nntp: filter out duplicate Message-IDs for leafnode

It's the unfortunate reality that there are some clients which
reuse Message-IDs (in which we generate + use another) or set
multiple Message-IDs on their own.  While the v2 format
addresses that, NNTP clients such as leafnode are not always
prepared to deal with that case.

So, ensure NNTP clients only see a single Message-ID, and
show the others as 'X-Alt-Message-ID'.

1 files changed, 17 insertions, 0 deletions

diff --git a/t/nntpd.t b/t/nntpd.t
index cce21eeb..a95fb6fc 100644
--- a/t/nntpd.t
+++ b/t/nntpd.t
@@ -250,6 +250,23 @@ Date: Fri, 02 Oct 1993 00:00:00 +0000
                 my $expect = qr/\AMessage-ID: /i . qr/\Q<$long_hdr>\E/;
                 ok(scalar(grep(/$expect/, @$hdr)), 'Message-ID not folded');
                 ok(scalar(grep(/^Path:/, @$hdr)), 'Path: header found');
+
+                # it's possible for v2 messages to have 2+ Message-IDs,
+                # but leafnode can't handle it
+                if ($version != 1) {
+                        my @mids = ("<$long_hdr>", '<2mid@wtf>');
+                        $for_leafnode->header_set('Message-ID', @mids);
+                        $for_leafnode->body_set('not-a-dupe');
+                        my $warn = '';
+                        $SIG{__WARN__} = sub { $warn .= join('', @_) };
+                        $im->add($for_leafnode);
+                        $im->done;
+                        like($warn, qr/reused/, 'warned for reused MID');
+                        $hdr = $n->head('<2mid@wtf>');
+                        my @hmids = grep(/\AMessage-ID: /i, @$hdr);
+                        is(scalar(@hmids), 1, 'Single Message-ID in header');
+                        like($hmids[0], qr/: <2mid\@wtf>/, 'got expected mid');
+                }
         }
 
         # pipelined requests: