* ## Preemptive Authentication
 *
 * To make HTTPS calls using an HTTP proxy server OkHttp must first negotiate a connection with
 * the proxy. This proxy connection is called a "TLS Tunnel" and is specified by
 * [RFC 2817][1]. The HTTP CONNECT request that creates this tunnel connection is special: it
 * does not participate in any [interceptors][Interceptor] or [event listeners][EventListener]. It

              .build(),
        ),
      )
    val response = call.execute()
    assertThat(response.isSuccessful).isTrue()

    server.takeRequest() // Discard the CONNECT tunnel.
    return server.takeRequest()
  }

 4. If it's a new route, it connects by building either a direct socket connection, a TLS tunnel (for HTTPS over an HTTP proxy), or a direct TLS connection. It does TLS handshakes as necessary. This step may be retried for tunnel challenges and TLS handshake failures.
 5. It sends the HTTP request and reads the response.

    replaceWith = ReplaceWith(expression = "socketAddress"),
    level = DeprecationLevel.ERROR,
  )
  fun socketAddress(): InetSocketAddress = socketAddress

  /**
   * Returns true if this route tunnels HTTPS or HTTP/2 through an HTTP proxy.
   * See [RFC 2817, Section 5.2][rfc_2817].
   *
   * [rfc_2817]: http://www.ietf.org/rfc/rfc2817.txt
   */
  fun requiresTunnel(): Boolean {

   * That may happen later by the connection pool thread.
   */
  fun cancel()

  /**
   * Carries an exchange. This is usually a connection, but it could also be a connect plan for
   * CONNECT tunnels. Note that CONNECT tunnels are significantly less capable than connections.
   */
  interface Carrier {
    val route: Route

    fun trackFailure(
      call: RealCall,
      e: IOException?,
    )

  internal var hasFailure: Boolean = false
    private set

  internal val connection: RealConnection
    get() = codec.carrier as? RealConnection ?: error("no connection for CONNECT tunnels")

  internal val isCoalescedConnection: Boolean
    get() = finder.routePlanner.address.url.host != codec.carrier.route.address.url.host

  @Throws(IOException::class)
  fun writeRequestHeaders(request: Request) {