htmlspecialchars and make links clickable - php

Question

I have a PHP script which processes user input. I need to escape all special characters, but also make links clickable (turn them into <a> elements). What I need is:
function specialCharsAndLinks($text) {
// magic goes here
}
$inp = "http://web.page/index.php?a1=hi&a2=hello\n<script src=\"http://bad-website.com/exploit.js\"></script>";
$out = specialCharsAndLinks($inp);
echo $out;
The output should be (in HTML):
http://web.page/index.php?a1=hi&a2=hello
<script src="http://bad-website.com/exploit.js"></script>
Note that the amperstand in the link stays in the href attribute, but is converted to & in the actual content of the link.
When viewed in a browser:
http://web.page/index.php?a1=hi&a2=hello
<script src="http://bad-website.com/exploit.js"></script>

Answer 1

I eventually solved it with:
function process_text($text) {
$text = htmlspecialchars($text);
$url_regex = "/(?:http|https|ftp|ftps)\:\/\/[a-zA-Z0-9\-\.]+(?:\/\S*)?/";
$text = preg_replace_callback($url_regex, function($matches){
return ''.$matches[0]."";
}, $text);
return $text;
}
The first line html-encodes the input.
The second line defines the URL regex. Could be improved, but working for now.
The 3rd line uses preg_replace_callback, a function which is like preg_replace, but instead of supplying it with a replacement string, you supply a replacement function that returns the replacement string.
The 4th line is the actual function. It's quite self-documenting. htmlspecialchars_decode undoes the actions of htmlspecialchars (therefore making the link valid if it contained an amperstand).

Answer 2

Try this:
$urlEscaped = htmlspecialchars("http://web.page/index.php?a1=hi&a2=hello");
$aTag = 'Hello';
echo $aTag;
Your example doesn't work because if escaping whole html tag, a tag will never get processed by the browser, instead it will just display as plain text.
As you can see, stackoverflow escapes our whole input (questions/answers ...), so we can actually see the code, and not letting browser to process it.