PHP output buffer control (Output Control) summary

Introduction to php buffering

In fact, my impression of the php ob series is still very vague. I don’t know much about how to play it. In my usual curd, I really don’t have an in-depth understanding of these contents. As a phper, I am very ashamed. After searching online and copying each other, the phenomenon described by the author cannot occur when running the code. This article is a conscientious product, and the code has been run by the author.

When executing output, such as echo, print. The output is not sent to the web server immediately, but the data is written to the php buffer. The benefits of the php output_buffering mechanism certainly improve performance. In fact, the php file is finally displayed on the browser and goes through three buffering stages: php buffer=》web server buffer=》browser buffer. Finally displayed in the browser

By default, php buffer is turned on, and the default value of the buffer is 4096, which is 4 kb. You can find the output_buffering configuration in the php.ini configuration file. Buffer is a memory address space. The default size of Linux system is generally 4096 (4kb), which is one memory page. It is mainly used to store data transfer areas between devices with unsynchronized speeds or devices with different priorities. Through the buffer, the processes can wait less for each other. Here is a more general example. When you open a text editor to edit a file, every time you enter a character, the operating system will not immediately write the character directly to the disk, but first write it to the buffer. When writing When a buffer is full, the data in the buffer will be written to the disk. Of course, when the kernel function flush() is called, it is mandatory to write the dirty data in the buffer back to the disk.

For example

<?php
echo "南无阿弥陀佛<br>";
header("content-type:text/html;charset=&#39;utf-8&#39;");
echo "真善忍好!";
//output
//南无阿弥陀佛
//真善忍好

header() must be called before any actual output, but our program has already output, but it runs normally. Looking at the code below:

<?php
echo "南无阿弥陀佛<br>";
ob_flush();
header("content-type:text/html;charset=&#39;utf-8&#39;");
echo "真善忍好!";
//output
//南无阿弥陀佛
//Cannot modify header information - headers already sent by (output started at E:\php\test.php:3)
//真善忍好

The above program shows that the program does not output immediately, but only refreshes the buffer and outputs when the ob_flush function is called.

ob_flush() and flush()

ob_flush() and flush() functions are detailed in the PHP manual, you can check them out. The difference between the two is:

ob_flush() is to refresh the buffer of PHP itself

flush() is to refresh the buffer of the WebServer server. Output to browser. However, the following situation will occur:

Individual web server programs, especially web server programs under Win32, will still cache the output of the script until the end of the program before sending the results to the browser.

Some Apache modules, such as mod_gzip, may cache their own output, which will cause the results generated by the flush() function to not be sent to the client browser immediately.

Even the browser will cache the received content before displaying it. For example, the Netscape browser caches content until it receives a line break or the beginning of an html tag, and does not display the entire table until it receives a tag.

Some versions of Microsoft Internet Explorer will only start displaying the page after receiving 256 bytes, so some extra spaces must be sent to allow these browsers to display the page content.

For example:

<?php
/**
Server:LightTPD/1.4.28 (Win32)
X-Powered-By:PHP/5.3.27
*/
echo &#39;佛法无边&#39;."<BR>";
ob_flush();
flush();
sleep(1);
echo &#39;法轮常转&#39;;
//output

The above code outputs line by line on the Chrome browser, but outputs all on the IE series browsers. In fact, it is the fourth item above. Some browsers only start displaying when they receive 256 characters. Change the above code to the following form:

<?php
/**
Server:LightTPD/1.4.28 (Win32)
X-Powered-By:PHP/5.3.27
*/
echo str_pad(&#39;&#39;,240)."\n"; 
echo &#39;佛法无边&#39;."<BR>";
ob_flush();
flush();
sleep(1);
echo &#39;法轮常转&#39;;
//output

This way it will be output line by line under IE because it exceeds 256 characters.

ob Other function descriptions

1. ob_end_flush and ob_end_clean

end end as their names suggest. They close the buffer and both close the output buffer. One is the output buffer and the other is clearing. For example,

<?php
/**
Server:LightTPD/1.4.28 (Win32)
X-Powered-By:PHP/5.3.27
*/
echo &#39;before&#39;;
ob_end_clean();
echo str_pad(&#39;&#39;,4096)."\n";
for ($i=10; $i>0; $i--) 
{ 
    echo $i;
    sleep(1);
}

The above code outputs the entire content at once, rather than outputting it one by one. Doesn't ob_end_clean() turn off the buffer? Why not output them one by one? In fact, as we said above, php is not output directly to the browser, but to the web server. Although php has no buffering. But the web server still exists. So the following code:

/**
Server:LightTPD/1.4.28 (Win32)
X-Powered-By:PHP/5.3.27
*/
echo 'before';
ob_end_clean();
echo str_pad('',4096)."\n";
for ($i=10; $i>0; $i--) 
{ 
    flush();
    echo $i;
    sleep(1);
}

加上flush(),就会一行一行输出。 如果把ob_end_clean 换成 ob_end_flush  会把 before 输出来。

其他函数 可参考手册，比较简单。

总结

php 脚本到浏览器，要经过  php buffer=》web server buffer=》browser buffer。 最后显示到浏览器。 缺一不可。 所以我们要 ob_flush 和  flush 以及加上  echo str_pad(”,4096) 才能调试出你想要的效果。