CMSCompressedDataParser.cs

using System.IO;

using Org.BouncyCastle.Asn1;
using Org.BouncyCastle.Asn1.Cms;
using Org.BouncyCastle.Utilities.IO.Compression;

namespace Org.BouncyCastle.Cms
{
    /**
     * Class for reading a CMS Compressed Data stream.
     * <pre>
     *     CMSCompressedDataParser cp = new CMSCompressedDataParser(inputStream);
     *
     *     process(cp.GetContent().GetContentStream());
     * </pre>
     *  Note: this class does not introduce buffering - if you are processing large files you should create
     *  the parser with:
     *  <pre>
     *      CMSCompressedDataParser     ep = new CMSCompressedDataParser(new BufferedStream(inputStream, bufSize));
     *  </pre>
     *  where bufSize is a suitably large buffer size.
     * <p>
     * <b>Stream handling note:</b>
     * <ul>
     *   <li>The constructor reads only the outer CMS ContentInfo header from the
     *       supplied Stream. The compressed content is drained lazily by the
     *       caller via {@link #GetContent()} and reading from the
     *       returned {@link CmsTypedStream}.</li>
     *   <li>The supplied Stream is <b>not closed automatically</b>. Call
     *       {@link #Close()} on this parser (inherited from
     *       {@link CmsContentInfoParser}) to close the underlying Stream, or close
     *       it yourself.</li>
     * </ul>
     * </p>
     */
    public class CmsCompressedDataParser
        : CmsContentInfoParser
    {
        public CmsCompressedDataParser(byte[] compressedData)
            : this(new MemoryStream(compressedData, false))
        {
        }

        public CmsCompressedDataParser(Stream compressedData)
            : base(compressedData)
        {
        }

        public CmsTypedStream GetContent()
        {
            try
            {
                CompressedDataParser comData = new CompressedDataParser(
                    (Asn1SequenceParser)this.contentInfo.GetContent(Asn1Tags.Sequence));
                ContentInfoParser content = comData.GetEncapContentInfo();

                Asn1OctetStringParser bytes = (Asn1OctetStringParser)content.GetContent(Asn1Tags.OctetString);
                Stream zIn = ZLib.DecompressInput(bytes.GetOctetStream());

                return new CmsTypedStream(content.ContentType, zIn);
            }
            catch (IOException e)
            {
                throw new CmsException("IOException reading compressed content.", e);
            }
        }
    }
}