method = self.METHOD

        def fetch_credentials():
            # HTTP headers are case insensitive filter out
            # all duplicate headers and pick one.
            headers = {}
            headers['content-type'] = 'application/x-www-form-urlencoded'
            headers['authorization'] = urllib3.make_headers(
                basic_auth='%s:%s' % (self.cid, self.csec))['authorization']

@pytest.mark.parametrize(
    "path",
    ["/optional-list-str", "/model-optional-list-str"],
)
def test_optional_list_str(path: str):
    client = TestClient(app)
    response = client.get(path, headers=[("p", "hello"), ("p", "world")])
    assert response.status_code == 200
    assert response.json() == {"p": ["hello", "world"]}


# =====================================================================================

def test_gzip_request(client: TestClient, compress):
    n = 1000
    headers = {}
    body = [1] * n
    data = json.dumps(body).encode()
    if compress:
        data = gzip.compress(data)
        headers["Content-Encoding"] = "gzip"
    headers["Content-Type"] = "application/json"
    response = client.post("/sum", content=data, headers=headers)
    assert response.json() == {"sum": n}

    method = "GET",
    target = "/",
    version = "HTTP/2",
  )

private fun requestUrl(
  socket: MockWebServerSocket,
  requestLine: RequestLine,
  headers: Headers,
): HttpUrl {
  val hostAndPort =
    headers[":authority"]
      ?: headers["Host"]
      ?: when (val inetAddress = socket.localAddress) {
        is Inet6Address -> "[${inetAddress.hostAddress}]:${socket.localPort}"

            - init_headers
            - headers
            - set_cookie
            - delete_cookie

::: fastapi.responses.HTMLResponse
    options:
        members:
            - charset
            - status_code
            - media_type
            - body
            - background
            - raw_headers
            - render
            - init_headers
            - headers
            - set_cookie

**FastAPI** 将从请求中接收到的 **headers** 中**提取**出**每个字段**的数据，并提供您定义的 Pydantic 模型。

## 查看文档

您可以在文档 UI 的 `/docs` 中查看所需的 headers：

<div class="screenshot">
<img src="/img/tutorial/header-param-models/image01.png">
</div>

## 禁止额外的 Headers

在某些特殊使用情况下（可能并不常见），您可能希望**限制**您想要接收的 headers。

您可以使用 Pydantic 的模型配置来禁止（ `forbid` ）任何额外（ `extra` ）字段：

from fastapi import FastAPI
from fastapi.responses import JSONResponse

app = FastAPI()


@app.get("/headers/")
def get_headers():
    content = {"message": "Hello World"}
    headers = {"X-Cat-Dog": "alone in the world", "Content-Language": "en-US"}

    filename: Annotated[Optional[str], Doc("The original file name.")]
    size: Annotated[Optional[int], Doc("The size of the file in bytes.")]
    headers: Annotated[Headers, Doc("The headers of the request.")]
    content_type: Annotated[
        Optional[str], Doc("The content type of the request, from the headers.")
    ]

    async def write(
        self,
        data: Annotated[
            bytes,
            Doc(
                """

    /**
     * Returns the subset of the headers in [requestHeaders] that impact the content of the
     * response's body.
     */
    private fun varyHeaders(
      requestHeaders: Headers,
      responseHeaders: Headers,
    ): Headers {
      val varyFields = responseHeaders.varyFields()
      if (varyFields.isEmpty()) return Headers.EMPTY

      val result = Headers.Builder()

    assert response.headers["content-type"] == orjson_type


def test_router_a_a_override():
    with client:
        response = client.get("/a/a/override")
    assert response.content == b"Hello A A"
    assert response.headers["content-type"] == text_type


def test_router_a_b():
    with client:
        response = client.get("/a/b")
    assert response.content == b"Hello A B"