org.apache.hadoop.fs.FSLinkResolver Maven / Gradle / Ivy
/**
* 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.hadoop.fs;
import java.io.IOException;
import java.net.URI;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
/**
* Used primarily by {@link FileContext} to operate on and resolve
* symlinks in a path. Operations can potentially span multiple
* {@link AbstractFileSystem}s.
*
* @see FileSystemLinkResolver
*/
@InterfaceAudience.Private
@InterfaceStability.Evolving
public abstract class FSLinkResolver {
/**
* Return a fully-qualified version of the given symlink target if it
* has no scheme and authority. Partially and fully-qualified paths
* are returned unmodified.
* @param pathURI URI of the filesystem of pathWithLink
* @param pathWithLink Path that contains the symlink
* @param target The symlink's absolute target
* @return Fully qualified version of the target.
*/
public static Path qualifySymlinkTarget(final URI pathURI,
Path pathWithLink, Path target) {
// NB: makeQualified uses the target's scheme and authority, if
// specified, and the scheme and authority of pathURI, if not.
final URI targetUri = target.toUri();
final String scheme = targetUri.getScheme();
final String auth = targetUri.getAuthority();
return (scheme == null && auth == null) ? target.makeQualified(pathURI,
pathWithLink.getParent()) : target;
}
/**
* Generic helper function overridden on instantiation to perform a
* specific operation on the given file system using the given path
* which may result in an UnresolvedLinkException.
* @param fs AbstractFileSystem to perform the operation on.
* @param p Path given the file system.
* @return Generic type determined by the specific implementation.
* @throws UnresolvedLinkException If symbolic link path could
* not be resolved
* @throws IOException an I/O error occurred
*/
abstract public T next(final AbstractFileSystem fs, final Path p)
throws IOException, UnresolvedLinkException;
/**
* Performs the operation specified by the next function, calling it
* repeatedly until all symlinks in the given path are resolved.
* @param fc FileContext used to access file systems.
* @param path The path to resolve symlinks on.
* @return Generic type determined by the implementation of next.
* @throws IOException
*/
public T resolve(final FileContext fc, final Path path) throws IOException {
int count = 0;
T in = null;
Path p = path;
// NB: More than one AbstractFileSystem can match a scheme, eg
// "file" resolves to LocalFs but could have come by RawLocalFs.
AbstractFileSystem fs = fc.getFSofPath(p);
// Loop until all symlinks are resolved or the limit is reached
for (boolean isLink = true; isLink;) {
try {
in = next(fs, p);
isLink = false;
} catch (UnresolvedLinkException e) {
if (!fc.resolveSymlinks) {
throw new IOException("Path " + path + " contains a symlink"
+ " and symlink resolution is disabled ("
+ CommonConfigurationKeys.FS_CLIENT_RESOLVE_REMOTE_SYMLINKS_KEY + ").", e);
}
if (!FileSystem.areSymlinksEnabled()) {
throw new IOException("Symlink resolution is disabled in"
+ " this version of Hadoop.");
}
if (count++ > FsConstants.MAX_PATH_LINKS) {
throw new IOException("Possible cyclic loop while " +
"following symbolic link " + path);
}
// Resolve the first unresolved path component
p = qualifySymlinkTarget(fs.getUri(), p, fs.getLinkTarget(p));
fs = fc.getFSofPath(p);
}
}
return in;
}
}