wp_check_filetype( string $filename, string[] $mimes = null )

Source

File: wp-includes/functions.php

function wp_check_filetype( $filename, $mimes = null ) {
	if ( empty( $mimes ) ) {
		$mimes = get_allowed_mime_types();
	}
	$type = false;
	$ext  = false;

	foreach ( $mimes as $ext_preg => $mime_match ) {
		$ext_preg = '!\.(' . $ext_preg . ')$!i';
		if ( preg_match( $ext_preg, $filename, $ext_matches ) ) {
			$type = $mime_match;
			$ext  = $ext_matches[1];
			break;
		}
	}

	return compact( 'ext', 'type' );
}