lei: drop $SIG{__DIE__}, add oneshot fallbacks

We'll force stdout+stderr to be a pipe the spawning client
controls, thus there's no need to lose error reporting by
prematurely redirecting stdout+stderr to /dev/null.

We can now rely exclusively on OnDestroy to write to syslog() on
uncaught die failures.

Also support falling back to oneshot mode on socket and cwd
failures, since some commands may still be useful if the current
working directory goes missing :P

1 files changed, 32 insertions, 35 deletions

diff --git a/lib/PublicInbox/LEI.pm b/lib/PublicInbox/LEI.pm
index 95b48095..fd412324 100644
--- a/lib/PublicInbox/LEI.pm
+++ b/lib/PublicInbox/LEI.pm
@@ -12,7 +12,7 @@ use parent qw(PublicInbox::DS);
 use Getopt::Long ();
 use Socket qw(AF_UNIX SOCK_STREAM pack_sockaddr_un);
 use Errno qw(EAGAIN ECONNREFUSED ENOENT);
-use POSIX qw(setsid);
+use POSIX ();
 use IO::Handle ();
 use Sys::Syslog qw(syslog openlog);
 use PublicInbox::Config;
@@ -584,60 +584,44 @@ sub noop {}
 
 # lei(1) calls this when it can't connect
 sub lazy_start {
-        my ($path, $err) = @_;
-        require IO::FDPass; # require this early so caller sees it
-        if ($err == ECONNREFUSED) {
+        my ($path, $errno) = @_;
+        if ($errno == ECONNREFUSED) {
                 unlink($path) or die "unlink($path): $!";
-        } elsif ($err != ENOENT) {
-                $! = $err; # allow interpolation to stringify in die
+        } elsif ($errno != ENOENT) {
+                $! = $errno; # allow interpolation to stringify in die
                 die "connect($path): $!";
         }
         umask(077) // die("umask(077): $!");
         socket(my $l, AF_UNIX, SOCK_STREAM, 0) or die "socket: $!";
         bind($l, pack_sockaddr_un($path)) or die "bind($path): $!";
-        listen($l, 1024) or die "listen $!";
+        listen($l, 1024) or die "listen: $!";
         my @st = stat($path) or die "stat($path): $!";
         my $dev_ino_expect = pack('dd', $st[0], $st[1]); # dev+ino
         pipe(my ($eof_r, $eof_w)) or die "pipe: $!";
         my $oldset = PublicInbox::Sigfd::block_signals();
-        my $pid = fork // die "fork: $!";
-        return if $pid;
+        require IO::FDPass;
         require PublicInbox::Listener;
         require PublicInbox::EOFpipe;
-        openlog($path, 'pid', 'user');
-        local $SIG{__DIE__} = sub {
-                syslog('crit', "@_");
-                die; # calls the default __DIE__ handler
-        };
-        local $SIG{__WARN__} = sub { syslog('warning', "@_") };
-        open(STDIN, '+<', '/dev/null') or die "redirect stdin failed: $!\n";
-        open STDOUT, '>&STDIN' or die "redirect stdout failed: $!\n";
-        open STDERR, '>&STDIN' or die "redirect stderr failed: $!\n";
-        setsid();
-        $pid = fork // die "fork: $!";
+        (-p STDOUT && -p STDERR) or die "E: stdout+stderr must be pipes\n";
+        open(STDIN, '+<', '/dev/null') or die "redirect stdin failed: $!";
+        POSIX::setsid() > 0 or die "setsid: $!";
+        my $pid = fork // die "fork: $!";
         return if $pid;
-        $SIG{__DIE__} = 'DEFAULT';
-        my $on_destroy = PublicInbox::OnDestroy->new(sub {
-                my ($owner_pid) = @_;
-                syslog('crit', "$@") if $@ && $$ == $owner_pid;
-        }, $$);
         $0 = "lei-daemon $path";
         local %PATH2CFG;
-        $l->blocking(0);
-        $eof_w->blocking(0);
-        $eof_r->blocking(0);
-        my $listener = PublicInbox::Listener->new($l, \&accept_dispatch, $l);
+        $_->blocking(0) for ($l, $eof_r, $eof_w);
+        $l = PublicInbox::Listener->new($l, \&accept_dispatch, $l);
         my $exit_code;
         local $quit = sub {
                 $exit_code //= shift;
-                my $tmp = $listener or exit($exit_code);
+                my $listener = $l or exit($exit_code);
                 unlink($path) if defined($path);
-                syswrite($eof_w, '.');
-                $l = $listener = $path = undef;
-                $tmp->close if $tmp; # DS::close
+                # closing eof_w triggers \&noop wakeup
+                $eof_w = $l = $path = undef;
+                $listener->close; # DS::close
                 PublicInbox::DS->SetLoopTimeout(1000);
         };
-        PublicInbox::EOFpipe->new($eof_r, sub {}, undef);
+        PublicInbox::EOFpipe->new($eof_r, \&noop, undef);
         my $sig = {
                 CHLD => \&PublicInbox::DS::enqueue_reap,
                 QUIT => $quit,
@@ -682,8 +666,21 @@ sub lazy_start {
                 }
                 $n; # true: continue, false: stop
         });
+
+        # STDIN was redirected to /dev/null above, closing STDOUT and
+        # STDERR will cause the calling `lei' client process to finish
+        # reading <$daemon> pipe.
+        open STDOUT, '>&STDIN' or die "redirect stdout failed: $!";
+        openlog($path, 'pid', 'user');
+        local $SIG{__WARN__} = sub { syslog('warning', "@_") };
+        my $owner_pid = $$;
+        my $on_destroy = PublicInbox::OnDestroy->new(sub {
+                syslog('crit', "$@") if $@ && $$ == $owner_pid;
+        });
+        open STDERR, '>&STDIN' or die "redirect stderr failed: $!";
+        # $daemon pipe to `lei' closed, main loop begins:
         PublicInbox::DS->EventLoop;
-        $@ = undef if $on_destroy; # quiet OnDestroy if we got here
+        @$on_destroy = (); # cancel on_destroy if we get here
         exit($exit_code // 0);
 }