93 lines
3.1 KiB
Java
93 lines
3.1 KiB
Java
/* ====================================================================
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Licensed to the Apache Software Foundation (ASF) under one or more
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contributor license agreements. See the NOTICE file distributed with
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this work for additional information regarding copyright ownership.
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The ASF licenses this file to You under the Apache License, Version 2.0
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(the "License"); you may not use this file except in compliance with
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the License. You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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==================================================================== */
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package org.apache.poi.hdgf.streams;
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import java.io.ByteArrayInputStream;
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import java.io.IOException;
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import org.apache.poi.hdgf.LZW4HDGF;
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/**
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* A StreamStore where the data on-disk is compressed,
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* using the crazy Visio LZW
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*/
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public class CompressedStreamStore extends StreamStore {
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/** The raw, compressed contents */
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private byte[] compressedContents;
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/**
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* We're not sure what this is, but it comes before the
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* real contents in the de-compressed data
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*/
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private byte[] blockHeader = new byte[4];
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private boolean blockHeaderInContents = false;
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protected byte[] _getCompressedContents() { return compressedContents; }
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protected byte[] _getBlockHeader() { return blockHeader; }
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/**
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* Creates a new compressed StreamStore, which will handle
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* the decompression.
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*/
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protected CompressedStreamStore(byte[] data, int offset, int length) throws IOException {
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this(decompress(data,offset,length));
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compressedContents = new byte[length];
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System.arraycopy(data, offset, compressedContents, 0, length);
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}
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/**
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* Handles passing the de-compressed data onto our superclass.
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*/
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private CompressedStreamStore(byte[][] decompressedData) {
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super(decompressedData[1], 0, decompressedData[1].length);
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blockHeader = decompressedData[0];
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}
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/**
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* Some kinds of streams expect their 4 byte header to be
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* on the front of the contents.
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* They can call this to have it sorted.
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*/
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protected void copyBlockHeaderToContents() {
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if(blockHeaderInContents) return;
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prependContentsWith(blockHeader);
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blockHeaderInContents = true;
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}
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/**
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* Decompresses the given data, returning it as header + contents
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*/
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public static byte[][] decompress(byte[] data, int offset, int length) throws IOException {
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ByteArrayInputStream bais = new ByteArrayInputStream(data, offset, length);
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// Decompress
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LZW4HDGF lzw = new LZW4HDGF();
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byte[] decompressed = lzw.decode(bais);
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// Split into header and contents
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byte[][] ret = new byte[2][];
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ret[0] = new byte[4];
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ret[1] = new byte[decompressed.length - 4];
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System.arraycopy(decompressed, 0, ret[0], 0, 4);
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System.arraycopy(decompressed, 4, ret[1], 0, ret[1].length);
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// All done
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return ret;
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}
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} |