Re: How to debug "Unknown: Headers already sent"?

for me that I use Magento, it is pretty easy we would use a controller specifically the one that is sending the requests to the client, then do a backtrace and log the backtrace and see where in the file that echo culprit is, however for your case I do not know with pure PHP but maybe try to debug where you are sending the HTTP requests whatever platform you are using. Negin On Fri, Jan 7, 2022 at 4:13 AM Jānis Elmeris <janis.elmeris@lv.lv> wrote: > Thank you for the reply! > > I added error_logs before all the ini_sets I could find. When I browsed > the Woocommerce, I got the error three times in about 10 minutes. Looking > at the error log, it seemed that one time the error occurred right before > one specific ini_set call, but the two other cases didn't have explicit > ini_set calls in the code around the time the "Unknown: Headers already > sent." error appeared. So, I guess that the first one was just a > coincidence. > > I'm somehow not too hopeful of finding the problem in the PHP code seeing > as PHP engine itself does not know which PHP code file causes the problem.. > So, I suppose, the problem should be on some other level, shouldn't it? > > I saw someone on the Internet mentioning XDebug as a way to debug > something like this but gave no details. Would you have any idea on how to > use XDebug for such cases? > > Janis > > ------------------------------ > *No:* AllenJB <php.lists@allenjb.me.uk> > *Nosūtīts:* ceturtdiena, 2022. gada 6. janvāris 21:28 > *Kam:* php-general@lists.php.net <php-general@lists.php.net> > *Tēma:* Re: How to debug "Unknown: Headers already sent"? > > > > On 06/01/2022 17:13, Jānis Elmeris wrote: > > How can I try debugging the "Unknown: Headers already sent. You cannot > change the session module's ini settings at this time in Unknown on line 0" > warning, when PHP is not giving any more details except that it happened > (no info on what's trying to send the headers or where the output had > started). > > This warning happens from time to time only. (In my case, it happens when > I browse a Woocommerce store. It has happened in the local dev environment > when I click on a product, when I click on adding product to the cart, when > I click to checkout. But it happens rarely. Mostly, all the requests are > processed all right, no PHP warnings.) > > Almost everything that I found about "headers already sent" on the > Internet, refers to the cases when the PHP code is written in a way that > outputs some content before sending the headers, in which case the PHP > gives a reference to the PHP code that's in some way related to the error.. > But the "unknown" cases are different. > > I found that this error may be caused by repeatedly loading the same PHP > extensions, or by some PHP extension working incorrectly. For example, > "zlib" extension has had such problem when executing "ob_gzhandler". > > I looked at the PHP configuration and didn't see an extension being loaded > more than once. Regarding "ob_gzhandler", I found only one place in the > Wordpress code using it, and added a log there. Then I got a headers > already sent warning message, but the "ob_gzhandler" had not been used in > that request. > > So, how could this warning be tracked down? Can I use XDebug somehow to do > it? > > I'm using PHP 7.4 FPM. > > Regards, > Janis > > > The error message is specifically complaining about ini settings being > set. I would check the code for any calls to ini_set(), specifically that > are modifying ini settings relating to sessions (which all start with > 'session.' - see > https://www.php.net/manual/en/session.configuration.php > ). If you can then trace when / where this code is called, this might help > you work out what's going on. > > > When the issue does occur, try to note down what you were doing when it > happened. What were the last few actions you did? These may help you to > work out how to reproduce the issue. > > > As you appear to be using WooCommerce, I would try their support forums / > chat as they may know of issues specific to that application or any popular > plugins / extensions: https://developer.woocommerce.com/ > > > You might also want to try forums / chat for WordPress as WooCommerce is > built on that. You may also want to check all your plugins are up-to-date, > look for any which haven't been updated by their developers in a long time > and disable any which aren't being used. >