PHP URL Validation

Guys I'm trying to validate urls froma form, for example someone enters http://yahoo.com that would not be a valid url, I want to make sure they insert http://www.yahoo.com which I have found the regular expressions for that, but the problem is http://subdomain.yahoo.com does not work properly.

So I need for them to be able to insert http://www.yahoo.com or http://subdomain.yahoo.com

Reason I'm doing this is because I'm running a check in the database using parse_url to make sure there is no duplicate entries, so no 2 urls can be entered twice would you guys have any clue on how I can do this?

 

what regexp do you use ?

Your Database can have a UNIQUE constraint on your url field and can assure you the unicity.

 

do you parse url for www?

I mean if url has www it is true (1)

and if url doesn`t have www , it is false (0)

to avoid enetering a url without www?

so because of that ur php program supposes that a subdomain url is incorrect?

Am I right?

 

Yes exactly the subdomain is wher I'm having the problem

 

It is simple to solve.

in parsing url "." is the key.

pay attention:

for example in parsing http://yahoo.com we have only one "."

but in subdomains like http://messenger.yahoo.com we have two "."

so the key is that if in parsing invalid URL you have only one "." it is like

http://yahoo.com but if we have two or more "." like http://

messenger.yahoo.com it is a subdomain.

but we have some exceptions like:

http://yourdoamin.com.au

it is a domain not a subdomain but has two "."

but in many cases you can use the assumption which I mentioned.

 

Why not check for a subdomain and add www. if it is not there?

$url = rtrim(preg_replace("~(.+?://)([^.]+\.[^.]+)/?~", '$1www.$2', $url), '/');

PHP:

rtrim() is to ensure only one version of the URL is inserted (instead of two with and without the trailing slash)