testers.add(ListHashCodeTester.class);
    testers.add(ListIndexOfTester.class);
    testers.add(ListLastIndexOfTester.class);
    testers.add(ListListIteratorTester.class);
    testers.add(ListRemoveAllTester.class);
    testers.add(ListRemoveAtIndexTester.class);
    testers.add(ListRemoveTester.class);
    testers.add(ListReplaceAllTester.class);
    testers.add(ListRetainAllTester.class);
    testers.add(ListSetTester.class);

  @JvmName("-deprecated_getHeaders")
  @Deprecated(
    message = "moved to var",
    replaceWith = ReplaceWith(expression = "headers"),
    level = DeprecationLevel.ERROR,
  )
  fun getHeaders(): Headers = headers

  fun setHeaders(headers: Headers) = apply { this.headers = headers }

  @JvmName("-deprecated_getTrailers")
  @Deprecated(
    message = "moved to var",

    List<Class<? extends AbstractTester>> testers = copyToList(super.getTesters());
    testers.add(CollectionSerializationEqualTester.class);
    testers.add(MultisetAddTester.class);
    testers.add(MultisetContainsTester.class);
    testers.add(MultisetCountTester.class);
    testers.add(MultisetElementSetTester.class);
    testers.add(MultisetEqualsTester.class);
    testers.add(MultisetReadsTester.class);

  }

  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(

    }
  }
  return null
}

internal fun Headers.Builder.commonAdd(
  name: String,
  value: String,
) = apply {
  headersCheckName(name)
  headersCheckValue(value, name)
  commonAddLenient(name, value)
}

internal fun Headers.Builder.commonAddAll(headers: Headers) =
  apply {
    for (i in 0 until headers.size) {
      commonAddLenient(headers.name(i), headers.value(i))
    }
  }

    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"

**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 }

      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
    }

    assertThat(connect.headers["Private"]).isNull()
    assertThat(connect.headers["User-Agent"]).isEqualTo(USER_AGENT)
    assertThat(connect.headers["Proxy-Connection"]).isEqualTo("Keep-Alive")
    assertThat(connect.headers["Host"]).isEqualTo("android.com:443")
    val get = server.takeRequest()
    assertThat(get.headers["Private"]).isEqualTo("Secret")
    assertThat(get.headers["User-Agent"]).isEqualTo("App 1.0")

        Map<String, List<String>> headers = new HashMap<>();
        headers.put("Content-Type", Arrays.asList("application/json"));
        headers.put("Content-Length", Arrays.asList("100"));

        response.setHeaders(headers);

        Map<String, List<String>> result = response.getHeaders();
        assertNotNull(result);
        // Headers should be stored in lowercase