Dev tools warning and console warning for document.write script blocking

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

 /*
  * Copyright (C) 2013 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 60 matching lines @@
 #include "platform/weborigin/SecurityPolicy.h"
 #include "public/platform/WebCachePolicy.h"
 #include "public/platform/WebFrameScheduler.h"
 
 #include <algorithm>
 
 namespace blink {
 
 namespace {
 
+void emitWarningForDocWriteScripts(const String& url, const Document& document)
+{
+    String message = "A Parser-blocking, cross-origin script " + url + " is invoked via document.write. This may get blocked by the browser in slow connections. It is recommended to invoke this script asynchronously.";

[jkarlin, 2016/06/10 18:38:36]

There should also be a link to a help page explaining (a little bit) how to make
code asynchronous. That can likely wait until after field trials however. Please
create a new bug to add the link so that we don't forget.

[jkarlin, 2016/06/10 18:38:36]

Commas needed around the url.

s/may get blocked/may be blocked/

s/in slow connections/if the device has poor network connectivity/

"recommended to invoke" doesn't make sense.

[shivanisha, 2016/06/20 14:28:06]

Created https://bugs.chromium.org/p/chromium/issues/detail?id=621520

Updated the warning string. Removed the "recommended to invoke" part as that
would be replaced by the help link.

+    const_cast <Document &>(document).addConsoleMessage(ConsoleMessage::create(JSMessageSource, WarningMessageLevel, message));

[Nate Chapin, 2016/06/10 23:34:32]

Nit: Pass the Document non-const instead of const_cast'ing.

[shivanisha, 2016/06/20 14:28:06]

done.

+    WTFLogAlways("%s", message.utf8().data());
+}
+
 bool shouldDisallowFetchForMainFrameScript(const ResourceRequest& request, FetchRequest::DeferOption defer, const Document& document)
 {
     // Only scripts inserted via document.write are candidates for having their
     // fetch disallowed.
     if (!document.isInDocumentWrite())
         return false;
 
     if (!document.settings())
         return false;
 
@@ skipping 15 matching lines @@
 
     // Do not block scripts if it is a page reload. This is to enable pages to
     // recover if blocking of a script is leading to a page break and the user
     // reloads the page.
     const FrameLoadType loadType = document.frame()->loader().loadType();
     const bool isReload = loadType == FrameLoadTypeReload || loadType == FrameLoadTypeReloadBypassingCache || loadType == FrameLoadTypeReloadMainResource;
     if (isReload) {
         // Recording this metric since an increase in number of reloads for pages
         // where a script was blocked could be indicative of a page break.
         document.loader()->didObserveLoadingBehavior(WebLoadingBehaviorFlag::WebLoadingBehaviorDocumentWriteBlockReload);
+        emitWarningForDocWriteScripts(request.url().getString(), document);
         return false;
     }
 
     // Add the metadata that this page has scripts inserted via document.write
     // that are eligible for blocking. Note that if there are multiple scripts
     // the flag will be conveyed to the browser process only once.
     document.loader()->didObserveLoadingBehavior(WebLoadingBehaviorFlag::WebLoadingBehaviorDocumentWriteBlock);
 
+    emitWarningForDocWriteScripts(request.url().getString(), document);
+
     const bool isSlowConnection = networkStateNotifier().connectionType() == WebConnectionTypeCellular2G;
     const bool disallowFetch = document.settings()->disallowFetchForDocWrittenScriptsInMainFrame() || (document.settings()->disallowFetchForDocWrittenScriptsInMainFrameOnSlowConnections() && isSlowConnection);
 
     return disallowFetch;
 }
 
 } // namespace
 
 FrameFetchContext::FrameFetchContext(DocumentLoader* loader, Document* document)
     : m_document(document)
@@ skipping 623 matching lines @@
 }
 
 DEFINE_TRACE(FrameFetchContext)
 {
     visitor->trace(m_document);
     visitor->trace(m_documentLoader);
     FetchContext::trace(visitor);
 }
 
 } // namespace blink