org.apache.hadoop.fs.FSLinkResolver.java Source code

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Here is the source code for org.apache.hadoop.fs.FSLinkResolver.java

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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.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<T> {

    /**
     * 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 <code>path</code> 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;
    }
}