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

search for session_start() in your code and replace it with this: (!isset($_SESSION)) { // server should keep session data for AT LEAST 24 hour ini_set('session.gc_maxlifetime', 60 * 60 * 24); // each client should remember their session id for EXACTLY 24 hour session_set_cookie_params(60 * 60 * 24); session_start(); } Sincerely Negin Nickparsa On Wed, Feb 9, 2022 at 11:52 AM 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. > >