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#region PDFsharp - A .NET library for processing PDF
//
// Authors:
// Stefan Lange (mailto:Stefan.Lange@pdfsharp.com)
//
// Copyright (c) 2005-2008 empira Software GmbH, Cologne (Germany)
//
// http://www.pdfsharp.com
// http://sourceforge.net/projects/pdfsharp
//
// Permission is hereby granted, free of charge, to any person obtaining a
// copy of this software and associated documentation files (the "Software"),
// to deal in the Software without restriction, including without limitation
// the rights to use, copy, modify, merge, publish, distribute, sublicense,
// and/or sell copies of the Software, and to permit persons to whom the
// Software is furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included
// in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
// THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.
#endregion
using System;
using System.Diagnostics;
using System.Text;
using System.IO;
#if NET_ZIP
using System.IO.Compression;
#else
using PdfSharp.SharpZipLib.Zip.Compression;
using PdfSharp.SharpZipLib.Zip.Compression.Streams;
#endif
namespace PdfSharp.Pdf.Filters
{
/// <summary>
/// Implements the FlateDecode filter by wrapping SharpZipLib.
/// </summary>
public class FlateDecode : Filter
{
/// <summary>
/// Encodes the specified data.
/// </summary>
public override byte[] Encode(byte[] data)
{
MemoryStream ms = new MemoryStream();
// DeflateStream/GZipStream does not work immediately and I have not the leisure to work it out.
// So I keep on using SharpZipLib even with .NET 2.0.
#if NET_ZIP
// See http://connect.microsoft.com/VisualStudio/feedback/ViewFeedback.aspx?FeedbackID=97064
//
// Excerpt from the RFC 1950 specs for first byte:
//
// CMF (Compression Method and flags)
// This byte is divided into a 4-bit compression method and a 4-
// bit information field depending on the compression method.
//
// bits 0 to 3 CM Compression method
// bits 4 to 7 CINFO Compression info
//
// CM (Compression method)
// This identifies the compression method used in the file. CM = 8
// denotes the "deflate" compression method with a window size up
// to 32K. This is the method used by gzip and PNG (see
// references [1] and [2] in Chapter 3, below, for the reference
// documents). CM = 15 is reserved. It might be used in a future
// version of this specification to indicate the presence of an
// extra field before the compressed data.
//
// CINFO (Compression info)
// For CM = 8, CINFO is the base-2 logarithm of the LZ77 window
// size, minus eight (CINFO=7 indicates a 32K window size). Values
// of CINFO above 7 are not allowed in this version of the
// specification. CINFO is not defined in this specification for
// CM not equal to 8.
ms.WriteByte(0x78);
// Excerpt from the RFC 1950 specs for second byte:
//
// FLG (FLaGs)
// This flag byte is divided as follows:
//
// bits 0 to 4 FCHECK (check bits for CMF and FLG)
// bit 5 FDICT (preset dictionary)
// bits 6 to 7 FLEVEL (compression level)
//
// The FCHECK value must be such that CMF and FLG, when viewed as
// a 16-bit unsigned integer stored in MSB order (CMF*256 + FLG),
// is a multiple of 31.
//
// FDICT (Preset dictionary)
// If FDICT is set, a DICT dictionary identifier is present
// immediately after the FLG byte. The dictionary is a sequence of
// bytes which are initially fed to the compressor without
// producing any compressed output. DICT is the Adler-32 checksum
// of this sequence of bytes (see the definition of ADLER32
// below). The decompressor can use this identifier to determine
// which dictionary has been used by the compressor.
//
// FLEVEL (Compression level)
// These flags are available for use by specific compression
// methods. The "deflate" method (CM = 8) sets these flags as
// follows:
//
// 0 - compressor used fastest algorithm
// 1 - compressor used fast algorithm
// 2 - compressor used default algorithm
// 3 - compressor used maximum compression, slowest algorithm
//
// The information in FLEVEL is not needed for decompression; it
// is there to indicate if recompression might be worthwhile.
ms.WriteByte(0x49);
DeflateStream zip = new DeflateStream(ms, CompressionMode.Compress, true);
zip.Write(data, 0, data.Length);
zip.Close();
#else
DeflaterOutputStream zip = new DeflaterOutputStream(ms, new Deflater(Deflater.DEFAULT_COMPRESSION, false));
zip.Write(data, 0, data.Length);
zip.Finish();
#endif
ms.Capacity = (int)ms.Length;
return ms.GetBuffer();
}
/// <summary>
/// Decodes the specified data.
/// </summary>
public override byte[] Decode(byte[] data, FilterParms parms)
{
MemoryStream msInput = new MemoryStream(data);
MemoryStream msOutput = new MemoryStream();
#if NET_ZIP
// See http://connect.microsoft.com/VisualStudio/feedback/ViewFeedback.aspx?FeedbackID=97064
// It seems to work when skipping the first two bytes.
byte header; // 0x30 0x59
header = (byte)msInput.ReadByte();
//Debug.Assert(header == 48);
header = (byte)msInput.ReadByte();
//Debug.Assert(header == 89);
DeflateStream zip = new DeflateStream(msInput, CompressionMode.Decompress, true);
int cbRead;
byte[] abResult = new byte[1024];
do
{
cbRead = zip.Read(abResult, 0, abResult.Length);
if (cbRead > 0)
msOutput.Write(abResult, 0, cbRead);
}
while (cbRead > 0);
zip.Close();
msOutput.Flush();
if (msOutput.Length >= 0)
{
msOutput.Capacity = (int)msOutput.Length;
return msOutput.GetBuffer();
}
return null;
#else
InflaterInputStream iis = new InflaterInputStream(msInput, new Inflater(false));
int cbRead;
byte[] abResult = new byte[32768];
do
{
cbRead = iis.Read(abResult, 0, abResult.Length);
if (cbRead > 0)
msOutput.Write(abResult, 0, cbRead);
}
while (cbRead > 0);
iis.Close();
msOutput.Flush();
if (msOutput.Length >= 0)
{
msOutput.Capacity = (int)msOutput.Length;
return msOutput.GetBuffer();
}
return null;
#endif
}
}
}
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