Detailed introduction to output_buffering in php

When I see the title, I believe that many people are confused and don’t know what output_buffering is. I also believe that many people know what output_buffering does. So today we will introduce to you the detailed introduction and knowledge of output_buffering in PHP. Those who know it can consolidate their knowledge points, and those who don’t know can learn it carefully!

1. Let’s talk about what are the caches in php!

In PHP, we can roughly divide cache into client cache (Browser cache) and server cache (Server cache). Since PHP is based on B/S architecture, we can understand it as browser-side cache and server-side cache.
In the cache that comes with PHP on the server side, it can be divided into two main types of cache! Program cache and OB cache! This is also the main content of our study of server-side caching!

The output sequence cached in PHP is:
PHP output cache is turned on:

echo,print -> php output_buffering -> server buffering -> browser buffering -> browser display

PHP output cache is not turned on:

echo,print -> server buffering -> browser buffering -> browser display

Browser output cache: It is 256Bytes for IE, 1000Bytes for Chrome and FireFox. The browser will output the data on the page only when the output data reaches this length or the script ends.

2. Server-side response process

A. The client sends a request response to the server!
B. The Apache server loads the PHP module, starts the corresponding process (or thread) and runs the corresponding PHP script page!
C. When OB cache is not turned on, all running results will be placed in the program cache, and then packaged and sent to the browser! The browser renders the page and generates the WEB page we last saw!
D. When the OB cache is turned on, the running results will be put into the OB cache and the program cache respectively. When the program runs to the last line, the data in the OB cache will be flushed back. The program is cached and then packaged and returned to the browser! The browser renders the page and generates the WEB page we see!

3. Common uses of OB cache!

a, output_buffering=4096, output less data (less than one buffer)

for($i=0; $i<5; $i++){ 
 
echo $i.&#39;<br>&#39;; 
 
sleep(1); 
 
}

Run result: wait until all scripts are completed before outputting, because the data has not been Full size of a buffer.

b, output_buffering=4096, output less data (less than one buffer), turn off output_buffering, modify output_buffering=0 in php.ini

echo str_repeat(" ",1024);//这里重复输出一个空白
for($i=0; $i<5; $i++){ 
echo $i."<br/>";
  flush(); 
  sleep(1); 
}

Running results: Because OB is disabled, There is no need to wait for the script to run before it can be output. The data does not stay in the OB and you can see intermittent output. echo ->browser buffering -> browser display

c, output_buffering=4096, output larger data (larger than one buffer), do not use ob_start()

for($i=0; $i<5; $i++){ 
  echo file_get_contents(&#39;f.txt&#39;).$i.&#39;<br/><br/><br/><br/>&#39;; 
  sleep(2); 
}

Running result: f. txt is a file larger than 4kb. Because it is larger than the default buffer value and the buffer space is not enough, it will be output every time the buffer is full, so you can see intermittent output.

d, output_buffering=4096, output larger data (larger than one buffer), use ob_start()

ob_start(); 
for($i=0; $i<5; $i++){ 
  echo file_get_contents(&#39;f.txt&#39;).$i.&#39;<br/><br/><br/><br/>&#39;; 
  sleep(2); 
}

Running results: Because ob_start() is used, a large enough size will be set for the buffer space, so it will be saved until the script is executed and then output.

e, output_buffering=On, use ob_start()

ob_start();
echo "abc-";
header("content-type:text/html;charset=utf-8");
echo "hello-";
ob_end_flush();
echo "aa-";
echo ob_get_contents();

Running result: abc-hello-aa-abc-hello-aa-

f, output_buffering=Off, Using ob_start()

ob_start();
echo "abc-";
header("content-type:text/html;charset=utf-8");
echo "hello-";
ob_end_flush();
echo "aa-";
echo ob_get_contents();

Running results:

abc-hello-aa-

The output buffer is stackable, which means that when one ob_start() is active, you can call another an ob_start(). Just make sure you call ob_end_flush() the correct number of times. If multiple output callback functions are active, the output content will always be filtered through them in nested order.

Note: In PHP5.2, OB is closed by default, and after 5.3 it is enabled by default;

Commonly used methods:

1.ob_start
Activate the output_buffering mechanism. Once activated, the script will no longer be output directly to the browser, but will be temporarily written to the php buffering area. It is not sent until the script has finished running.

2.ob_get_contents
Get the data in php buffering. Note: it must be called before ob_end_clean(), otherwise you will only get null characters.

3.ob_end_flush and ob_end_clean
ob_end_flush will output the data in php buffering, but will not clear it.
ob_end_clean will not output, but will only clear the data in php buffering.

4.ob_flush, flush, ob_implicit_flush
ob_flush will refresh the data in php buffering to the program cache

flush will refresh the program Cache into browser cache

ob_implicit_flush will turn absolute (implicit) flushing on or off. Absolute (implicit) flushing will result in a flushing operation after each output call, so that explicit calls to flush() are no longer needed

4. The role of OB cache!

OB cache is used in various aspects, but what I know is mainly in two aspects!
a. When the website is going to be staticized, choosing OB cache is a good choice!

b. Solve the error of Warning: Cannot modify header information - headers already sent by!
The reason for the error: it is caused by the misalignment of the response header and the corresponding body! Under normal circumstances, the corresponding content returned by the server to the browser should be: response header + response body!

However, if we turn on the OB cache, then the corresponding header information (generally the information set by the header() function) will be placed in the program cache!
Other output content, such as: echo print_r var_dump, etc., will be put into the OB cache first!
When the program ends, or the OB cache is closed, put the contents of the OB cache into the program cache! This ensures that the response header information always precedes the response body content!

Summary:

# I believe that through studying this article, friends who don’t know output_buffering will have knowledge and understanding. Partners can consolidate their own knowledge points, I hope it will be helpful to your work!

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