SslStream check data available

SslStream check data available

A while ago i wrote some basic Http webserver in vb.net. I tried to avoid
blocking IO, so basically i made one polling thread for all current
connections.
While True
For Each oNetworkstream In lstNetworkstream
If oNetworkstream.DataAvailable Then
'Read from stream
End If
Next
End While
So whenever a connection had some new data, i could read it, otherwise
immediately check the next connection.
Now i'm extending the webserver with https. Therefore, i used the .Net
SslStream Class. I would like to apply the same principle (one polling
thread to read all streams)
Since there is no .DataAvailable property, i tried width .Length > 0, but
this gives a NotSupportedException (This stream does not support seek
operations)
Dim oSslStream As New SslStream(oStream, False)
oSslStream.AuthenticateAsServer(moCertificateKeyPair)
MsgBox(oSslStream.Length)
So, how could i determine if a certain decrypted stream has data available
without blocking the thread?