/* * 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.pdfbox.filter; import java.io.IOException; import java.io.InputStream; import java.io.OutputStream; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.apache.pdfbox.cos.COSDictionary; /** * This is a filter for the RunLength Decoder. * * From the PDF Reference * <pre> * The RunLengthDecode filter decodes data that has been encoded in a simple * byte-oriented format based on run length. The encoded data is a sequence of * runs, where each run consists of a length byte followed by 1 to 128 bytes of data. If * the length byte is in the range 0 to 127, the following length + 1 (1 to 128) bytes * are copied literally during decompression. If length is in the range 129 to 255, the * following single byte is to be copied 257 ? length (2 to 128) times during decompression. * A length value of 128 denotes EOD. * * The compression achieved by run-length encoding depends on the input data. In * the best case (all zeros), a compression of approximately 64:1 is achieved for long * files. The worst case (the hexadecimal sequence 00 alternating with FF) results in * an expansion of 127:128. * </pre> * * @author <a href="mailto:ben@benlitchfield.com">Ben Litchfield</a> * @version $Revision: 1.6 $ */ public class RunLengthDecodeFilter implements Filter { /** * Log instance. */ private static final Log log = LogFactory.getLog(RunLengthDecodeFilter.class); private static final int RUN_LENGTH_EOD = 128; /** * Constructor. */ public RunLengthDecodeFilter() { //default constructor } /** * {@inheritDoc} */ public void decode( InputStream compressedData, OutputStream result, COSDictionary options, int filterIndex ) throws IOException { int dupAmount = -1; byte[] buffer = new byte[128]; while( (dupAmount = compressedData.read()) != -1 && dupAmount != RUN_LENGTH_EOD ) { if( dupAmount <= 127 ) { int amountToCopy = dupAmount+1; int compressedRead = 0; while( amountToCopy > 0 ) { compressedRead = compressedData.read( buffer, 0, amountToCopy ); result.write( buffer, 0, compressedRead ); amountToCopy -= compressedRead; } } else { int dupByte = compressedData.read(); for( int i=0; i<257-dupAmount; i++ ) { result.write( dupByte ); } } } } /** * {@inheritDoc} */ public void encode( InputStream rawData, OutputStream result, COSDictionary options, int filterIndex ) throws IOException { log.warn( "RunLengthDecodeFilter.encode is not implemented yet, skipping this stream." ); } }