nntp: set Xref across multiple inboxes

Noted by Jonathan Corbet in https://lwn.net/Articles/748184/

2 files changed, 32 insertions, 17 deletions

diff --git a/lib/PublicInbox/NNTP.pm b/lib/PublicInbox/NNTP.pm
index e5179350..fa890cb2 100644
--- a/lib/PublicInbox/NNTP.pm
+++ b/lib/PublicInbox/NNTP.pm
@@ -407,12 +407,30 @@ sub header_append ($$$) {
         $hdr->header_set($k, @v, $v);
 }
 
-sub set_nntp_headers {
-        my ($hdr, $ng, $n, $mid) = @_;
+sub xref ($$$$) {
+        my ($self, $ng, $n, $mid) = @_;
+        my $ret = "$ng->{domain} $ng->{newsgroup}:$n";
+
+        # num_for is pretty cheap and sometimes we'll lookup the existence
+        # of an article without getting even the OVER info.  In other words,
+        # I'm not sure if its worth optimizing by scanning To:/Cc: and
+        # PublicInbox::ExtMsg on the PSGI end is just as expensive
+        foreach my $other (@{$self->{nntpd}->{grouplist}}) {
+                next if $ng eq $other;
+                my $num = eval { $other->mm->num_for($mid) } or next;
+                $ret .= " $other->{newsgroup}:$num";
+        }
+        $ret;
+}
+
+sub set_nntp_headers ($$$$$) {
+        my ($self, $hdr, $ng, $n, $mid) = @_;
 
         # clobber some
-        $hdr->header_set('Newsgroups', $ng->{newsgroup});
-        $hdr->header_set('Xref', xref($ng, $n));
+        my $xref = xref($self, $ng, $n, $mid);
+        $hdr->header_set('Xref', $xref);
+        $xref =~ s/:\d+//g;
+        $hdr->header_set('Newsgroups', (split(/ /, $xref, 2))[1]);
         header_append($hdr, 'List-Post', "<mailto:$ng->{-primary_address}>");
         if (my $url = $ng->base_url) {
                 $mid = mid_escape($mid);
@@ -461,7 +479,7 @@ found:
         my $msg = $ng->msg_by_smsg($smsg) or return $err;
         my $s = Email::Simple->new($msg);
         if ($set_headers) {
-                set_nntp_headers($s->header_obj, $ng, $n, $mid);
+                set_nntp_headers($self, $s->header_obj, $ng, $n, $mid);
 
                 # must be last
                 $s->body_set('') if ($set_headers == 2);
@@ -635,11 +653,6 @@ sub hdr_message_id ($$$) { # optimize XHDR Message-ID [range] for slrnpull.
         }
 }
 
-sub xref ($$) {
-        my ($ng, $n) = @_;
-        "$ng->{domain} $ng->{newsgroup}:$n"
-}
-
 sub mid_lookup ($$) {
         my ($self, $mid) = @_;
         my $self_ng = $self->{ng};
@@ -659,9 +672,11 @@ sub hdr_xref ($$$) { # optimize XHDR Xref [range] for rtin
         my ($self, $xhdr, $range) = @_;
 
         if (defined $range && $range =~ /\A<(.+)>\z/) { # Message-ID
-                my ($ng, $n) = mid_lookup($self, $1);
+                my $mid = $1;
+                my ($ng, $n) = mid_lookup($self, $mid);
                 return r430 unless $n;
-                hdr_mid_response($self, $xhdr, $ng, $n, $range, xref($ng, $n));
+                hdr_mid_response($self, $xhdr, $ng, $n, $range,
+                                xref($self, $ng, $n, $mid));
         } else { # numeric range
                 $range = $self->{article} unless defined $range;
                 my $r = get_range($self, $range);
@@ -674,10 +689,8 @@ sub hdr_xref ($$$) { # optimize XHDR Xref [range] for rtin
                         my $r = $mm->msg_range(\$beg, $end);
                         @$r or return;
                         more($self, join("\r\n", map {
-                                # TODO: use $_->[1] (mid) to fill
-                                # Xref: from other inboxes
                                 my $num = $_->[0];
-                                "$num ".xref($ng, $num);
+                                "$num ".xref($self, $ng, $num, $_->[1]);
                         } @$r));
                         1;
                 });
diff --git a/t/nntp.t b/t/nntp.t
index 03c7f083..57fef48b 100644
--- a/t/nntp.t
+++ b/t/nntp.t
@@ -109,7 +109,9 @@ use_ok 'PublicInbox::Inbox';
         is($ng->base_url, $u, 'URL expanded');
         my $mid = 'a@b';
         my $mime = Email::MIME->new("Message-ID: <$mid>\r\n\r\n");
-        PublicInbox::NNTP::set_nntp_headers($mime->header_obj, $ng, 1, $mid);
+        my $hdr = $mime->header_obj;
+        my $mock_self = { nntpd => { grouplist => [] } };
+        PublicInbox::NNTP::set_nntp_headers($mock_self, $hdr, $ng, 1, $mid);
         is_deeply([ $mime->header('Message-ID') ], [ "<$mid>" ],
                 'Message-ID unchanged');
         is_deeply([ $mime->header('Archived-At') ], [ "<${u}a\@b/>" ],
@@ -124,7 +126,7 @@ use_ok 'PublicInbox::Inbox';
                 'Xref: set');
 
         $ng->{-base_url} = 'http://mirror.example.com/m/';
-        PublicInbox::NNTP::set_nntp_headers($mime->header_obj, $ng, 2, $mid);
+        PublicInbox::NNTP::set_nntp_headers($mock_self, $hdr, $ng, 2, $mid);
         is_deeply([ $mime->header('Message-ID') ], [ "<$mid>" ],
                 'Message-ID unchanged');
         is_deeply([ $mime->header('Archived-At') ],