How to check if a string is a valid URL

Question

WordPress provides a helpful function called is_email() which checks if a given email address is valid. Is there a similar function available to check if a URL is valid?

I tried is_url() but that was just wishful thinking on my part.

Ref: http://codex.wordpress.org/Function_Reference/is_email

Answer 1

Use the native php function Filter Validator

if (filter_var($url, FILTER_VALIDATE_URL) === FALSE) {
    die('Not a valid URL');
}

Answer 2

I know this is an old post, but for anyone visiting it's also worth considering the WP functions esc_url() and esc_url_raw(), the latter being safe for databases entries etc, as it does not encode entities. esc_url() does encode entities and so is good for display to users.

In the source you can see that esc_url() checks for a whitelist of allowed protocols and structure and so avoids some of the vulnerabilities of FILTER_VALIDATE_URL noted by the link posed by @tobltobs.

Answer 3

I found wp_http_validate_url quite convenient to check if a string in valid URL or not while working on my project.

Take a reference from here: https://developer.wordpress.org/reference/functions/wp_http_validate_url/

For example:

$val = 'http://somevalidurl.com';
if ( wp_http_validate_url( $val ) ) {

    // It's valid URL;

} else {

    // It's NOT valid URL;

}

It returns the URL itself if it's valid,else false.

Answer 4

To ensure user-submitted URL is valid and safe to store and later display, I suggest

esc_url_raw($url) === $url

esc_url_raw(), like @orionrush mentioned above, sanitizes the URL by removing anything invalid or malicious from it. So, if there string has nothing invalid or malicious, then it's ok.

Eg

if( esc_url_raw($url) === $url ) {
   // URL is valid. Use it...
} else {
   // URL is invalid or malicious. Don't use it...
}

I wrote a longer blog post on that here: https://cmljnelson.wordpress.com/2018/08/31/url-validation-in-wordpress/

Answer 5

In my opinion is better to use wp_http_validate_url.

Example 1:

filter_var( '//website.com', FILTER_VALIDATE_URL )

Return false.

Example 2:

wp_http_validate_url( '//website.com' )

Return url.

1. When you don't know is website use https or http protocol, it's better to use '//'.
2. wp_http_validate_url is improved by WP developers (is more specific).
3. Theoretically you can use some hooks (filters & actions) for wp_http_validate_url. You can't use hooks for filter_var.

Ref: https://developer.wordpress.org/reference/functions/wp_http_validate_url/

Ref: https://www.php.net/manual/en/function.filter-var.php

Answer 6

is_email(), actually do not check if an email address is valid, only if it is conforming to spec. The email I gladly supply for many sites that show pointless interest in my email address is a@b.com which is conforming address but it is unlikely to have anyone using it.

Checking out urls is best done by pinging them. You can try to check conformance, but in theory there are very little limitation to what an encoded url can be.