[Tickets #9854] iCalendar attachment may not be available in notification message

[bugs at horde.org]

DO NOT REPLY TO THIS MESSAGE. THIS EMAIL ADDRESS IS NOT MONITORED.

Ticket URL: http://bugs.horde.org/ticket/9854
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  Ticket             | 9854
  Created By         | Michael Slusarz <slusarz at horde.org>
  Summary            | iCalendar attachment may not be available in
                     | notification message
  Queue              | Kronolith
  Version            | Git master
  Type               | Bug
  State              | Unconfirmed
  Priority           | 1. Low
  Milestone          |
  Patch              |
  Owners             |
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Michael Slusarz <slusarz at horde.org> (2011-04-08 22:16) wrote:

Another example of the multipart/alternative problem.  We send out  
notification messages that look like this:

multipart/alternative
   text/plain
   multipart/related
     text/html
     image/png
   text/calendar

The problem comes if a MUA does not know how to handle text/calendar.   
Both the plain and html contains language about an attached iCalendar  
file.  But as discussed in other bugs, text/calendar, if it can't be  
displayed, must NOT be shown as an attachment.  Multipart/alternative  
is only designed to provide different viewable representations, it is  
not intended to be a container for downloadable attachments.

The proper way of doing this would be as follows:

multipart/alternative
   multipart/mixed
     multipart/alternative
       text/plain
       multipart/related
         text/html
       image/png
     text/calendar
   text/calendar

Yes - text/calendar is repeated twice.  However, this is expected (and  
necessary) behavior.

A rarely used MIME type (message/external-body - RFC 1873) was  
designed to solve such issues - it allows data to be defined in one  
MIME part, and the data to be duplicated in other body parts by  
reference to the first MIME part.  But I'm not sure how many MUAs  
support this.