imap: FETCH: try to make fake MSNs sequentially

This appears to significantly improve header caching behavior
with mutt.  With the current public-inbox.org/git mirror(*),
mutt will only re-FETCH the last ~300 or so messages in the
final "inbox.comp.version-control.git.7" mailbox, instead of
~49,000 messages every time.

It's not perfect, but a 500ms query is better than a >10s query
and mutt itself spends as much time loading its header cache.

(*) there are many gaps in NNTP article numbers (UIDs) due to
    spam removal from public-inbox-learn.

2 files changed, 13 insertions, 13 deletions

diff --git a/lib/PublicInbox/IMAP.pm b/lib/PublicInbox/IMAP.pm
index fe3c7d1a..d0683530 100644
--- a/lib/PublicInbox/IMAP.pm
+++ b/lib/PublicInbox/IMAP.pm
@@ -475,12 +475,12 @@ sub requeue_once ($) {
         $self->requeue if $new_size == 1;
 }
 
-# my ($uid_base, $UID) = @_;
-sub fetch_msn_uid ($$) { '* '.($_[1] - $_[0]).' FETCH (UID '.$_[1] }
+# my ($msn, $UID) = @_;
+sub fetch_msn_uid ($$) { '* '.(${$_[0]}++).' FETCH (UID '.$_[1] }
 
 sub fetch_run_ops {
-        my ($self, $uid_base, $smsg, $bref, $ops, $partial) = @_;
-        $self->msg_more(fetch_msn_uid($uid_base, $smsg->{num}));
+        my ($self, $msn, $smsg, $bref, $ops, $partial) = @_;
+        $self->msg_more(fetch_msn_uid($msn, $smsg->{num}));
         my ($eml, $k);
         for (my $i = 0; $i < @$ops;) {
                 $k = $ops->[$i++];
@@ -492,7 +492,7 @@ sub fetch_run_ops {
 
 sub fetch_blob_cb { # called by git->cat_async via git_async_cat
         my ($bref, $oid, $type, $size, $fetch_arg) = @_;
-        my ($self, undef, $msgs, undef, $ops, $partial) = @$fetch_arg;
+        my ($self, undef, $msgs, $range_info, $ops, $partial) = @$fetch_arg;
         my $smsg = shift @$msgs or die 'BUG: no smsg';
         if (!defined($oid)) {
                 # it's possible to have TOCTOU if an admin runs
@@ -501,7 +501,7 @@ sub fetch_blob_cb { # called by git->cat_async via git_async_cat
         } else {
                 $smsg->{blob} eq $oid or die "BUG: $smsg->{blob} != $oid";
         }
-        fetch_run_ops($self, $self->{uid_base}, $smsg, $bref, $ops, $partial);
+        fetch_run_ops($self, $range_info->[3], $smsg, $bref, $ops, $partial);
         requeue_once($self);
 }
 
@@ -601,7 +601,8 @@ sub range_step ($$) {
                 return 'BAD fetch range';
         }
         uid_clamp($self, \$beg, \$end) if defined($range);
-        [ $beg, $end, $$range_csv ];
+        my $msn = $beg - $self->{uid_base};
+        [ $beg, $end, $$range_csv, \$msn ];
 }
 
 sub refill_range ($$$) {
@@ -638,8 +639,7 @@ sub fetch_smsg { # long_response
                         return;
                 }
         }
-        my $uid_base = $self->{uid_base};
-        fetch_run_ops($self, $uid_base, $_, undef, $ops) for @$msgs;
+        fetch_run_ops($self, $range_info->[3], $_, undef, $ops) for @$msgs;
         @$msgs = ();
         1; # more
 }
@@ -665,10 +665,10 @@ sub fetch_uid { # long_response
                 }
                 # continue looping
         }
-        my $uid_base = $self->{uid_base};
         my ($i, $k);
+        my $msn = $range_info->[3];
         for (@$uids) {
-                $self->msg_more(fetch_msn_uid($uid_base, $_));
+                $self->msg_more(fetch_msn_uid($msn, $_));
                 for ($i = 0; $i < @$ops;) {
                         $k = $ops->[$i++];
                         $ops->[$i++]->($self, $k);
diff --git a/t/imapd.t b/t/imapd.t
index c691e1a9..fdab074a 100644
--- a/t/imapd.t
+++ b/t/imapd.t
@@ -349,8 +349,8 @@ is(scalar keys %$ret, 3, 'got all 3 messages');
 }
 my $r2 = $mic->fetch_hash('1:*', 'BODY.PEEK[]') or BAIL_OUT "FETCH $@";
 is(scalar keys %$r2, 2, 'did not get all 3 messages');
-is($r2->{2}->{'BODY[]'}, $ret->{2}->{RFC822}, 'message 2 unchanged');
-is($r2->{3}->{'BODY[]'}, $ret->{3}->{RFC822}, 'message 3 unchanged');
+is($r2->{1}->{'BODY[]'}, $ret->{2}->{RFC822}, 'message 2 unchanged');
+is($r2->{2}->{'BODY[]'}, $ret->{3}->{RFC822}, 'message 3 unchanged');
 $r2 = $mic->fetch_hash(2, 'BODY.PEEK[HEADER.FIELDS (message-id)]')
                         or BAIL_OUT "FETCH $@";
 is($r2->{2}->{'BODY[HEADER.FIELDS (MESSAGE-ID)]'},