Replace functionality with more-robust decoder.

Author: dmsnell

src/wp-includes/formatting.php

@@ -3804,31 +3804,13 @@ function is_email( $email, $deprecated = false ) {
  * Converts to ASCII from email subjects.
  *
  * @since 1.2.0
+ * @deprecated {WP_VERSION} Use {@see rfc2047_decode()}.
  *
  * @param string $subject Subject line.
  * @return string Converted string to ASCII.
  */
 function wp_iso_descrambler( $subject ) {
-	/* this may only work with iso-8859-1, I'm afraid */
-	if ( ! preg_match( '#\=\?(.+)\?Q\?(.+)\?\=#i', $subject, $matches ) ) {
-		return $subject;
-	}
-
-	$subject = str_replace( '_', ' ', $matches[2] );
-	return preg_replace_callback( '#\=([0-9a-f]{2})#i', '_wp_iso_convert', $subject );
-}
-
-/**
- * Helper function to convert hex encoded chars to ASCII.
- *
- * @since 3.1.0
- * @access private
- *
- * @param array $matches The preg_replace_callback matches array.
- * @return string Converted chars.
- */
-function _wp_iso_convert( $matches ) {
-	return chr( hexdec( strtolower( $matches[1] ) ) );
+	return rfc2047_decode( $subject );
 }
 
 /**

src/wp-mail.php

@@ -124,11 +124,7 @@
 				$subject = trim( $line );
 				$subject = substr( $subject, 9, strlen( $subject ) - 9 );
 				// Captures any text in the subject before $phone_delim as the subject.
-				if ( function_exists( 'iconv_mime_decode' ) ) {
-					$subject = iconv_mime_decode( $subject, 2, get_option( 'blog_charset' ) );
-				} else {
-					$subject = wp_iso_descrambler( $subject );
-				}
+				$subject = rfc2047_decode( $subject );
 				$subject = explode( $phone_delim, $subject );
 				$subject = $subject[0];
 			}