From c17c44d9e0ef28f0f0521656f335f836ad8b7754 Mon Sep 17 00:00:00 2001
From: Eric Wong <e@80x24.org>
Date: Sun, 10 Jan 2021 12:15:02 +0000
Subject: cmd_ipc: send FDs with buffer payload

For another step in in syscall reduction, we'll support
transferring 3 FDs and a buffer with a single sendmsg/recvmsg
syscall using Socket::MsgHdr if available.

Beyond script/lei itself, this will be used for internal IPC
between search backends (perhaps with SOCK_SEQPACKET).  There's
a chance this could make it to the public-facing daemons, too.

This adds an optional dependency on the Socket::MsgHdr package,
available as libsocket-msghdr-perl on Debian-based distros
(but not CentOS 7.x and FreeBSD 11.x, at least).

Our Inline::C version in PublicInbox::Spawn remains the last
choice for script/lei due to the high startup time, and
IO::FDPass remains supported for non-Debian distros.

Since the socket name prefix changes from 3 to 4, we'll also
take this opportunity to make the argv+env buffer transfer less
error-prone by relying on argc instead of designated delimiters.
---
 script/lei | 53 ++++++++++++++++++++++++++---------------------------
 1 file changed, 26 insertions(+), 27 deletions(-)

(limited to 'script')

diff --git a/script/lei b/script/lei
index 2ea98da4..d954b9eb 100755
--- a/script/lei
+++ b/script/lei
@@ -4,17 +4,20 @@
 use strict;
 use v5.10.1;
 use Socket qw(AF_UNIX SOCK_STREAM pack_sockaddr_un);
-my ($send_3fds, $nfd);
-if (my ($sock, $pwd) = eval {
-	$send_3fds = eval {
-		require IO::FDPass;
-		$nfd = 1; # 1 FD per-sendmsg
-		sub { IO::FDPass::send($_[0], $_[$_]) for (1..3) }
-	} // do {
-		require PublicInbox::Spawn; # takes ~50ms even if built *sigh*
-		$nfd = 3; # 3 FDs per-sendmsg(2)
-		PublicInbox::Spawn->can('send_3fds');
-	} // die "IO::FDPass missing or Inline::C not installed/configured\n";
+use PublicInbox::CmdIPC4;
+my $narg = 4;
+my $send_cmd = PublicInbox::CmdIPC4->can('send_cmd4') // do {
+	require PublicInbox::CmdIPC1; # 2nd choice
+	$narg = 1;
+	PublicInbox::CmdIPC1->can('send_cmd1');
+} // do {
+	require PublicInbox::Spawn; # takes ~50ms even if built *sigh*
+	$narg = 4;
+	PublicInbox::Spawn->can('send_cmd4');
+};
+
+my ($sock, $pwd);
+if ($send_cmd && eval {
 	my $path = do {
 		my $runtime_dir = ($ENV{XDG_RUNTIME_DIR} // '') . '/lei';
 		if ($runtime_dir eq '/lei') {
@@ -25,29 +28,27 @@ if (my ($sock, $pwd) = eval {
 			require File::Path;
 			File::Path::mkpath($runtime_dir, 0, 0700);
 		}
-		"$runtime_dir/$nfd.sock";
+		"$runtime_dir/$narg.sock";
 	};
 	my $addr = pack_sockaddr_un($path);
-	socket(my $sock, AF_UNIX, SOCK_STREAM, 0) or die "socket: $!";
+	socket($sock, AF_UNIX, SOCK_STREAM, 0) or die "socket: $!";
 	unless (connect($sock, $addr)) { # start the daemon if not started
 		local $ENV{PERL5LIB} = join(':', @INC);
 		open(my $daemon, '-|', $^X, qw[-MPublicInbox::LEI
 			-E PublicInbox::LEI::lazy_start(@ARGV)],
-			$path, $! + 0, $nfd) or die "popen: $!";
+			$path, $! + 0, $narg) or die "popen: $!";
 		while (<$daemon>) { warn $_ } # EOF when STDERR is redirected
 		close($daemon) or warn <<"";
 lei-daemon could not start, exited with \$?=$?
 
 		# try connecting again anyways, unlink+bind may be racy
-		unless (connect($sock, $addr)) {
-			die <<"";
+		connect($sock, $addr) or die <<"";
 connect($path): $! (after attempted daemon start)
 Falling back to (slow) one-shot mode
 
-		}
 	}
 	require Cwd;
-	my $pwd = $ENV{PWD} // '';
+	$pwd = $ENV{PWD} // '';
 	my $cwd = Cwd::fastcwd() // die "fastcwd(PWD=$pwd): $!";
 	if ($pwd ne $cwd) { # prefer ENV{PWD} if it's a symlink to real cwd
 		my @st_cwd = stat($cwd) or die "stat(cwd=$cwd): $!";
@@ -58,23 +59,21 @@ Falling back to (slow) one-shot mode
 	} else {
 		$pwd = $cwd;
 	}
-	($sock, $pwd);
-}) { # IO::FDPass, $sock, $pwd are all available:
+	1;
+}) { # (Socket::MsgHdr|IO::FDPass|Inline::C), $sock, $pwd are all available:
 	local $ENV{PWD} = $pwd;
-	my $buf = "$$\0\0>" . join("]\0[", @ARGV) . "\0\0>";
-	while (my ($k, $v) = each %ENV) { $buf .= "$k=$v\0" }
+	my $buf = join("\0", $$, scalar(@ARGV), @ARGV);
+	while (my ($k, $v) = each %ENV) { $buf .= "\0$k=$v" }
 	$buf .= "\0\0";
 	select $sock;
 	$| = 1; # unbuffer selected $sock
-	$send_3fds->(fileno($sock), 0, 1, 2);
-	print $sock $buf or die "print(sock, buf): $!";
+	$send_cmd->($sock, 0, 1, 2, $buf, 0);
 	while ($buf = <$sock>) {
 		$buf =~ /\Aexit=([0-9]+)\n\z/ and exit($1 + 0);
 		die $buf;
 	}
-} else { # for systems lacking IO::FDPass
-	# don't warn about IO::FDPass since it's not commonly installed
-	warn $@ if $@ && index($@, 'IO::FDPass') < 0;
+} else { # for systems lacking Socket::MsgHdr, IO::FDPass or Inline::C
+	warn $@ if $@;
 	require PublicInbox::LEI;
 	PublicInbox::LEI::oneshot(__PACKAGE__);
 }
-- 
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