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I run a giant community. Many spammers will use link shorteners or .tk domains that 301 to their spam offer. How are sites detecting the final domain and is this a viable solution to block spam?
ex. I'll just block the spam: bit.ly/xdfd but then they will just use a different shortened link.
There is plenty solutions to expand short url:
When user submit a new post, you can apply a function that expand url for all url inside the post. Then you will have the real url. So you can appy what ever spam solution you use to reject / accept the post.
You can also replace the shorten url by the full one to avoid short link on your commutiy board.
Many forums simply forbid all url shorteners. There is no simple solution to that, you may try also specific solutions for your platform (phpBB, vBulletin, etc.)
I looked at this a decided the best solution was to simply ban all shortened links, it will be very rare that a user will want to post such, but spammers love them.
I used code based on the accepted answer here https://stackoverflow.com/questions/9557116/regex-php-code-to-check-if-a-url-is-a-short-url
http://bk.com/faq is a short url, but not a "url shortener". Conversely, http://tinyurl.com/example is a longer url from a legit url shortener. Whatever solution you use, it won't be accurate if it's based solely on length.
– Maximillian Laumeister
Jun 27 '20 at 20:13
