DeflateStream not decompressing data (the first time)

So here's a strange one. I have this method to take a Base64-encoded deflated string and return the original data:

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());
            }
        }
    }
}

This returns an e开发者_如何学Gompty string unless I add a second call to 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 on ds have no effect.)

Why does the DeflateStream copy 0 bytes on the first call? I've also tried looping with Read(), but it also returns zero on the first call, then works on the second.

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());
        }
    }
}

This happens when the compressed bytes are incomplete (i.e., not all blocks are written out).

If I use your Base64Compress with the following Decompress method I will get an InvalidDataException with the message 'Unknown block type. Stream might be corrupted.'

Decompress

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());
  }
}

Note that everything works as expected when using the following Compress method

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();
  }
}

Update

Oops, foolish me... you cannot ToArray the memory stream until you dispose the DeflateStream (as flush is acutally not implemented (and Deflate/GZip compress blocks of data); the final block is only written on close/dispose.

Re-write compress as:

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());
  }
}