feed: speed up blob checks if Git.pm is usable

Git::cat_blob is a handy interface to read multiple emails
without incurring fork + exec overhead.  Git.pm is GPLv2+,
not GPLv2-only, so we may link to it.

1 files changed, 30 insertions, 11 deletions

diff --git a/lib/PublicInbox/Feed.pm b/lib/PublicInbox/Feed.pm
index 75290c9e..9733190c 100644
--- a/lib/PublicInbox/Feed.pm
+++ b/lib/PublicInbox/Feed.pm
@@ -12,6 +12,7 @@ use Encode::MIME::Header;
 use CGI qw(escapeHTML);
 use POSIX qw(strftime);
 use Date::Parse qw(strptime str2time);
+eval { require Git }; # this is GPLv2+, so we are OK to use it
 use constant {
         DATEFMT => '%Y-%m-%dT%H:%M:%SZ',
         MAX_PER_PAGE => 25,
@@ -45,9 +46,10 @@ sub generate {
                 updated => strftime(DATEFMT, gmtime),
         );
 
+        my $git = try_git_pm($args->{git_dir});
         each_recent_blob($args, sub {
                 my ($add) = @_;
-                add_to_feed($feed_opts, $feed, $add, $top);
+                add_to_feed($feed_opts, $feed, $add, $top, $git);
         });
         $feed->as_string;
 }
@@ -60,10 +62,10 @@ sub generate_html_index {
         my $feed_opts = get_feedopts($args);
         my $title = xs_html($feed_opts->{description} || "");
         my @messages;
+        my $git = try_git_pm($args->{git_dir});
         my ($first, $last) = each_recent_blob($args, sub {
-                my $str = `git cat-file blob $_[0]`;
-                return 0 if $? != 0;
-                my $simple = Email::Simple->new($str);
+                my $simple = do_cat_mail($git, 'Email::Simple', $_[0])
+                        or return 0;
                 if ($top && ($simple->header("In-Reply-To") ||
                              $simple->header("References"))) {
                         return 0;
@@ -240,14 +242,9 @@ sub feed_date {
 
 # returns 0 (skipped) or 1 (added)
 sub add_to_feed {
-        my ($feed_opts, $feed, $add, $top) = @_;
-
-        # we can use git cat-file --batch if performance becomes a
-        # problem, but I doubt it...
-        my $str = `git cat-file blob $add`;
-        return 0 if $? != 0;
-        my $mime = Email::MIME->new($str);
+        my ($feed_opts, $feed, $add, $top, $git) = @_;
 
+        my $mime = do_cat_mail($git, 'Email::MIME', $add) or return 0;
         if ($top && $mime->header("In-Reply-To")) {
                 return 0;
         }
@@ -316,4 +313,26 @@ sub xs_html {
                         Encode::HTMLCREF);
 }
 
+sub try_git_pm {
+        my ($dir) = @_;
+        eval { Git->repository(Directory => $dir) };
+};
+
+sub do_cat_mail {
+        my ($git, $class, $sha1) = @_;
+        my $str;
+        if ($git) {
+                open my $fh, '>', \$str or
+                                die "failed to setup string handle: $!\n";
+                binmode $fh;
+                my $bytes = $git->cat_blob($sha1, $fh);
+                return if $bytes <= 0;
+                close $fh or die "failed to close string handle: $!\n";
+        } else {
+                $str = `git cat-file blob $sha1`;
+                return if $? != 0 || length($str) == 0;
+        }
+        $class->new($str);
+}
+
 1;