= ! empty( $schema['properties'] ) ? $schema['properties'] : array();
	$endpoint_args           = array();
	$valid_schema_properties = rest_get_allowed_schema_keywords();
	$valid_schema_properties = array_diff( $valid_schema_properties, array( 'default', 'required' ) );

	foreach ( $schema_properties as $field_id => $params ) {

		// Arguments specified as `readonly` are not allowed to be set.
		if ( ! empty( $params['readonly'] ) ) {
			continue;
		}

		$endpoint_args[ $field_id ] = array(
			'validate_callback' => 'rest_validate_request_arg',
			'sanitize_callback' => 'rest_sanitize_request_arg',
		);

		if ( WP_REST_Server::CREATABLE === $method && isset( $params['default'] ) ) {
			$endpoint_args[ $field_id ]['default'] = $params['default'];
		}

		if ( WP_REST_Server::CREATABLE === $method && ! empty( $params['required'] ) ) {
			$endpoint_args[ $field_id ]['required'] = true;
		}

		foreach ( $valid_schema_properties as $schema_prop ) {
			if ( isset( $params[ $schema_prop ] ) ) {
				$endpoint_args[ $field_id ][ $schema_prop ] = $params[ $schema_prop ];
			}
		}

		// Merge in any options provided by the schema property.
		if ( isset( $params['arg_options'] ) ) {

			// Only use required / default from arg_options on CREATABLE endpoints.
			if ( WP_REST_Server::CREATABLE !== $method ) {
				$params['arg_options'] = array_diff_key(
					$params['arg_options'],
					array(
						'required' => '',
						'default'  => '',
					)
				);
			}

			$endpoint_args[ $field_id ] = array_merge( $endpoint_args[ $field_id ], $params['arg_options'] );
		}
	}

	return $endpoint_args;
}


/**
 * Converts an error to a response object.
 *
 * This iterates over all error codes and messages to change it into a flat
 * array. This enables simpler client behaviour, as it is represented as a
 * list in JSON rather than an object/map.
 *
 * @since 5.7.0
 *
 * @param WP_Error $error WP_Error instance.
 *
 * @return WP_REST_Response List of associative arrays with code and message keys.
 */
function rest_convert_error_to_response( $error ) {
	$status = array_reduce(
		$error->get_all_error_data(),
		function ( $status, $error_data ) {
			return is_array( $error_data ) && isset( $error_data['status'] ) ? $error_data['status'] : $status;
		},
		500
	);

	$errors = array();

	foreach ( (array) $error->errors as $code => $messages ) {
		$all_data  = $error->get_all_error_data( $code );
		$last_data = array_pop( $all_data );

		foreach ( (array) $messages as $message ) {
			$formatted = array(
				'code'    => $code,
				'message' => $message,
				'data'    => $last_data,
			);

			if ( $all_data ) {
				$formatted['additional_data'] = $all_data;
			}

			$errors[] = $formatted;
		}
	}

	$data = $errors[0];
	if ( count( $errors ) > 1 ) {
		// Remove the primary error.
		array_shift( $errors );
		$data['additional_errors'] = $errors;
	}

	return new WP_REST_Response( $data, $status );
}