recv_cmd: do not undef recvmsg buffer arg on errors

It's a waste of ops and cycles, and inconsistent with perl
sysread() behavior which doesn't touch the supplied buffer on
errors.

diff --git a/lib/PublicInbox/CmdIPC4.pm b/lib/PublicInbox/CmdIPC4.pm
index c3a7f56ec7e3f356243d270447402aa3217c499a..76938b6d36dc4c16a89ecf63be1ff487a2e6217d 100644 (file)
--- a/lib/PublicInbox/CmdIPC4.pm
+++ b/lib/PublicInbox/CmdIPC4.pm
@@ -1,4 +1,4 @@
-# Copyright (C) 2020-2021 all contributors <meta@public-inbox.org>
+# Copyright (C) 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)
@@ -32,7 +32,7 @@ no warnings 'once';
 *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, $mh, 0) // return ($_[1] = undef);
+       my $r = Socket::MsgHdr::recvmsg($s, $mh, 0) // return (undef);
        $_[1] = $mh->buf;
        return () if $r == 0;
        my (undef, undef, $data) = $mh->cmsghdr;