Some sw
           
    use sw = new StreamWriter(fileName)
    let! response = Http.InnerRequest(url, true, ?headers=headers, ?query=query, ?meth=meth, ?body=body, ?cookies=cookies, ?cookieContainer=cookieContainer, ?certificate=certificate, ?streamWriter=Some sw)
           
    /// Read the contents of a stream asynchronously and return it as a string
      static let asyncReadToEnd (stream:Stream) isText streamWriter = async {
        // Allocate 4kb buffer for downloading dat
        let buffer = Array.zeroCreate (4 * 1024)
        use output =
            match streamWriter with
            | Some (sw) -> sw
            | None -> new MemoryStream()
        let reading = ref true
        ....
     
      static member private InnerRequest(url:string, forceText, ?query, ?headers, ?meth, ?body, ?cookies, ?cookieContainer, ?certificate, ?streamWriter) = async {
        ....
        return! Http.augmentWebExceptionsWithDetails <| fun () -> async {
          use! resp = Async.FromBeginEnd(req.BeginGetResponse, req.EndGetResponse)
          use stream = resp.GetResponseStream()
          let! respBody = asyncReadToEnd stream (forceText || (isText resp.ContentType)) streamWriter
          let cookies = Map.ofList [ for cookie in cookieContainer.GetCookies uri |> Seq.cast<Cookie> -> cookie.Name, cookie.Value ]  
          let headers = Map.ofList [ for header in resp.Headers.AllKeys -> header, resp.Headers.[header] ]
          let statusCode =
            match resp with
            | :? HttpWebResponse as resp -> int resp.StatusCode
            | _ -> 0
          return { Body = respBody
                   Headers = headers
                   ResponseUrl = resp.ResponseUri.OriginalString
                   Cookies = cookies
                   StatusCode = statusCode } }
      }
     
      static member AsyncRequestFile(url, (fileName:string), ?query, ?headers, ?meth, ?body, ?cookies, ?cookieContainer, ?certificate) = async {
        use sw = new StreamWriter(fileName)
        let! response = Http.InnerRequest(url, true, ?headers=headers, ?query=query, ?meth=meth, ?body=body, ?cookies=cookies, ?cookieContainer=cookieContainer, ?certificate=certificate, ?streamWriter=Some sw)
        return
            match response.Body with
            | ResponseBody.Text text -> text
            | ResponseBody.Binary binary -> failwithf "Expecting text, but got a binary response (%d bytes)" binary.Length
      }
           
    use output =
            match streamWriter with
            | Some (sw) -> sw
            | None -> new MemoryStream()