Source

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

public function get_routes( $namespace = '' ) {
		$endpoints = $this->endpoints;

		if ( $namespace ) {
			$endpoints = wp_list_filter( $endpoints, array( 'namespace' => $namespace ) );
		}

		/**
		 * Filters the array of available endpoints.
		 *
		 * @since 4.4.0
		 *
		 * @param array $endpoints The available endpoints. An array of matching regex patterns, each mapped
		 *                         to an array of callbacks for the endpoint. These take the format
		 *                         `'/path/regex' => array( $callback, $bitmask )` or
		 *                         `'/path/regex' => array( array( $callback, $bitmask ).
		 */
		$endpoints = apply_filters( 'rest_endpoints', $endpoints );

		// Normalise the endpoints.
		$defaults = array(
			'methods'       => '',
			'accept_json'   => false,
			'accept_raw'    => false,
			'show_in_index' => true,
			'args'          => array(),
		);

		foreach ( $endpoints as $route => &$handlers ) {

			if ( isset( $handlers['callback'] ) ) {
				// Single endpoint, add one deeper.
				$handlers = array( $handlers );
			}

			if ( ! isset( $this->route_options[ $route ] ) ) {
				$this->route_options[ $route ] = array();
			}

			foreach ( $handlers as $key => &$handler ) {

				if ( ! is_numeric( $key ) ) {
					// Route option, move it to the options.
					$this->route_options[ $route ][ $key ] = $handler;
					unset( $handlers[ $key ] );
					continue;
				}

				$handler = wp_parse_args( $handler, $defaults );

				// Allow comma-separated HTTP methods.
				if ( is_string( $handler['methods'] ) ) {
					$methods = explode( ',', $handler['methods'] );
				} elseif ( is_array( $handler['methods'] ) ) {
					$methods = $handler['methods'];
				} else {
					$methods = array();
				}

				$handler['methods'] = array();

				foreach ( $methods as $method ) {
					$method                        = strtoupper( trim( $method ) );
					$handler['methods'][ $method ] = true;
				}
			}
		}

		return $endpoints;
	}