org.apache.jxtadoop.fs.FileSystem.java Source code

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/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.jxtadoop.fs;

import java.io.Closeable;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.net.URI;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.IdentityHashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.TreeSet;
import java.util.concurrent.atomic.AtomicLong;
import java.util.regex.Pattern;

import javax.security.auth.login.LoginException;

import org.apache.commons.logging.*;

import org.apache.jxtadoop.conf.Configuration;
import org.apache.jxtadoop.conf.Configured;
import org.apache.jxtadoop.fs.permission.FsPermission;
import org.apache.jxtadoop.hdfs.server.namenode.NameNode;
import org.apache.jxtadoop.io.MultipleIOException;
import org.apache.jxtadoop.security.UserGroupInformation;
import org.apache.jxtadoop.util.Progressable;
import org.apache.jxtadoop.util.ReflectionUtils;
import org.apache.jxtadoop.hdfs.p2p.P2PConstants;
import org.apache.jxtadoop.hdfs.protocol.FSConstants;

/****************************************************************
 * An abstract base class for a fairly generic filesystem.  It
 * may be implemented as a distributed filesystem, or as a "local"
 * one that reflects the locally-connected disk.  The local version
 * exists for small Hadoop instances and for testing.
 *
 * <p>
 *
 * All user code that may potentially use the Hadoop Distributed
 * File System should be written to use a FileSystem object.  The
 * Hadoop DFS is a multi-machine system that appears as a single
 * disk.  It's useful because of its fault tolerance and potentially
 * very large capacity.
 * 
 * <p>
 * The local implementation is {@link LocalFileSystem} and distributed
 * implementation is DistributedFileSystem.
 *****************************************************************/
@SuppressWarnings({ "unused" })
public abstract class FileSystem extends Configured implements Closeable {
    private static final String FS_DEFAULT_NAME_KEY = "fs.default.name";

    public static final Log LOG = LogFactory.getLog(FileSystem.class);

    /** FileSystem cache */
    private static final Cache CACHE = new Cache();

    /** The key this instance is stored under in the cache. */
    private Cache.Key key;

    /** Recording statistics per a FileSystem class */
    private static final Map<Class<? extends FileSystem>, Statistics> statisticsTable = new IdentityHashMap<Class<? extends FileSystem>, Statistics>();

    /**
     * The statistics for this file system.
     */
    protected Statistics statistics;

    /**
     * A cache of files that should be deleted when filsystem is closed
     * or the JVM is exited.
     */
    private Set<Path> deleteOnExit = new TreeSet<Path>();

    /** Returns the configured filesystem implementation.*/
    public static FileSystem get(Configuration conf) throws IOException {
        return get(getDefaultUri(conf), conf);
    }

    /** Get the default filesystem URI from a configuration.
     * @param conf the configuration to access
     * @return the uri of the default filesystem
     */
    public static URI getDefaultUri(Configuration conf) {
        return URI.create(fixName(conf.get(FS_DEFAULT_NAME_KEY, "file:///")));
    }

    /** Set the default filesystem URI in a configuration.
     * @param conf the configuration to alter
     * @param uri the new default filesystem uri
     */
    public static void setDefaultUri(Configuration conf, URI uri) {
        conf.set(FS_DEFAULT_NAME_KEY, uri.toString());
    }

    /** Set the default filesystem URI in a configuration.
     * @param conf the configuration to alter
     * @param uri the new default filesystem uri
     */
    public static void setDefaultUri(Configuration conf, String uri) {
        setDefaultUri(conf, URI.create(fixName(uri)));
    }

    /** Called after a new FileSystem instance is constructed.
     * @param name a uri whose authority section names the host, port, etc.
     *   for this FileSystem
     * @param conf the configuration
     */
    public void initialize(URI name, Configuration conf) throws IOException {
        statistics = getStatistics(name.getScheme(), getClass());
    }

    /** Returns a URI whose scheme and authority identify this FileSystem.*/
    public abstract URI getUri();

    /** @deprecated call #getUri() instead.*/
    public String getName() {
        return getUri().toString();
    }

    /** @deprecated call #get(URI,Configuration) instead. */
    public static FileSystem getNamed(String name, Configuration conf) throws IOException {
        return get(URI.create(fixName(name)), conf);
    }

    /** Update old-format filesystem names, for back-compatibility.  This should
     * eventually be replaced with a checkName() method that throws an exception
     * for old-format names. */
    private static String fixName(String name) {
        // convert old-format name to new-format name
        if (name.equals("hdfs://") || name.equals("hdfs://null")) {
            name = "hdfs://"
                    + NameNode.getNameNode().getNameNodePeerID().toString().replaceAll("urn:jxta:cbid-", "");
        } else if (name.equals("local")) { // "local" is now "file:///".
            //LOG.warn("\"local\" is a deprecated filesystem name."
            //         +" Use \"file:///\" instead.");
            name = "file:///";
        } else if (name.indexOf('/') == -1) { // unqualified is "hdfs://"
            //LOG.warn("\""+name+"\" is a deprecated filesystem name."
            //         +" Use \"hdfs://"+name+"/\" instead.");
            name = "hdfs://" + name;
        }
        return name;
    }

    /**
     * Get the local file syste
     * @param conf the configuration to configure the file system with
     * @return a LocalFileSystem
     */
    public static LocalFileSystem getLocal(Configuration conf) throws IOException {
        return (LocalFileSystem) get(LocalFileSystem.NAME, conf);
    }

    /** Returns the FileSystem for this URI's scheme and authority.  The scheme
     * of the URI determines a configuration property name,
     * <tt>fs.<i>scheme</i>.class</tt> whose value names the FileSystem class.
     * The entire URI is passed to the FileSystem instance's initialize method.
     */
    public static FileSystem get(URI uri, Configuration conf) throws IOException {
        String scheme = uri.getScheme();
        String authority = uri.getAuthority();

        if (scheme == null) { // no scheme: use default FS
            return get(conf);
        }

        if (authority == null) { // no authority
            URI defaultUri = getDefaultUri(conf);
            if (scheme.equals(defaultUri.getScheme()) // if scheme matches default
                    && defaultUri.getAuthority() != null) { // & default has authority
                return get(defaultUri, conf); // return default
            }
        }

        return CACHE.get(uri, conf);
    }

    private static class ClientFinalizer extends Thread {
        public synchronized void run() {
            try {
                FileSystem.closeAll();
            } catch (IOException e) {
                LOG.info("FileSystem.closeAll() threw an exception:\n" + e);
            }
        }
    }

    private static final ClientFinalizer clientFinalizer = new ClientFinalizer();

    /**
     * Close all cached filesystems. Be sure those filesystems are not
     * used anymore.
     * 
     * @throws IOException
     */
    public static void closeAll() throws IOException {
        CACHE.closeAll();
    }

    /** Make sure that a path specifies a FileSystem. */
    public Path makeQualified(Path path) {
        checkPath(path);
        return path.makeQualified(this);
    }

    /** create a file with the provided permission
     * The permission of the file is set to be the provided permission as in
     * setPermission, not permission&~umask
     * 
     * It is implemented using two RPCs. It is understood that it is inefficient,
     * but the implementation is thread-safe. The other option is to change the
     * value of umask in configuration to be 0, but it is not thread-safe.
     * 
     * @param fs file system handle
     * @param file the name of the file to be created
     * @param permission the permission of the file
     * @return an output stream
     * @throws IOException
     */
    public static FSDataOutputStream create(FileSystem fs, Path file, FsPermission permission) throws IOException {
        // create the file with default permission
        FSDataOutputStream out = fs.create(file);
        // set its permission to the supplied one
        fs.setPermission(file, permission);
        return out;
    }

    /** create a directory with the provided permission
     * The permission of the directory is set to be the provided permission as in
     * setPermission, not permission&~umask
     * 
     * @see #create(FileSystem, Path, FsPermission)
     * 
     * @param fs file system handle
     * @param dir the name of the directory to be created
     * @param permission the permission of the directory
     * @return true if the directory creation succeeds; false otherwise
     * @throws IOException
     */
    public static boolean mkdirs(FileSystem fs, Path dir, FsPermission permission) throws IOException {
        // create the directory using the default permission
        boolean result = fs.mkdirs(dir);
        // set its permission to be the supplied one
        fs.setPermission(dir, permission);
        return result;
    }

    ///////////////////////////////////////////////////////////////
    // FileSystem
    ///////////////////////////////////////////////////////////////

    protected FileSystem() {
        super(null);
    }

    /** Check that a Path belongs to this FileSystem. */
    protected void checkPath(Path path) {
        URI uri = path.toUri();
        if (uri.getScheme() == null) // fs is relative 
            return;
        String thisScheme = this.getUri().getScheme();
        String thatScheme = uri.getScheme();
        String thisAuthority = this.getUri().getAuthority();
        String thatAuthority = uri.getAuthority();
        //authority and scheme are not case sensitive
        if (thisScheme.equalsIgnoreCase(thatScheme)) {// schemes match
            if (thisAuthority == thatAuthority || // & authorities match
                    (thisAuthority != null && thisAuthority.equalsIgnoreCase(thatAuthority)))
                return;

            if (thatAuthority == null && // path's authority is null
                    thisAuthority != null) { // fs has an authority
                URI defaultUri = getDefaultUri(getConf()); // & is the conf default 
                if (thisScheme.equalsIgnoreCase(defaultUri.getScheme())
                        && thisAuthority.equalsIgnoreCase(defaultUri.getAuthority()))
                    return;
                try { // or the default fs's uri
                    defaultUri = get(getConf()).getUri();
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
                if (thisScheme.equalsIgnoreCase(defaultUri.getScheme())
                        && thisAuthority.equalsIgnoreCase(defaultUri.getAuthority()))
                    return;
            }
        }
        throw new IllegalArgumentException("Wrong FS: " + path + ", expected: " + this.getUri());
    }

    /**
     * Return an array containing hostnames, offset and size of 
     * portions of the given file.  For a nonexistent 
     * file or regions, null will be returned.
     *
     * This call is most helpful with DFS, where it returns 
     * hostnames of machines that contain the given file.
     *
     * The FileSystem will simply return an elt containing 'localhost'.
     */
    public BlockLocation[] getFileBlockLocations(FileStatus file, long start, long len) throws IOException {
        if (file == null) {
            return null;
        }

        if ((start < 0) || (len < 0)) {
            throw new IllegalArgumentException("Invalid start or len parameter");
        }

        if (file.getLen() < start) {
            return new BlockLocation[0];

        }
        String[] name = { "localhost:50010" };
        String[] host = { "localhost" };
        return new BlockLocation[] { new BlockLocation(name, host, 0, file.getLen()) };
    }

    /**
     * Opens an FSDataInputStream at the indicated Path.
     * @param f the file name to open
     * @param bufferSize the size of the buffer to be used.
     */
    public abstract FSDataInputStream open(Path f, int bufferSize) throws IOException;

    /**
     * Opens an FSDataInputStream at the indicated Path.
     * @param f the file to open
     */
    public FSDataInputStream open(Path f) throws IOException {
        return open(f, getConf().getInt("io.file.buffer.size", P2PConstants.IO_FILE_BUFFER_SIZE));
    }

    /**
     * Opens an FSDataOutputStream at the indicated Path.
     * Files are overwritten by default.
     */
    public FSDataOutputStream create(Path f) throws IOException {
        return create(f, true);
    }

    /**
     * Opens an FSDataOutputStream at the indicated Path.
     */
    public FSDataOutputStream create(Path f, boolean overwrite) throws IOException {
        return create(f, overwrite, getConf().getInt("io.file.buffer.size", P2PConstants.IO_FILE_BUFFER_SIZE),
                getDefaultReplication(), getDefaultBlockSize());
    }

    /**
     * Create an FSDataOutputStream at the indicated Path with write-progress
     * reporting.
     * Files are overwritten by default.
     */
    public FSDataOutputStream create(Path f, Progressable progress) throws IOException {
        return create(f, true, getConf().getInt("io.file.buffer.size", P2PConstants.IO_FILE_BUFFER_SIZE),
                getDefaultReplication(), getDefaultBlockSize(), progress);
    }

    /**
     * Opens an FSDataOutputStream at the indicated Path.
     * Files are overwritten by default.
     */
    public FSDataOutputStream create(Path f, short replication) throws IOException {
        return create(f, true, getConf().getInt("io.file.buffer.size", P2PConstants.IO_FILE_BUFFER_SIZE),
                replication, getDefaultBlockSize());
    }

    /**
     * Opens an FSDataOutputStream at the indicated Path with write-progress
     * reporting.
     * Files are overwritten by default.
     */
    public FSDataOutputStream create(Path f, short replication, Progressable progress) throws IOException {
        return create(f, true, getConf().getInt("io.file.buffer.size", P2PConstants.IO_FILE_BUFFER_SIZE),
                replication, getDefaultBlockSize(), progress);
    }

    /**
     * Opens an FSDataOutputStream at the indicated Path.
     * @param f the file name to open
     * @param overwrite if a file with this name already exists, then if true,
     *   the file will be overwritten, and if false an error will be thrown.
     * @param bufferSize the size of the buffer to be used.
     */
    public FSDataOutputStream create(Path f, boolean overwrite, int bufferSize) throws IOException {
        return create(f, overwrite, bufferSize, getDefaultReplication(), getDefaultBlockSize());
    }

    /**
     * Opens an FSDataOutputStream at the indicated Path with write-progress
     * reporting.
     * @param f the file name to open
     * @param overwrite if a file with this name already exists, then if true,
     *   the file will be overwritten, and if false an error will be thrown.
     * @param bufferSize the size of the buffer to be used.
     */
    public FSDataOutputStream create(Path f, boolean overwrite, int bufferSize, Progressable progress)
            throws IOException {
        return create(f, overwrite, bufferSize, getDefaultReplication(), getDefaultBlockSize(), progress);
    }

    /**
     * Opens an FSDataOutputStream at the indicated Path.
     * @param f the file name to open
     * @param overwrite if a file with this name already exists, then if true,
     *   the file will be overwritten, and if false an error will be thrown.
     * @param bufferSize the size of the buffer to be used.
     * @param replication required block replication for the file. 
     */
    public FSDataOutputStream create(Path f, boolean overwrite, int bufferSize, short replication, long blockSize)
            throws IOException {
        return create(f, overwrite, bufferSize, replication, blockSize, null);
    }

    /**
     * Opens an FSDataOutputStream at the indicated Path with write-progress
     * reporting.
     * @param f the file name to open
     * @param overwrite if a file with this name already exists, then if true,
     *   the file will be overwritten, and if false an error will be thrown.
     * @param bufferSize the size of the buffer to be used.
     * @param replication required block replication for the file. 
     */
    public FSDataOutputStream create(Path f, boolean overwrite, int bufferSize, short replication, long blockSize,
            Progressable progress) throws IOException {
        return this.create(f, FsPermission.getDefault(), overwrite, bufferSize, replication, blockSize, progress);
    }

    /**
     * Opens an FSDataOutputStream at the indicated Path with write-progress
     * reporting.
     * @param f the file name to open
     * @param permission
     * @param overwrite if a file with this name already exists, then if true,
     *   the file will be overwritten, and if false an error will be thrown.
     * @param bufferSize the size of the buffer to be used.
     * @param replication required block replication for the file.
     * @param blockSize
     * @param progress
     * @throws IOException
     * @see #setPermission(Path, FsPermission)
     */
    public abstract FSDataOutputStream create(Path f, FsPermission permission, boolean overwrite, int bufferSize,
            short replication, long blockSize, Progressable progress) throws IOException;

    /**
     * Creates the given Path as a brand-new zero-length file.  If
     * create fails, or if it already existed, return false.
     */
    public boolean createNewFile(Path f) throws IOException {
        if (exists(f)) {
            return false;
        } else {
            create(f, false, getConf().getInt("io.file.buffer.size", P2PConstants.IO_FILE_BUFFER_SIZE)).close();
            return true;
        }
    }

    /**
     * Append to an existing file (optional operation).
     * Same as append(f, getConf().getInt("io.file.buffer.size", P2PConstants.IO_FILE_BUFFER_SIZE), null)
     * @param f the existing file to be appended.
     * @throws IOException
     */
    public FSDataOutputStream append(Path f) throws IOException {
        return append(f, getConf().getInt("io.file.buffer.size", P2PConstants.IO_FILE_BUFFER_SIZE), null);
    }

    /**
     * Append to an existing file (optional operation).
     * Same as append(f, bufferSize, null).
     * @param f the existing file to be appended.
     * @param bufferSize the size of the buffer to be used.
     * @throws IOException
     */
    public FSDataOutputStream append(Path f, int bufferSize) throws IOException {
        return append(f, bufferSize, null);
    }

    /**
     * Append to an existing file (optional operation).
     * @param f the existing file to be appended.
     * @param bufferSize the size of the buffer to be used.
     * @param progress for reporting progress if it is not null.
     * @throws IOException
     */
    public abstract FSDataOutputStream append(Path f, int bufferSize, Progressable progress) throws IOException;

    /**
     * Get replication.
     * 
     * @deprecated Use getFileStatus() instead
     * @param src file name
     * @return file replication
     * @throws IOException
     */
    @Deprecated
    public short getReplication(Path src) throws IOException {
        return getFileStatus(src).getReplication();
    }

    /**
     * Set replication for an existing file.
     * 
     * @param src file name
     * @param replication new replication
     * @throws IOException
     * @return true if successful;
     *         false if file does not exist or is a directory
     */
    public boolean setReplication(Path src, short replication) throws IOException {
        return true;
    }

    /**
     * Renames Path src to Path dst.  Can take place on local fs
     * or remote DFS.
     */
    public abstract boolean rename(Path src, Path dst) throws IOException;

    /** Delete a file. */
    /** @deprecated Use delete(Path, boolean) instead */
    @Deprecated
    public abstract boolean delete(Path f) throws IOException;

    /** Delete a file.
     *
     * @param f the path to delete.
     * @param recursive if path is a directory and set to 
     * true, the directory is deleted else throws an exception. In
     * case of a file the recursive can be set to either true or false. 
     * @return  true if delete is successful else false. 
     * @throws IOException
     */
    public abstract boolean delete(Path f, boolean recursive) throws IOException;

    /**
     * Mark a path to be deleted when FileSystem is closed.
     * When the JVM shuts down,
     * all FileSystem objects will be closed automatically.
     * Then,
     * the marked path will be deleted as a result of closing the FileSystem.
     *
     * The path has to exist in the file system.
     * 
     * @param f the path to delete.
     * @return  true if deleteOnExit is successful, otherwise false.
     * @throws IOException
     */
    public boolean deleteOnExit(Path f) throws IOException {
        if (!exists(f)) {
            return false;
        }
        synchronized (deleteOnExit) {
            deleteOnExit.add(f);
        }
        return true;
    }

    /**
     * Delete all files that were marked as delete-on-exit. This recursively
     * deletes all files in the specified paths.
     */
    protected void processDeleteOnExit() {
        synchronized (deleteOnExit) {
            for (Iterator<Path> iter = deleteOnExit.iterator(); iter.hasNext();) {
                Path path = iter.next();
                try {
                    delete(path, true);
                } catch (IOException e) {
                    LOG.info("Ignoring failure to deleteOnExit for path " + path);
                }
                iter.remove();
            }
        }
    }

    /** Check if exists.
     * @param f source file
     */
    public boolean exists(Path f) throws IOException {
        try {
            return getFileStatus(f) != null;
        } catch (FileNotFoundException e) {
            return false;
        }
    }

    /** True iff the named path is a directory. */
    /** @deprecated Use getFileStatus() instead */
    @Deprecated
    public boolean isDirectory(Path f) throws IOException {
        try {
            return getFileStatus(f).isDir();
        } catch (FileNotFoundException e) {
            return false; // f does not exist
        }
    }

    /** True iff the named path is a regular file. */
    public boolean isFile(Path f) throws IOException {
        try {
            return !getFileStatus(f).isDir();
        } catch (FileNotFoundException e) {
            return false; // f does not exist
        }
    }

    /** The number of bytes in a file. */
    /** @deprecated Use getFileStatus() instead */
    @Deprecated
    public long getLength(Path f) throws IOException {
        return getFileStatus(f).getLen();
    }

    /** Return the {@link ContentSummary} of a given {@link Path}. */
    public ContentSummary getContentSummary(Path f) throws IOException {
        FileStatus status = getFileStatus(f);
        if (!status.isDir()) {
            // f is a file
            return new ContentSummary(status.getLen(), 1, 0);
        }
        // f is a directory
        long[] summary = { 0, 0, 1 };
        for (FileStatus s : listStatus(f)) {
            ContentSummary c = s.isDir() ? getContentSummary(s.getPath()) : new ContentSummary(s.getLen(), 1, 0);
            summary[0] += c.getLength();
            summary[1] += c.getFileCount();
            summary[2] += c.getDirectoryCount();
        }
        return new ContentSummary(summary[0], summary[1], summary[2]);
    }

    final private static PathFilter DEFAULT_FILTER = new PathFilter() {
        public boolean accept(Path file) {
            return true;
        }
    };

    /**
     * List the statuses of the files/directories in the given path if the path is
     * a directory.
     * 
     * @param f
     *          given path
     * @return the statuses of the files/directories in the given patch
     * @throws IOException
     */
    public abstract FileStatus[] listStatus(Path f) throws IOException;

    /*
     * Filter files/directories in the given path using the user-supplied path
     * filter. Results are added to the given array <code>results</code>.
     */
    private void listStatus(ArrayList<FileStatus> results, Path f, PathFilter filter) throws IOException {
        FileStatus listing[] = listStatus(f);
        if (listing != null) {
            for (int i = 0; i < listing.length; i++) {
                if (filter.accept(listing[i].getPath())) {
                    results.add(listing[i]);
                }
            }
        }
    }

    /**
     * Filter files/directories in the given path using the user-supplied path
     * filter.
     * 
     * @param f
     *          a path name
     * @param filter
     *          the user-supplied path filter
     * @return an array of FileStatus objects for the files under the given path
     *         after applying the filter
     * @throws IOException
     *           if encounter any problem while fetching the status
     */
    public FileStatus[] listStatus(Path f, PathFilter filter) throws IOException {
        ArrayList<FileStatus> results = new ArrayList<FileStatus>();
        listStatus(results, f, filter);
        return results.toArray(new FileStatus[results.size()]);
    }

    /**
     * Filter files/directories in the given list of paths using default
     * path filter.
     * 
     * @param files
     *          a list of paths
     * @return a list of statuses for the files under the given paths after
     *         applying the filter default Path filter
     * @exception IOException
     */
    public FileStatus[] listStatus(Path[] files) throws IOException {
        return listStatus(files, DEFAULT_FILTER);
    }

    /**
     * Filter files/directories in the given list of paths using user-supplied
     * path filter.
     * 
     * @param files
     *          a list of paths
     * @param filter
     *          the user-supplied path filter
     * @return a list of statuses for the files under the given paths after
     *         applying the filter
     * @exception IOException
     */
    public FileStatus[] listStatus(Path[] files, PathFilter filter) throws IOException {
        ArrayList<FileStatus> results = new ArrayList<FileStatus>();
        for (int i = 0; i < files.length; i++) {
            listStatus(results, files[i], filter);
        }
        return results.toArray(new FileStatus[results.size()]);
    }

    /**
     * <p>Return all the files that match filePattern and are not checksum
     * files. Results are sorted by their names.
     * 
     * <p>
     * A filename pattern is composed of <i>regular</i> characters and
     * <i>special pattern matching</i> characters, which are:
     *
     * <dl>
     *  <dd>
     *   <dl>
     *    <p>
     *    <dt> <tt> ? </tt>
     *    <dd> Matches any single character.
     *
     *    <p>
     *    <dt> <tt> * </tt>
     *    <dd> Matches zero or more characters.
     *
     *    <p>
     *    <dt> <tt> [<i>abc</i>] </tt>
     *    <dd> Matches a single character from character set
     *     <tt>{<i>a,b,c</i>}</tt>.
     *
     *    <p>
     *    <dt> <tt> [<i>a</i>-<i>b</i>] </tt>
     *    <dd> Matches a single character from the character range
     *     <tt>{<i>a...b</i>}</tt>.  Note that character <tt><i>a</i></tt> must be
     *     lexicographically less than or equal to character <tt><i>b</i></tt>.
     *
     *    <p>
     *    <dt> <tt> [^<i>a</i>] </tt>
     *    <dd> Matches a single character that is not from character set or range
     *     <tt>{<i>a</i>}</tt>.  Note that the <tt>^</tt> character must occur
     *     immediately to the right of the opening bracket.
     *
     *    <p>
     *    <dt> <tt> \<i>c</i> </tt>
     *    <dd> Removes (escapes) any special meaning of character <i>c</i>.
     *
     *    <p>
     *    <dt> <tt> {ab,cd} </tt>
     *    <dd> Matches a string from the string set <tt>{<i>ab, cd</i>} </tt>
     *    
     *    <p>
     *    <dt> <tt> {ab,c{de,fh}} </tt>
     *    <dd> Matches a string from the string set <tt>{<i>ab, cde, cfh</i>}</tt>
     *
     *   </dl>
     *  </dd>
     * </dl>
     *
     * @param pathPattern a regular expression specifying a pth pattern
        
     * @return an array of paths that match the path pattern
     * @throws IOException
     */
    public FileStatus[] globStatus(Path pathPattern) throws IOException {
        return globStatus(pathPattern, DEFAULT_FILTER);
    }

    /**
     * Return an array of FileStatus objects whose path names match pathPattern
     * and is accepted by the user-supplied path filter. Results are sorted by
     * their path names.
     * Return null if pathPattern has no glob and the path does not exist.
     * Return an empty array if pathPattern has a glob and no path matches it. 
     * 
     * @param pathPattern
     *          a regular expression specifying the path pattern
     * @param filter
     *          a user-supplied path filter
     * @return an array of FileStatus objects
     * @throws IOException if any I/O error occurs when fetching file status
     */
    public FileStatus[] globStatus(Path pathPattern, PathFilter filter) throws IOException {
        String filename = pathPattern.toUri().getPath();
        List<String> filePatterns = GlobExpander.expand(filename);
        if (filePatterns.size() == 1) {
            return globStatusInternal(pathPattern, filter);
        } else {
            List<FileStatus> results = new ArrayList<FileStatus>();
            for (String filePattern : filePatterns) {
                FileStatus[] files = globStatusInternal(new Path(filePattern), filter);
                for (FileStatus file : files) {
                    results.add(file);
                }
            }
            return results.toArray(new FileStatus[results.size()]);
        }
    }

    private FileStatus[] globStatusInternal(Path pathPattern, PathFilter filter) throws IOException {
        Path[] parents = new Path[1];
        int level = 0;
        String filename = pathPattern.toUri().getPath();

        // path has only zero component
        if ("".equals(filename) || Path.SEPARATOR.equals(filename)) {
            return getFileStatus(new Path[] { pathPattern });
        }

        // path has at least one component
        String[] components = filename.split(Path.SEPARATOR);
        // get the first component
        if (pathPattern.isAbsolute()) {
            parents[0] = new Path(Path.SEPARATOR);
            level = 1;
        } else {
            parents[0] = new Path(Path.CUR_DIR);
        }

        // glob the paths that match the parent path, i.e., [0, components.length-1]
        boolean[] hasGlob = new boolean[] { false };
        Path[] parentPaths = globPathsLevel(parents, components, level, hasGlob);
        FileStatus[] results;
        if (parentPaths == null || parentPaths.length == 0) {
            results = null;
        } else {
            // Now work on the last component of the path
            GlobFilter fp = new GlobFilter(components[components.length - 1], filter);
            if (fp.hasPattern()) { // last component has a pattern
                // list parent directories and then glob the results
                results = listStatus(parentPaths, fp);
                hasGlob[0] = true;
            } else { // last component does not have a pattern
                // get all the path names
                ArrayList<Path> filteredPaths = new ArrayList<Path>(parentPaths.length);
                for (int i = 0; i < parentPaths.length; i++) {
                    parentPaths[i] = new Path(parentPaths[i], components[components.length - 1]);
                    if (fp.accept(parentPaths[i])) {
                        filteredPaths.add(parentPaths[i]);
                    }
                }
                // get all their statuses
                results = getFileStatus(filteredPaths.toArray(new Path[filteredPaths.size()]));
            }
        }

        // Decide if the pathPattern contains a glob or not
        if (results == null) {
            if (hasGlob[0]) {
                results = new FileStatus[0];
            }
        } else {
            if (results.length == 0) {
                if (!hasGlob[0]) {
                    results = null;
                }
            } else {
                Arrays.sort(results);
            }
        }
        return results;
    }

    /*
     * For a path of N components, return a list of paths that match the
     * components [<code>level</code>, <code>N-1</code>].
     */
    private Path[] globPathsLevel(Path[] parents, String[] filePattern, int level, boolean[] hasGlob)
            throws IOException {
        if (level == filePattern.length - 1)
            return parents;
        if (parents == null || parents.length == 0) {
            return null;
        }
        GlobFilter fp = new GlobFilter(filePattern[level]);
        if (fp.hasPattern()) {
            parents = FileUtil.stat2Paths(listStatus(parents, fp));
            hasGlob[0] = true;
        } else {
            for (int i = 0; i < parents.length; i++) {
                parents[i] = new Path(parents[i], filePattern[level]);
            }
        }
        return globPathsLevel(parents, filePattern, level + 1, hasGlob);
    }

    /* A class that could decide if a string matches the glob or not */
    private static class GlobFilter implements PathFilter {
        private PathFilter userFilter = DEFAULT_FILTER;
        private Pattern regex;
        private boolean hasPattern = false;

        /** Default pattern character: Escape any special meaning. */
        private static final char PAT_ESCAPE = '\\';
        /** Default pattern character: Any single character. */
        private static final char PAT_ANY = '.';
        /** Default pattern character: Character set close. */
        private static final char PAT_SET_CLOSE = ']';

        GlobFilter() {
        }

        GlobFilter(String filePattern) throws IOException {
            setRegex(filePattern);
        }

        GlobFilter(String filePattern, PathFilter filter) throws IOException {
            userFilter = filter;
            setRegex(filePattern);
        }

        private boolean isJavaRegexSpecialChar(char pChar) {
            return pChar == '.' || pChar == '$' || pChar == '(' || pChar == ')' || pChar == '|' || pChar == '+';
        }

        void setRegex(String filePattern) throws IOException {
            int len;
            int setOpen;
            int curlyOpen;
            boolean setRange;

            StringBuilder fileRegex = new StringBuilder();

            // Validate the pattern
            len = filePattern.length();
            if (len == 0)
                return;

            setOpen = 0;
            setRange = false;
            curlyOpen = 0;

            for (int i = 0; i < len; i++) {
                char pCh;

                // Examine a single pattern character
                pCh = filePattern.charAt(i);
                if (pCh == PAT_ESCAPE) {
                    fileRegex.append(pCh);
                    i++;
                    if (i >= len)
                        error("An escaped character does not present", filePattern, i);
                    pCh = filePattern.charAt(i);
                } else if (isJavaRegexSpecialChar(pCh)) {
                    fileRegex.append(PAT_ESCAPE);
                } else if (pCh == '*') {
                    fileRegex.append(PAT_ANY);
                    hasPattern = true;
                } else if (pCh == '?') {
                    pCh = PAT_ANY;
                    hasPattern = true;
                } else if (pCh == '{') {
                    fileRegex.append('(');
                    pCh = '(';
                    curlyOpen++;
                    hasPattern = true;
                } else if (pCh == ',' && curlyOpen > 0) {
                    fileRegex.append(")|");
                    pCh = '(';
                } else if (pCh == '}' && curlyOpen > 0) {
                    // End of a group
                    curlyOpen--;
                    fileRegex.append(")");
                    pCh = ')';
                } else if (pCh == '[' && setOpen == 0) {
                    setOpen++;
                    hasPattern = true;
                } else if (pCh == '^' && setOpen > 0) {
                } else if (pCh == '-' && setOpen > 0) {
                    // Character set range
                    setRange = true;
                } else if (pCh == PAT_SET_CLOSE && setRange) {
                    // Incomplete character set range
                    error("Incomplete character set range", filePattern, i);
                } else if (pCh == PAT_SET_CLOSE && setOpen > 0) {
                    // End of a character set
                    if (setOpen < 2)
                        error("Unexpected end of set", filePattern, i);
                    setOpen = 0;
                } else if (setOpen > 0) {
                    // Normal character, or the end of a character set range
                    setOpen++;
                    setRange = false;
                }
                fileRegex.append(pCh);
            }

            // Check for a well-formed pattern
            if (setOpen > 0 || setRange || curlyOpen > 0) {
                // Incomplete character set or character range
                error("Expecting set closure character or end of range, or }", filePattern, len);
            }
            regex = Pattern.compile(fileRegex.toString());
        }

        boolean hasPattern() {
            return hasPattern;
        }

        public boolean accept(Path path) {
            return regex.matcher(path.getName()).matches() && userFilter.accept(path);
        }

        private void error(String s, String pattern, int pos) throws IOException {
            throw new IOException("Illegal file pattern: " + s + " for glob " + pattern + " at " + pos);
        }
    }

    /** Return the current user's home directory in this filesystem.
     * The default implementation returns "/user/$USER/".
     */
    public Path getHomeDirectory() {
        return new Path("/user/" + System.getProperty("user.name")).makeQualified(this);
    }

    /**
     * Set the current working directory for the given file system. All relative
     * paths will be resolved relative to it.
     * 
     * @param new_dir
     */
    public abstract void setWorkingDirectory(Path new_dir);

    /**
     * Get the current working directory for the given file system
     * @return the directory pathname
     */
    public abstract Path getWorkingDirectory();

    /**
     * Call {@link #mkdirs(Path, FsPermission)} with default permission.
     */
    public boolean mkdirs(Path f) throws IOException {
        return mkdirs(f, FsPermission.getDefault());
    }

    /**
     * Make the given file and all non-existent parents into
     * directories. Has the semantics of Unix 'mkdir -p'.
     * Existence of the directory hierarchy is not an error.
     */
    public abstract boolean mkdirs(Path f, FsPermission permission) throws IOException;

    /**
     * The src file is on the local disk.  Add it to FS at
     * the given dst name and the source is kept intact afterwards
     */
    public void copyFromLocalFile(Path src, Path dst) throws IOException {
        copyFromLocalFile(false, src, dst);
    }

    /**
     * The src files is on the local disk.  Add it to FS at
     * the given dst name, removing the source afterwards.
     */
    public void moveFromLocalFile(Path[] srcs, Path dst) throws IOException {
        copyFromLocalFile(true, true, srcs, dst);
    }

    /**
     * The src file is on the local disk.  Add it to FS at
     * the given dst name, removing the source afterwards.
     */
    public void moveFromLocalFile(Path src, Path dst) throws IOException {
        copyFromLocalFile(true, src, dst);
    }

    /**
     * The src file is on the local disk.  Add it to FS at
     * the given dst name.
     * delSrc indicates if the source should be removed
     */
    public void copyFromLocalFile(boolean delSrc, Path src, Path dst) throws IOException {
        copyFromLocalFile(delSrc, true, src, dst);
    }

    /**
     * The src files are on the local disk.  Add it to FS at
     * the given dst name.
     * delSrc indicates if the source should be removed
     */
    public void copyFromLocalFile(boolean delSrc, boolean overwrite, Path[] srcs, Path dst) throws IOException {
        Configuration conf = getConf();
        FileUtil.copy(getLocal(conf), srcs, this, dst, delSrc, overwrite, conf);
    }

    /**
     * The src file is on the local disk.  Add it to FS at
     * the given dst name.
     * delSrc indicates if the source should be removed
     */
    public void copyFromLocalFile(boolean delSrc, boolean overwrite, Path src, Path dst) throws IOException {
        Configuration conf = getConf();
        FileUtil.copy(getLocal(conf), src, this, dst, delSrc, overwrite, conf);
    }

    /**
     * The src file is under FS, and the dst is on the local disk.
     * Copy it from FS control to the local dst name.
     */
    public void copyToLocalFile(Path src, Path dst) throws IOException {
        copyToLocalFile(false, src, dst);
    }

    /**
     * The src file is under FS, and the dst is on the local disk.
     * Copy it from FS control to the local dst name.
     * Remove the source afterwards
     */
    public void moveToLocalFile(Path src, Path dst) throws IOException {
        copyToLocalFile(true, src, dst);
    }

    /**
     * The src file is under FS, and the dst is on the local disk.
     * Copy it from FS control to the local dst name.
     * delSrc indicates if the src will be removed or not.
     */
    public void copyToLocalFile(boolean delSrc, Path src, Path dst) throws IOException {
        FileUtil.copy(this, src, getLocal(getConf()), dst, delSrc, getConf());
    }

    /**
     * Returns a local File that the user can write output to.  The caller
     * provides both the eventual FS target name and the local working
     * file.  If the FS is local, we write directly into the target.  If
     * the FS is remote, we write into the tmp local area.
     */
    public Path startLocalOutput(Path fsOutputFile, Path tmpLocalFile) throws IOException {
        return tmpLocalFile;
    }

    /**
     * Called when we're all done writing to the target.  A local FS will
     * do nothing, because we've written to exactly the right place.  A remote
     * FS will copy the contents of tmpLocalFile to the correct target at
     * fsOutputFile.
     */
    public void completeLocalOutput(Path fsOutputFile, Path tmpLocalFile) throws IOException {
        moveFromLocalFile(tmpLocalFile, fsOutputFile);
    }

    /**
     * No more filesystem operations are needed.  Will
     * release any held locks.
     */
    public void close() throws IOException {
        // delete all files that were marked as delete-on-exit.
        processDeleteOnExit();
        CACHE.remove(this.key, this);
    }

    /** Return the total size of all files in the filesystem.*/
    public long getUsed() throws IOException {
        long used = 0;
        FileStatus[] files = listStatus(new Path("/"));
        for (FileStatus file : files) {
            used += file.getLen();
        }
        return used;
    }

    /**
     * Get the block size for a particular file.
     * @param f the filename
     * @return the number of bytes in a block
     */
    /** @deprecated Use getFileStatus() instead */
    @Deprecated
    public long getBlockSize(Path f) throws IOException {
        return getFileStatus(f).getBlockSize();
    }

    /** Return the number of bytes that large input files should be optimally
     * be split into to minimize i/o time. */
    public long getDefaultBlockSize() {
        // default to 32MB: large enough to minimize the impact of seeks
        return getConf().getLong("fs.local.block.size", P2PConstants.DEFAULT_LOCAL_BLOCK_SIZE);
    }

    /**
     * Get the default replication.
     */
    public short getDefaultReplication() {
        return 1;
    }

    /**
     * Return a file status object that represents the path.
     * @param f The path we want information from
     * @return a FileStatus object
     * @throws FileNotFoundException when the path does not exist;
     *         IOException see specific implementation
     */
    public abstract FileStatus getFileStatus(Path f) throws IOException;

    /**
     * Get the checksum of a file.
     *
     * @param f The file path
     * @return The file checksum.  The default return value is null,
     *  which indicates that no checksum algorithm is implemented
     *  in the corresponding FileSystem.
     */
    public FileChecksum getFileChecksum(Path f) throws IOException {
        return null;
    }

    /**
     * Set the verify checksum flag. This is only applicable if the 
     * corresponding FileSystem supports checksum. By default doesn't do anything.
     * @param verifyChecksum
     */
    public void setVerifyChecksum(boolean verifyChecksum) {
        //doesn't do anything
    }

    /**
     * Return a list of file status objects that corresponds to the list of paths
     * excluding those non-existent paths.
     * 
     * @param paths
     *          the list of paths we want information from
     * @return a list of FileStatus objects
     * @throws IOException
     *           see specific implementation
     */
    private FileStatus[] getFileStatus(Path[] paths) throws IOException {
        if (paths == null) {
            return null;
        }
        ArrayList<FileStatus> results = new ArrayList<FileStatus>(paths.length);
        for (int i = 0; i < paths.length; i++) {
            try {
                results.add(getFileStatus(paths[i]));
            } catch (FileNotFoundException e) { // do nothing
            }
        }
        return results.toArray(new FileStatus[results.size()]);
    }

    /**
     * Set permission of a path.
     * @param p
     * @param permission
     */
    public void setPermission(Path p, FsPermission permission) throws IOException {
    }

    /**
     * Set owner of a path (i.e. a file or a directory).
     * The parameters username and groupname cannot both be null.
     * @param p The path
     * @param username If it is null, the original username remains unchanged.
     * @param groupname If it is null, the original groupname remains unchanged.
     */
    public void setOwner(Path p, String username, String groupname) throws IOException {
    }

    /**
     * Set access time of a file
     * @param p The path
     * @param mtime Set the modification time of this file.
     *              The number of milliseconds since Jan 1, 1970. 
     *              A value of -1 means that this call should not set modification time.
     * @param atime Set the access time of this file.
     *              The number of milliseconds since Jan 1, 1970. 
     *              A value of -1 means that this call should not set access time.
     */
    public void setTimes(Path p, long mtime, long atime) throws IOException {
    }

    private static FileSystem createFileSystem(URI uri, Configuration conf) throws IOException {
        Class<?> clazz = conf.getClass("fs." + uri.getScheme() + ".impl", null);
        if (clazz == null) {
            throw new IOException("No FileSystem for scheme: " + uri.getScheme());
        }
        FileSystem fs = (FileSystem) ReflectionUtils.newInstance(clazz, conf);
        fs.initialize(uri, conf);
        return fs;
    }

    /** Caching FileSystem objects */
    static class Cache {
        private final Map<Key, FileSystem> map = new HashMap<Key, FileSystem>();

        synchronized FileSystem get(URI uri, Configuration conf) throws IOException {
            Key key = new Key(uri, conf);
            FileSystem fs = map.get(key);
            if (fs == null) {
                fs = createFileSystem(uri, conf);
                if (map.isEmpty() && !clientFinalizer.isAlive()) {
                    Runtime.getRuntime().addShutdownHook(clientFinalizer);
                }
                fs.key = key;
                map.put(key, fs);
            }

            return fs;
        }

        synchronized void remove(Key key, FileSystem fs) {
            if (map.containsKey(key) && fs == map.get(key)) {
                map.remove(key);
                if (map.isEmpty() && !clientFinalizer.isAlive()) {
                    if (!Runtime.getRuntime().removeShutdownHook(clientFinalizer)) {
                        LOG.info("Could not cancel cleanup thread, though no " + "FileSystems are open");
                    }
                }
            }
        }

        synchronized void closeAll() throws IOException {
            List<IOException> exceptions = new ArrayList<IOException>();
            for (; !map.isEmpty();) {
                Map.Entry<Key, FileSystem> e = map.entrySet().iterator().next();
                final Key key = e.getKey();
                final FileSystem fs = e.getValue();

                //remove from cache
                remove(key, fs);

                if (fs != null) {
                    try {
                        fs.close();
                    } catch (IOException ioe) {
                        exceptions.add(ioe);
                    }
                }
            }

            if (!exceptions.isEmpty()) {
                throw MultipleIOException.createIOException(exceptions);
            }
        }

        /** FileSystem.Cache.Key */
        static class Key {
            final String scheme;
            final String authority;
            final String username;

            Key(URI uri, Configuration conf) throws IOException {
                scheme = uri.getScheme() == null ? "" : uri.getScheme().toLowerCase();
                authority = uri.getAuthority() == null ? "" : uri.getAuthority().toLowerCase();
                UserGroupInformation ugi = UserGroupInformation.readFrom(conf);
                if (ugi == null) {
                    try {
                        ugi = UserGroupInformation.login(conf);
                    } catch (LoginException e) {
                        LOG.warn("uri=" + uri, e);
                    }
                }
                username = ugi == null ? null : ugi.getUserName();
            }

            /** {@inheritDoc} */
            public int hashCode() {
                return (scheme + authority + username).hashCode();
            }

            static boolean isEqual(Object a, Object b) {
                return a == b || (a != null && a.equals(b));
            }

            /** {@inheritDoc} */
            public boolean equals(Object obj) {
                if (obj == this) {
                    return true;
                }
                if (obj != null && obj instanceof Key) {
                    Key that = (Key) obj;
                    return isEqual(this.scheme, that.scheme) && isEqual(this.authority, that.authority)
                            && isEqual(this.username, that.username);
                }
                return false;
            }

            /** {@inheritDoc} */
            public String toString() {
                return username + "@" + scheme + "://" + authority;
            }
        }
    }

    public static final class Statistics {
        private final String scheme;
        private AtomicLong bytesRead = new AtomicLong();
        private AtomicLong bytesWritten = new AtomicLong();

        public Statistics(String scheme) {
            this.scheme = scheme;
        }

        /**
         * Increment the bytes read in the statistics
         * @param newBytes the additional bytes read
         */
        public void incrementBytesRead(long newBytes) {
            bytesRead.getAndAdd(newBytes);
        }

        /**
         * Increment the bytes written in the statistics
         * @param newBytes the additional bytes written
         */
        public void incrementBytesWritten(long newBytes) {
            bytesWritten.getAndAdd(newBytes);
        }

        /**
         * Get the total number of bytes read
         * @return the number of bytes
         */
        public long getBytesRead() {
            return bytesRead.get();
        }

        /**
         * Get the total number of bytes written
         * @return the number of bytes
         */
        public long getBytesWritten() {
            return bytesWritten.get();
        }

        public String toString() {
            return bytesRead + " bytes read and " + bytesWritten + " bytes written";
        }

        /**
         * Reset the counts of bytes to 0.
         */
        public void reset() {
            bytesWritten.set(0);
            bytesRead.set(0);
        }

        /**
         * Get the uri scheme associated with this statistics object.
         * @return the schema associated with this set of statistics
         */
        public String getScheme() {
            return scheme;
        }
    }

    /**
     * Get the Map of Statistics object indexed by URI Scheme.
     * @return a Map having a key as URI scheme and value as Statistics object
     * @deprecated use {@link #getAllStatistics} instead
     */
    public static synchronized Map<String, Statistics> getStatistics() {
        Map<String, Statistics> result = new HashMap<String, Statistics>();
        for (Statistics stat : statisticsTable.values()) {
            result.put(stat.getScheme(), stat);
        }
        return result;
    }

    /**
     * Return the FileSystem classes that have Statistics
     */
    public static synchronized List<Statistics> getAllStatistics() {
        return new ArrayList<Statistics>(statisticsTable.values());
    }

    /**
     * Get the statistics for a particular file system
     * @param cls the class to lookup
     * @return a statistics object
     */
    public static synchronized Statistics getStatistics(String scheme, Class<? extends FileSystem> cls) {
        Statistics result = statisticsTable.get(cls);
        if (result == null) {
            result = new Statistics(scheme);
            statisticsTable.put(cls, result);
        }
        return result;
    }

    public static synchronized void clearStatistics() {
        for (Statistics stat : statisticsTable.values()) {
            stat.reset();
        }
    }

    public static synchronized void printStatistics() throws IOException {
        for (Map.Entry<Class<? extends FileSystem>, Statistics> pair : statisticsTable.entrySet()) {
            System.out.println("  FileSystem " + pair.getKey().getName() + ": " + pair.getValue());
        }
    }
}