///

ここでは、Pydantic の `Settings` クラス内で設定 `env_file` を定義し、使用したい dotenv ファイルのファイル名を指定しています。

### `lru_cache` で `Settings` を一度だけ作成 { #creating-the-settings-only-once-with-lru-cache }

ディスクからファイルを読むのは通常コスト（遅延）が高い処理なので、1回だけ実行して同じ設定オブジェクトを再利用し、各リクエストごとに読み直さないのが望ましいです。

しかし、次のようにするたびに:

```Python
Settings()
```

新しい `Settings` オブジェクトが作成され、その作成時に `.env` ファイルが再度読み込まれます。

	return s2.NewReader(nil, s2.ReaderAllocBlock(16<<10))
}}

// metacacheReader allows reading a cache stream.
type metacacheReader struct {
	mr      *msgp.Reader
	current metaCacheEntry
	err     error // stateful error
	closer  func()
	creator func() error
}

// newMetacacheReader creates a new cache reader.
// Nothing will be read from the stream yet.
func newMetacacheReader(r io.Reader) *metacacheReader {

            public String getIndexFieldHasCache() {
                return "has_cache";
            }

            @Override
            public String getIndexFieldCache() {
                return "cache";
            }

            @Override
            public String getIndexFieldLabel() {
                return "label";
            }

            @Override

        entry.updateChild("file1.txt", 1024L, 1000L, false, 0x20, 500L, 800L);
        entry.updateChild("file2.txt", 2048L, 2000L, false, 0x20, 600L, 900L);
        entry.markComplete();

        // Invalidate the cache
        entry.invalidate();

        assertFalse(entry.isComplete());
        assertTrue(entry.hasChanges());
        assertTrue(entry.getChildren().isEmpty());
    }

    @Test

 * @since 11.0
 */
@GwtCompatible
public final class HttpHeaders {
  private HttpHeaders() {}

  // HTTP Request and Response header fields

  /** The HTTP {@code Cache-Control} header field name. */
  public static final String CACHE_CONTROL = "Cache-Control";

  /** The HTTP {@code Content-Length} header field name. */
  public static final String CONTENT_LENGTH = "Content-Length";

    //
    // Used by Tycho and will break users and force them to upgrade to Maven 3.1 so we should really leave
    // this here, possibly indefinitely.
    //
    public ArtifactResolutionRequest setCache(RepositoryCache cache) {
        return this;
    }

* `expose_headers` - Indicate any response headers that should be made accessible to the browser. Defaults to `[]`.
* `max_age` - Sets a maximum time in seconds for browsers to cache CORS responses. Defaults to `600`.

The middleware responds to two particular types of HTTP request...

### CORS preflight requests { #cors-preflight-requests }

	// returns 'nil' once healing is complete or if the disk
	// has never been replaced.
	Healing() *healingTracker
	DiskInfo(ctx context.Context, opts DiskInfoOptions) (info DiskInfo, err error)
	NSScanner(ctx context.Context, cache dataUsageCache, updates chan<- dataUsageEntry, scanMode madmin.HealScanMode, shouldSleep func() bool) (dataUsageCache, error)

	// Volume operations.
	MakeVol(ctx context.Context, volume string) (err error)

	var wc io.WriteCloser = gzip.NewWriter(gw)
	if _, err = io.Copy(wc, r); err != nil {
		return err
	}

	if err = wc.Close(); err != nil {
		return err
	}

	// Persist to disk any caches.
	if err = gw.Sync(); err != nil {
		return err
	}

	// close everything before we delete.
	if err = gw.Close(); err != nil {
		return err
	}

	if err = r.Close(); err != nil {
		return err

* `expose_headers` - Indica quaisquer cabeçalhos de resposta que devem ser disponibilizados ao navegador. O padrão é `[]`.
* `max_age` - Define um tempo máximo em segundos para os navegadores armazenarem em cache as respostas CORS. O padrão é `600`.

O middleware responde a dois tipos específicos de solicitação HTTP...

### Requisições CORS pré-voo (preflight) { #cors-preflight-requests }