External Libraries: Upgrade PHPMailer to version 6.9.1.

This is a maintenance and feature release, adding support for the official release of PHP 8.3, methods for removing and replacing custom headers, XCLIENT support, and links to a new way of implementing XOAUTH2 authentication.

The only change likely to have any impact on existing code is that PHPMailer previously attempted to use opportunistic STARTTLS encryption when connecting to `localhost`, which was unlikely to work. The workaround required setting `SMTPAutoTLS = false`, but that's no longer required. You may still need to use this setting when connecting to literal IPs.

References:
* [https://github.com/PHPMailer/PHPMailer/releases/tag/v6.9.1 PHPMailer 6.9.1 release notes]
* [PHPMailer/PHPMailer@v6.8.1...v6.9.1 Full list of changes in PHPMailer 6.9.1]

Follow-up to [50628], [50799], [51169], [51634], [51635], [52252], [52749], [52811], [53500], [53535], [53917], [54427], [54937], [55557], [56484].

Props jrf, Synchro.
Fixes #59966.

git-svn-id: https://develop.svn.wordpress.org/trunk@57137 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/PHPMailer/PHPMailer.php

@@ -357,6 +357,13 @@ class PHPMailer
      */
     public $AuthType = '';
 
+    /**
+     * SMTP SMTPXClient command attibutes
+     *
+     * @var array
+     */
+    protected $SMTPXClient = [];
+
     /**
      * An implementation of the PHPMailer OAuthTokenProvider interface.
      *
@@ -750,7 +757,7 @@ class PHPMailer
      *
      * @var string
      */
-    const VERSION = '6.8.1';
+    const VERSION = '6.9.1';
 
     /**
      * Error severity: message only, continue processing.
@@ -1573,6 +1580,10 @@ public function preSend()
 
             //Validate From, Sender, and ConfirmReadingTo addresses
             foreach (['From', 'Sender', 'ConfirmReadingTo'] as $address_kind) {
+                if ($this->{$address_kind} === null) {
+                    $this->{$address_kind} = '';
+                    continue;
+                }
                 $this->{$address_kind} = trim($this->{$address_kind});
                 if (empty($this->{$address_kind})) {
                     continue;
@@ -1999,6 +2010,38 @@ public function setSMTPInstance(SMTP $smtp)
         return $this->smtp;
     }
 
+    /**
+     * Provide SMTP XCLIENT attributes
+     *
+     * @param string $name  Attribute name
+     * @param ?string $value Attribute value
+     *
+     * @return bool
+     */
+    public function setSMTPXclientAttribute($name, $value)
+    {
+        if (!in_array($name, SMTP::$xclient_allowed_attributes)) {
+            return false;
+        }
+        if (isset($this->SMTPXClient[$name]) && $value === null) {
+            unset($this->SMTPXClient[$name]);
+        } elseif ($value !== null) {
+            $this->SMTPXClient[$name] = $value;
+        }
+
+        return true;
+    }
+
+    /**
+     * Get SMTP XCLIENT attributes
+     *
+     * @return array
+     */
+    public function getSMTPXclientAttributes()
+    {
+        return $this->SMTPXClient;
+    }
+
     /**
      * Send mail via SMTP.
      * Returns false if there is a bad MAIL FROM, RCPT, or DATA input.
@@ -2027,6 +2070,9 @@ protected function smtpSend($header, $body)
         } else {
             $smtp_from = $this->Sender;
         }
+        if (count($this->SMTPXClient)) {
+            $this->smtp->xclient($this->SMTPXClient);
+        }
         if (!$this->smtp->mail($smtp_from)) {
             $this->setError($this->lang('from_failed') . $smtp_from . ' : ' . implode(',', $this->smtp->getError()));
             throw new Exception($this->ErrorInfo, self::STOP_CRITICAL);
@@ -2189,10 +2235,17 @@ public function smtpConnect($options = null)
                     $this->smtp->hello($hello);
                     //Automatically enable TLS encryption if:
                     //* it's not disabled
+                    //* we are not connecting to localhost
                     //* we have openssl extension
                     //* we are not already using SSL
                     //* the server offers STARTTLS
-                    if ($this->SMTPAutoTLS && $sslext && 'ssl' !== $secure && $this->smtp->getServerExt('STARTTLS')) {
+                    if (
+                        $this->SMTPAutoTLS &&
+                        $this->Host !== 'localhost' &&
+                        $sslext &&
+                        $secure !== 'ssl' &&
+                        $this->smtp->getServerExt('STARTTLS')
+                    ) {
                         $tls = true;
                     }
                     if ($tls) {
@@ -4049,6 +4102,79 @@ public function clearCustomHeaders()
         $this->CustomHeader = [];
     }
 
+    /**
+     * Clear a specific custom header by name or name and value.
+     * $name value can be overloaded to contain
+     * both header name and value (name:value).
+     *
+     * @param string      $name  Custom header name
+     * @param string|null $value Header value
+     *
+     * @return bool True if a header was replaced successfully
+     */
+    public function clearCustomHeader($name, $value = null)
+    {
+        if (null === $value && strpos($name, ':') !== false) {
+            //Value passed in as name:value
+            list($name, $value) = explode(':', $name, 2);
+        }
+        $name = trim($name);
+        $value = (null === $value) ? null : trim($value);
+
+        foreach ($this->CustomHeader as $k => $pair) {
+            if ($pair[0] == $name) {
+                // We remove the header if the value is not provided or it matches.
+                if (null === $value ||  $pair[1] == $value) {
+                    unset($this->CustomHeader[$k]);
+                }
+            }
+        }
+
+        return true;
+    }
+
+    /**
+     * Replace a custom header.
+     * $name value can be overloaded to contain
+     * both header name and value (name:value).
+     *
+     * @param string      $name  Custom header name
+     * @param string|null $value Header value
+     *
+     * @return bool True if a header was replaced successfully
+     * @throws Exception
+     */
+    public function replaceCustomHeader($name, $value = null)
+    {
+        if (null === $value && strpos($name, ':') !== false) {
+            //Value passed in as name:value
+            list($name, $value) = explode(':', $name, 2);
+        }
+        $name = trim($name);
+        $value = (null === $value) ? '' : trim($value);
+
+        $replaced = false;
+        foreach ($this->CustomHeader as $k => $pair) {
+            if ($pair[0] == $name) {
+                if ($replaced) {
+                    unset($this->CustomHeader[$k]);
+                    continue;
+                }
+                if (strpbrk($name . $value, "\r\n") !== false) {
+                    if ($this->exceptions) {
+                        throw new Exception($this->lang('invalid_header'));
+                    }
+
+                    return false;
+                }
+                $this->CustomHeader[$k] = [$name, $value];
+                $replaced = true;
+            }
+        }
+
+        return true;
+    }
+
     /**
      * Add an error message to the error container.
      *

src/wp-includes/PHPMailer/SMTP.php

@@ -35,7 +35,7 @@ class SMTP
      *
      * @var string
      */
-    const VERSION = '6.8.1';
+    const VERSION = '6.9.1';
 
     /**
      * SMTP line break constant.
@@ -198,6 +198,18 @@ class SMTP
         'Mailjet' => '/[\d]{3} OK queued as (.*)/',
     ];
 
+    /**
+     * Allowed SMTP XCLIENT attributes.
+     * Must be allowed by the SMTP server. EHLO response is not checked.
+     *
+     * @see https://www.postfix.org/XCLIENT_README.html
+     *
+     * @var array
+     */
+    public static $xclient_allowed_attributes = [
+        'NAME', 'ADDR', 'PORT', 'PROTO', 'HELO', 'LOGIN', 'DESTADDR', 'DESTPORT'
+    ];
+
     /**
      * The last transaction ID issued in response to a DATA command,
      * if one was detected.
@@ -971,6 +983,25 @@ public function recipient($address, $dsn = '')
         );
     }
 
+    /**
+     * Send SMTP XCLIENT command to server and check its return code.
+     *
+     * @return bool True on success
+     */
+    public function xclient(array $vars)
+    {
+        $xclient_options = "";
+        foreach ($vars as $key => $value) {
+            if (in_array($key, SMTP::$xclient_allowed_attributes)) {
+                $xclient_options .= " {$key}={$value}";
+            }
+        }
+        if (!$xclient_options) {
+            return true;
+        }
+        return $this->sendCommand('XCLIENT', 'XCLIENT' . $xclient_options, 250);
+    }
+
     /**
      * Send an SMTP RSET command.
      * Abort any transaction that is currently in progress.