How do I validate URL, but ignore if http:// or blank?

I want to validate a form field for URL. I have set the default for the field to http://. When the user doesn't enter a URL, and leaves the http://, it says invalid URL. URL is not required, so if it's only http://, it should not show error message. How can I make it ignore if the person submits http:// as the URL?

Thanks

http:// is not a valid url, so if you want to allow it anyway there are 2 options

1. create a custom validation rule, that returns true for a real url + http://
2. use the before validate callback and set the url field to blank if it is just http://

hope that helps

EDIT

I forgot: you don't need to set required but 'allowEmpty' => true

required -> the form must contain a field xyz that is send to the server

allowEmpty-> a field may be blank

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I added the link to the callback function above, but anyway .. here it is:

in your model class (I just suppose it's User):

class User extends AppModel {
    ..

    function beforeValidate() {
        if (isset($this->data['User']['url']) && $this->data['User']['url'] == 'http://') {
            $this->data['User']['url'] = '';
        }
        return true;
    }
    ..
}

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