): ConnectPlan {
    if (route.address.sslSocketFactory == null) {
      if (ConnectionSpec.CLEARTEXT !in route.address.connectionSpecs) {
        throw UnknownServiceException("CLEARTEXT communication not enabled for client")
      }

      val host = route.address.url.host
      if (!Platform.get().isCleartextTrafficPermitted(host)) {
        throw UnknownServiceException(

     *
     * This implements Happy Eyeballs ([RFC 6555][rfc_6555]), balancing connect latency vs.
     * wasted resources.
     *
     * Defaults to enabled, call with [fastFallback] = false to revert to 4.x behaviour.
     *
     * [rfc_6555]: https://datatracker.ietf.org/doc/html/rfc6555
     */
    fun fastFallback(fastFallback: Boolean) =
      apply {

    assertFailsWith<UnknownServiceException> {
      client.newCall(request).execute()
    }.also { expected ->
      assertThat(expected.message).isEqualTo(
        "CLEARTEXT communication not enabled for client",
      )
    }
  }

  @Test
  fun httpsCallsFailWhenProtocolIsH2PriorKnowledge() {
    client =
      client.newBuilder()
        .protocols(listOf(Protocol.H2_PRIOR_KNOWLEDGE))

    proxy: Proxy,
    protocol: Protocol?,
  ) {
  }

  /**
   * Invoked when a connection attempt fails. This failure is not terminal if further routes are
   * available and failure recovery is enabled.
   *
   * If the `call` uses HTTPS, this will be invoked after [secureConnectStart], otherwise it will
   * invoked after [connectStart].
   */
  open fun connectFailed(
    call: Call,

changes we've made over time to OkHttp's default TLS options.

[OkHttp 3.14][OkHttp314]
------------------------

_2019-03-14_

Remove 2 TLSv1.3 cipher suites that are neither available on OkHttp’s host platforms nor enabled in releases of Chrome and Firefox.

##### RESTRICTED_TLS cipher suites

 * TLS_AES_128_GCM_SHA256[¹][tlsv13_only]
 * TLS_AES_256_GCM_SHA384[¹][tlsv13_only]
 * TLS_CHACHA20_POLY1305_SHA256[¹][tlsv13_only]

object OkHttpDebugLogging {
  // Keep references to loggers to prevent their configuration from being GC'd.
  private val configuredLoggers = CopyOnWriteArraySet<Logger>()

  fun enableHttp2() = enable(Http2::class)

  fun enableTaskRunner() = enable(TaskRunner::class)

  fun logHandler() =
    ConsoleHandler().apply {
      level = Level.FINE
      formatter =
        object : SimpleFormatter() {

  fun size(): Int = Integer.bitCount(set)

  // TODO: honor this setting.
  fun getEnablePush(defaultValue: Boolean): Boolean {
    val bit = 1 shl ENABLE_PUSH
    return if (bit and set != 0) values[ENABLE_PUSH] == 1 else defaultValue
  }

  fun getMaxConcurrentStreams(): Int {
    val bit = 1 shl MAX_CONCURRENT_STREAMS

OkHttp Brotli Implementation
============================

This module is an implementation of [Brotli][1] compression.
It enables Brotli support in addition to tranparent Gzip support,
provided Accept-Encoding is not set previously.  Modern web servers
must choose to return Brotli responses.  n.b. It is not used for
sending requests.

```java
OkHttpClient client = new OkHttpClient.Builder()
  .addInterceptor(BrotliInterceptor.INSTANCE)
  .build();

    sslSocket: SSLSocket,
    hostname: String?,
    protocols: List<@JvmSuppressWildcards Protocol>,
  ) {
    if (sslSocket is BCSSLSocket) {
      val sslParameters = sslSocket.parameters

      // Enable ALPN.
      val names = alpnProtocolNames(protocols)
      sslParameters.applicationProtocols = names.toTypedArray()

      sslSocket.parameters = sslParameters
    } else {

    if (headerName.equals(name(h), ignoreCase = true)) {
      val header = Buffer().writeUtf8(value(h))
      try {
        header.readChallengeHeader(result)
      } catch (e: EOFException) {
        Platform.get().log("Unable to parse challenge", Platform.WARN, e)
      }
    }
  }
  return result
}

@Throws(EOFException::class)
private fun Buffer.readChallengeHeader(result: MutableList<Challenge>) {
  var peek: String? = null