nntp: support optional [range] arg in LISTGROUP

RFC3977 6.1.2.2 LISTGROUP allows a [range] arg after [group],
and supporting it allows NNTP support in neomutt to work again.

Tested with NeoMutt 20170113 (1.7.2) on Debian stretch
(oldstable)

1 files changed, 23 insertions, 11 deletions

diff --git a/lib/PublicInbox/NNTP.pm b/lib/PublicInbox/NNTP.pm
index 800ce926..7c3f68a2 100644
--- a/lib/PublicInbox/NNTP.pm
+++ b/lib/PublicInbox/NNTP.pm
@@ -221,22 +221,34 @@ sub cmd_list ($;$$) {
         '.'
 }
 
-sub cmd_listgroup ($;$) {
-        my ($self, $group) = @_;
+sub cmd_listgroup ($;$$) {
+        my ($self, $group, $range) = @_;
         if (defined $group) {
                 my $res = cmd_group($self, $group);
                 return $res if ($res !~ /\A211 /);
                 more($self, $res);
         }
-
-        $self->{ng} or return '412 no newsgroup selected';
-        my $n = 0;
-        long_response($self, sub {
-                my $ary = $self->{ng}->mm->ids_after(\$n);
-                scalar @$ary or return;
-                more($self, join("\r\n", @$ary));
-                1;
-        });
+        my $ng = $self->{ng} or return '412 no newsgroup selected';
+        my $mm = $ng->mm;
+        if (defined $range) {
+                my $r = get_range($self, $range);
+                return $r unless ref $r;
+                my ($beg, $end) = @$r;
+                long_response($self, sub {
+                        $r = $mm->msg_range(\$beg, $end, 'num');
+                        scalar(@$r) or return;
+                        more($self, join("\r\n", map { "$_->[0]\r\n" } @$r));
+                        1;
+                });
+        } else { # grab every article number
+                my $n = 0;
+                long_response($self, sub {
+                        my $ary = $mm->ids_after(\$n);
+                        scalar(@$ary) or return;
+                        more($self, join("\r\n", @$ary));
+                        1;
+                });
+        }
 }
 
 sub parse_time ($$;$) {