mbox: be fair to other HTTP clients

At least for public-inbox-httpd, this allows us to avoid having
a client monopolize one event loop tick of the server for too
long.  It hurts throughput for the /all.mbox.gz endpoint, but I
doubt anybody cares and the latency improvement for other
clients would be appreciated.

We already do the same fairness thing for HTML pages.

1 files changed, 3 insertions, 0 deletions

diff --git a/lib/PublicInbox/Mbox.pm b/lib/PublicInbox/Mbox.pm
index 1e3de5b0..dc41548b 100644
--- a/lib/PublicInbox/Mbox.pm
+++ b/lib/PublicInbox/Mbox.pm
@@ -138,6 +138,9 @@ sub getline {
                                 ${$self->{buf}} = '';
                                 return $ret;
                         }
+
+                        # be fair to other clients on public-inbox-httpd:
+                        return '';
                 }
                 $res = $self->{cb}->($self->{opts});
                 $self->{msgs} = $res->{msgs};