{!../../docs_src/middleware/tutorial001.py!}
```

/// tip | "Tipp"

Beachten Sie, dass benutzerdefinierte proprietäre Header hinzugefügt werden können. <a href="https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers" class="external-link" target="_blank">Verwenden Sie dafür das Präfix 'X-'</a>.

	if len(p) == 0 {
		return 0, r.readErr(false)
	}

	r.mu.Lock()
	defer r.mu.Unlock()
	if err := r.readErr(true); err != nil {
		return 0, err
	}

	r.wg.Add(1)
	defer r.wg.Done()
	n, err = r.read(p)
	for err == ErrIsEmpty && r.block {
		r.writeCond.Wait()
		if err = r.readErr(true); err != nil {
			break
		}
		n, err = r.read(p)
	}

        length = 0,
        type = TYPE_SETTINGS,
        flags = FLAG_ACK,
      )
      sink.flush()
    }
  }

  /**
   * HTTP/2 only. Send a push promise header block.
   *
   * A push promise contains all the headers that pertain to a server-initiated request, and a
   * `promisedStreamId` to which response frames will be delivered. Push promise frames are sent as

	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"

* `content` – Ein `str` oder `bytes`.
* `status_code` – Ein `int`-HTTP-Statuscode.
* `headers` – Ein `dict` von Strings.
* `media_type` – Ein `str`, der den Medientyp angibt. Z. B. `"text/html"`.

FastAPI (eigentlich Starlette) fügt automatisch einen Content-Length-Header ein. Außerdem wird es einen Content-Type-Header einfügen, der auf dem media_type basiert, und für Texttypen einen Zeichensatz (charset) anfügen.

    internal val reader: Http2Reader,
  ) : Http2Reader.Handler, () -> Unit {
    override fun invoke() {
      var connectionErrorCode = ErrorCode.INTERNAL_ERROR
      var streamErrorCode = ErrorCode.INTERNAL_ERROR
      var errorException: IOException? = null
      try {
        reader.readConnectionPreface(this)
        while (reader.nextFrame(false, this)) {
        }

    if current_user is None:
        return {"msg": "Create an account first"}
    return current_user


client = TestClient(app)


def test_security_api_key():
    response = client.get("/users/me", headers={"key": "secret"})
    assert response.status_code == 200, response.text
    assert response.json() == {"username": "secret"}


def test_security_api_key_no_key():
    response = client.get("/users/me")

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()

        .build()
    val request =
      originalRequest.newBuilder()
        .header("Upgrade", "websocket")
        .header("Connection", "Upgrade")
        .header("Sec-WebSocket-Key", key)
        .header("Sec-WebSocket-Version", "13")
        .header("Sec-WebSocket-Extensions", "permessage-deflate")
        .build()
    call = RealCall(webSocketClient, request, forWebSocket = true)
    call!!.enqueue(