Making sure http appears in a web address

Question

I have people posting their website address but variations are posted such as:

• theirsite.com
• www.theirsite.com
• http://theirsite.com
• http://www.theirsite.com

When I link to an address without http:// it takes the link as internal

<a href="theirsite.com">their site</a>

sending people to something like: http://mysite.com/thiersite.com

Another option I've tried is linking to something like mysite.com/?link=theirsite.com - This way I can do some link tracking etc then redirect people to the link but it has the same problem:

//do some tracking etc here
$link =$_GET['link'];
header("Location: $link");

Answer 1

I would provide some validation or sanitation. Use a regex to see if http:// starts with it. If it doesn't, either throw an validation error or put http:// at the start.

Answer 2

if not "://" in users_url:
    users_url = "http://" + users_url

...or equivalent, in the language of your choice.

Answer 3

You could use regular expressions to test input

Regex exp = new Regex(
    @"http://(www\.)?([^\.]+)\.com",
    RegexOptions.IgnoreCase);

Answer 4

put "http://" in the field by default, then validate the URL with something like

if(eregi("^((http|https)://)?([[:alnum:]-])+(\.)([[:alnum:]]){2,4}([[:alnum:]/+=%&_.~?-]*)$", stripslashes(trim($_POST['link'])))){
    //link is valid
}

if link does not validate, just print them a message saying "the link you entered is invalid, make sure it starts with 'http://'"

Answer 5

I would use something like this:

$link = str_replace(array("\r", "\n"), '', trim($link));
if (!preg_match('/^https?:\/\//', $link)) {
    $link = 'http://'.$link;
}
header('Location: '.$link);

Another way would be the parse_url function to parse the given URL, see what parts are missing and add them.

Answer 6

Please note, there's a real difference between www.site.com and site.com, usually both works, but on some website each leads to a different path (some badly defined website won't work without the www for instance). So You can't always prepend 'www' to the input.

Another note, do handle prepending space, so that ' http://' would not be prepended with additional http://.

My Javascript Regex based solution

'http://'+field.replace(/^ *http:\/\//,'')

You can verify that on the client size, just put a code in similar spirit on the onSubmit of your form.

Answer 7

No need to use regular expressions here. PHP has URL validation built in.

Filter Var

var_dump((bool) filter_var('http://www.website.com', FILTER_VALIDATE_URL, FILTER_FLAG_HOST_REQUIRED));
var_dump((bool) filter_var('http://website.com', FILTER_VALIDATE_URL, FILTER_FLAG_HOST_REQUIRED));
var_dump((bool) filter_var('www.website.com', FILTER_VALIDATE_URL, FILTER_FLAG_HOST_REQUIRED));
var_dump((bool) filter_var('website.com', FILTER_VALIDATE_URL, FILTER_FLAG_HOST_REQUIRED));

Output

bool(true)
bool(true)
bool(false)
bool(false)

Please do not jump straight to regular expressions for validation, PHP has a lot of methods built in to deal with these scenarios.

-Mathew