**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 { #check-the-docs }

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 { #forbid-extra-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：

        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']

    val expected = Date(0L)
    val headers =
      Headers
        .Builder()
        .add("testDate", expected)
        .build()
    assertThat(headers["testDate"]).isEqualTo("Thu, 01 Jan 1970 00:00:00 GMT")
    assertThat(headers.getDate("testDate")).isEqualTo(Date(0L))
  }

  @Test fun addInstant() {
    val expected = Instant.ofEpochMilli(0L)
    val headers =
      Headers
        .Builder()

    /**
     * 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()

    val authority = request.headers["Host"] // Has host and port.
    val fancyRequest =
      Request
        .Builder()
        .url("$scheme://$authority/")
        .headers(request.headers)
        .build()
    val fancyResponse =
      Response
        .Builder()
        .code(webSocketResponse.code)
        .message(webSocketResponse.message)
        .headers(webSocketResponse.headers)

import mockwebserver3.internal.decodeRequestLine
import okhttp3.Headers
import okhttp3.Headers.Companion.headersOf
import okio.Buffer
import okio.ByteString
import org.junit.jupiter.api.Test
import org.junit.jupiter.api.Timeout

@Timeout(30)
class RecordedRequestTest {
  private val headers: Headers = Headers.EMPTY

  @Test fun testIPv4() {
    val socket =
      MockWebServerSocket(

  internal constructor(
    requestLine: String,
    headers: Headers,
    chunkSizes: List<Int>,
    bodySize: Long,
    body: Buffer,
    sequenceNumber: Int,
    failure: IOException?,
    method: String?,
    path: String?,
    handshake: Handshake?,
    requestUrl: HttpUrl?,
  ) {
    this.requestLine = requestLine
    this.headers = headers
    this.chunkSizes = chunkSizes
    this.bodySize = bodySize

            logger.debug("MarkdownRenderer initialized with commonmark and OWASP sanitizer");
        }
    }

    /**
     * Renders markdown text to sanitized HTML.
     *
     * @param markdown the markdown text to render
     * @return sanitized HTML string
     */
    public String render(final String markdown) {
        if (markdown == null || markdown.isEmpty()) {
            return "";
        }

        try {

	ttfbBody   time.Duration

	StartTime time.Time
	// number of bytes written
	bytesWritten int
	// number of bytes of response headers written
	headerBytesWritten int
	// Internal recording buffer
	headers bytes.Buffer
	body    bytes.Buffer
	// Indicate if headers are written in the log
	headersLogged bool
}

// Hijack - hijacks the underlying connection

/// warning | Advertencia

Antes de establecer `convert_underscores` a `False`, ten en cuenta que algunos proxies y servidores HTTP no permiten el uso de headers con guiones bajos.

///

## Headers duplicados { #duplicate-headers }

Es posible recibir headers duplicados. Eso significa, el mismo header con múltiples valores.

Puedes definir esos casos usando una lista en la declaración del tipo.