Detailed explanation of how PHP limits file download speed

How to limit file download speed in php? This article mainly introduces the code for limiting file download speed in PHP, with detailed code analysis, which has certain reference value. Friends in need can refer to it. I hope to be helpful.

Sometimes you will need to slow down the file download speed for some purpose, for example, you want to implement the file download progress bar function. The biggest benefit of limiting download speed is to save bandwidth and avoid network congestion caused by excessive instantaneous traffic. This article will share with you how to limit the download speed of files through PHP code.
First, let’s take a look at the code that uses php to limit the file download speed:

<?php 
// 将发送到客户端的本地文件 
$local_file=&#39;abc.zip&#39;; 
// 文件名 
$download_file=&#39;your-download-name.zip&#39;; 
// 设置下载速率(=> 31.2 kb/s) 
$download_rate=31.2; 
if(file_exists($local_file)&&is_file($local_file)){ 
 header(&#39;Cache-control: private&#39;);// 发送 headers 
 header(&#39;Content-Type: application/octet-stream&#39;); 
 header(&#39;Content-Length: &#39;.filesize($local_file)); 
 header(&#39;Content-Disposition: filename=&#39;.$download_file); 
 flush();// 刷新内容 
 $file=fopen($local_file,"r"); 
 while (!feof($file)){ 
  print fread($file,round($download_rate*1024));// 发送当前部分文件给浏览者 
  flush();// flush 内容输出到浏览器端 
  sleep(1);// 终端1秒后继续 
 } 
 fclose($file);// 关闭文件流 
}else{ 
 die(&#39;Error: 文件 &#39;.$local_file.&#39; 不存在!&#39;); 
}

Let’s do some analysis of the above code:
1. Limit the file download speed to 31.2kb/s , that is, only 20.5kb file stream is sent to the client per second until the entire file is sent. If there is no such limit, the files will be sent to the client together in the form of a stream. How many files will be sent? What will happen? If the file size is 2m, then transmitting the 2m data stream all at once may cause network congestion and interrupt the execution of the script. This download method cannot be used in actual applications.
2. Technical aspect, first add the header file, declare Content-Type as application/octet-stream, indicating that the request will be sent in a stream, and declare Content-Length, that is, declare the file The size of the stream. Flush() is used in the code. The flush function is to refresh the buffer of the php program and realize dynamic output of print.

Another reminder: Cleverly using the above code, you can also realize the function of the client displaying the file download progress bar. Friends who are interested can try it, so I won’t write more here.

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