# COSInputStream.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.cos;

    import java.io.ByteArrayInputStream;
    import java.io.ByteArrayOutputStream;
    import java.io.FilterInputStream;
    import java.io.IOException;
    import java.io.InputStream;
    import java.util.ArrayList;
    import java.util.Collections;
    import java.util.HashSet;
    import java.util.List;
    import java.util.Set;

    import org.apache.pdfbox.filter.DecodeOptions;
    import org.apache.pdfbox.filter.DecodeResult;
    import org.apache.pdfbox.filter.Filter;

    /**
     * An InputStream which reads from an encoded COS stream.
     *
     * @author John Hewson
     */
    public final class COSInputStream extends FilterInputStream
    {
        /**
         * Creates a new COSInputStream from an encoded input stream.
         *
         * @param filters Filters to be applied.
         * @param parameters Filter parameters.
         * @param in Encoded input stream.
         * @return Decoded stream.
         * @throws IOException If the stream could not be read.
         */
        static COSInputStream create(List<Filter> filters, COSDictionary parameters, InputStream in)
                throws IOException
        {
            return create(filters, parameters, in, DecodeOptions.DEFAULT);
        }

        /**
         * Creates a new COSInputStream from an encoded input stream.
         *
         * @param filters Filters to be applied.
         * @param parameters Filter parameters.
         * @param in Encoded input stream.
         * @param options decode options for the encoded stream
         * @return Decoded stream.
         * @throws IOException If the stream could not be read.
         */
        static COSInputStream create(List<Filter> filters, COSDictionary parameters, InputStream in,
                DecodeOptions options) throws IOException
        {
            if (filters.isEmpty())
            {
                return new COSInputStream(in, Collections.<DecodeResult>emptyList());
            }

            List<DecodeResult> results = new ArrayList<>(filters.size());
            InputStream input = in;
            if (filters.size() > 1)
            {
                Set<Filter> filterSet = new HashSet<>(filters);
                if (filterSet.size() != filters.size())
                {
                    throw new IOException("Duplicate");
                }
            }
            ByteArrayOutputStream output = new ByteArrayOutputStream();
            // apply filters
            for (int i = 0; i < filters.size(); i++)
            {
                output.reset();
                results.add(filters.get(i).decode(input, output, parameters, i, options));
                input = new ByteArrayInputStream(output.toByteArray());
            }
            return new COSInputStream(input, results);
        }

        private final List<DecodeResult> decodeResults;

        /**
         * Constructor.
         *
         * @param input decoded stream
         * @param decodeResults results of decoding
         */
        private COSInputStream(InputStream input, List<DecodeResult> decodeResults)
        {
            super(input);
            this.decodeResults = decodeResults;
        }

        /**
         * Returns the result of the last filter, for use by repair mechanisms.
         */
        public DecodeResult getDecodeResult()
        {
            if (decodeResults.isEmpty())
            {
                return DecodeResult.createDefault();
            }
            else
            {
                return decodeResults.get(decodeResults.size() - 1);
            }
        }
    }