[Extra] Design of a new Sieve action to process iMIP messages

[Ken Murchison <[e-mail]>]

All,

We (Fastmail) are in the process of designing and implementing a new 
Sieve action which will process iMIP messages and add/update resources 
on a CalDAV calendar.  The main issue that I'm facing is that a user may 
want to have additional actions be executed depending on whether the 
'processimip' action [un]successfully updates the calendar (E.g., add 
flags to and/or fileinto the email message into different mailbox).  
Neither RFC 5528 nor any extension that I'm aware of defines a mechanism 
for determining whether an action was successful.  Failure of some 
actions, such as fileinto cause script execution to stop.  Failure of 
others such as vacation/notify are usually ignored.

I have come up with 3 ways to solve this issue for the new 'processimip' 
action, in order of preference:

 1. Have 'processimip' set a variable with a return code/status. This
    variable can then be checked with a 'string' test.  There is
    precedent for an action setting a variable with the 'extracttext'
    action.
 2. Make 'processimip' a test rather than an action.  This would be the
    first test that I'm aware of with side-effects (other than setting
    match variables).
 3. Add optional :flags and :mailbox (and :mailboxid, :specialuse) args
    to 'processimip' which are only used if the action is successful and
    are used to execute an implicit 'fileinto'.  This is very ugly
    IMHO.  I'd prefer that an explicit 'fileinto' action be used.

What do others think?  Any different/better design ideas?

-- 
Kenneth Murchison
Senior Software Developer
Fastmail US LLC