Add Blink support for showing image placeholders using range requests.

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

 /*
  * Copyright (C) 2012 Google, Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
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  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
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  * THIS SOFTWARE IS PROVIDED BY GOOGLE INC. ``AS IS'' AND ANY
  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE COMPUTER, INC. OR
  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
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 #include "core/fetch/FetchRequest.h"
 
 #include "core/fetch/CrossOriginAccessControl.h"
 #include "core/fetch/ResourceFetcher.h"
+#include "platform/weborigin/KURL.h"
 
 namespace blink {
 
 FetchRequest::FetchRequest(const ResourceRequest& resourceRequest,
                            const AtomicString& initiator,
                            const String& charset)
     : m_resourceRequest(resourceRequest),
       m_charset(charset),
       m_options(ResourceFetcher::defaultResourceOptions()),
       m_forPreload(false),
       m_linkPreload(false),
       m_preloadDiscoveryTime(0.0),
       m_defer(NoDefer),
-      m_originRestriction(UseDefaultOriginRestrictionForType) {
+      m_originRestriction(UseDefaultOriginRestrictionForType),
+      m_placeholderImageRequestType(DisallowPlaceholder) {
   m_options.initiatorInfo.name = initiator;
 }
 
 FetchRequest::FetchRequest(const ResourceRequest& resourceRequest,
                            const AtomicString& initiator,
                            const ResourceLoaderOptions& options)
     : m_resourceRequest(resourceRequest),
       m_options(options),
       m_forPreload(false),
       m_linkPreload(false),
       m_preloadDiscoveryTime(0.0),
       m_defer(NoDefer),
-      m_originRestriction(UseDefaultOriginRestrictionForType) {
+      m_originRestriction(UseDefaultOriginRestrictionForType),
+      m_placeholderImageRequestType(
+          PlaceholderImageRequestType::DisallowPlaceholder) {
   m_options.initiatorInfo.name = initiator;
 }
 
 FetchRequest::FetchRequest(const ResourceRequest& resourceRequest,
                            const FetchInitiatorInfo& initiator)
     : m_resourceRequest(resourceRequest),
       m_options(ResourceFetcher::defaultResourceOptions()),
       m_forPreload(false),
       m_linkPreload(false),
       m_preloadDiscoveryTime(0.0),
       m_defer(NoDefer),
-      m_originRestriction(UseDefaultOriginRestrictionForType) {
+      m_originRestriction(UseDefaultOriginRestrictionForType),
+      m_placeholderImageRequestType(
+          PlaceholderImageRequestType::DisallowPlaceholder) {
   m_options.initiatorInfo = initiator;
 }
 
 FetchRequest::~FetchRequest() {}
 
 void FetchRequest::setCrossOriginAccessControl(
     SecurityOrigin* origin,
     CrossOriginAttributeValue crossOrigin) {
   DCHECK_NE(crossOrigin, CrossOriginAttributeNotSet);
   const bool useCredentials = crossOrigin == CrossOriginAttributeUseCredentials;
@@ skipping 33 matching lines @@
 }
 
 void FetchRequest::makeSynchronous() {
   // Synchronous requests should always be max priority, lest they hang the
   // renderer.
   m_resourceRequest.setPriority(ResourceLoadPriorityHighest);
   m_resourceRequest.setTimeoutInterval(10);
   m_options.synchronousPolicy = RequestSynchronously;
 }
 
+void FetchRequest::setAllowImagePlaceholder() {
+  DCHECK_EQ(DisallowPlaceholder, m_placeholderImageRequestType);
+  if (!m_resourceRequest.url().protocolIsInHTTPFamily() ||
+      m_resourceRequest.httpMethod() != "GET" ||
+      !m_resourceRequest.httpHeaderField("range").isNull()) {
+    return;
+  }
+
+  m_placeholderImageRequestType = AllowPlaceholder;
+
+  // 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.
+  m_resourceRequest.setHTTPHeaderField("range", "bytes=0-2047");
+
+  // TODO(sclittle): Indicate somehow (e.g. through a new request bit) to the
+  // embedder that it should return the full resource if the entire resource is
+  // fresh in the cache.
+}
+
 }  // namespace blink