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 package org.apache.hadoop.hdfs;
019
020 import java.io.IOException;
021 import java.util.EnumSet;
022
023 import org.apache.hadoop.fs.ByteBufferReadable;
024 import org.apache.hadoop.fs.ReadOption;
025 import org.apache.hadoop.hdfs.client.ClientMmap;
026 import org.apache.hadoop.hdfs.client.ClientMmapManager;
027 import org.apache.hadoop.hdfs.protocol.LocatedBlock;
028
029 /**
030 * A BlockReader is responsible for reading a single block
031 * from a single datanode.
032 */
033 public interface BlockReader extends ByteBufferReadable {
034
035
036 /* same interface as inputStream java.io.InputStream#read()
037 * used by DFSInputStream#read()
038 * This violates one rule when there is a checksum error:
039 * "Read should not modify user buffer before successful read"
040 * because it first reads the data to user buffer and then checks
041 * the checksum.
042 * Note: this must return -1 on EOF, even in the case of a 0-byte read.
043 * See HDFS-5762 for details.
044 */
045 int read(byte[] buf, int off, int len) throws IOException;
046
047 /**
048 * Skip the given number of bytes
049 */
050 long skip(long n) throws IOException;
051
052 /**
053 * Returns an estimate of the number of bytes that can be read
054 * (or skipped over) from this input stream without performing
055 * network I/O.
056 */
057 int available() throws IOException;
058
059 /**
060 * Close the block reader.
061 *
062 * @throws IOException
063 */
064 void close() throws IOException;
065
066 /**
067 * Read exactly the given amount of data, throwing an exception
068 * if EOF is reached before that amount
069 */
070 void readFully(byte[] buf, int readOffset, int amtToRead) throws IOException;
071
072 /**
073 * Similar to {@link #readFully(byte[], int, int)} except that it will
074 * not throw an exception on EOF. However, it differs from the simple
075 * {@link #read(byte[], int, int)} call in that it is guaranteed to
076 * read the data if it is available. In other words, if this call
077 * does not throw an exception, then either the buffer has been
078 * filled or the next call will return EOF.
079 */
080 int readAll(byte[] buf, int offset, int len) throws IOException;
081
082 /**
083 * @return true only if this is a local read.
084 */
085 boolean isLocal();
086
087 /**
088 * @return true only if this is a short-circuit read.
089 * All short-circuit reads are also local.
090 */
091 boolean isShortCircuit();
092
093 /**
094 * Get a ClientMmap object for this BlockReader.
095 *
096 * @param opts The read options to use.
097 * @return The ClientMmap object, or null if mmap is not
098 * supported.
099 */
100 ClientMmap getClientMmap(EnumSet<ReadOption> opts,
101 ClientMmapManager mmapManager);
102 }