[PATCH 3/8] http: avoid needless time2str calls

[Eric Wong <e@80x24.org>]

Checking the time is nearly free on modern systems with
vDSO/vsyscall/similar while sprintf is always expensive.
---
 lib/PublicInbox/HTTP.pm | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/lib/PublicInbox/HTTP.pm b/lib/PublicInbox/HTTP.pm
index a472388..14971f4 100644
--- a/lib/PublicInbox/HTTP.pm
+++ b/lib/PublicInbox/HTTP.pm
@@ -17,7 +17,6 @@ use HTTP::Parser::XS qw(parse_http_request); # supports pure Perl fallback
 use HTTP::Status qw(status_message);
 use HTTP::Date qw(time2str);
 use IO::File;
-my $null_io = IO::File->new('/dev/null', '<');
 use constant {
 	CHUNK_START => -1,   # [a-f0-9]+\r\n
 	CHUNK_END => -2,     # \r\n
@@ -25,6 +24,14 @@ use constant {
 	CHUNK_MAX_HDR => 256,
 };
 
+my $null_io = IO::File->new('/dev/null', '<');
+my $http_date;
+my $prev = 0;
+sub http_date () {
+	my $now = time;
+	$now == $prev ? $http_date : ($http_date = time2str($prev = $now));
+}
+
 sub new ($$$) {
 	my ($class, $sock, $addr, $httpd) = @_;
 	my $self = fields::new($class);
@@ -148,7 +155,7 @@ sub response_header_write {
 			($conn =~ /\bkeep-alive\b/i);
 
 	$h .= 'Connection: ' . ($alive ? 'keep-alive' : 'close');
-	$h .= "\r\nDate: " . time2str(time) . "\r\n\r\n";
+	$h .= "\r\nDate: " . http_date() . "\r\n\r\n";
 
 	if (($len || $chunked) && $env->{REQUEST_METHOD} ne 'HEAD') {
 		more($self, $h);
-- 
EW