nntpdeflate: reduce overhead of idle clients

We don't need to keep an empty buffer around in the common case
when a client is sending us completely inflatable requests and
we're able to read them in one go.

This only seems to save about 2M with 10K NNTPS clients using
COMPRESS, so it's not a huge win, but better than nothing.

1 files changed, 8 insertions, 5 deletions

diff --git a/lib/PublicInbox/NNTPdeflate.pm b/lib/PublicInbox/NNTPdeflate.pm
index f2de0f38..c143488f 100644
--- a/lib/PublicInbox/NNTPdeflate.pm
+++ b/lib/PublicInbox/NNTPdeflate.pm
@@ -56,7 +56,7 @@ sub enable {
         unlock_hash(%$self);
         $self->res('206 Compression active');
         bless $self, $class;
-        $self->{zin} = [ $in, '' ];
+        $self->{zin} = $in;
 }
 
 # overrides PublicInbox::NNTP::compressed
@@ -67,13 +67,16 @@ sub do_read ($$$$) {
         my ($self, $rbuf, $len, $off) = @_;
 
         my $zin = $self->{zin} or return; # closed
-        my $deflated = \($zin->[1]);
-        my $r = PublicInbox::DS::do_read($self, $deflated, $len) or return;
+        my $doff;
+        my $dbuf = delete($self->{dbuf}) // '';
+        $doff = length($dbuf);
+        my $r = PublicInbox::DS::do_read($self, \$dbuf, $len, $doff) or return;
 
         # assert(length($$rbuf) == $off) as far as NNTP.pm is concerned
-        # -ConsumeInput is true, so $deflated is automatically emptied
-        my $err = $zin->[0]->inflate($deflated, $rbuf);
+        # -ConsumeInput is true, so $dbuf is automatically emptied
+        my $err = $zin->inflate($dbuf, $rbuf);
         if ($err == Z_OK) {
+                $self->{dbuf} = $dbuf if $dbuf ne '';
                 $r = length($$rbuf) and return $r;
                 # nothing ready, yet, get more, later
                 $self->requeue;