/**
* 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.server.namenode;
import java.io.Closeable;
import java.io.IOException;
/**
* A generic abstract class to support reading edits log data from
* persistent storage.
*
* It should stream bytes from the storage exactly as they were written
* into the #{@link EditLogOutputStream}.
*/
abstract class EditLogInputStream implements JournalStream, Closeable {
/**
* Close the stream.
* @throws IOException if an error occurred while closing
*/
public abstract void close() throws IOException;
/**
* Read an operation from the stream
* @return an operation from the stream or null if at end of stream
* @throws IOException if there is an error reading from the stream
*/
public abstract FSEditLogOp readOp() throws IOException;
/**
* Get the layout version of the data in the stream.
* @return the layout version of the ops in the stream.
* @throws IOException if there is an error reading the version
*/
public abstract int getVersion() throws IOException;
/**
* Get the "position" of in the stream. This is useful for
* debugging and operational purposes.
*
* Different stream types can have a different meaning for
* what the position is. For file streams it means the byte offset
* from the start of the file.
*
* @return the position in the stream
*/
public abstract long getPosition();
/**
* Return the size of the current edits log.
*/
abstract long length() throws IOException;
}