Don't show a placeholder if the response contains the full image.

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 0a454391815e5909ea81d4e931931a92341c7884..858260812eb7ee24b4e76ae7f7f5b59960771a1e 100644
--- a/third_party/WebKit/Source/core/fetch/ImageResource.cpp
+++ b/third_party/WebKit/Source/core/fetch/ImageResource.cpp
@@ -36,6 +36,7 @@
 #include "platform/geometry/IntSize.h"
 #include "platform/graphics/BitmapImage.h"
 #include "platform/graphics/PlaceholderImage.h"
+#include "platform/network/HTTPParsers.h"
 #include "platform/tracing/TraceEvent.h"
 #include "public/platform/Platform.h"
 #include "public/platform/WebCachePolicy.h"
@@ -44,6 +45,7 @@
 #include "wtf/StdLibExtras.h"
 #include "wtf/Vector.h"
 #include <memory>
+#include <stdint.h>
 #include <v8.h>
 
 namespace blink {
@@ -461,6 +463,37 @@ inline void ImageResource::clearImage() {
   m_sizeAvailable = Image::SizeUnavailable;
 }
 
+// Determines if |response| likely contains the entire resource for the purposes
+// of determining whether or not to show a placeholder, e.g. if the server
+// responded with a full 200 response or if the full image is smaller than the
+// requested range.
+static bool isEntireResource(const ResourceResponse& response) {
+  if (response.httpStatusCode() != 206)
+    return true;
+
+  int64_t firstBytePosition = -1, lastBytePosition = -1, instanceLength = -1;
+  return parseContentRangeHeader(response.httpHeaderField("Content-Range"),
+                                 &firstBytePosition, &lastBytePosition,
+                                 &instanceLength) &&
+         firstBytePosition == 0 && lastBytePosition + 1 == instanceLength;
+}
+
+static bool shouldShowFullImageInsteadOfPlaceholder(
+    const ResourceResponse& response,
+    const Image* image) {
+  if (!isEntireResource(response))
+    return false;
+  if (image && !image->isNull())
+    return true;
+
+  // Don't treat a complete and broken image as a placeholder if the response
+  // code is something other than a 4xx or 5xx error. This is done to prevent
+  // reissuing the request in cases like "204 No Content" responses to tracking
+  // requests triggered by <img> tags, and <img> tags used to preload non-image
+  // resources.
+  return response.httpStatusCode() < 400 || response.httpStatusCode() >= 600;
+}
+
 void ImageResource::updateImage(bool allDataReceived) {
   TRACE_EVENT0("blink", "ImageResource::updateImage");
 
@@ -481,18 +514,13 @@ void ImageResource::updateImage(bool allDataReceived) {
   if (m_sizeAvailable == Image::SizeUnavailable && !allDataReceived)
     return;
 
-  if (m_isPlaceholder && allDataReceived && m_image && !m_image->isNull()) {
-    if (m_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.
+  if (m_isPlaceholder && allDataReceived) {
+    if (shouldShowFullImageInsteadOfPlaceholder(response(), m_image.get())) {
+      m_isPlaceholder = false;
+    } else if (m_image && !m_image->isNull()) {
       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();
     }
   }