org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/file/PackFileSnapshotTest.java - jgit - Git at Google

 /*
  * Copyright (C) 2019, Matthias Sohn <matthias.sohn@sap.com>
  * 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.file;

 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
 import static org.junit.Assume.assumeFalse;
 import static org.junit.Assume.assumeTrue;

 import java.io.File;
 import java.io.IOException;
 import java.io.OutputStream;
 import java.io.Writer;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.nio.file.StandardCopyOption;
 import java.nio.file.StandardOpenOption;
 //import java.nio.file.attribute.BasicFileAttributes;
 import java.text.ParseException;
 import java.time.Instant;
 import java.util.Collection;
 import java.util.Iterator;
 import java.util.Random;
 import java.util.zip.Deflater;

 import org.eclipse.jgit.api.GarbageCollectCommand;
 import org.eclipse.jgit.api.Git;
 import org.eclipse.jgit.api.errors.AbortedByHookException;
 import org.eclipse.jgit.api.errors.ConcurrentRefUpdateException;
 import org.eclipse.jgit.api.errors.GitAPIException;
 import org.eclipse.jgit.api.errors.NoFilepatternException;
 import org.eclipse.jgit.api.errors.NoHeadException;
 import org.eclipse.jgit.api.errors.NoMessageException;
 import org.eclipse.jgit.api.errors.UnmergedPathsException;
 import org.eclipse.jgit.api.errors.WrongRepositoryStateException;
 import org.eclipse.jgit.junit.RepositoryTestCase;
 import org.eclipse.jgit.lib.AnyObjectId;
 import org.eclipse.jgit.lib.ConfigConstants;
 import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.storage.file.FileBasedConfig;
 import org.eclipse.jgit.storage.pack.PackConfig;
 import org.eclipse.jgit.util.FS;
 import org.junit.Test;

 public class PackFileSnapshotTest extends RepositoryTestCase {

 	private static ObjectId unknownID = ObjectId
 			.fromString("1234567890123456789012345678901234567890");

 	@Test
 	public void testSamePackDifferentCompressionDetectChecksumChanged()
 			throws Exception {
 		Git git = Git.wrap(db);
 		File f = writeTrashFile("file", "foobar ");
 		for (int i = 0; i < 10; i++) {
 			appendRandomLine(f);
 			git.add().addFilepattern("file").call();
 			git.commit().setMessage("message" + i).call();
 		}

 		FileBasedConfig c = db.getConfig();
 		c.setInt(ConfigConstants.CONFIG_GC_SECTION, null,
 				ConfigConstants.CONFIG_KEY_AUTOPACKLIMIT, 1);
 		c.save();
 		Collection<PackFile> packs = gc(Deflater.NO_COMPRESSION);
 		assertEquals("expected 1 packfile after gc", 1, packs.size());
 		PackFile p1 = packs.iterator().next();
 		PackFileSnapshot snapshot = p1.getFileSnapshot();

 		packs = gc(Deflater.BEST_COMPRESSION);
 		assertEquals("expected 1 packfile after gc", 1, packs.size());
 		PackFile p2 = packs.iterator().next();
 		File pf = p2.getPackFile();

 		// changing compression level with aggressive gc may change size,
 		// fileKey (on *nix) and checksum. Hence FileSnapshot.isModified can
 		// return true already based on size or fileKey.
 		// So the only thing we can test here is that we ensure that checksum
 		// also changed when we read it here in this test
 		assertTrue("expected snapshot to detect modified pack",
 				snapshot.isModified(pf));
 		assertTrue("expected checksum changed", snapshot.isChecksumChanged(pf));
 	}

 	private void appendRandomLine(File f, int length, Random r)
 			throws IOException {
 		try (Writer w = Files.newBufferedWriter(f.toPath(),
 				StandardOpenOption.APPEND)) {
 			appendRandomLine(w, length, r);
 		}
 	}

 	private void appendRandomLine(File f) throws IOException {
 		appendRandomLine(f, 5, new Random());
 	}

 	private void appendRandomLine(Writer w, int len, Random r)
 			throws IOException {
 		final int c1 = 32; // ' '
 		int c2 = 126; // '~'
 		for (int i = 0; i < len; i++) {
 			w.append((char) (c1 + r.nextInt(1 + c2 - c1)));
 		}
 	}

 	private ObjectId createTestRepo(int testDataSeed, int testDataLength)
 			throws IOException, GitAPIException, NoFilepatternException,
 			NoHeadException, NoMessageException, UnmergedPathsException,
 			ConcurrentRefUpdateException, WrongRepositoryStateException,
 			AbortedByHookException {
 		// Create a repo with two commits and one file. Each commit adds
 		// testDataLength number of bytes. Data are random bytes. Since the
 		// seed for the random number generator is specified we will get
 		// the same set of bytes for every run and for every platform
 		Random r = new Random(testDataSeed);
 		Git git = Git.wrap(db);
 		File f = writeTrashFile("file", "foobar ");
 		appendRandomLine(f, testDataLength, r);
 		git.add().addFilepattern("file").call();
 		git.commit().setMessage("message1").call();
 		appendRandomLine(f, testDataLength, r);
 		git.add().addFilepattern("file").call();
 		return git.commit().setMessage("message2").call().getId();
 	}

 	// Try repacking so fast that you get two new packs which differ only in
 	// content/chksum but have same name, size and lastmodified.
 	// Since this is done with standard gc (which creates new tmp files and
 	// renames them) the filekeys of the new packfiles differ helping jgit
 	// to detect the fast modification
 	@Test
 	public void testDetectModificationAlthoughSameSizeAndModificationtime()
 			throws Exception {
 		int testDataSeed = 1;
 		int testDataLength = 100;
 		FileBasedConfig config = db.getConfig();
 		// don't use mtime of the parent folder to detect pack file
 		// modification.
 		config.setBoolean(ConfigConstants.CONFIG_CORE_SECTION, null,
 				ConfigConstants.CONFIG_KEY_TRUSTFOLDERSTAT, false);
 		config.save();

 		createTestRepo(testDataSeed, testDataLength);

 		// repack to create initial packfile
 		PackFile pf = repackAndCheck(5, null, null, null);
 		Path packFilePath = pf.getPackFile().toPath();
 		AnyObjectId chk1 = pf.getPackChecksum();
 		String name = pf.getPackName();
 		Long length = Long.valueOf(pf.getPackFile().length());
 		FS fs = db.getFS();
 		Instant m1 = fs.lastModifiedInstant(packFilePath);

 		// Wait for a filesystem timer tick to enhance probability the rest of
 		// this test is done before the filesystem timer ticks again.
 		fsTick(packFilePath.toFile());

 		// Repack to create packfile with same name, length. Lastmodified and
 		// content and checksum are different since compression level differs
 		AnyObjectId chk2 = repackAndCheck(6, name, length, chk1)
 				.getPackChecksum();
 		Instant m2 = fs.lastModifiedInstant(packFilePath);
 		assumeFalse(m2.equals(m1));

 		// Repack to create packfile with same name, length. Lastmodified is
 		// equal to the previous one because we are in the same filesystem timer
 		// slot. Content and its checksum are different
 		AnyObjectId chk3 = repackAndCheck(7, name, length, chk2)
 				.getPackChecksum();
 		Instant m3 = fs.lastModifiedInstant(packFilePath);

 		// ask for an unknown git object to force jgit to rescan the list of
 		// available packs. If we would ask for a known objectid then JGit would
 		// skip searching for new/modified packfiles
 		db.getObjectDatabase().has(unknownID);
 		assertEquals(chk3, getSinglePack(db.getObjectDatabase().getPacks())
 				.getPackChecksum());
 		assumeTrue(m3.equals(m2));
 	}

 	// Try repacking so fast that we get two new packs which differ only in
 	// content and checksum but have same name, size and lastmodified.
 	// To avoid that JGit detects modification by checking the filekey create
 	// two new packfiles upfront and create copies of them. Then modify the
 	// packfiles in-place by opening them for write and then copying the
 	// content.
 	@Test
 	public void testDetectModificationAlthoughSameSizeAndModificationtimeAndFileKey()
 			throws Exception {
 		int testDataSeed = 1;
 		int testDataLength = 100;
 		FileBasedConfig config = db.getConfig();
 		config.setBoolean(ConfigConstants.CONFIG_CORE_SECTION, null,
 				ConfigConstants.CONFIG_KEY_TRUSTFOLDERSTAT, false);
 		config.save();

 		createTestRepo(testDataSeed, testDataLength);

 		// Repack to create initial packfile. Make a copy of it
 		PackFile pf = repackAndCheck(5, null, null, null);
 		Path packFilePath = pf.getPackFile().toPath();
 		Path packFileBasePath = packFilePath.resolveSibling(
 				packFilePath.getFileName().toString().replaceAll(".pack", ""));
 		AnyObjectId chk1 = pf.getPackChecksum();
 		String name = pf.getPackName();
 		Long length = Long.valueOf(pf.getPackFile().length());
 		copyPack(packFileBasePath, "", ".copy1");

 		// Repack to create second packfile. Make a copy of it
 		AnyObjectId chk2 = repackAndCheck(6, name, length, chk1)
 				.getPackChecksum();
 		copyPack(packFileBasePath, "", ".copy2");

 		// Repack to create third packfile
 		AnyObjectId chk3 = repackAndCheck(7, name, length, chk2)
 				.getPackChecksum();
 		FS fs = db.getFS();
 		Instant m3 = fs.lastModifiedInstant(packFilePath);
 		db.getObjectDatabase().has(unknownID);
 		assertEquals(chk3, getSinglePack(db.getObjectDatabase().getPacks())
 				.getPackChecksum());

 		// Wait for a filesystem timer tick to enhance probability the rest of
 		// this test is done before the filesystem timer ticks.
 		fsTick(packFilePath.toFile());

 		// Copy copy2 to packfile data to force modification of packfile without
 		// changing the packfile's filekey.
 		copyPack(packFileBasePath, ".copy2", "");
 		Instant m2 = fs.lastModifiedInstant(packFilePath);
 		assumeFalse(m3.equals(m2));

 		db.getObjectDatabase().has(unknownID);
 		assertEquals(chk2, getSinglePack(db.getObjectDatabase().getPacks())
 				.getPackChecksum());

 		// Copy copy2 to packfile data to force modification of packfile without
 		// changing the packfile's filekey.
 		copyPack(packFileBasePath, ".copy1", "");
 		Instant m1 = fs.lastModifiedInstant(packFilePath);
 		assumeTrue(m2.equals(m1));
 		db.getObjectDatabase().has(unknownID);
 		assertEquals(chk1, getSinglePack(db.getObjectDatabase().getPacks())
 				.getPackChecksum());
 	}

 	// Copy file from src to dst but avoid creating a new File (with new
 	// FileKey) if dst already exists
 	private Path copyFile(Path src, Path dst) throws IOException {
 		if (Files.exists(dst)) {
 			dst.toFile().setWritable(true);
 			try (OutputStream dstOut = Files.newOutputStream(dst)) {
 				Files.copy(src, dstOut);
 				return dst;
 			}
 		} else {
 			return Files.copy(src, dst, StandardCopyOption.REPLACE_EXISTING);
 		}
 	}

 	private Path copyPack(Path base, String srcSuffix, String dstSuffix)
 			throws IOException {
 		copyFile(Paths.get(base + ".idx" + srcSuffix),
 				Paths.get(base + ".idx" + dstSuffix));
 		copyFile(Paths.get(base + ".bitmap" + srcSuffix),
 				Paths.get(base + ".bitmap" + dstSuffix));
 		return copyFile(Paths.get(base + ".pack" + srcSuffix),
 				Paths.get(base + ".pack" + dstSuffix));
 	}

 	private PackFile repackAndCheck(int compressionLevel, String oldName,
 			Long oldLength, AnyObjectId oldChkSum)
 			throws IOException, ParseException {
 		PackFile p = getSinglePack(gc(compressionLevel));
 		File pf = p.getPackFile();
 		// The following two assumptions should not cause the test to fail. If
 		// on a certain platform we get packfiles (containing the same git
 		// objects) where the lengths differ or the checksums don't differ we
 		// just skip this test. A reason for that could be that compression
 		// works differently or random number generator works differently. Then
 		// we have to search for more consistent test data or checkin these
 		// packfiles as test resources
 		assumeTrue(oldLength == null || pf.length() == oldLength.longValue());
 		assumeTrue(oldChkSum == null || !p.getPackChecksum().equals(oldChkSum));
 		assertTrue(oldName == null || p.getPackName().equals(oldName));
 		return p;
 	}

 	private PackFile getSinglePack(Collection<PackFile> packs) {
 		Iterator<PackFile> pIt = packs.iterator();
 		PackFile p = pIt.next();
 		assertFalse(pIt.hasNext());
 		return p;
 	}

 	private Collection<PackFile> gc(int compressionLevel)
 			throws IOException, ParseException {
 		GC gc = new GC(db);
 		PackConfig pc = new PackConfig(db.getConfig());
 		pc.setCompressionLevel(compressionLevel);

 		pc.setSinglePack(true);

 		// --aggressive
 		pc.setDeltaSearchWindowSize(
 				GarbageCollectCommand.DEFAULT_GC_AGGRESSIVE_WINDOW);
 		pc.setMaxDeltaDepth(GarbageCollectCommand.DEFAULT_GC_AGGRESSIVE_DEPTH);
 		pc.setReuseObjects(false);

 		gc.setPackConfig(pc);
 		gc.setExpireAgeMillis(0);
 		gc.setPackExpireAgeMillis(0);
 		return gc.gc();
 	}

 }
	/*
	* Copyright (C) 2019, Matthias Sohn <matthias.sohn@sap.com>
	* 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.file;

	import static org.junit.Assert.assertEquals;
	import static org.junit.Assert.assertFalse;
	import static org.junit.Assert.assertTrue;
	import static org.junit.Assume.assumeFalse;
	import static org.junit.Assume.assumeTrue;

	import java.io.File;
	import java.io.IOException;
	import java.io.OutputStream;
	import java.io.Writer;
	import java.nio.file.Files;
	import java.nio.file.Path;
	import java.nio.file.Paths;
	import java.nio.file.StandardCopyOption;
	import java.nio.file.StandardOpenOption;
	//import java.nio.file.attribute.BasicFileAttributes;
	import java.text.ParseException;
	import java.time.Instant;
	import java.util.Collection;
	import java.util.Iterator;
	import java.util.Random;
	import java.util.zip.Deflater;

	import org.eclipse.jgit.api.GarbageCollectCommand;
	import org.eclipse.jgit.api.Git;
	import org.eclipse.jgit.api.errors.AbortedByHookException;
	import org.eclipse.jgit.api.errors.ConcurrentRefUpdateException;
	import org.eclipse.jgit.api.errors.GitAPIException;
	import org.eclipse.jgit.api.errors.NoFilepatternException;
	import org.eclipse.jgit.api.errors.NoHeadException;
	import org.eclipse.jgit.api.errors.NoMessageException;
	import org.eclipse.jgit.api.errors.UnmergedPathsException;
	import org.eclipse.jgit.api.errors.WrongRepositoryStateException;
	import org.eclipse.jgit.junit.RepositoryTestCase;
	import org.eclipse.jgit.lib.AnyObjectId;
	import org.eclipse.jgit.lib.ConfigConstants;
	import org.eclipse.jgit.lib.ObjectId;
	import org.eclipse.jgit.storage.file.FileBasedConfig;
	import org.eclipse.jgit.storage.pack.PackConfig;
	import org.eclipse.jgit.util.FS;
	import org.junit.Test;

	public class PackFileSnapshotTest extends RepositoryTestCase {

	private static ObjectId unknownID = ObjectId
	.fromString("1234567890123456789012345678901234567890");

	@Test
	public void testSamePackDifferentCompressionDetectChecksumChanged()
	throws Exception {
	Git git = Git.wrap(db);
	File f = writeTrashFile("file", "foobar ");
	for (int i = 0; i < 10; i++) {
	appendRandomLine(f);
	git.add().addFilepattern("file").call();
	git.commit().setMessage("message" + i).call();
	}

	FileBasedConfig c = db.getConfig();
	c.setInt(ConfigConstants.CONFIG_GC_SECTION, null,
	ConfigConstants.CONFIG_KEY_AUTOPACKLIMIT, 1);
	c.save();
	Collection<PackFile> packs = gc(Deflater.NO_COMPRESSION);
	assertEquals("expected 1 packfile after gc", 1, packs.size());
	PackFile p1 = packs.iterator().next();
	PackFileSnapshot snapshot = p1.getFileSnapshot();

	packs = gc(Deflater.BEST_COMPRESSION);
	assertEquals("expected 1 packfile after gc", 1, packs.size());
	PackFile p2 = packs.iterator().next();
	File pf = p2.getPackFile();

	// changing compression level with aggressive gc may change size,
	// fileKey (on *nix) and checksum. Hence FileSnapshot.isModified can
	// return true already based on size or fileKey.
	// So the only thing we can test here is that we ensure that checksum
	// also changed when we read it here in this test
	assertTrue("expected snapshot to detect modified pack",
	snapshot.isModified(pf));
	assertTrue("expected checksum changed", snapshot.isChecksumChanged(pf));
	}

	private void appendRandomLine(File f, int length, Random r)
	throws IOException {
	try (Writer w = Files.newBufferedWriter(f.toPath(),
	StandardOpenOption.APPEND)) {
	appendRandomLine(w, length, r);
	}
	}

	private void appendRandomLine(File f) throws IOException {
	appendRandomLine(f, 5, new Random());
	}

	private void appendRandomLine(Writer w, int len, Random r)
	throws IOException {
	final int c1 = 32; // ' '
	int c2 = 126; // '~'
	for (int i = 0; i < len; i++) {
	w.append((char) (c1 + r.nextInt(1 + c2 - c1)));
	}
	}

	private ObjectId createTestRepo(int testDataSeed, int testDataLength)
	throws IOException, GitAPIException, NoFilepatternException,
	NoHeadException, NoMessageException, UnmergedPathsException,
	ConcurrentRefUpdateException, WrongRepositoryStateException,
	AbortedByHookException {
	// Create a repo with two commits and one file. Each commit adds
	// testDataLength number of bytes. Data are random bytes. Since the
	// seed for the random number generator is specified we will get
	// the same set of bytes for every run and for every platform
	Random r = new Random(testDataSeed);
	Git git = Git.wrap(db);
	File f = writeTrashFile("file", "foobar ");
	appendRandomLine(f, testDataLength, r);
	git.add().addFilepattern("file").call();
	git.commit().setMessage("message1").call();
	appendRandomLine(f, testDataLength, r);
	git.add().addFilepattern("file").call();
	return git.commit().setMessage("message2").call().getId();
	}

	// Try repacking so fast that you get two new packs which differ only in
	// content/chksum but have same name, size and lastmodified.
	// Since this is done with standard gc (which creates new tmp files and
	// renames them) the filekeys of the new packfiles differ helping jgit
	// to detect the fast modification
	@Test
	public void testDetectModificationAlthoughSameSizeAndModificationtime()
	throws Exception {
	int testDataSeed = 1;
	int testDataLength = 100;
	FileBasedConfig config = db.getConfig();
	// don't use mtime of the parent folder to detect pack file
	// modification.
	config.setBoolean(ConfigConstants.CONFIG_CORE_SECTION, null,
	ConfigConstants.CONFIG_KEY_TRUSTFOLDERSTAT, false);
	config.save();

	createTestRepo(testDataSeed, testDataLength);

	// repack to create initial packfile
	PackFile pf = repackAndCheck(5, null, null, null);
	Path packFilePath = pf.getPackFile().toPath();
	AnyObjectId chk1 = pf.getPackChecksum();
	String name = pf.getPackName();
	Long length = Long.valueOf(pf.getPackFile().length());
	FS fs = db.getFS();
	Instant m1 = fs.lastModifiedInstant(packFilePath);

	// Wait for a filesystem timer tick to enhance probability the rest of
	// this test is done before the filesystem timer ticks again.
	fsTick(packFilePath.toFile());

	// Repack to create packfile with same name, length. Lastmodified and
	// content and checksum are different since compression level differs
	AnyObjectId chk2 = repackAndCheck(6, name, length, chk1)
	.getPackChecksum();
	Instant m2 = fs.lastModifiedInstant(packFilePath);
	assumeFalse(m2.equals(m1));

	// Repack to create packfile with same name, length. Lastmodified is
	// equal to the previous one because we are in the same filesystem timer
	// slot. Content and its checksum are different
	AnyObjectId chk3 = repackAndCheck(7, name, length, chk2)
	.getPackChecksum();
	Instant m3 = fs.lastModifiedInstant(packFilePath);

	// ask for an unknown git object to force jgit to rescan the list of
	// available packs. If we would ask for a known objectid then JGit would
	// skip searching for new/modified packfiles
	db.getObjectDatabase().has(unknownID);
	assertEquals(chk3, getSinglePack(db.getObjectDatabase().getPacks())
	.getPackChecksum());
	assumeTrue(m3.equals(m2));
	}

	// Try repacking so fast that we get two new packs which differ only in
	// content and checksum but have same name, size and lastmodified.
	// To avoid that JGit detects modification by checking the filekey create
	// two new packfiles upfront and create copies of them. Then modify the
	// packfiles in-place by opening them for write and then copying the
	// content.
	@Test
	public void testDetectModificationAlthoughSameSizeAndModificationtimeAndFileKey()
	throws Exception {
	int testDataSeed = 1;
	int testDataLength = 100;
	FileBasedConfig config = db.getConfig();
	config.setBoolean(ConfigConstants.CONFIG_CORE_SECTION, null,
	ConfigConstants.CONFIG_KEY_TRUSTFOLDERSTAT, false);
	config.save();

	createTestRepo(testDataSeed, testDataLength);

	// Repack to create initial packfile. Make a copy of it
	PackFile pf = repackAndCheck(5, null, null, null);
	Path packFilePath = pf.getPackFile().toPath();
	Path packFileBasePath = packFilePath.resolveSibling(
	packFilePath.getFileName().toString().replaceAll(".pack", ""));
	AnyObjectId chk1 = pf.getPackChecksum();
	String name = pf.getPackName();
	Long length = Long.valueOf(pf.getPackFile().length());
	copyPack(packFileBasePath, "", ".copy1");

	// Repack to create second packfile. Make a copy of it
	AnyObjectId chk2 = repackAndCheck(6, name, length, chk1)
	.getPackChecksum();
	copyPack(packFileBasePath, "", ".copy2");

	// Repack to create third packfile
	AnyObjectId chk3 = repackAndCheck(7, name, length, chk2)
	.getPackChecksum();
	FS fs = db.getFS();
	Instant m3 = fs.lastModifiedInstant(packFilePath);
	db.getObjectDatabase().has(unknownID);
	assertEquals(chk3, getSinglePack(db.getObjectDatabase().getPacks())
	.getPackChecksum());

	// Wait for a filesystem timer tick to enhance probability the rest of
	// this test is done before the filesystem timer ticks.
	fsTick(packFilePath.toFile());

	// Copy copy2 to packfile data to force modification of packfile without
	// changing the packfile's filekey.
	copyPack(packFileBasePath, ".copy2", "");
	Instant m2 = fs.lastModifiedInstant(packFilePath);
	assumeFalse(m3.equals(m2));

	db.getObjectDatabase().has(unknownID);
	assertEquals(chk2, getSinglePack(db.getObjectDatabase().getPacks())
	.getPackChecksum());

	// Copy copy2 to packfile data to force modification of packfile without
	// changing the packfile's filekey.
	copyPack(packFileBasePath, ".copy1", "");
	Instant m1 = fs.lastModifiedInstant(packFilePath);
	assumeTrue(m2.equals(m1));
	db.getObjectDatabase().has(unknownID);
	assertEquals(chk1, getSinglePack(db.getObjectDatabase().getPacks())
	.getPackChecksum());
	}

	// Copy file from src to dst but avoid creating a new File (with new
	// FileKey) if dst already exists
	private Path copyFile(Path src, Path dst) throws IOException {
	if (Files.exists(dst)) {
	dst.toFile().setWritable(true);
	try (OutputStream dstOut = Files.newOutputStream(dst)) {
	Files.copy(src, dstOut);
	return dst;
	}
	} else {
	return Files.copy(src, dst, StandardCopyOption.REPLACE_EXISTING);
	}
	}

	private Path copyPack(Path base, String srcSuffix, String dstSuffix)
	throws IOException {
	copyFile(Paths.get(base + ".idx" + srcSuffix),
	Paths.get(base + ".idx" + dstSuffix));
	copyFile(Paths.get(base + ".bitmap" + srcSuffix),
	Paths.get(base + ".bitmap" + dstSuffix));
	return copyFile(Paths.get(base + ".pack" + srcSuffix),
	Paths.get(base + ".pack" + dstSuffix));
	}

	private PackFile repackAndCheck(int compressionLevel, String oldName,
	Long oldLength, AnyObjectId oldChkSum)
	throws IOException, ParseException {
	PackFile p = getSinglePack(gc(compressionLevel));
	File pf = p.getPackFile();
	// The following two assumptions should not cause the test to fail. If
	// on a certain platform we get packfiles (containing the same git
	// objects) where the lengths differ or the checksums don't differ we
	// just skip this test. A reason for that could be that compression
	// works differently or random number generator works differently. Then
	// we have to search for more consistent test data or checkin these
	// packfiles as test resources
	assumeTrue(oldLength == null \|\| pf.length() == oldLength.longValue());
	assumeTrue(oldChkSum == null \|\| !p.getPackChecksum().equals(oldChkSum));
	assertTrue(oldName == null \|\| p.getPackName().equals(oldName));
	return p;
	}

	private PackFile getSinglePack(Collection<PackFile> packs) {
	Iterator<PackFile> pIt = packs.iterator();
	PackFile p = pIt.next();
	assertFalse(pIt.hasNext());
	return p;
	}

	private Collection<PackFile> gc(int compressionLevel)
	throws IOException, ParseException {
	GC gc = new GC(db);
	PackConfig pc = new PackConfig(db.getConfig());
	pc.setCompressionLevel(compressionLevel);

	pc.setSinglePack(true);

	// --aggressive
	pc.setDeltaSearchWindowSize(
	GarbageCollectCommand.DEFAULT_GC_AGGRESSIVE_WINDOW);
	pc.setMaxDeltaDepth(GarbageCollectCommand.DEFAULT_GC_AGGRESSIVE_DEPTH);
	pc.setReuseObjects(false);

	gc.setPackConfig(pc);
	gc.setExpireAgeMillis(0);
	gc.setPackExpireAgeMillis(0);
	return gc.gc();
	}

	}