Prerender: Disable prefetch if there's an appcache.

third_party/WebKit/Source/core/html/parser/HTMLPreloadScanner.cpp

Index: third_party/WebKit/Source/core/html/parser/HTMLPreloadScanner.cpp
diff --git a/third_party/WebKit/Source/core/html/parser/HTMLPreloadScanner.cpp b/third_party/WebKit/Source/core/html/parser/HTMLPreloadScanner.cpp
index e224331a875c29409d023e158995ded88b9199b2..0f24e9f5b01ae68be5e0b958d63b2464ce9c14a4 100644
--- a/third_party/WebKit/Source/core/html/parser/HTMLPreloadScanner.cpp
+++ b/third_party/WebKit/Source/core/html/parser/HTMLPreloadScanner.cpp
@@ -537,6 +537,7 @@ TokenPreloadScanner::TokenPreloadScanner(
       m_inStyle(false),
       m_inPicture(false),
       m_inScript(false),
+      m_isAppCacheEnabled(false),
       m_templateCount(0),
       m_documentParameters(std::move(documentParameters)),
       m_mediaValues(MediaValuesCached::create(mediaValuesCachedData)),
@@ -552,7 +553,8 @@ TokenPreloadScanner::~TokenPreloadScanner() {}
 TokenPreloadScannerCheckpoint TokenPreloadScanner::createCheckpoint() {
   TokenPreloadScannerCheckpoint checkpoint = m_checkpoints.size();
   m_checkpoints.push_back(Checkpoint(m_predictedBaseElementURL, m_inStyle,
-                                     m_inScript, m_templateCount));
+                                     m_inScript, m_isAppCacheEnabled,
+                                     m_templateCount));
   return checkpoint;
 }
 
@@ -563,6 +565,7 @@ void TokenPreloadScanner::rewindTo(
   const Checkpoint& checkpoint = m_checkpoints[checkpointIndex];
   m_predictedBaseElementURL = checkpoint.predictedBaseElementURL;
   m_inStyle = checkpoint.inStyle;
+  m_isAppCacheEnabled = checkpoint.isAppCacheEnabled;
   m_templateCount = checkpoint.templateCount;
 
   m_didRewind = true;
@@ -715,6 +718,13 @@ void TokenPreloadScanner::scanCommon(const Token& token,
   if (!m_documentParameters->doHtmlPreloadScanning)
     return;
 
+  // If the document is prefetching, AppCache support has not yet been enabled,
+  // and fetches will go to the network even if there is an AppCache
+  // manifest. Therefore if a manifest is seen prefetching is stopped to avoid
+  // incorrect behavior.
+  if (m_documentParameters->isPrefetchOnly && m_isAppCacheEnabled)

[michaeln, 2017/03/27 23:27:44]

Could this be done more directly and with less code in the renderer?

Prior to HTMLPreloadScannerConstruction in the renderer, does the Document have
it's mainResourceResponse? If so, would it make sense to replace the test in the
firstg snapshot for appCached'ness with a different test based on the value of
ResourceResponse.appCacheID(). The CachedDocumentParameters struct could be
modified tell is if the doc was loaded from an appcache.


CachedDocumentParameters::CachedDocumentParameters(Document* document) {
  DCHECK(isMainThread());
  DCHECK(document);
  ...
  isLoadedFromAppCache = document->loader()->response().appCacheID() != 0;
  ...
}

Here we could test...

  if (m_documentParameters->isPrefetchOnly &&
      m_documentParameters->isLoadedFromAppCache) {
    return;
  }

+    return;
+
   switch (token.type()) {
     case HTMLToken::Character: {
       if (m_inStyle) {
@@ -776,6 +786,10 @@ void TokenPreloadScanner::scanCommon(const Token& token,
         updatePredictedBaseURL(token);
         return;
       }
+      if (match(tagImpl, htmlTag) && token.getAttributeItem(manifestAttr)) {
+        m_isAppCacheEnabled = true;
+        return;
+      }
       if (match(tagImpl, metaTag)) {
         const typename Token::Attribute* equivAttribute =
             token.getAttributeItem(http_equivAttr);
@@ -896,6 +910,7 @@ CachedDocumentParameters::CachedDocumentParameters(Document* document) {
   viewportMetaEnabled =
       document->settings() && document->settings()->getViewportMetaEnabled();
   referrerPolicy = document->getReferrerPolicy();
+  isPrefetchOnly = document->isPrefetchOnly();
 }
 
 }  // namespace blink