/*
* 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.tools.ant.util;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import org.apache.tools.ant.BuildException;
import org.apache.tools.ant.Task;
import org.apache.tools.ant.taskdefs.Execute;
/**
* Contains methods related to symbolic links - or what Ant thinks is
* a symbolic link based on the absent support for them in Java.
*
* @since Ant 1.8.0
*/
public class SymbolicLinkUtils {
private static final FileUtils FILE_UTILS = FileUtils.getFileUtils();
/**
* Shared instance.
*/
private static final SymbolicLinkUtils PRIMARY_INSTANCE =
new SymbolicLinkUtils();
/**
* Method to retrieve The SymbolicLinkUtils, which is shared by
* all users of this method.
* @return an instance of SymbolicLinkUtils.
*/
public static SymbolicLinkUtils getSymbolicLinkUtils() {
// keep the door open for Java X.Y specific subclass if symbolic
// links ever become supported in the classlib
return PRIMARY_INSTANCE;
}
/**
* Empty constructor.
*/
protected SymbolicLinkUtils() {
}
/**
* Checks whether a given file is a symbolic link.
*
* <p>It doesn't really test for symbolic links but whether the
* canonical and absolute paths of the file are identical--this
* may lead to false positives on some platforms.</p>
*
* @param file the file to test. Must not be null.
*
* @return true if the file is a symbolic link.
* @throws IOException on error.
*/
public boolean isSymbolicLink(final File file) throws IOException {
return isSymbolicLink(file.getParentFile(), file.getName());
}
/**
* Checks whether a given file is a symbolic link.
*
* <p>It doesn't really test for symbolic links but whether the
* canonical and absolute paths of the file are identical--this
* may lead to false positives on some platforms.</p>
*
* @param name the name of the file to test.
*
* @return true if the file is a symbolic link.
* @throws IOException on error.
*/
public boolean isSymbolicLink(final String name) throws IOException {
return isSymbolicLink(new File(name));
}
/**
* Checks whether a given file is a symbolic link.
*
* <p>It doesn't really test for symbolic links but whether the
* canonical and absolute paths of the file are identical--this
* may lead to false positives on some platforms.</p>
*
* @param parent the parent directory of the file to test
* @param name the name of the file to test.
*
* @return true if the file is a symbolic link.
* @throws IOException on error.
*/
public boolean isSymbolicLink(final File parent, final String name)
throws IOException {
final File toTest = parent != null
? new File(parent.getCanonicalPath(), name)
: new File(name);
return !toTest.getAbsolutePath().equals(toTest.getCanonicalPath());
}
/**
* Checks whether a given file is a broken symbolic link.
*
* <p>It doesn't really test for symbolic links but whether Java
* reports that the File doesn't exist but its parent's child list
* contains it--this may lead to false positives on some
* platforms.</p>
*
* <p>Note that #isSymbolicLink returns false if this method
* returns true since Java won't produce a canonical name
* different from the abolute one if the link is broken.</p>
*
* @param name the name of the file to test.
*
* @return true if the file is a broken symbolic link.
* @throws IOException on error.
*/
public boolean isDanglingSymbolicLink(final String name) throws IOException {
return isDanglingSymbolicLink(new File(name));
}
/**
* Checks whether a given file is a broken symbolic link.
*
* <p>It doesn't really test for symbolic links but whether Java
* reports that the File doesn't exist but its parent's child list
* contains it--this may lead to false positives on some
* platforms.</p>
*
* <p>Note that #isSymbolicLink returns false if this method
* returns true since Java won't produce a canonical name
* different from the abolute one if the link is broken.</p>
*
* @param file the file to test.
*
* @return true if the file is a broken symbolic link.
* @throws IOException on error.
*/
public boolean isDanglingSymbolicLink(final File file) throws IOException {
return isDanglingSymbolicLink(file.getParentFile(), file.getName());
}
/**
* Checks whether a given file is a broken symbolic link.
*
* <p>It doesn't really test for symbolic links but whether Java
* reports that the File doesn't exist but its parent's child list
* contains it--this may lead to false positives on some
* platforms.</p>
*
* <p>Note that #isSymbolicLink returns false if this method
* returns true since Java won't produce a canonical name
* different from the abolute one if the link is broken.</p>
*
* @param parent the parent directory of the file to test
* @param name the name of the file to test.
*
* @return true if the file is a broken symbolic link.
* @throws IOException on error.
*/
public boolean isDanglingSymbolicLink(final File parent, final String name)
throws IOException {
final File f = new File(parent, name);
if (!f.exists()) {
final String localName = f.getName();
final String[] c = parent.list((d, n) -> localName.equals(n));
return c != null && c.length > 0;
}
return false;
}
/**
* Delete a symlink (without deleting the associated resource).
*
* <p>This is a utility method that removes a unix symlink without
* removing the resource that the symlink points to. If it is
* accidentally invoked on a real file, the real file will not be
* harmed, but silently ignored.</p>
*
* <p>Normally this method works by
* getting the canonical path of the link, using the canonical path to
* rename the resource (breaking the link) and then deleting the link.
* The resource is then returned to its original name inside a finally
* block to ensure that the resource is unharmed even in the event of
* an exception.</p>
*
* <p>There may be cases where the algorithm described above doesn't work,
* in that case the method tries to use the native "rm" command on
* the symlink instead.</p>
*
* @param link A <code>File</code> object of the symlink to delete.
* @param task An Ant Task required if "rm" needs to be invoked.
*
* @throws IOException If calls to <code>File.rename</code>,
* <code>File.delete</code> or <code>File.getCanonicalPath</code>
* fail.
* @throws BuildException if the execution of "rm" failed.
*/
public void deleteSymbolicLink(File link, final Task task)
throws IOException {
if (isDanglingSymbolicLink(link)) {
if (!link.delete()) {
throw new IOException("failed to remove dangling symbolic link "
+ link);
}
return;
}
if (!isSymbolicLink(link)) {
// plain file, not a link
return;
}
if (!link.exists()) {
throw new FileNotFoundException("No such symbolic link: " + link);
}
// find the resource of the existing link:
final File target = link.getCanonicalFile();
// no reason to try the renaming algorithm if we aren't allowed to
// write to the target's parent directory. Let's hope that
// File.canWrite works on all platforms.
if (task == null || target.getParentFile().canWrite()) {
// rename the resource, thus breaking the link:
final File temp = FILE_UTILS.createTempFile("symlink", ".tmp",
target.getParentFile(), false,
false);
if (FILE_UTILS.isLeadingPath(target, link)) {
// link points to a parent directory, renaming the parent
// will rename the file
link = new File(temp,
FILE_UTILS.removeLeadingPath(target, link));
}
boolean renamedTarget = false;
boolean success = false;
try {
try {
FILE_UTILS.rename(target, temp);
renamedTarget = true;
} catch (final IOException e) {
throw new IOException("Couldn't rename resource when "
+ "attempting to delete '" + link
+ "'. Reason: " + e.getMessage());
}
// delete the (now) broken link:
if (!link.delete()) {
throw new IOException("Couldn't delete symlink: "
+ link
+ " (was it a real file? is this "
+ "not a UNIX system?)");
}
success = true;
} finally {
if (renamedTarget) {
// return the resource to its original name:
try {
FILE_UTILS.rename(temp, target);
} catch (final IOException e) {
String msg = "Couldn't return resource "
+ temp
+ " to its original name: "
+ target.getAbsolutePath()
+ ". Reason: " + e.getMessage()
+ "\n THE RESOURCE'S NAME ON DISK"
+ " HAS BEEN CHANGED BY THIS"
+ " ERROR!\n";
if (success) {
throw new IOException(msg); //NOSONAR
} else {
System.err.println(msg);
}
}
}
}
} else {
Execute.runCommand(task,
new String[] {"rm", link.getAbsolutePath()});
}
}
}