* @param host an IP address or hostname.
     * @param port the IP port associated with the service.
     * @param maxAge time in seconds that this alternative is considered fresh.
     */
    fun alternateService(
      streamId: Int,
      origin: String,
      protocol: ByteString,
      host: String,
      port: Int,
      maxAge: Long,
    )
  }

  companion object {

      streamId: Int,
      promisedStreamId: Int,
      requestHeaders: List<Header>,
    ) {
      pushRequestLater(promisedStreamId, requestHeaders)
    }

    override fun alternateService(
      streamId: Int,
      origin: String,
      protocol: ByteString,
      host: String,
      port: Int,
      maxAge: Long,
    ) {
      // TODO: register alternate service.
    }
  }