如何使用7z SDK压缩和解压文件

Question

根据此链接 How do I create 7-Zip archives with . NET？，WOPR告诉我们如何使用7z SDK（http://www.7-zip.org/sdk.html ）

using SevenZip.Compression.LZMA;
private static void CompressFileLZMA(string inFile, string outFile)
{
   SevenZip.Compression.LZMA.Encoder coder = new SevenZip.Compression.LZMA.Encoder();

   using (FileStream input = new FileStream(inFile, FileMode.Open))
   {
      using (FileStream output = new FileStream(outFile, FileMode.Create))
      {
          coder.Code(input, output, -1, -1, null);
          output.Flush();
      }
   }
}

但是如何解压呢？

我尝试：

private static void DecompressFileLZMA(string inFile, string outFile)
        {
            SevenZip.Compression.LZMA.Decoder coder = new SevenZip.Compression.LZMA.Decoder();
            using (FileStream input = new FileStream(inFile, FileMode.Open))
            {
                using (FileStream output = new FileStream(outFile, FileMode.Create))
                {
                    coder.Code(input, output, input.Length, -1, null);
                    output.Flush();
                }
            }
        }

但没有成功。

你有一个有效的例子吗？

谢谢

PS: 根据其他代码 http://www.koders.com/csharp/fid43E85EE5AE7BB255C69D18ECC3288285AD67A4A4.aspx?s=zip+encoder#L5 ，看来解码器需要一个 header，开头的一个字典文件工作。 Koders 生成的此文件不是 7z 存档。

   public static void Decompress(Stream inStream, Stream outStream)
    {
        byte[] properties = new byte[5];
        inStream.Read(properties, 0, 5);
        SevenZip.Compression.LZMA.Decoder decoder = new SevenZip.Compression.LZMA.Decoder();
        decoder.SetDecoderProperties(properties);
        long outSize = 0;
        for (int i = 0; i < 8; i++)
        {
            int v = inStream.ReadByte();
            outSize |= ((long)(byte)v) << (8 * i);
        }
        long compressedSize = inStream.Length - inStream.Position;
        decoder.Code(inStream, outStream, compressedSize, outSize, null);
    }

outSize 的计算方式与其 Compress 方法相同。但是如何计算输出大小呢？

Answer 1

这个问题有点老了，但谷歌未能提供令人满意的答案，所以这适合像我这样仍在寻找答案的人。如果您查看 SDK 的 LMZAAlone 文件夹，就会发现压缩和解压缩文件的代码。以它为例，您似乎需要写入和读取编码器属性并将文件大小解压缩到输出文件：

private static void CompressFileLZMA(string inFile, string outFile)
    {
        SevenZip.Compression.LZMA.Encoder coder = new SevenZip.Compression.LZMA.Encoder();
        FileStream input = new FileStream(inFile, FileMode.Open);
        FileStream output = new FileStream(outFile, FileMode.Create);

        // Write the encoder properties
        coder.WriteCoderProperties(output);

        // Write the decompressed file size.
        output.Write(BitConverter.GetBytes(input.Length), 0, 8);

        // Encode the file.
        coder.Code(input, output, input.Length, -1, null);
        output.Flush();
        output.Close();
    }

    private static void DecompressFileLZMA(string inFile, string outFile)
    {
        SevenZip.Compression.LZMA.Decoder coder = new SevenZip.Compression.LZMA.Decoder();
        FileStream input = new FileStream(inFile, FileMode.Open);
        FileStream output = new FileStream(outFile, FileMode.Create);

        // Read the decoder properties
        byte[] properties = new byte[5];
        input.Read(properties, 0, 5);

        // Read in the decompress file size.
        byte [] fileLengthBytes = new byte[8];
        input.Read(fileLengthBytes, 0, 8);
        long fileLength = BitConverter.ToInt64(fileLengthBytes, 0);

        coder.SetDecoderProperties(properties);
        coder.Code(input, output, input.Length, fileLength, null);
        output.Flush();
        output.Close();
    }

请注意，以这种方式创建的文件也可以由 7zip 程序提取，但不会保留其文件名或任何内容其他元数据。

Answer 2

我需要 LZMA 压缩来通过网络发送图像，不确定它是最好的选择，但至少它在我的生态系统中有效！因此，这里有一些可以立即用于此目的的东西。

using System;
using System.IO;
using SevenZip;

  public class LZMA{
    public static byte[] Compress(byte[] toCompress)
      {
        SevenZip.Compression.LZMA.Encoder coder = new SevenZip.Compression.LZMA.Encoder();

        using(MemoryStream input = new MemoryStream(toCompress))
        using(MemoryStream output = new MemoryStream()){

          coder.WriteCoderProperties(output);

          for (int i = 0; i < 8; i++) {
            output.WriteByte((byte)(input.Length >> (8 * i)));
          }

          coder.Code(input, output, -1, -1, null);
          return output.ToArray();
        }
      }

    public static byte[] Decompress(byte[] toDecompress)
    {
        SevenZip.Compression.LZMA.Decoder coder = new SevenZip.Compression.LZMA.Decoder();

        using(MemoryStream input = new MemoryStream(toDecompress))
        using(MemoryStream output = new MemoryStream()){

          // Read the decoder properties
          byte[] properties = new byte[5];
          input.Read(properties, 0, 5);


          // Read in the decompress file size.
          byte [] fileLengthBytes = new byte[8];
          input.Read(fileLengthBytes, 0, 8);
          long fileLength = BitConverter.ToInt64(fileLengthBytes, 0);

          coder.SetDecoderProperties(properties);
          coder.Code(input, output, input.Length, fileLength, null);

          return output.ToArray();
        }
    }
  }

Answer 3

我强烈推荐 Managed-lzma：
它将

文件信息和目录结构保存在文件编码。

Answer 4

类似于@Dominic Grenier 解决方案。解压缩器必须知道使用哪些属性来解压缩有效负载。您有责任对它们进行序列化/反序列化。

public static void 
Compress7Zip(this Stream input, Stream output) {
    var coder = new SevenZip.Compression.LZMA.Encoder();
    coder.WriteCoderProperties(output);
    output.WriteInt64(input.Length);
    coder.Code(input, output, -1, -1, null);
}

public static void 
Decompress7Zip(this Stream input, Stream output) {
    var coder = new SevenZip.Compression.LZMA.Decoder();
    var properties = new byte[5];
    input.Read(properties, 0, 5);
    var payloadLength = input.ReadInt64();
    coder.SetDecoderProperties(properties);
    coder.Code(input, output, input.Length, payloadLength, null);
}