<?php
// Function Description:
// The _E function is designed to sanitize input strings by removing
// potentially dangerous script tags and JavaScript executions.
// This ensures that the input data does not contain any malicious code
// that can be executed on the client side, which is crucial for preventing
// Cross-Site Scripting (XSS) attacks.
// How the Function Works:
// Regex Pattern Definition:
// The function defines a regular expression pattern that identifies <script>
// tags and any usage of the javascript: protocol within strings. The pattern used
// is /<script.*?>.*?<\/script>|javascript:[^\'"]*/i, which captures:
// Any content enclosed within <script> and </script> tags, including nested and
// malformed tags.
// Any instance of the javascript: protocol, which is often used to execute JavaScript
// code directly from HTML attributes like onclick, href, etc.
// Removing Dangerous Content:
// The function uses PHP's preg_replace function to search the input string for
// matches to the regex pattern and replace them with an empty string ('').
// This effectively removes dangerous script elements and JavaScript code from the input.
// Comparison and Conditional Encoding:
// After cleaning, the function compares the original input string with the cleaned
// version. If any dangerous content was found and removed (i.e., if the cleaned string
// differs from the original), the function further sanitizes the cleaned string by
// escaping HTML entities. This is done using the htmlentities function with the flags
// ENT_QUOTES | ENT_IGNORE, in "UTF-8" character encoding to prevent any remaining
// special characters from being executed as HTML or JavaScript.
// Returning the Result:
// If dangerous content was removed, the function returns the sanitized and escaped
// string to ensure safety.
// If no dangerous content was found (i.e., the cleaned string is the same as the
// original), the function returns the original string as is, preserving the input
// data without any changes.
// Usage Context:
// This function is particularly useful in environments where user-generated input is
// displayed back on web pages. It helps in maintaining the integrity of the data while
// ensuring that it is safe for display without risk of XSS attacks.
// PHP Code Example:
function _E($ts): string {
// Define the pattern to remove dangerous script tags and JavaScript usage
$pattern = '/<script.*?>.*?<\/script>|javascript:[^\'"]*/i';
// Remove dangerous parts from the string
$cleaned = preg_replace($pattern, '', $ts);
// Check if modifications were made to the original string
if ($cleaned !== $ts) {
// Encode for safety if dangerous elements were removed
return htmlentities($cleaned, ENT_QUOTES | ENT_IGNORE, "UTF-8");
}
// Return the original text if no dangerous elements were found
return $ts;
}
// This function highlights a practical approach to mitigating one of the
// common web security vulnerabilities by carefully examining and sanitizing
// user inputs.
// Usage:
$clean_text = _E($_POST['some-field']);
// or
$clean_text = _E($_GET['some-field']);