let listenWs onMessage port action ct = async {
  let address = sprintf "ws://localhost:%i/%s" port action

  use ws = new ClientWebSocket()

  //set big buffer, otherwise messages are split
  ws.Options.SetBuffer(65535,65535)

  do! ws.ConnectAsync(System.Uri(address), ct) |> Async.AwaitTask

  let receivedBytes = ArraySegment(Array.init 10000000 (fun _ -> 0uy))

  let rec receive messageHead = async {
      let! result = ws.ReceiveAsync(receivedBytes, ct) |> Async.AwaitTask
      let messagePart = System.Text.Encoding.UTF8.GetString(receivedBytes.Array, 0, result.Count)
      let nextMessageHead =
        match result.EndOfMessage with
        | true ->
            let message = messageHead + messagePart
            onMessage message
        | false -> ""
      return! receive nextMessageHead
      }

  return! receive ""
  }