lucene/replicator/src/java/org/apache/lucene/replicator/Replicator.java

/*
 * 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.lucene.replicator;

import java.io.Closeable;
import java.io.IOException;
import java.io.InputStream;

/**
 * An interface for replicating files. Allows a producer to {@link #publish(Revision) publish}
 * {@link Revision}s and consumers to {@link #checkForUpdate(String) check for updates}. When a
 * client needs to be updated, it is given a {@link SessionToken} through which it can {@link
 * #obtainFile(String, String, String) obtain} the files of that revision. After the client has
 * finished obtaining all the files, it should {@link #release(String) release} the given session,
 * so that the files can be reclaimed if they are not needed anymore.
 *
 * <p>A client is always updated to the newest revision available. That is, if a client is on
 * revision <em>r1</em> and revisions <em>r2</em> and <em>r3</em> were published, then when the
 * cllient will next check for update, it will receive <em>r3</em>.
 *
 * @lucene.experimental
 */
public interface Replicator extends Closeable {

  /**
   * Publish a new {@link Revision} for consumption by clients. It is the caller's responsibility to
   * verify that the revision files exist and can be read by clients. When the revision is no longer
   * needed, it will be {@link Revision#release() released} by the replicator.
   */
  public void publish(Revision revision) throws IOException;

  /**
   * Check whether the given version is up-to-date and returns a {@link SessionToken} which can be
   * used for fetching the revision files, otherwise returns {@code null}.
   *
   * <p><b>NOTE:</b> when the returned session token is no longer needed, you should call {@link
   * #release(String)} so that the session resources can be reclaimed, including the revision files.
   */
  public SessionToken checkForUpdate(String currVersion) throws IOException;

  /** Notify that the specified {@link SessionToken} is no longer needed by the caller. */
  public void release(String sessionID) throws IOException;

  /**
   * Returns an {@link InputStream} for the requested file and source in the context of the given
   * {@link SessionToken#id session}.
   *
   * <p><b>NOTE:</b> it is the caller's responsibility to close the returned stream.
   *
   * @throws SessionExpiredException if the specified session has already expired
   */
  public InputStream obtainFile(String sessionID, String source, String fileName)
      throws IOException;
}