Move HTML purification to own method in Content\Text\HTML

src/Content/Text/BBCode.php

@@ -29,12 +29,10 @@ use Friendica\Content\Item;
 use Friendica\Content\OEmbed;
 use Friendica\Content\PageInfo;
 use Friendica\Content\Smilies;
-use Friendica\Content\Text\HTMLPurifier_URIScheme_cid;
 use Friendica\Core\Hook;
 use Friendica\Core\Logger;
 use Friendica\Core\Protocol;
 use Friendica\Core\Renderer;
-use Friendica\Core\System;
 use Friendica\DI;
 use Friendica\Model\Contact;
 use Friendica\Model\Event;
@@ -1877,28 +1875,16 @@ class BBCode
 			$text
 		);
 
-		\HTMLPurifier_URISchemeRegistry::instance()->register('cid', new HTMLPurifier_URIScheme_cid());
+		// Default iframe allowed domains/path
+		$allowedIframeDomains = [
+			DI::baseUrl()->getHostname()
+			. (DI::baseUrl()->getUrlPath() ? '/' . DI::baseUrl()->getUrlPath() : '')
+			. '/oembed/', # The path part has to change with the source in Content\Oembed::iframe
+			'www.youtube.com/embed/',
+			'player.vimeo.com/video/',
+		];
 
-		$config = \HTMLPurifier_HTML5Config::createDefault();
-		$config->set('HTML.Doctype', 'HTML5');
-		$config->set('HTML.SafeIframe', true);
-		$config->set('URI.SafeIframeRegexp', '%^(?:
-			https://www.youtube.com/embed/
-			|
-			https://player.vimeo.com/video/
-			|
-			' . DI::baseUrl() . '/oembed/ # Has to change with the source in Content\Oembed::iframe
-		)%xi');
-		$config->set('Attr.AllowedRel', [
-			'noreferrer' => true,
-			'noopener' => true,
-		]);
-		$config->set('Attr.AllowedFrameTargets', [
-			'_blank' => true,
-		]);
-
-		$HTMLPurifier = new \HTMLPurifier($config);
-		$text = $HTMLPurifier->purify($text);
+		$text = HTML::purify($text, $allowedIframeDomains);
 
 		return $text;
 	}

src/Content/Text/HTML.php

@@ -961,4 +961,63 @@ class HTML
 	{
 		return str_replace('&', '&', $s);
 	}
+
+	/**
+	 * Clean an HTML text for potentially harmful code
+	 *
+	 * @param string $text
+	 * @param array  $allowedIframeDomains List of allowed iframe source domains without the scheme
+	 * @return string
+	 */
+	public static function purify(string $text, array $allowedIframeDomains = []): string
+	{
+		// Allows cid: URL scheme
+		\HTMLPurifier_URISchemeRegistry::instance()->register('cid', new HTMLPurifier_URIScheme_cid());
+
+		$config = \HTMLPurifier_HTML5Config::createDefault();
+		$config->set('HTML.Doctype', 'HTML5');
+
+		// Used to remove iframe with src attribute filtered out
+		$config->set('AutoFormat.RemoveEmpty', true);
+
+		$config->set('HTML.SafeIframe', true);
+
+		array_walk($allowedIframeDomains, function (&$domain) {
+			// Allow the domain and all its eventual sub-domains
+			$domain = '(?:(?!-)[A-Za-z0-9-]{1,63}(?<!-)\.)*' . preg_quote(trim($domain, '/'), '%');
+		});
+
+		$config->set('URI.SafeIframeRegexp',
+			'%^https://(?:
+				' . implode('|', $allowedIframeDomains) . '
+			)
+			(?:/|$) # Prevents bogus domains like youtube.com.fake.tld
+			%xi'
+		);
+
+		$config->set('Attr.AllowedRel', [
+			'noreferrer' => true,
+			'noopener' => true,
+		]);
+		$config->set('Attr.AllowedFrameTargets', [
+			'_blank' => true,
+		]);
+
+		/* Uncomment to debug HTMLPurifier behavior
+		$config->set('Core.CollectErrors', true);
+		$config->set('Core.MaintainLineNumbers', true);
+		*/
+
+		$HTMLPurifier = new \HTMLPurifier($config);
+
+		$text = $HTMLPurifier->purify($text);
+
+		/** @var \HTMLPurifier_ErrorCollector $errorCollector */
+		/* Uncomment to debug HTML Purifier behavior
+		$errorCollector = $HTMLPurifier->context->get('ErrorCollector');
+		var_dump($errorCollector->getRaw());
+		*/
+
+		return $text;
+	}
 }

src/Module/Debug/Babel.php

@@ -180,9 +180,7 @@ class Babel extends BaseModule
 						'content' => $html
 					];
 
-					$config = \HTMLPurifier_Config::createDefault();
-					$HTMLPurifier = new \HTMLPurifier($config);
-					$purified = $HTMLPurifier->purify($html);
+					$purified = Text\HTML::purify($html);
 
 					$results[] = [
 						'title'   => DI::l10n()->t('HTML Purified (raw)'),