[PATCH 88/95] lei_mirror: use curl -z/--timecond if manifest exists

[Eric Wong]

This lets us save cycles and avoid scanning + comparing manifest
contents by relying on the Last-Modified HTTP response header.
---
 lib/PublicInbox/LeiMirror.pm | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/lib/PublicInbox/LeiMirror.pm b/lib/PublicInbox/LeiMirror.pm
index b30cc519..cc5ea1d2 100644
--- a/lib/PublicInbox/LeiMirror.pm
+++ b/lib/PublicInbox/LeiMirror.pm
@@ -995,6 +995,7 @@ sub try_manifest {
        }
        my $ft = File::Temp->new(TEMPLATE => '.manifest-XXXX', %opt);
        my $cmd = $curl->for_uri($lei, $uri, qw(-f -R -o), $ft->filename);
+       push(@$cmd, '-z', $manifest) if -f $manifest;
        my $mf_url = "$uri";
        %opt = map { $_ => $lei->{$_} } (0..2);
        my $cerr = run_reap($lei, $cmd, \%opt);
@@ -1002,6 +1003,10 @@ sub try_manifest {
                return try_scrape($self) if ($cerr >> 8) == 22; # 404 missing
                return $lei->child_error($cerr, "@$cmd failed");
        }
+
+       # bail out if curl -z/--timecond hit 304 Not Modified, $ft will be empty
+       return $lei->qerr("# $manifest unchanged") if -f $manifest && !-s $ft;
+
        my $m = eval { decode_manifest($ft, $ft, $uri) };
        if ($@) {
                warn $@;