* connection the socket may be shared by multiple concurrent calls.
   */
  fun socket(): Socket

  /**
   * Returns the TLS handshake used to establish this connection, or null if the connection is not
   * HTTPS.
   */
  fun handshake(): Handshake?

  /**
   * Returns the protocol negotiated by this connection, or [Protocol.HTTP_1_1] if no protocol

 * Keep whichever TCP connection succeeds first and cancel all the others.
 * Race TCP only. Only attempt a TLS handshake on the winning TCP connection.

    assertThat(request.url.scheme).isEqualTo("https")
    val handshake = request.handshake
    assertThat(handshake!!.tlsVersion).isNotNull()
    assertThat(handshake.cipherSuite).isNotNull()
    assertThat(handshake.localPrincipal).isNotNull()
    assertThat(handshake.localCertificates.size).isEqualTo(1)
    assertThat(handshake.peerPrincipal).isNull()
    assertThat(handshake.peerCertificates.size).isEqualTo(0)
  }

  @Test

        delegate.secureConnectStart(call)
      }
    }

    override fun secureConnectEnd(
      call: Call,
      handshake: Handshake?,
    ) {
      for (delegate in eventListeners) {
        delegate.secureConnectEnd(call, handshake)
      }
    }

    override fun connectEnd(
      call: Call,
      inetSocketAddress: InetSocketAddress,
      proxy: Proxy,

   * client presents a certificate that is [trusted][TrustManager] the handshake will
   * proceed normally. The connection will also proceed normally if the client presents no
   * certificate at all! But if the client presents an untrusted certificate the handshake
   * will fail and no connection will be established.
   */
  public fun requestClientAuth() {

    .build();
```

### Debugging TLS Handshake Failures

The TLS handshake requires clients and servers to share a common TLS version and cipher suite. This
depends on the JVM or Android version, OkHttp version, and web server configuration. If there is no
common cipher suite and TLS version, your call will fail like this:

```
Caused by: javax.net.ssl.SSLProtocolException: SSL handshake aborted: ssl=0x7f2719a89e80:

  private val retryableException = SSLHandshakeException("Simulated handshake exception")

  @RegisterExtension
  val clientTestRule = OkHttpClientTestRule()

  private var client = clientTestRule.newClient()

  @AfterEach internal fun tearDown() {
    factory.close()
  }

  @Test fun nonRetryableIOException() {
    val exception = IOException("Non-handshake exception")
    assertThat(retryTlsHandshake(exception)).isFalse()
  }

  }

  override fun secureConnectStart(call: Call) {
    logWithTime("secureConnectStart")
  }

  override fun secureConnectEnd(
    call: Call,
    handshake: Handshake?,
  ) {
    logWithTime("secureConnectEnd: $handshake")
  }

  override fun connectEnd(
    call: Call,
    inetSocketAddress: InetSocketAddress,
    proxy: Proxy,
    protocol: Protocol?,
  ) {

        .build();

    Call call = client.newCall(new Request.Builder()
        .url(server.url("/"))
        .build());
    Response response = call.execute();
    System.out.println(response.handshake().tlsVersion());
  }

  public static void main(String... args) throws Exception {
    new HttpsServer().run();
  }

      printEvent("connectStart");
    }

    @Override public void secureConnectStart(Call call) {
      printEvent("secureConnectStart");
    }

    @Override public void secureConnectEnd(Call call, Handshake handshake) {
      printEvent("secureConnectEnd");
    }

    @Override public void connectEnd(
        Call call, InetSocketAddress inetSocketAddress, Proxy proxy, Protocol protocol) {
      printEvent("connectEnd");