HTTP Response GZip Compression

Question

I have a Proxy which handles HTTP Requests.

Now when I get a GZipped HTTP Response, I'm decompressing it like :

MemoryStream ms = new MemoryStream();

if (response.ContentLength > 0)
  buffer = new Byte[response.ContentLength];
else
  buffer = new Byte[BUFFER_SIZE];

int bytesRead;
while ((bytesRead = responseStream.Read(buffer, 0, buffer.Length)) > 0)
{
  ms.Write(buffer, 0, bytesRead);
}

string resp = "";
if (response.ContentEncoding == "gzip")
  resp = Utilities.GZip.Unzip(ms.ToArray());
else
  resp = Encoding.UTF8.GetString(ms.ToArray());

Where Utilities.GZip.Unzip does:

using (var msi = new MemoryStream(bytes))
using (var mso = new MemoryStream())
{
  using (var gs = new GZipStream(msi, CompressionMode.Decompress))
  {
    CopyTo(gs, mso);
  }
  return Encoding.UTF8.GetString(mso.ToArray());
}

So far everything's fine, I can read the HTML.

Now I have to Write the Response back to the Client who requested it.

Like this:

byte[] outByte;
if (response.ContentEncoding == "gzip")
  outByte = Utilities.GZip.Zip(resp);
else
  outByte = Encoding.UTF8.GetBytes(resp);
outStream.Write(outByte, 0, outByte.Length);

Where Utilities.GZip.Zip does:

var bytes = Encoding.UTF8.GetBytes(str);
using (var msi = new MemoryStream(bytes))
using (var mso = new MemoryStream())
{
  using (var gs = new GZipStream(mso, CompressionMode.Compress))
  {
    CopyTo(msi, gs);
  }
  return mso.ToArray();
}

Now it's a really strange behaviour, the response byte-Array has a Length of 16990 (zipped), but my own zipped byte-Array has a Length of 19379.

The client get's a response, but it's cutted off.

Any suggestions?

EDIT:

For your information, as I send the original MemoryStream unchanged to the Client everythings fine!