DO NOT SUBMIT really old prototype of sprite recognition for image replacement

third_party/WebKit/Source/core/fetch/ImageResource.cpp

Index: third_party/WebKit/Source/core/fetch/ImageResource.cpp
diff --git a/third_party/WebKit/Source/core/fetch/ImageResource.cpp b/third_party/WebKit/Source/core/fetch/ImageResource.cpp
index be3e5de6e7041ee64971b7cbd566affdb0d64bc1..c697eb3efb1384d4f8e67ff6db09dbb4904def71 100644
--- a/third_party/WebKit/Source/core/fetch/ImageResource.cpp
+++ b/third_party/WebKit/Source/core/fetch/ImageResource.cpp
@@ -29,10 +29,12 @@
 #include "core/fetch/ResourceFetcher.h"
 #include "core/fetch/ResourceLoader.h"
 #include "core/fetch/ResourceLoadingLog.h"
+#include "core/fetch/SubstituteData.h"
 #include "core/svg/graphics/SVGImage.h"
 #include "platform/RuntimeEnabledFeatures.h"
 #include "platform/SharedBuffer.h"
 #include "platform/TraceEvent.h"
+#include "platform/geometry/IntSize.h"
 #include "platform/graphics/BitmapImage.h"
 #include "public/platform/Platform.h"
 #include "public/platform/WebCachePolicy.h"
@@ -40,12 +42,286 @@
 #include "wtf/HashCountedSet.h"
 #include "wtf/StdLibExtras.h"
 #include "wtf/Vector.h"
+#include "wtf/text/StringToNumber.h"
+#include <cstdio>
 #include <memory>
 #include <v8.h>
 
 namespace blink {
 
-ImageResource* ImageResource::fetch(FetchRequest& request, ResourceFetcher* fetcher)
+// Helper class that manages the state involved with attempting to load a
+// placeholder for an image.
+class ImageResource::PlaceholderLoaderJob : public GarbageCollectedFinalized<PlaceholderLoaderJob> {
+public:
+    explicit PlaceholderLoaderJob(ResourceFetcher*);
+    ~PlaceholderLoaderJob();
+
+    DECLARE_TRACE();
+
+    void onImageFetchComplete(ImageResource*);
+
+private:
+    enum class State {
+        Range = 0,
+        CacheOnly,
+        Placeholder,
+        BypassCacheFull
+    };
+
+    void finish(ImageResource* image)
+    {
+        DCHECK_EQ(image->m_placeholderLoaderJob.get(), this);
+        image->m_placeholderLoaderJob = nullptr;
+    }
+
+    void onRangeFetchComplete(ImageResource*);
+    void doCacheOnlyFetch(ImageResource*);
+    void onCacheOnlyFetchComplete(ImageResource*);
+    void loadPlaceholderOrBypassCache(ImageResource*);
+    void doPlaceholderFetch(ImageResource*, const IntSize&);
+    void doBypassCacheFullFetch(ImageResource*);
+
+    State m_state;
+    Member<ResourceFetcher> m_fetcher;
+    IntSize m_dimensionsFromRange;
+};
+
+ImageResource::PlaceholderLoaderJob::PlaceholderLoaderJob(ResourceFetcher* fetcher)
+    : m_state(State::Range)
+    , m_fetcher(fetcher)
+{
+    DCHECK(fetcher);
+}
+
+ImageResource::PlaceholderLoaderJob::~PlaceholderLoaderJob() {}
+
+DEFINE_TRACE(ImageResource::PlaceholderLoaderJob)
+{
+    visitor->trace(m_fetcher);
+}
+
+void ImageResource::PlaceholderLoaderJob::onImageFetchComplete(ImageResource* image)
+{
+    DCHECK(image);
+
+    switch (m_state) {
+    case State::Range:
+        onRangeFetchComplete(image);
+        break;
+    case State::CacheOnly:
+        onCacheOnlyFetchComplete(image);
+        break;
+    default:
+        finish(image);
+        break;
+    }
+}
+
+// Parses the values from a Content-Range response header of the form
+// "bytes %u-%u/%u". Returns true iff parsing is successful.
+static bool parseContentRangeHeader(const String& contentRange, uint64_t* rangeFirst, uint64_t* rangeLast, uint64_t* totalSize)
+{
+    // Example Content-Range header: "bytes 0-2047/16366".
+    if (!contentRange.startsWith("bytes "))
+        return false;
+    size_t dashPos = contentRange.find('-', arraysize("bytes ") - 1);
+    if (dashPos == kNotFound)
+        return false;
+    size_t slashPos = contentRange.find('/', dashPos + 1);
+    if (slashPos == kNotFound)
+        return false;
+
+    const size_t rangeFirstPos = arraysize("bytes ") - 1, rangeLastPos = dashPos + 1, totalSizePos = slashPos + 1;
+    bool rangeFirstOk = false, rangeLastOk = false, totalSizeOk = false;
+    if (contentRange.is8Bit()) {
+        *rangeFirst = charactersToUInt64Strict(contentRange.characters8() + rangeFirstPos, dashPos - rangeFirstPos, &rangeFirstOk);
+        *rangeLast = charactersToUInt64Strict(contentRange.characters8() + rangeLastPos, slashPos - rangeLastPos, &rangeLastOk);
+        *totalSize = charactersToUInt64Strict(contentRange.characters8() + totalSizePos, contentRange.length() - totalSizePos, &totalSizeOk);
+    } else {
+        *rangeFirst = charactersToUInt64Strict(contentRange.characters16() + rangeFirstPos, dashPos - rangeFirstPos, &rangeFirstOk);
+        *rangeLast = charactersToUInt64Strict(contentRange.characters16() + rangeLastPos, slashPos - rangeLastPos, &rangeLastOk);
+        *totalSize = charactersToUInt64Strict(contentRange.characters16() + totalSizePos, contentRange.length() - totalSizePos, &totalSizeOk);
+    }
+    return rangeFirstOk && rangeLastOk && totalSizeOk;
+}
+
+// Returns true if |response| likely represents the entire resource instead of
+// just a partial range.
+static bool hasEntireResource(const ResourceResponse& response)
+{
+    if (response.httpStatusCode() != 206)
+        return true;
+
+    const String& contentRangeHeader = response.httpHeaderField("content-range");
+    if (contentRangeHeader.isNull()) {
+        // If there's no Content-Range header, then assume that the response is
+        // the entire resource.
+        return true;
+    }
+
+    uint64_t rangeFirst, rangeLast, totalSize;
+    if (!parseContentRangeHeader(contentRangeHeader, &rangeFirst, &rangeLast, &totalSize))
+        return false;
+
+    // Check if the returned range is the entire resource.
+    return rangeFirst == 0 && rangeLast + 1 == totalSize;
+}
+
+void ImageResource::PlaceholderLoaderJob::onRangeFetchComplete(ImageResource* image)
+{
+    DCHECK_EQ(State::Range, m_state);
+
+    // If the response consists of the entire image, e.g. if the image was
+    // smaller than the requested range or if the server responded with a 200
+    // response for the full image, then just use the full response to show the
+    // full image.
+    // Also avoid re-fetching requests that led to 204 responses, since those
+    // typically indicate that it was for a tracking request, and there's likely
+    // no point in attempting to re-fetch the image.
+    if ((image->response().httpStatusCode() == 204 || !image->willPaintBrokenImage()) && hasEntireResource(image->response())) {
+        image->setIsPlaceholder(false);
+        finish(image);
+        return;
+    }
+
+    if (image->hasImage())
+        m_dimensionsFromRange = image->getImage()->size();
+
+    if (image->response().wasCached() && image->response().httpStatusCode() == 206 && image->resourceRequest().getCachePolicy() != WebCachePolicy::BypassingCache) {
+        // If the range response came from the cache, then that means that it
+        // was fresh in the cache and there's a chance that the entire image
+        // response is fresh and in the cache, so attempt to fetch the entire
+        // image from the cache.
+        doCacheOnlyFetch(image);
+        return;
+    }
+    loadPlaceholderOrBypassCache(image);
+}
+
+void ImageResource::PlaceholderLoaderJob::doCacheOnlyFetch(ImageResource* image)
+{
+    m_state = State::CacheOnly;
+
+    ResourceRequest request = image->getOriginalResourceRequest();
+    request.setCachePolicy(WebCachePolicy::ReturnCacheDataDontLoad);
+    image->reload(m_fetcher.get(), request, SubstituteData());
+}
+
+void ImageResource::PlaceholderLoaderJob::onCacheOnlyFetchComplete(ImageResource* image)
+{
+    DCHECK_EQ(State::CacheOnly, m_state);
+
+    if (!image->willPaintBrokenImage() && hasEntireResource(image->response())) {
+        image->setIsPlaceholder(false);
+        finish(image);
+        return;
+    }
+    loadPlaceholderOrBypassCache(image);
+}
+
+void ImageResource::PlaceholderLoaderJob::loadPlaceholderOrBypassCache(ImageResource* image)
+{
+    if (!m_dimensionsFromRange.isEmpty()) {
+        doPlaceholderFetch(image, m_dimensionsFromRange);
+        return;
+    }
+    if (image->getOriginalResourceRequest().getCachePolicy() != WebCachePolicy::ReturnCacheDataDontLoad) {
+        doBypassCacheFullFetch(image);
+        return;
+    }
+    // Return the broken image since there's nothing else that can be done here.
+    image->setIsPlaceholder(false);
+    finish(image);
+}
+
+static Vector<char> generatePlaceholderBox(const IntSize& dimensions)
+{
+    DCHECK(!dimensions.isEmpty());
+
+    static const char kFormat[] = "<?xml version=\"1.0\" encoding=\"UTF-8\" standalone=\"no\"?>\n"
+                                  "<svg xmlns=\"http://www.w3.org/2000/svg\" width=\"%d\" height=\"%d\">\n"
+                                  "<rect width=\"100%%\" height=\"100%%\" style=\"fill:rgba(127,127,127,0.4);stroke-width:%d;stroke:black\" />\n"
+                                  "</svg>";
+    // Don't add the black border to tiny images, to avoid coloring the entire image black.
+    int strokeWidth = dimensions.width() >= 10 && dimensions.height() >= 10 ? 2 : 0;
+
+    int expectedResult = std::snprintf(nullptr, 0, kFormat, dimensions.width(), dimensions.height(), strokeWidth);
+    DCHECK_LE(0, expectedResult);
+    Vector<char> out(safeCast<size_t>(expectedResult) + 1 /* for trailing '\0' */);
+    int result = std::snprintf(out.data(), out.size(), kFormat, dimensions.width(), dimensions.height(), strokeWidth);
+    DCHECK_EQ(expectedResult, result);
+    DCHECK_EQ('\0', out.last());
+    out.removeLast(); // Cut off the trailing '\0'.
+    return out;
+}
+
+void ImageResource::PlaceholderLoaderJob::doPlaceholderFetch(ImageResource* image, const IntSize& dimensions)
+{
+    DCHECK(!dimensions.isEmpty());
+    m_state = State::Placeholder;
+
+    Vector<char> svgBox = generatePlaceholderBox(dimensions);
+    SubstituteData substituteData(SharedBuffer::adoptVector(svgBox), "image/svg+xml", "utf-8", KURL(), LoadNormally);
+    DCHECK(image->isPlaceholder());
+    image->reload(m_fetcher.get(), image->getOriginalResourceRequest(), substituteData);
+}
+
+void ImageResource::PlaceholderLoaderJob::doBypassCacheFullFetch(ImageResource* image)
+{
+    m_state = State::BypassCacheFull;
+
+    // This reload is done bypassing the cache for several reasons:
+    //
+    // (1) CacheOnly fetches fail for sparse entries in the disk cache even if
+    // all the ranges of the full resource are available separately, so
+    // bypassing the cache here ensures that the full response is cached
+    // non-sparsely, so future fetches of the same image will be properly
+    // satisfied by the full cached response, reducing the cost of future
+    // fetches of this same image.
+    //
+    // (2) It's possible that the origin server doesn't understand ranges,
+    // and it returned a broken range, so bypassing the cache for this reload
+    // will hopefully return the full unbroken image instead of attempting to
+    // fetch the latter range of the image and combine that with the existing
+    // potentially broken range.
+    //
+    // TODO(sclittle): Investigate if the issue with (1) can be fixed, i.e. make
+    // the disk cache support sparse cache entries together with
+    // WebCachePolicy::ReturnCacheDataDontLoad.
+    ResourceRequest request = image->getOriginalResourceRequest();
+    request.setCachePolicy(WebCachePolicy::BypassingCache);
+    image->setIsPlaceholder(false);
+    image->reload(m_fetcher.get(), request, SubstituteData());
+}
+
+static void modifyRequestToFetchPlaceholderRange(ResourceRequest* request)
+{
+    DCHECK_EQ(nullAtom, request->httpHeaderField("range"));
+
+    // Fetch the first few bytes of the image. This number is tuned to both (a)
+    // likely capture the entire image for small images and (b) likely contain the
+    // dimensions for larger images.
+    // TODO(sclittle): Calculate the optimal value for this number.
+    request->setHTTPHeaderField("range", "bytes=0-2047");
+}
+
+static void unmodifyRequestToFetchPlaceholderRange(ResourceRequest* request)
+{
+    DCHECK_EQ("bytes=0-2047", request->httpHeaderField("range"));
+    request->clearHTTPHeaderField("range");
+}
+
+Resource* ImageResource::ImageResourceFactory::create(const ResourceRequest& request, const ResourceLoaderOptions& options, const String&) const
+{
+    if (m_isPlaceholder) {
+        ResourceRequest originalRequest = request;
+        unmodifyRequestToFetchPlaceholderRange(&originalRequest);
+        return new ImageResource(request, options, originalRequest, m_isPlaceholder);
+    }
+    return new ImageResource(request, options, request, m_isPlaceholder);
+}
+
+ImageResource* ImageResource::fetch(FetchRequest& request, ResourceFetcher* fetcher, PlaceholderRequestType placeholderRequestType)
 {
     if (request.resourceRequest().requestContext() == WebURLRequest::RequestContextUnspecified)
         request.mutableResourceRequest().setRequestContext(WebURLRequest::RequestContextImage);
@@ -56,14 +332,42 @@ ImageResource* ImageResource::fetch(FetchRequest& request, ResourceFetcher* fetc
         return nullptr;
     }
 
-    return toImageResource(fetcher->requestResource(request, ImageResourceFactory()));
+    bool attemptPlaceholder = placeholderRequestType == PlaceholderRequestType::AllowPlaceholder && request.url().protocolIsInHTTPFamily()
+        // Only issue range requests for GET requests, since that way it should
+        // be safe to re-issue the request without side effects.
+        && request.resourceRequest().httpMethod() == "GET"
+        // If the request already has a range request header, then don't
+        // overwrite that range header, and just attempt to fetch the image
+        // normally without generating a placeholder.
+        && request.resourceRequest().httpHeaderField("range").isNull();
+
+    if (attemptPlaceholder)
+        modifyRequestToFetchPlaceholderRange(&request.mutableResourceRequest());
+    ImageResource* image = toImageResource(fetcher->requestResource(request, ImageResourceFactory(attemptPlaceholder)));
+
+    // Check if the image is loading a placeholder already, otherwise add a PlaceholderLoaderJob.
+    if (attemptPlaceholder && (image->isLoading() || image->stillNeedsLoad()) && image->isPlaceholder() && !image->m_placeholderLoaderJob)
+        image->m_placeholderLoaderJob = new PlaceholderLoaderJob(fetcher);
+
+    // If this image shouldn't be a placeholder but it is, then reload it as not a placeholder.
+    if (!attemptPlaceholder && image->isPlaceholder()) {
+        image->m_placeholderLoaderJob = nullptr;
+        // Note that the cache is not bypassed for this reload - it should be fine
+        // to use a cached copy if it exists.
+        image->setIsPlaceholder(false);
+        image->reload(fetcher, request.resourceRequest(), SubstituteData());
+    }
+    return image;
 }
 
-ImageResource::ImageResource(const ResourceRequest& resourceRequest, const ResourceLoaderOptions& options)
+ImageResource::ImageResource(const ResourceRequest& resourceRequest, const ResourceLoaderOptions& options, const ResourceRequest& originalRequest, bool isPlaceholder)
     : Resource(resourceRequest, Image, options)
     , m_devicePixelRatioHeaderValue(1.0)
     , m_image(nullptr)
     , m_hasDevicePixelRatioHeaderValue(false)
+    , m_originalRequest(originalRequest)
+    , m_isPlaceholder(isPlaceholder)
+    , m_isSchedulingReload(false)
 {
     RESOURCE_LOADING_DVLOG(1) << "new ImageResource(ResourceRequest) " << this;
 }
@@ -73,6 +377,9 @@ ImageResource::ImageResource(blink::Image* image, const ResourceLoaderOptions& o
     , m_devicePixelRatioHeaderValue(1.0)
     , m_image(image)
     , m_hasDevicePixelRatioHeaderValue(false)
+    , m_originalRequest(resourceRequest())
+    , m_isPlaceholder(false)
+    , m_isSchedulingReload(false)
 {
     RESOURCE_LOADING_DVLOG(1) << "new ImageResource(Image) " << this;
     setStatus(Cached);
@@ -87,6 +394,7 @@ ImageResource::~ImageResource()
 DEFINE_TRACE(ImageResource)
 {
     visitor->trace(m_multipartParser);
+    visitor->trace(m_placeholderLoaderJob);
     Resource::trace(visitor);
     ImageObserver::trace(visitor);
     MultipartImageResourceParser::Client::trace(visitor);
@@ -94,6 +402,15 @@ DEFINE_TRACE(ImageResource)
 
 void ImageResource::checkNotify()
 {
+    if (m_isSchedulingReload)
+        return;
+
+    if (m_placeholderLoaderJob)
+        m_placeholderLoaderJob->onImageFetchComplete(this);
+
+    if (m_isSchedulingReload || m_placeholderLoaderJob)
+        return;
+
     notifyObserversInternal(MarkFinishedOption::ShouldMarkFinished);
     Resource::checkNotify();
 }
@@ -114,6 +431,9 @@ void ImageResource::notifyObserversInternal(MarkFinishedOption markFinishedOptio
 
 void ImageResource::markObserverFinished(ImageResourceObserver* observer)
 {
+    if (m_isSchedulingReload || m_placeholderLoaderJob)
+        return;
+
     if (m_observers.contains(observer)) {
         m_finishedObservers.add(observer);
         m_observers.remove(observer);
@@ -345,11 +665,19 @@ void ImageResource::clear()
 
 inline void ImageResource::createImage()
 {
+    bool wantSVGImage = response().mimeType() == "image/svg+xml";
+    // It's possible for the existing |m_image| to be a bitmap image while the
+    // response is now an SVG image, or vice versa, when an image is reloaded.
+    // In these cases, clear and delete the existing image so that a new image
+    // of the correct type can be created and used instead.
+    if (m_image && m_image->isSVGImage() != wantSVGImage)
+        clearImage();
+
     // Create the image if it doesn't yet exist.
     if (m_image)
         return;
 
-    if (response().mimeType() == "image/svg+xml") {
+    if (wantSVGImage) {
         m_image = SVGImage::create(this);
     } else {
         m_image = BitmapImage::create(this);
@@ -399,7 +727,11 @@ void ImageResource::updateImage(bool allDataReceived)
             setStatus(DecodeError);
         if (!allDataReceived && loader())
             loader()->didFinishLoading(nullptr, monotonicallyIncreasingTime(), size);
-        memoryCache()->remove(this);
+        // It's possible that the error could have been resolved by the
+        // didFinishLoading() call, so check again that the image is still in an
+        // error state before proceeding.
+        if (errorOccurred())
+            memoryCache()->remove(this);
     }
 
     // It would be nice to only redraw the decoded band of the image, but with the current design
@@ -534,18 +866,62 @@ void ImageResource::updateImageAnimationPolicy()
 
 void ImageResource::reloadIfLoFi(ResourceFetcher* fetcher)
 {
-    if (resourceRequest().loFiState() != WebURLRequest::LoFiOn)
+    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;
-    setCachePolicyBypassingCache();
-    setLoFiStateOff();
+
+    ResourceRequest reloadRequest = m_originalRequest;
+    reloadRequest.setCachePolicy(WebCachePolicy::BypassingCache);
+    reloadRequest.setLoFiState(WebURLRequest::LoFiOff);
+    m_isPlaceholder = false;
+    m_placeholderLoaderJob = nullptr;
+
+    reload(fetcher, reloadRequest, SubstituteData());
+}
+
+static void loadStaticResponse(ImageResource* resource, const SubstituteData& substituteData)
+{
+    DCHECK(resource);
+    DCHECK(substituteData.isValid());
+
+    // This code was adapted from ResourceFetcher::resourceForStaticData().
+    ResourceResponse response(resource->resourceRequest().url(), substituteData.mimeType(), substituteData.content()->size(), substituteData.textEncoding(), String());
+    response.setHTTPStatusCode(200);
+    response.setHTTPStatusText("OK");
+
+    resource->setNeedsSynchronousCacheHit(substituteData.forceSynchronousLoad());
+    resource->responseReceived(response, nullptr);
+    resource->setDataBufferingPolicy(BufferData);
+    resource->setResourceBuffer(PassRefPtr<SharedBuffer>(substituteData.content()));
+    resource->finish();
+}
+
+void ImageResource::reload(ResourceFetcher* fetcher, const ResourceRequest& request, const SubstituteData& substituteData)
+{
+    DCHECK(!m_isSchedulingReload);
+    m_isSchedulingReload = true;
+
     if (isLoading())
         loader()->cancel();
+    clearError();
     clear();
-    notifyObservers();
 
+    if (!substituteData.isValid()) {
+        // If the reload will be done asynchronously, notify observers to update
+        // the image's appearance while waiting for the async reload to
+        // complete.
+        notifyObservers();
+    }
     setStatus(NotStarted);
+
+    DCHECK(m_isSchedulingReload);
+    m_isSchedulingReload = false;
+
+    setResourceRequest(request);
+
+    if (substituteData.isValid()) {
+        loadStaticResponse(this, substituteData);
+        return;
+    }
     fetcher->startLoad(this);
 }