<div class="screenshot">
<img src="/img/tutorial/header-param-models/image01.png">
</div>

## Forbid Extra Headers { #forbid-extra-headers }

In some special use cases (probably not very common), you might want to **restrict** the headers that you want to receive.

You can use Pydantic's model configuration to `forbid` any `extra` fields:

{* ../../docs_src/header_param_models/tutorial002_an_py310.py hl[10] *}

            when(src.getContext()).thenReturn(ctx);

            // Force failure before any stream construction
            when(src.openUnshared(anyInt(), anyInt(), anyInt(), anyInt(), anyInt())).thenThrow(new SmbException("boom"));

            SmbTreeHandleImpl sh = newTreeHandle(false); // force non-SMB2 path to avoid server-side branch
            SmbTreeHandleImpl dh = newTreeHandle(false);

 * [system DNS service][SYSTEM], which is the default. Some applications may provide their own
 * implementation to use a different DNS server, to prefer IPv6 addresses, to prefer IPv4 addresses,
 * or to force a specific known IP address.
 *
 * Implementations of this interface must be safe for concurrent use.
 */
fun interface Dns {
  /**

Puedes verificarlo en la interfaz de documentación en `/docs`:

<div class="screenshot">
<img src="/img/tutorial/request-form-models/image01.png">
</div>

## Prohibir Campos de Formulario Extra { #forbid-extra-form-fields }

En algunos casos de uso especiales (probablemente no muy comunes), podrías querer **restringir** los campos de formulario a solo aquellos declarados en el modelo de Pydantic. Y **prohibir** cualquier campo **extra**.

		metadata[MetaDataEncryptionKey] = base64.StdEncoding.EncodeToString(kmsKey)
	}
	return metadata
}

// ParseMetadata extracts all SSE-KMS related values from the object metadata
// and checks whether they are well-formed. It returns the sealed object key
// on success. If the metadata contains both, a KMS master key ID and a sealed
// KMS data key it returns both. If the metadata does not contain neither a

 * is meant for exclusive consumption by the model builder and is opaque to the cache implementation. The cache key is
 * formed by a combination of group id, artifact id, version and tag. The first three components generally refer to the
 * identity of a model. The tag allows for further classification of the associated data on the sole discretion of the

 * under the License.
 */
package org.apache.maven.artifact.repository.metadata.io;

import java.io.IOException;

/**
 * Signals a failure to parse the metadata due to invalid syntax (e.g. non well formed XML or unknown elements).
 *
 */
public class MetadataParseException extends IOException {

    /**
     * The one-based index of the line containing the error.
     */
    private final int lineNumber;

@GwtCompatible
abstract class CommonPattern {
  public abstract CommonMatcher matcher(CharSequence t);

  public abstract String pattern();

  public abstract int flags();

  // Re-declare this as abstract to force subclasses to override.
  @Override
  public abstract String toString();

  public static CommonPattern compile(String pattern) {
    return Platform.compilePattern(pattern);
  }

    /** Whether to use Unicode encoding for strings */
    protected boolean useUnicode = true;
    /** Force use of Unicode encoding regardless of negotiation */
    protected boolean forceUnicode = false;
    /** Whether SMB signing is preferred but not required */
    protected boolean signingPreferred = false;
    /** Whether SMB signing is enforced (required) */
    protected boolean signingEnforced = false;

</div>

## Как запретить дополнительные заголовки { #forbid-extra-headers }

В некоторых случаях (не особо часто встречающихся) вам может понадобиться **ограничить** заголовки, которые вы хотите получать.

Вы можете использовать возможности конфигурации Pydantic-модели для того, чтобы запретить (`forbid`) любые дополнительные (`extra`) поля: