Enable srcset support in HTMLImageElement

Source/core/html/parser/HTMLPreloadScanner.cpp

 /*
  * Copyright (C) 2008 Apple Inc. All Rights Reserved.
  * Copyright (C) 2009 Torch Mobile, Inc. http://www.torchmobile.com/
  * Copyright (C) 2010 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
@@ skipping 11 matching lines @@
  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #include "config.h"
 #include "core/html/parser/HTMLPreloadScanner.h"
 
 #include "HTMLNames.h"
+#include "RuntimeEnabledFeatures.h"
 #include "core/html/InputTypeNames.h"
 #include "core/html/LinkRelAttribute.h"
 #include "core/html/parser/HTMLParserIdioms.h"
 #include "core/html/parser/HTMLTokenizer.h"
 #include "core/platform/chromium/TraceEvent.h"
 #include "wtf/MainThread.h"
 
 namespace WebCore {
 
 using namespace HTMLNames;
@@ skipping 41 matching lines @@
     if (match(tagImpl, linkTag))
         return linkTag.localName();
     if (match(tagImpl, scriptTag))
         return scriptTag.localName();
     ASSERT_NOT_REACHED();
     return emptyString();
 }
 
 class TokenPreloadScanner::StartTagScanner {
 public:
-    explicit StartTagScanner(const StringImpl* tagImpl)
+    explicit StartTagScanner(const StringImpl* tagImpl, float deviceScaleFactor = 1.0)

[abarth-chromium, 2013/09/13 05:54:07]

Please remove the default argument.  All callers should be forced to supply a
device scale factor.

         : m_tagImpl(tagImpl)
         , m_linkIsStyleSheet(false)
         , m_inputIsImage(false)
+        , m_deviceScaleFactor(deviceScaleFactor)
     {
         if (!match(m_tagImpl, imgTag)
             && !match(m_tagImpl, inputTag)
             && !match(m_tagImpl, linkTag)
             && !match(m_tagImpl, scriptTag))
             m_tagImpl = 0;
     }
 
+    void applySrcset()
+    {
+        // Resolve between src and srcSet if we have them.
+        if (RuntimeEnabledFeatures::srcsetEnabled() && !m_srcSetAttribute.isEmpty()) {

[ojan, 2013/09/12 23:26:38]

Nit: single line if should not have curly braces.

+            setUrlToLoad(bestFitSourceForImageAttributes(m_deviceScaleFactor, m_urlToLoad, m_srcSetAttribute), true);

[abarth-chromium, 2013/09/13 05:54:07]

This line of code isn't correct.  You haven't distinguished between srcset on
images and srcset on other elements, which means you're preloading srcset for
iframes as well.  Please add a test for this case.

+        }
+    }
+
     void processAttributes(const HTMLToken::AttributeList& attributes)
     {
         ASSERT(isMainThread());
         if (!m_tagImpl)
             return;
         for (HTMLToken::AttributeList::const_iterator iter = attributes.begin(); iter != attributes.end(); ++iter) {
             AtomicString attributeName(iter->name);
             String attributeValue = StringImpl::create8BitIfPossible(iter->value);
             processAttribute(attributeName, attributeValue);
         }
+
+        applySrcset();

[abarth-chromium, 2013/09/13 05:54:07]

Instead of doing the after every tag, we should only do it when it could
possibly matter, specifically when m_tagImpl matches imgTag.  Please don't just
add a branch here for m_tagImpl.  We already take that branch in
processAttribute.  We don't want to take it twice.

[Yoav Weiss, 2013/09/13 10:04:18]

Assuming m_srcSetAttribute is only initialized for images, is going into
applySrcset() and doing nothing there acceptable? 

I prefer to keep a single if statement inside the function and call it twice.
Alternatively, I can simply inline applySrcset()'s content in both calls.

[abarth-chromium, 2013/09/13 17:58:12]

The important thing is to only do srcset-specific work for imgTags.  Here you're
doing srcset-specific work for all tags.

     }
 
     void processAttributes(const Vector<CompactHTMLToken::Attribute>& attributes)
     {
         if (!m_tagImpl)
             return;
         for (Vector<CompactHTMLToken::Attribute>::const_iterator iter = attributes.begin(); iter != attributes.end(); ++iter)
             processAttribute(iter->name, iter->value);
+
+        applySrcset();
     }
 
     PassOwnPtr<PreloadRequest> createPreloadRequest(const KURL& predictedBaseURL, const SegmentedString& source)
     {
         if (!shouldPreload())
             return nullptr;
 
         TRACE_EVENT_INSTANT1("net", "PreloadRequest", "url", m_urlToLoad.ascii());
         TextPosition position = TextPosition(source.currentLine(), source.currentColumn());
         OwnPtr<PreloadRequest> request = PreloadRequest::create(initiatorFor(m_tagImpl), position, m_urlToLoad, predictedBaseURL, resourceType(), m_mediaAttribute);
@@ skipping 28 matching lines @@
                 m_inputIsImage = equalIgnoringCase(attributeValue, InputTypeNames::image());
         }
     }
 
     static bool relAttributeIsStyleSheet(const String& attributeValue)
     {
         LinkRelAttribute rel(attributeValue);
         return rel.isStyleSheet() && !rel.isAlternate() && rel.iconType() == InvalidIcon && !rel.isDNSPrefetch();
     }
 
-    void setUrlToLoad(const String& attributeValue)
+    void setUrlToLoad(const String& value, bool allowReplacement = false)

[abarth-chromium, 2013/09/13 05:54:07]

Please remove the default value for the last argument and use an enum instead of
a boolean so that callers can see what the second argument means.

     {
         // We only respect the first src/href, per HTML5:
         // http://www.whatwg.org/specs/web-apps/current-work/multipage/tokenization.html#attribute-name-state
-        if (!m_urlToLoad.isEmpty())
+        if (!allowReplacement && !m_urlToLoad.isEmpty())
             return;
-        m_urlToLoad = stripLeadingAndTrailingHTMLSpaces(attributeValue);
+        String url = stripLeadingAndTrailingHTMLSpaces(value);
+        if (url.isEmpty())
+            return;
+        m_urlToLoad = url;
     }
 
     const String& charset() const
     {
         // FIXME: Its not clear that this if is needed, the loader probably ignores charset for image requests anyway.
         if (match(m_tagImpl, imgTag))
             return emptyString();
         return m_charset;
     }
 
@@ skipping 20 matching lines @@
         return true;
     }
 
     bool crossOriginModeAllowsCookies()
     {
         return m_crossOriginMode.isNull() || equalIgnoringCase(m_crossOriginMode, "use-credentials");
     }
 
     const StringImpl* m_tagImpl;
     String m_urlToLoad;
+    String m_srcSetAttribute;

[abarth-chromium, 2013/09/13 05:54:07]

Where did you ever assign this member?

Please add a test that verifies that preloading works correctly.

[Yoav Weiss, 2013/09/13 10:04:18]

That is a bug (assignment lost in merge). Thanks!

     String m_charset;
     String m_crossOriginMode;
     bool m_linkIsStyleSheet;
     String m_mediaAttribute;
     bool m_inputIsImage;
+    float m_deviceScaleFactor;
 };
 
-TokenPreloadScanner::TokenPreloadScanner(const KURL& documentURL)
+TokenPreloadScanner::TokenPreloadScanner(const KURL& documentURL, float deviceScaleFactor)
     : m_documentURL(documentURL)
     , m_inStyle(false)
+    , m_deviceScaleFactor(deviceScaleFactor)
     , m_templateCount(0)
 {
 }
 
 TokenPreloadScanner::~TokenPreloadScanner()
 {
 }
 
 TokenPreloadScannerCheckpoint TokenPreloadScanner::createCheckpoint()
 {
@@ skipping 60 matching lines @@
             return;
         }
         if (match(tagImpl, baseTag)) {
             // The first <base> element is the one that wins.
             if (!m_predictedBaseElementURL.isEmpty())
                 return;
             updatePredictedBaseURL(token);
             return;
         }
 
-        StartTagScanner scanner(tagImpl);
+        StartTagScanner scanner(tagImpl, m_deviceScaleFactor);
         scanner.processAttributes(token.attributes());
         OwnPtr<PreloadRequest> request = scanner.createPreloadRequest(m_predictedBaseElementURL, source);
         if (request)
             requests.append(request.release());
         return;
     }
     default: {
         return;
     }
     }
 }
 
 template<typename Token>
 void TokenPreloadScanner::updatePredictedBaseURL(const Token& token)
 {
     ASSERT(m_predictedBaseElementURL.isEmpty());
     if (const typename Token::Attribute* hrefAttribute = token.getAttributeItem(hrefAttr))
         m_predictedBaseElementURL = KURL(m_documentURL, stripLeadingAndTrailingHTMLSpaces(hrefAttribute->value)).copy();
 }
 
-HTMLPreloadScanner::HTMLPreloadScanner(const HTMLParserOptions& options, const KURL& documentURL)
-    : m_scanner(documentURL)
+HTMLPreloadScanner::HTMLPreloadScanner(const HTMLParserOptions& options, const KURL& documentURL, float deviceScaleFactor)
+    : m_scanner(documentURL, deviceScaleFactor)
     , m_tokenizer(HTMLTokenizer::create(options))
 {
 }
 
 HTMLPreloadScanner::~HTMLPreloadScanner()
 {
 }
 
 void HTMLPreloadScanner::appendToEnd(const SegmentedString& source)
 {
@@ skipping 14 matching lines @@
         if (m_token.type() == HTMLToken::StartTag)
             m_tokenizer->updateStateFor(AtomicString(m_token.name()));
         m_scanner.scan(m_token, m_source, requests);
         m_token.clear();
     }
 
     preloader->takeAndPreload(requests);
 }
 
 }