/*
    * Copyright (C) 2008-2011, Google Inc.
    * Copyright (C) 2006-2008, 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.internal.storage.dfs;
  
  import static org.eclipse.jgit.internal.storage.dfs.DfsObjDatabase.PackSource.UNREACHABLE_GARBAGE;
  import static org.eclipse.jgit.lib.Constants.OBJECT_ID_LENGTH;
  
  import java.io.IOException;
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.Collections;
  import java.util.Comparator;
  import java.util.HashSet;
  import java.util.Iterator;
  import java.util.LinkedList;
  import java.util.List;
  import java.util.Set;
  import java.util.zip.DataFormatException;
  import java.util.zip.Inflater;
  
  import org.eclipse.jgit.errors.IncorrectObjectTypeException;
  import org.eclipse.jgit.errors.MissingObjectException;
  import org.eclipse.jgit.errors.StoredObjectRepresentationNotAvailableException;
  import org.eclipse.jgit.internal.JGitText;
  import org.eclipse.jgit.internal.storage.dfs.DfsObjDatabase.PackList;
  import org.eclipse.jgit.internal.storage.file.BitmapIndexImpl;
  import org.eclipse.jgit.internal.storage.file.PackBitmapIndex;
  import org.eclipse.jgit.internal.storage.file.PackIndex;
  import org.eclipse.jgit.internal.storage.file.PackReverseIndex;
  import org.eclipse.jgit.internal.storage.pack.CachedPack;
  import org.eclipse.jgit.internal.storage.pack.ObjectReuseAsIs;
  import org.eclipse.jgit.internal.storage.pack.ObjectToPack;
  import org.eclipse.jgit.internal.storage.pack.PackOutputStream;
  import org.eclipse.jgit.internal.storage.pack.PackWriter;
  import org.eclipse.jgit.lib.AbbreviatedObjectId;
  import org.eclipse.jgit.lib.AnyObjectId;
  import org.eclipse.jgit.lib.AsyncObjectLoaderQueue;
  import org.eclipse.jgit.lib.AsyncObjectSizeQueue;
  import org.eclipse.jgit.lib.BitmapIndex;
  import org.eclipse.jgit.lib.BitmapIndex.BitmapBuilder;
  import org.eclipse.jgit.lib.InflaterCache;
  import org.eclipse.jgit.lib.ObjectId;
  import org.eclipse.jgit.lib.ObjectLoader;
  import org.eclipse.jgit.lib.ObjectReader;
  import org.eclipse.jgit.lib.ProgressMonitor;
  import org.eclipse.jgit.util.BlockList;
  
  /**
   * Reader to access repository content through.
   * <p>
   * See the base {@link org.eclipse.jgit.lib.ObjectReader} documentation for
   * details. Notably, a reader is not thread safe.
   */
  public class DfsReader extends ObjectReader implements ObjectReuseAsIs {
  	private static final int MAX_RESOLVE_MATCHES = 256;
  
  	/** Temporary buffer large enough for at least one raw object id. */
 	final byte[] tempId = new byte[OBJECT_ID_LENGTH];
 
 	/** Database this reader loads objects from. */
 	final DfsObjDatabase db;
 
 	final DfsReaderIoStats.Accumulator stats = new DfsReaderIoStats.Accumulator();
 
 	private Inflater inf;
 	private DfsBlock block;
 	private DeltaBaseCache baseCache;
 	private DfsPackFile last;
 	private boolean avoidUnreachable;
 
 	/**
 	 * Initialize a new DfsReader
 	 *
 	 * @param db
 	 *            parent DfsObjDatabase.
 	 */
 	protected DfsReader(DfsObjDatabase db) {
 		this.db = db;
 		this.streamFileThreshold = db.getReaderOptions().getStreamFileThreshold();
 	}
 
 	DfsReaderOptions getOptions() {
 		return db.getReaderOptions();
 	}
 
 	DeltaBaseCache getDeltaBaseCache() {
 		if (baseCache == null)
 			baseCache = new DeltaBaseCache(this);
 		return baseCache;
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public ObjectReader newReader() {
 		return db.newReader();
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public void setAvoidUnreachableObjects(boolean avoid) {
 		avoidUnreachable = avoid;
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public BitmapIndex getBitmapIndex() throws IOException {
 		for (DfsPackFile pack : db.getPacks()) {
 			PackBitmapIndex bitmapIndex = pack.getBitmapIndex(this);
 			if (bitmapIndex != null)
 				return new BitmapIndexImpl(bitmapIndex);
 		}
 		return null;
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public Collection<CachedPack> getCachedPacksAndUpdate(
 		BitmapBuilder needBitmap) throws IOException {
 		for (DfsPackFile pack : db.getPacks()) {
 			PackBitmapIndex bitmapIndex = pack.getBitmapIndex(this);
 			if (needBitmap.removeAllOrNone(bitmapIndex))
 				return Collections.<CachedPack> singletonList(
 						new DfsCachedPack(pack));
 		}
 		return Collections.emptyList();
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public Collection<ObjectId> resolve(AbbreviatedObjectId id)
 			throws IOException {
 		if (id.isComplete())
 			return Collections.singleton(id.toObjectId());
 		HashSet<ObjectId> matches = new HashSet<>(4);
 		PackList packList = db.getPackList();
 		resolveImpl(packList, id, matches);
 		if (matches.size() < MAX_RESOLVE_MATCHES && packList.dirty()) {
 			stats.scanPacks++;
 			resolveImpl(db.scanPacks(packList), id, matches);
 		}
 		return matches;
 	}
 
 	private void resolveImpl(PackList packList, AbbreviatedObjectId id,
 			HashSet<ObjectId> matches) throws IOException {
 		for (DfsPackFile pack : packList.packs) {
 			if (skipGarbagePack(pack)) {
 				continue;
 			}
 			pack.resolve(this, matches, id, MAX_RESOLVE_MATCHES);
 			if (matches.size() >= MAX_RESOLVE_MATCHES) {
 				break;
 			}
 		}
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public boolean has(AnyObjectId objectId) throws IOException {
 		if (last != null
 				&& !skipGarbagePack(last)
 				&& last.hasObject(this, objectId))
 			return true;
 		PackList packList = db.getPackList();
 		if (hasImpl(packList, objectId)) {
 			return true;
 		} else if (packList.dirty()) {
 			stats.scanPacks++;
 			return hasImpl(db.scanPacks(packList), objectId);
 		}
 		return false;
 	}
 
 	private boolean hasImpl(PackList packList, AnyObjectId objectId)
 			throws IOException {
 		for (DfsPackFile pack : packList.packs) {
 			if (pack == last || skipGarbagePack(pack))
 				continue;
 			if (pack.hasObject(this, objectId)) {
 				last = pack;
 				return true;
 			}
 		}
 		return false;
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public ObjectLoader open(AnyObjectId objectId, int typeHint)
 			throws MissingObjectException, IncorrectObjectTypeException,
 			IOException {
 		ObjectLoader ldr;
 		if (last != null && !skipGarbagePack(last)) {
 			ldr = last.get(this, objectId);
 			if (ldr != null) {
 				return checkType(ldr, objectId, typeHint);
 			}
 		}
 
 		PackList packList = db.getPackList();
 		ldr = openImpl(packList, objectId);
 		if (ldr != null) {
 			return checkType(ldr, objectId, typeHint);
 		}
 		if (packList.dirty()) {
 			stats.scanPacks++;
 			ldr = openImpl(db.scanPacks(packList), objectId);
 			if (ldr != null) {
 				return checkType(ldr, objectId, typeHint);
 			}
 		}
 
 		if (typeHint == OBJ_ANY)
 			throw new MissingObjectException(objectId.copy(),
 					JGitText.get().unknownObjectType2);
 		throw new MissingObjectException(objectId.copy(), typeHint);
 	}
 
 	private static ObjectLoader checkType(ObjectLoader ldr, AnyObjectId id,
 			int typeHint) throws IncorrectObjectTypeException {
 		if (typeHint != OBJ_ANY && ldr.getType() != typeHint) {
 			throw new IncorrectObjectTypeException(id.copy(), typeHint);
 		}
 		return ldr;
 	}
 
 	private ObjectLoader openImpl(PackList packList, AnyObjectId objectId)
 			throws IOException {
 		for (DfsPackFile pack : packList.packs) {
 			if (pack == last || skipGarbagePack(pack)) {
 				continue;
 			}
 			ObjectLoader ldr = pack.get(this, objectId);
 			if (ldr != null) {
 				last = pack;
 				return ldr;
 			}
 		}
 		return null;
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public Set<ObjectId> getShallowCommits() {
 		return Collections.emptySet();
 	}
 
 	private static final Comparator<FoundObject<?>> FOUND_OBJECT_SORT = new Comparator<FoundObject<?>>() {
 		@Override
 		public int compare(FoundObject<?> a, FoundObject<?> b) {
 			int cmp = a.packIndex - b.packIndex;
 			if (cmp == 0)
 				cmp = Long.signum(a.offset - b.offset);
 			return cmp;
 		}
 	};
 
 	private static class FoundObject<T extends ObjectId> {
 		final T id;
 		final DfsPackFile pack;
 		final long offset;
 		final int packIndex;
 
 		FoundObject(T objectId, int packIdx, DfsPackFile pack, long offset) {
 			this.id = objectId;
 			this.pack = pack;
 			this.offset = offset;
 			this.packIndex = packIdx;
 		}
 
 		FoundObject(T objectId) {
 			this.id = objectId;
 			this.pack = null;
 			this.offset = 0;
 			this.packIndex = 0;
 		}
 	}
 
 	private <T extends ObjectId> Iterable<FoundObject<T>> findAll(
 			Iterable<T> objectIds) throws IOException {
 		Collection<T> pending = new LinkedList<>();
 		for (T id : objectIds) {
 			pending.add(id);
 		}
 
 		PackList packList = db.getPackList();
 		List<FoundObject<T>> r = new ArrayList<>();
 		findAllImpl(packList, pending, r);
 		if (!pending.isEmpty() && packList.dirty()) {
 			stats.scanPacks++;
 			findAllImpl(db.scanPacks(packList), pending, r);
 		}
 		for (T t : pending) {
 			r.add(new FoundObject<>(t));
 		}
 		Collections.sort(r, FOUND_OBJECT_SORT);
 		return r;
 	}
 
 	private <T extends ObjectId> void findAllImpl(PackList packList,
 			Collection<T> pending, List<FoundObject<T>> r) {
 		DfsPackFile[] packs = packList.packs;
 		if (packs.length == 0) {
 			return;
 		}
 		int lastIdx = 0;
 		DfsPackFile lastPack = packs[lastIdx];
 
 		OBJECT_SCAN: for (Iterator<T> it = pending.iterator(); it.hasNext();) {
 			T t = it.next();
 			if (!skipGarbagePack(lastPack)) {
 				try {
 					long p = lastPack.findOffset(this, t);
 					if (0 < p) {
 						r.add(new FoundObject<>(t, lastIdx, lastPack, p));
 						it.remove();
 						continue;
 					}
 				} catch (IOException e) {
 					// Fall though and try to examine other packs.
 				}
 			}
 
 			for (int i = 0; i < packs.length; i++) {
 				if (i == lastIdx)
 					continue;
 				DfsPackFile pack = packs[i];
 				if (skipGarbagePack(pack))
 					continue;
 				try {
 					long p = pack.findOffset(this, t);
 					if (0 < p) {
 						r.add(new FoundObject<>(t, i, pack, p));
 						it.remove();
 						lastIdx = i;
 						lastPack = pack;
 						continue OBJECT_SCAN;
 					}
 				} catch (IOException e) {
 					// Examine other packs.
 				}
 			}
 		}
 
 		last = lastPack;
 	}
 
 	private boolean skipGarbagePack(DfsPackFile pack) {
 		return avoidUnreachable && pack.isGarbage();
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public <T extends ObjectId> AsyncObjectLoaderQueue<T> open(
 			Iterable<T> objectIds, final boolean reportMissing) {
 		Iterable<FoundObject<T>> order;
 		IOException error = null;
 		try {
 			order = findAll(objectIds);
 		} catch (IOException e) {
 			order = Collections.emptyList();
 			error = e;
 		}
 
 		final Iterator<FoundObject<T>> idItr = order.iterator();
 		final IOException findAllError = error;
 		return new AsyncObjectLoaderQueue<T>() {
 			private FoundObject<T> cur;
 
 			@Override
 			public boolean next() throws MissingObjectException, IOException {
 				if (idItr.hasNext()) {
 					cur = idItr.next();
 					return true;
 				} else if (findAllError != null) {
 					throw findAllError;
 				} else {
 					return false;
 				}
 			}
 
 			@Override
 			public T getCurrent() {
 				return cur.id;
 			}
 
 			@Override
 			public ObjectId getObjectId() {
 				return cur.id;
 			}
 
 			@Override
 			public ObjectLoader open() throws IOException {
 				if (cur.pack == null)
 					throw new MissingObjectException(cur.id,
 							JGitText.get().unknownObjectType2);
 				return cur.pack.load(DfsReader.this, cur.offset);
 			}
 
 			@Override
 			public boolean cancel(boolean mayInterruptIfRunning) {
 				return true;
 			}
 
 			@Override
 			public void release() {
 				// Nothing to clean up.
 			}
 		};
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public <T extends ObjectId> AsyncObjectSizeQueue<T> getObjectSize(
 			Iterable<T> objectIds, final boolean reportMissing) {
 		Iterable<FoundObject<T>> order;
 		IOException error = null;
 		try {
 			order = findAll(objectIds);
 		} catch (IOException e) {
 			order = Collections.emptyList();
 			error = e;
 		}
 
 		final Iterator<FoundObject<T>> idItr = order.iterator();
 		final IOException findAllError = error;
 		return new AsyncObjectSizeQueue<T>() {
 			private FoundObject<T> cur;
 			private long sz;
 
 			@Override
 			public boolean next() throws MissingObjectException, IOException {
 				if (idItr.hasNext()) {
 					cur = idItr.next();
 					if (cur.pack == null)
 						throw new MissingObjectException(cur.id,
 								JGitText.get().unknownObjectType2);
 					sz = cur.pack.getObjectSize(DfsReader.this, cur.offset);
 					return true;
 				} else if (findAllError != null) {
 					throw findAllError;
 				} else {
 					return false;
 				}
 			}
 
 			@Override
 			public T getCurrent() {
 				return cur.id;
 			}
 
 			@Override
 			public ObjectId getObjectId() {
 				return cur.id;
 			}
 
 			@Override
 			public long getSize() {
 				return sz;
 			}
 
 			@Override
 			public boolean cancel(boolean mayInterruptIfRunning) {
 				return true;
 			}
 
 			@Override
 			public void release() {
 				// Nothing to clean up.
 			}
 		};
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public long getObjectSize(AnyObjectId objectId, int typeHint)
 			throws MissingObjectException, IncorrectObjectTypeException,
 			IOException {
 		if (last != null && !skipGarbagePack(last)) {
 			long sz = last.getObjectSize(this, objectId);
 			if (0 <= sz) {
 				return sz;
 			}
 		}
 
 		PackList packList = db.getPackList();
 		long sz = getObjectSizeImpl(packList, objectId);
 		if (0 <= sz) {
 			return sz;
 		}
 		if (packList.dirty()) {
 			sz = getObjectSizeImpl(packList, objectId);
 			if (0 <= sz) {
 				return sz;
 			}
 		}
 
 		if (typeHint == OBJ_ANY) {
 			throw new MissingObjectException(objectId.copy(),
 					JGitText.get().unknownObjectType2);
 		}
 		throw new MissingObjectException(objectId.copy(), typeHint);
 	}
 
 	private long getObjectSizeImpl(PackList packList, AnyObjectId objectId)
 			throws IOException {
 		for (DfsPackFile pack : packList.packs) {
 			if (pack == last || skipGarbagePack(pack)) {
 				continue;
 			}
 			long sz = pack.getObjectSize(this, objectId);
 			if (0 <= sz) {
 				last = pack;
 				return sz;
 			}
 		}
 		return -1;
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public DfsObjectToPack newObjectToPack(AnyObjectId objectId, int type) {
 		return new DfsObjectToPack(objectId, type);
 	}
 
 	private static final Comparator<DfsObjectToPack> OFFSET_SORT = new Comparator<DfsObjectToPack>() {
 		@Override
 		public int compare(DfsObjectToPack a, DfsObjectToPack b) {
 			return Long.signum(a.getOffset() - b.getOffset());
 		}
 	};
 
 	@Override
 	public void selectObjectRepresentation(PackWriter packer,
 			ProgressMonitor monitor, Iterable<ObjectToPack> objects)
 			throws IOException, MissingObjectException {
 		// Don't check dirty bit on PackList; assume ObjectToPacks all came
 		// from the current list.
 		List<DfsPackFile> packs = sortPacksForSelectRepresentation();
 		trySelectRepresentation(packer, monitor, objects, packs, false);
 
 		List<DfsPackFile> garbage = garbagePacksForSelectRepresentation();
 		if (!garbage.isEmpty() && checkGarbagePacks(objects)) {
 			trySelectRepresentation(packer, monitor, objects, garbage, true);
 		}
 	}
 
 	private void trySelectRepresentation(PackWriter packer,
 			ProgressMonitor monitor, Iterable<ObjectToPack> objects,
 			List<DfsPackFile> packs, boolean skipFound) throws IOException {
 		for (DfsPackFile pack : packs) {
 			List<DfsObjectToPack> tmp = findAllFromPack(pack, objects, skipFound);
 			if (tmp.isEmpty())
 				continue;
 			Collections.sort(tmp, OFFSET_SORT);
 			PackReverseIndex rev = pack.getReverseIdx(this);
 			DfsObjectRepresentation rep = new DfsObjectRepresentation(pack);
 			for (DfsObjectToPack otp : tmp) {
 				pack.representation(rep, otp.getOffset(), this, rev);
 				otp.setOffset(0);
 				packer.select(otp, rep);
 				if (!otp.isFound()) {
 					otp.setFound();
 					monitor.update(1);
 				}
 			}
 		}
 	}
 
 	private static final Comparator<DfsPackFile> PACK_SORT_FOR_REUSE =
 		Comparator.comparing(
 				DfsPackFile::getPackDescription, DfsPackDescription.reuseComparator());
 
 	private List<DfsPackFile> sortPacksForSelectRepresentation()
 			throws IOException {
 		DfsPackFile[] packs = db.getPacks();
 		List<DfsPackFile> sorted = new ArrayList<>(packs.length);
 		for (DfsPackFile p : packs) {
 			if (p.getPackDescription().getPackSource() != UNREACHABLE_GARBAGE) {
 				sorted.add(p);
 			}
 		}
 		Collections.sort(sorted, PACK_SORT_FOR_REUSE);
 		return sorted;
 	}
 
 	private List<DfsPackFile> garbagePacksForSelectRepresentation()
 			throws IOException {
 		DfsPackFile[] packs = db.getPacks();
 		List<DfsPackFile> garbage = new ArrayList<>(packs.length);
 		for (DfsPackFile p : packs) {
 			if (p.getPackDescription().getPackSource() == UNREACHABLE_GARBAGE) {
 				garbage.add(p);
 			}
 		}
 		return garbage;
 	}
 
 	private static boolean checkGarbagePacks(Iterable<ObjectToPack> objects) {
 		for (ObjectToPack otp : objects) {
 			if (!((DfsObjectToPack) otp).isFound()) {
 				return true;
 			}
 		}
 		return false;
 	}
 
 	private List<DfsObjectToPack> findAllFromPack(DfsPackFile pack,
 			Iterable<ObjectToPack> objects, boolean skipFound)
 					throws IOException {
 		List<DfsObjectToPack> tmp = new BlockList<>();
 		PackIndex idx = pack.getPackIndex(this);
 		for (ObjectToPack obj : objects) {
 			DfsObjectToPack otp = (DfsObjectToPack) obj;
 			if (skipFound && otp.isFound()) {
 				continue;
 			}
 			long p = idx.findOffset(otp);
 			if (0 < p && !pack.isCorrupt(p)) {
 				otp.setOffset(p);
 				tmp.add(otp);
 			}
 		}
 		return tmp;
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public void copyObjectAsIs(PackOutputStream out, ObjectToPack otp,
 			boolean validate) throws IOException,
 			StoredObjectRepresentationNotAvailableException {
 		DfsObjectToPack src = (DfsObjectToPack) otp;
 		src.pack.copyAsIs(out, src, validate, this);
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public void writeObjects(PackOutputStream out, List<ObjectToPack> list)
 			throws IOException {
 		for (ObjectToPack otp : list)
 			out.writeObject(otp);
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public void copyPackAsIs(PackOutputStream out, CachedPack pack)
 			throws IOException {
 		((DfsCachedPack) pack).copyAsIs(out, this);
 	}
 
 	/**
 	 * Copy bytes from the window to a caller supplied buffer.
 	 *
 	 * @param file
 	 *            the file the desired window is stored within.
 	 * @param position
 	 *            position within the file to read from.
 	 * @param dstbuf
 	 *            destination buffer to copy into.
 	 * @param dstoff
 	 *            offset within <code>dstbuf</code> to start copying into.
 	 * @param cnt
 	 *            number of bytes to copy. This value may exceed the number of
 	 *            bytes remaining in the window starting at offset
 	 *            <code>pos</code>.
 	 * @return number of bytes actually copied; this may be less than
 	 *         <code>cnt</code> if <code>cnt</code> exceeded the number of bytes
 	 *         available.
 	 * @throws IOException
 	 *             this cursor does not match the provider or id and the proper
 	 *             window could not be acquired through the provider's cache.
 	 */
 	int copy(BlockBasedFile file, long position, byte[] dstbuf, int dstoff,
 			int cnt) throws IOException {
 		if (cnt == 0)
 			return 0;
 
 		long length = file.length;
 		if (0 <= length && length <= position)
 			return 0;
 
 		int need = cnt;
 		do {
 			pin(file, position);
 			int r = block.copy(position, dstbuf, dstoff, need);
 			position += r;
 			dstoff += r;
 			need -= r;
 			if (length < 0)
 				length = file.length;
 		} while (0 < need && position < length);
 		return cnt - need;
 	}
 
 	/**
 	 * Inflate a region of the pack starting at {@code position}.
 	 *
 	 * @param pack
 	 *            the file the desired window is stored within.
 	 * @param position
 	 *            position within the file to read from.
 	 * @param dstbuf
 	 *            destination buffer the inflater should output decompressed
 	 *            data to. Must be large enough to store the entire stream,
 	 *            unless headerOnly is true.
 	 * @param headerOnly
 	 *            if true the caller wants only {@code dstbuf.length} bytes.
 	 * @return number of bytes inflated into <code>dstbuf</code>.
 	 * @throws IOException
 	 *             this cursor does not match the provider or id and the proper
 	 *             window could not be acquired through the provider's cache.
 	 * @throws DataFormatException
 	 *             the inflater encountered an invalid chunk of data. Data
 	 *             stream corruption is likely.
 	 */
 	int inflate(DfsPackFile pack, long position, byte[] dstbuf,
 			boolean headerOnly) throws IOException, DataFormatException {
 		prepareInflater();
 		pin(pack, position);
 		position += block.setInput(position, inf);
 		for (int dstoff = 0;;) {
 			int n = inf.inflate(dstbuf, dstoff, dstbuf.length - dstoff);
 			dstoff += n;
 			if (inf.finished() || (headerOnly && dstoff == dstbuf.length)) {
 				stats.inflatedBytes += dstoff;
 				return dstoff;
 			} else if (inf.needsInput()) {
 				pin(pack, position);
 				position += block.setInput(position, inf);
 			} else if (n == 0)
 				throw new DataFormatException();
 		}
 	}
 
 	DfsBlock quickCopy(DfsPackFile p, long pos, long cnt)
 			throws IOException {
 		pin(p, pos);
 		if (block.contains(p.key, pos + (cnt - 1)))
 			return block;
 		return null;
 	}
 
 	Inflater inflater() {
 		prepareInflater();
 		return inf;
 	}
 
 	private void prepareInflater() {
 		if (inf == null)
 			inf = InflaterCache.get();
 		else
 			inf.reset();
 	}
 
 	void pin(BlockBasedFile file, long position) throws IOException {
 		if (block == null || !block.contains(file.key, position)) {
 			// If memory is low, we may need what is in our window field to
 			// be cleaned up by the GC during the get for the next window.
 			// So we always clear it, even though we are just going to set
 			// it again.
 			block = null;
 			block = file.getOrLoadBlock(position, this);
 		}
 	}
 
 	void unpin() {
 		block = null;
 	}
 
 	/**
 	 * Get IO statistics accumulated by this reader.
 	 *
 	 * @return IO statistics accumulated by this reader.
 	 */
 	public DfsReaderIoStats getIoStats() {
 		return new DfsReaderIoStats(stats);
 	}
 
 	/**
 	 * {@inheritDoc}
 	 * <p>
 	 * Release the current window cursor.
 	 */
 	@Override
 	public void close() {
 		last = null;
 		block = null;
 		baseCache = null;
 		try {
 			InflaterCache.release(inf);
 		} finally {
 			inf = null;
 		}
 	}
 }