org.apache.hadoop.fs.FileSystemLinkResolver 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 org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
/**
* FileSystem-specific class used to operate on and resolve symlinks in a path.
* Operation can potentially span multiple {@link FileSystem}s.
*
* @see FSLinkResolver
*/
@InterfaceAudience.Private
@InterfaceStability.Evolving
public abstract class FileSystemLinkResolver {
/**
* FileSystem subclass-specific implementation of superclass method.
* Overridden on instantiation to perform the actual method call, which throws
* an UnresolvedLinkException if called on an unresolved {@link Path}.
* @param p Path on which to perform an operation
* @return Generic type returned by operation
* @throws IOException
* @throws UnresolvedLinkException
*/
abstract public T doCall(final Path p) throws IOException,
UnresolvedLinkException;
/**
* Calls the abstract FileSystem call equivalent to the specialized subclass
* implementation in {@link #doCall(Path)}. This is used when retrying the
* call with a newly resolved Path and corresponding new FileSystem.
*
* @param fs
* FileSystem with which to retry call
* @param p
* Resolved Target of path
* @return Generic type determined by implementation
* @throws IOException
*/
abstract public T next(final FileSystem fs, final Path p) throws IOException;
/**
* Attempt calling overridden {@link #doCall(Path)} method with
* specified {@link FileSystem} and {@link Path}. If the call fails with an
* UnresolvedLinkException, it will try to resolve the path and retry the call
* by calling {@link #next(FileSystem, Path)}.
* @param filesys FileSystem with which to try call
* @param path Path with which to try call
* @return Generic type determined by implementation
* @throws IOException
*/
public T resolve(final FileSystem filesys, final Path path)
throws IOException {
int count = 0;
T in = null;
Path p = path;
// Assumes path belongs to this FileSystem.
// Callers validate this by passing paths through FileSystem#checkPath
FileSystem fs = filesys;
for (boolean isLink = true; isLink;) {
try {
in = doCall(p);
isLink = false;
} catch (UnresolvedLinkException e) {
if (!filesys.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 = FSLinkResolver.qualifySymlinkTarget(fs.getUri(), p,
filesys.resolveLink(p));
fs = FileSystem.getFSofPath(p, filesys.getConf());
// Have to call next if it's a new FS
if (!fs.equals(filesys)) {
return next(fs, p);
}
// Else, we keep resolving with this filesystem
}
}
// Successful call, path was fully resolved
return in;
}
}