caching: don't respect vary when cache-extending either

By default we don't respect Vary headers we find on resources.  People who do want us to respect them can set 'RespectVary on' in their configuration.  The cache-extender was not considering the value of the RespectVary option in deciding whether things were cachable, and was instead assuming RespectVary=true.

Fixes #1373

net/instaweb/rewriter/cache_extender.cc

@@ -303,16 +303,22 @@ RewriteResult CacheExtender::RewriteLoadedResource(
   // See if the resource is cacheable; and if so whether there is any need
   // to cache extend it.
   bool ok = false;
+  // Assume that it may have cookies; see comment in
+  // CacheableResourceBase::IsValidAndCacheableImpl.
+  RequestHeaders::Properties req_properties;
   const ContentType* output_type = NULL;
   if (!server_context()->http_cache()->force_caching() &&
-      !headers->IsProxyCacheable()) {
+      !headers->IsProxyCacheable(
+          req_properties,
+          ResponseHeaders::GetVaryOption(driver()->options()->respect_vary()),
+          ResponseHeaders::kNoValidator)) {
     // Note: RewriteContextTest.PreserveNoCacheWithFailedRewrites
     // relies on CacheExtender failing rewrites in this case.
     // If you change this behavior that test MUST be updated as it covers
     // security.
     not_cacheable_count_->Add(1);
   } else if (ShouldRewriteResource(
-                 headers, now_ms, input_resource,url, result)) {
+      headers, now_ms, input_resource, url, result)) {
     // We must be careful what Content-Types we allow to be cache extended.
     // Specifically, we do not want to cache extend any Content-Types that
     // could execute scripts when loaded in a browser because that could

net/instaweb/rewriter/cache_extender_test.cc

@@ -1140,6 +1140,22 @@ TEST_F(CacheExtenderTest, SrcSet) {
                           a_url, " 1x, ", b_url, " 2x\">"));
 }
 
+TEST_F(CacheExtenderTest, VaryOrigin) {
+  options()->EnableExtendCacheFilters();
+  rewrite_driver()->AddFilters();
+
+  GoogleString url = AbsolutifyUrl("a.css");
+  ResponseHeaders response_headers;
+  DefaultResponseHeaders(kContentTypeCss, 100 /* ttl */, &response_headers);
+  response_headers.Add("Vary", "Origin");
+  SetFetchResponse(url, response_headers, "css file");
+
+  GoogleString cache_extended_css = Encode("", kFilterId, "0", "a.css", "css");
+  ValidateExpected("vary origin",
+                   StringPrintf(kCssFormat, "a.css"),
+                   StringPrintf(kCssFormat, cache_extended_css.c_str()));
+}
+
 }  // namespace
 
 }  // namespace net_instaweb