[pfx] Re: Postfix Milter, the gift that keeps on giving (was: PATCH: using Milter to change a PREPENDed header)

[Wietse Venema via Postfix-users]

Carlos Velasco via Postfix-users:
> 
> Wietse Venema via Postfix-users escribi? el 11/12/2023 a las 22:30:
> > Wietse Venema:
> >> Patch below.
> > Carlos Velasco:
> >> Tested patch against 3.8.3, now it works as expected. Thank you.
> >> No duplicated "Received-SPF" and *removing "Received" in position
> >> 1 is now not the own generated, is really the first one Received
> >> seen in the milter.*
> > Your second comment (text between "*" and "*") led me to a better
> > problem analysis.
> >
> > - The real problem was not with the Postfix order of headers.
> >
> > - The real problem also was not with the Postfix code that exposes
> >    message headers with remote smfi_header() calls in the Milter;
> >    that code was already fixed to handle prepended headers on 20141018.
> >
> > - The real problem was that the Postfix code that handles header
> >    update/delete requests from a Milter was not fixed on 20141018.
> >
> > Thus, the Postfix code that handles header update/delete requests
> > was still naively skipping the first header, making calls to delete
> > the prepended Received-SPF: header ineffective, and mis-directing
> > calls to delete the first Milter-visible Received: header, instead
> > deleting the invisible Postfix-generated Received: header (wtf).
> >
> > To maintain protocol compatibility, the Postfix code that handles
> > header update/delete requests will need to skip the Postfix-generated
> > Received: header, instead of the first message header.
> >
> > Once that mess is handled with, we can consider adding a flag to
> > expose Postfix-generated Received: headers to Milters.
> >
> I think you are absolutely correct in your analysis.
> I've been looking over the code and, although there is a lot I still don't 
> understand, your yesterday patch seems more a (good) workaround to the real 
> problem.
> I also located the cleanup_header_done_callback where I can make an (ugly) 
> change to expose the header, but, IMHO, a flag should be the way to go.
> 
> Regards,
> Carlos Velasco
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