*/
  public var protocols: List<Protocol> = immutableListOf(Protocol.HTTP_2, Protocol.HTTP_1_1)
    set(value) {
      val protocolList = value.toImmutableList()
      require(Protocol.H2_PRIOR_KNOWLEDGE !in protocolList || protocolList.size == 1) {
        "protocols containing h2_prior_knowledge cannot use other protocols: $protocolList"
      }

Kotlin does have properties and we take advantage of them in OkHttp.

 * **Address**: certificatePinner, connectionSpecs, dns, hostnameVerifier, protocols, proxy,
   proxyAuthenticator, proxySelector, socketFactory, sslSocketFactory, url
 * **Cache**: directory
 * **CacheControl**: immutable, maxAgeSeconds, maxStaleSeconds, minFreshSeconds, mustRevalidate,

        HTTP_1_0.protocol -> HTTP_1_0
        HTTP_1_1.protocol -> HTTP_1_1
        H2_PRIOR_KNOWLEDGE.protocol -> H2_PRIOR_KNOWLEDGE
        HTTP_2.protocol -> HTTP_2
        SPDY_3.protocol -> SPDY_3
        QUIC.protocol -> QUIC
        else -> {
          // Support HTTP3 draft like h3-29
          if (protocol.startsWith(HTTP_3.protocol)) HTTP_3 else throw IOException("Unexpected protocol: $protocol")
        }

   *
   * For cipher suites, at least one of the [required cipher suites][cipherSuites] must match the
   * socket's enabled cipher suites. If there are no required cipher suites the socket must have at
   * least one cipher suite enabled.
   *
   * For protocols, at least one of the [required protocols][tlsVersions] must match the socket's
   * enabled protocols.

      }
    }
  }

  private fun MockResponse.Builder.body(
    protocol: Protocol,
    body: String,
  ) = apply {
    when (protocol) {
      Protocol.HTTP_1_1 -> chunkedBody(body, 1024) // Force multiple chunks.
      else -> body(body)
    }
  }

  private fun enableProtocol(protocol: Protocol) {
    if (protocol == Protocol.HTTP_2) {
      enableTls()
      client =
        client

  private val eventRecorder = EventRecorder()
  private val bootstrapClient =
    OkHttpClient
      .Builder()
      .protocols(listOf(Protocol.HTTP_2, Protocol.HTTP_1_1))
      .eventListener(eventRecorder.eventListener)
      .build()

  @BeforeEach
  fun setUp() {
    server.protocols = bootstrapClient.protocols
    dns = buildLocalhost(bootstrapClient, false)
  }

  @Test
  fun getOne() {
    server.enqueue(

    dnsResults =
      listOf(
        localhostIpv4,
        localhostIpv6,
        TestUtil.UNREACHABLE_ADDRESS_IPV4.address,
      )
    serverIpv4.protocols = listOf(Protocol.H2_PRIOR_KNOWLEDGE)
    serverIpv6.protocols = listOf(Protocol.H2_PRIOR_KNOWLEDGE)

    // Yield the first IP address so the second IP address completes first.
    val firstConnectLatch = CountDownLatch(1)
    val socketFactory =

  fun configureTlsExtensions(
    sslSocket: SSLSocket,
    hostname: String?,
    protocols: List<Protocol>,
  )

  fun getSelectedProtocol(sslSocket: SSLSocket): String?

            sslSocketFactory(
              sslSocketFactory,
              handshakeCertificates.trustManager,
            )

            when (socketMode.protocol) {
              HTTP_2 -> protocols(listOf(HTTP_2, HTTP_1_1))
              HTTP_1_1 -> protocols(listOf(HTTP_1_1))
              else -> TODO()
            }

            val serverSslSocketFactory =

  override fun configureTlsExtensions(
    sslSocket: SSLSocket,
    hostname: String?,
    protocols: List<@JvmSuppressWildcards Protocol>,
  ) {
    // No TLS extensions if the socket class is custom.
    socketAdapters
      .find { it.matchesSocket(sslSocket) }
      ?.configureTlsExtensions(sslSocket, hostname, protocols)
  }

  override fun getSelectedProtocol(sslSocket: SSLSocket): String? =