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 */
018package org.apache.hadoop.hdfs;
019
020import org.apache.hadoop.classification.InterfaceAudience;
021import org.apache.hadoop.classification.InterfaceStability;
022import org.apache.hadoop.conf.Configuration;
023
024/**
025 * The public API for creating a new ReplicaAccessor.
026 */
027@InterfaceAudience.Public
028@InterfaceStability.Stable
029public abstract class ReplicaAccessorBuilder {
030  /**
031   * Set the file name which is being opened.  Provided for debugging purposes.
032   */
033  public abstract ReplicaAccessorBuilder setFileName(String fileName);
034
035  /** Set the block ID and block pool ID which are being opened. */
036  public abstract ReplicaAccessorBuilder
037      setBlock(long blockId, String blockPoolId);
038
039  /**
040   * Set whether checksums must be verified.  Checksums should be skipped if
041   * the user has disabled checksum verification in the configuration.  Users
042   * may wish to do this if their software does checksum verification at a
043   * higher level than HDFS.
044   */
045  public abstract ReplicaAccessorBuilder
046      setVerifyChecksum(boolean verifyChecksum);
047
048  /** Set the name of the HDFS client.  Provided for debugging purposes. */
049  public abstract ReplicaAccessorBuilder setClientName(String clientName);
050
051  /**
052   * Set whether short-circuit is enabled.  Short-circuit may be disabled if
053   * the user has set dfs.client.read.shortcircuit to false, or if the block
054   * being read is under construction.  The fact that this bit is enabled does
055   * not mean that the user has permission to do short-circuit reads or to
056   * access the replica-- that must be checked separately by the
057   * ReplicaAccessorBuilder implementation.
058   */
059  public abstract ReplicaAccessorBuilder
060      setAllowShortCircuitReads(boolean allowShortCircuit);
061
062  /**
063   * Set the length of the replica which is visible to this client.  If bytes
064   * are added later, they will not be visible to the ReplicaAccessor we are
065   * building.  In order to see more of the replica, the client must re-open
066   * this HDFS file.  The visible length provides an upper bound, but not a
067   * lower one.  If the replica is deleted or truncated, fewer bytes may be
068   * visible than specified here.
069   */
070  public abstract ReplicaAccessorBuilder setVisibleLength(long visibleLength);
071
072  /**
073   * Set the configuration to use.  ReplicaAccessorBuilder subclasses should
074   * define their own configuration prefix.  For example, the foobar plugin
075   * could look for configuration keys like foo.bar.parameter1,
076   * foo.bar.parameter2.
077   */
078  public abstract ReplicaAccessorBuilder setConfiguration(Configuration conf);
079
080  /**
081   * Set the block access token to use.
082   */
083  public abstract ReplicaAccessorBuilder setBlockAccessToken(byte[] token);
084
085  /**
086   * Build a new ReplicaAccessor.
087   *
088   * The implementation must perform any necessary access checks before
089   * constructing the ReplicaAccessor.  If there is a hardware-level or
090   * network-level setup operation that could fail, it should be done here.  If
091   * the implementation returns a ReplicaAccessor, we will assume that it works
092   * and not attempt to construct a normal BlockReader.
093   *
094   * If the ReplicaAccessor could not be built, implementations may wish to log
095   * a message at TRACE level indicating why.
096   *
097   * @return    null if the ReplicaAccessor could not be built; the
098   *                ReplicaAccessor otherwise.
099   */
100  public abstract ReplicaAccessor build();
101}