gitweb: refactor If-Modified-Since handling

The current gitweb only generates Last-Modified and handles
If-Modified-Since headers for the git_feed action.  This patch breaks
the Last-Modified and If-Modified-Since handling code out from
git_feed into a new function exit_if_unmodified_since.  This makes the
code easy to reuse for other actions.

Only gitweb actions which can easily calculate a modification time
should use exit_if_unmodified_since, as the goal is to balance local
processing time vs. upload bandwidth.

Signed-off-by: W Trevor King <wking@drexel.edu>
Acked-by: Jakub Narebski <jnareb@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

gitweb/gitweb.perl

@@ -7003,6 +7003,28 @@ sub snapshot_name {
 	return wantarray ? ($name, $name) : $name;
 }
 
+sub exit_if_unmodified_since {
+	my ($latest_epoch) = @_;
+	our $cgi;
+
+	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 <= $since) {
+			my %latest_date = parse_date($latest_epoch);
+			print $cgi->header(
+				-last_modified => $latest_date{'rfc2822'},
+				-status => '304 Not Modified');
+			goto DONE_GITWEB;
+		}
+	}
+}
+
 sub git_snapshot {
 	my $format = $input_params{'snapshot_format'};
 	if (!@snapshot_fmts) {
@@ -7820,35 +7842,14 @@ sub git_feed {
 	if (defined($commitlist[0])) {
 		%latest_commit = %{$commitlist[0]};
 		my $latest_epoch = $latest_commit{'committer_epoch'};
-		%latest_date   = parse_date($latest_epoch, $latest_commit{'comitter_tz'});
-		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',
-			-last_modified => $latest_date{'rfc2822'},
-			-status => '200 OK');
-	} else {
-		print $cgi->header(
-			-type => $content_type,
-			-charset => 'utf-8',
-			-status => '200 OK');
+		exit_if_unmodified_since($latest_epoch);
+		%latest_date = parse_date($latest_epoch, $latest_commit{'comitter_tz'});
 	}
+	print $cgi->header(
+		-type => $content_type,
+		-charset => 'utf-8',
+		%latest_date ? (-last_modified => $latest_date{'rfc2822'}) : (),
+		-status => '200 OK');
 
 	# Optimization: skip generating the body if client asks only
 	# for Last-Modified date.

t/t9501-gitweb-standalone-http-status.sh

@@ -92,7 +92,7 @@ test_debug 'cat gitweb.output'
 test_expect_success 'snapshots: bad tree-ish id (tagged object)' '
 	echo object > tag-object &&
 	git add tag-object &&
-	git commit -m "Object to be tagged" &&
+	test_tick && git commit -m "Object to be tagged" &&
 	git tag tagged-object `git hash-object tag-object` &&
 	gitweb_run "p=.git;a=snapshot;h=tagged-object;sf=tgz" &&
 	grep "400 - Object is not a tree-ish" gitweb.output
@@ -112,6 +112,31 @@ test_expect_success 'snapshots: bad object id' '
 '
 test_debug 'cat gitweb.output'
 
+# ----------------------------------------------------------------------
+# modification times (Last-Modified and If-Modified-Since)
+
+test_expect_success 'modification: feed last-modified' '
+	gitweb_run "p=.git;a=atom;h=master" &&
+	grep "Status: 200 OK" gitweb.headers &&
+	grep "Last-modified: Thu, 7 Apr 2005 22:14:13 +0000" gitweb.headers
+'
+test_debug 'cat gitweb.headers'
+
+test_expect_success 'modification: feed if-modified-since (modified)' '
+	export HTTP_IF_MODIFIED_SINCE="Wed, 6 Apr 2005 22:14:13 +0000" &&
+	test_when_finished "unset HTTP_IF_MODIFIED_SINCE" &&
+	gitweb_run "p=.git;a=atom;h=master" &&
+	grep "Status: 200 OK" gitweb.headers
+'
+test_debug 'cat gitweb.headers'
+
+test_expect_success 'modification: feed if-modified-since (unmodified)' '
+	export HTTP_IF_MODIFIED_SINCE="Thu, 7 Apr 2005 22:14:13 +0000" &&
+	test_when_finished "unset HTTP_IF_MODIFIED_SINCE" &&
+	gitweb_run "p=.git;a=atom;h=master" &&
+	grep "Status: 304 Not Modified" gitweb.headers
+'
+test_debug 'cat gitweb.headers'
 
 # ----------------------------------------------------------------------
 # load checking