An in-depth analysis of PHP lock file anti-deletion technology

In the PHP development process, we often need to use file operations, including read, write, delete and other operations. In terms of file deletion, we may need to consider some special situations, for example, a user or malicious program deletes an important file accidentally or intentionally, which will have an unpredictable impact on the entire application. How to protect files from malicious deletion? This requires the use of PHP lock file anti-deletion technology.

What is a lock file?

A lock file is a special file used to control access to shared resources. In multi-process or multi-thread applications, we often need to use shared resources, such as database connections, file resources, etc. If these shared resources are accessed simultaneously without control, many problems may occur, such as data confusion, deadlock, etc. Therefore, we need to use some means to control access to these shared resources to avoid these problems. Among them, locking files is a commonly used method.

In PHP, we can use flock function to lock and unlock files. The flock function is a file locking mechanism that can lock a file to exclusively hold it until the lock expires or is unlocked. This lock can be a shared lock or an exclusive lock. A shared lock means locking a file to allow reading it, but not writing to it; an exclusive lock means locking a file preventing any other process or thread from accessing it until the lock expires or is unlocked.

php lock file anti-deletion principle

php lock file anti-deletion principle is to lock the file to be deleted. Specifically, when we want to delete a file, we first lock the file and then perform the deletion operation. If the file is already locked by another process or thread, the deletion operation will fail, thereby preventing the file from being maliciously deleted.

How to prevent deletion of PHP lock files? Below we will illustrate with an example.

php lock file anti-deletion example

In this example, we will use the flock function of php to implement the lock and unlock operation of the file, so as to prevent the file from being maliciously deleted. .

<?php
$filename = "test.txt"; // 待删除的文件名
$lockfile = $filename . ".lock"; // 锁定文件名

// 判断待删除文件是否存在
if (!file_exists($filename)) {
    echo "文件不存在！";
    exit;
}

// 创建锁定文件
$fp = fopen($lockfile, "w");
flock($fp, LOCK_EX); // 独占锁

// 删除文件
if (!unlink($filename)) {
    echo "删除失败！";
    flock($fp, LOCK_UN); // 解锁
    exit;
}

// 解锁
flock($fp, LOCK_UN);
fclose($fp);

echo "删除成功！";
?>

In this example, we first determine whether the file to be deleted exists. If the file does not exist, exit the program. Next, we create a lock file and lock the file using an exclusive lock. Then we try to delete the file we want to delete. If deletion fails, output "Deletion failed" and release the lock on the locked file, exiting the program. Otherwise, we release the lock on the locked file and close the locked file, outputting "Delete Successfully".

It should be noted that if another process or thread is using the file to be deleted, the deletion operation will fail when trying to delete the file. Therefore, the principle of PHP lock file anti-deletion is to lock the file to be deleted, and the deletion operation can only be performed after the file is successfully locked.

Summary

PHP locking files to prevent deletion is a relatively common technology, which can improve the security and stability of applications. When performing a file deletion operation, we can first lock the file to be deleted, and then perform the deletion operation. The locking operation can be implemented using PHP's flock function. If the lock fails, it means that the file has been locked by other processes or threads, and we cannot perform the deletion operation at this time, thereby preventing the file from being maliciously deleted.

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