internal val streams = mutableMapOf<Int, Http2Stream>()
  internal val connectionName: String = builder.connectionName
  internal var lastGoodStreamId = 0

  /** http://tools.ietf.org/html/draft-ietf-httpbis-http2-17#section-5.1.1 */
  internal var nextStreamId = if (builder.client) 3 else 2

  private var isShutdown = false

  /** For scheduling everything asynchronous. */

     * the server responds with `HTTP/1.0`, that will be exposed by [Response.protocol].
     *
     * [alpn]: http://tools.ietf.org/html/draft-ietf-tls-applayerprotoneg
     * [rfc_2616]: http://www.w3.org/Protocols/rfc2616/rfc2616.html
     * [rfc_7540]: https://tools.ietf.org/html/rfc7540
     * [rfc_7540_34]: https://tools.ietf.org/html/rfc7540#section-3.4

 * https, etc.) of the URL, not the protocol (http/1.1, spdy/3.1, etc.). OkHttp uses the word
 * *protocol* to identify how HTTP messages are framed.
 *
 * [ietf_alpn]: http://tools.ietf.org/html/draft-ietf-tls-applayerprotoneg
 */
enum class Protocol(private val protocol: String) {
  /**
   * An obsolete plaintext framing that does not use persistent sockets by default.
   */
  HTTP_1_0("http/1.0"),

  /**

 * > of this section.  The DNS API server defines the URI used by the
 * > request through the use of a URI Template.
 *
 * [doh_spec]: https://tools.ietf.org/html/draft-ietf-doh-dns-over-https-13
 */
class DnsOverHttps internal constructor(
  @get:JvmName("client") val client: OkHttpClient,
  @get:JvmName("url") val url: HttpUrl,
  @get:JvmName("includeIPv6") val includeIPv6: Boolean,