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Monday, November 14, 2016

PHP Send data to browser, but keep executing script in background

How to echo or print PHP script while its still executing?


ob_flush writes the buffer. In other words, ob_flush tells PHP to give Apache (or nginx/lighttpd/whatever) the output and then for PHP to forget about it. Once Apache has the output, it does whatever it wants with it. (In other words, after ob_flush it's out of your control whether or not it gets immediately written to the browser).
So, short answer: There's no guaranteed way to do that.
Just a guess, you're likely looking for AJAX. Whenever people are trying to manipulate when page content loads as you're doing, AJAX is almost always the correct path.
If you want to continue a task in the background, you can use ignore_user_abort,  however, that is often not the optimal approach. You essentially lose control over that thread, and in my opinion, a web server thread is not where heavy processing belongs.
I would try to extract it out of the web facing stuff. This could mean a cron entry or just spawning a background process from inside of PHP (a process that though started from inside of script execution will not die with the script, and the script will not wait for it to finish before dying).
If you do go that route, it will mean that you can even make some kind of status system if necessary. Then you could monitor the execution and give the user periodic updates on the progress. (Technically you could make a status system with a ignore_user_abort-ed script too, but it doesn't seem as clean to me.)

I have done this in the past and this is how I solved it:
ob_start();

/*
 * Generate your output here
 */ 

// Ignore connection-closing by the client/user
ignore_user_abort(true);

// Set your timelimit to a length long enough for your script to run, 
// but not so long it will bog down your server in case multiple versions run 
// or this script get's in an endless loop.
if ( 
     !ini_get('safe_mode') 
     && strpos(ini_get('disable_functions'), 'set_time_limit') === FALSE 
){
    set_time_limit(60);
}

// Get your output and send it to the client
$content = ob_get_contents();         // Get the content of the output buffer
ob_end_clean();                      // Close current output buffer
$len = strlen($content);             // Get the length
header('Connection: close');         // Tell the client to close connection
header("Content-Length: $len");     // Close connection after $len characters
echo $content;                       // Output content
flush();                             // Force php-output-cache to flush to browser.
                                     // See caveats below.

// Optional: kill all other output buffering
while (ob_get_level() > 0) {
    ob_end_clean();
}

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