Dont preload from link headers if the response came from MemoryCache

third_party/WebKit/Source/core/loader/LinkLoader.cpp

 /*
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 295 matching lines @@
 {
     if (!document || headerValue.isEmpty())
         return;
     LinkHeaderSet headerSet(headerValue);
     for (auto& header : headerSet) {
         if (!header.valid() || header.url().isEmpty() || header.rel().isEmpty())
             continue;
 
         LinkRelAttribute relAttribute(header.rel());
         KURL url(baseURL, header.url());
+        // Sanity check to avoid re-entrancy here.
+        if (url == baseURL)
+            continue;

[Yoav Weiss, 2016/07/19 21:14:22]

Is this specific to MemoryCache? Seems like if I'm serving a response with a
link preload for the same URL, this would protect me from that as well
(regardless of MemoryCache)

[Charlie Harrison, 2016/07/19 21:23:52]

Ah no this isn't specific to memory cache. I added this as a sanity check to
make sure that this kind of problem doesn't come back in a slightly different
form. Happy to remove it but I feel like we might as well abort early and avoid
looking up the resource in memory cache, etc.

[Yoav Weiss, 2016/07/19 21:29:48]

I don't think you should remove it. I'm probably missing something, but I guess
my main trouble with this CL is to figure out which parts of the code do what
the title says it does. (so "Dont preload from link headers if the response came
from MemoryCache")

Is there code in the CL that's doing something MemoryCache specific? If not,
maybe a title change is appropriate

         if (canLoadResources != OnlyLoadResources) {
             if (RuntimeEnabledFeatures::linkHeaderEnabled())
                 dnsPrefetchIfNeeded(relAttribute, url, *document, networkHintsInterface, LinkCalledFromHeader);
 
             if (RuntimeEnabledFeatures::linkPreconnectEnabled())
                 preconnectIfNeeded(relAttribute, url, *document, crossOriginAttributeValue(header.crossOrigin()), networkHintsInterface, LinkCalledFromHeader);
         }
         if (canLoadResources != DoNotLoadResources) {
             bool errorOccurred = false;
             if (RuntimeEnabledFeatures::linkPreloadEnabled()) {
@@ skipping 67 matching lines @@
 DEFINE_TRACE(LinkLoader)
 {
     visitor->trace(m_client);
     visitor->trace(m_prerender);
     visitor->trace(m_linkPreloadResourceClient);
     ResourceOwner<Resource, ResourceClient>::trace(visitor);
     PrerenderClient::trace(visitor);
 }
 
 } // namespace blink