# FlateFilter.java

    /*
     * 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 java.util.zip.DataFormatException;
    import java.util.zip.Deflater;
    import java.util.zip.DeflaterOutputStream;
    import java.util.zip.Inflater;
    import org.apache.commons.logging.Log;
    import org.apache.commons.logging.LogFactory;
    import org.apache.pdfbox.cos.COSDictionary;
    import org.apache.pdfbox.io.IOUtils;

    /**
     * Decompresses data encoded using the zlib/deflate compression method,
     * reproducing the original text or binary data.
     *
     * @author Ben Litchfield
     * @author Marcel Kammer
     */
    final class FlateFilter extends Filter
    {
        private static final Log LOG = LogFactory.getLog(FlateFilter.class);

        @Override
        public DecodeResult decode(InputStream encoded, OutputStream decoded,
                                             COSDictionary parameters, int index) throws IOException
        {
            final COSDictionary decodeParams = getDecodeParams(parameters, index);

            try
            {
                decompress(encoded, Predictor.wrapPredictor(decoded, decodeParams));
            }
            catch (DataFormatException e)
            {
                // if the stream is corrupt a DataFormatException may occur
                LOG.error("FlateFilter: stop reading corrupt stream due to a DataFormatException");

                // re-throw the exception
                throw new IOException(e);
            }
            return new DecodeResult(parameters);
        }

        // Use Inflater instead of InflateInputStream to avoid an EOFException due to a probably
        // missing Z_STREAM_END, see PDFBOX-1232 for details
        private void decompress(InputStream in, OutputStream out) throws IOException, DataFormatException
        {
            byte[] buf = new byte[2048];
            // skip zlib header
            in.read();
            in.read();
            int read = in.read(buf);
            if (read > 0)
            {
                // use nowrap mode to bypass zlib-header and checksum to avoid a DataFormatException
                Inflater inflater = new Inflater(true);
                inflater.setInput(buf,0,read);
                byte[] res = new byte[1024];
                boolean dataWritten = false;
                try
                {
                    while (true)
                    {
                        int resRead = 0;
                        try
                        {
                            resRead = inflater.inflate(res);
                        }
                        catch(DataFormatException exception)
                        {
                            if (dataWritten)
                            {
                                // some data could be read -> don't throw an exception
                                LOG.warn("FlateFilter: premature end of stream due to a DataFormatException");
                                break;
                            }
                            else
                            {
                                // nothing could be read -> re-throw exception
                                throw exception;
                            }
                        }
                        if (resRead != 0)
                        {
                            out.write(res,0,resRead);
                            dataWritten = true;
                            continue;
                        }
                        if (inflater.finished() || inflater.needsDictionary() || in.available() == 0)
                        {
                            break;
                        }
                        read = in.read(buf);
                        inflater.setInput(buf,0,read);
                    }
                }
                finally
                {
                    inflater.end();
                }
            }
            out.flush();
        }

        @Override
        protected void encode(InputStream input, OutputStream encoded, COSDictionary parameters)
                throws IOException
        {
            int compressionLevel = getCompressionLevel();
            Deflater deflater = new Deflater(compressionLevel);
            try (DeflaterOutputStream out = new DeflaterOutputStream(encoded,deflater))
            {
                IOUtils.copy(input, out);
            }
            encoded.flush();
            deflater.end();
        }
    }