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Date: Sun, 13 Apr 2025 15:37:31 +0100
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Subject: Re: [PHP-DEV] [RFC] [Discussion] Change default for
 zend.exception_ignore_args INI setting
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From: imsop.php@rwec.co.uk ("Rowan Tommins [IMSoP]")

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On 13/04/2025 15:07, Kamil Tekiela wrote:
>> This discussion seems to have overlooked that the setting doesn't just
>> restrict the*display* of arguments, it restricts the*collection* of
>> those arguments into the Exception object, which has visible effects on
>> the behaviour and performance of the program.
> Oh, I didn't know that. I assumed the arguments wouldn't be freed
> until the exception is destructed with it either on or off. In that
> case, please ignore everything I said previously.


For reference, this is the code in question: 
https://github.com/php/php-src/blob/1684c52a88d1429cf19d4927fe2edf7ff37c66be/Zend/zend_exceptions.c#L257

When the exception is created, it calls the internal implementation of 
debug_backtrace, passing either DEBUG_BACKTRACE_IGNORE_ARGS or 0 (which 
is why it never captures $this). The result is then stored in the 
private $trace property, to be used by whatever wants it later.

zend.exception_string_param_max_len, on the other hand, is used only in 
zend_trace_to_string - i.e. when converting the stored trace for 
display, or on call to the getTraceAsString() method. It has no effect 
if zend.exception_ignore_args was set to 1 when the exception was 
created, because the 'args' key won't be there to display.

It might be useful to have a "middle way" for both debug_backtrace() and 
exception traces which directly summarised the arguments in some way, 
and stored only that summary, thus limiting the performance and 
side-effects of capturing the original values. This wouldn't solve the 
sensitive information problem, though, so I'm not sure how good an idea 
it would be.


-- 
Rowan Tommins
[IMSoP]

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    <div class="moz-cite-prefix">On 13/04/2025 15:07, Kamil Tekiela
      wrote:<br>
    </div>
    <blockquote type="cite"
cite="mid:CAGBsUrdDptWTdaALL3EZPb-29Mo0VWe5xbYmTNdwmOhPdb-AGA@mail.gmail.com">
      <pre class="moz-quote-pre" wrap=""><blockquote type="cite"
      style="color: #007cff;"><pre wrap="" class="moz-quote-pre">This discussion seems to have overlooked that the setting doesn't just
restrict the <b class="moz-txt-star"><span class="moz-txt-tag">*</span>display<span
      class="moz-txt-tag">*</span></b> of arguments, it restricts the <b
      class="moz-txt-star"><span class="moz-txt-tag">*</span>collection<span
      class="moz-txt-tag">*</span></b> of
those arguments into the Exception object, which has visible effects on
the behaviour and performance of the program.
</pre></blockquote></pre>
    </blockquote>
    <blockquote type="cite"
cite="mid:CAGBsUrdDptWTdaALL3EZPb-29Mo0VWe5xbYmTNdwmOhPdb-AGA@mail.gmail.com">
      <pre class="moz-quote-pre" wrap=""><pre wrap=""
      class="moz-quote-pre">
Oh, I didn't know that. I assumed the arguments wouldn't be freed
until the exception is destructed with it either on or off. In that
case, please ignore everything I said previously.</pre></pre>
    </blockquote>
    <p><br>
    </p>
    <p>For reference, this is the code in question:
<a class="moz-txt-link-freetext" href="https://github.com/php/php-src/blob/1684c52a88d1429cf19d4927fe2edf7ff37c66be/Zend/zend_exceptions.c#L257">https://github.com/php/php-src/blob/1684c52a88d1429cf19d4927fe2edf7ff37c66be/Zend/zend_exceptions.c#L257</a></p>
    <p>When the exception is created, it calls the internal
      implementation of debug_backtrace, passing either
      DEBUG_BACKTRACE_IGNORE_ARGS or 0 (which is why it never captures
      $this). The result is then stored in the private $trace property,
      to be used by whatever wants it later.<br>
    </p>
    <p>zend.exception_string_param_max_len, on the other hand, is used
      only in zend_trace_to_string - i.e. when converting the stored
      trace for display, or on call to the getTraceAsString() method. It
      has no effect if zend.exception_ignore_args was set to 1 when the
      exception was created, because the 'args' key won't be there to
      display.<br>
    </p>
    <p>It might be useful to have a "middle way" for both
      debug_backtrace() and exception traces which directly summarised
      the arguments in some way, and stored only that summary, thus
      limiting the performance and side-effects of capturing the
      original values. This wouldn't solve the sensitive information
      problem, though, so I'm not sure how good an idea it would be.<br>
    </p>
    <p><br>
    </p>
    <pre class="moz-signature" cols="72">-- 
Rowan Tommins
[IMSoP]</pre>
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