@app.middleware("http")
async def add_process_time_header(request: Request, call_next):
    start_time = time.perf_counter()
    response = await call_next(request)
    process_time = time.perf_counter() - start_time
    response.headers["X-Process-Time"] = str(process_time)

{* ../../docs_src/middleware/tutorial001.py hl[8:9,11,14] *}

/// tip | Порада

Не забувайте, що власні заголовки можна додавати, використовуючи <a href="https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers" class="external-link" target="_blank">префікс 'X-'</a>.

```python
from fastapi import UploadFile
```

::: fastapi.UploadFile
    options:
        members:
            - file
            - filename
            - size
            - headers
            - content_type
            - read
            - write
            - seek

    app,
    base_url="https://example.com",
    follow_redirects=False,
)


def test_redirect() -> None:
    response = client.get("/items")
    assert response.status_code == 307
    assert response.headers["location"] == "https://example.com/items/"


def test_no_redirect() -> None:
    response = client.get("/items/")
    assert response.status_code == 200

Прежде чем установить для `convert_underscores` значение `False`, имейте в виду, что некоторые HTTP-прокси и серверы запрещают использование заголовков с подчеркиванием.

///

## Повторяющиеся заголовки { #duplicate-headers }

Есть возможность получать несколько заголовков с одним и тем же именем, но разными значениями.

Вы можете определить эти случаи, используя список в объявлении типа.

client = TestClient(app)


def test_redirect_response_class():
    response = client.get("/fastapi", follow_redirects=False)
    assert response.status_code == 307
    assert response.headers["location"] == "https://fastapi.tiangolo.com"


def test_openapi_schema():
    response = client.get("/openapi.json")
    assert response.status_code == 200, response.text
    assert response.json() == {

Cache Miss will be typical if the item has not been read from the network, is uncacheable, or is past it's 
lifetime based on Response cache headers.

 - CallStart 
 - **CacheMiss**
 - ProxySelectStart
 - ... Standard Events ...
 - CallEnd
        
### Conditional Cache Hit
 

    }
  }

  override fun loadForRequest(url: HttpUrl): List<Cookie> {
    val cookieHeaders =
      try {
        // The RI passes all headers. We don't have 'em, so we don't pass 'em!
        cookieHandler.get(url.toUri(), emptyMap<String, List<String>>())
      } catch (e: IOException) {

    mod = importlib.import_module(f"docs_src.openapi_callbacks.{request.param}")
    return mod


@pytest.fixture(name="client")
def get_client(mod: ModuleType):
    client = TestClient(mod.app)
    client.headers.clear()
    return client


def test_get(client: TestClient):
    response = client.post(
        "/invoices/", json={"id": "fooinvoice", "customer": "John", "total": 5.3}
    )

    assertThat(cacheControl.onlyIfCached).isTrue()
    assertThat(cacheControl.noTransform).isTrue()
    assertThat(cacheControl.immutable).isTrue()

    // These members are accessible to response headers only.
    assertThat(cacheControl.sMaxAgeSeconds).isEqualTo(-1)
    assertThat(cacheControl.isPrivate).isFalse()
    assertThat(cacheControl.isPublic).isFalse()
    assertThat(cacheControl.mustRevalidate).isFalse()
  }