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.fs;
019
020import java.io.FileNotFoundException;
021import java.io.IOException;
022import java.util.EnumSet;
023
024import org.apache.hadoop.HadoopIllegalArgumentException;
025import org.apache.hadoop.classification.InterfaceAudience;
026import org.apache.hadoop.classification.InterfaceStability;
027
028/****************************************************************
029 * CreateFlag specifies the file create semantic. Users can combine flags like: <br>
030 * <code>
031 * EnumSet.of(CreateFlag.CREATE, CreateFlag.APPEND)
032 * <code>
033 * <p>
034 * 
035 * Use the CreateFlag as follows:
036 * <ol>
037 * <li> CREATE - to create a file if it does not exist, 
038 * else throw FileAlreadyExists.</li>
039 * <li> APPEND - to append to a file if it exists, 
040 * else throw FileNotFoundException.</li>
041 * <li> OVERWRITE - to truncate a file if it exists, 
042 * else throw FileNotFoundException.</li>
043 * <li> CREATE|APPEND - to create a file if it does not exist, 
044 * else append to an existing file.</li>
045 * <li> CREATE|OVERWRITE - to create a file if it does not exist, 
046 * else overwrite an existing file.</li>
047 * <li> SYNC_BLOCK - to force closed blocks to the disk device.
048 * In addition {@link Syncable#hsync()} should be called after each write,
049 * if true synchronous behavior is required.</li>
050 * </ol>
051 * 
052 * Following combination is not valid and will result in 
053 * {@link HadoopIllegalArgumentException}:
054 * <ol>
055 * <li> APPEND|OVERWRITE</li>
056 * <li> CREATE|APPEND|OVERWRITE</li>
057 * </ol>
058 *****************************************************************/
059@InterfaceAudience.Public
060@InterfaceStability.Evolving
061public enum CreateFlag {
062
063  /**
064   * Create a file. See javadoc for more description
065   * already exists
066   */
067  CREATE((short) 0x01),
068
069  /**
070   * Truncate/overwrite a file. Same as POSIX O_TRUNC. See javadoc for description.
071   */
072  OVERWRITE((short) 0x02),
073
074  /**
075   * Append to a file. See javadoc for more description.
076   */
077  APPEND((short) 0x04),
078
079  /**
080   * Force closed blocks to disk. Similar to POSIX O_SYNC. See javadoc for description.
081   */
082  SYNC_BLOCK((short) 0x08),
083
084  /**
085   * Create the block on transient storage (RAM) if available. If
086   * transient storage is unavailable then the block will be created
087   * on disk.
088   *
089   * HDFS will make a best effort to lazily write these files to persistent
090   * storage, however file contents may be lost at any time due to process/
091   * node restarts, hence there is no guarantee of data durability.
092   *
093   * This flag must only be used for intermediate data whose loss can be
094   * tolerated by the application.
095   */
096  LAZY_PERSIST((short) 0x10);
097
098  private final short mode;
099
100  private CreateFlag(short mode) {
101    this.mode = mode;
102  }
103
104  short getMode() {
105    return mode;
106  }
107  
108  /**
109   * Validate the CreateFlag and throw exception if it is invalid
110   * @param flag set of CreateFlag
111   * @throws HadoopIllegalArgumentException if the CreateFlag is invalid
112   */
113  public static void validate(EnumSet<CreateFlag> flag) {
114    if (flag == null || flag.isEmpty()) {
115      throw new HadoopIllegalArgumentException(flag
116          + " does not specify any options");
117    }
118    final boolean append = flag.contains(APPEND);
119    final boolean overwrite = flag.contains(OVERWRITE);
120    
121    // Both append and overwrite is an error
122    if (append && overwrite) {
123      throw new HadoopIllegalArgumentException(
124          flag + "Both append and overwrite options cannot be enabled.");
125    }
126  }
127  
128  /**
129   * Validate the CreateFlag for create operation
130   * @param path Object representing the path; usually String or {@link Path}
131   * @param pathExists pass true if the path exists in the file system
132   * @param flag set of CreateFlag
133   * @throws IOException on error
134   * @throws HadoopIllegalArgumentException if the CreateFlag is invalid
135   */
136  public static void validate(Object path, boolean pathExists,
137      EnumSet<CreateFlag> flag) throws IOException {
138    validate(flag);
139    final boolean append = flag.contains(APPEND);
140    final boolean overwrite = flag.contains(OVERWRITE);
141    if (pathExists) {
142      if (!(append || overwrite)) {
143        throw new FileAlreadyExistsException("File already exists: "
144            + path.toString()
145            + ". Append or overwrite option must be specified in " + flag);
146      }
147    } else if (!flag.contains(CREATE)) {
148      throw new FileNotFoundException("Non existing file: " + path.toString()
149          + ". Create option is not specified in " + flag);
150    }
151  }
152}