imap: support isearch and reduce Xapian queries

Since IMAP search (either with Isearch or traditional per-Inbox
search) only returns UIDs, we can safely set the limit to the
UID slice size(*).  With isearch, we can also trust the Xapian
result to fit any docid range we specify.

Limiting Xapian results to 1000 was making ->ALL docid <=>
per-Inbox UID impossible since results could overlap between
ranges unpredictably.

Finally, we can map the ->ALL docids into per-Inbox UIDs and
show them to the client in the UID order of the Inbox, not the
docid order of the ->ALL extindex.

This also lets us get rid of the "uid:" query parser prefix
and use the Xapian::Query API directly to reduce our search
prefix footprint.

For mbox.gz downloads in WWW, we'll also make a best effort to
preserve the order from the Inbox, not the order of extindex;
though it's possible large result sets can have non-overlapping
windows.

(*) by definition, UID slice size is a "safe" value which
    shouldn't OOM either the server or clients.

1 files changed, 10 insertions, 31 deletions

diff --git a/lib/PublicInbox/IMAP.pm b/lib/PublicInbox/IMAP.pm
index 9599f494..f123eb01 100644
--- a/lib/PublicInbox/IMAP.pm
+++ b/lib/PublicInbox/IMAP.pm
@@ -1122,33 +1122,6 @@ sub parse_query ($$) {
         $q;
 }
 
-sub refill_xap ($$$$) {
-        my ($self, $uids, $range_info, $q) = @_;
-        my ($beg, $end) = @$range_info;
-        my $srch = $self->{ibx}->search;
-        my $opt = { mset => 2, limit => 1000 };
-        my $mset = $srch->mset("$q uid:$beg..$end", $opt);
-        @$uids = @{$srch->mset_to_artnums($mset)};
-        if (@$uids) {
-                $range_info->[0] = $uids->[-1] + 1; # update $beg
-                return; # possibly more
-        }
-        0; # all done
-}
-
-sub search_xap_range { # long_response
-        my ($self, $tag, $q, $range_info, $want_msn) = @_;
-        my $uids = [];
-        if (defined(my $err = refill_xap($self, $uids, $range_info, $q))) {
-                $err ||= 'OK Search done';
-                $self->write("\r\n$tag $err\r\n");
-                return;
-        }
-        msn_convert($self, $uids) if $want_msn;
-        $self->msg_more(join(' ', '', @$uids));
-        1; # more
-}
-
 sub search_common {
         my ($self, $tag, $query, $want_msn) = @_;
         my $ibx = $self->{ibx} or return "$tag BAD No mailbox selected\r\n";
@@ -1160,11 +1133,17 @@ sub search_common {
                 long_response($self, \&search_uid_range,
                                 $tag, $sql, $range_info, $want_msn);
         } elsif ($q = $q->{xap}) {
-                $self->{ibx}->search or
+                my $srch = $self->{ibx}->isrch or
                         return "$tag BAD search not available for mailbox\r\n";
-                $self->msg_more('* SEARCH');
-                long_response($self, \&search_xap_range,
-                                $tag, $q, $range_info, $want_msn);
+                my $opt = {
+                        mset => 2,
+                        limit => UID_SLICE,
+                        uid_range => $range_info
+                };
+                my $mset = $srch->mset($q, $opt);
+                my $uids = $srch->mset_to_artnums($mset, $opt);
+                msn_convert($self, $uids) if $want_msn;
+                "* SEARCH @$uids\r\n$tag OK Search done\r\n";
         } else {
                 "$tag BAD Error\r\n";
         }