www: gzip_filter: avoid errors after ->write failure

->zflush must return a string to its caller, not undef.
Additionally, {http_out} may be deleted on ->write if ->close
recurses.

This should fix the following errors:
  Use of uninitialized value $_[1] in string eq at PublicInbox/HTTP.pm line 211.
  E: Can't call method "close" on an undefined value at GzipFilter.pm line 167.

Fixes: a6d50dc1098c01a1 (www: gzip_filter: gracefully handle socket ->write failures, 2022-08-03)

1 files changed, 2 insertions, 2 deletions

diff --git a/lib/PublicInbox/GzipFilter.pm b/lib/PublicInbox/GzipFilter.pm
index d41748c4..bdd313f5 100644
--- a/lib/PublicInbox/GzipFilter.pm
+++ b/lib/PublicInbox/GzipFilter.pm
@@ -154,7 +154,7 @@ sub zflush ($;$) {
                 $err = $gz->deflate($_[1], $zbuf);
                 die "gzip->deflate: $err" if $err != Z_OK;
         }
-        $gz // return; # not a bug, recursing on DS->write failure
+        $gz // return ''; # not a bug, recursing on DS->write failure
         $err = $gz->flush($zbuf);
         die "gzip->flush: $err" if $err != Z_OK;
         $zbuf;
@@ -164,7 +164,7 @@ sub close {
         my ($self) = @_;
         my $http_out = http_out($self) // return;
         $http_out->write(zflush($self));
-        delete($self->{http_out})->close;
+        (delete($self->{http_out}) // return)->close;
 }
 
 sub bail  {