#!/usr/local/bin/perl
#
# make an ARC prepass over a message and add an arc clause to
# Authentication-Results header

use strict;
use Getopt::Std;
use Mail::DKIM::ARC::Verifier;

# local A-R server name
my $srvid = "example.com";
my ($arseen, $chain);

my @msg = <STDIN>;

my $arc = new Mail::DKIM::ARC::Verifier(Strict => 1);

for $_ (@msg) {
    last if m{$^} and not $arseen;	# don't bother if no A-R

    $arseen = 1 if m{^Authentication-Results: *$srvid;}i;

    # remove local line terminators
    my $l = $_;
    chomp($l);

    # use SMTP line terminators
    $arc->PRINT("$l\015\012");
}

if($arseen) {				# don't do ARC evaluation if no A-R
    $arc->CLOSE;
    $chain = $arc->result;
}

for $_ (@msg) {
    if($chain and m{^Authentication-Results: *$srvid;(.*)}) {
	print "Authentication-Results: $srvid; arc=$chain;$1\n";
	$chain = undef;			# once is plenty
    } else {
	print $_;
    }
}