@needs_py310
@pytest.mark.parametrize(
    "path,headers,expected_status,expected_response",
    [
        ("/items", None, 200, {"X-Token values": None}),
        ("/items", {"x-token": "foo"}, 200, {"X-Token values": ["foo"]}),
        # TODO: fix this, is it a bug?
        # ("/items", [("x-token", "foo"), ("x-token", "bar")], 200, {"X-Token values": ["foo", "bar"]}),
    ],
)

      client.newRequest(server.url("/").toUri())
        .header("Accept", "text/plain")
    val response = request.send()
    assertThat(response.status).isEqualTo(200)
    assertThat(response.contentAsString).isEqualTo("hello, Jetty HTTP Client")

    val recorded = server.takeRequest()
    assertThat(recorded.headers["Accept"]).isEqualTo("text/plain")
    assertThat(recorded.headers["Accept-Encoding"]).isEqualTo("gzip")

	o = msgp.Require(b, z.Msgsize())
	// map header, size 5
	// string "APIVersion"
	o = append(o, 0x85, 0xaa, 0x41, 0x50, 0x49, 0x56, 0x65, 0x72, 0x73, 0x69, 0x6f, 0x6e)
	o = msgp.AppendString(o, z.APIVersion)
	// string "Flags"
	o = append(o, 0xa5, 0x46, 0x6c, 0x61, 0x67, 0x73)
	// map header, size 3
	// string "Filter"
	o = append(o, 0x83, 0xa6, 0x46, 0x69, 0x6c, 0x74, 0x65, 0x72)

		return
	}
	for za0001 := range z {
		// map header, size 2
		// write "Totals"
		err = en.Append(0x82, 0xa6, 0x54, 0x6f, 0x74, 0x61, 0x6c, 0x73)
		if err != nil {
			return
		}
		err = en.WriteArrayHeader(uint32(60))
		if err != nil {
			err = msgp.WrapError(err, za0001, "Totals")
			return
		}
		for za0002 := range z[za0001].Totals {
			// map header, size 3
			// write "Total"

...

    // The most common case is that from is a Reader (like InputStreamReader or StringReader) so
    // take advantage of that.
    if (from instanceof Reader) {
      // optimize for common output types which are optimized to deal with char[]
      if (to instanceof StringBuilder) {
        return copyReaderToBuilder((Reader) from, (StringBuilder) to);
      } else {
        return copyReaderToWriter((Reader) from, asWriter(to));
      }
    }

```

////

**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

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

package cmd

// Code generated by github.com/tinylib/msgp DO NOT EDIT.

import (
	"github.com/tinylib/msgp/msgp"
)

// DecodeMsg implements msgp.Decodable
func (z *nsScannerOptions) DecodeMsg(dc *msgp.Reader) (err error) {
	var field []byte
	_ = field
	var zb0001 uint32
	zb0001, err = dc.ReadMapHeader()
	if err != nil {
		err = msgp.WrapError(err)
		return
	}
	for zb0001 > 0 {
		zb0001--
		field, err = dc.ReadMapKeyPtr()

        }
    }

    @Override
    public org.apache.maven.model.Model read(Reader reader, Map<String, ?> options) throws IOException {
        Objects.requireNonNull(reader, "reader cannot be null");
        try (Reader r = reader) {
            org.apache.maven.api.model.Model model = read(null, null, r, options);
            return new org.apache.maven.model.Model(model);

    assertThat(response.protocol).isEqualTo(protocol)
    val logs = testLogHandler.takeAll()
    assertThat(firstFrame(logs, "HEADERS")!!, "header logged")
      .contains("HEADERS       END_HEADERS")
    // While MockWebServer waits to read the client's HEADERS frame before sending the response, it
    // doesn't wait to read the client's DATA frame and may send a DATA frame before the client