| /* |
| * 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 { |
| |
| private static final int SKIP_BUFFER_SIZE = 1024; |
| |
| /* This buffer is used when skipping bytes in skipBytes(). Skipping bytes |
| * still requires reading in the bytes we skip in order to update the checksum. |
| * The reason we need to use an instance member instead of sharing a single |
| * static instance across threads is that multiple instances invoking skipBytes() |
| * concurrently on different threads can clobber the contents of a shared buffer, |
| * corrupting the checksum. See LUCENE-5583 for additional context. |
| */ |
| private byte[] skipBuffer; |
| |
| /** |
| * 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 + ")"); |
| } |
| skipByReading(skip); |
| } |
| |
| /** |
| * Skip over <code>numBytes</code> bytes. The contract on this method is that it should have the |
| * same behavior as reading the same number of bytes into a buffer and discarding its content. |
| * Negative values of <code>numBytes</code> are not supported. |
| */ |
| private void skipByReading(long numBytes) throws IOException { |
| if (skipBuffer == null) { |
| skipBuffer = new byte[SKIP_BUFFER_SIZE]; |
| } |
| assert skipBuffer.length == SKIP_BUFFER_SIZE; |
| for (long skipped = 0; skipped < numBytes; ) { |
| final int step = (int) Math.min(SKIP_BUFFER_SIZE, numBytes - skipped); |
| readBytes(skipBuffer, 0, step, false); |
| skipped += step; |
| } |
| } |
| } |