export function bind_sendPacketStream(wstream) ::
  const pkt_hdr_1 = Buffer.from @# 0
  const pkt_hdr_3 = Buffer.from @# 254, 0, 0
  const pkt_hdr_5 = Buffer.from @# 255, 0, 0, 0, 0

  let p_drain = null, on_drain

  ::
    let p = new Promise @ resolve => ::
      wstream.on @ 'drain', _drained
      wstream.once @ 'error', shutdown
      wstream.once @ 'close', shutdown

      function shutdown() ::
        if null !== wstream ::
          wstream.off @ 'drain', _drained
          wstream.end()
          wstream = null
          resolve()

    return @[] send_packed, p

  function send_packed(d_pkt) ::
    if null === wstream ::
      // blackhole extra packets
      return Promise.resolve(false)

    d_pkt = Buffer.from(d_pkt)
    let len = d_pkt.byteLength

    let pkt_hdr
    if len < 254 ::
      ; (pkt_hdr = pkt_hdr_1).writeUInt8 @ len, 0
    else if len < 65536 ::
      ; (pkt_hdr = pkt_hdr_3).writeUInt16BE @ len, 1
    else ::
      ; (pkt_hdr = pkt_hdr_5).writeUInt32BE @ len, 1

    let s_pkt = Buffer.concat @# pkt_hdr, d_pkt
    if wstream.write(s_pkt) ::
      return true // sent immediate, no backpressure promise
    // backpressure as promise for next drain event
    return next_drain()

  function next_drain() ::
    if null === p_drain ::
      p_drain = new Promise @
        resolve => :: on_drain = resolve
    return p_drain

  function _drained() ::
    p_drain = null
    if null !== on_drain ::
      on_drain(true)
      on_drain = null