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'.

2 files changed, 33 insertions, 0 deletions

diff --git a/lib/PublicInbox/NNTP.pm b/lib/PublicInbox/NNTP.pm
index d409e782..8a31b910 100644
--- a/lib/PublicInbox/NNTP.pm
+++ b/lib/PublicInbox/NNTP.pm
@@ -438,6 +438,22 @@ sub set_nntp_headers ($$$$$) {
         # reason.  We'll fake the shortest one possible.
         $hdr->header_set('Path', 'y');
 
+        # leafnode (and maybe other NNTP clients) have trouble dealing
+        # with v2 messages which have multiple Message-IDs (either due
+        # to our own content-based dedupe or buggy git-send-email versions).
+        my @mids = $hdr->header('Message-ID');
+        if (scalar(@mids) > 1) {
+                my $mid0 = "<$mid>";
+                $hdr->header_set('Message-ID', $mid0);
+                my @alt = $hdr->header('X-Alt-Message-ID');
+                my %seen = map { $_ => 1 } (@alt, $mid0);
+                foreach my $m (@mids) {
+                        next if $seen{$m}++;
+                        push @alt, $m;
+                }
+                $hdr->header_set('X-Alt-Message-ID', @alt);
+        }
+
         # clobber some
         my $xref = xref($self, $ng, $n, $mid);
         $hdr->header_set('Xref', $xref);
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: