pop3: remove untouched rows on QUIT/disconnect

Some POP3 clients may connect and never retrieve messages nor
trigger deletes.  In that case, save some storage by removing
unused rows from the `deletes' and `users' tables.

1 files changed, 30 insertions, 7 deletions

diff --git a/lib/PublicInbox/POP3.pm b/lib/PublicInbox/POP3.pm
index 53fb2e05..c993e558 100644
--- a/lib/PublicInbox/POP3.pm
+++ b/lib/PublicInbox/POP3.pm
@@ -301,6 +301,27 @@ sub close {
         $self->SUPER::close;
 }
 
+# must be called inside a state_dbh transaction with flock held
+sub __cleanup_state {
+        my ($self, $txn_id) = @_;
+        my $user_id = $self->{user_id} // die 'BUG: no {user_id}';
+        $self->{pop3d}->{-state_dbh}->prepare_cached(<<'')->execute($txn_id);
+DELETE FROM deletes WHERE txn_id = ? AND uid_dele = -1
+
+        my $sth = $self->{pop3d}->{-state_dbh}->prepare_cached(<<'');
+SELECT COUNT(*) FROM deletes WHERE user_id = ?
+
+        $sth->execute($user_id);
+        my $nr = $sth->fetchrow_array;
+        if ($nr == 0) {
+                $sth = $self->{pop3d}->{-state_dbh}->prepare_cached(<<'');
+DELETE FROM users WHERE user_id = ?
+
+                $sth->execute($user_id);
+        }
+        $nr;
+}
+
 sub cmd_quit {
         my ($self) = @_;
         if (defined(my $txn_id = $self->{txn_id})) {
@@ -308,23 +329,25 @@ sub cmd_quit {
                 if (my $exp = delete $self->{expire}) {
                         mark_dele($self, $_) for unpack('S*', $exp);
                 }
+                my $keep = 1;
                 my $dbh = $self->{pop3d}->{-state_dbh};
                 my $lk = $self->{pop3d}->lock_for_scope;
-                my $sth;
                 $dbh->begin_work;
 
-                if (defined $self->{txn_max_uid}) {
-                        $sth = $dbh->prepare_cached(<<'');
+                if (defined(my $max = $self->{txn_max_uid})) {
+                        $dbh->prepare_cached(<<'')->execute($max, $txn_id, $max)
 UPDATE deletes SET uid_dele = ? WHERE txn_id = ? AND uid_dele < ?
 
-                        $sth->execute($self->{txn_max_uid}, $txn_id,
-                                        $self->{txn_max_uid});
+                } else {
+                        $keep = $self->__cleanup_state($txn_id);
                 }
-                $sth = $dbh->prepare_cached(<<'');
+                $dbh->prepare_cached(<<'')->execute(time, $user_id) if $keep;
 UPDATE users SET last_seen = ? WHERE user_id = ?
 
-                $sth->execute(time, $user_id);
                 $dbh->commit;
+                # we MUST do txn_id F_UNLCK here inside ->lock_for_scope:
+                $self->{did_quit} = 1;
+                $self->{pop3d}->unlock_mailbox($self);
         }
         $self->write(\"+OK public-inbox POP3 server signing off\r\n");
         $self->close;