nntp: speed up XHDR for the Message-ID case

We can use our msgmap database to implement "XHDR Message-ID [range]"
commands quickly.  This helps immensely with slrnpull, which prefers
XHDR to LISTGROUP for some reason...

1 files changed, 36 insertions, 0 deletions

diff --git a/lib/PublicInbox/NNTP.pm b/lib/PublicInbox/NNTP.pm
index 8275ef08..47b03e02 100644
--- a/lib/PublicInbox/NNTP.pm
+++ b/lib/PublicInbox/NNTP.pm
@@ -505,9 +505,45 @@ sub long_response ($$$$) {
         undef;
 }
 
+sub xhdr_message_id ($$) { # optimize XHDR Message-ID [range] for slrnpull.
+        my ($self, $range) = @_;
+
+        my $mm = $self->{ng}->mm;
+        if (defined $range && $range =~ /\A<(.+)>\z/) { # Message-ID
+                my $n = $mm->num_for($range);
+                more($self, '221 Header follows');
+                more($self, "<$range> <$range>") if defined $n;
+                '.';
+        } else { # numeric range
+                $range = $self->{article} unless defined $range;
+                my $r = get_range($self, $range);
+                return $r unless ref $r;
+                my ($beg, $end) = @$r;
+                more($self, '221 Header follows');
+                $self->long_response($beg, $end, sub {
+                        my ($i) = @_;
+                        my $mid = $mm->mid_for($$i);
+                        more($self, "$$i <$mid>") if defined $mid;
+                });
+        }
+}
+
 sub cmd_xhdr ($$;$) {
         my ($self, $header, $range) = @_;
         defined $self->{ng} or return '412 no news group currently selected';
+        my $sub = $header;
+        $sub =~ tr/A-Z-/a-z_/;
+        $sub = eval {
+                no strict 'refs';
+                $sub = *{'xhdr_'.$sub}{CODE};
+        };
+        return xhdr_slow($self, $header, $range) unless defined $sub;
+        $sub->($self, $range);
+}
+
+sub xhdr_slow ($$$) {
+        my ($self, $header, $range) = @_;
+
         if (defined $range && $range =~ /\A<(.+)>\z/) { # Message-ID
                 my $r = $self->art_lookup($range, 2);
                 return $r unless ref $r;