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PODoes calling ob_end_clean() once at the top of a script guarantee ob_flush() is never needed?
 

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  1. PODoes calling ob_end_clean() once at the top of a script guarantee ob_flush() is never needed?
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    <p>When using PHP as the back-end for SSE (Server Sent Events) and similar server streaming solutions, I have been using the <code>@ob_flush();@flush()</code> idiom to make sure the data gets spat out immediately. (The ordering is important: <code>ob_flush()</code> flushes PHP's buffers, <code>flush()</code> then tells Apache to flush it too.)</p> <p>I started thinking about it after reading that <code>@</code> is slow. (In fact, according to comments in the PHP manual it adds roughly 0.005ms, so I've reclassified "slow" as "don't worry about it unless inside a tight loop"). I need the <code>@</code> on <code>ob_flush()</code> to stop it complaining when the output buffer is empty. BTW, I've followed through the source code until it reached Apache and it appears <code>flush()</code> does not throw any PHP errors.</p> <p>Now I'm wondering if I can reduce the above <code>@ob_flush();@flush()</code> to just <code>@flush()</code> (or even just <code>flush()</code>)? Again in PHP manual comments I find someone saying you could do this at the top of your script: <code>if (ob_get_level()) ob_end_clean();</code> (Which can be abbreviated to simply <code>@ob_end_clean();</code>)</p> <p>My question is: Is that a reliable command to mean output buffering will never be used and <code>ob_flush()</code> will never be needed? Across all PHP versions (well at least php 5.2 onwards) and all supported operating systems, with whatever weird settings a user might have put in php.ini?</p> <p>(If your answer is "no", please describe under which situations <code>ob_flush()</code> could still be needed.)</p>
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