Sharing the method of implementing HTML tag filtering in PHP

Sharing of methods for implementing HTML tag filtering in PHP

In web development, we often encounter situations where it is necessary to filter HTML tags input by users to prevent malicious scripts Or code injection to ensure the security of the website. As a popular server-side language, PHP provides a variety of methods to implement HTML tag filtering. Next, we will share a simple and effective method, with specific code examples.

1. Use the strip_tags() function

PHP provides the strip_tags() function, which can be used to filter HTML and PHP tags in strings. The implementation is simple, you can specify which tags are allowed to be retained, and other tags will be removed. Here is a sample code:

$input = '<p>This is a <strong>sample</strong> text with <a href="#">link</a>.</p>';
$clean_input = strip_tags($input, '<strong><a>');

echo $clean_input; // 输出：This is a <strong>sample</strong> text with <a href="#">link</a>.

In the above example, the strip_tags() function will retain the <strong></strong> and <a></a> tags and remove them other tags. This ensures that user input contains only specified security labels.

2. Use the htmlspecialchars() function

Another commonly used method is to use the htmlspecialchars() function to escape special characters into HTML entities to prevent XSS attacks. The following is a sample code:

$input = '<script>alert("XSS attack")</script>';
$clean_input = htmlspecialchars($input, ENT_QUOTES);

echo $clean_input; // 输出：<script>alert("XSS attack")</script>

htmlspecialchars() function will 、<code>>、"、'## Characters such as # are escaped into corresponding HTML entities to avoid malicious code execution. When outputting to the page, decoding it again can ensure that the content input by the user is output safely.

3. Best Practices

In order to improve security, it is recommended to combine the strip_tags() and htmlspecialchars() functions to filter the HTML content entered by the user. First use the strip_tags() function to filter out unsafe tags, and then use the htmlspecialchars() function to escape special characters, which can be effective Prevent XSS attacks.

$input = '<p>This is a <script>alert("XSS attack")</script> text with <a href="#">link</a>.</p>';
$clean_input = strip_tags($input, '<strong><a>');
$clean_input = htmlspecialchars($clean_input, ENT_QUOTES);

echo $clean_input; // 输出：This is a <script>alert("XSS attack")</script> text with <a href="#">link</a>.

The above is the sharing of methods for using PHP to implement HTML tag filtering. By combining the strip_tags() and htmlspecialchars() functions, the website can be effectively protected from malicious code attacks. During the development process, Please be sure to properly filter and process user input to ensure the security of the website.

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