/*
* 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.lucene.store;
import java.io.IOException;
/**
* Extension of IndexInput, computing checksum as it goes.
* Callers can retrieve the checksum via {@link #getChecksum()}.
*/
public abstract class ChecksumIndexInput extends IndexInput {
/** resourceDescription should be a non-null, opaque string
* describing this resource; it's returned from
* {@link #toString}. */
protected ChecksumIndexInput(String resourceDescription) {
super(resourceDescription);
}
/** Returns the current checksum value */
public abstract long getChecksum() throws IOException;
/**
* {@inheritDoc}
*
* {@link ChecksumIndexInput} can only seek forward and seeks are expensive
* since they imply to read bytes in-between the current position and the
* target position in order to update the checksum.
*/
@Override
public void seek(long pos) throws IOException {
final long curFP = getFilePointer();
final long skip = pos - curFP;
if (skip < 0) {
throw new IllegalStateException(getClass() + " cannot seek backwards (pos=" + pos + " getFilePointer()=" + curFP + ")");
}
skipBytes(skip);
}
}