| /** |
| * 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.hadoop.hdfs; |
| |
| import java.io.IOException; |
| import java.net.Socket; |
| |
| /** |
| * A BlockReader is responsible for reading a single block |
| * from a single datanode. |
| */ |
| public interface BlockReader { |
| |
| /* same interface as inputStream java.io.InputStream#read() |
| * used by DFSInputStream#read() |
| * This violates one rule when there is a checksum error: |
| * "Read should not modify user buffer before successful read" |
| * because it first reads the data to user buffer and then checks |
| * the checksum. |
| */ |
| int read(byte[] buf, int off, int len) throws IOException; |
| |
| /** |
| * Skip the given number of bytes |
| */ |
| long skip(long n) throws IOException; |
| |
| void close() throws IOException; |
| |
| /** |
| * Read exactly the given amount of data, throwing an exception |
| * if EOF is reached before that amount |
| */ |
| void readFully(byte[] buf, int readOffset, int amtToRead) throws IOException; |
| |
| /** |
| * Similar to {@link #readFully(byte[], int, int)} except that it will |
| * not throw an exception on EOF. However, it differs from the simple |
| * {@link #read(byte[], int, int)} call in that it is guaranteed to |
| * read the data if it is available. In other words, if this call |
| * does not throw an exception, then either the buffer has been |
| * filled or the next call will return EOF. |
| */ |
| int readAll(byte[] buf, int offset, int len) throws IOException; |
| |
| /** |
| * Take the socket used to talk to the DN. |
| */ |
| Socket takeSocket(); |
| |
| /** |
| * Whether the BlockReader has reached the end of its input stream |
| * and successfully sent a status code back to the datanode. |
| */ |
| boolean hasSentStatusCode(); |
| |
| } |