001/**
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018
019package org.apache.hadoop.crypto.key;
020
021import java.io.IOException;
022import java.net.URI;
023import java.net.URISyntaxException;
024import java.util.ArrayList;
025import java.util.Iterator;
026import java.util.List;
027import java.util.ServiceLoader;
028
029import org.apache.hadoop.classification.InterfaceAudience;
030import org.apache.hadoop.classification.InterfaceStability;
031import org.apache.hadoop.conf.Configuration;
032
033/**
034 * A factory to create a list of KeyProvider based on the path given in a
035 * Configuration. It uses a service loader interface to find the available
036 * KeyProviders and create them based on the list of URIs.
037 */
038@InterfaceAudience.Public
039@InterfaceStability.Unstable
040public abstract class KeyProviderFactory {
041  public static final String KEY_PROVIDER_PATH =
042      "hadoop.security.key.provider.path";
043
044  public abstract KeyProvider createProvider(URI providerName,
045                                             Configuration conf
046                                             ) throws IOException;
047
048  private static final ServiceLoader<KeyProviderFactory> serviceLoader =
049      ServiceLoader.load(KeyProviderFactory.class,
050          KeyProviderFactory.class.getClassLoader());
051
052  // Iterate through the serviceLoader to avoid lazy loading.
053  // Lazy loading would require synchronization in concurrent use cases.
054  static {
055    Iterator<KeyProviderFactory> iterServices = serviceLoader.iterator();
056    while (iterServices.hasNext()) {
057      iterServices.next();
058    }
059  }
060  
061  public static List<KeyProvider> getProviders(Configuration conf
062                                               ) throws IOException {
063    List<KeyProvider> result = new ArrayList<KeyProvider>();
064    for(String path: conf.getStringCollection(KEY_PROVIDER_PATH)) {
065      try {
066        URI uri = new URI(path);
067        KeyProvider kp = get(uri, conf);
068        if (kp != null) {
069          result.add(kp);
070        } else {
071          throw new IOException("No KeyProviderFactory for " + uri + " in " +
072              KEY_PROVIDER_PATH);
073        }
074      } catch (URISyntaxException error) {
075        throw new IOException("Bad configuration of " + KEY_PROVIDER_PATH +
076            " at " + path, error);
077      }
078    }
079    return result;
080  }
081
082  /**
083   * Create a KeyProvider based on a provided URI.
084   *
085   * @param uri key provider URI
086   * @param conf configuration to initialize the key provider
087   * @return the key provider for the specified URI, or <code>NULL</code> if
088   *         a provider for the specified URI scheme could not be found.
089   * @throws IOException thrown if the provider failed to initialize.
090   */
091  public static KeyProvider get(URI uri, Configuration conf)
092      throws IOException {
093    KeyProvider kp = null;
094    for (KeyProviderFactory factory : serviceLoader) {
095      kp = factory.createProvider(uri, conf);
096      if (kp != null) {
097        break;
098      }
099    }
100    return kp;
101  }
102
103}