PHP valid url, including subdomains and also subpath

Question

I need to check if a given string is valid. For me, the following and any other similar combinations are all valid URLs

'https://example.com/api/',
'https://www.example.com/test-subpath',
'https://www.example.com',
'example.com/test/page',
'www.example.com',
'www.subdomain.example.com',
'https://www.subdomain.example.com',
'subdomain.example.com',
'http://subdomain.example.com',
'https://subdomain.example.com'

while

'user-service/api/'

is invalid. I tried parse_url() and filter_var($url, FILTER_VALIDATE_URL) methods but non worked.

Thanks in advance.

Answer 1

Your script and the filter method works as expected. As www.example.com is just a hostname and only a part of a URL, it needs to return false.

The definition of a URL sais

<scheme>:<scheme-specific-part>

In your case, you may apply following ruleset

(Demo: https://3v4l.org/oX2as)

• Check if the URL is valid
  • yes -> return true
  • no -> add the scheme and check again
    • yes -> return true
    • no -> validation failed

As already stated in the comments, it is no good idea to use a regex, which may come over complicated to check for all rules, or write custom functions, i.e. with missing check for charsets.

Use whenever possible well known and tested supplied PHP functions.

$urls = [
    'https://example.com/api/',
    'https://www.example.com/test-subpath',
    'https://www.example.com',
    'example.com/test/page',
    'www.example.com',
    'www.subdomain.example.com',
    'https://www.subdomain.example.com',
    'subdomain.example.com',
    'http://subdomain.example.com',
    'https://subdomain.example.com',
];

function checkUrl(string $url): bool
{
    return (bool)filter_var($url, FILTER_VALIDATE_URL);
}

foreach ($urls as $url) {
    if (checkUrl($url)) {
        echo $url . ' is a valid URL', PHP_EOL;
        continue;
    }

    $urlWithProtocol = 'https://' . $url;
    if (checkUrl($urlWithProtocol)) {
        echo $urlWithProtocol, ' with added protocol is a valid URL', PHP_EOL;
        continue;
    }

    echo $url, ' is not a valid URL', PHP_EOL;
}

will result in

https://example.com/api/ is a valid URL
https://www.example.com/test-subpath is a valid URL
https://www.example.com is a valid URL
https://example.com/test/page with added protocol is a valid URL
https://www.example.com with added protocol is a valid URL
https://www.subdomain.example.com with added protocol is a valid URL
https://www.subdomain.example.com is a valid URL
https://subdomain.example.com with added protocol is a valid URL
http://subdomain.example.com is a valid URL
https://subdomain.example.com is a valid URL