ResourceFetcher::requestPreload should set its requestContext

Source/core/fetch/ResourceFetcher.cpp

 /*
     Copyright (C) 1998 Lars Knoll (knoll@mpi-hd.mpg.de)
     Copyright (C) 2001 Dirk Mueller (mueller@kde.org)
     Copyright (C) 2002 Waldo Bastian (bastian@kde.org)
     Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
     Copyright (C) 2009 Torch Mobile Inc. http://www.torchmobile.com/
 
     This library is free software; you can redistribute it and/or
     modify it under the terms of the GNU Library General Public
     License as published by the Free Software Foundation; either
@@ skipping 1235 matching lines @@
     if (type == Resource::Script || type == Resource::CSSStyleSheet)
         encoding = charset.isEmpty() ? m_document->charset().string() : charset;
 
     request.setCharset(encoding);
     request.setForPreload(true);
 
     ResourcePtr<Resource> resource;
     // Loading images involves several special cases, so use dedicated fetch method instead.
     if (type == Resource::Image)
         resource = fetchImage(request);
+
+    request.mutableResourceRequest().setRequestContext(WebURLRequest::RequestContextPrefetch);

[tyoshino (SeeGerritForStatus), 2014/11/11 07:57:26]

This looked the "context" defined in the Fetch Standard or something corresponds
to it.
https://fetch.spec.whatwg.org/#concept-request-context-frame-type
The comment on the enum definition says so. But after some study, it's similar
but it's not (yet).

Introduced to WebKit on this revision. Was Chromium specific before that.
https://chromium.googlesource.com/chromium/blink/+/ea0fe8306fdc519755ec85027d...

mkwst@ has renamed it to "context" as they're similar concepts.
https://chromium.googlesource.com/chromium/blink/+/6741e56bdbab3c9acebfe3caa0...

If we're making them closer in the future, we should investigate if it's
appropriate use of RequestContextPrefetch.

The "prefetch" context defined in the Fetch Standard is used for a link element
when its rel attribute is set to "prefetch". Blink does use it for this purpose,
but there're some other code using this in Chromium.

Hmm, I'd recommend that you call determineRequestContext() as
ResourceFetcher::createResourceForLoading() does unless you're sure you need to
use RequestContextPreftch context here.

[Mike West, 2014/11/11 08:08:04]

I don't understand this comment? The `prefetch` context is part of Fetch, which
is why it's part of the RequestContext enum.
(Because that's what Fetch calls it :) ).
The `<link prefetch>` comment in Fetch is an example, not an exhaustive list of
the points in the platform where the `prefetch` context is appropriate.
The practical question is whether requests that go through this path should be
checked for Mixed Content violations or not. So far, we've allowed prefetch
requests. If we change our minds on that (to match the spec), then we'll need to
know that this is a prefetch request.

[tyoshino (SeeGerritForStatus), 2014/11/11 08:20:36]

I wrote "not yet" since you've renamed it in
https://chromium.googlesource.com/chromium/blink/+/6741e56bdbab3c9acebfe3caa0...
and said "it's the first step towards a higher fidelity implementation of
Fetch's semantics".

I compared the current definition of the enum and the list of contexts defined
in the Fetch spec again. Yeah, they're same now. Sorry, my bad.
Oh, ok.

[tyoshino (SeeGerritForStatus), 2014/11/11 08:24:41]

OK.

Regarding mixed content, just issuing a request over the network bypassing mixed
content check is bad. Right? Then, we should have it set to appropriate context
even for preload.

Regarding CSP, it's ok to issue a request over the network bypassing CSP is ok
(though waste of bandwidth) but it's not fine to deliver the result bypassing
CSP. Right?

[tyoshino (SeeGerritForStatus), 2014/11/11 08:30:44]

By "deliver", I mean having it evaluated, displayed, etc.

     if (!resource)
         resource = requestResource(type, request);
     if (!resource || (m_preloads && m_preloads->contains(resource.get())))
         return;
     TRACE_EVENT_ASYNC_STEP_INTO0("net", "Resource", resource.get(), "Preload");
     resource->increasePreloadCount();
 
     if (!m_preloads)
         m_preloads = adoptPtr(new ListHashSet<Resource*>);
     m_preloads->add(resource.get());
@@ skipping 297 matching lines @@
 
 void ResourceFetcher::trace(Visitor* visitor)
 {
     visitor->trace(m_document);
     visitor->trace(m_loaders);
     visitor->trace(m_multipartLoaders);
     ResourceLoaderHost::trace(visitor);
 }
 
 }