**FastAPI** will **extract** the data for **each field** from the **headers** in the request and give you the Pydantic model you defined.

## Check the Docs { #check-the-docs }

You can see the required headers in the docs UI at `/docs`:

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

## Forbid Extra Headers { #forbid-extra-headers }

  }

  class Part private constructor(
    @get:JvmName("headers") val headers: Headers?,
    @get:JvmName("body") val body: RequestBody,
  ) {
    @JvmName("-deprecated_headers")
    @Deprecated(
      message = "moved to val",
      replaceWith = ReplaceWith(expression = "headers"),
      level = DeprecationLevel.ERROR,
    )
    fun headers(): Headers? = headers

    @JvmName("-deprecated_body")
    @Deprecated(

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

      for (i in 0 until headers.size) {
        // header names must be lowercase.
        val name = headers.name(i).lowercase(Locale.US)
        if (name !in HTTP_2_SKIPPED_REQUEST_HEADERS ||
          name == TE &&
          headers.value(i) == "trailers"
        ) {
          result.add(Header(name, headers.value(i)))
        }
      }
      return result
    }

// getCanonicalHeaders generate a list of request headers with their values
func getCanonicalHeaders(signedHeaders http.Header) string {
	var headers []string
	vals := make(http.Header, len(signedHeaders))
	for k, vv := range signedHeaders {
		k = strings.ToLower(k)
		headers = append(headers, k)
		vals[k] = vv
	}
	sort.Strings(headers)

	var buf bytes.Buffer
	for _, k := range headers {
		buf.WriteString(k)
		buf.WriteByte(':')

      .build()
  }

  companion object {
    /** Combines cached headers with a network headers as defined by RFC 7234, 4.3.4. */
    private fun combine(
      cachedHeaders: Headers,
      networkHeaders: Headers,
    ): Headers {
      val result = Headers.Builder()

      for (index in 0 until cachedHeaders.size) {
        val fieldName = cachedHeaders.name(index)

      headers.name(-1)
    }
    assertThat(headers.name(0)).isEqualTo("a")
    assertThat(headers.name(1)).isEqualTo("c")
    assertFailsWith<IndexOutOfBoundsException> {
      headers.name(2)
    }
  }

  @Test fun valueIndexesAreStrict() {
    val headers = headersOf("a", "b", "c", "d")
    assertFailsWith<IndexOutOfBoundsException> {
      headers.value(-1)
    }
    assertThat(headers.value(0)).isEqualTo("b")

    assert response.status_code == 401, response.text
    assert response.headers["WWW-Authenticate"] == 'Basic realm="simple"'


def test_security_http_basic_invalid_credentials():
    response = client.get(
        "/users/me", headers={"Authorization": "Basic notabase64token"}
    )
    assert response.status_code == 401, response.text
    assert response.headers["WWW-Authenticate"] == 'Basic realm="simple"'

	public final fun getThrottleBytesPerPeriod ()J
	public final fun getThrottlePeriodNanos ()J
	public final fun getTrailers ()Lokhttp3/Headers;
	public final fun getTrailersDelayNanos ()J
	public final fun getWebSocketListener ()Lokhttp3/WebSocketListener;
	public final fun headers (Lokhttp3/Headers;)Lmockwebserver3/MockResponse$Builder;
	public final fun headersDelay (JLjava/util/concurrent/TimeUnit;)Lmockwebserver3/MockResponse$Builder;

        headers = Headers.headersOf("content-type", "application/json"),
      ),
    )
    server.enqueue(
      MockResponse(
        body =
          """
          |data: hey
          |
          |
          """.trimMargin(),
        headers = Headers.headersOf("content-type", "text/event-stream"),
      ),
    )