Remove duplication of encoded image data

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 63 matching lines @@
     , m_image(image)
     , m_hasDevicePixelRatioHeaderValue(false)
 {
     WTF_LOG(Timers, "new ImageResource(Image) %p", this);
     setStatus(Cached);
 }
 
 ImageResource::~ImageResource()
 {
     WTF_LOG(Timers, "~ImageResource %p", this);
-    clearImage();
 }
 
 DEFINE_TRACE(ImageResource)
 {
     visitor->trace(m_multipartParser);
     Resource::trace(visitor);
     ImageObserver::trace(visitor);
     MultipartImageResourceParser::Client::trace(visitor);
 }
 
@@ skipping 22 matching lines @@
 
 void ImageResource::addObserver(ImageResourceObserver* observer)
 {
     willAddClientOrObserver();
 
     m_observers.add(observer);
 
     if (isCacheValidator())
         return;
 
-    if (m_data && !m_image && !errorOccurred()) {
-        createImage();
-        m_image->setData(m_data, true);
-    }
+    DCHECK(!m_data || m_image);
 
     if (m_image && !m_image->isNull()) {
         observer->imageChanged(this);
     }
 
     if (isLoaded()) {
         observer->imageNotifyFinished(this);
         if (m_observers.contains(observer)) {
             m_finishedObservers.add(observer);
             m_observers.remove(observer);
@@ skipping 42 matching lines @@
 }
 
 bool ImageResource::isSafeToUnlock() const
 {
     // Note that |m_image| holds a reference to |m_data| in addition to the one held by the Resource parent class.
     return !m_image || (m_image->hasOneRef() && m_data->refCount() == 2);
 }
 
 void ImageResource::destroyDecodedDataForFailedRevalidation()
 {
-    m_image = nullptr;
-    setDecodedSize(0);
+    m_image->destroyDecodedData();

[hiroshige, 2016/06/29 07:04:06]

I think we have to clear |m_image| here, because we have to re-create |m_image|
in failed revalidation -- and it means we lack tests for that case. I'll add a
test.

[hiroshige, 2016/06/29 08:20:52]

Created the tests. https://codereview.chromium.org/2101103004/

[hajimehoshi, 2016/07/04 10:46:24]

Done.

 }
 
 void ImageResource::destroyDecodedDataIfPossible()
 {
-    if (!hasClientsOrObservers() && !isLoading() && (!m_image || (m_image->hasOneRef() && m_image->isBitmapImage()))) {
-        m_image = nullptr;
-        setDecodedSize(0);
-    } else if (m_image && !errorOccurred()) {
+    if (!m_image)
+        return;
+    if ((!hasClientsOrObservers() && !isLoading() && m_image->hasOneRef() && m_image->isBitmapImage()) || !errorOccurred())

[hiroshige, 2016/06/29 07:04:06]

I'm not sure, but can we simplify this condition to just |!errorOccurred()|?

The condition |!hasClientsOrObservers() && !isLoading() && (!m_image
||m_image->hasOneRef() && m_image->isBitmapImage()))| looks like for disposing
|m_image|, and this CL makes |m_image| to be not disposal.

[hajimehoshi, 2016/07/04 10:46:24]

As we talked offline, let's keep this condition as it is. If we need
refactoring, we'll do it in another CL.

         m_image->destroyDecodedData();
-    }
 }
 
 void ImageResource::doResetAnimation()
 {
     if (m_image)
         m_image->resetAnimation();
 }
 
 void ImageResource::allClientsAndObserversRemoved()
 {
     if (m_image && !errorOccurred()) {
         // If possible, delay the resetting until back at the event loop.
         // Doing so after a conservative GC prevents resetAnimation() from
         // upsetting ongoing animation updates (crbug.com/613709)
         if (!ThreadHeap::willObjectBeLazilySwept(this))
             Platform::current()->currentThread()->getWebTaskRunner()->postTask(BLINK_FROM_HERE, bind(&ImageResource::doResetAnimation, wrapWeakPersistent(this)));
         else
             m_image->resetAnimation();
     }
     if (m_multipartParser)
         m_multipartParser->cancel();
     Resource::allClientsAndObserversRemoved();
 }
 
+PassRefPtr<SharedBuffer> ImageResource::resourceBuffer() const
+{
+    RefPtr<SharedBuffer> data = Resource::resourceBuffer();
+    if (data)
+        return data;

[f(malita), 2016/06/30 18:21:46]

Nit: return data.release();

[hajimehoshi, 2016/07/04 10:46:24]

Done.

+    if (m_image)
+        return m_image->data();
+    return nullptr;
+}
+
 void ImageResource::appendData(const char* data, size_t length)
 {
     if (m_multipartParser) {
         m_multipartParser->appendData(data, length);
     } else {
         Resource::appendData(data, length);
         updateImage(false);
     }
 }
 
@@ skipping 83 matching lines @@
 
     ImageResourceObserverWalker walker(m_observers);
     while (auto* observer = walker.next()) {
         observer->imageChanged(this, changeRect);
     }
 }
 
 void ImageResource::clear()
 {
     prune();
-    clearImage();

[hiroshige, 2016/06/29 07:04:06]

Perhaps, we need to call clearImage() here, because clear() is called when an
error occurs. Clearing |m_image| in case of error looks reasonable for me.

[hajimehoshi, 2016/07/04 10:46:24]

Done.

     m_data.clear();
     setEncodedSize(0);
 }
 
 inline void ImageResource::createImage()
 {
-    // Create the image if it doesn't yet exist.
+    // When |m_image| exists here, this is a previous part of a multipart
+    // response. Recreate it.
     if (m_image)
-        return;
+        m_image = nullptr;

[scroggo_chromium, 2016/06/28 15:33:44]

It's not obvious to me how this relates to the rest of the change, and I don't
know enough about a multi-part response to judge whether this makes sense.

One place where this seems wrong to me if the following is true:
1. No m_multipartParser
2. We have already appended some data (but not all), so m_image is not NULL, and
neither is m_data.
3. More data is appended in appendData()

This will call updateImage(false).
This method will clear m_image.

This means we'll have to recreate m_image from scratch, and previously we would
have reused the old one.

[hiroshige, 2016/06/29 07:04:06]

I think it's better to call clearImage() explicitly when a multipart image needs
to clear |m_image|, than clearing |m_image| here implicitly depending on
|m_image|. (Generally, implicit assumptions on the status of Resources are
frequently wrong...)

[hajimehoshi, 2016/07/04 10:46:24]

Done.

 
     if (m_response.mimeType() == "image/svg+xml") {
         m_image = SVGImage::create(this);
     } else {
         m_image = BitmapImage::create(this);
     }
 }
 
-inline void ImageResource::clearImage()
-{
-    if (!m_image)
-        return;
-
-    // If our Image has an observer, it's always us so we need to clear the back pointer
-    // before dropping our reference.
-    m_image->clearImageObserver();

[scroggo_chromium, 2016/06/28 15:33:44]

Why is it okay to drop this line? My first thought was that we're about to
delete m_image, which would clear the observer anyway, but some other class
could hold a reference to m_image (e.g. by calling getImage() [1]), and I assume
we still want to clear the observer?

[1]
https://cs.chromium.org/chromium/src/third_party/WebKit/Source/core/fetch/Ima...

[hajimehoshi, 2016/07/04 10:46:24]

Ah, you're right. I'll revert this function and callers. 

-    m_image.clear();
-}
-
 void ImageResource::updateImage(bool allDataReceived)
 {
     TRACE_EVENT0("blink", "ImageResource::updateImage");
 
     if (m_data)
         createImage();
 
     bool sizeAvailable = false;
 
     // Have the image update its data from its internal buffer.
     // It will not do anything now, but will delay decoding until
     // queried for info (like size or specific image frames).
-    if (m_image)
+    if (m_image && m_data)

[scroggo_chromium, 2016/06/28 15:33:44]

If we have m_data, aren't we guaranteed to also have m_image, since
createImage() would have been called above?

Could you change this to:

if (m_data) {
  DCHECK(m_image);
  sizeAvailable = m_image->setData(m_data, allDataReceived);
}

?

[hajimehoshi, 2016/07/04 10:46:24]

Right, now m_image's lifetime should include m_data's. Done.

         sizeAvailable = m_image->setData(m_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 || allDataReceived) {
         if (!m_image || m_image->isNull()) {
             if (!errorOccurred())
                 setStatus(DecodeError);
             clear();
             if (memoryCache()->contains(this))
                 memoryCache()->remove(this);
         }
 
         // It would be nice to only redraw the decoded band of the image, but with the current design
         // (decoding delayed until painting) that seems hard.
         notifyObservers();
     }
-}
 
-void ImageResource::updateImageAndClearBuffer()
-{
-    clearImage();
-    updateImage(true);
-    m_data.clear();
+    if (allDataReceived)
+        m_data.clear();
 }
 
 void ImageResource::finish(double loadFinishTime)
 {
     if (m_multipartParser) {
         m_multipartParser->finish();
         if (m_data)
-            updateImageAndClearBuffer();
+            updateImage(true);
     } else {
         updateImage(true);
     }
     Resource::finish(loadFinishTime);
 }
 
 void ImageResource::error(const ResourceError& error)
 {
     if (m_multipartParser)
         m_multipartParser->cancel();
@@ skipping 93 matching lines @@
 
 void ImageResource::reloadIfLoFi(ResourceFetcher* fetcher)
 {
     if (!m_response.httpHeaderField("chrome-proxy").contains("q=low"))
         return;
     m_resourceRequest.setCachePolicy(WebCachePolicy::BypassingCache);
     m_resourceRequest.setLoFiState(WebURLRequest::LoFiOff);
     if (isLoading())
         m_loader->cancel();
     else
-        updateImageAndClearBuffer();
+        updateImage(true);
     setStatus(NotStarted);
     fetcher->startLoad(this);
 }
 
 void ImageResource::changedInRect(const blink::Image* image, const IntRect& rect)
 {
     if (!image || image != m_image)
         return;
     notifyObservers(&rect);
 }
 
 void ImageResource::onePartInMultipartReceived(const ResourceResponse& response)
 {
     ASSERT(m_multipartParser);
 
     m_response = response;
     if (m_multipartParsingState == MultipartParsingState::WaitingForFirstPart) {
         // We have nothing to do because we don't have any data.
         m_multipartParsingState = MultipartParsingState::ParsingFirstPart;
         return;
     }
-    updateImageAndClearBuffer();
+    updateImage(true);
 
     if (m_multipartParsingState == MultipartParsingState::ParsingFirstPart) {
         m_multipartParsingState = MultipartParsingState::FinishedParsingFirstPart;
         // Notify finished when the first part ends.
         if (!errorOccurred())
             setStatus(Cached);
         checkNotify();
         if (m_loader)
             m_loader->didFinishLoadingFirstPartInMultipart();
     }
@@ skipping 10 matching lines @@
     if (response().wasFetchedViaServiceWorker())
         return response().serviceWorkerResponseType() != WebServiceWorkerResponseTypeOpaque;
     if (!getImage()->currentFrameHasSingleSecurityOrigin())
         return false;
     if (passesAccessControlCheck(securityOrigin))
         return true;
     return !securityOrigin->taintsCanvas(response().url());
 }
 
 } // namespace blink