Source

File: wp-includes/rest-api/class-wp-rest-server.php

public function get_data_for_route( $route, $callbacks, $context = 'view' ) {
		$data = array(
			'namespace' => '',
			'methods'   => array(),
			'endpoints' => array(),
		);

		if ( isset( $this->route_options[ $route ] ) ) {
			$options = $this->route_options[ $route ];

			if ( isset( $options['namespace'] ) ) {
				$data['namespace'] = $options['namespace'];
			}

			if ( isset( $options['schema'] ) && 'help' === $context ) {
				$data['schema'] = call_user_func( $options['schema'] );
			}
		}

		$route = preg_replace( '#\(\?P<(\w+?)>.*?\)#', '{$1}', $route );

		foreach ( $callbacks as $callback ) {
			// Skip to the next route if any callback is hidden.
			if ( empty( $callback['show_in_index'] ) ) {
				continue;
			}

			$data['methods'] = array_merge( $data['methods'], array_keys( $callback['methods'] ) );
			$endpoint_data   = array(
				'methods' => array_keys( $callback['methods'] ),
			);

			if ( isset( $callback['args'] ) ) {
				$endpoint_data['args'] = array();

				foreach ( $callback['args'] as $key => $opts ) {
					$arg_data = array(
						'required' => ! empty( $opts['required'] ),
					);
					if ( isset( $opts['default'] ) ) {
						$arg_data['default'] = $opts['default'];
					}
					if ( isset( $opts['enum'] ) ) {
						$arg_data['enum'] = $opts['enum'];
					}
					if ( isset( $opts['description'] ) ) {
						$arg_data['description'] = $opts['description'];
					}
					if ( isset( $opts['type'] ) ) {
						$arg_data['type'] = $opts['type'];
					}
					if ( isset( $opts['items'] ) ) {
						$arg_data['items'] = $opts['items'];
					}
					$endpoint_data['args'][ $key ] = $arg_data;
				}
			}

			$data['endpoints'][] = $endpoint_data;

			// For non-variable routes, generate links.
			if ( strpos( $route, '{' ) === false ) {
				$data['_links'] = array(
					'self' => array(
						array(
							'href' => rest_url( $route ),
						),
					),
				);
			}
		}

		if ( empty( $data['methods'] ) ) {
			// No methods supported, hide the route.
			return null;
		}

		return $data;
	}