = openDatabase(obj, new ObjectTypeAndSize());
		final byte[] readBuffer = buffer();
		final byte[] curBuffer = new byte[readBuffer.length];
		long sz = info.size;
		try (ObjectStream cur = readCurs.open(obj, info.type).openStream()) {
			if (cur.getSize() != sz) {
				throw new IOException(MessageFormat.format(
						JGitText.get().collisionOn, obj.name()));
			}
			try (InputStream pck = inflate(Source.DATABASE, sz)) {
				while (0 < sz) {
					int n = (int) Math.min(readBuffer.length, sz);
					IO.readFully(cur, curBuffer, 0, n);
					IO.readFully(pck, readBuffer, 0, n);
					for (int i = 0; i < n; i++) {
						if (curBuffer[i] != readBuffer[i]) {
							throw new IOException(MessageFormat.format(
									JGitText.get().collisionOn, obj.name()));
						}
					}
					sz -= n;
				}
			}
		} catch (MissingObjectException notLocal) {
			// This is OK, we don't have a copy of the object locally
			// but the API throws when we try to read it as usually it's
			// an error to read something that doesn't exist.
		}
	}

	private void checkObjectCollision(AnyObjectId obj, int type, byte[] data)
			throws IOException {
		try {
			final ObjectLoader ldr = readCurs.open(obj, type);
			final byte[] existingData = ldr.getCachedBytes(data.length);
			if (!Arrays.equals(data, existingData)) {
				throw new IOException(MessageFormat.format(
						JGitText.get().collisionOn, obj.name()));
			}
		} catch (MissingObjectException notLocal) {
			// This is OK, we don't have a copy of the object locally
			// but the API throws when we try to read it as usually its
			// an error to read something that doesn't exist.
		}
	}

	
Returns:
current position of the input stream being parsed./** @return current position of the input stream being parsed. */
	private long streamPosition() {
		return bBase + bOffset;
	}

	private ObjectTypeAndSize openDatabase(PackedObjectInfo obj,
			ObjectTypeAndSize info) throws IOException {
		bOffset = 0;
		bAvail = 0;
		return seekDatabase(obj, info);
	}

	private ObjectTypeAndSize openDatabase(UnresolvedDelta delta,
			ObjectTypeAndSize info) throws IOException {
		bOffset = 0;
		bAvail = 0;
		return seekDatabase(delta, info);
	}

	// Consume exactly one byte from the buffer and return it.
	private int readFrom(Source src) throws IOException {
		if (bAvail == 0)
			fill(src, 1);
		bAvail--;
		return buf[bOffset++] & 0xff;
	}

	// Consume cnt bytes from the buffer.
	void use(int cnt) {
		bOffset += cnt;
		bAvail -= cnt;
	}

	// Ensure at least need bytes are available in {@link #buf}.
	int fill(Source src, int need) throws IOException {
		while (bAvail < need) {
			int next = bOffset + bAvail;
			int free = buf.length - next;
			if (free + bAvail < need) {
				switch (src) {
				case INPUT:
					sync();
					break;
				case DATABASE:
					if (bAvail > 0)
						System.arraycopy(buf, bOffset, buf, 0, bAvail);
					bOffset = 0;
					break;
				}
				next = bAvail;
				free = buf.length - next;
			}
			switch (src) {
			case INPUT:
				next = in.read(buf, next, free);
				break;
			case DATABASE:
				next = readDatabase(buf, next, free);
				break;
			}
			if (next <= 0)
				throw new EOFException(
						JGitText.get().packfileIsTruncatedNoParam);
			bAvail += next;
		}
		return bOffset;
	}

	// Store consumed bytes in {@link #buf} up to {@link #bOffset}.
	private void sync() throws IOException {
		packDigest.update(buf, 0, bOffset);
		onStoreStream(buf, 0, bOffset);
		if (expectDataAfterPackFooter) {
			if (bAvail > 0) {
				in.reset();
				IO.skipFully(in, bOffset);
				bAvail = 0;
			}
			in.mark(buf.length);
		} else if (bAvail > 0)
			System.arraycopy(buf, bOffset, buf, 0, bAvail);
		bBase += bOffset;
		bOffset = 0;
	}

	
Get a temporary byte array for use by the caller.
Returns:
a temporary byte array for use by the caller./**
	 * Get a temporary byte array for use by the caller.
	 *
	 * @return a temporary byte array for use by the caller.
	 */
	protected byte[] buffer() {
		return tempBuffer;
	}

	
Construct a PackedObjectInfo instance for this parser.
Params:
id – 
           identity of the object to be tracked.
delta – 
           if the object was previously an unresolved delta, this is the
           delta object that was tracking it. Otherwise null.
deltaBase – 
           if the object was previously an unresolved delta, this is the
           ObjectId of the base of the delta. The base may be outside of
           the pack stream if the stream was a thin-pack.
Returns:
info object containing this object's data./**
	 * Construct a PackedObjectInfo instance for this parser.
	 *
	 * @param id
	 *            identity of the object to be tracked.
	 * @param delta
	 *            if the object was previously an unresolved delta, this is the
	 *            delta object that was tracking it. Otherwise null.
	 * @param deltaBase
	 *            if the object was previously an unresolved delta, this is the
	 *            ObjectId of the base of the delta. The base may be outside of
	 *            the pack stream if the stream was a thin-pack.
	 * @return info object containing this object's data.
	 */
	protected PackedObjectInfo newInfo(AnyObjectId id, UnresolvedDelta delta,
			ObjectId deltaBase) {
		PackedObjectInfo oe = new PackedObjectInfo(id);
		if (delta != null)
			oe.setCRC(delta.crc);
		return oe;
	}

	
Set the expected number of objects in the pack stream.

The object count in the pack header is not always correct for some Dfs
pack files. e.g. INSERT pack always assume 1 object in the header since
the actual object count is unknown when the pack is written.
 If external implementation wants to overwrite the expectedObjectCount, they should call this method during onPackHeader(long). 
Params:
expectedObjectCount – a long.
Since:
4.9/**
	 * Set the expected number of objects in the pack stream.
	 * <p>
	 * The object count in the pack header is not always correct for some Dfs
	 * pack files. e.g. INSERT pack always assume 1 object in the header since
	 * the actual object count is unknown when the pack is written.
	 * <p>
	 * If external implementation wants to overwrite the expectedObjectCount,
	 * they should call this method during {@link #onPackHeader(long)}.
	 *
	 * @param expectedObjectCount a long.
	 * @since 4.9
	 */
	protected void setExpectedObjectCount(long expectedObjectCount) {
		this.expectedObjectCount = expectedObjectCount;
	}

	
Store bytes received from the raw stream.
 This method is invoked during parse(ProgressMonitor) as data is consumed from the incoming stream. Implementors may use this event to archive the raw incoming stream to the destination repository in large chunks, without paying attention to object boundaries. 
 The only component of the pack not supplied to this method is the last 20 bytes of the pack that comprise the trailing SHA-1 checksum. Those are passed to onPackFooter(byte[]). 
Params:
raw – 
           buffer to copy data out of.
pos – 
           first offset within the buffer that is valid.
len – 
           number of bytes in the buffer that are valid.
Throws:
IOException – 
            the stream cannot be archived./**
	 * Store bytes received from the raw stream.
	 * <p>
	 * This method is invoked during {@link #parse(ProgressMonitor)} as data is
	 * consumed from the incoming stream. Implementors may use this event to
	 * archive the raw incoming stream to the destination repository in large
	 * chunks, without paying attention to object boundaries.
	 * <p>
	 * The only component of the pack not supplied to this method is the last 20
	 * bytes of the pack that comprise the trailing SHA-1 checksum. Those are
	 * passed to {@link #onPackFooter(byte[])}.
	 *
	 * @param raw
	 *            buffer to copy data out of.
	 * @param pos
	 *            first offset within the buffer that is valid.
	 * @param len
	 *            number of bytes in the buffer that are valid.
	 * @throws java.io.IOException
	 *             the stream cannot be archived.
	 */
	protected abstract void onStoreStream(byte[] raw, int pos, int len)
			throws IOException;

	
Store (and/or checksum) an object header.
 Invoked after any of the onBegin() events. The entire header is supplied in a single invocation, before any object data is supplied. 
Params:
src – 
           where the data came from
raw – 
           buffer to read data from.
pos – 
           first offset within buffer that is valid.
len – 
           number of bytes in buffer that are valid.
Throws:
IOException – 
            the stream cannot be archived./**
	 * Store (and/or checksum) an object header.
	 * <p>
	 * Invoked after any of the {@code onBegin()} events. The entire header is
	 * supplied in a single invocation, before any object data is supplied.
	 *
	 * @param src
	 *            where the data came from
	 * @param raw
	 *            buffer to read data from.
	 * @param pos
	 *            first offset within buffer that is valid.
	 * @param len
	 *            number of bytes in buffer that are valid.
	 * @throws java.io.IOException
	 *             the stream cannot be archived.
	 */
	protected abstract void onObjectHeader(Source src, byte[] raw, int pos,
			int len) throws IOException;

	
Store (and/or checksum) a portion of an object's data.

This method may be invoked multiple times per object, depending on the
size of the object, the size of the parser's internal read buffer, and
the alignment of the object relative to the read buffer.
 Invoked after onObjectHeader(Source, byte[], int, int). 
Params:
src – 
           where the data came from
raw – 
           buffer to read data from.
pos – 
           first offset within buffer that is valid.
len – 
           number of bytes in buffer that are valid.
Throws:
IOException – 
            the stream cannot be archived./**
	 * Store (and/or checksum) a portion of an object's data.
	 * <p>
	 * This method may be invoked multiple times per object, depending on the
	 * size of the object, the size of the parser's internal read buffer, and
	 * the alignment of the object relative to the read buffer.
	 * <p>
	 * Invoked after {@link #onObjectHeader(Source, byte[], int, int)}.
	 *
	 * @param src
	 *            where the data came from
	 * @param raw
	 *            buffer to read data from.
	 * @param pos
	 *            first offset within buffer that is valid.
	 * @param len
	 *            number of bytes in buffer that are valid.
	 * @throws java.io.IOException
	 *             the stream cannot be archived.
	 */
	protected abstract void onObjectData(Source src, byte[] raw, int pos,
			int len) throws IOException;

	
Invoked for commits, trees, tags, and small blobs.
Params:
obj – 
           the object info, populated.
typeCode – 
           the type of the object.
data – 
           inflated data for the object.
Throws:
IOException – 
            the object cannot be archived./**
	 * Invoked for commits, trees, tags, and small blobs.
	 *
	 * @param obj
	 *            the object info, populated.
	 * @param typeCode
	 *            the type of the object.
	 * @param data
	 *            inflated data for the object.
	 * @throws java.io.IOException
	 *             the object cannot be archived.
	 */
	protected abstract void onInflatedObjectData(PackedObjectInfo obj,
			int typeCode, byte[] data) throws IOException;

	
Provide the implementation with the original stream's pack header.
Params:
objCnt – 
           number of objects expected in the stream.
Throws:
IOException – 
            the implementation refuses to work with this many objects./**
	 * Provide the implementation with the original stream's pack header.
	 *
	 * @param objCnt
	 *            number of objects expected in the stream.
	 * @throws java.io.IOException
	 *             the implementation refuses to work with this many objects.
	 */
	protected abstract void onPackHeader(long objCnt) throws IOException;

	
Provide the implementation with the original stream's pack footer.
Params:
hash – 
           the trailing 20 bytes of the pack, this is a SHA-1 checksum of
           all of the pack data.
Throws:
IOException – 
            the stream cannot be archived./**
	 * Provide the implementation with the original stream's pack footer.
	 *
	 * @param hash
	 *            the trailing 20 bytes of the pack, this is a SHA-1 checksum of
	 *            all of the pack data.
	 * @throws java.io.IOException
	 *             the stream cannot be archived.
	 */
	protected abstract void onPackFooter(byte[] hash) throws IOException;

	
Provide the implementation with a base that was outside of the pack.

This event only occurs on a thin pack for base objects that were outside
of the pack and came from the local repository. Usually an implementation
uses this event to compress the base and append it onto the end of the
pack, so the pack stays self-contained.
Params:
typeCode – 
           type of the base object.
data – 
           complete content of the base object.
info – 
           packed object information for this base. Implementors must
           populate the CRC and offset members if returning true.
Throws:
IOException – 
            the base could not be included into the pack.
Returns:
true if the info should be included in the object list returned by getSortedObjectList(Comparator<PackedObjectInfo>), false if it should not be included./**
	 * Provide the implementation with a base that was outside of the pack.
	 * <p>
	 * This event only occurs on a thin pack for base objects that were outside
	 * of the pack and came from the local repository. Usually an implementation
	 * uses this event to compress the base and append it onto the end of the
	 * pack, so the pack stays self-contained.
	 *
	 * @param typeCode
	 *            type of the base object.
	 * @param data
	 *            complete content of the base object.
	 * @param info
	 *            packed object information for this base. Implementors must
	 *            populate the CRC and offset members if returning true.
	 * @return true if the {@code info} should be included in the object list
	 *         returned by {@link #getSortedObjectList(Comparator)}, false if it
	 *         should not be included.
	 * @throws java.io.IOException
	 *             the base could not be included into the pack.
	 */
	protected abstract boolean onAppendBase(int typeCode, byte[] data,
			PackedObjectInfo info) throws IOException;

	
Event indicating a thin pack has been completely processed.

This event is invoked only if a thin pack has delta references to objects
external from the pack. The event is called after all of those deltas
have been resolved.
Throws:
IOException – 
            the pack cannot be archived./**
	 * Event indicating a thin pack has been completely processed.
	 * <p>
	 * This event is invoked only if a thin pack has delta references to objects
	 * external from the pack. The event is called after all of those deltas
	 * have been resolved.
	 *
	 * @throws java.io.IOException
	 *             the pack cannot be archived.
	 */
	protected abstract void onEndThinPack() throws IOException;

	
Reposition the database to re-read a previously stored object.

If the database is computing CRC-32 checksums for object data, it should
reset its internal CRC instance during this method call.
Params:
obj –  the object position to begin reading from. This is from newInfo(AnyObjectId, UnresolvedDelta, ObjectId).
info – 
           object to populate with type and size.
Throws:
IOException – 
            the database cannot reposition to this location.
Returns:
the info object./**
	 * Reposition the database to re-read a previously stored object.
	 * <p>
	 * If the database is computing CRC-32 checksums for object data, it should
	 * reset its internal CRC instance during this method call.
	 *
	 * @param obj
	 *            the object position to begin reading from. This is from
	 *            {@link #newInfo(AnyObjectId, UnresolvedDelta, ObjectId)}.
	 * @param info
	 *            object to populate with type and size.
	 * @return the {@code info} object.
	 * @throws java.io.IOException
	 *             the database cannot reposition to this location.
	 */
	protected abstract ObjectTypeAndSize seekDatabase(PackedObjectInfo obj,
			ObjectTypeAndSize info) throws IOException;

	
Reposition the database to re-read a previously stored object.

If the database is computing CRC-32 checksums for object data, it should
reset its internal CRC instance during this method call.
Params:
delta –  the object position to begin reading from. This is an instance previously returned by onEndDelta().
info – 
           object to populate with type and size.
Throws:
IOException – 
            the database cannot reposition to this location.
Returns:
the info object./**
	 * Reposition the database to re-read a previously stored object.
	 * <p>
	 * If the database is computing CRC-32 checksums for object data, it should
	 * reset its internal CRC instance during this method call.
	 *
	 * @param delta
	 *            the object position to begin reading from. This is an instance
	 *            previously returned by {@link #onEndDelta()}.
	 * @param info
	 *            object to populate with type and size.
	 * @return the {@code info} object.
	 * @throws java.io.IOException
	 *             the database cannot reposition to this location.
	 */
	protected abstract ObjectTypeAndSize seekDatabase(UnresolvedDelta delta,
			ObjectTypeAndSize info) throws IOException;

	
Read from the database's current position into the buffer.
Params:
dst – 
           the buffer to copy read data into.
pos –  position within dst to start copying data into.
cnt – 
           ideal target number of bytes to read. Actual read length may
           be shorter.
Throws:
IOException – 
            the database cannot be accessed.
Returns:
number of bytes stored./**
	 * Read from the database's current position into the buffer.
	 *
	 * @param dst
	 *            the buffer to copy read data into.
	 * @param pos
	 *            position within {@code dst} to start copying data into.
	 * @param cnt
	 *            ideal target number of bytes to read. Actual read length may
	 *            be shorter.
	 * @return number of bytes stored.
	 * @throws java.io.IOException
	 *             the database cannot be accessed.
	 */
	protected abstract int readDatabase(byte[] dst, int pos, int cnt)
			throws IOException;

	
Check the current CRC matches the expected value.

This method is invoked when an object is read back in from the database
and its data is used during delta resolution. The CRC is validated after
the object has been fully read, allowing the parser to verify there was
no silent data corruption.

Implementations are free to ignore this check by always returning true if
they are performing other data integrity validations at a lower level.
Params:
oldCRC – 
           the prior CRC that was recorded during the first scan of the
           object from the pack stream.
Returns:
true if the CRC matches; false if it does not./**
	 * Check the current CRC matches the expected value.
	 * <p>
	 * This method is invoked when an object is read back in from the database
	 * and its data is used during delta resolution. The CRC is validated after
	 * the object has been fully read, allowing the parser to verify there was
	 * no silent data corruption.
	 * <p>
	 * Implementations are free to ignore this check by always returning true if
	 * they are performing other data integrity validations at a lower level.
	 *
	 * @param oldCRC
	 *            the prior CRC that was recorded during the first scan of the
	 *            object from the pack stream.
	 * @return true if the CRC matches; false if it does not.
	 */
	protected abstract boolean checkCRC(int oldCRC);

	
Event notifying the start of an object stored whole (not as a delta).
Params:
streamPosition – 
           position of this object in the incoming stream.
type –  type of the object; one of Constants.OBJ_COMMIT, Constants.OBJ_TREE, Constants.OBJ_BLOB, or Constants.OBJ_TAG.
inflatedSize – 
           size of the object when fully inflated. The size stored within
           the pack may be larger or smaller, and is not yet known.
Throws:
IOException – 
            the object cannot be recorded./**
	 * Event notifying the start of an object stored whole (not as a delta).
	 *
	 * @param streamPosition
	 *            position of this object in the incoming stream.
	 * @param type
	 *            type of the object; one of
	 *            {@link org.eclipse.jgit.lib.Constants#OBJ_COMMIT},
	 *            {@link org.eclipse.jgit.lib.Constants#OBJ_TREE},
	 *            {@link org.eclipse.jgit.lib.Constants#OBJ_BLOB}, or
	 *            {@link org.eclipse.jgit.lib.Constants#OBJ_TAG}.
	 * @param inflatedSize
	 *            size of the object when fully inflated. The size stored within
	 *            the pack may be larger or smaller, and is not yet known.
	 * @throws java.io.IOException
	 *             the object cannot be recorded.
	 */
	protected abstract void onBeginWholeObject(long streamPosition, int type,
			long inflatedSize) throws IOException;

	
Event notifying the current object.
Params:
info – 
           object information.
Throws:
IOException – 
            the object cannot be recorded./**
	 * Event notifying the current object.
	 *
	 *@param info
	 *            object information.
	 * @throws java.io.IOException
	 *             the object cannot be recorded.
	 */
	protected abstract void onEndWholeObject(PackedObjectInfo info)
			throws IOException;

	
Event notifying start of a delta referencing its base by offset.
Params:
deltaStreamPosition – 
           position of this object in the incoming stream.
baseStreamPosition –  position of the base object in the incoming stream. The base must be before the delta, therefore baseStreamPosition
           &lt; deltaStreamPosition. This is not the position
           returned by a prior end object event.
inflatedSize – 
           size of the delta when fully inflated. The size stored within
           the pack may be larger or smaller, and is not yet known.
Throws:
IOException – 
            the object cannot be recorded./**
	 * Event notifying start of a delta referencing its base by offset.
	 *
	 * @param deltaStreamPosition
	 *            position of this object in the incoming stream.
	 * @param baseStreamPosition
	 *            position of the base object in the incoming stream. The base
	 *            must be before the delta, therefore {@code baseStreamPosition
	 *            &lt; deltaStreamPosition}. This is <b>not</b> the position
	 *            returned by a prior end object event.
	 * @param inflatedSize
	 *            size of the delta when fully inflated. The size stored within
	 *            the pack may be larger or smaller, and is not yet known.
	 * @throws java.io.IOException
	 *             the object cannot be recorded.
	 */
	protected abstract void onBeginOfsDelta(long deltaStreamPosition,
			long baseStreamPosition, long inflatedSize) throws IOException;

	
Event notifying start of a delta referencing its base by ObjectId.
Params:
deltaStreamPosition – 
           position of this object in the incoming stream.
baseId – 
           name of the base object. This object may be later in the
           stream, or might not appear at all in the stream (in the case
           of a thin-pack).
inflatedSize – 
           size of the delta when fully inflated. The size stored within
           the pack may be larger or smaller, and is not yet known.
Throws:
IOException – 
            the object cannot be recorded./**
	 * Event notifying start of a delta referencing its base by ObjectId.
	 *
	 * @param deltaStreamPosition
	 *            position of this object in the incoming stream.
	 * @param baseId
	 *            name of the base object. This object may be later in the
	 *            stream, or might not appear at all in the stream (in the case
	 *            of a thin-pack).
	 * @param inflatedSize
	 *            size of the delta when fully inflated. The size stored within
	 *            the pack may be larger or smaller, and is not yet known.
	 * @throws java.io.IOException
	 *             the object cannot be recorded.
	 */
	protected abstract void onBeginRefDelta(long deltaStreamPosition,
			AnyObjectId baseId, long inflatedSize) throws IOException;

	
Event notifying the current object.
Throws:
IOException – 
            the object cannot be recorded.
Returns:
object information that must be populated with at least the
        offset./**
	 * Event notifying the current object.
	 *
	 *@return object information that must be populated with at least the
	 *         offset.
	 * @throws java.io.IOException
	 *             the object cannot be recorded.
	 */
	protected UnresolvedDelta onEndDelta() throws IOException {
		return new UnresolvedDelta();
	}

	
Type and size information about an object in the database buffer. /** Type and size information about an object in the database buffer. */
	public static class ObjectTypeAndSize {
		
The type of the object. /** The type of the object. */
		public int type;

		
The inflated size of the object. /** The inflated size of the object. */
		public long size;
	}

	private void inflateAndSkip(Source src, long inflatedSize)
			throws IOException {
		try (InputStream inf = inflate(src, inflatedSize)) {
			IO.skipFully(inf, inflatedSize);
		}
	}

	private byte[] inflateAndReturn(Source src, long inflatedSize)
			throws IOException {
		final byte[] dst = new byte[(int) inflatedSize];
		try (InputStream inf = inflate(src, inflatedSize)) {
			IO.readFully(inf, dst, 0, dst.length);
		}
		return dst;
	}

	private InputStream inflate(Source src, long inflatedSize)
			throws IOException {
		inflater.open(src, inflatedSize);
		return inflater;
	}

	private static class DeltaChain extends ObjectIdOwnerMap.Entry {
		UnresolvedDelta head;

		DeltaChain(AnyObjectId id) {
			super(id);
		}

		UnresolvedDelta remove() {
			final UnresolvedDelta r = head;
			if (r != null)
				head = null;
			return r;
		}

		void add(UnresolvedDelta d) {
			d.next = head;
			head = d;
		}
	}

	
Information about an unresolved delta in this pack stream. /** Information about an unresolved delta in this pack stream. */
	public static class UnresolvedDelta {
		long position;

		int crc;

		UnresolvedDelta next;

		
Returns:
offset within the input stream./** @return offset within the input stream. */
		public long getOffset() {
			return position;
		}

		
Returns:
the CRC-32 checksum of the stored delta data./** @return the CRC-32 checksum of the stored delta data. */
		public int getCRC() {
			return crc;
		}

		
Params:
crc32 – 
           the CRC-32 checksum of the stored delta data./**
		 * @param crc32
		 *            the CRC-32 checksum of the stored delta data.
		 */
		public void setCRC(int crc32) {
			crc = crc32;
		}
	}

	private static class DeltaVisit {
		final UnresolvedDelta delta;

		ObjectId id;

		byte[] data;

		DeltaVisit parent;

		UnresolvedDelta nextChild;

		DeltaVisit() {
			this.delta = null; // At the root of the stack we have a base.
		}

		DeltaVisit(DeltaVisit parent) {
			this.parent = parent;
			this.delta = parent.nextChild;
			parent.nextChild = delta.next;
		}

		DeltaVisit next() {
			// If our parent has no more children, discard it.
			if (parent != null && parent.nextChild == null) {
				parent.data = null;
				parent = parent.parent;
			}

			if (nextChild != null)
				return new DeltaVisit(this);

			// If we have no child ourselves, our parent must (if it exists),
			// due to the discard rule above. With no parent, we are done.
			if (parent != null)
				return new DeltaVisit(parent);
			return null;
		}
	}

	private void addObjectAndTrack(PackedObjectInfo oe) {
		entries[entryCount++] = oe;
		if (needNewObjectIds())
			newObjectIds.add(oe);
	}

	private class InflaterStream extends InputStream {
		private final Inflater inf;

		private final byte[] skipBuffer;

		private Source src;

		private long expectedSize;

		private long actualSize;

		private int p;

		InflaterStream() {
			inf = InflaterCache.get();
			skipBuffer = new byte[512];
		}

		void release() {
			inf.reset();
			InflaterCache.release(inf);
		}

		void open(Source source, long inflatedSize) throws IOException {
			src = source;
			expectedSize = inflatedSize;
			actualSize = 0;

			p = fill(src, 1);
			inf.setInput(buf, p, bAvail);
		}

		@Override
		public long skip(long toSkip) throws IOException {
			long n = 0;
			while (n < toSkip) {
				final int cnt = (int) Math.min(skipBuffer.length, toSkip - n);
				final int r = read(skipBuffer, 0, cnt);
				if (r <= 0)
					break;
				n += r;
			}
			return n;
		}

		@Override
		public int read() throws IOException {
			int n = read(skipBuffer, 0, 1);
			return n == 1 ? skipBuffer[0] & 0xff : -1;
		}

		@Override
		public int read(byte[] dst, int pos, int cnt) throws IOException {
			try {
				int n = 0;
				while (n < cnt) {
					int r = inf.inflate(dst, pos + n, cnt - n);
					n += r;
					if (inf.finished())
						break;
					if (inf.needsInput()) {
						onObjectData(src, buf, p, bAvail);
						use(bAvail);

						p = fill(src, 1);
						inf.setInput(buf, p, bAvail);
					} else if (r == 0) {
						throw new CorruptObjectException(MessageFormat.format(
								JGitText.get().packfileCorruptionDetected,
								JGitText.get().unknownZlibError));
					}
				}
				actualSize += n;
				return 0 < n ? n : -1;
			} catch (DataFormatException dfe) {
				throw new CorruptObjectException(MessageFormat.format(JGitText
						.get().packfileCorruptionDetected, dfe.getMessage()));
			}
		}

		@Override
		public void close() throws IOException {
			// We need to read here to enter the loop above and pump the
			// trailing checksum into the Inflater. It should return -1 as the
			// caller was supposed to consume all content.
			//
			if (read(skipBuffer) != -1 || actualSize != expectedSize) {
				throw new CorruptObjectException(MessageFormat.format(JGitText
						.get().packfileCorruptionDetected,
						JGitText.get().wrongDecompressedLength));
			}

			int used = bAvail - inf.getRemaining();
			if (0 < used) {
				onObjectData(src, buf, p, used);
				use(used);
			}

			inf.reset();
		}
	}
}