DeflateStream不解压缩数据(第一次)

Question

所以这是一个奇怪的.我有这个方法来采取Base64编码的缩小字符串并返回原始数据:

public static string Base64Decompress(string base64data)
{
    byte[] b = Convert.FromBase64String(base64data);
    using (var orig = new MemoryStream(b))
    {
        using (var inflate = new MemoryStream())
        {
            using (var ds = new DeflateStream(orig, CompressionMode.Decompress))
            {
                ds.CopyTo(inflate);
                return Encoding.ASCII.GetString(inflate.ToArray());
            }
        }
    }
}

这将返回一个空字符串,除非我添加第二个调用ds.CopyTo(inflate).(WTF？)

   ...
            using (var ds = new DeflateStream(orig, CompressionMode.Decompress))
            {
                ds.CopyTo(inflate);
                ds.CopyTo(inflate);
                return Encoding.ASCII.GetString(inflate.ToArray());
            }
   ...

(Flush/ Close/ Dispose上ds没有任何效果.)

为什么DeflateStream第一次调用时复制0个字节？我也尝试过循环Read(),但它在第一次调用时也返回零,然后在第二次调用时工作.

---

更新:这是我用来压缩数据的方法.

public static string Base64Compress(string data, Encoding enc)
{
    using (var ms = new MemoryStream())
    {
        using (var ds = new DeflateStream(ms, CompressionMode.Compress))
        {
            byte[] b = enc.GetBytes(data);
            ds.Write(b, 0, b.Length);
            ds.Flush();
            return Convert.ToBase64String(ms.ToArray());
        }
    }
}

Answer 1

当压缩字节不完整时(即,并非所有块都被写出),就会发生这种情况.

如果我使用带有以下Decompress方法的Base64Compress,我将得到一个带有"Unknown block type"消息的InvalidDataException.流可能已损坏.

解压缩

public static string Decompress(Byte[] bytes)
{
  using (var uncompressed = new MemoryStream())
  using (var compressed = new MemoryStream(bytes))
  using (var ds = new DeflateStream(compressed, CompressionMode.Decompress))
  {
    ds.CopyTo(uncompressed);
    return Encoding.ASCII.GetString(uncompressed.ToArray());
  }
}

请注意,使用以下Compress方法时,一切都按预期工作

public Byte[] Compress(Byte[] bytes)
{
  using (var memoryStream = new MemoryStream())
  {
    using (var deflateStream = new DeflateStream(memoryStream, CompressionMode.Compress))
      deflateStream.Write(bytes, 0, bytes.Length);

    return memoryStream.ToArray();
  }
}

更新

哎呀,愚蠢的我......在处理DeflateStream之前你不能ToArray内存流(因为实际上没有实现flush(和Deflate/GZip压缩数据块);最后一个块只写在close/dispose上.

重写压缩为:

public static string Base64Compress(string data, Encoding enc)
{
  using (var ms = new MemoryStream())
  {
    using (var ds = new DeflateStream(ms, CompressionMode.Compress))
    {
      byte[] b = enc.GetBytes(data);
      ds.Write(b, 0, b.Length);
    }

    return Convert.ToBase64String(ms.ToArray());
  }
}