Merge pull request #9336 from annando/issue-9303

Issue 9303: Detect AP accesses as backend, prevent ping pong

src/App.php

@@ -448,7 +448,7 @@ class App
 				Core\Worker::executeIfIdle();
 			}
 
-			if ($this->mode->isNormal()) {
+			if ($this->mode->isNormal() && !$this->mode->isBackend()) {
 				$requester = HTTPSignature::getSigner('', $_SERVER);
 				if (!empty($requester)) {
 					Profile::addVisitorCookieForHandle($requester);
@@ -456,7 +456,7 @@ class App
 			}
 
 			// ZRL
-			if (!empty($_GET['zrl']) && $this->mode->isNormal()) {
+			if (!empty($_GET['zrl']) && $this->mode->isNormal() && !$this->mode->isBackend()) {
 				if (!local_user()) {
 					// Only continue when the given profile link seems valid
 					// Valid profile links contain a path with "/profile/" and no query parameters

src/App/Mode.php

@@ -38,6 +38,9 @@ class Mode
 	const DBCONFIGAVAILABLE   = 4;
 	const MAINTENANCEDISABLED = 8;
 
+	const BACKEND_CONTENT_TYPES = ['application/jrd+json', 'application/xrd+xml', 'text/xml',
+		'application/rss+xml', 'application/atom+xml', 'application/activity+json'];
+
 	/***
 	 * @var int The mode of this Application
 	 *
@@ -134,8 +137,13 @@ class Mode
 	 */
 	public function determineRunMode(bool $isBackend, Module $module, array $server, MobileDetect $mobileDetect)
 	{
-		$isBackend = $isBackend ||
+		foreach (self::BACKEND_CONTENT_TYPES as $type) {
-		             $module->isBackend();
+			if (strpos(strtolower($server['HTTP_ACCEPT'] ?? ''), $type) !== false) {
+				$isBackend = true;
+			}
+		}
+
+		$isBackend = $isBackend || $module->isBackend();
 		$isMobile  = $mobileDetect->isMobile();
 		$isTablet  = $mobileDetect->isTablet();
 		$isAjax    = strtolower($server['HTTP_X_REQUESTED_WITH'] ?? '') == 'xmlhttprequest';

src/Model/APContact.php

@@ -22,8 +22,11 @@
 namespace Friendica\Model;
 
 use Friendica\Content\Text\HTML;
+use Friendica\Core\Cache\Duration;
 use Friendica\Core\Logger;
+use Friendica\Core\System;
 use Friendica\Database\DBA;
+use Friendica\DI;
 use Friendica\Network\Probe;
 use Friendica\Protocol\ActivityNamespace;
 use Friendica\Protocol\ActivityPub;
@@ -40,7 +43,7 @@ class APContact
 	 * @param string $addr Address
 	 * @return array webfinger data
 	 */
-	public static function fetchWebfingerData(string $addr)
+	private static function fetchWebfingerData(string $addr)
 	{
 		$addr_parts = explode('@', $addr);
 		if (count($addr_parts) != 2) {
@@ -154,6 +157,16 @@ class APContact
 			return $fetched_contact;
 		}
 
+		// Detect multiple fast repeating request to the same address
+		// See https://github.com/friendica/friendica/issues/9303
+		$cachekey = 'apcontact:getByURL:' . $url;
+		$result = DI::cache()->get($cachekey);
+		if (!is_null($result)) {
+			Logger::notice('Multiple requests for the address', ['url' => $url, 'update' => $update, 'callstack' => System::callstack(20), 'result' => $result]);
+		} else {
+			DI::cache()->set($cachekey, System::callstack(20), Duration::FIVE_MINUTES);
+		}
+
 		$apcontact['url'] = $compacted['@id'];
 		$apcontact['uuid'] = JsonLD::fetchElement($compacted, 'diaspora:guid', '@value');
 		$apcontact['type'] = str_replace('as:', '', JsonLD::fetchElement($compacted, '@type'));