object ConnectInterceptor : Interceptor {

  @Throws(IOException::class)
  override fun intercept(chain: Interceptor.Chain): Response {
    val realChain = chain as RealInterceptorChain
    val request = realChain.request()
    val transmitter = realChain.transmitter()

    // We need the network to satisfy this request. Possibly for validating a conditional GET.
    val doExtensiveHealthChecks = request.method != "GET"
    val exchange = transmitter.newExchange(chain, doExtensiveHealthChecks)

    return realChain.proceed(request, transmitter, exchange)
  }
}

  internal fun newExchange(chain: Interceptor.Chain, doExtensiveHealthChecks: Boolean): Exchange {
    synchronized(connectionPool) {
      check(!noMoreExchanges) { "released" }
      check(exchange == null) {
        "cannot make a new request because the previous response is still open: " +
            "please call response.close()"
      }
    }

    val codec = exchangeFinder!!.find(client, chain, doExtensiveHealthChecks)
    val result = Exchange(this, call, eventListener, exchangeFinder!!, codec)

    synchronized(connectionPool) {
      this.exchange = result
      this.exchangeRequestDone = false
      this.exchangeResponseDone = false
      return result
    }
  }

  fun find(
    ...
  ): ExchangeCodec {
    ...
    try {
      val resultConnection = findHealthyConnection(
        ...
      )
      return resultConnection.newCodec(client, chain)
    ...
  }
  ...
  @Throws(IOException::class)
  private fun findHealthyConnection(
    ...
  ): RealConnection {
    while (true) {
      val candidate = findConnection(
          connectTimeout = connectTimeout,
          readTimeout = readTimeout,
          writeTimeout = writeTimeout,
          pingIntervalMillis = pingIntervalMillis,
          connectionRetryEnabled = connectionRetryEnabled
      )

      // If this is a brand new connection, we can skip the extensive health checks.
      synchronized(connectionPool) {
        if (candidate.successCount == 0) {
          return candidate
        }
      }

      // Do a (potentially slow) check to confirm that the pooled connection is still good. If it
      // isn't, take it out of the pool and start again.
      if (!candidate.isHealthy(doExtensiveHealthChecks)) {
        candidate.noNewExchanges()
        continue
      }

      return candidate
    }
  }

 @Throws(IOException::class)
  private fun findConnection(
    ...
  ): RealConnection {
    ...
    synchronized(connectionPool) {
      if (transmitter.isCanceled) throw IOException("Canceled")
      hasStreamFailure = false // This is a fresh attempt.

      releasedConnection = transmitter.connection
      toClose = if (transmitter.connection != null && transmitter.connection!!.noNewExchanges) {
        transmitter.releaseConnectionNoEvents()
      } else {
        null
      }

      if (transmitter.connection != null) {
        // We had an already-allocated connection and it's good.
        result = transmitter.connection
        releasedConnection = null
      }

      if (result == null) {
        // Attempt to get a connection from the pool.
        if (connectionPool.transmitterAcquirePooledConnection(address, transmitter, null, false)) {
          foundPooledConnection = true
          result = transmitter.connection
        } else if (nextRouteToTry != null) {
          selectedRoute = nextRouteToTry
          nextRouteToTry = null
        } else if (retryCurrentRoute()) {
          selectedRoute = transmitter.connection!!.route()
        }
      }
    }
    ...
    if (result != null) {
      // If we found an already-allocated or pooled connection, we're done.
      return result!!
    }

    // If we need a route selection, make one. This is a blocking operation.
    var newRouteSelection = false
    if (selectedRoute == null && (routeSelection == null || !routeSelection!!.hasNext())) {
      newRouteSelection = true
      routeSelection = routeSelector.next()
    }

    var routes: List<Route>? = null
    synchronized(connectionPool) {
      if (transmitter.isCanceled) throw IOException("Canceled")

      if (newRouteSelection) {
        // Now that we have a set of IP addresses, make another attempt at getting a connection from
        // the pool. This could match due to connection coalescing.
        routes = routeSelection!!.routes
        if (connectionPool.transmitterAcquirePooledConnection(
                address, transmitter, routes, false)) {
          foundPooledConnection = true
          result = transmitter.connection
        }
      }

      if (!foundPooledConnection) {
        if (selectedRoute == null) {
          selectedRoute = routeSelection!!.next()
        }

        // Create a connection and assign it to this allocation immediately. This makes it possible
        // for an asynchronous cancel() to interrupt the handshake we're about to do.
        result = RealConnection(connectionPool, selectedRoute!!)
        connectingConnection = result
      }
    }

    // If we found a pooled connection on the 2nd time around, we're done.
    if (foundPooledConnection) {
      eventListener.connectionAcquired(call, result!!)
      return result!!
    }
    ...
  }

  private fun resetNextInetSocketAddress(proxy: Proxy) {
    // Clear the addresses. Necessary if getAllByName() below throws!
    val mutableInetSocketAddresses = mutableListOf<InetSocketAddress>()
    inetSocketAddresses = mutableInetSocketAddresses

    val socketHost: String
    val socketPort: Int
    if (proxy.type() == Proxy.Type.DIRECT || proxy.type() == Proxy.Type.SOCKS) {
      socketHost = address.url.host
      socketPort = address.url.port
    } else {
      val proxyAddress = proxy.address()
      require(proxyAddress is InetSocketAddress) {
        "Proxy.address() is not an InetSocketAddress: ${proxyAddress.javaClass}"
      }
      socketHost = proxyAddress.socketHost
      socketPort = proxyAddress.port
    }

    if (socketPort !in 1..65535) {
      throw SocketException("No route to $socketHost:$socketPort; port is out of range")
    }

    if (proxy.type() == Proxy.Type.SOCKS) {
      mutableInetSocketAddresses += InetSocketAddress.createUnresolved(socketHost, socketPort)
    } else {
      eventListener.dnsStart(call, socketHost)

      // Try each address for best behavior in mixed IPv4/IPv6 environments.
      val addresses = address.dns.lookup(socketHost)
      if (addresses.isEmpty()) {
        throw UnknownHostException("${address.dns} returned no addresses for $socketHost")
      }

      eventListener.dnsEnd(call, socketHost, addresses)

      for (inetAddress in addresses) {
        mutableInetSocketAddresses += InetSocketAddress(inetAddress, socketPort)
      }
    }
  }

  @Throws(IOException::class)
  private fun findConnection(
    ...
  ): RealConnection {
    ...
    // Do TCP + TLS handshakes. This is a blocking operation.
    result!!.connect(
        connectTimeout,
        readTimeout,
        writeTimeout,
        pingIntervalMillis,
        connectionRetryEnabled,
        call,
        eventListener
    )
    connectionPool.routeDatabase.connected(result!!.route())

    var socket: Socket? = null
    synchronized(connectionPool) {
      connectingConnection = null
      // Last attempt at connection coalescing, which only occurs if we attempted multiple
      // concurrent connections to the same host.
      if (connectionPool.transmitterAcquirePooledConnection(address, transmitter, routes, true)) {
        // We lost the race! Close the connection we created and return the pooled connection.
        result!!.noNewExchanges = true
        socket = result!!.socket()
        result = transmitter.connection
      } else {
        connectionPool.put(result!!)
        transmitter.acquireConnectionNoEvents(result!!)
      }
    }
    socket?.closeQuietly()

    eventListener.connectionAcquired(call, result!!)
    return result!!
    ...
  }

  fun connect(
    connectTimeout: Int,
    readTimeout: Int,
    writeTimeout: Int,
    pingIntervalMillis: Int,
    connectionRetryEnabled: Boolean,
    call: Call,
    eventListener: EventListener
  ) {
    check(protocol == null) { "already connected" }

    var routeException: RouteException? = null
    val connectionSpecs = route.address.connectionSpecs
    val connectionSpecSelector = ConnectionSpecSelector(connectionSpecs)
    ...

    while (true) {
      try {
        if (route.requiresTunnel()) {
          connectTunnel(connectTimeout, readTimeout, writeTimeout, call, eventListener)
          if (rawSocket == null) {
            // We were unable to connect the tunnel but properly closed down our resources.
            break
          }
        } else {
          connectSocket(connectTimeout, readTimeout, call, eventListener)
        }
        establishProtocol(connectionSpecSelector, pingIntervalMillis, call, eventListener)
        eventListener.connectEnd(call, route.socketAddress, route.proxy, protocol)
        break
      } catch (e: IOException) {
        ...

        if (routeException == null) {
          routeException = RouteException(e)
        } else {
          routeException.addConnectException(e)
        }

        if (!connectionRetryEnabled || !connectionSpecSelector.connectionFailed(e)) {
          throw routeException
        }
      }
    }
    ...
    val http2Connection = this.http2Connection
    if (http2Connection != null) {
      synchronized(connectionPool) {
        allocationLimit = http2Connection.maxConcurrentStreams()
      }
    }
  }

private fun connectTls(connectionSpecSelector: ConnectionSpecSelector) {
      val address = route.address
    val sslSocketFactory = address.sslSocketFactory
    var success = false
    var sslSocket: SSLSocket? = null
    try {
      // Create the wrapper over the connected socket.
      sslSocket = sslSocketFactory!!.createSocket(
          rawSocket, address.url.host, address.url.port, true /* autoClose */) as SSLSocket

      // Configure the socket's ciphers, TLS versions, and extensions.
      val connectionSpec = connectionSpecSelector.configureSecureSocket(sslSocket)
      if (connectionSpec.supportsTlsExtensions) {
        Platform.get().configureTlsExtensions(sslSocket, address.url.host, address.protocols)
      }

      // Force handshake. This can throw!
      sslSocket.startHandshake()
      // block for session establishment
      val sslSocketSession = sslSocket.session
      val unverifiedHandshake = sslSocketSession.handshake()

      // Verify that the socket's certificates are acceptable for the target host.
      if (!address.hostnameVerifier!!.verify(address.url.host, sslSocketSession)) {
        ...
      }

      val certificatePinner = address.certificatePinner!!

      handshake = Handshake(unverifiedHandshake.tlsVersion, unverifiedHandshake.cipherSuite,
          unverifiedHandshake.localCertificates) {
        certificatePinner.certificateChainCleaner!!.clean(unverifiedHandshake.peerCertificates,
            address.url.host)
      }

      // Check that the certificate pinner is satisfied by the certificates presented.
      certificatePinner.check(address.url.host) {
        handshake!!.peerCertificates.map { it as X509Certificate }
      }

      // Success! Save the handshake and the ALPN protocol.
      val maybeProtocol = if (connectionSpec.supportsTlsExtensions) {
        Platform.get().getSelectedProtocol(sslSocket)
      } else {
        null
      }
}

  private val cleanupTask = object : Task("$okHttpName ConnectionPool") {
    override fun runOnce() = cleanup(System.nanoTime())
  }