sirius-press/plugins/sirius-press-sia-export/includes/class-spe-renderer.php

<?php
/**
 * Turning a live WordPress page into a file that stands on its own.
 *
 * The export is fetched over a loopback HTTP request rather than rendered
 * in-process. That costs a round trip, and it is worth it: a theme's output
 * depends on the whole request lifecycle — the main query, `wp_head`,
 * enqueued assets, late-filtered content, caching plugins. Re-creating that
 * by calling `get_the_content()` produces something that looks like the page
 * and is not the page, and the differences only show up in whichever theme
 * the site owner actually uses.
 *
 * URLs are then rewritten to be document-relative. Not absolute, because the
 * exported copy is served from the name, not from this WordPress host, and
 * every absolute link would drag readers back to the origin the export exists
 * to make optional. Not root-relative either, because the same bucket is
 * browsable under `/bns/<name>/` on the public gateway, where a root-relative
 * link points outside the site. Document-relative is the only form that works
 * in both places.
 *
 * @package SiriusPress
 */

defined( 'ABSPATH' ) || exit;

final class SPE_Renderer {

	/** Marks a request as the exporter's own, so the site can render for it. */
	const FLAG = 'sirius_export';

	/**
	 * Fetch a URL as an anonymous visitor would see it.
	 *
	 * @param string $url
	 * @return array{ok:bool,body:string,mime:string,error:string}
	 */
	public static function fetch( $url ) {
		$request_url = add_query_arg( self::FLAG, self::token(), $url );

		$response = wp_remote_get(
			$request_url,
			array(
				'timeout'     => 60,
				'redirection' => 3,
				// No cookies: the export must be what a logged-out reader
				// sees, not what the admin who triggered it sees.
				'cookies'     => array(),
				'sslverify'   => apply_filters( 'sirius_press_export_sslverify', true ),
				'headers'     => array(
					'user-agent'      => 'SiriusPress/' . SIRIUS_PRESS_EXPORT_VERSION . ' (static export)',
					'accept-encoding' => 'identity',
				),
			)
		);

		if ( is_wp_error( $response ) ) {
			return self::error( $response->get_error_message() );
		}
		$code = (int) wp_remote_retrieve_response_code( $response );
		if ( 200 !== $code ) {
			return self::error( sprintf( 'the site returned HTTP %d for %s', $code, $url ) );
		}
		$body = wp_remote_retrieve_body( $response );
		if ( '' === $body ) {
			return self::error( sprintf( '%s rendered an empty page', $url ) );
		}
		return array(
			'ok'    => true,
			'body'  => $body,
			'mime'  => (string) wp_remote_retrieve_header( $response, 'content-type' ),
			'error' => '',
		);
	}

	/**
	 * A token proving a loopback request came from this site.
	 *
	 * Not a security boundary — the pages being fetched are public. It exists
	 * so the site can recognise its own exporter and suppress things that
	 * make no sense in a static copy (admin bar, nonce-bearing markup) without
	 * giving a stranger a way to request that same altered output.
	 */
	public static function token() {
		return substr( hash_hmac( 'sha256', 'sirius-export', wp_salt( 'nonce' ) ), 0, 24 );
	}

	/** True when the current request is the exporter fetching a page. */
	public static function is_export_request() {
		// phpcs:ignore WordPress.Security.NonceVerification.Recommended
		return isset( $_GET[ self::FLAG ] ) && hash_equals( self::token(), sanitize_text_field( wp_unslash( $_GET[ self::FLAG ] ) ) );
	}

	/**
	 * Rewrite a page's URLs for life outside this host.
	 *
	 * @param string $html
	 * @param string $doc_path Where this document will live, e.g. 'blog/hi/index.html'.
	 * @return array{html:string,assets:array<string,string>} Rewritten HTML and the
	 *         local assets it referenced, as path => absolute source URL.
	 */
	public static function rewrite( $html, $doc_path ) {
		$home   = untrailingslashit( home_url() );
		$site   = untrailingslashit( site_url() );
		$assets = array();

		// The exporter's own marker must never survive into the output, or
		// every internal link in the static copy carries it.
		$html = preg_replace( '/([?&])' . preg_quote( self::FLAG, '/' ) . '=[^"\'&\s]*(&amp;|&)?/', '$1', $html );
		$html = str_replace( array( '?"', "?'" ), array( '"', "'" ), $html );

		$bases = array_unique( array( $home, $site, set_url_scheme( $home, 'http' ), set_url_scheme( $home, 'https' ) ) );

		// Protocol-relative references to our own host (`//example.test/…`)
		// are normalised to absolute first, so the pass below only has one
		// shape to match.
		//
		// Two details, both of which produced mangled links when they were
		// missing. The lookbehind stops this from also matching the
		// `//example.test` sitting inside every `https://example.test`, which
		// would give every absolute URL on the page a second scheme. And the
		// authority has to include the port: replacing `//host` alone inside
		// `//host:8760/x` leaves the port behind, producing `//host:8760:8760/x`.
		foreach ( array_unique( array_filter( array( $home, $site ) ) ) as $base ) {
			$authority = preg_replace( '#^https?:#', '', $base ); // '//host[:port]'
			if ( '' === $authority ) {
				continue;
			}
			$html = preg_replace(
				'#(?<!:)' . preg_quote( $authority, '#' ) . '#',
				$base,
				$html
			);
		}

		$pattern = '#(?:' . implode( '|', array_map( function ( $b ) {
			return preg_quote( $b, '#' );
		}, $bases ) ) . ')(/[^"\'\s<>\\\\)]*)?#';

		$html = preg_replace_callback(
			$pattern,
			function ( $matches ) use ( $doc_path, &$assets ) {
				$path = isset( $matches[1] ) ? $matches[1] : '/';
				return self::localise( $path, $doc_path, $assets );
			},
			$html
		);

		return array(
			'html'   => $html,
			'assets' => $assets,
		);
	}

	/**
	 * One absolute URL becomes one relative one, and any asset it names gets
	 * remembered so the caller can queue it.
	 */
	private static function localise( $path, $doc_path, &$assets ) {
		$parts    = wp_parse_url( $path );
		$clean    = isset( $parts['path'] ) ? $parts['path'] : '/';
		$suffix   = ( isset( $parts['query'] ) && '' !== $parts['query'] ? '?' . $parts['query'] : '' )
			. ( isset( $parts['fragment'] ) ? '#' . $parts['fragment'] : '' );
		$target   = SPE_Mapper::path_for_url_path( $clean );

		if ( '' === $target ) {
			// Nothing sensible to point at — an upload directory listing, a
			// path with characters the bucket will not take. Leave the URL
			// absolute rather than producing a link to nowhere.
			return untrailingslashit( home_url() ) . $path;
		}

		if ( SPE_Mapper::is_asset( $target ) ) {
			$assets[ $target ] = home_url( $clean );
			// Assets are versioned with ?ver=; the bucket stores one copy, so
			// the query string would only ever produce a 404.
			$suffix = isset( $parts['fragment'] ) ? '#' . $parts['fragment'] : '';
		}

		return self::relative( $doc_path, $target ) . $suffix;
	}

	/**
	 * Path of `$target` as seen from the document at `$from`.
	 *
	 * `blog/post/index.html` referring to `assets/app.css` yields
	 * `../../assets/app.css`.
	 */
	public static function relative( $from, $target ) {
		$from_dir = explode( '/', $from );
		array_pop( $from_dir ); // Drop the file name.
		$to = explode( '/', $target );

		while ( $from_dir && $to && $from_dir[0] === $to[0] ) {
			array_shift( $from_dir );
			array_shift( $to );
		}
		$up  = str_repeat( '../', count( $from_dir ) );
		$rel = $up . implode( '/', $to );
		return '' === $rel ? './' : $rel;
	}

	private static function error( $message ) {
		return array(
			'ok'    => false,
			'body'  => '',
			'mime'  => '',
			'error' => $message,
		);
	}

	/**
	 * Strip the parts of a page that only make sense on the live site.
	 *
	 * Runs on the *live* request when the exporter is the one asking, which
	 * is why it is here rather than in the rewriting pass: removing the admin
	 * bar after the fact means also unpicking the styles and spacing it added.
	 */
	public static function hooks() {
		add_action(
			'init',
			function () {
				if ( ! self::is_export_request() ) {
					return;
				}
				show_admin_bar( false );
				/**
				 * Fires on a page being rendered for static export.
				 *
				 * The place for a theme or plugin to drop anything that cannot
				 * work without PHP behind it — a live search box, a comment
				 * form, a cart widget.
				 */
				do_action( 'sirius_press_rendering_export' );
			},
			1
		);
	}
}