/**
   * A plan holds either an immediately-usable connection, or one that must be connected first.
   * These steps are split so callers can call [connectTcp] on a background thread if attempting
   * multiple plans concurrently.
   */
  interface Plan {
    val isReady: Boolean

    fun connectTcp(): ConnectResult

    fun connectTlsEtc(): ConnectResult

    fun handleSuccess(): RealConnection

    fun cancel()

    /**

      routes = routes,
      attempt = attempt,
      tunnelRequest = tunnelRequest,
      connectionSpecIndex = connectionSpecIndex,
      isTlsFallback = isTlsFallback,
    )

  override fun connectTcp(): ConnectResult {
    check(rawSocket == null) { "TCP already connected" }

    var success = false

    // Tell the call about the connecting call so async cancels work.
    user.addPlanToCancel(this)