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;

[Nate Chapin, 2016/10/18 18:23:17]

Instead of stashing the FetchRequest here and adding a parameter to the
constructor, could we just detect the range header on the ResourceRequest in the
constructor?

[sclittle, 2016/10/18 23:53:03]

I'm hesitant to just detect the range header, since there's nothing stopping
some other caller of ImageResource::fetch() from adding their own range header
for an image fetch for some reason. Currently, the code only adds Range header
and starts the placeholder logic if there isn't already a Range header on the
request.

I don't know of any other feature that uses range headers for images, or if it's
possible for JS to add a range header somehow. I can change this to just check
the range header if you think that's better though.

+};
+
 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 (resource &&
+      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->reloadIfLoFiOrPlaceholder(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::reloadIfLoFiOrPlaceholder(ResourceFetcher* fetcher,
+                                              bool bypassCache) {

[Nate Chapin, 2016/10/18 18:23:17]

bypassCache should probably be an enum.

[sclittle, 2016/10/18 23:53:03]

Done.

+  if (!m_isPlaceholder &&

[Nate Chapin, 2016/10/18 18:23:17]

This if-statement is sufficiently complex that it might be be time to pull it
out into a helper, even though there's only one callsite.

[sclittle, 2016/10/18 23:53:03]

Done.

+      (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();
+
+  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