gitweb: check if-modified-since for feeds

Offering Last-modified header for feeds is only half the work, even if
we bail out early on HEAD requests. We should also check that same date
against If-modified-since, and bail out early with 304 Not Modified if
that's the case.

Signed-off-by: Giuseppe Bilotta <giuseppe.bilotta@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/gitweb/gitweb.perl b/gitweb/gitweb.perl
index 8c49c75f10648aff7b2573bd0a8b0fae4deae545..f4defb01d9bd4c27b486838fdb5189064fc601c3 100755 (executable)
--- a/gitweb/gitweb.perl
+++ b/gitweb/gitweb.perl
@@ -6015,7 +6015,25 @@ sub git_feed {
        }
        if (defined($commitlist[0])) {
                %latest_commit = %{$commitlist[0]};
-               %latest_date   = parse_date($latest_commit{'committer_epoch'});
+               my $latest_epoch = $latest_commit{'committer_epoch'};
+               %latest_date   = parse_date($latest_epoch);
+               my $if_modified = $cgi->http('IF_MODIFIED_SINCE');
+               if (defined $if_modified) {
+                       my $since;
+                       if (eval { require HTTP::Date; 1; }) {
+                               $since = HTTP::Date::str2time($if_modified);
+                       } elsif (eval { require Time::ParseDate; 1; }) {
+                               $since = Time::ParseDate::parsedate($if_modified, GMT => 1);
+                       }
+                       if (defined $since && $latest_epoch <= $since) {
+                               print $cgi->header(
+                                       -type => $content_type,
+                                       -charset => 'utf-8',
+                                       -last_modified => $latest_date{'rfc2822'},
+                                       -status => '304 Not Modified');
+                               return;
+                       }
+               }
                print $cgi->header(
                        -type => $content_type,
                        -charset => 'utf-8',