gistfile1.cs

return input.Do(a => a.Act("Body", ((HttpWebResponse) WebRequest.Create(a.GetValue<String>()).GetResponse())
    .If(
        r => (Int32) r.StatusCode < 300,
        r => new Byte[r.ContentLength].Apply(b => r.GetResponseStream().Dispose(s => s.Read(b, 0, b.Length))),
        r => new Byte[0]
    ))
);