qspawn: handle ENOENT (and other errors on exec)

As sqlite3(1) and other executables may become unavailable or
uninstalled while a daemon runs, we need to gracefully handle
errors in those cases.

1 files changed, 33 insertions, 25 deletions

diff --git a/lib/PublicInbox/Qspawn.pm b/lib/PublicInbox/Qspawn.pm
index 52aea3eb..34b6912f 100644
--- a/lib/PublicInbox/Qspawn.pm
+++ b/lib/PublicInbox/Qspawn.pm
@@ -45,7 +45,7 @@ sub new ($$$;) {
 sub _do_spawn {
         my ($self, $start_cb, $limiter) = @_;
         my $err;
-        my ($cmd, $cmd_env, $opt) = @{$self->{args}};
+        my ($cmd, $cmd_env, $opt) = @{delete $self->{args}};
         my %o = %{$opt || {}};
         $self->{limiter} = $limiter;
         foreach my $k (PublicInbox::Spawn::RLIMITS()) {
@@ -53,20 +53,17 @@ sub _do_spawn {
                         $o{$k} = $rlimit;
                 }
         }
+        $self->{cmd} = $o{quiet} ? undef : $cmd;
         eval {
                 # popen_rd may die on EMFILE, ENFILE
                 ($self->{rpipe}, $self->{pid}) = popen_rd($cmd, $cmd_env, \%o);
-                $self->{args} = $o{quiet} ? undef : $cmd;
 
                 die "E: $!" unless defined($self->{pid});
 
                 $limiter->{running}++;
                 $start_cb->($self); # EPOLL_CTL_ADD may ENOSPC/ENOMEM
         };
-        if ($@) {
-                $self->{err} = $@;
-                finish($self);
-        }
+        finish($self, $@) if $@;
 }
 
 sub child_err ($) {
@@ -83,16 +80,8 @@ sub log_err ($$) {
         $env->{'psgi.errors'}->print($msg, "\n");
 }
 
-# callback for dwaitpid
-sub waitpid_err ($$) {
-        my ($self, $pid) = @_;
-        my $xpid = delete $self->{pid};
-        my $err;
-        if ($pid > 0) { # success!
-                $err = child_err($?);
-        } elsif ($pid < 0) { # ??? does this happen in our case?
-                $err = "W: waitpid($xpid, 0) => $pid: $!";
-        } # else should not be called with pid == 0
+sub finalize ($$) {
+        my ($self, $err) = @_;
 
         my ($env, $qx_cb, $qx_arg, $qx_buf) =
                 delete @$self{qw(psgi_env qx_cb qx_arg qx_buf)};
@@ -108,16 +97,37 @@ sub waitpid_err ($$) {
         }
 
         if ($err) {
-                if ($self->{err}) {
+                if (defined $self->{err}) {
                         $self->{err} .= "; $err";
                 } else {
                         $self->{err} = $err;
                 }
-                if ($env && $self->{args}) {
-                        log_err($env, join(' ', @{$self->{args}}) . ": $err");
+                if ($env && $self->{cmd}) {
+                        log_err($env, join(' ', @{$self->{cmd}}) . ": $err");
                 }
         }
-        eval { $qx_cb->($qx_buf, $qx_arg) } if $qx_cb;
+        if ($qx_cb) {
+                eval { $qx_cb->($qx_buf, $qx_arg) };
+        } elsif (my $wcb = delete $env->{'qspawn.wcb'}) {
+                # have we started writing, yet?
+                require PublicInbox::WwwStatic;
+                $wcb->(PublicInbox::WwwStatic::r(500));
+        }
+}
+
+# callback for dwaitpid
+sub waitpid_err ($$) {
+        my ($self, $pid) = @_;
+        my $xpid = delete $self->{pid};
+        my $err;
+        if (defined $pid) {
+                if ($pid > 0) { # success!
+                        $err = child_err($?);
+                } elsif ($pid < 0) { # ??? does this happen in our case?
+                        $err = "W: waitpid($xpid, 0) => $pid: $!";
+                } # else should not be called with pid == 0
+        }
+        finalize($self, $err);
 }
 
 sub do_waitpid ($) {
@@ -133,14 +143,12 @@ sub do_waitpid ($) {
         }
 }
 
-sub finish ($) {
-        my ($self) = @_;
+sub finish ($;$) {
+        my ($self, $err) = @_;
         if (delete $self->{rpipe}) {
                 do_waitpid($self);
         } else {
-                my ($env, $qx_cb, $qx_arg, $qx_buf) =
-                        delete @$self{qw(psgi_env qx_cb qx_arg qx_buf)};
-                eval { $qx_cb->($qx_buf, $qx_arg) } if $qx_cb;
+                finalize($self, $err);
         }
 }