1 files changed, 34 insertions, 0 deletions
diff --git a/lib/PublicInbox/CmdIPC4.pm b/lib/PublicInbox/CmdIPC4.pm
new file mode 100644
index 00000000..90fca62d
--- /dev/null
+++ b/lib/PublicInbox/CmdIPC4.pm
@@ -0,0 +1,34 @@
+# Copyright (C) 2020-2021 all contributors <meta@public-inbox.org>
+# License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
+
+# callers should use PublicInbox::CmdIPC4->can('send_cmd4') (or recv_cmd4)
+# first choice for script/lei front-end and 2nd choice for lei backend
+# libsocket-msghdr-perl is in Debian but many other distros as of 2021.
+package PublicInbox::CmdIPC4;
+use strict;
+use v5.10.1;
+use Socket qw(SOL_SOCKET SCM_RIGHTS);
+BEGIN { eval {
+require Socket::MsgHdr; # XS
+no warnings 'once';
+
+# 3 FDs per-sendmsg(2) + buffer
+*send_cmd4 = sub ($$$$$$) { # (sock, in, out, err, buf, flags) = @_;
+        my $mh = Socket::MsgHdr->new(buf => $_[4]);
+        $mh->cmsghdr(SOL_SOCKET, SCM_RIGHTS, pack('iii', @_[1,2,3]));
+        Socket::MsgHdr::sendmsg($_[0], $mh, $_[5]) or die "sendmsg: $!";
+};
+
+*recv_cmd4 = sub ($$$) {
+        my ($s, undef, $len) = @_; # $_[1] = destination buffer
+        my $mh = Socket::MsgHdr->new(buflen => $len, controllen => 256);
+        my $r = Socket::MsgHdr::recvmsg($s, $mh, 0) // die "recvmsg: $!";
+        $_[1] = $mh->buf;
+        return () if $r == 0;
+        my (undef, undef, $data) = $mh->cmsghdr;
+        unpack('iii', $data);
+};
+
+} } # /eval /BEGIN
+
+1;