How to Detect and Convert URLs to HTML Links in PHP?

Detect and Convert URLs to HTML Links in Text

In various online applications, converting URLs mentioned in text to clickable links is a common requirement. Let's explore how to accomplish this in PHP.

Requirements

1. Detect URLs with or without the "http://" prefix.
2. Allow domains, IP addresses, and valid top-level domains (TLDs).
3. Recognize URLs within normal sentence contexts.
4. Support "https://" URLs and potentially others.
5. Prevent cross-site scripting (XSS) vulnerabilities.
6. Support email addresses (optional).

Solution

Regular Expression-Based Approach

Let's create a regular expression that matches valid URLs and their constituent parts:

$rexProtocol = '(https?://)?';
$rexDomain   = '((?:[-a-zA-Z0-9]{1,63}\.)+[-a-zA-Z0-9]{2,63}|(?:[0-9]{1,3}\.){3}[0-9]{1,3})';
$rexPort     = '(:[0-9]{1,5})?';
$rexPath     = '(/[!$-/0-9:;=@_\':;!a-zA-Z\x7f-\xff]*?)?';
$rexQuery    = '(\?[!$-/0-9:;=@_\':;!a-zA-Z\x7f-\xff]+?)?';
$rexFragment = '(#[!$-/0-9:;=@_\':;!a-zA-Z\x7f-\xff]+?)?';

$rex = "&\b$rexProtocol$rexDomain$rexPort$rexPath$rexQuery$rexFragment(?=[?.!,;:\"]?(\s|$))&";

Implementation

We can use preg_match_all() to find all URL matches in the text:

preg_match_all($rex, htmlspecialchars($text), $matches, PREG_OFFSET_CAPTURE);

Convert to HTML Links

We'll loop through the matches and create the appropriate HTML links:

foreach ($matches[0] as $match) {
    $url = $match[0];
    $domain = $matches[2][0];
    $path = $matches[4][0];

    $completeUrl = $matches[1][0] ? $url : "http://$url";

    $htmlLink = "<a href="%24completeUrl">$domain$path</a>";

    $text = str_replace($url, $htmlLink, $text);
}

This approach handles most URL formats efficiently while maintaining security against XSS attacks.

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