[原]使用SevenZipSharp压缩/解压7z格式

7z格式采用的LZMA算法，号称具有现今最高压缩率。笔者在nuget上搜索7z，在搜索结果中最终选择了SevenZipSharp来进行压缩/解压。不得不说，SevenZipSharp的API设计得非常方便。

压缩调用：

using (FileStream ostream = new FileStream(outputpath, FileMode.Create, FileAccess.Write))
{
    using (FileStream istream = new FileStream(inputpath, FileMode.Open, FileAccess.Read))
    {
        SevenZipCompressor compressor = new SevenZipCompressor();
        // 这里可以输入多个文件名/流对
        Dictionary<string, Stream> dict = new Dictionary<string, Stream> { { inputpath, istream } };
        compressor.CompressStreamDictionary(dict, ostream);
    }
}

解压调用：

using (FileStream istream = new FileStream(inputpath, FileMode.Open, FileAccess.Read))
{
    SevenZip.SevenZipExtractor extractor = new SevenZip.SevenZipExtractor(istream);
    extractor.ExtractArchive(outputpath);    // 全部解压到指定目录
    using (FileStream ostream = new FileStream(outputpath, FileMode.Create, FileAccess.Write))
    {
        extractor.ExtractFile(0, ostream);        // 流式解压指定文件
    }
}

顺便附上zlib的压缩/解压(使用zlib.net库)：

// 压缩
static void Compress(string inputpath, string outputpath)
{
    using (FileStream ostream = new FileStream(outputpath, FileMode.Create, FileAccess.Write))
    {
        using (FileStream istream = new FileStream(inputpath, FileMode.Open, FileAccess.Read))
        {
            using (ZOutputStream zstream = new ZOutputStream(ostream, zlibConst.Z_BEST_COMPRESSION))
            {
                CopyStream(istream, zstream);
            }
        }
    }
}

// 解压
static void Decompress(string inputpath, string outputpath)
{
    using (FileStream ostream = new FileStream(outputpath, FileMode.Create, FileAccess.Write))
    {
        using (FileStream istream = new FileStream(inputpath, FileMode.Open, FileAccess.Read))
        {
            using (ZOutputStream zstream = new ZOutputStream(ostream))
            {
                CopyStream(istream, zstream);
            }
        }
    }
}

static void CopyStream(Stream input, Stream output)
{
    byte[] buffer = new byte[2000];
    int len;
    while ((len = input.Read(buffer, 0, 2000)) > 0)
    {
        output.Write(buffer, 0, len);
    }
    output.Flush();
}