PHP outputs data line by line and solves two common buffering problems

The blogger is keen on various Internet technologies. He is often wordy and often accompanied by obsessive-compulsive disorder. He updates frequently. If you think the article is helpful to you, you can follow me. Please indicate "Dark Blue Scythe" when reprinting

---

1. Encountered a problem

I wonder if you have encountered these two situations:

1. The boss wants you to add the database to the database All the data is displayed in the browser. Because the data needs to be compared, the boss requires not to use paging, so okay, it is no problem to output 1,000 pieces of data and print it out in a loop, but what if the data is millions of pieces? The browser freezes immediately. When you leave your seat, go out to drink a cup of coffee, go to the toilet, and chat with the receptionist for a long time, you come back and find that the browser has "program not responding." What should you do?
2. The boss asked you to improve the download link of the website, requiring you to directly left-click the mouse to download the file (for some file types, directly left-clicking will open the file, and many websites will prompt you to "right-click and save as"), You used the header function and the readfile function to easily implement this function, but after going online, you found that the browser will still freeze if the file is too large. This time the boss wants to buy you coffee, what should you do?

Okay, if you encounter the above two situations, or you may face such a problem in the future, you can mark it so that it can be solved quickly next time.

2. Principle

Back to business.

The following is a grand introduction to PHP output control Output buffer

First of all, try the effect of the following code

<?php
if (ob_get_level() == 0){ ob_start() }else{ exit(0);};//开始缓冲

for ($i = 0; $i<10; $i++){
    echo "Line to show.\n<br />";//不直接输出，先存入缓冲区中
    ob_flush();//将缓冲区的数据输出出来
    flush();//将缓冲区的数据输出出来
    sleep(2);//暂停两秒
}

echo "Done.";

ob_end_flush();//关闭并清理缓冲区

I didn’t expect that PHP can also achieve this kind of delayed loading Function, Isn’t it a very awesome feeling?

The principle is that PHP puts the data into the Buffer before outputting the data, and then outputs the buffered data when needed. Please be careful not to confuse this with the Cache.

The advantage of this is that on the one hand, it can achieve cool effects similar to delayed loading, on the other hand, it can also reduce the pressure on the server and client, otherwise there will be insufficient memory when outputting big data.

Note: ob_flush() and flush() are both used to flush buffer data, but the official recommendation is to use them together, because although only ob_flush() is used in most WebServers You can flush out the buffer, but in some cases, such as apache, you sometimes need to call flush(), so for the portability of your code, it is recommended to see ob_flush() and add it immediately after flush().

Now that we know the principle, let’s solve the two problems mentioned at the beginning.

3. Solve the problem of stuck output of millions of data in a single page

<?php
ob_start();
$data = [1,2,3,4,5,6,7,8,9,10];//实际数据更多，为方便距离假设浏览器一次输出10条会卡死
$per = 3;//每次输出3条,可以改成1000 

for ($i = 0;$i < count($data); $i+= $per){
    for($j = $i; $j < $i + $per && $j <count($data); $j++){
        echo $data[$j];
    }
    ob_flush();
    flush();
    sleep(2);
}

echo "Done.";

ob_end_flush();

4. Solve the problem of stuck when the header implementation file is downloaded because the file is too large

<?php
header('Content-type: application/txt');//输出类型
ob_start();

$data = "qwertyuioasdfghjkl";//文件内容，file_get_contents($file)
$per = 15;//每次输出15个字符,可以改成1000或更大 


for ($i = 0;$i < strlen($data); $i+= $per){
    for($j = $i; $j < $i + $per && $j <strlen($data); $j++){
        echo $data[$j];
    }
    sleep(2);
    ob_flush();
    flush();
}


echo "Done."; 
    
ob_end_flush(); 

The above introduces PHP to output data line by line and solves two common buffering problems, including aspects. I hope it will be helpful to friends who are interested in PHP tutorials.