Adding standard functions for parsing phone numbers

[Hinjiriyo]

There are functions in the WP core for testing and sanitizing URLs and mail addresses.

Since the protocols 'tel' and 'fax' are standard protocols, see RFC 2806 and RFC 3966, standard functions for testing and sanitizing phone numbers (and fax numbers, mobile numbers) are helpful.

Draft of a test function:

// check if the number is callable by technical devices
function is_phonenumber ( $string ) {
	if ( is_string( $string ) ) {
		return (bool) preg_match( '/^[+]?[0-9 ]{2,14}[0-9]$/', $string );
	} else {
		return false;
	}
}

Draft of a sanitizing function:

// makes a visual reprentation of a phone number callable by technical devices
function esc_phonenumber ( $tel ) {
	
	// only strings
	if ( ! is_string( $tel ) ) {
		return '';
	}

	// remove invalid chars
	$tel = preg_replace( '/[^0-9a-z+]/i', '', $tel );
	
	// remove plus sign within the number, only keep it at the start
	$tel_first_sign = substr( $tel, 0, 1 );
	$tel_substr = substr( $tel, 1 );
	$tel_substr = preg_replace( '/[+]/', '', $tel_substr );
	$tel = $tel_first_sign . $tel_substr;

	// convert vanity numbers
	if ( preg_match( '/[a-z]/i', $tel ) ) {
		$tel = preg_replace( '/[abc]/i', '2', $tel );
		$tel = preg_replace( '/[def]/i', '3', $tel );
		$tel = preg_replace( '/[ghi]/i', '4', $tel );
		$tel = preg_replace( '/[jkl]/i', '5', $tel );
		$tel = preg_replace( '/[mno]/i', '6', $tel );
		$tel = preg_replace( '/[pqrs]/i', '7', $tel );
		$tel = preg_replace( '/[tuv]/i', '8', $tel );
		$tel = preg_replace( '/[wxyz]/i', '9', $tel );
	}

	// E.164: maximum number of digits: 15
	$tel = substr( $tel, 0, 15 );
	
	// change country area sign
	$tel = preg_replace( '|^[+]|i', '00', $tel );

	// return sanitized phone number
	return $tel;
	
}

In use:

<?php
$tel = '+49 (0)89 / 123 45-120';
// or: $tel = '+1-44-HOLIDAY';
$escaped_tel = esc_phonenumber ( $tel );
if ( is_phonenumber( $escaped_tel ) ) {
?>
<a href="tel:<?php echo $escaped_tel; ?>">Call John at <?php echo $tel; ?></a>

[shooper]

Two thoughts:

1. Great idea, however not sure if it belongs in core. Sanitizing URLs and e-mail addresses makes sense as both of those types of data are stored as part of the default core data (email in _users and URLs in the user_url usermeta). Telephone numbers would be a custom field.

2. If this were to be added to core, my second thought would be how does it handle telephone extensions, like:

+1-613-555-1212 x 200

[Hinjiriyo]

Your number would be escaped to

001613555121220 // omitting last zero because too long

[Hinjiriyo]

My simple logic on why this belongs to the core is:

The protocols for URLs ('http:') and mailaddresses ('mailto:') are standard protocols.

Wordpress core offers functions for URLs and mailaddresses.

Protocols for phone numbers ('tel:') and fax numbers ('fax:') are standard protocols.

Wordpress core can offer function for them. Because they are standards.

[helen]

@shooper's comment is precisely correct. We have functions for field types we store and use out of the box, and phone number formatting varies quite widely making a good data validation approach specific to each implementation. Including a function that does some things but not others is unpleasant territory, particularly once sanitization and conversion/transformation are mixed together as per your proposal.