www: cgit: fall back to WwwCoderepo on 404s

We can't rely on 3-element array response when calling
WwwCoderepo for ViewVCS endpoints since that uses Qspawn
internally.  Thus, we have to allow two Qspawn objects to run in
parallel and ensure `qspawn.wcb' only gets called once, so we
end up duplicating the entire $ctx to ensure this.

1 files changed, 16 insertions, 3 deletions

diff --git a/lib/PublicInbox/GitHTTPBackend.pm b/lib/PublicInbox/GitHTTPBackend.pm
index ba3a8f20..61a13560 100644
--- a/lib/PublicInbox/GitHTTPBackend.pm
+++ b/lib/PublicInbox/GitHTTPBackend.pm
@@ -1,4 +1,4 @@
-# Copyright (C) 2016-2021 all contributors <meta@public-inbox.org>
+# Copyright (C) all contributors <meta@public-inbox.org>
 # License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
 
 # when no endpoints match, fallback to this and serve a static file
@@ -132,7 +132,7 @@ sub input_prepare {
 }
 
 sub parse_cgi_headers {
-        my ($r, $bref) = @_;
+        my ($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;
         my $h = $1;
@@ -146,7 +146,20 @@ sub parse_cgi_headers {
                         push @h, $k, $v;
                 }
         }
-        [ $code, \@h ]
+
+        # fallback to WwwCoderepo if cgit 404s.  Duplicating $ctx prevents
+        # ->finalize from the current Qspawn from using qspawn.wcb
+        if ($code == 404 && $ctx->{www} && !$ctx->{_coderepo_tried}++) {
+                my %ctx = %$ctx;
+                $ctx{env} = +{ %{$ctx->{env}} };
+                delete $ctx->{env}->{'qspawn.wcb'};
+                $ctx->{env}->{'plack.skip-deflater'} = 1; # prevent 2x gzip
+                my $res = $ctx->{www}->coderepo->srv(\%ctx);
+                $res->(delete $ctx{env}->{'qspawn.wcb'}) if ref($res) eq 'CODE';
+                $res; # non ARRAY ref for ->psgi_return_init_cb
+        } else {
+                [ $code, \@h ]
+        }
 }
 
 1;