[PATCH 1/4] httpd: avoid crash on cgit -> coderepo 404 fallback

[Eric Wong <e@80x24.org>]

A trickled cgit response can cause HTTPD::Async->event_step to
fire an extra time after header parsing.  We need to account for
the lack of async_pass call populating ->{fh} and ->{http} in
that case and avoid calling $self->{fh}->write when there's
no {fh}.
---
 lib/PublicInbox/GitHTTPBackend.pm | 6 ++++--
 lib/PublicInbox/HTTPD/Async.pm    | 3 ++-
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/lib/PublicInbox/GitHTTPBackend.pm b/lib/PublicInbox/GitHTTPBackend.pm
index 1eb51f27..974a1831 100644
--- a/lib/PublicInbox/GitHTTPBackend.pm
+++ b/lib/PublicInbox/GitHTTPBackend.pm
@@ -128,7 +128,7 @@ sub input_prepare {
 	{ 0 => $in };
 }
 
-sub parse_cgi_headers {
+sub parse_cgi_headers { # {parse_hdr} for Qspawn
 	my ($r, $bref, $ctx) = @_;
 	return r(500) unless defined $r && $r >= 0;
 	$$bref =~ s/\A(.*?)\r?\n\r?\n//s or return $r == 0 ? r(500) : undef;
@@ -145,7 +145,9 @@ sub parse_cgi_headers {
 	}
 
 	# fallback to WwwCoderepo if cgit 404s.  Duplicating $ctx prevents
-	# ->finalize from the current Qspawn from using qspawn.wcb
+	# ->finalize from the current Qspawn from using qspawn.wcb.
+	# This makes qspawn skip ->async_pass and causes
+	# PublicInbox::HTTPD::Async::event_step to close shortly after
 	if ($code == 404 && $ctx->{www} && !$ctx->{_coderepo_tried}++) {
 		my %ctx = %$ctx;
 		$ctx{env} = +{ %{$ctx->{env}} };
diff --git a/lib/PublicInbox/HTTPD/Async.pm b/lib/PublicInbox/HTTPD/Async.pm
index cb76cfab..9e592f47 100644
--- a/lib/PublicInbox/HTTPD/Async.pm
+++ b/lib/PublicInbox/HTTPD/Async.pm
@@ -48,7 +48,8 @@ sub event_step {
 		# this may call async_pass when headers are done
 		$cb->(my $refcnt_guard = delete $self->{arg});
 	} elsif (my $sock = $self->{sock}) {
-		my $http = $self->{http};
+		# $http may be undef if discarding body output from cgit on 404
+		my $http = $self->{http} or return $self->close;
 		# $self->{sock} is a read pipe for git-http-backend or cgit
 		# and 65536 is the default Linux pipe size
 		my $r = sysread($sock, my $buf, 65536);