| /* |
| * 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} |
| * |
| * <p>{@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 + ")"); |
| } |
| // we must skip slowly to ensure skipped bytes are still read and used |
| // to update checksums |
| // TODO: this "slow skip" logic should be moved into this class once |
| // no longer needed as default logic in DataInput |
| skipBytesSlowly(skip); |
| } |
| } |