--- /dev/null
+# Copyright (C) 2020 all contributors <meta@public-inbox.org>
+# License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
+# TODO: reduce duplication from PublicInbox::NNTPdeflate
+
+# RFC 4978
+package PublicInbox::IMAPdeflate;
+use strict;
+use warnings;
+use 5.010_001;
+use base qw(PublicInbox::IMAP);
+use Compress::Raw::Zlib;
+use Hash::Util qw(unlock_hash); # dependency of fields for perl 5.10+, anyways
+
+my %IN_OPT = (
+ -Bufsize => 1024,
+ -WindowBits => -15, # RFC 1951
+ -AppendOutput => 1,
+);
+
+# global deflate context and buffer
+my $zbuf = \(my $buf = '');
+my $zout;
+{
+ my $err;
+ ($zout, $err) = Compress::Raw::Zlib::Deflate->new(
+ # nnrpd (INN) and Compress::Raw::Zlib favor MemLevel=9,
+ # the zlib C library and git use MemLevel=8 as the default
+ # -MemLevel => 9,
+ -Bufsize => 65536, # same as nnrpd
+ -WindowBits => -15, # RFC 1951
+ -AppendOutput => 1,
+ );
+ $err == Z_OK or die "Failed to initialize zlib deflate stream: $err";
+}
+
+sub enable {
+ my ($class, $self, $tag) = @_;
+ my ($in, $err) = Compress::Raw::Zlib::Inflate->new(%IN_OPT);
+ if ($err != Z_OK) {
+ $self->err("Inflate->new failed: $err");
+ $self->write(\"$tag BAD failed to activate compression\r\n");
+ return;
+ }
+ unlock_hash(%$self);
+ $self->write(\"$tag OK DEFLATE active\r\n");
+ bless $self, $class;
+ $self->{zin} = $in;
+}
+
+# overrides PublicInbox::NNTP::compressed
+sub compressed { 1 }
+
+# $_[1] may be a reference or not
+sub do_read ($$$$) {
+ my ($self, $rbuf, $len, $off) = @_;
+
+ my $zin = $self->{zin} or return; # closed
+ my $doff;
+ my $dbuf = delete($self->{dbuf}) // '';
+ $doff = length($dbuf);
+ my $r = PublicInbox::DS::do_read($self, \$dbuf, $len, $doff) or return;
+
+ # assert(length($$rbuf) == $off) as far as NNTP.pm is concerned
+ # -ConsumeInput is true, so $dbuf is automatically emptied
+ my $err = $zin->inflate($dbuf, $rbuf);
+ if ($err == Z_OK) {
+ $self->{dbuf} = $dbuf if $dbuf ne '';
+ $r = length($$rbuf) and return $r;
+ # nothing ready, yet, get more, later
+ $self->requeue;
+ } else {
+ delete $self->{zin};
+ $self->close;
+ }
+ 0;
+}
+
+# override PublicInbox::DS::msg_more
+sub msg_more ($$) {
+ my $self = $_[0];
+
+ # $_[1] may be a reference or not for ->deflate
+ my $err = $zout->deflate($_[1], $zbuf);
+ $err == Z_OK or die "->deflate failed $err";
+ 1;
+}
+
+sub zflush ($) {
+ my ($self) = @_;
+
+ my $deflated = $zbuf;
+ $zbuf = \(my $next = '');
+
+ my $err = $zout->flush($deflated, Z_FULL_FLUSH);
+ $err == Z_OK or die "->flush failed $err";
+
+ # We can still let the lower socket layer do buffering:
+ PublicInbox::DS::msg_more($self, $$deflated);
+}
+
+# compatible with PublicInbox::DS::write, so $_[1] may be a reference or not
+sub write ($$) {
+ my $self = $_[0];
+ return PublicInbox::DS::write($self, $_[1]) if ref($_[1]) eq 'CODE';
+
+ my $deflated = $zbuf;
+ $zbuf = \(my $next = '');
+
+ # $_[1] may be a reference or not for ->deflate
+ my $err = $zout->deflate($_[1], $deflated);
+ $err == Z_OK or die "->deflate failed $err";
+ $err = $zout->flush($deflated, Z_FULL_FLUSH);
+ $err == Z_OK or die "->flush failed $err";
+
+ # We can still let the socket layer do buffering:
+ PublicInbox::DS::write($self, $deflated);
+}
+
+1;