org.eclipse.jgit/src/org/eclipse/jgit/util/SystemReader.java - gerrit/jgit/jgit - Git at Google

 /*
  * Copyright (C) 2009, Google Inc.
  * Copyright (C) 2009, Robin Rosenberg <robin.rosenberg@dewire.com>
  * Copyright (C) 2009, Yann Simon <yann.simon.fr@gmail.com>
  * Copyright (C) 2012, Daniel Megert <daniel_megert@ch.ibm.com> and others
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Distribution License v. 1.0 which is available at
  * https://www.eclipse.org/org/documents/edl-v10.php.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */

 package org.eclipse.jgit.util;

 import java.io.File;
 import java.io.IOException;
 import java.net.InetAddress;
 import java.net.UnknownHostException;
 import java.nio.file.Files;
 import java.nio.file.InvalidPathException;
 import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.security.AccessController;
 import java.security.PrivilegedAction;
 import java.text.DateFormat;
 import java.text.SimpleDateFormat;
 import java.util.Locale;
 import java.util.TimeZone;
 import java.util.concurrent.atomic.AtomicReference;

 import org.eclipse.jgit.errors.ConfigInvalidException;
 import org.eclipse.jgit.errors.CorruptObjectException;
 import org.eclipse.jgit.internal.JGitText;
 import org.eclipse.jgit.lib.Config;
 import org.eclipse.jgit.lib.Constants;
 import org.eclipse.jgit.lib.ObjectChecker;
 import org.eclipse.jgit.lib.StoredConfig;
 import org.eclipse.jgit.storage.file.FileBasedConfig;
 import org.eclipse.jgit.util.time.MonotonicClock;
 import org.eclipse.jgit.util.time.MonotonicSystemClock;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;

 /**
  * Interface to read values from the system.
  * <p>
  * When writing unit tests, extending this interface with a custom class
  * permits to simulate an access to a system variable or property and
  * permits to control the user's global configuration.
  * </p>
  */
 public abstract class SystemReader {

 	private static final Logger LOG = LoggerFactory
 			.getLogger(SystemReader.class);

 	private static final SystemReader DEFAULT;

 	private static Boolean isMacOS;

 	private static Boolean isWindows;

 	static {
 		SystemReader r = new Default();
 		r.init();
 		DEFAULT = r;
 	}

 	private static class Default extends SystemReader {
 		private volatile String hostname;

 		@Override
 		public String getenv(String variable) {
 			return System.getenv(variable);
 		}

 		@Override
 		public String getProperty(String key) {
 			return System.getProperty(key);
 		}

 		@Override
 		public FileBasedConfig openSystemConfig(Config parent, FS fs) {
 			if (StringUtils
 					.isEmptyOrNull(getenv(Constants.GIT_CONFIG_NOSYSTEM_KEY))) {
 				File configFile = fs.getGitSystemConfig();
 				if (configFile != null) {
 					return new FileBasedConfig(parent, configFile, fs);
 				}
 			}
 			return new FileBasedConfig(parent, null, fs) {
 				@Override
 				public void load() {
 					// empty, do not load
 				}

 				@Override
 				public boolean isOutdated() {
 					// regular class would bomb here
 					return false;
 				}
 			};
 		}

 		@Override
 		public FileBasedConfig openUserConfig(Config parent, FS fs) {
 			return new FileBasedConfig(parent, new File(fs.userHome(), ".gitconfig"), //$NON-NLS-1$
 					fs);
 		}

 		private Path getXDGConfigHome(FS fs) {
 			String configHomePath = getenv(Constants.XDG_CONFIG_HOME);
 			if (StringUtils.isEmptyOrNull(configHomePath)) {
 				configHomePath = new File(fs.userHome(), ".config") //$NON-NLS-1$
 						.getAbsolutePath();
 			}
 			try {
 				Path xdgHomePath = Paths.get(configHomePath);
 				Files.createDirectories(xdgHomePath);
 				return xdgHomePath;
 			} catch (IOException | InvalidPathException e) {
 				LOG.error(JGitText.get().createXDGConfigHomeFailed,
 						configHomePath, e);
 			}
 			return null;
 		}

 		@Override
 		public FileBasedConfig openJGitConfig(Config parent, FS fs) {
 			Path xdgPath = getXDGConfigHome(fs);
 			if (xdgPath != null) {
 				Path configPath = null;
 				try {
 					configPath = xdgPath.resolve("jgit"); //$NON-NLS-1$
 					Files.createDirectories(configPath);
 					configPath = configPath.resolve(Constants.CONFIG);
 					return new FileBasedConfig(parent, configPath.toFile(), fs);
 				} catch (IOException e) {
 					LOG.error(JGitText.get().createJGitConfigFailed, configPath,
 							e);
 				}
 			}
 			return new FileBasedConfig(parent,
 					new File(fs.userHome(), ".jgitconfig"), fs); //$NON-NLS-1$
 		}

 		@Override
 		public String getHostname() {
 			if (hostname == null) {
 				try {
 					InetAddress localMachine = InetAddress.getLocalHost();
 					hostname = localMachine.getCanonicalHostName();
 				} catch (UnknownHostException e) {
 					// we do nothing
 					hostname = "localhost"; //$NON-NLS-1$
 				}
 				assert hostname != null;
 			}
 			return hostname;
 		}

 		@Override
 		public long getCurrentTime() {
 			return System.currentTimeMillis();
 		}

 		@Override
 		public int getTimezone(long when) {
 			return getTimeZone().getOffset(when) / (60 * 1000);
 		}
 	}

 	private static volatile SystemReader INSTANCE = DEFAULT;

 	/**
 	 * Get the current SystemReader instance
 	 *
 	 * @return the current SystemReader instance.
 	 */
 	public static SystemReader getInstance() {
 		return INSTANCE;
 	}

 	/**
 	 * Set a new SystemReader instance to use when accessing properties.
 	 *
 	 * @param newReader
 	 *            the new instance to use when accessing properties, or null for
 	 *            the default instance.
 	 */
 	public static void setInstance(SystemReader newReader) {
 		isMacOS = null;
 		isWindows = null;
 		if (newReader == null)
 			INSTANCE = DEFAULT;
 		else {
 			newReader.init();
 			INSTANCE = newReader;
 		}
 	}

 	private ObjectChecker platformChecker;

 	private AtomicReference<FileBasedConfig> systemConfig = new AtomicReference<>();

 	private AtomicReference<FileBasedConfig> userConfig = new AtomicReference<>();

 	private AtomicReference<FileBasedConfig> jgitConfig = new AtomicReference<>();

 	private void init() {
 		// Creating ObjectChecker must be deferred. Unit tests change
 		// behavior of is{Windows,MacOS} in constructor of subclass.
 		if (platformChecker == null)
 			setPlatformChecker();
 	}

 	/**
 	 * Should be used in tests when the platform is explicitly changed.
 	 *
 	 * @since 3.6
 	 */
 	protected final void setPlatformChecker() {
 		platformChecker = new ObjectChecker()
 			.setSafeForWindows(isWindows())
 			.setSafeForMacOS(isMacOS());
 	}

 	/**
 	 * Gets the hostname of the local host. If no hostname can be found, the
 	 * hostname is set to the default value "localhost".
 	 *
 	 * @return the canonical hostname
 	 */
 	public abstract String getHostname();

 	/**
 	 * Get value of the system variable
 	 *
 	 * @param variable
 	 *            system variable to read
 	 * @return value of the system variable
 	 */
 	public abstract String getenv(String variable);

 	/**
 	 * Get value of the system property
 	 *
 	 * @param key
 	 *            of the system property to read
 	 * @return value of the system property
 	 */
 	public abstract String getProperty(String key);

 	/**
 	 * Open the git configuration found in the user home. Use
 	 * {@link #getUserConfig()} to get the current git configuration in the user
 	 * home since it manages automatic reloading when the gitconfig file was
 	 * modified and avoids unnecessary reloads.
 	 *
 	 * @param parent
 	 *            a config with values not found directly in the returned config
 	 * @param fs
 	 *            the file system abstraction which will be necessary to perform
 	 *            certain file system operations.
 	 * @return the git configuration found in the user home
 	 */
 	public abstract FileBasedConfig openUserConfig(Config parent, FS fs);

 	/**
 	 * Open the gitconfig configuration found in the system-wide "etc"
 	 * directory. Use {@link #getSystemConfig()} to get the current system-wide
 	 * git configuration since it manages automatic reloading when the gitconfig
 	 * file was modified and avoids unnecessary reloads.
 	 *
 	 * @param parent
 	 *            a config with values not found directly in the returned
 	 *            config. Null is a reasonable value here.
 	 * @param fs
 	 *            the file system abstraction which will be necessary to perform
 	 *            certain file system operations.
 	 * @return the gitconfig configuration found in the system-wide "etc"
 	 *         directory
 	 */
 	public abstract FileBasedConfig openSystemConfig(Config parent, FS fs);

 	/**
 	 * Open the jgit configuration located at $XDG_CONFIG_HOME/jgit/config. Use
 	 * {@link #getJGitConfig()} to get the current jgit configuration in the
 	 * user home since it manages automatic reloading when the jgit config file
 	 * was modified and avoids unnecessary reloads.
 	 *
 	 * @param parent
 	 *            a config with values not found directly in the returned config
 	 * @param fs
 	 *            the file system abstraction which will be necessary to perform
 	 *            certain file system operations.
 	 * @return the jgit configuration located at $XDG_CONFIG_HOME/jgit/config
 	 * @since 5.5.2
 	 */
 	public abstract FileBasedConfig openJGitConfig(Config parent, FS fs);

 	/**
 	 * Get the git configuration found in the user home. The configuration will
 	 * be reloaded automatically if the configuration file was modified. Also
 	 * reloads the system config if the system config file was modified. If the
 	 * configuration file wasn't modified returns the cached configuration.
 	 *
 	 * @return the git configuration found in the user home
 	 * @throws ConfigInvalidException
 	 *             if configuration is invalid
 	 * @throws IOException
 	 *             if something went wrong when reading files
 	 * @since 5.1.9
 	 */
 	public StoredConfig getUserConfig()
 			throws ConfigInvalidException, IOException {
 		FileBasedConfig c = userConfig.get();
 		if (c == null) {
 			userConfig.compareAndSet(null,
 					openUserConfig(getSystemConfig(), FS.DETECTED));
 			c = userConfig.get();
 		}
 		// on the very first call this will check a second time if the system
 		// config is outdated
 		updateAll(c);
 		return c;
 	}

 	/**
 	 * Get the jgit configuration located at $XDG_CONFIG_HOME/jgit/config. The
 	 * configuration will be reloaded automatically if the configuration file
 	 * was modified. If the configuration file wasn't modified returns the
 	 * cached configuration.
 	 *
 	 * @return the jgit configuration located at $XDG_CONFIG_HOME/jgit/config
 	 * @throws ConfigInvalidException
 	 *             if configuration is invalid
 	 * @throws IOException
 	 *             if something went wrong when reading files
 	 * @since 5.5.2
 	 */
 	public StoredConfig getJGitConfig()
 			throws ConfigInvalidException, IOException {
 		FileBasedConfig c = jgitConfig.get();
 		if (c == null) {
 			jgitConfig.compareAndSet(null,
 					openJGitConfig(null, FS.DETECTED));
 			c = jgitConfig.get();
 		}
 		updateAll(c);
 		return c;
 	}

 	/**
 	 * Get the gitconfig configuration found in the system-wide "etc" directory.
 	 * The configuration will be reloaded automatically if the configuration
 	 * file was modified otherwise returns the cached system level config.
 	 *
 	 * @return the gitconfig configuration found in the system-wide "etc"
 	 *         directory
 	 * @throws ConfigInvalidException
 	 *             if configuration is invalid
 	 * @throws IOException
 	 *             if something went wrong when reading files
 	 * @since 5.1.9
 	 */
 	public StoredConfig getSystemConfig()
 			throws ConfigInvalidException, IOException {
 		FileBasedConfig c = systemConfig.get();
 		if (c == null) {
 			systemConfig.compareAndSet(null,
 					openSystemConfig(getJGitConfig(), FS.DETECTED));
 			c = systemConfig.get();
 		}
 		updateAll(c);
 		return c;
 	}

 	/**
 	 * Update config and its parents if they seem modified
 	 *
 	 * @param config
 	 *            configuration to reload if outdated
 	 * @throws ConfigInvalidException
 	 *             if configuration is invalid
 	 * @throws IOException
 	 *             if something went wrong when reading files
 	 */
 	private void updateAll(Config config)
 			throws ConfigInvalidException, IOException {
 		if (config == null) {
 			return;
 		}
 		updateAll(config.getBaseConfig());
 		if (config instanceof FileBasedConfig) {
 			FileBasedConfig cfg = (FileBasedConfig) config;
 			if (cfg.isOutdated()) {
 				LOG.debug("loading config {}", cfg); //$NON-NLS-1$
 				cfg.load();
 			}
 		}
 	}

 	/**
 	 * Get the current system time
 	 *
 	 * @return the current system time
 	 */
 	public abstract long getCurrentTime();

 	/**
 	 * Get clock instance preferred by this system.
 	 *
 	 * @return clock instance preferred by this system.
 	 * @since 4.6
 	 */
 	public MonotonicClock getClock() {
 		return new MonotonicSystemClock();
 	}

 	/**
 	 * Get the local time zone
 	 *
 	 * @param when
 	 *            a system timestamp
 	 * @return the local time zone
 	 */
 	public abstract int getTimezone(long when);

 	/**
 	 * Get system time zone, possibly mocked for testing
 	 *
 	 * @return system time zone, possibly mocked for testing
 	 * @since 1.2
 	 */
 	public TimeZone getTimeZone() {
 		return TimeZone.getDefault();
 	}

 	/**
 	 * Get the locale to use
 	 *
 	 * @return the locale to use
 	 * @since 1.2
 	 */
 	public Locale getLocale() {
 		return Locale.getDefault();
 	}

 	/**
 	 * Returns a simple date format instance as specified by the given pattern.
 	 *
 	 * @param pattern
 	 *            the pattern as defined in
 	 *            {@link java.text.SimpleDateFormat#SimpleDateFormat(String)}
 	 * @return the simple date format
 	 * @since 2.0
 	 */
 	public SimpleDateFormat getSimpleDateFormat(String pattern) {
 		return new SimpleDateFormat(pattern);
 	}

 	/**
 	 * Returns a simple date format instance as specified by the given pattern.
 	 *
 	 * @param pattern
 	 *            the pattern as defined in
 	 *            {@link java.text.SimpleDateFormat#SimpleDateFormat(String)}
 	 * @param locale
 	 *            locale to be used for the {@code SimpleDateFormat}
 	 * @return the simple date format
 	 * @since 3.2
 	 */
 	public SimpleDateFormat getSimpleDateFormat(String pattern, Locale locale) {
 		return new SimpleDateFormat(pattern, locale);
 	}

 	/**
 	 * Returns a date/time format instance for the given styles.
 	 *
 	 * @param dateStyle
 	 *            the date style as specified in
 	 *            {@link java.text.DateFormat#getDateTimeInstance(int, int)}
 	 * @param timeStyle
 	 *            the time style as specified in
 	 *            {@link java.text.DateFormat#getDateTimeInstance(int, int)}
 	 * @return the date format
 	 * @since 2.0
 	 */
 	public DateFormat getDateTimeInstance(int dateStyle, int timeStyle) {
 		return DateFormat.getDateTimeInstance(dateStyle, timeStyle);
 	}

 	/**
 	 * Whether we are running on Windows.
 	 *
 	 * @return true if we are running on Windows.
 	 */
 	public boolean isWindows() {
 		if (isWindows == null) {
 			String osDotName = getOsName();
 			isWindows = Boolean.valueOf(osDotName.startsWith("Windows")); //$NON-NLS-1$
 		}
 		return isWindows.booleanValue();
 	}

 	/**
 	 * Whether we are running on Mac OS X
 	 *
 	 * @return true if we are running on Mac OS X
 	 */
 	public boolean isMacOS() {
 		if (isMacOS == null) {
 			String osDotName = getOsName();
 			isMacOS = Boolean.valueOf(
 					"Mac OS X".equals(osDotName) || "Darwin".equals(osDotName)); //$NON-NLS-1$ //$NON-NLS-2$
 		}
 		return isMacOS.booleanValue();
 	}

 	private String getOsName() {
 		return AccessController.doPrivileged(
 				(PrivilegedAction<String>) () -> getProperty("os.name") //$NON-NLS-1$
 		);
 	}

 	/**
 	 * Check tree path entry for validity.
 	 * <p>
 	 * Scans a multi-directory path string such as {@code "src/main.c"}.
 	 *
 	 * @param path path string to scan.
 	 * @throws org.eclipse.jgit.errors.CorruptObjectException path is invalid.
 	 * @since 3.6
 	 */
 	public void checkPath(String path) throws CorruptObjectException {
 		platformChecker.checkPath(path);
 	}

 	/**
 	 * Check tree path entry for validity.
 	 * <p>
 	 * Scans a multi-directory path string such as {@code "src/main.c"}.
 	 *
 	 * @param path
 	 *            path string to scan.
 	 * @throws org.eclipse.jgit.errors.CorruptObjectException
 	 *             path is invalid.
 	 * @since 4.2
 	 */
 	public void checkPath(byte[] path) throws CorruptObjectException {
 		platformChecker.checkPath(path, 0, path.length);
 	}
 }
	/*
	* Copyright (C) 2009, Google Inc.
	* Copyright (C) 2009, Robin Rosenberg <robin.rosenberg@dewire.com>
	* Copyright (C) 2009, Yann Simon <yann.simon.fr@gmail.com>
	* Copyright (C) 2012, Daniel Megert <daniel_megert@ch.ibm.com> and others
	*
	* This program and the accompanying materials are made available under the
	* terms of the Eclipse Distribution License v. 1.0 which is available at
	* https://www.eclipse.org/org/documents/edl-v10.php.
	*
	* SPDX-License-Identifier: BSD-3-Clause
	*/

	package org.eclipse.jgit.util;

	import java.io.File;
	import java.io.IOException;
	import java.net.InetAddress;
	import java.net.UnknownHostException;
	import java.nio.file.Files;
	import java.nio.file.InvalidPathException;
	import java.nio.file.Path;
	import java.nio.file.Paths;
	import java.security.AccessController;
	import java.security.PrivilegedAction;
	import java.text.DateFormat;
	import java.text.SimpleDateFormat;
	import java.util.Locale;
	import java.util.TimeZone;
	import java.util.concurrent.atomic.AtomicReference;

	import org.eclipse.jgit.errors.ConfigInvalidException;
	import org.eclipse.jgit.errors.CorruptObjectException;
	import org.eclipse.jgit.internal.JGitText;
	import org.eclipse.jgit.lib.Config;
	import org.eclipse.jgit.lib.Constants;
	import org.eclipse.jgit.lib.ObjectChecker;
	import org.eclipse.jgit.lib.StoredConfig;
	import org.eclipse.jgit.storage.file.FileBasedConfig;
	import org.eclipse.jgit.util.time.MonotonicClock;
	import org.eclipse.jgit.util.time.MonotonicSystemClock;
	import org.slf4j.Logger;
	import org.slf4j.LoggerFactory;

	/**
	* Interface to read values from the system.
	* <p>
	* When writing unit tests, extending this interface with a custom class
	* permits to simulate an access to a system variable or property and
	* permits to control the user's global configuration.
	* </p>
	*/
	public abstract class SystemReader {

	private static final Logger LOG = LoggerFactory
	.getLogger(SystemReader.class);

	private static final SystemReader DEFAULT;

	private static Boolean isMacOS;

	private static Boolean isWindows;

	static {
	SystemReader r = new Default();
	r.init();
	DEFAULT = r;
	}

	private static class Default extends SystemReader {
	private volatile String hostname;

	@Override
	public String getenv(String variable) {
	return System.getenv(variable);
	}

	@Override
	public String getProperty(String key) {
	return System.getProperty(key);
	}

	@Override
	public FileBasedConfig openSystemConfig(Config parent, FS fs) {
	if (StringUtils
	.isEmptyOrNull(getenv(Constants.GIT_CONFIG_NOSYSTEM_KEY))) {
	File configFile = fs.getGitSystemConfig();
	if (configFile != null) {
	return new FileBasedConfig(parent, configFile, fs);
	}
	}
	return new FileBasedConfig(parent, null, fs) {
	@Override
	public void load() {
	// empty, do not load
	}

	@Override
	public boolean isOutdated() {
	// regular class would bomb here
	return false;
	}
	};
	}

	@Override
	public FileBasedConfig openUserConfig(Config parent, FS fs) {
	return new FileBasedConfig(parent, new File(fs.userHome(), ".gitconfig"), //$NON-NLS-1$
	fs);
	}

	private Path getXDGConfigHome(FS fs) {
	String configHomePath = getenv(Constants.XDG_CONFIG_HOME);
	if (StringUtils.isEmptyOrNull(configHomePath)) {
	configHomePath = new File(fs.userHome(), ".config") //$NON-NLS-1$
	.getAbsolutePath();
	}
	try {
	Path xdgHomePath = Paths.get(configHomePath);
	Files.createDirectories(xdgHomePath);
	return xdgHomePath;
	} catch (IOException \| InvalidPathException e) {
	LOG.error(JGitText.get().createXDGConfigHomeFailed,
	configHomePath, e);
	}
	return null;
	}

	@Override
	public FileBasedConfig openJGitConfig(Config parent, FS fs) {
	Path xdgPath = getXDGConfigHome(fs);
	if (xdgPath != null) {
	Path configPath = null;
	try {
	configPath = xdgPath.resolve("jgit"); //$NON-NLS-1$
	Files.createDirectories(configPath);
	configPath = configPath.resolve(Constants.CONFIG);
	return new FileBasedConfig(parent, configPath.toFile(), fs);
	} catch (IOException e) {
	LOG.error(JGitText.get().createJGitConfigFailed, configPath,
	e);
	}
	}
	return new FileBasedConfig(parent,
	new File(fs.userHome(), ".jgitconfig"), fs); //$NON-NLS-1$
	}

	@Override
	public String getHostname() {
	if (hostname == null) {
	try {
	InetAddress localMachine = InetAddress.getLocalHost();
	hostname = localMachine.getCanonicalHostName();
	} catch (UnknownHostException e) {
	// we do nothing
	hostname = "localhost"; //$NON-NLS-1$
	}
	assert hostname != null;
	}
	return hostname;
	}

	@Override
	public long getCurrentTime() {
	return System.currentTimeMillis();
	}

	@Override
	public int getTimezone(long when) {
	return getTimeZone().getOffset(when) / (60 * 1000);
	}
	}

	private static volatile SystemReader INSTANCE = DEFAULT;

	/**
	* Get the current SystemReader instance
	*
	* @return the current SystemReader instance.
	*/
	public static SystemReader getInstance() {
	return INSTANCE;
	}

	/**
	* Set a new SystemReader instance to use when accessing properties.
	*
	* @param newReader
	* the new instance to use when accessing properties, or null for
	* the default instance.
	*/
	public static void setInstance(SystemReader newReader) {
	isMacOS = null;
	isWindows = null;
	if (newReader == null)
	INSTANCE = DEFAULT;
	else {
	newReader.init();
	INSTANCE = newReader;
	}
	}

	private ObjectChecker platformChecker;

	private AtomicReference<FileBasedConfig> systemConfig = new AtomicReference<>();

	private AtomicReference<FileBasedConfig> userConfig = new AtomicReference<>();

	private AtomicReference<FileBasedConfig> jgitConfig = new AtomicReference<>();

	private void init() {
	// Creating ObjectChecker must be deferred. Unit tests change
	// behavior of is{Windows,MacOS} in constructor of subclass.
	if (platformChecker == null)
	setPlatformChecker();
	}

	/**
	* Should be used in tests when the platform is explicitly changed.
	*
	* @since 3.6
	*/
	protected final void setPlatformChecker() {
	platformChecker = new ObjectChecker()
	.setSafeForWindows(isWindows())
	.setSafeForMacOS(isMacOS());
	}

	/**
	* Gets the hostname of the local host. If no hostname can be found, the
	* hostname is set to the default value "localhost".
	*
	* @return the canonical hostname
	*/
	public abstract String getHostname();

	/**
	* Get value of the system variable
	*
	* @param variable
	* system variable to read
	* @return value of the system variable
	*/
	public abstract String getenv(String variable);

	/**
	* Get value of the system property
	*
	* @param key
	* of the system property to read
	* @return value of the system property
	*/
	public abstract String getProperty(String key);

	/**
	* Open the git configuration found in the user home. Use
	* {@link #getUserConfig()} to get the current git configuration in the user
	* home since it manages automatic reloading when the gitconfig file was
	* modified and avoids unnecessary reloads.
	*
	* @param parent
	* a config with values not found directly in the returned config
	* @param fs
	* the file system abstraction which will be necessary to perform
	* certain file system operations.
	* @return the git configuration found in the user home
	*/
	public abstract FileBasedConfig openUserConfig(Config parent, FS fs);

	/**
	* Open the gitconfig configuration found in the system-wide "etc"
	* directory. Use {@link #getSystemConfig()} to get the current system-wide
	* git configuration since it manages automatic reloading when the gitconfig
	* file was modified and avoids unnecessary reloads.
	*
	* @param parent
	* a config with values not found directly in the returned
	* config. Null is a reasonable value here.
	* @param fs
	* the file system abstraction which will be necessary to perform
	* certain file system operations.
	* @return the gitconfig configuration found in the system-wide "etc"
	* directory
	*/
	public abstract FileBasedConfig openSystemConfig(Config parent, FS fs);

	/**
	* Open the jgit configuration located at $XDG_CONFIG_HOME/jgit/config. Use
	* {@link #getJGitConfig()} to get the current jgit configuration in the
	* user home since it manages automatic reloading when the jgit config file
	* was modified and avoids unnecessary reloads.
	*
	* @param parent
	* a config with values not found directly in the returned config
	* @param fs
	* the file system abstraction which will be necessary to perform
	* certain file system operations.
	* @return the jgit configuration located at $XDG_CONFIG_HOME/jgit/config
	* @since 5.5.2
	*/
	public abstract FileBasedConfig openJGitConfig(Config parent, FS fs);

	/**
	* Get the git configuration found in the user home. The configuration will
	* be reloaded automatically if the configuration file was modified. Also
	* reloads the system config if the system config file was modified. If the
	* configuration file wasn't modified returns the cached configuration.
	*
	* @return the git configuration found in the user home
	* @throws ConfigInvalidException
	* if configuration is invalid
	* @throws IOException
	* if something went wrong when reading files
	* @since 5.1.9
	*/
	public StoredConfig getUserConfig()
	throws ConfigInvalidException, IOException {
	FileBasedConfig c = userConfig.get();
	if (c == null) {
	userConfig.compareAndSet(null,
	openUserConfig(getSystemConfig(), FS.DETECTED));
	c = userConfig.get();
	}
	// on the very first call this will check a second time if the system
	// config is outdated
	updateAll(c);
	return c;
	}

	/**
	* Get the jgit configuration located at $XDG_CONFIG_HOME/jgit/config. The
	* configuration will be reloaded automatically if the configuration file
	* was modified. If the configuration file wasn't modified returns the
	* cached configuration.
	*
	* @return the jgit configuration located at $XDG_CONFIG_HOME/jgit/config
	* @throws ConfigInvalidException
	* if configuration is invalid
	* @throws IOException
	* if something went wrong when reading files
	* @since 5.5.2
	*/
	public StoredConfig getJGitConfig()
	throws ConfigInvalidException, IOException {
	FileBasedConfig c = jgitConfig.get();
	if (c == null) {
	jgitConfig.compareAndSet(null,
	openJGitConfig(null, FS.DETECTED));
	c = jgitConfig.get();
	}
	updateAll(c);
	return c;
	}

	/**
	* Get the gitconfig configuration found in the system-wide "etc" directory.
	* The configuration will be reloaded automatically if the configuration
	* file was modified otherwise returns the cached system level config.
	*
	* @return the gitconfig configuration found in the system-wide "etc"
	* directory
	* @throws ConfigInvalidException
	* if configuration is invalid
	* @throws IOException
	* if something went wrong when reading files
	* @since 5.1.9
	*/
	public StoredConfig getSystemConfig()
	throws ConfigInvalidException, IOException {
	FileBasedConfig c = systemConfig.get();
	if (c == null) {
	systemConfig.compareAndSet(null,
	openSystemConfig(getJGitConfig(), FS.DETECTED));
	c = systemConfig.get();
	}
	updateAll(c);
	return c;
	}

	/**
	* Update config and its parents if they seem modified
	*
	* @param config
	* configuration to reload if outdated
	* @throws ConfigInvalidException
	* if configuration is invalid
	* @throws IOException
	* if something went wrong when reading files
	*/
	private void updateAll(Config config)
	throws ConfigInvalidException, IOException {
	if (config == null) {
	return;
	}
	updateAll(config.getBaseConfig());
	if (config instanceof FileBasedConfig) {
	FileBasedConfig cfg = (FileBasedConfig) config;
	if (cfg.isOutdated()) {
	LOG.debug("loading config {}", cfg); //$NON-NLS-1$
	cfg.load();
	}
	}
	}

	/**
	* Get the current system time
	*
	* @return the current system time
	*/
	public abstract long getCurrentTime();

	/**
	* Get clock instance preferred by this system.
	*
	* @return clock instance preferred by this system.
	* @since 4.6
	*/
	public MonotonicClock getClock() {
	return new MonotonicSystemClock();
	}

	/**
	* Get the local time zone
	*
	* @param when
	* a system timestamp
	* @return the local time zone
	*/
	public abstract int getTimezone(long when);

	/**
	* Get system time zone, possibly mocked for testing
	*
	* @return system time zone, possibly mocked for testing
	* @since 1.2
	*/
	public TimeZone getTimeZone() {
	return TimeZone.getDefault();
	}

	/**
	* Get the locale to use
	*
	* @return the locale to use
	* @since 1.2
	*/
	public Locale getLocale() {
	return Locale.getDefault();
	}

	/**
	* Returns a simple date format instance as specified by the given pattern.
	*
	* @param pattern
	* the pattern as defined in
	* {@link java.text.SimpleDateFormat#SimpleDateFormat(String)}
	* @return the simple date format
	* @since 2.0
	*/
	public SimpleDateFormat getSimpleDateFormat(String pattern) {
	return new SimpleDateFormat(pattern);
	}

	/**
	* Returns a simple date format instance as specified by the given pattern.
	*
	* @param pattern
	* the pattern as defined in
	* {@link java.text.SimpleDateFormat#SimpleDateFormat(String)}
	* @param locale
	* locale to be used for the {@code SimpleDateFormat}
	* @return the simple date format
	* @since 3.2
	*/
	public SimpleDateFormat getSimpleDateFormat(String pattern, Locale locale) {
	return new SimpleDateFormat(pattern, locale);
	}

	/**
	* Returns a date/time format instance for the given styles.
	*
	* @param dateStyle
	* the date style as specified in
	* {@link java.text.DateFormat#getDateTimeInstance(int, int)}
	* @param timeStyle
	* the time style as specified in
	* {@link java.text.DateFormat#getDateTimeInstance(int, int)}
	* @return the date format
	* @since 2.0
	*/
	public DateFormat getDateTimeInstance(int dateStyle, int timeStyle) {
	return DateFormat.getDateTimeInstance(dateStyle, timeStyle);
	}

	/**
	* Whether we are running on Windows.
	*
	* @return true if we are running on Windows.
	*/
	public boolean isWindows() {
	if (isWindows == null) {
	String osDotName = getOsName();
	isWindows = Boolean.valueOf(osDotName.startsWith("Windows")); //$NON-NLS-1$
	}
	return isWindows.booleanValue();
	}

	/**
	* Whether we are running on Mac OS X
	*
	* @return true if we are running on Mac OS X
	*/
	public boolean isMacOS() {
	if (isMacOS == null) {
	String osDotName = getOsName();
	isMacOS = Boolean.valueOf(
	"Mac OS X".equals(osDotName) \|\| "Darwin".equals(osDotName)); //$NON-NLS-1$ //$NON-NLS-2$
	}
	return isMacOS.booleanValue();
	}

	private String getOsName() {
	return AccessController.doPrivileged(
	(PrivilegedAction<String>) () -> getProperty("os.name") //$NON-NLS-1$
	);
	}

	/**
	* Check tree path entry for validity.
	* <p>
	* Scans a multi-directory path string such as {@code "src/main.c"}.
	*
	* @param path path string to scan.
	* @throws org.eclipse.jgit.errors.CorruptObjectException path is invalid.
	* @since 3.6
	*/
	public void checkPath(String path) throws CorruptObjectException {
	platformChecker.checkPath(path);
	}

	/**
	* Check tree path entry for validity.
	* <p>
	* Scans a multi-directory path string such as {@code "src/main.c"}.
	*
	* @param path
	* path string to scan.
	* @throws org.eclipse.jgit.errors.CorruptObjectException
	* path is invalid.
	* @since 4.2
	*/
	public void checkPath(byte[] path) throws CorruptObjectException {
	platformChecker.checkPath(path, 0, path.length);
	}
	}