Re: Adding custom mail headers via a filter?

Sean, for now I've had to put the filtering idea on hold because I've 
been contacted by a procmail developer who suggested that missing "F" 
from the From_ is a known , but difficult problem to solve because it's 
not easily reproduced in other "environments" so when I get a chance 
I'll diagnose this some more. But in my case it's 100% consistent that 
I end up missing the leading F from From_ if I enable filtmail as a 
filter.
For now, I don't want to "lose" mail by having a missing F so I'll 
defer further diagnosis until later.
On Thursday, October 17, 2002, at 12:16 AM, Professional Software 
Engineering wrote:
> At 11:02 2002-10-16 +0700, Robert Nicholson did say:
> > Why is it inconceivable that you'd want to in addition to returning a 
> > value also filter?
> It isn't inconceivable.  You were complaining that your recipes 
> weren't paying attention to the filter because you were running your 
> program as a CONDITION operation.  I pointed out that it was because 
> you're not invoking it as a filter.
> Procmail has flags (see 'man procmailrc') for whether it ignores write 
> errors (the delivered-to _filter_ not reading the entire message) or 
> whether it waits for the message filter to complete AND pays attention 
> to the return value or ignores it -- if you set up your filter to 
> return an error value when it decides that it DOES NOT need to filter, 
> and success when it does, then procmail can disreguard the filtered 
> output on error.
> Of course, if the only thing you're doing is adding another header, if 
> the filter always outputs everything - either with, or without that 
> extra header, then there isn't a great deal of need to return a 
> success/fail value, except perhaps as a slight performance > improvement.
> My filter shouldn't have to be responsible for mail delivery ie. 
> writing the message into a mailbox. That's procmails job so what I'm 
> seeking is a way to conditionally tell procmail to write the mail to 
> the designated mailbox but in addition also be able to change the 
> message content.
> :0Wf
> | /path/to/yourfilter
>
> :0a:
> some_mailbox
>
>
> 'a' means that the previous recipe must have been successfully 
> completed.
> 'f' means to filter (change it and continue processing using that 
> changed version) the message.
> 'W' suppresses program failure messages, but waits for the filter to 
> complete and considers the message UNFILTERED (that is, ignore the 
> filter output and stick with the original message) if the invoked 
> filter program returneds an error.
> > $Headers, $Body are defined in another file.
> >
> > RFC says that Headers ie. Mail Headers are separated from the Body by 
> > a newline.
> > The last line of the $Headers isn't terminated by a newline.
> Which I guess is a function of how you parsed them.  Might I suggest 
> adding a newline to the neaders right off when you initially parse 
> them, and in your filter, appending the new header line to the > headers:
>         $Headers .= "newheader: content\n" ;
>
> or:
>
>         $ExtraHeaders .= "newheader: content\n";
>
> (for those coming into this late or from the archives, that's for an 
> external PERL recipe Robert wrote.)
> Set a success flag, and exit your filter from the main function (not 
> presented to us) so that the $Headers\n$Body (or, 
> $Headers$ExtraHeaders\n$Body) is emitted IF the success flag is set.  
> This would allow you to have MULTIPLE filtering operations going on, 
> and any one of them could add different headers.
>
> ---
>  Sean B. Straw / Professional Software Engineering
>
>  Procmail disclaimer: 
> <http://www.professional.org/procmail/disclaimer.html>
>  Please DO NOT carbon me on list replies.  I'll get my copy from the 
> list.
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