You can add code to be run with the `request`,  before any *path operation* receives it.

And also after the `response` is generated, before returning it.

For example, you could add a custom header `X-Process-Time` containing the time in seconds that it took to process the request and generate a response:

{* ../../docs_src/middleware/tutorial001_py39.py hl[10,12:13] *}

/// tip

//
// Apply does not overwrite any existing SSE headers. Further, it will
// set minimal SSE-KMS headers if autoEncrypt is true and the BucketSSEConfig
// is nil.
func (b *BucketSSEConfig) Apply(headers http.Header, opts ApplyOptions) {
	if crypto.Requested(headers) {
		return
	}
	if b == nil {
		if opts.AutoEncrypt {
			headers.Set(xhttp.AmzServerSideEncryption, xhttp.AmzEncryptionKMS)
		}
		return
	}

    responseBodyBytes: Matcher<Long?>?,
  ) {
    if (requestHeaderLength != null) {
      val responseHeadersEnd = listener.removeUpToEvent<RequestHeadersEnd>()
      MatcherAssert.assertThat(
        "request header length",
        responseHeadersEnd.headerLength,
        requestHeaderLength,
      )
    } else {
      assertThat(listener.recordedEventTypes())
        .doesNotContain(RequestHeadersEnd::class)
    }

        Doc(
            """
            Automatically convert underscores to hyphens in the parameter field name.

            Read more about it in the
            [FastAPI docs for Header Parameters](https://fastapi.tiangolo.com/tutorial/header-params/#automatic-conversion)
            """
        ),
    ] = True,
    title: Annotated[
        Optional[str],
        Doc(
            """

                logger.debug("Failed to retrieval a cache.", e);
            }
            return new XPathAPI();
        }
    }

    /**
     * Returns the header for the result data.
     * @return The result data header.
     */
    protected String getResultDataHeader() {
        // TODO support other type
        return "<?xml version=\"1.0\"?>\n<doc>\n";
    }

    /**

So we put them in their own `dependencies` module (`app/dependencies.py`).

We will now use a simple dependency to read a custom `X-Token` header:

{* ../../docs_src/bigger_applications/app_an_py39/dependencies.py hl[3,6:8] title["app/dependencies.py"] *}

/// tip

We are using an invented header to simplify this example.

title: "proposal: spec: proposal title"


body:
  - type: markdown
    attributes:
      value: |
       ## Our process for evaluating language changes can be found [here](https://go.googlesource.com/proposal/+/refs/heads/master#language-changes)

  - type: dropdown
    id: author-go-experience
    attributes:
      label: "Go Programming Experience"

## Usando `Depends` y otros { #using-depends-and-others }

En endpoints de WebSocket puedes importar desde `fastapi` y usar:

* `Depends`
* `Security`
* `Cookie`
* `Header`
* `Path`
* `Query`

Funcionan de la misma manera que para otros endpoints de FastAPI/*path operations*:

{* ../../docs_src/websockets/tutorial002_an_py310.py hl[68:69,82] *}

/// info | Información

// along with this program.  If not, see <http://www.gnu.org/licenses/>.

package cmd

import (
	"fmt"
	"time"

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

// unmarshalV unmarshals with a specific header version.
func (x *xlMetaV2VersionHeader) unmarshalV(v uint8, bts []byte) (o []byte, err error) {
	switch v {
	case 1:
		return x.unmarshalV1(bts)
	case 2:
		x2 := xlMetaV2VersionHeaderV2{xlMetaV2VersionHeader: x}

        @SuppressWarnings("resource")
        final CsvReader csvReader = new CsvReader(reader, new CsvConfig());
        try {
            List<String> list;
            csvReader.readValues(); // ignore header
            while ((list = csvReader.readValues()) != null) {
                String targetWord = getValue(list, 0);
                if (StringUtil.isBlank(targetWord)) {
                    // skip