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 <[email protected]> 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 <[email protected]>
> *Nosūtīts:* otrdiena, 2022. gada 8. februāris 21:01
> *Kam:* Jānis Elmeris <[email protected]>
> *Kopija:* [email protected] <[email protected]>
> *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 <[email protected]> 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 <[email protected]>
> *Nosūtīts:* otrdiena, 2022. gada 8. februāris 06:34
> *Kam:* Jānis Elmeris <[email protected]>
> *Kopija:* AllenJB <[email protected]>; [email protected] <
> [email protected]>
> *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 <[email protected]> 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 <[email protected]>
> *Nosūtīts:* ceturtdiena, 2022. gada 6. janvāris 21:28
> *Kam:* [email protected] <[email protected]>
> *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.
>
>