Detailed explanation of examples of buffers in php

PHP buffer is enabled by default, its default parameters are in the php.ini configuration file, and the value is 4096 bytes. Find the output_buffering configuration parameter in it to modify the size of the PHP buffer.

Developers can also manually handle the PHP buffer mechanism in scripts through the ob_start() function. In this way, even if the output content exceeds the size of the configuration parameters, the data will not be transmitted to the browser. ob_start()Set the PHP buffer space to be large enough. Only after the script execution ends or is called The ob_end_flush() function will send the data to the browser.

We edit the php.ini configuration file, modify the output_buffering value and do the following tests. When output_buffering is modified to 4096, less data is output, making it smaller than a PHP buffer. The code is as follows:

for ($i = 0; $i< 10; $i++) {    
echo $i . &#39;<br/>&#39;;
    sleep($i + 1);      
    //}

After execution, you will find that it will not output every few seconds like conventional logic, but will output all at once until the script loop ends. In this case, the browser interface will remain blank until the script processing is completed. This is because the amount of data is too small and the output buffer is not full. The order of writing data: the echo statement is output to the PHP buffer, TCP buffer, and browser.

Next, we modify output_buffering=0, which still outputs less data, but the actual data is already larger than the PHP buffer. The code is as follows:

 for ($i = 0; $i< 10; $i++) {    echo $i . &#39;<br/>&#39;;
    flush();  //通知操作系统底层，尽快把数据发给客户端浏览器
    sleep($i + 1);      //}

The result of this script must be inconsistent with just now, because the capacity of the buffer is set to 0, that is, the PHP buffer mechanism is disabled. At this time, we will see intermittent output in the browser without having to wait until the script is executed to see the output. This is because the data does not stay in the output cache. The order of writing data is that echo is output to the TCP buffer and then output to the browser. We then change the parameter to output_buffering=4096, and the output data is larger than one buffer. The ob_start() function is not called in this example. Prepare a 4KB file or use the dd command to create a file under the shell:

 $dd if=/dev/zero of=f4096 bs=4096 count=1

Use the following code to verify:

for ($i = 0; $i< 10; $i++) {    
echo file_get_contents(&#39;./f4096&#39;) . $i . &#39;<br/>&#39;;
    sleep($i +1);
    }

You can see that the program response has not ended yet (HTTP connection and not closed), you can see intermittent output, and the browser interface will not remain blank all the time. Although the PHP output buffer mechanism is enabled, there will still be intermittent output instead of one-time output. This is because the PHP buffer space is not enough. Every time a buffer is filled, the data will be sent to the client browser.

The parameters are the same as the above example, that is, output_buffering=4096, the output data is larger than one PHP buffer. This time we call ob_start(), the code is as follows:

ob_start();      
//开启PHP缓冲区
for ($i = 0; $i< 10; $i++) {    
echo file_get_contents(&#39;./f4096&#39;) . $i . &#39;<br/>&#39;;
    sleep($i + 1);
}
ob_end_flush();

The complete output will not be seen until the server script is completely processed and the response is completed. The intervals between outputs are so short that no pause is felt. Before outputting, the browser will remain blank, waiting for server-side data. This is because once PHP calls the ob_start() function, it will expand the PHP buffer to a large enough size and will not send the PHP buffer until the ob_end_flush function is called or the script ends. data to the client browser.

ob_startActivate the output_buffering mechanism. Once activated, the script no longer outputs directly to the browser, but temporarily writes to the PHP buffer first. PHP enables the output_buffering mechanism by default, and expands the output_buffering value to a large enough value by calling the ob_start() function. You can also specify the value of output_buffering through $chunk_size. $chunk_sizeThe default value is 0, which means that the data in the PHP buffer will not be sent to the browser until the script is finished running. If the size of $chunk_size is set, it means that as long as the data length in the buffer reaches this value, the data in the buffer will be sent to the browser.

You can process the data in the PHP buffer by specifying the $ouput_callback parameter, such as the function ob_gzhandler(), which compresses the data in the buffer and then transmits it to browser.

ob_get_contents()The function is to obtain a copy of the data in the PHP buffer. This is an important function. Please see the following example:

<?phpob_start();   
?>
<html>
<body>today is <?php echo date(&#39;Y-m-d h：i：s&#39;);  
 ?>
</body>
</html>
<?php
$output = ob_get_contents();
ob_end_flush();echo &#39;<! output>&#39;.$output;?>

After the above script is run, check the source code, and two identical pieces of HTML will appear. The latter is to obtain the contents of the buffer through the ob_get_contents() function.

ob_end_flush() and ob_end_clean()Both functions will turn off the output buffer.

The difference is that ob_end_flush() just sends the data in the PHP buffer to the client browser, while ob_clean_clean() sends the data in the PHP buffer The data is deleted but not sent to the client.

ob_end_flush()After the call, the data in the PHP buffer still exists, ob_get_contents()You can still get a copy of the data in the PHP buffer.

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