gitweb: add If-Modified-Since handling to git_snapshot().

Because snapshots can be large, you can save some bandwidth by
supporting caching via If-Modified-Since.  This patch adds support for
the i-m-s request to git_snapshot() if the request is a commit.
Requests for snapshots of trees, which lack well defined timestamps,
are still handled as they were before.
Signed-off-by: NW Trevor King <wking@drexel.edu>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

gitweb/gitweb.perl

@@ -7051,6 +7051,10 @@ sub git_snapshot {
 
 	my ($name, $prefix) = snapshot_name($project, $hash);
 	my $filename = "$name$known_snapshot_formats{$format}{'suffix'}";
+
+	my %co = parse_commit($hash);
+	exit_if_unmodified_since($co{'committer_epoch'}) if %co;
+
 	my $cmd = quote_command(
 		git_cmd(), 'archive',
 		"--format=$known_snapshot_formats{$format}{'format'}",
@@ -7060,9 +7064,15 @@ sub git_snapshot {
 	}
 
 	$filename =~ s/(["\\])/\\$1/g;
+	my %latest_date;
+	if (%co) {
+		%latest_date = parse_date($co{'committer_epoch'}, $co{'committer_tz'});
+	}
+
 	print $cgi->header(
 		-type => $known_snapshot_formats{$format}{'type'},
 		-content_disposition => 'inline; filename="' . $filename . '"',
+		%co ? (-last_modified => $latest_date{'rfc2822'}) : (),
 		-status => '200 OK');
 
 	open my $fd, "-|", $cmd

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

@@ -138,6 +138,39 @@ test_expect_success 'modification: feed if-modified-since (unmodified)' '
 '
 test_debug 'cat gitweb.headers'
 
+test_expect_success 'modification: snapshot last-modified' '
+	gitweb_run "p=.git;a=snapshot;h=master;sf=tgz" &&
+	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: snapshot 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=snapshot;h=master;sf=tgz" &&
+	grep "Status: 200 OK" gitweb.headers
+'
+test_debug 'cat gitweb.headers'
+
+test_expect_success 'modification: snapshot 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=snapshot;h=master;sf=tgz" &&
+	grep "Status: 304 Not Modified" gitweb.headers
+'
+test_debug 'cat gitweb.headers'
+
+test_expect_success 'modification: tree snapshot' '
+	ID=`git rev-parse --verify HEAD^{tree}` &&
+	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=snapshot;h=$ID;sf=tgz" &&
+	grep "Status: 200 OK" gitweb.headers &&
+	! grep -i "last-modified" gitweb.headers
+'
+test_debug 'cat gitweb.headers'
+
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