Add Blink support for showing image placeholders using range requests.

third_party/WebKit/Source/core/fetch/ImageResource.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) 2006 Samuel Weinig (sam.weinig@gmail.com)
     Copyright (C) 2004, 2005, 2006, 2007 Apple Inc. All rights reserved.
 
     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 14 matching lines @@
 
 #include "core/fetch/ImageResourceObserver.h"
 #include "core/fetch/MemoryCache.h"
 #include "core/fetch/ResourceClient.h"
 #include "core/fetch/ResourceFetcher.h"
 #include "core/fetch/ResourceLoader.h"
 #include "core/fetch/ResourceLoadingLog.h"
 #include "core/svg/graphics/SVGImage.h"
 #include "platform/RuntimeEnabledFeatures.h"
 #include "platform/SharedBuffer.h"
+#include "platform/geometry/IntSize.h"
 #include "platform/graphics/BitmapImage.h"
+#include "platform/graphics/PlaceholderImage.h"
 #include "platform/tracing/TraceEvent.h"
 #include "public/platform/Platform.h"
 #include "public/platform/WebCachePolicy.h"
 #include "wtf/CurrentTime.h"
 #include "wtf/HashCountedSet.h"
 #include "wtf/StdLibExtras.h"
 #include "wtf/Vector.h"
 #include <memory>
 #include <v8.h>
 
 namespace blink {
 
+class ImageResource::ImageResourceFactory : public ResourceFactory {
+  STACK_ALLOCATED();
+
+ public:
+  ImageResourceFactory(const FetchRequest& fetchRequest)
+      : ResourceFactory(Resource::Image), m_fetchRequest(&fetchRequest) {}
+
+  Resource* create(const ResourceRequest& request,
+                   const ResourceLoaderOptions& options,
+                   const String&) const override {
+    return new ImageResource(request, options,
+                             m_fetchRequest->placeholderImageRequestType() ==
+                                 FetchRequest::AllowPlaceholder);
+  }
+
+ private:
+  // Weak, unowned pointer. Must outlive |this|.
+  const FetchRequest* m_fetchRequest;
+};
+
 ImageResource* ImageResource::fetch(FetchRequest& request,
                                     ResourceFetcher* fetcher) {
   if (request.resourceRequest().requestContext() ==
       WebURLRequest::RequestContextUnspecified) {
     request.mutableResourceRequest().setRequestContext(
         WebURLRequest::RequestContextImage);
   }
   if (fetcher->context().pageDismissalEventBeingDispatched()) {
     KURL requestURL = request.resourceRequest().url();
     if (requestURL.isValid() &&
         fetcher->context().canRequest(Resource::Image,
                                       request.resourceRequest(), requestURL,
                                       request.options(), request.forPreload(),
                                       request.getOriginRestriction()))
       fetcher->context().sendImagePing(requestURL);
     return nullptr;
   }
 
-  return toImageResource(
-      fetcher->requestResource(request, ImageResourceFactory()));
+  ImageResource* resource = toImageResource(
+      fetcher->requestResource(request, ImageResourceFactory(request)));
+  if (request.placeholderImageRequestType() != FetchRequest::AllowPlaceholder &&
+      resource->m_isPlaceholder) {
+    // If the image is a placeholder, but this fetch doesn't allow a
+    // placeholder, then load the original image. Note that the cache is not
+    // bypassed here - it should be fine to use a cached copy if possible.
+    resource->reloadIfLoFi(fetcher, false);
+  }
+  return resource;
 }
 
 ImageResource::ImageResource(const ResourceRequest& resourceRequest,
-                             const ResourceLoaderOptions& options)
+                             const ResourceLoaderOptions& options,
+                             bool isPlaceholder)
     : Resource(resourceRequest, Image, options),
       m_devicePixelRatioHeaderValue(1.0),
       m_image(nullptr),
       m_hasDevicePixelRatioHeaderValue(false),
-      m_isSchedulingReload(false) {
+      m_isSchedulingReload(false),
+      m_isPlaceholder(isPlaceholder) {
   RESOURCE_LOADING_DVLOG(1) << "new ImageResource(ResourceRequest) " << this;
 }
 
 ImageResource::ImageResource(blink::Image* image,
                              const ResourceLoaderOptions& options)
     : Resource(ResourceRequest(""), Image, options),
       m_devicePixelRatioHeaderValue(1.0),
       m_image(image),
       m_hasDevicePixelRatioHeaderValue(false),
-      m_isSchedulingReload(false) {
+      m_isSchedulingReload(false),
+      m_isPlaceholder(false) {
   RESOURCE_LOADING_DVLOG(1) << "new ImageResource(Image) " << this;
   setStatus(Cached);
 }
 
 ImageResource::~ImageResource() {
   RESOURCE_LOADING_DVLOG(1) << "~ImageResource " << this;
   clearImage();
 }
 
 DEFINE_TRACE(ImageResource) {
   visitor->trace(m_multipartParser);
   Resource::trace(visitor);
   ImageObserver::trace(visitor);
   MultipartImageResourceParser::Client::trace(visitor);
 }
 
 void ImageResource::checkNotify() {
   // Don't notify observers and clients of completion if this ImageResource is
   // about to be reloaded.
-  if (m_isSchedulingReload)
+  if (m_isSchedulingReload || shouldReloadBrokenPlaceholder())
     return;
 
   notifyObserversInternal(MarkFinishedOption::ShouldMarkFinished);
   Resource::checkNotify();
 }
 
 void ImageResource::notifyObserversInternal(
     MarkFinishedOption markFinishedOption) {
   if (isLoading())
     return;
@@ skipping 12 matching lines @@
     m_finishedObservers.add(observer);
     m_observers.remove(observer);
   }
 }
 
 void ImageResource::didAddClient(ResourceClient* client) {
   DCHECK((m_multipartParser && isLoading()) || !data() || m_image);
 
   // Don't notify observers and clients of completion if this ImageResource is
   // about to be reloaded.
-  if (m_isSchedulingReload)
+  if (m_isSchedulingReload || shouldReloadBrokenPlaceholder())
     return;
 
   Resource::didAddClient(client);
 }
 
 void ImageResource::addObserver(ImageResourceObserver* observer) {
   willAddClientOrObserver(MarkAsReferenced);
 
   m_observers.add(observer);
 
   if (isCacheValidator())
     return;
 
   // When the response is not multipart, if |data()| exists, |m_image| must be
   // created. This is assured that |updateImage()| is called when |appendData()|
   // is called.
   //
   // On the other hand, when the response is multipart, |updateImage()| is not
   // called in |appendData()|, which means |m_image| might not be created even
   // when |data()| exists. This is intentional since creating a |m_image| on
   // receiving data might destroy an existing image in a previous part.
   DCHECK((m_multipartParser && isLoading()) || !data() || m_image);
 
   if (m_image && !m_image->isNull()) {
     observer->imageChanged(this);
   }
 
-  if (isLoaded() && !m_isSchedulingReload) {
+  if (isLoaded() && !m_isSchedulingReload && !shouldReloadBrokenPlaceholder()) {
     markObserverFinished(observer);
     observer->imageNotifyFinished(this);
   }
 }
 
 void ImageResource::removeObserver(ImageResourceObserver* observer) {
   DCHECK(observer);
 
   if (m_observers.contains(observer))
     m_observers.remove(observer);
@@ skipping 217 matching lines @@
   if (data()) {
     DCHECK(m_image);
     sizeAvailable = m_image->setData(data(), allDataReceived);
   }
 
   // Go ahead and tell our observers to try to draw if we have either received
   // all the data or the size is known. Each chunk from the network causes
   // observers to repaint, which will force that chunk to decode.
   if (sizeAvailable == Image::SizeUnavailable && !allDataReceived)
     return;
+
+  if (m_isPlaceholder && allDataReceived && m_image && !m_image->isNull()) {
+    if (sizeAvailable == Image::SizeAvailable) {
+      // TODO(sclittle): Show the original image if the response consists of the
+      // entire image, such as if the entire image response body is smaller than
+      // the requested range.
+      IntSize dimensions = m_image->size();
+      clearImage();
+      m_image = PlaceholderImage::create(this, dimensions);
+    } else {
+      // Clear the image so that it gets treated like a decoding error, since
+      // the attempt to build a placeholder image failed.
+      clearImage();
+    }
+  }
+
   if (!m_image || m_image->isNull()) {
     size_t size = encodedSize();
     clear();
     if (!errorOccurred())
       setStatus(DecodeError);
     if (!allDataReceived && loader())
       loader()->didFinishLoading(nullptr, monotonicallyIncreasingTime(), size);
     memoryCache()->remove(this);
   }
 
@@ skipping 113 matching lines @@
         observer->getImageAnimationPolicy(newPolicy))
       break;
   }
 
   if (m_image->animationPolicy() != newPolicy) {
     m_image->resetAnimation();
     m_image->setAnimationPolicy(newPolicy);
   }
 }
 
-void ImageResource::reloadIfLoFi(ResourceFetcher* fetcher) {
-  if (resourceRequest().loFiState() != WebURLRequest::LoFiOn)
+void ImageResource::reloadIfLoFi(ResourceFetcher* fetcher, bool bypassCache) {
+  if (!m_isPlaceholder &&
+      (resourceRequest().loFiState() != WebURLRequest::LoFiOn ||
+       (isLoaded() &&
+        !response().httpHeaderField("chrome-proxy").contains("q=low")))) {
     return;
-  if (isLoaded() &&
-      !response().httpHeaderField("chrome-proxy").contains("q=low"))
-    return;
+  }
 
   // Prevent clients and observers from being notified of completion while the
   // reload is being scheduled, so that e.g. canceling an existing load in
   // progress doesn't cause clients and observers to be notified of completion
   // prematurely.
   DCHECK(!m_isSchedulingReload);
   m_isSchedulingReload = true;
 
-  setCachePolicyBypassingCache();
+  if (bypassCache)
+    setCachePolicyBypassingCache();
   setLoFiStateOff();

[Stephen Chennney, 2016/10/17 18:09:17]

It concerns me a little that if you reload the placehlder you're also changing
the LoFiState. It's not clear to me that the two should be linked. Do we ever
expect to load lo-fi once the placeholder is done?

[sclittle, 2016/10/18 00:54:11]

We don't want to load a Lo-Fi image if a placeholder is reloaded. A placeholder
image is shown to the user as a substitute for the original image with the hope
that the user will never need to load the original image, in order to save data.

The main use case of this placeholder functionality that we're focusing on right
now is to essentially extend the Data Saver Lo-Fi feature so that we can save
data on images that aren't proxied through the Data Saver proxy (e.g. https://
images), via this range request + placeholder mechanism.

There isn't really any advantage to generating a placeholder for a Lo-Fi image,
since Lo-Fi images are already tiny. Ideally, Blink would favor the Lo-Fi image
response over generating a placeholder, and this will be handled in practice by
showing the original image if the subrange response received is the entire
resource, see the TODO in ImageResource::updateImage().

See the design doc linked in the CL description and the Intent to Implement
thread on blink-dev
(https://groups.google.com/a/chromium.org/d/msg/blink-dev/pOTcSsMsAuo/YFiYRy7f...)
for more details.

+
+  if (m_isPlaceholder) {
+    m_isPlaceholder = false;
+    clearRangeRequestHeader();
+  }
+
   if (isLoading()) {
     loader()->cancel();
     // Canceling the loader causes error() to be called, which in turn calls
     // clear() and notifyObservers(), so there's no need to call these again
     // here.
   } else {
     clear();
     notifyObservers();
   }
 
@@ skipping 49 matching lines @@
            WebServiceWorkerResponseTypeOpaque;
   }
   if (!getImage()->currentFrameHasSingleSecurityOrigin())
     return false;
   if (passesAccessControlCheck(securityOrigin))
     return true;
   return !securityOrigin->taintsCanvas(response().url());
 }
 
 }  // namespace blink