Issue #3451611 by mfb, xjm, smustgrave, quietone: Fix the format=flowed;...

Issue #3451611 by mfb, xjm, smustgrave, quietone: Fix the format=flowed; delsp=yes encoding of email messages

(cherry picked from commit c29768f4)

core/lib/Drupal/Core/Mail/MailFormatHelper.php

@@ -311,7 +311,7 @@ protected static function wrapMailLine(&$line, $key, $values) {
     }
     if (!$line_is_mime_header) {
       // Use soft-breaks only for purely quoted or un-indented text.
-      $line = wordwrap($line, 77 - $values['length'], $values['soft'] ? " \n" : "\n");
+      $line = wordwrap($line, 77 - $values['length'], $values['soft'] ? "  \n" : "\n");
     }
     // Break really long words at the maximum width allowed.
     $line = wordwrap($line, 996 - $values['length'], $values['soft'] ? " \n" : "\n", TRUE);

core/lib/Drupal/Core/Mail/Plugin/Mail/PhpMail.php

@@ -64,10 +64,8 @@ public function format(array $message) {
     // Join the body array into one string.
     $message['body'] = implode("\n\n", $message['body']);
 
-    // Convert any HTML to plain-text.
+    // Convert any HTML to plain text (which also wraps the mail body).
     $message['body'] = MailFormatHelper::htmlToText($message['body']);
-    // Wrap the mail body for sending.
-    $message['body'] = MailFormatHelper::wrapMail($message['body']);
 
     return $message;
   }

core/lib/Drupal/Core/Mail/Plugin/Mail/SymfonyMailer.php

@@ -98,11 +98,14 @@ public function __construct(
   }
 
   public function format(array $message) {
-    // Convert any HTML to plain-text.
     foreach ($message['body'] as &$part) {
+      // If the message contains HTML, convert it to plain text (which also
+      // wraps the mail body).
       if ($part instanceof MarkupInterface) {
         $part = MailFormatHelper::htmlToText($part);
       }
+      // If the message does not contain HTML, it still needs to be wrapped
+      // properly.
       else {
         $part = MailFormatHelper::wrapMail($part);
       }

core/tests/Drupal/Tests/Core/Mail/MailFormatHelperTest.php

@@ -32,8 +32,11 @@ public function testWrapMail(): void {
     // Check that the body headers were not wrapped even though some exceeded
     // 77 characters.
     $this->assertEquals($headers_in_body, $processed_headers, 'Headers in the body are not wrapped.');
-    // Check that the body text is wrapped.
-    $this->assertEquals(wordwrap($body, 77, " \n"), $processed_body, 'Body text is wrapped.');
+    // Check that the body text is soft-wrapped according to the
+    // "format=flowed; delsp=yes" encoding. When interpreting this encoding,
+    // mail readers will delete a space at the end of the line; therefore an
+    // extra trailing space should be present in the raw body (see RFC 3676).
+    $this->assertEquals(wordwrap($body, 77, "  \n"), $processed_body, 'Body text is soft-wrapped.');
   }
 
 }