FilePath.java

/*
 * The MIT License
 * 
 * Copyright (c) 2004-2009, Sun Microsystems, Inc., Kohsuke Kawaguchi, Eric Lefevre-Ardant, Erik Ramfelt, Michael B. Donohue
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
package hudson;

import hudson.Launcher.LocalLauncher;
import hudson.Launcher.RemoteLauncher;
import hudson.model.Hudson;
import hudson.model.TaskListener;
import hudson.model.AbstractProject;
import hudson.model.Item;
import hudson.remoting.Callable;
import hudson.remoting.Channel;
import hudson.remoting.DelegatingCallable;
import hudson.remoting.Future;
import hudson.remoting.Pipe;
import hudson.remoting.RemoteOutputStream;
import hudson.remoting.VirtualChannel;
import hudson.remoting.RemoteInputStream;
import hudson.util.IOException2;
import hudson.util.HeadBufferingStream;
import hudson.util.FormValidation;
import static hudson.util.jna.GNUCLibrary.LIBC;
import static hudson.Util.fixEmpty;
import static hudson.FilePath.TarCompression.GZIP;
import hudson.os.PosixAPI;
import hudson.org.apache.tools.tar.TarOutputStream;
import hudson.org.apache.tools.tar.TarInputStream;
import org.apache.tools.ant.BuildException;
import org.apache.tools.ant.DirectoryScanner;
import org.apache.tools.ant.Project;
import org.apache.tools.ant.taskdefs.Copy;
import org.apache.tools.ant.types.FileSet;
import org.apache.tools.tar.TarEntry;
import org.apache.tools.zip.ZipOutputStream;
import org.apache.tools.zip.ZipEntry;
import org.apache.commons.io.IOUtils;
import org.apache.commons.fileupload.FileItem;
import org.kohsuke.stapler.Stapler;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileFilter;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.OutputStream;
import java.io.Serializable;
import java.io.Writer;
import java.io.OutputStreamWriter;
import java.net.URI;
import java.net.URL;
import java.net.URLConnection;
import java.util.ArrayList;
import java.util.List;
import java.util.StringTokenizer;
import java.util.Arrays;
import java.util.Comparator;
import java.util.regex.Pattern;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import java.util.zip.GZIPOutputStream;
import java.util.zip.GZIPInputStream;
import java.util.zip.ZipInputStream;

import com.sun.jna.Native;

/**
 * {@link File} like object with remoting support.
 *
 * <p>
 * Unlike {@link File}, which always implies a file path on the current computer,
 * {@link FilePath} represents a file path on a specific slave or the master.
 *
 * Despite that, {@link FilePath} can be used much like {@link File}. It exposes
 * a bunch of operations (and we should add more operations as long as they are
 * generally useful), and when invoked against a file on a remote node, {@link FilePath}
 * executes the necessary code remotely, thereby providing semi-transparent file
 * operations.
 *
 * <h2>Using {@link FilePath} smartly</h2>
 * <p>
 * The transparency makes it easy to write plugins without worrying too much about
 * remoting, by making it works like NFS, where remoting happens at the file-system
 * later.
 *
 * <p>
 * But one should note that such use of remoting may not be optional. Sometimes,
 * it makes more sense to move some computation closer to the data, as opposed to
 * move the data to the computation. For example, if you are just computing a MD5
 * digest of a file, then it would make sense to do the digest on the host where
 * the file is located, as opposed to send the whole data to the master and do MD5
 * digesting there.
 *
 * <p>
 * {@link FilePath} supports this "code migration" by in the
 * {@link #act(FileCallable)} method. One can pass in a custom implementation
 * of {@link FileCallable}, to be executed on the node where the data is located.
 * The following code shows the example:
 *
 * <pre>
 * FilePath file = ...;
 *
 * // make 'file' a fresh empty directory.
 * file.act(new FileCallable&lt;Void>() {
 *   // if 'file' is on a different node, this FileCallable will
 *   // be transfered to that node and executed there.
 *   public Void invoke(File f,VirtualChannel channel) {
 *     // f and file represents the same thing
 *     f.deleteContents();
 *     f.mkdirs();
 *   }
 * });
 * </pre>
 *
 * <p>
 * When {@link FileCallable} is transfered to a remote node, it will be done so
 * by using the same Java serialization scheme that the remoting module uses.
 * See {@link Channel} for more about this. 
 *
 * <p>
 * {@link FilePath} itself can be sent over to a remote node as a part of {@link Callable}
 * serialization. For example, sending a {@link FilePath} of a remote node to that
 * node causes {@link FilePath} to become "local". Similarly, sending a
 * {@link FilePath} that represents the local computer causes it to become "remote."
 *
 * @author Kohsuke Kawaguchi
 */
public final class FilePath implements Serializable {
    /**
     * When this {@link FilePath} represents the remote path,
     * this field is always non-null on master (the field represents
     * the channel to the remote slave.) When transferred to a slave via remoting,
     * this field reverts back to null, since it's transient.
     *
     * When this {@link FilePath} represents a path on the master,
     * this field is null on master. When transferred to a slave via remoting,
     * this field becomes non-null, representing the {@link Channel}
     * back to the master.
     *
     * This is used to determine whether we are running on the master or the slave.
     */
    private transient VirtualChannel channel;

    // since the platform of the slave might be different, can't use java.io.File
    private final String remote;

    /**
     * Creates a {@link FilePath} that represents a path on the given node.
     *
     * @param channel
     *      To create a path that represents a remote path, pass in a {@link Channel}
     *      that's connected to that machine. If null, that means the local file path.
     */
    public FilePath(VirtualChannel channel, String remote) {
        this.channel = channel;
        this.remote = remote;
    }

    /**
     * To create {@link FilePath} that represents a "local" path.
     *
     * <p>
     * A "local" path means a file path on the computer where the
     * constructor invocation happened.
     */
    public FilePath(File localPath) {
        this.channel = null;
        this.remote = localPath.getPath();
    }

    /**
     * Construct a path starting with a base location.
     * @param base starting point for resolution, and defines channel
     * @param rel a path which if relative will be resolved against base
     */
    public FilePath(FilePath base, String rel) {
        this.channel = base.channel;
        if(isAbsolute(rel)) {
            // absolute
            this.remote = rel;
        } else 
        if(base.isUnix()) {
            this.remote = base.remote+'/'+rel;
        } else {
            this.remote = base.remote+'\\'+rel;
        }
    }

    private static boolean isAbsolute(String rel) {
        return rel.startsWith("/") || DRIVE_PATTERN.matcher(rel).matches();
    }

    private static final Pattern DRIVE_PATTERN = Pattern.compile("[A-Za-z]:\\\\.+");

    /**
     * Checks if the remote path is Unix.
     */
    private boolean isUnix() {
        // if the path represents a local path, there' no need to guess.
        if(!isRemote())
            return File.pathSeparatorChar!=';';
            
        // note that we can't use the usual File.pathSeparator and etc., as the OS of
        // the machine where this code runs and the OS that this FilePath refers to may be different.

        // Windows absolute path is 'X:\...', so this is usually a good indication of Windows path
        if(remote.length()>3 && remote.charAt(1)==':' && remote.charAt(2)=='\\')
            return false;
        // Windows can handle '/' as a path separator but Unix can't,
        // so err on Unix side
        return remote.indexOf("\\")==-1;
    }

    public String getRemote() {
        return remote;
    }

    /**
     * Creates a zip file from this directory or a file and sends that to the given output stream.
     */
    public void createZipArchive(OutputStream os) throws IOException, InterruptedException {
        final OutputStream out = (channel!=null)?new RemoteOutputStream(os):os;
        act(new FileCallable<Void>() {
            private transient byte[] buf;
            public Void invoke(File f, VirtualChannel channel) throws IOException {
                buf = new byte[8192];

                ZipOutputStream zip = new ZipOutputStream(out);
                zip.setEncoding(System.getProperty("file.encoding"));
                scan(f,zip,"");
                zip.close();
                return null;
            }

            private void scan(File f, ZipOutputStream zip, String path) throws IOException {
                // Bitmask indicating directories in 'external attributes' of a ZIP archive entry.
                final long BITMASK_IS_DIRECTORY = 1<<4;
              
                if (f.canRead()) {
                    if(f.isDirectory()) {
                        ZipEntry dirZipEntry = new ZipEntry(path+f.getName()+'/');
                        // Setting this bit explicitly is needed by some unzipping applications (see HUDSON-3294).
                        dirZipEntry.setExternalAttributes(BITMASK_IS_DIRECTORY);
                        zip.putNextEntry(dirZipEntry);
                        zip.closeEntry();
                        for( File child : f.listFiles() )
                            scan(child,zip,path+f.getName()+'/');
                    } else {
                        zip.putNextEntry(new ZipEntry(path+f.getName()));
                        FileInputStream in = new FileInputStream(f);
                        int len;
                        while((len=in.read(buf))>0)
                            zip.write(buf,0,len);
                        in.close();
                        zip.closeEntry();
                    }
                }
            }
            
            private static final long serialVersionUID = 1L;
        });
    }

    /**
     * Creates a zip file from this directory by only including the files that match the given glob.
     *
     * @param glob
     *      Ant style glob, like "**&#x2F;*.xml". If empty or null, this method
     *      works like {@link #createZipArchive(OutputStream)}
     *
     * @since 1.129
     */
    public void createZipArchive(OutputStream os, final String glob) throws IOException, InterruptedException {
        if(glob==null || glob.length()==0) {
            createZipArchive(os);
            return;
        }
        
        final OutputStream out = (channel!=null)?new RemoteOutputStream(os):os;
        act(new FileCallable<Void>() {
            public Void invoke(File dir, VirtualChannel channel) throws IOException {
                byte[] buf = new byte[8192];

                ZipOutputStream zip = new ZipOutputStream(out);
                zip.setEncoding(System.getProperty("file.encoding"));
                for( String entry : glob(dir,glob) ) {
                    File file = new File(dir,entry);
                    if (file.canRead()) {
                        zip.putNextEntry(new ZipEntry(dir.getName()+'/'+entry));
                        FileInputStream in = new FileInputStream(file);
                        int len;
                        while((len=in.read(buf))>0)
                            zip.write(buf,0,len);
                        in.close();
                        zip.closeEntry();
                    }
                }

                zip.close();
                return null;
            }

            private static final long serialVersionUID = 1L;
        });
    }

    /**
     * When this {@link FilePath} represents a zip file, extracts that zip file.
     *
     * @param target
     *      Target directory to expand files to. All the necessary directories will be created.
     * @since 1.248
     * @see #unzipFrom(InputStream)
     */
    public void unzip(final FilePath target) throws IOException, InterruptedException {
        target.act(new FileCallable<Void>() {
            public Void invoke(File dir, VirtualChannel channel) throws IOException {
                unzip(dir,FilePath.this.read());
                return null;
            }
            private static final long serialVersionUID = 1L;
        });
    }

    /**
     * When this {@link FilePath} represents a tar file, extracts that tar file.
     *
     * @param target
     *      Target directory to expand files to. All the necessary directories will be created.
     * @param compression
     *      Compression mode of this tar file.
     * @since 1.292
     * @see #untarFrom(InputStream, TarCompression)
     */
    public void untar(final FilePath target, final TarCompression compression) throws IOException, InterruptedException {
        target.act(new FileCallable<Void>() {
            public Void invoke(File dir, VirtualChannel channel) throws IOException {
                readFromTar(FilePath.this.getName(),dir,compression.extract(FilePath.this.read()));
                return null;
            }
            private static final long serialVersionUID = 1L;
        });
    }

    /**
     * Reads the given InputStream as a zip file and extracts it into this directory.
     *
     * @param _in
     *      The stream will be closed by this method after it's fully read.
     * @since 1.283
     * @see #unzip(FilePath)
     */
    public void unzipFrom(InputStream _in) throws IOException, InterruptedException {
        final InputStream in = new RemoteInputStream(_in);
        act(new FileCallable<Void>() {
            public Void invoke(File dir, VirtualChannel channel) throws IOException {
                unzip(dir, in);
                return null;
            }
            private static final long serialVersionUID = 1L;
        });
    }

    private void unzip(File dir, InputStream in) throws IOException {
        dir = dir.getAbsoluteFile();    // without absolutization, getParentFile below seems to fail
        ZipInputStream zip = new ZipInputStream(new BufferedInputStream(in));
        java.util.zip.ZipEntry e;

        try {
            while((e=zip.getNextEntry())!=null) {
                File f = new File(dir,e.getName());
                if(e.isDirectory()) {
                    f.mkdirs();
                } else {
                    File p = f.getParentFile();
                    if(p!=null) p.mkdirs();
                    FileOutputStream out = new FileOutputStream(f);
                    try {
                        IOUtils.copy(zip, out);
                    } finally {
                        out.close();
                    }
                    f.setLastModified(e.getTime());
                    zip.closeEntry();
                }
            }
        } finally {
            zip.close();
        }
    }

    /**
     * Absolutizes this {@link FilePath} and returns the new one.
     */
    public FilePath absolutize() throws IOException, InterruptedException {
        return new FilePath(channel,act(new FileCallable<String>() {
            public String invoke(File f, VirtualChannel channel) throws IOException {
                return f.getAbsolutePath();
            }
        }));
    }

    /**
     * Supported tar file compression methods.
     */
    public enum TarCompression {
        NONE {
            public InputStream extract(InputStream in) {
                return in;
            }
            public OutputStream compress(OutputStream out) {
                return out;
            }
        },
        GZIP {
            public InputStream extract(InputStream _in) throws IOException {
                HeadBufferingStream in = new HeadBufferingStream(_in,SIDE_BUFFER_SIZE);
                try {
                    return new GZIPInputStream(in,8192);
                } catch (IOException e) {
                    // various people reported "java.io.IOException: Not in GZIP format" here, so diagnose this problem better
                    in.fillSide();
                    throw new IOException2(e.getMessage()+"\nstream="+Util.toHexString(in.getSideBuffer()),e);
                }
            }
            public OutputStream compress(OutputStream out) throws IOException {
                return new GZIPOutputStream(new BufferedOutputStream(out));
            }
        };

        public abstract InputStream extract(InputStream in) throws IOException;
        public abstract OutputStream compress(OutputStream in) throws IOException;
    }

    /**
     * Reads the given InputStream as a tar file and extracts it into this directory.
     *
     * @param _in
     *      The stream will be closed by this method after it's fully read.
     * @param compression
     *      The compression method in use.
     * @since 1.292
     */
    public void untarFrom(InputStream _in, final TarCompression compression) throws IOException, InterruptedException {
        try {
            final InputStream in = new RemoteInputStream(_in);
            act(new FileCallable<Void>() {
                public Void invoke(File dir, VirtualChannel channel) throws IOException {
                    readFromTar("input stream",dir, compression.extract(in));
                    return null;
                }
                private static final long serialVersionUID = 1L;
            });
        } finally {
            IOUtils.closeQuietly(_in);
        }
    }

    /**
     * Given a tgz/zip file, extracts it to the given target directory, if necessary.
     *
     * <p>
     * This method is a convenience method designed for installing a binary package to a location
     * that supports upgrade and downgrade. Specifically,
     *
     * <ul>
     * <li>If the target directory doesn't exist {@linkplain #mkdirs() it'll be created}.
     * <li>The timestamp of the .tgz file is left in the installation directory upon extraction.
     * <li>If the timestamp left in the directory doesn't match with the timestamp of the current archive file,
     *     the directory contents will be discarded and the archive file will be re-extracted.
     * <li>If the connection is refused but the target directory already exists, it is left alone.
     * </ul>
     *
     * @param archive
     *      The resource that represents the tgz/zip file. This URL must support the "Last-Modified" header.
     *      (Most common usage is to get this from {@link ClassLoader#getResource(String)})
     * @param listener
     *      If non-null, a message will be printed to this listener once this method decides to
     *      extract an archive.
     * @return
     *      true if the archive was extracted. false if the extraction was skipped because the target directory
     *      was considered up to date.
     * @since 1.299
     */
    public boolean installIfNecessaryFrom(URL archive, TaskListener listener, String message) throws IOException, InterruptedException {
        URLConnection con;
        try {
            con = archive.openConnection();
            con.connect();
        } catch (IOException x) {
            if (this.exists()) {
                // Cannot connect now, so assume whatever was last unpacked is still OK.
                if (listener != null) {
                    listener.getLogger().println("Skipping installation of " + archive + " to " + remote + ": " + x);
                }
                return false;
            } else {
                throw x;
            }
        }
        long sourceTimestamp = con.getLastModified();
        FilePath timestamp = this.child(".timestamp");

        if(this.exists()) {
            if(timestamp.exists() && sourceTimestamp ==timestamp.lastModified())
                return false;   // already up to date
            this.deleteContents();
        }

        if(listener!=null)
            listener.getLogger().println(message);
        if(archive.toExternalForm().endsWith(".zip"))
            unzipFrom(con.getInputStream());
        else
            untarFrom(con.getInputStream(),GZIP);
        timestamp.touch(sourceTimestamp);
        return true;
    }

    /**
     * Reads the URL on the current VM, and writes all the data to this {@link FilePath}
     * (this is different from resolving URL remotely.)
     *
     * @since 1.293
     */
    public void copyFrom(URL url) throws IOException, InterruptedException {
        InputStream in = url.openStream();
        try {
            copyFrom(in);
        } finally {
            in.close();
        }
    }

    /**
     * Replaces the content of this file by the data from the given {@link InputStream}.
     *
     * @since 1.293
     */
    public void copyFrom(InputStream in) throws IOException, InterruptedException {
        OutputStream os = write();
        try {
            IOUtils.copy(in, os);
        } finally {
            os.close();
        }
    }

    /**
     * Conveniene method to call {@link FilePath#copyTo(FilePath)}.
     * 
     * @since 1.311
     */
    public void copyFrom(FilePath src) throws IOException, InterruptedException {
        src.copyTo(this);
    }

    /**
     * Place the data from {@link FileItem} into the file location specified by this {@link FilePath} object.
     */
    public void copyFrom(FileItem file) throws IOException, InterruptedException {
        if(channel==null) {
            try {
                file.write(new File(remote));
            } catch (IOException e) {
                throw e;
            } catch (Exception e) {
                throw new IOException2(e);
            }
        } else {
            InputStream i = file.getInputStream();
            OutputStream o = write();
            try {
                IOUtils.copy(i,o);
            } finally {
                o.close();
                i.close();
            }
        }
    }

    /**
     * Code that gets executed on the machine where the {@link FilePath} is local.
     * Used to act on {@link FilePath}.
     *
     * @see FilePath#act(FileCallable)
     */
    public static interface FileCallable<T> extends Serializable {
        /**
         * Performs the computational task on the node where the data is located.
         *
         * @param f
         *      {@link File} that represents the local file that {@link FilePath} has represented.
         * @param channel
         *      The "back pointer" of the {@link Channel} that represents the communication
         *      with the node from where the code was sent.
         */
        T invoke(File f, VirtualChannel channel) throws IOException;
    }

    /**
     * Executes some program on the machine that this {@link FilePath} exists,
     * so that one can perform local file operations.
     */
    public <T> T act(final FileCallable<T> callable) throws IOException, InterruptedException {
        return act(callable,callable.getClass().getClassLoader());
    }

    private <T> T act(final FileCallable<T> callable, ClassLoader cl) throws IOException, InterruptedException {
        if(channel!=null) {
            // run this on a remote system
            try {
                return channel.call(new FileCallableWrapper<T>(callable,cl));
            } catch (AbortException e) {
                throw e;    // pass through so that the caller can catch it as AbortException
            } catch (IOException e) {
                // wrap it into a new IOException so that we get the caller's stack trace as well.
                throw new IOException2("remote file operation failed",e);
            }
        } else {
            // the file is on the local machine.
            return callable.invoke(new File(remote), Hudson.MasterComputer.localChannel);
        }
    }

    /**
     * Executes some program on the machine that this {@link FilePath} exists,
     * so that one can perform local file operations.
     */
    public <T> Future<T> actAsync(final FileCallable<T> callable) throws IOException, InterruptedException {
        try {
            return (channel!=null ? channel : Hudson.MasterComputer.localChannel)
                .callAsync(new FileCallableWrapper<T>(callable));
        } catch (IOException e) {
            // wrap it into a new IOException so that we get the caller's stack trace as well.
            throw new IOException2("remote file operation failed",e);
        }
    }

    /**
     * Executes some program on the machine that this {@link FilePath} exists,
     * so that one can perform local file operations.
     */
    public <V,E extends Throwable> V act(Callable<V,E> callable) throws IOException, InterruptedException, E {
        if(channel!=null) {
            // run this on a remote system
            return channel.call(callable);
        } else {
            // the file is on the local machine
            return callable.call();
        }
    }

    /**
     * Converts this file to the URI, relative to the machine
     * on which this file is available.
     */
    public URI toURI() throws IOException, InterruptedException {
        return act(new FileCallable<URI>() {
            public URI invoke(File f, VirtualChannel channel) {
                return f.toURI();
            }
        });
    }

    /**
     * Creates this directory.
     */
    public void mkdirs() throws IOException, InterruptedException {
        if(!act(new FileCallable<Boolean>() {
            public Boolean invoke(File f, VirtualChannel channel) throws IOException {
                if(f.mkdirs() || f.exists())
                    return true;    // OK

                // following Ant <mkdir> task to avoid possible race condition.
                try {
                    Thread.sleep(10);
                } catch (InterruptedException e) {
                    // ignore
                }

                return f.mkdirs() || f.exists();
            }
        }))
            throw new IOException("Failed to mkdirs: "+remote);
    }

    /**
     * Deletes this directory, including all its contents recursively.
     */
    public void deleteRecursive() throws IOException, InterruptedException {
        act(new FileCallable<Void>() {
            public Void invoke(File f, VirtualChannel channel) throws IOException {
                Util.deleteRecursive(f);
                return null;
            }
        });
    }

    /**
     * Deletes all the contents of this directory, but not the directory itself
     */
    public void deleteContents() throws IOException, InterruptedException {
        act(new FileCallable<Void>() {
            public Void invoke(File f, VirtualChannel channel) throws IOException {
                Util.deleteContentsRecursive(f);
                return null;
            }
        });
    }

    /**
     * Gets just the file name portion.
     *
     * This method assumes that the file name is the same between local and remote.
     */
    public String getName() {
        String r = remote;
        if(r.endsWith("\\") || r.endsWith("/"))
            r = r.substring(0,r.length()-1);

        int len = r.length()-1;
        while(len>=0) {
            char ch = r.charAt(len);
            if(ch=='\\' || ch=='/')
                break;
            len--;
        }

        return r.substring(len+1);
    }

    /**
     * The same as {@link FilePath#FilePath(FilePath,String)} but more OO.
     * @param rel a relative or absolute path
     * @return a file on the same channel
     */
    public FilePath child(String rel) {
        return new FilePath(this,rel);
    }

    /**
     * Gets the parent file.
     */
    public FilePath getParent() {
        int len = remote.length()-1;
        while(len>=0) {
            char ch = remote.charAt(len);
            if(ch=='\\' || ch=='/')
                break;
            len--;
        }

        return new FilePath( channel, remote.substring(0,len) );
    }

    /**
     * Creates a temporary file in the directory that this {@link FilePath} object designates.
     */
    public FilePath createTempFile(final String prefix, final String suffix) throws IOException, InterruptedException {
        try {
            return new FilePath(this,act(new FileCallable<String>() {
                public String invoke(File dir, VirtualChannel channel) throws IOException {
                    File f = File.createTempFile(prefix, suffix, dir);
                    return f.getName();
                }
            }));
        } catch (IOException e) {
            throw new IOException2("Failed to create a temp file on "+remote,e);
        }
    }

    /**
     * Creates a temporary file in this directory and set the contents by the
     * given text (encoded in the platform default encoding)
     */
    public FilePath createTextTempFile(final String prefix, final String suffix, final String contents) throws IOException, InterruptedException {
        return createTextTempFile(prefix,suffix,contents,true);
    }

    /**
     * Creates a temporary file in this directory and set the contents by the
     * given text (encoded in the platform default encoding)
     */
    public FilePath createTextTempFile(final String prefix, final String suffix, final String contents, final boolean inThisDirectory) throws IOException, InterruptedException {
        try {
            return new FilePath(channel,act(new FileCallable<String>() {
                public String invoke(File dir, VirtualChannel channel) throws IOException {
                    if(!inThisDirectory)
                        dir = new File(System.getProperty("java.io.tmpdir"));
                    else
                        dir.mkdirs();

                    File f;
                    try {
                        f = File.createTempFile(prefix, suffix, dir);
                    } catch (IOException e) {
                        throw new IOException2("Failed to create a temporary directory in "+dir,e);
                    }

                    Writer w = new FileWriter(f);
                    w.write(contents);
                    w.close();

                    return f.getAbsolutePath();
                }
            }));
        } catch (IOException e) {
            throw new IOException2("Failed to create a temp file on "+remote,e);
        }
    }

    /**
     * Creates a temporary directory inside the directory represented by 'this'
     * @since 1.311
     */
    public FilePath createTempDir(final String prefix, final String suffix) throws IOException, InterruptedException {
        try {
            return new FilePath(this,act(new FileCallable<String>() {
                public String invoke(File dir, VirtualChannel channel) throws IOException {
                    File f = File.createTempFile(prefix, suffix, dir);
                    f.delete();
                    f.mkdir();
                    return f.getName();
                }
            }));
        } catch (IOException e) {
            throw new IOException2("Failed to create a temp directory on "+remote,e);
        }
    }

    /**
     * Deletes this file.
     */
    public boolean delete() throws IOException, InterruptedException {
        return act(new FileCallable<Boolean>() {
            public Boolean invoke(File f, VirtualChannel channel) throws IOException {
                return f.delete();
            }
        });
    }

    /**
     * Checks if the file exists.
     */
    public boolean exists() throws IOException, InterruptedException {
        return act(new FileCallable<Boolean>() {
            public Boolean invoke(File f, VirtualChannel channel) throws IOException {
                return f.exists();
            }
        });
    }

    /**
     * Gets the last modified time stamp of this file, by using the clock
     * of the machine where this file actually resides.
     *
     * @see File#lastModified()
     * @see #touch(long)
     */
    public long lastModified() throws IOException, InterruptedException {
        return act(new FileCallable<Long>() {
            public Long invoke(File f, VirtualChannel channel) throws IOException {
                return f.lastModified();
            }
        });
    }

    /**
     * Creates a file (if not already exist) and sets the timestamp.
     *
     * @since 1.299
     */
    public void touch(final long timestamp) throws IOException, InterruptedException {
        act(new FileCallable<Void>() {
            public Void invoke(File f, VirtualChannel channel) throws IOException {
                if(!f.exists())
                    new FileOutputStream(f).close();
                if(!f.setLastModified(timestamp))
                    throw new IOException("Failed to set the timestamp of "+f+" to "+timestamp);
                return null;
            }
        });
    }

    /**
     * Checks if the file is a directory.
     */
    public boolean isDirectory() throws IOException, InterruptedException {
        return act(new FileCallable<Boolean>() {
            public Boolean invoke(File f, VirtualChannel channel) throws IOException {
                return f.isDirectory();
            }
        });
    }
    
    /**
     * Returns the file size in bytes.
     *
     * @since 1.129
     */
    public long length() throws IOException, InterruptedException {
        return act(new FileCallable<Long>() {
            public Long invoke(File f, VirtualChannel channel) throws IOException {
                return f.length();
            }
        });
    }

    /**
     * Sets the file permission.
     *
     * On Windows, no-op.
     *
     * @param mask
     *      File permission mask. To simplify the permission copying,
     *      if the parameter is -1, this method becomes no-op.
     * @since 1.303
     * @see #mode()
     */
    public void chmod(final int mask) throws IOException, InterruptedException {
        if(!isUnix() || mask==-1)   return;
        act(new FileCallable<Void>() {
            public Void invoke(File f, VirtualChannel channel) throws IOException {
                if(LIBC.chmod(f.getAbsolutePath(),mask)!=0)
                    throw new IOException("Failed to chmod "+f+" : "+LIBC.strerror(Native.getLastError()));
                return null;
            }
        });
    }

    /**
     * Gets the file permission bit mask.
     *
     * @return
     *      -1 on Windows, since such a concept doesn't make sense.
     * @since 1.311
     * @see #chmod(int)
     */
    public int mode() throws IOException, InterruptedException {
        if(!isUnix())   return -1;
        return act(new FileCallable<Integer>() {
            public Integer invoke(File f, VirtualChannel channel) throws IOException {
                return PosixAPI.get().stat(f.getPath()).mode();
            }
        });
    }

    /**
     * List up files and directories in this directory.
     *
     * <p>
     * This method returns direct children of the directory denoted by the 'this' object.
     */
    public List<FilePath> list() throws IOException, InterruptedException {
        return list((FileFilter)null);
    }

    /**
     * List up subdirectories.
     *
     * @return can be empty but never null. Doesn't contain "." and ".."
     */
    public List<FilePath> listDirectories() throws IOException, InterruptedException {
        return list(new DirectoryFilter());
    }

    private static final class DirectoryFilter implements FileFilter, Serializable {
        public boolean accept(File f) {
            return f.isDirectory();
        }
        private static final long serialVersionUID = 1L;
    }

    /**
     * List up files in this directory, just like {@link File#listFiles(FileFilter)}.
     *
     * @param filter
     *      The optional filter used to narrow down the result.
     *      If non-null, must be {@link Serializable}.
     *      If this {@link FilePath} represents a remote path,
     *      the filter object will be executed on the remote machine.
     */
    public List<FilePath> list(final FileFilter filter) throws IOException, InterruptedException {
        if (filter != null && !(filter instanceof Serializable)) {
            throw new IllegalArgumentException("Non-serializable filter of " + filter.getClass());
        }
        return act(new FileCallable<List<FilePath>>() {
            public List<FilePath> invoke(File f, VirtualChannel channel) throws IOException {
                File[] children = f.listFiles(filter);
                if(children ==null)     return null;

                ArrayList<FilePath> r = new ArrayList<FilePath>(children.length);
                for (File child : children)
                    r.add(new FilePath(child));

                return r;
            }
        }, (filter!=null?filter:this).getClass().getClassLoader());
    }

    /**
     * List up files in this directory that matches the given Ant-style filter.
     *
     * @param includes
     *      See {@link FileSet} for the syntax. String like "foo/*.zip" or "foo/*&#42;/*.xml"
     * @return
     *      can be empty but always non-null.
     */
    public FilePath[] list(final String includes) throws IOException, InterruptedException {
        return act(new FileCallable<FilePath[]>() {
            public FilePath[] invoke(File f, VirtualChannel channel) throws IOException {
                String[] files = glob(f,includes);

                FilePath[] r = new FilePath[files.length];
                for( int i=0; i<r.length; i++ )
                    r[i] = new FilePath(new File(f,files[i]));

                return r;
            }
        });
    }

    /**
     * Runs Ant glob expansion.
     *
     * @return
     *      A set of relative file names from the base directory.
     */
    private static String[] glob(File dir, String includes) throws IOException {
        if(isAbsolute(includes))
            throw new IOException("Expecting Ant GLOB pattern, but saw '"+includes+"'. See http://ant.apache.org/manual/CoreTypes/fileset.html for syntax");
        FileSet fs = Util.createFileSet(dir,includes);
        DirectoryScanner ds = fs.getDirectoryScanner(new Project());
        String[] files = ds.getIncludedFiles();
        return files;
    }

    /**
     * Reads this file.
     */
    public InputStream read() throws IOException {
        if(channel==null)
            return new FileInputStream(new File(remote));

        final Pipe p = Pipe.createRemoteToLocal();
        channel.callAsync(new Callable<Void,IOException>() {
            public Void call() throws IOException {
                FileInputStream fis=null;
                try {
                    fis = new FileInputStream(new File(remote));
                    Util.copyStream(fis,p.getOut());
                    return null;
                } finally {
                    IOUtils.closeQuietly(fis);
                    IOUtils.closeQuietly(p.getOut());
                }
            }
        });

        return p.getIn();
    }

    /**
     * Reads this file into a string, by using the current system encoding.
     */
    public String readToString() throws IOException {
        InputStream in = read();
        try {
            return IOUtils.toString(in);
        } finally {
            in.close();
        }
    }

    /**
     * Writes to this file.
     * If this file already exists, it will be overwritten.
     * If the directory doesn't exist, it will be created.
     */
    public OutputStream write() throws IOException, InterruptedException {
        if(channel==null) {
            File f = new File(remote).getAbsoluteFile();
            f.getParentFile().mkdirs();
            return new FileOutputStream(f);
        }

        return channel.call(new Callable<OutputStream,IOException>() {
            public OutputStream call() throws IOException {
                File f = new File(remote).getAbsoluteFile();
                f.getParentFile().mkdirs();
                FileOutputStream fos = new FileOutputStream(f);
                return new RemoteOutputStream(fos);
            }
        });
    }

    /**
     * Overwrites this file by placing the given String as the content.
     *
     * @param encoding
     *      Null to use the platform default encoding.
     * @since 1.105
     */
    public void write(final String content, final String encoding) throws IOException, InterruptedException {
        act(new FileCallable<Void>() {
            public Void invoke(File f, VirtualChannel channel) throws IOException {
                f.getParentFile().mkdirs();
                FileOutputStream fos = new FileOutputStream(f);
                Writer w = encoding != null ? new OutputStreamWriter(fos, encoding) : new OutputStreamWriter(fos);
                try {
                    w.write(content);
                } finally {
                    w.close();
                }
                return null;
            }
        });
    }

    /**
     * Computes the MD5 digest of the file in hex string.
     */
    public String digest() throws IOException, InterruptedException {
        return act(new FileCallable<String>() {
            public String invoke(File f, VirtualChannel channel) throws IOException {
                return Util.getDigestOf(new FileInputStream(f));
            }
        });
    }

    /**
     * Rename this file/directory to the target filepath.  This FilePath and the target must
     * be on the some host
     */
    public void renameTo(final FilePath target) throws IOException, InterruptedException {
    	if(this.channel != target.channel) {
    		throw new IOException("renameTo target must be on the same host");
    	}
        act(new FileCallable<Void>() {
            public Void invoke(File f, VirtualChannel channel) throws IOException {
            	f.renameTo(new File(target.remote));
                return null;
            }
        });
    }

    /**
     * Moves all the contents of this directory into the specified directory, then delete this directory itself.
     *
     * @since 1.308.
     */
    public void moveAllChildrenTo(final FilePath target) throws IOException, InterruptedException {
        if(this.channel != target.channel) {
            throw new IOException("pullUpTo target must be on the same host");
        }
        act(new FileCallable<Void>() {
            public Void invoke(File f, VirtualChannel channel) throws IOException {
                File t = new File(target.getRemote());
                
                for(File child : f.listFiles()) {
                    File target = new File(t, child.getName());
                    if(!child.renameTo(target))
                        throw new IOException("Failed to rename "+child+" to "+target);
                }
                f.delete();
                return null;
            }
        });
    }

    /**
     * Copies this file to the specified target.
     */
    public void copyTo(FilePath target) throws IOException, InterruptedException {
        OutputStream out = target.write();
        try {
            copyTo(out);
        } finally {
            out.close();
        }
    }

    /**
     * Copies this file to the specified target, with file permissions intact.
     * @since 1.311
     */
    public void copyToWithPermission(FilePath target) throws IOException, InterruptedException {
        copyTo(target);
        // copy file permission
        target.chmod(mode());
    }

    /**
     * Sends the contents of this file into the given {@link OutputStream}.
     */
    public void copyTo(OutputStream os) throws IOException, InterruptedException {
        final OutputStream out = new RemoteOutputStream(os);

        act(new FileCallable<Void>() {
            public Void invoke(File f, VirtualChannel channel) throws IOException {
                FileInputStream fis = null;
                try {
                    fis = new FileInputStream(f);
                    Util.copyStream(fis,out);
                    return null;
                } finally {
                    IOUtils.closeQuietly(fis);
                    IOUtils.closeQuietly(out);
                }
            }
        });
    }

    /**
     * Remoting interface used for {@link FilePath#copyRecursiveTo(String, FilePath)}.
     *
     * TODO: this might not be the most efficient way to do the copy.
     */
    interface RemoteCopier {
        /**
         * @param fileName
         *      relative path name to the output file. Path separator must be '/'.
         */
        void open(String fileName) throws IOException;
        void write(byte[] buf, int len) throws IOException;
        void close() throws IOException;
    }

    public int copyRecursiveTo(String fileMask, FilePath target) throws IOException, InterruptedException {
        return copyRecursiveTo(fileMask,null,target);
    }

    /**
     * Copies the files that match the given file mask to the specified target node.
     *
     * @param fileMask
     *      Ant GLOB pattern.
     *      String like "foo/bar/*.xml" Multiple patterns can be separated
     *      by ',', and whitespace can surround ',' (so that you can write
     *      "abc, def" and "abc,def" to mean the same thing.
     * @param excludes
     *      Files to be excluded. Can be null.
     * @return
     *      the number of files copied.
     */
    public int copyRecursiveTo(final String fileMask, final String excludes, final FilePath target) throws IOException, InterruptedException {
        if(this.channel==target.channel) {
            // local to local copy.
            return act(new FileCallable<Integer>() {
                public Integer invoke(File base, VirtualChannel channel) throws IOException {
                    if(!base.exists())  return 0;
                    assert target.channel==null;

                    try {
                        class CopyImpl extends Copy {
                            private int copySize;

                            public CopyImpl() {
                                setProject(new org.apache.tools.ant.Project());
                            }

                            protected void doFileOperations() {
                                copySize = super.fileCopyMap.size();
                                super.doFileOperations();
                            }

                            public int getNumCopied() {
                                return copySize;
                            }
                        }

                        CopyImpl copyTask = new CopyImpl();
                        copyTask.setTodir(new File(target.remote));
                        copyTask.addFileset(Util.createFileSet(base,fileMask,excludes));
                        copyTask.setIncludeEmptyDirs(false);

                        copyTask.execute();
                        return copyTask.getNumCopied();
                    } catch (BuildException e) {
                        throw new IOException2("Failed to copy "+base+"/"+fileMask+" to "+target,e);
                    }
                }
            });
        } else
        if(this.channel==null) {
            // local -> remote copy
            final Pipe pipe = Pipe.createLocalToRemote();

            Future<Void> future = target.actAsync(new FileCallable<Void>() {
                public Void invoke(File f, VirtualChannel channel) throws IOException {
                    try {
                        readFromTar(remote+'/'+fileMask, f,TarCompression.GZIP.extract(pipe.getIn()));
                        return null;
                    } finally {
                        pipe.getIn().close();
                    }
                }
            });
            int r = writeToTar(new File(remote),fileMask,excludes,TarCompression.GZIP.compress(pipe.getOut()));
            try {
                future.get();
            } catch (ExecutionException e) {
                throw new IOException2(e);
            }
            return r;
        } else {
            // remote -> local copy
            final Pipe pipe = Pipe.createRemoteToLocal();

            Future<Integer> future = actAsync(new FileCallable<Integer>() {
                public Integer invoke(File f, VirtualChannel channel) throws IOException {
                    try {
                        return writeToTar(f,fileMask,excludes,TarCompression.GZIP.compress(pipe.getOut()));
                    } finally {
                        pipe.getOut().close();
                    }
                }
            });
            try {
                readFromTar(remote+'/'+fileMask,new File(target.remote),TarCompression.GZIP.extract(pipe.getIn()));
            } catch (IOException e) {// BuildException or IOException
                try {
                    future.get(3,TimeUnit.SECONDS);
                    throw e;    // the remote side completed successfully, so the error must be local
                } catch (ExecutionException x) {
                    // report both errors
                    throw new IOException2(Functions.printThrowable(e),x);
                } catch (TimeoutException _) {
                    // remote is hanging
                    throw e;
                }
            }
            try {
                return future.get();
            } catch (ExecutionException e) {
                throw new IOException2(e);
            }
        }
    }

    /**
     * Writes to a tar stream and stores obtained files to the base dir.
     *
     * @return
     *      number of files/directories that are written.
     */
    private Integer writeToTar(File baseDir, String fileMask, String excludes, OutputStream out) throws IOException {
        FileSet fs = Util.createFileSet(baseDir,fileMask,excludes);

        byte[] buf = new byte[8192];

        TarOutputStream tar = new TarOutputStream(new BufferedOutputStream(out) {
            // TarOutputStream uses TarBuffer internally,
            // which flushes the stream for each block. this creates unnecessary
            // data stream fragmentation, and flush request to a remote, which slows things down.
            public void flush() throws IOException {
                // so don't do anything in flush
            }
        });
        tar.setLongFileMode(TarOutputStream.LONGFILE_GNU);
        String[] files;
        if(baseDir.exists()) {
            DirectoryScanner ds = fs.getDirectoryScanner(new org.apache.tools.ant.Project());
            files = ds.getIncludedFiles();
        } else {
            files = new String[0];
        }
        for( String f : files) {
            if(Functions.isWindows())
                f = f.replace('\\','/');

            File file = new File(baseDir, f);

            TarEntry te = new TarEntry(f);
            te.setModTime(file.lastModified());
            if(!file.isDirectory())
                te.setSize(file.length());

            tar.putNextEntry(te);

            if (!file.isDirectory()) {
                FileInputStream in = new FileInputStream(file);
                int len;
                while((len=in.read(buf))>=0)
                    tar.write(buf,0,len);
                in.close();
            }

            tar.closeEntry();
        }

        tar.close();

        return files.length;
    }

    /**
     * Reads from a tar stream and stores obtained files to the base dir.
     */
    private static void readFromTar(String name, File baseDir, InputStream in) throws IOException {
        TarInputStream t = new TarInputStream(in);
        try {
            TarEntry te;
            while ((te = t.getNextEntry()) != null) {
                File f = new File(baseDir,te.getName());
                if(te.isDirectory()) {
                    f.mkdirs();
                } else {
                    File parent = f.getParentFile();
                    if (parent != null) parent.mkdirs();

                    OutputStream fos = new FileOutputStream(f);
                    try {
                        IOUtils.copy(t,fos);
                    } finally {
                        fos.close();
                    }
                    f.setLastModified(te.getModTime().getTime());
                    int mode = te.getMode()&0777;
                    if(mode!=0 && !Hudson.isWindows()) // be defensive
                        try {
                            LIBC.chmod(f.getPath(),mode);
                        } catch (NoClassDefFoundError e) {
                            // be defensive. see http://www.nabble.com/-3.0.6--Site-copy-problem%3A-hudson.util.IOException2%3A--java.lang.NoClassDefFoundError%3A-Could-not-initialize-class--hudson.util.jna.GNUCLibrary-td23588879.html
                        }
                }
            }
        } catch(IOException e) {
            throw new IOException2("Failed to extract "+name,e);
        } finally {
            t.close();
        }
    }

    /**
     * Creates a {@link Launcher} for starting processes on the node
     * that has this file.
     * @since 1.89
     */
    public Launcher createLauncher(TaskListener listener) throws IOException, InterruptedException {
        if(channel==null)
            return new LocalLauncher(listener);
        else
            return new RemoteLauncher(listener,channel,channel.call(new IsUnix()));
    }

    private static final class IsUnix implements Callable<Boolean,IOException> {
        public Boolean call() throws IOException {
            return File.pathSeparatorChar==':';
        }
        private static final long serialVersionUID = 1L;
    }

    /**
     * Validates the ant file mask (like "foo/bar/*.txt, zot/*.jar")
     * against this directory, and try to point out the problem.
     *
     * <p>
     * This is useful in conjunction with {@link FormValidation}.
     *
     * @return
     *      null if no error was found. Otherwise returns a human readable error message.
     * @since 1.90
     * @see #validateFileMask(FilePath, String)
     */
    public String validateAntFileMask(final String fileMasks) throws IOException, InterruptedException {
        return act(new FileCallable<String>() {
            public String invoke(File dir, VirtualChannel channel) throws IOException {
                if(fileMasks.startsWith("~"))
                    return Messages.FilePath_TildaDoesntWork();

                StringTokenizer tokens = new StringTokenizer(fileMasks,",");

                while(tokens.hasMoreTokens()) {
                    final String fileMask = tokens.nextToken().trim();
                    if(hasMatch(dir,fileMask))
                        continue;   // no error on this portion

                    // in 1.172 we introduced an incompatible change to stop using ' ' as the separator
                    // so see if we can match by using ' ' as the separator
                    if(fileMask.contains(" ")) {
                        boolean matched = true;
                        for (String token : Util.tokenize(fileMask))
                            matched &= hasMatch(dir,token);
                        if(matched)
                            return Messages.FilePath_validateAntFileMask_whitespaceSeprator();
                    }

                    // a common mistake is to assume the wrong base dir, and there are two variations
                    // to this: (1) the user gave us aa/bb/cc/dd where cc/dd was correct
                    // and (2) the user gave us cc/dd where aa/bb/cc/dd was correct.

                    {// check the (1) above first
                        String f=fileMask;
                        while(true) {
                            int idx = findSeparator(f);
                            if(idx==-1)     break;
                            f=f.substring(idx+1);

                            if(hasMatch(dir,f))
                                return Messages.FilePath_validateAntFileMask_doesntMatchAndSuggest(fileMask,f);
                        }
                    }

                    {// check the (1) above next as this is more expensive.
                        // Try prepending "**/" to see if that results in a match
                        FileSet fs = Util.createFileSet(dir,"**/"+fileMask);
                        DirectoryScanner ds = fs.getDirectoryScanner(new Project());
                        if(ds.getIncludedFilesCount()!=0) {
                            // try shorter name first so that the suggestion results in least amount of changes
                            String[] names = ds.getIncludedFiles();
                            Arrays.sort(names,SHORTER_STRING_FIRST);
                            for( String f : names) {
                                // now we want to decompose f to the leading portion that matched "**"
                                // and the trailing portion that matched the file mask, so that
                                // we can suggest the user error.
                                //
                                // this is not a very efficient/clever way to do it, but it's relatively simple

                                String prefix="";
                                while(true) {
                                    int idx = findSeparator(f);
                                    if(idx==-1)     break;

                                    prefix+=f.substring(0,idx)+'/';
                                    f=f.substring(idx+1);
                                    if(hasMatch(dir,prefix+fileMask))
                                        return Messages.FilePath_validateAntFileMask_doesntMatchAndSuggest(fileMask, prefix+fileMask);
                                }
                            }
                        }
                    }

                    {// finally, see if we can identify any sub portion that's valid. Otherwise bail out
                        String previous = null;
                        String pattern = fileMask;

                        while(true) {
                            if(hasMatch(dir,pattern)) {
                                // found a match
                                if(previous==null)
                                    return String.format("'%s' doesn't match anything, although '%s' exists",
                                        fileMask, pattern );
                                else
                                    return String.format("'%s' doesn't match anything: '%s' exists but not '%s'",
                                        fileMask, pattern, previous );
                            }

                            int idx = findSeparator(pattern);
                            if(idx<0) {// no more path component left to go back
                                if(pattern.equals(fileMask))
                                    return String.format("'%s' doesn't match anything", fileMask );
                                else
                                    return String.format("'%s' doesn't match anything: even '%s' doesn't exist",
                                        fileMask, pattern );
                            }

                            // cut off the trailing component and try again
                            previous = pattern;
                            pattern = pattern.substring(0,idx);
                        }
                    }
                }

                return null; // no error
            }

            private boolean hasMatch(File dir, String pattern) {
                FileSet fs = Util.createFileSet(dir,pattern);
                DirectoryScanner ds = fs.getDirectoryScanner(new Project());

                return ds.getIncludedFilesCount()!=0 || ds.getIncludedDirsCount()!=0;
            }

            /**
             * Finds the position of the first path separator.
             */
            private int findSeparator(String pattern) {
                int idx1 = pattern.indexOf('\\');
                int idx2 = pattern.indexOf('/');
                if(idx1==-1)    return idx2;
                if(idx2==-1)    return idx1;
                return Math.min(idx1,idx2);
            }
        });
    }

    /**
     * Shortcut for {@link #validateFileMask(String)} in case the left-hand side can be null.
     */
    public static FormValidation validateFileMask(FilePath pathOrNull, String value) throws IOException {
        if(pathOrNull==null) return FormValidation.ok();
        return pathOrNull.validateFileMask(value);
    }

    /**
     * Short for {@code validateFileMask(value,true)} 
     */
    public FormValidation validateFileMask(String value) throws IOException {
        return validateFileMask(value,true);
    }

    /**
     * Checks the GLOB-style file mask. See {@link #validateAntFileMask(String)} 
     * @since 1.294
     */
    public FormValidation validateFileMask(String value, boolean errorIfNotExist) throws IOException {
        value = fixEmpty(value);
        if(value==null)
            return FormValidation.ok();

        try {
            if(!exists()) // no workspace. can't check
                return FormValidation.ok();

            String msg = validateAntFileMask(value);
            if(errorIfNotExist)     return FormValidation.error(msg);
            else                    return FormValidation.warning(msg);
        } catch (InterruptedException e) {
            return FormValidation.ok();
        }
    }

    /**
     * Validates a relative file path from this {@link FilePath}.
     *
     * @param value
     *      The relative path being validated.
     * @param errorIfNotExist
     *      If true, report an error if the given relative path doesn't exist. Otherwise it's a warning.
     * @param expectingFile
     *      If true, we expect the relative path to point to a file.
     *      Otherwise, the relative path is expected to be pointing to a directory.
     */
    public FormValidation validateRelativePath(String value, boolean errorIfNotExist, boolean expectingFile) throws IOException {
        AbstractProject subject = Stapler.getCurrentRequest().findAncestorObject(AbstractProject.class);
        subject.checkPermission(Item.CONFIGURE);

        value = fixEmpty(value);

        // none entered yet, or something is seriously wrong
        if(value==null || (AbstractProject<?,?>)subject ==null) return FormValidation.ok();

        // a common mistake is to use wildcard
        if(value.contains("*")) return FormValidation.error("Wildcard is not allowed here");

        try {
            if(!exists())    // no base directory. can't check
                return FormValidation.ok();

            FilePath path = child(value);
            if(path.exists()) {
                if (expectingFile) {
                    if(!path.isDirectory())
                        return FormValidation.ok();
                    else
                        return FormValidation.error(value+" is not a file");
                } else {
                    if(path.isDirectory())
                        return FormValidation.ok();
                    else
                        return FormValidation.error(value+" is not a directory");
                }
            }

            String msg = "No such "+(expectingFile?"file":"directory")+": " + value;
            if(errorIfNotExist)     return FormValidation.error(msg);
            else                    return FormValidation.warning(msg);
        } catch (InterruptedException e) {
            return FormValidation.ok();
        }
    }

    /**
     * A convenience method over {@link #validateRelativePath(String, boolean, boolean)}.
     */
    public FormValidation validateRelativeDirectory(String value, boolean errorIfNotExist) throws IOException {
        return validateRelativePath(value,errorIfNotExist,false);
    }

    public FormValidation validateRelativeDirectory(String value) throws IOException {
        return validateRelativeDirectory(value,true);
    }

    @Deprecated
    public String toString() {
        // to make writing JSPs easily, return local
        return remote;
    }

    public VirtualChannel getChannel() {
        if(channel!=null)   return channel;
        else                return Hudson.MasterComputer.localChannel;
    }

    /**
     * Returns true if this {@link FilePath} represents a remote file. 
     */
    public boolean isRemote() {
        return channel!=null;
    }

    private void writeObject(ObjectOutputStream oos) throws IOException {
        Channel target = Channel.current();

        if(channel!=null && channel!=target)
            throw new IllegalStateException("Can't send a remote FilePath to a different remote channel");

        oos.defaultWriteObject();
        oos.writeBoolean(channel==null);
    }

    private void readObject(ObjectInputStream ois) throws IOException, ClassNotFoundException {
        Channel channel = Channel.current();
        assert channel!=null;

        ois.defaultReadObject();
        if(ois.readBoolean()) {
            this.channel = channel;
        } else {
            this.channel = null;
        }
    }

    private static final long serialVersionUID = 1L;

    public static int SIDE_BUFFER_SIZE = 1024;

    /**
     * Adapts {@link FileCallable} to {@link Callable}.
     */
    private class FileCallableWrapper<T> implements DelegatingCallable<T,IOException> {
        private final FileCallable<T> callable;
        private transient ClassLoader classLoader;

        public FileCallableWrapper(FileCallable<T> callable) {
            this.callable = callable;
            this.classLoader = callable.getClass().getClassLoader();
        }

        private FileCallableWrapper(FileCallable<T> callable, ClassLoader classLoader) {
            this.callable = callable;
            this.classLoader = classLoader;
        }

        public T call() throws IOException {
            return callable.invoke(new File(remote), Channel.current());
        }

        public ClassLoader getClassLoader() {
            return classLoader;
        }

        private static final long serialVersionUID = 1L;
    }

    private static final Comparator<String> SHORTER_STRING_FIRST = new Comparator<String>() {
        public int compare(String o1, String o2) {
            return o1.length()-o2.length();
        }
    };
}