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

How do I get off this thread? Sent from my iPhone > On Feb 9, 2022, at 2:53 PM, Jānis Elmeris <janis.elmeris@lv.lv> wrote: > >  > Thank you for the suggestions! > > The big problem of debugging by disabling/enabling plugins is that the error cannot be > reproduced consistently. You may browse the store, doing similar actions for 10 min, and you're > lucky if you get one "headers already sent" error message. So, if you keep browsing for 10 > min and no error occurs, it doesn't mean it will not occur in the next 10 min. > > 'WP_DEBUG', 'WP_DEBUG_LOG' constants would not really help, because the > message gets output before those constants are defined or getting checked. As I wrote, the warning > occurs before any of the WordPress' PHP code gets executed. > > And as I told, the error message does not tell me 'headers already sent by "plugin > name"'. The full error message is as follows: > "PHP Warning: Unknown: Headers already sent. You cannot change the session module's > ini settings at this time in Unknown on line 0" > > I'm not sure what is trying to change what session settings before any PHP code gets > executed, and how can the headers already be sent at that point. > > Janis > > No: Negin Nickparsa <nickparsa@gmail.com> > Nosūtīts: otrdiena, 2022. gada 8. februāris 21:01 > Kam: Jānis Elmeris <janis.elmeris@lv.lv> > Kopija: php-general@lists.php.net <php-general@lists.php.net> > Tēma: Re: Atb.: How to debug "Unknown: Headers already sent"? > > you can post this in wordpress community support, they should be able to help you. > > enable your debugs first and show more details > define('WP_DEBUG', true); > define('WP_DEBUG_LOG', true); > define('WP_DEBUG_DISPLAY', false); > Issue is not nginx, your best bet is plugins, one of them is sending it early, it usually > should tell you headers already sent by "plugin name" if you have all logs enabled. > > After this, when you see a better presentation of errors, if the error was inside a plugin, by > this far you would know the plugin name inside the error. > If not , still disable plugins half and half and if an issue happens in that half of plugins > again disable half until you find the culprit. > > somewhere in plugins should be your focus. also switch templates and see if culprit is there. > > Negin Nickparsa > > > On Tue, Feb 8, 2022 at 2:04 AM Jānis Elmeris <janis.elmeris@lv.lv> wrote: > Thank you for the reply! > > So, in Magento, every time the site sends any kind of response back to the client, you log the > backtrace of who has called the response controller? > > I don't think it would help me (in my case it's Wordpress), because the headers > warning is output even before the Wordpress code starts to get executed (even before > "auto_prepend_file" gets executed). > > Janis > > No: Negin Nickparsa <nickparsa@gmail.com> > Nosūtīts: otrdiena, 2022. gada 8. februāris 06:34 > Kam: Jānis Elmeris <janis.elmeris@lv.lv> > Kopija: AllenJB <php.lists@allenjb.me.uk>; php-general@lists.php.net > <php-general@lists.php.net> > Tēma: 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.