Question

How does the server knows that i’ve closed the browser in a code like this?

<?php
$i = 0;
while (1) {
    echo "a";
    flush();
    $fp = fopen("$i.txt", "w");
    fclose($fp);
    sleep(1);
    $i++;
}
?>

If i close the browser, the script stops and no more files are created.

Answer 1

This is because when you try to output something, such as echo "a"; flush();", PHP sees that the request has been aborted, and therefore stops the request.

Just a quick note. This only happens when you output something. I’m guessing this is because PHP was primarily used for templating, and designed mainly for outputting content. Well, if the content is not going to go anywhere, why continue processing the script?

If you don’t want it to stop. Do one of the following:

Option A: Don’t output anything.

flush() and echo are both considered outputs, along with many other functions. PHP only checks to see if a user has aborted when it goes to send content, so not outputting anything will make sure it doesn’t check. Although that is probably not as reliable as…

Option B: use ignore_user_abort(true)

This will make sure that the script continues to output even if the user leaves the page. You can then check with connection_aborted() to find out if the connection has been aborted.

You can read all of this on PHP’s Connection Handling Documentation.