}
  }

  /** No SNI for literal IPv6 addresses. */
  @Test
  fun ipv6() {
    val recordedRequest = requestToHostnameViaProxy("2607:f8b0:400b:804::200e")
    assertThat(recordedRequest.url.host).isEqualTo("2607:f8b0:400b:804::200e")
    assertThat(recordedRequest.handshakeServerNames).isEmpty()
  }

  /** No SNI for literal IPv4 addresses. */
  @Test
  fun ipv4() {

        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
          val parameters = sslSocket.sslParameters
          val sni = parameters.serverNames
          Log.d("CustomSSLSocketFactory", "old SNI: $sni")
          parameters.serverNames = mutableListOf<SNIServerName>(SNIHostName("cloudflare-dns.com"))
          sslSocket.sslParameters = parameters
        }

        return sslSocket

* There's an **extension** to the **TLS** protocol (the one handling the encryption at the TCP level, before HTTP) called **[<abbr title="Server Name Indication">SNI</abbr>](https://en.wikipedia.org/wiki/Server_Name_Indication)**.
    * This SNI extension allows one single server (with a **single IP address**) to have **several HTTPS certificates** and serve **multiple HTTPS domains/applications**.

用戶端與伺服器為建立 TLS 連線而進行的這段互動稱為 **TLS 握手**。

### 帶 SNI 擴充的 TLS { #tls-with-sni-extension }

在特定的**IP 位址**與特定**埠**上，同一時間**只能有一個行程**在監聽。可以在同一個 IP 上監聽不同埠，但每個 IP 與埠的組合只能有一個行程。

TLS（HTTPS）預設使用 `443` 埠，因此我們需要用到這個埠。

由於只能有一個行程監聽該埠，負責監聽的會是 **TLS 終止代理**。

TLS 終止代理會存取一張或多張 **TLS 憑證**（HTTPS 憑證）。

透過上面提到的 **SNI 擴充**，TLS 終止代理會根據用戶端預期的網域，從可用的 TLS（HTTPS）憑證中挑選本次連線要用的憑證。

    * これは、サーバーの規模やアプリケーションの規模に寄りません。
    * しかし、これには**解決策**があります。
* **TLS**プロトコル(HTTPの前に、TCPレベルで暗号化を処理するもの)には、**[<abbr title="Server Name Indication - サーバー名表示">SNI</abbr>](https://en.wikipedia.org/wiki/Server_Name_Indication)**と呼ばれる**拡張**があります。
    * このSNI拡張機能により、1つのサーバー（**単一のIPアドレス**を持つ）が**複数のHTTPS証明書**を持ち、**複数のHTTPSドメイン/アプリケーション**にサービスを提供できるようになります。

   * received without TLS.
   */
  public val handshake: Handshake?,
  /**
   * Returns the name of the server the client requested via the SNI (Server Name Indication)
   * attribute in the TLS handshake. Unlike the rest of the HTTP exchange, this name is sent in
   * cleartext and may be monitored or blocked by a proxy or other middlebox.
   */

 *
 * ## Modern TLS
 *
 * There are trade-offs when selecting which options to include when negotiating a secure connection
 * to a remote host. Newer TLS options are quite useful:
 *
 *  * Server Name Indication (SNI) enables one IP address to negotiate secure connections for
 *    multiple domain names.
 *
 *  * Application Layer Protocol Negotiation (ALPN) enables the HTTPS port (443) to be used to
 *    negotiate HTTP/2.
 *

  }

  /** Returns the negotiated protocol, or null if no protocol was negotiated. */
  open fun getSelectedProtocol(sslSocket: SSLSocket): String? = null

  /** For MockWebServer. This returns the inbound SNI names. */
  @Suppress("NewApi")
  @IgnoreJRERequirement // This function is overridden to require API >= 24.
  open fun getHandshakeServerNames(sslSocket: SSLSocket): List<String> {

    didn't have it.
 *  Fix: Explicitly specify the remote server name when making HTTPS connections on Android 5. In
    4.3.0 we introduced a regression where server name indication (SNI) was broken on Android 5.


## Version 4.3.0

_2019-12-31_

 *  Fix: Degrade HTTP/2 connections after a timeout. When an HTTP/2 stream times out it may impact

    * Ancak bunun bir **çözümü** vardır.
* **TLS** protokolüne (TCP seviyesinde, HTTP’den önce şifrelemeyi yapan) eklenen **[<abbr title="Server Name Indication - Sunucu Adı Belirtimi">SNI</abbr>](https://en.wikipedia.org/wiki/Server_Name_Indication)** adlı bir **extension** vardır.
    * Bu SNI extension’ı, tek bir server’ın (tek bir **IP adresiyle**) **birden fazla HTTPS sertifikası** kullanmasına ve **birden fazla HTTPS domain/uygulama** sunmasına izin verir.