/**
     * Extension header set by OkHttp specifying the timestamp when the cached HTTP response was
     * first received.
     */
    private var receivedResponseMillis = 0L

    /** Etag of the cached response. */
    private var etag: String? = null

    /** Age of the cached response. */
    private var ageSeconds = -1

    /**
     * Returns true if computeFreshnessLifetime used a heuristic. If we used a heuristic to serve a

    // Special case some of the weird HTTP Header names...
    ImmutableBiMap<String, String> specialCases =
        ImmutableBiMap.<String, String>builder()
            .put("CDN_LOOP", "CDN-Loop")
            .put("ETAG", "ETag")
            .put("SOURCE_MAP", "SourceMap")
            .put("SEC_CH_UA_WOW64", "Sec-CH-UA-WoW64")
            .put("SEC_WEBSOCKET_ACCEPT", "Sec-WebSocket-Accept")

    assertThat(invalidate.body.string()).isEqualTo("")
    assertThat(get(url).body.string()).isEqualTo("C")
  }

  @Test
  fun etag() {
    val conditionalRequest =
      assertConditionallyCached(
        MockResponse
          .Builder()
          .addHeader("ETag: v1")
          .build(),
      )
    assertThat(conditionalRequest.headers["If-None-Match"]).isEqualTo("v1")
  }

    postBodyRetransmittedOnFailureRecovery()
  }

  @Test
  fun cacheHit() {
    server.enqueue(
      MockResponse(
        headers =
          headersOf(
            "ETag",
            "v1",
            "Cache-Control",
            "max-age=60",
            "Vary",
            "Accept-Charset",
          ),
        body = "A",
      ),
    )
    client =

   *
   * @since 28.2
   */
  public static final String CROSS_ORIGIN_OPENER_POLICY = "Cross-Origin-Opener-Policy";

  /** The HTTP {@code ETag} header field name. */
  public static final String ETAG = "ETag";

  /** The HTTP {@code Expires} header field name. */
  public static final String EXPIRES = "Expires";

  /** The HTTP {@code Last-Modified} header field name. */

    enableCache()
    server.enqueue(
      MockResponse
        .Builder()
        .addHeader("ETag: v1")
        .body("abc")
        .build(),
    )
    server.enqueue(
      MockResponse
        .Builder()
        .code(HttpURLConnection.HTTP_OK)
        .addHeader("ETag: v2")
        .body("abd")
        .build(),
    )
    var call =
      client.newCallWithListener(

* `filename` - If set, this will be included in the response `Content-Disposition`.

File responses will include appropriate `Content-Length`, `Last-Modified` and `ETag` headers.

{* ../../docs_src/custom_response/tutorial009_py310.py hl[2,10] *}

You can also use the `response_class` parameter:

{* ../../docs_src/custom_response/tutorial009b_py310.py hl[2,8,10] *}

      Header("content-length", ""),
      Header("content-location", ""),
      Header("content-range", ""),
      Header("content-type", ""),
      Header("cookie", ""),
      Header("date", ""),
      Header("etag", ""),
      Header("expect", ""),
      Header("expires", ""),
      Header("from", ""),
      Header("host", ""),
      Header("if-match", ""),
      Header("if-modified-since", ""),

- `path` - 要串流的檔案路徑。
- `headers` - 要包含的自訂標頭，字典形式。
- `media_type` - 描述 media type 的字串。若未設定，將根據檔名或路徑推斷 media type。
- `filename` - 若設定，會包含在回應的 `Content-Disposition` 中。

檔案回應會包含適當的 `Content-Length`、`Last-Modified` 與 `ETag` 標頭。

{* ../../docs_src/custom_response/tutorial009_py310.py hl[2,10] *}

你也可以使用 `response_class` 參數：

{* ../../docs_src/custom_response/tutorial009b_py310.py hl[2,8,10] *}

在此情況下，你可以在「路徑操作函式」中直接回傳檔案路徑。

Go 1.23 changed
[`net/http.ServeContent`](/pkg/net/http#ServeContent),
[`net/http.ServeFile`](/pkg/net/http#ServeFile), and
[`net/http.ServeFS`](/pkg/net/http#ServeFS) to
remove Cache-Control, Content-Encoding, Etag, and Last-Modified headers
when serving an error. This behavior is controlled by
the [`httpservecontentkeepheaders` setting](/pkg/net/http#ServeContent).
Using `httpservecontentkeepheaders=1` restores the pre-Go 1.23 behavior.