[PATCH 09/10] lei: fix error reporting from lei/store -> lei-daemon

[Eric Wong]

We must set autoflush to ensure timely notification of clients;
and lei-daemon must not block when waiting on reads in case of
spurious wakeups.

Finally, if no clients are connected to lei-daemon, write to
syslog to ensure the error is visible.
---
 lib/PublicInbox/LeiStore.pm    |  2 ++
 lib/PublicInbox/LeiStoreErr.pm | 14 ++++++++++++--
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/lib/PublicInbox/LeiStore.pm b/lib/PublicInbox/LeiStore.pm
index 5a48c064..0652137e 100644
--- a/lib/PublicInbox/LeiStore.pm
+++ b/lib/PublicInbox/LeiStore.pm
@@ -28,6 +28,7 @@ use PublicInbox::Spawn qw(spawn);
 use List::Util qw(max);
 use File::Temp ();
 use POSIX ();
+use IO::Handle (); # ->autoflush
 
 sub new {
        my (undef, $dir, $opt) = @_;
@@ -514,6 +515,7 @@ sub write_prepare {
                $self->ipc_lock_init("$dir/ipc.lock");
                substr($dir, -length('/lei/store'), 10, '');
                pipe(my ($r, $w)) or die "pipe: $!";
+               $w->autoflush(1);
                # Mail we import into lei are private, so headers filtered out
                # by -mda for public mail are not appropriate
                local @PublicInbox::MDA::BAD_HEADERS = ();
diff --git a/lib/PublicInbox/LeiStoreErr.pm b/lib/PublicInbox/LeiStoreErr.pm
index 68ce96d6..5f9ba24d 100644
--- a/lib/PublicInbox/LeiStoreErr.pm
+++ b/lib/PublicInbox/LeiStoreErr.pm
@@ -8,22 +8,32 @@ use strict;
 use v5.10.1;
 use parent qw(PublicInbox::DS);
 use PublicInbox::Syscall qw(EPOLLIN EPOLLONESHOT);
+use Sys::Syslog qw(openlog syslog closelog);
+use IO::Handle (); # ->blocking
 
 sub new {
        my ($cls, $rd, $lei) = @_;
        my $self = bless { sock => $rd, store_path => $lei->store_path }, $cls;
+       $rd->blocking(0);
        $self->SUPER::new($rd, EPOLLIN | EPOLLONESHOT);
 }
 
 sub event_step {
        my ($self) = @_;
-       $self->do_read(\(my $rbuf), 4096) or return;
+       my $rbuf = $self->{rbuf} // \(my $x = '');
+       $self->do_read($rbuf, 8192, length($$rbuf)) or return;
        my $cb;
+       my $printed;
        for my $lei (values %PublicInbox::DS::DescriptorMap) {
                $cb = $lei->can('store_path') // next;
                next if $cb->($lei) ne $self->{store_path};
                my $err = $lei->{2} // next;
-               print $err $rbuf;
+               print $err $$rbuf and $printed = 1;
+       }
+       if (!$printed) {
+               openlog('lei-store', 'pid,nowait,nofatal,ndelay', 'user');
+               for my $l (split(/\n/, $$rbuf)) { syslog('warning', '%s', $l) }
+               closelog(); # don't share across fork
        }
 }
 
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