}

    /**
     * Gets the appropriate extractor for the given response data.
     * Selects an extractor based on the MIME type or falls back to the Tika extractor.
     *
     * @param responseData the response data containing the document to extract
     * @return the extractor instance for processing the document
     * @throws FessSystemException if no suitable extractor can be found
     */
    @Override

And if you declared a `response_model`, it will still be used to filter and convert the object you returned.

**FastAPI** will use that *temporal* response to extract the headers (also cookies and status code), and will put them in the final response that contains the value you returned, filtered by any `response_model`.

`Header` has a little extra functionality on top of what `Path`, `Query` and `Cookie` provide.

Most of the standard headers are separated by a "hyphen" character, also known as the "minus symbol" (`-`).

But a variable like `user-agent` is invalid in Python.

So, by default, `Header` will convert the parameter names characters from underscore (`_`) to hyphen (`-`) to extract and document the headers.

            PluginEntry(id, implementationClass)
        }.toList()
    }
} catch (cause: IOException) {
    throw IllegalArgumentException(
        "Failed to extract plugin metadata from '" + jar.path + "'",
        cause
    )
}


private
fun isGradlePluginPropertiesFile(entry: JarEntry) = entry.run {

        }
        if (extractor == null) {
            throw new CrawlerSystemException("Extractor instance is null. Cannot register null extractor.");
        }
        if (extractorMap.containsKey(key)) {
            final Extractor[] existingExtractors = extractorMap.get(key);

// All values stored with a key starting with one of the following prefixes
// must be extracted from the header.
var userMetadataKeyPrefixes = []string{
	"x-amz-meta-",
	"x-minio-meta-",
}

// extractMetadataFromReq extracts metadata from HTTP header and HTTP queryString.
func extractMetadataFromReq(ctx context.Context, r *http.Request) (metadata map[string]string, err error) {

**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 }

There's a whole chapter here in the documentation about it, you can read it at [Additional Responses in OpenAPI](additional-responses.md){.internal-link target=_blank}.

## OpenAPI Extra { #openapi-extra }

When you declare a *path operation* in your application, **FastAPI** automatically generates the relevant metadata about that *path operation* to be included in the OpenAPI schema.

/// note | Technical details

	var lpVolumeSerialNumber uint32
	var lpFileSystemFlags, lpMaximumComponentLength uint32
	var lpFileSystemNameBuffer, volumeName [260]uint16
	ps := syscall.StringToUTF16Ptr(filepath.VolumeName(path))

	// Extract values safely
	// BOOL WINAPI GetVolumeInformation(
	// _In_opt_  LPCTSTR lpRootPathName,
	// _Out_opt_ LPTSTR  lpVolumeNameBuffer,
	// _In_      DWORD   nVolumeNameSize,
	// _Out_opt_ LPDWORD lpVolumeSerialNumber,

        return logger;
    }

    /**
     * Gets the appropriate extractor for the given response data.
     * Selects an extractor based on the MIME type of the file.
     *
     * @param responseData the response data containing the file to extract
     * @return the extractor instance for processing the file
     * @throws FessSystemException if no suitable extractor factory can be found
     */
    @Override