Drupal 6 core RTL email support

Updated: June 20, 2007: RTL HTML Email now possible with my patch to the new htmlmail module.

Requirements for Drupal 6 core RTL email support - Request for comments

It has been 8 months since I've implemented a Drupal 4.7 user.module patch to support RTL emails (attached).

My next target is to ask for the RTL/i18n community help to update the code and migrate those proven changes into the Drupal 6 core. This will save tons of later headache.

Here are the basic requirements - I will need your feedback on the concept (implementation is quite straightforward).

Why do we need special treatment for RTL emails?

1.1. In a perfect world, all people would read RTL emails with RTL mail readers.

In practice, this is not the case. People read RTL emails on LTR readers, for various reasons, e.g.:
* Even though gmail has Hebrew support, chat is only available on the English interface, so if I want to see which of my gmail friends is online, I must use the english interface.
* People love Yahoo's new unlimited storage capacity, but then they must read RTL emails in an LTR direction.

1.2 In a perfect world, RTL email don't contain any English words.

In practice, this is not the case. Technical RTL emails contain many words in English. This causes the email to look terrible on RTL mail readers. Each English word in the middle of the line, breaks the line to two more parts, scrambled in an opposite direction.

Technology Considerations

Theoretically, there are two ways to go to get RTL email - CSS and HTML.

In a perfect world, CSS would be the ultimate answer.

However, in practice, CSS Email is not compatible and causes lots of trouble. GMail, Msn, Thunderbird, Outlook - all have different CSS implementations, if at all. Stylesheets are not supported at all. Some webmails don't crop the local CSS, since it's in the browser anyway, so sometimes it has effect, if it doesn't contradict the global CSS. But this has lots of variations.

HTML Email support is now the lowest common denominator for RTL email readers.
Virtually all mail readers now support html.

I have good experience with sending HTML formatted Hebrew emails since 2003.
This is the proven, compatible, solution.

To get RTL HTML email, all we need to do is to surround the text with a

<

div> tag with a 'dir=rtl' attribute.

Suggested implementation

Take a look at the new drupal_mail function found in includes/common.inc

The following requirements are sufficient to get RTL on all outgoing emails.

1. The default message content type should be text/html, not text/plain (at least for RTL languages). See lines 3-6 and line 10 of the code below.
   <?php
function drupal_mail($mailkey, $to, $subject, $body, $from = NULL, $headers = array()) {

  $is_rtl = defined('LANGUAGE_RTL') && $language->direction == LANGUAGE_RTL; /* Same as drupal_get_css */
  $encoding='text/plain'; if ($is_rtl){ $encoding='text/html;'}
 
  $defaults = array(
    'MIME-Version' => '1.0',
    'Content-Type' => $encoding . ' charset=UTF-8; format=flowed',
    'Content-Transfer-Encoding' => '8Bit',
    'X-Mailer' => 'Drupal'
  );
?>
2. Next, we should wrap the message in a div tag, with dir="rtl" , replacing newlines with
   tags:
   
   <?php
     $message = '<div dir="rtl">' . str_replace("\n", '<br />', $message) . "</div>";

?>
3. Process the message with URL filter, since some HTML mail readers doesn't automatically highlight URLs.

   URL filtering was done in version 4.7 in the following way (How to implement it? a new implementation is needed since URL filter is now embedded in core):

   <?php
     if (module_exist('urlfilter')) $message = urlfilter_filter ('process', 0, 300, $message);
?>

Notes

1. Your comments are welcome.
2. The filtering process exposes other new exiting possibilities for compatible HTML emails in general. Virtually, we can use any other drupal filter we want! I am sure that some LTR developers would like HTML emails to be an option for their emails a well, so I this might later become a config option - but I wouldn't want to hold the whole issue until such an issue is decided.
3. The RTL email patch for Drupal 4.7 was quite simple - I am attaching it here for reference.

My Questions

Please give feedback on the best place to put the abovementioned code, and give me the green light to go ahead with asking people to help with the patch.

Amnon
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