PHP function to turn all URLs in clickable links

linkify.php

<?php
    /**
     * Turn all URLs in clickable links.
     * 
     * @param string $value
     * @param array  $protocols  http/https, ftp, mail, twitter
     * @param array  $attributes
     * @return string
     */
    public function linkify($value, $protocols = array('http', 'mail'), array $attributes = array())
    {
        // Link attributes
        $attr = '';
        foreach ($attributes as $key => $val) {
            $attr .= ' ' . $key . '="' . htmlentities($val) . '"';
        }
        
        $links = array();
        
        // Extract existing links and tags
        $value = preg_replace_callback('~(<a .*?>.*?</a>|<.*?>)~i', function ($match) use (&$links) { return '<' . array_push($links, $match[1]) . '>'; }, $value);
        
        // Extract text links for each protocol
        foreach ((array)$protocols as $protocol) {
            switch ($protocol) {
                case 'http':
                case 'https':   $value = preg_replace_callback('~(?:(https?)://([^\s<]+)|(www\.[^\s<]+?\.[^\s<]+))(?<![\.,:])~i', function ($match) use ($protocol, &$links, $attr) { if ($match[1]) $protocol = $match[1]; $link = $match[2] ?: $match[3]; return '<' . array_push($links, "<a $attr href=\"$protocol://$link\">$link</a>") . '>'; }, $value); break;
                case 'mail':    $value = preg_replace_callback('~([^\s<]+?@[^\s<]+?\.[^\s<]+)(?<![\.,:])~', function ($match) use (&$links, $attr) { return '<' . array_push($links, "<a $attr href=\"mailto:{$match[1]}\">{$match[1]}</a>") . '>'; }, $value); break;
                case 'twitter': $value = preg_replace_callback('~(?<!\w)[@#](\w++)~', function ($match) use (&$links, $attr) { return '<' . array_push($links, "<a $attr href=\"https://twitter.com/" . ($match[0][0] == '@' ? '' : 'search/%23') . $match[1]  . "\">{$match[0]}</a>") . '>'; }, $value); break;
                default:        $value = preg_replace_callback('~' . preg_quote($protocol, '~') . '://([^\s<]+?)(?<![\.,:])~i', function ($match) use ($protocol, &$links, $attr) { return '<' . array_push($links, "<a $attr href=\"$protocol://{$match[1]}\">{$match[1]}</a>") . '>'; }, $value); break;
            }
        }
        
        // Insert all link
        return preg_replace_callback('/<(\d+)>/', function ($match) use (&$links) { return $links[$match[1] - 1]; }, $value);
    }

z.LICENSE

This is free and unencumbered software released into the public domain.

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@userofit123 to accomplish that you'd have to query all the links and get the headers in return to change it to the desired output. If you have a lot of links the script will timeout or slow down the html output. Plus, you could be banned for sending too many server requests. So probably no one will try to add this.

@userofit123 to accomplish that you'd have to query all the links and get the headers in return to change it to the desired output. If you have a lot of links the script will timeout or slow down the html output. Plus, you could be banned for sending too many server requests. So probably no one will try to add this.

Yes makes sense!

How about changing the output URL to be just the target domain rather than the full URL?

So instead of it being:
<a href="https://github.com">https://github.com</a>

It would be:
<a href="https://github.com">github.com</a>

Or
<a href="https://github.com">github</a>

@userofit123 on line #27 you could try to change $link output:
<a $attr href=\"$protocol://$link\">$link</a>

<a $attr href=\"$protocol://$link\">'.str_replace("www.","",$link).'</a>

(untested, just the idea)

preg_replace('/^(www\.)?/i',"", parse_url($link, PHP_URL_HOST)))

That's what I ended up doing, similar to hat you suggested, thanks!
I also added the part to remove www so that it will be just the actual domain.

@caspChristian .. is that even a real-world use case? Why bother with invalid formats anyway?

I don't mean to be rude, on the contrary - I'm quite interested where you got this 🦊

@S1SYPHOS
In regards to: https://https://github.com
Would like to have only https://github.com since there is no port number after hostname.
Posting this as an interesting test case, of course depending on use case.

This is an example of user input, Or rather output from incorrect parsing of relative URL for redirect.
The data itself is from https://b800.org/3NynQ

@NiKiZe IMHO it's the developer's responsibility to prepare input before passing it to a function, simply replace https://https with https:// yourself! The function itself should only work for 'valid' URIs .. jm2c