wp_check_invalid_utf8() │ WP 2.8.0

Checks for the presence of invalid UTF8 characters in a string.

The function does nothing if the option get_option( 'blog_charset' ) is not equal to one of utf8, utf-8, UTF8, UTF-8.

For testing, there is a special text with invalid UTF-8 characters. It contains examples of many UTF-8 violations, including single leading bytes, missing continuation bytes, excessively long sequences, etc.

Uses: is_utf8_charset()
Used By: sanitize_text_field(), esc_html()

No Hooks.

Returns

String. Checked text.

Usage

wp_check_invalid_utf8( $string, $strip );
$string(string) (required)
Text to be checked.
$strip(true/false)
Whether to attempt to remove invalid UTF-8 characters.
Default: false

Examples

0

#1 Checking the function 

$examples = [
	'Valid ASCII'                               => "a",
	'Valid 2 Octet Sequence'                    => "\xc3\xb1",
	'Valid 3 Octet Sequence'                    => "\xe2\x82\xa1",
	'Valid 4 Octet Sequence'                    => "\xf0\x90\x8c\xbc",
	'Valid 5 Octet Sequence (but not Unicode!)' => "\xf8\xa1\xa1\xa1\xa1",
	'Valid 6 Octet Sequence (but not Unicode!)' => "\xfc\xa1\xa1\xa1\xa1\xa1",
	'Invalid 2 Octet Sequence'                  => "\xc3\x28",
	'Invalid Sequence Identifier'               => "\xa0\xa1",
	'Invalid 3 Octet Sequence (in 2nd Octet)'   => "\xe2\x28\xa1",
	'Invalid 3 Octet Sequence (in 3rd Octet)'   => "\xe2\x82\x28",
	'Invalid 4 Octet Sequence (in 2nd Octet)'   => "\xf0\x28\x8c\xbc",
	'Invalid 4 Octet Sequence (in 3rd Octet)'   => "\xf0\x90\x28\xbc",
	'Invalid 4 Octet Sequence (in 4th Octet)'   => "\xf0\x28\x8c\x28",
];

$result = [];

foreach ( $examples as $key => $value ) {
	$result[ $key ] = wp_check_invalid_utf8( $value );
}

var_dump( $result );

Result:

array(13) {
  ["Valid ASCII"]=>                               string(1) "a"
  ["Valid 2 Octet Sequence"]=>                    string(2) "ñ"
  ["Valid 3 Octet Sequence"]=>                    string(3) "₡"
  ["Valid 4 Octet Sequence"]=>                    string(4) "?"
  ["Valid 5 Octet Sequence (but not Unicode!)"]=> string(0) ""
  ["Valid 6 Octet Sequence (but not Unicode!)"]=> string(0) ""
  ["Invalid 2 Octet Sequence"]=>                  string(0) ""
  ["Invalid Sequence Identifier"]=>               string(0) ""
  ["Invalid 3 Octet Sequence (in 2nd Octet)"]=>   string(0) ""
  ["Invalid 3 Octet Sequence (in 3rd Octet)"]=>   string(0) ""
  ["Invalid 4 Octet Sequence (in 2nd Octet)"]=>   string(0) ""
  ["Invalid 4 Octet Sequence (in 3rd Octet)"]=>   string(0) ""
  ["Invalid 4 Octet Sequence (in 4th Octet)"]=>   string(0) ""
}

Changelog

Since 2.8.0 Introduced.
Since 6.9.0 Stripping replaces invalid byte sequences with the Unicode replacement character U+FFFD (�).

wp_check_invalid_utf8() code WP 6.9

wp-includes/formatting.php 
function wp_check_invalid_utf8( $text, $strip = false ) {
	$text = (string) $text;

	if ( 0 === strlen( $text ) ) {
		return '';
	}

	// Store the site charset as a static to avoid multiple calls to get_option().
	static $is_utf8 = null;
	if ( ! isset( $is_utf8 ) ) {
		$is_utf8 = is_utf8_charset();
	}

	if ( ! $is_utf8 || wp_is_valid_utf8( $text ) ) {
		return $text;
	}

	return $strip
		? wp_scrub_utf8( $text )
		: '';
}

sanitize_

Sanitizing, Escaping