Failed to start the session because headers have already been sent

Symfony\Component\HttpFoundation\Session\Storage\NativeSessionStorage->start() (Line: 164) Drupal\Core\Session\SessionManager->startNow() (Line: 118) Drupal\Core\Session\SessionManager->start() (Line: 323) Symfony\Component\HttpFoundation\Session\Storage\NativeSessionStorage->getBag('attributes') (Line: 249) Symfony\Component\HttpFoundation\Session\Session->getBag('attributes') (Line: 271) Symfony\Component\HttpFoundation\Session\Session->getAttributeBag() (Line: 81) Symfony\Component\HttpFoundation\Session\Session->set('ignore_replica_server', 1612152100) (Line: 69) Drupal\Core\Database\ReplicaKillSwitch->trigger() (Line: 139) Drupal\replica_cache\Cache\ReplicaDatabaseBackend->triggerKillSwitch() (Line: 98) Drupal\replica_cache\Cache\ReplicaDatabaseBackend->setMultiple(Array) (Line: 181) Drupal\Core\Cache\DatabaseBackend->set('module_implements', Array, -1, Array) (Line: 180) Drupal\Core\Cache\ChainedFastBackend->set('module_implements', Array) (Line: 337) Drupal\Core\Extension\ModuleHandler->writeCache() (Line: 42) Drupal\Core\EventSubscriber\RequestCloseSubscriber->onTerminate(Object, 'kernel.terminate', Object) call_user_func(Array, Object, 'kernel.terminate', Object) (Line: 142) Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher->dispatch(Object, 'kernel.terminate') (Line: 100) Symfony\Component\HttpKernel\HttpKernel->terminate(Object, Object) (Line: 32) Stack\StackedHttpKernel->terminate(Object, Object) (Line: 684) Drupal\Core\DrupalKernel->terminate(Object, Object) (Line: 22)

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Comment about 1 year ago →
🇺🇸United States mtdaveo
Where is the old/new code mentioned in #17?
Comment 8 months ago →
hudsom
In a controller I send a Response and have a fallback RedirectResponse if that or other things didn't work; also because a controller needs to return some sort of response. For some reason this didn't work anymore and I got the described error message.
With the following changes it worked:

Old:

try { $service->getResponse($destination, $langcode)->send(); catch { // ... } return new RedirectResponse($destination, 302);
New:

try { $response = $service->getResponse($destination, $langcode); return new Response($response->getContent(), $response->getStatusCode(), $response->headers->all()); catch { // ... } return new RedirectResponse($destination, 302);
PS: I couldn't return the Response directly because it was a TrustedRedirectResponse with an external link which caused whole bunch of other problems.
Comment 3 months ago →
🇮🇳India sourabhutani
#17 worked for me. Thanks!