Analyzing Output Buffering in PHP_PHP Tutorial-PHP Tutorial-php.cn

Analyzing Output Buffering in PHP_PHP Tutorial

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Release： 2016-07-21 15:58:29

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Let’s look at a piece of code first:

〈?php
for ($i=10; $i〉0; $i--)
{
echo $i;
flush();
sleep(1);
}
?〉

According to the PHP manual, this function sends all the output of the program so far to the user's browser.

The above code should output $i every one second. But this is not necessarily the case in practice. It is possible that after waiting for 10 seconds, all output is presented at the same time.

OK, let’s change this code to

〈?php
ob_end_clean();//Modify part
for ($i=10; $i 〉0; $i--)
{
echo $i;
flush();
sleep(1);
}
?〉
Hey, added This sentence ob_end_clean(); is actually OK. In fact, it is also OK if we replace ob_end_clean() with ob_end_flush().

I will change it again.

〈?php
for ($i=10; $i〉0; $i--)
{
echo $i;
ob_flush();//Modify Part
flush();
sleep(1);
}
?〉
Run it, do you find that $i is also output every second? Why is this?
Don’t worry, let’s take a look at php.ini.

Open php.ini, search for output_buffering, we will see a setting like this output_buffering = 4096. Just like its name output_buffering, the function of this setting is to buffer the output. The buffer size is 4096bytes.

In our first piece of code, the reason why the output is not as expected is precisely because of this output_buffering Buffer those outputs. The output will not be sent before 4096 bytes is reached or the script ends.

The function of ob_end_clean() and ob_end_flush() in the second piece of code is to terminate the buffering. In this way, there is no need to wait until there is a buffer of 4096 bytes before being sent out.

In the third piece of code, ob_flush() is used. Its function is to send the buffered data, but it does not terminate the buffering, so it must be used before each flush().

If we don’t want to use ob_end_clean(), ob_end_flush() and ob_flush(), we must set the output_buffering in php.ini small enough, for example, set to 0. It should be noted that if you plan to use ini_set("output_buffering", "0") to set it in a script, then please stop, this method will not work. Because at the beginning of the script, the buffering settings have been loaded, and then buffering starts.

You may ask, since ob_flush() sends the buffered data, why do you need to use flush()??? Can't you just use the following code? ?

〈?php
for ($i=10; $i〉0; $i--)
{
echo $i;
ob_flush();
sleep(1);
}
?〉
Please note the difference between ob_flush() and flush(). The former is to release data from PHP's buffer, and the latter is to send data that is not in the buffer or has been released to the browser. So when the buffer exists, we must use ob_flush() and flush() at the same time.

Is flush() indispensable here? No, we have another method so that when data is output, it is immediately sent to the browser. The following two pieces of code do not need to use flush().(When you set output_buffering to 0, you don’t even need ob_flush() and ob_end_clean())

　?php
ob_implicit_flush(true);
for ($i=10 ; $i〉0; $i--)
{
echo $i;
ob_flush();
sleep(1);
}
?〉
〈 ?php
ob_end_clean();
ob_implicit_flush(true);
for ($i=10; $i〉0; $i--)
{
echo $i;
sleep(1); In this way, there is no need to use flush() to send it to the browser after each output (echo).

The above complaint may not be true in some browsers. Because browsers also have their own rules. I used Firefox1.5, IE6, opera8.5 to test. Among them, opera cannot output normally because it has a rule that if it does not encounter an HTML tag, it will never output unless the script ends. FireFox and IE are relatively normal.

Finally, here is a very interesting piece of code written by PuTTYshell. In a script cycle, each output will overwrite the previous output.
The following code is only available under firefox. Other browsers do not support the Content-Type of multipart/x-mixed-replace.

〈?php
header('Content-type: multipart/ x-mixed-replace;boundary=endofsection');
print “n--endofsectionn“;

$pmt = array(“-“, “\“, “|“, “/“) ;
for( $i = 0; $i 〈10; $i ++ ){
sleep(1);
print “Content-type: text/plainnn“;
print “Part $it".$pmt[$i % 4];
print "--endofsectionn";
ob_flush();
flush();
}
print "Content-type: text/plainnn";
print "The endn";
print "--endofsection--n";
?〉