In this case the middleware will intercept the incoming request and respond with appropriate CORS headers, and either a `200` or `400` response for informational purposes.

### Simple requests { #simple-requests }

Any request with an `Origin` header. In this case the middleware will pass the request through as normal, but will include appropriate CORS headers on the response.

from fastapi import FastAPI, HTTPException

app = FastAPI()

items = {"foo": "The Foo Wrestlers"}


@app.get("/items-header/{item_id}")
async def read_item_header(item_id: str):
    if item_id not in items:
        raise HTTPException(
            status_code=404,
            detail="Item not found",
            headers={"X-Error": "There goes my error"},
        )

Rene Groeschke <******@****.***> 1622539170 +0200

        .build(),
    )
    val call = client.newCall(Request(url = server.url("/")))
    assertFailsWith<IOException> {
      call.execute()
    }
  }

  /** A collection of headers that collectively exceed the limits. */
  @Test
  fun largeResponseHeadersList() {
    server.enqueue(
      MockResponse
        .Builder()
        .addHeader("Set-Cookie", "a=${"A".repeat(255 * 1024)}")

{* ../../docs_src/middleware/tutorial001_py310.py hl[8:9,11,14] *}

/// tip | Consejo

Ten en cuenta que los custom proprietary headers se pueden añadir [usando el prefijo `X-`](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers).

{* ../../docs_src/middleware/tutorial001_py310.py hl[8:9,11,14] *}

/// tip | Tipp

Beachten Sie, dass benutzerdefinierte proprietäre Header hinzugefügt werden können [unter Verwendung des `X-`-Präfixes](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers).

 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package okhttp3.internal.http

import java.io.IOException
import okhttp3.Headers
import okhttp3.Request
import okhttp3.Response
import okhttp3.Route
import okhttp3.internal.connection.RealCall
import okio.Sink
import okio.Socket
import okio.Source

而且你还可以根据你的需要响应不同的对象，比如常用的 `dict`，数据库model等。

如果你定义了 `response_model`，程序会自动根据`response_model`来过滤和转换你响应的对象。

**FastAPI** 会使用这个 *临时* 响应对象去装在这些cookies信息 (同样还有headers和状态码等信息), 最终会将这些信息和通过`response_model`转化过的数据合并到最终的响应里。

你也可以在依赖中定义`Response`参数，并设置cookie和header。

## 直接响应 `Response` { #return-a-response-directly }

你还可以在直接响应`Response`时直接创建cookies。

为此，你可以按照[直接返回 Response](response-directly.md)中的说明创建一个响应。

然后设置Cookies，并返回：

        file("/build/${testIntermediateDir}/transformed/rest-api-spec/test/" + test).exists()
        file("/build/${testIntermediateDir}/transformed/rest-api-spec/test/" + test).text.contains("headers") //transformation adds this
        file("/build/resources/yamlRestCompatTest/rest-api-spec/test/" + additionalTest).exists()

import okhttp3.CallEvent.ResponseBodyEnd
import okhttp3.CallEvent.ResponseBodyStart
import okhttp3.CallEvent.ResponseHeadersEnd
import okhttp3.CallEvent.ResponseHeadersStart
import okhttp3.EventRecorder
import okhttp3.Headers.Companion.headersOf
import okhttp3.OkHttpClientTestRule
import okhttp3.Protocol
import okhttp3.RecordingHostnameVerifier
import okhttp3.Request
import okhttp3.RequestBody
import okhttp3.RequestBody.Companion.toRequestBody