src/net/instaweb/rewriter/delay_images_filter.cc - incubator-pagespeed-debian - Git at Google

 /*
  * Copyright 2011 Google Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 // Author: pulkitg@google.com (Pulkit Goyal)
 //
 // Contains implementation of DelayImagesFilter, which delays all the high
 // quality images whose low quality inlined data url are available within their
 // respective image tag.

 #include "net/instaweb/rewriter/public/delay_images_filter.h"

 #include <map>
 #include <utility>

 #include "base/logging.h"
 #include "net/instaweb/http/public/log_record.h"
 #include "net/instaweb/rewriter/public/critical_images_finder.h"
 #include "net/instaweb/rewriter/public/request_properties.h"
 #include "net/instaweb/rewriter/public/resource_tag_scanner.h"
 #include "net/instaweb/rewriter/public/rewrite_driver.h"
 #include "net/instaweb/rewriter/public/rewrite_options.h"
 #include "net/instaweb/rewriter/public/server_context.h"
 #include "net/instaweb/rewriter/public/static_asset_manager.h"
 #include "pagespeed/kernel/base/string.h"
 #include "pagespeed/kernel/html/html_element.h"
 #include "pagespeed/kernel/html/html_name.h"
 #include "pagespeed/kernel/http/semantic_type.h"
 #include "pagespeed/opt/logging/enums.pb.h"

 namespace net_instaweb {

 const char DelayImagesFilter::kDelayImagesSuffix[] =
     "\npagespeed.delayImagesInit();";

 const char DelayImagesFilter::kDelayImagesInlineSuffix[] =
     "\npagespeed.delayImagesInlineInit();";

 const char DelayImagesFilter::kImageOnloadCode[] =
     "pagespeed.switchToHighResAndMaybeBeacon(this);";

 // Js snippet with the code for image elements to load the high resolution
 // image once onload triggers (for the low resolution data url). This code
 // also adds the checkImageForCriticality logic when the page has been
 // instrumented (i.e. when pagespeed.CriticalImages is defined).
 const char DelayImagesFilter::kImageOnloadJsSnippet[] =
     "window['pagespeed'] = window['pagespeed'] || {};"
     "var pagespeed = window['pagespeed'];"
     "pagespeed.switchToHighResAndMaybeBeacon = function(elem) {"
     "setTimeout(function(){elem.onload = null;"
     // Set srcset before src to avoid potentially loading 2 sizes.
     "var srcset = elem.getAttribute('data-pagespeed-high-res-srcset');"
     "if (srcset) {elem.srcset = srcset;}"
     "elem.src = elem.getAttribute('data-pagespeed-high-res-src');"
     "if (pagespeed.CriticalImages) {elem.onload = "
     "pagespeed.CriticalImages.checkImageForCriticality(elem);}"
     "}, 0);"
     "};";

 DelayImagesFilter::DelayImagesFilter(RewriteDriver* driver)
     : CommonFilter(driver),
       num_low_res_inlined_images_(0),
       insert_low_res_images_inplace_(false),
       lazyload_highres_images_(false),
       is_script_inserted_(false),
       added_image_onload_js_(false) {
 }

 DelayImagesFilter::~DelayImagesFilter() {}

 void DelayImagesFilter::StartDocumentImpl() {
   num_low_res_inlined_images_ = 0;
   // Low res images will be placed inside the respective image tag if the user
   // agent is not a mobile, or if mobile aggressive rewriters are turned off.
   // Otherwise, the low res images are inserted at the end of the flush window.
   insert_low_res_images_inplace_ = ShouldRewriteInplace();
   lazyload_highres_images_ = driver()->options()->lazyload_highres_images() &&
       driver()->request_properties()->IsMobile();
   is_script_inserted_ = false;
   added_image_onload_js_ = false;
 }

 void DelayImagesFilter::MaybeAddImageOnloadJsSnippet(HtmlElement* element) {
   if (added_image_onload_js_) {
     return;
   }
   added_image_onload_js_ = true;
   HtmlElement* script = driver()->NewElement(NULL, HtmlName::kScript);
   driver()->AddAttribute(script, HtmlName::kDataPagespeedNoDefer, NULL);
   // Always add the image-onload js before the current node, because the
   // current node might be an img node that needs the image-onload js for
   // setting its onload handler.
   driver()->InsertNodeBeforeNode(element, script);
   AddJsToElement(kImageOnloadJsSnippet, script);
 }

 void DelayImagesFilter::EndDocument() {
   low_res_data_map_.clear();
 }

 void DelayImagesFilter::EndElementImpl(HtmlElement* element) {
   if (element->keyword() == HtmlName::kBody) {
     InsertLowResImagesAndJs(element, /* insert_after_element */ false);
     InsertHighResJs(element);
   } else if (driver()->IsRewritable(element) &&
              (element->keyword() == HtmlName::kImg ||
               element->keyword() == HtmlName::kInput)) {
     // We only handle img and input tag images.  Note that delay_images.js and
     // delay_images_inline.js must be modified to handle other possible tags.
     // We should probably specifically *not* include low res images for link
     // tags of various sorts (favicons, mobile desktop icons, etc.). Use of low
     // res for explicit background images is a more interesting case, but the
     // current DOM walk in the above js files would need to be modified to
     // handle the large number of tags that we can identify in
     // resource_tag_scanner::ScanElement.
     HtmlElement::Attribute* low_res_src =
         element->FindAttribute(HtmlName::kDataPagespeedLowResSrc);
     if (low_res_src == NULL || low_res_src->DecodedValueOrNull() == NULL) {
       return;
     }
     HtmlElement::Attribute* src = element->FindAttribute(HtmlName::kSrc);
     semantic_type::Category category =
         resource_tag_scanner::CategorizeAttribute(
             element, src, driver()->options());
     if (category != semantic_type::kImage ||
         src->DecodedValueOrNull() == NULL) {
       return;  // Failed to find valid Image-valued src attribute.
     }
     ++num_low_res_inlined_images_;
     if (CanAddPagespeedOnloadToImage(*element)) {
       driver()->log_record()->SetRewriterLoggingStatus(
           RewriteOptions::FilterId(RewriteOptions::kDelayImages),
           RewriterApplication::APPLIED_OK);
       // Rename src -> data-pagespeed-high-res-src
       driver()->SetAttributeName(src, HtmlName::kDataPagespeedHighResSrc);
       // Rename srcset -> data-pagespeed-high-res-srcset
       HtmlElement::Attribute* srcset =
           element->FindAttribute(HtmlName::kSrcset);
       if (srcset != NULL) {
         driver()->SetAttributeName(
             srcset, HtmlName::kDataPagespeedHighResSrcset);
       }
       if (insert_low_res_images_inplace_) {
         // Set the src as the low resolution image.
         driver()->AddAttribute(element, HtmlName::kSrc,
                               low_res_src->DecodedValueOrNull());
         // Add an onload function to set the high resolution image after
         // deleting any existing onload handler. Since we check
         // CanAddPagespeedOnloadToImage before coming here, the only onload
         // handler that we would delete would be the one added by our very own
         // beaconing code. We re-introduce this beaconing onload logic via
         // kImageOnloadCode.
         element->DeleteAttribute(HtmlName::kOnload);
         driver()->AddAttribute(element, HtmlName::kOnload, kImageOnloadCode);
         // Add onerror handler just in case the low res image doesn't load.
         element->DeleteAttribute(HtmlName::kOnerror);
         // Note: this.onerror=null to avoid infinitely repeating on failure:
         //   See: http://stackoverflow.com/questions/3984287
         driver()->AddAttribute(element, HtmlName::kOnerror,
                                StrCat("this.onerror=null;", kImageOnloadCode));
         MaybeAddImageOnloadJsSnippet(element);
       } else {
         // Low res image data is collected in low_res_data_map_ map. This
         // low_res_src will be moved just after last low res image in the flush
         // window.
         // It is better to move inlined low resolution data later in the DOM,
         // otherwise they will block further parsing and rendering of the html
         // page.
         // Note that the high resolution images are loaded at end of body.
         const GoogleString& src_content = src->DecodedValueOrNull();
         low_res_data_map_[src_content] = low_res_src->DecodedValueOrNull();
       }
     }
     if (num_low_res_inlined_images_ == driver()->num_inline_preview_images()) {
       if (!insert_low_res_images_inplace_) {
         InsertLowResImagesAndJs(element, /* insert_after_element */ true);
       }
     }
   }
   element->DeleteAttribute(HtmlName::kDataPagespeedLowResSrc);
 }

 void DelayImagesFilter::InsertLowResImagesAndJs(HtmlElement* element,
                                                 bool insert_after_element) {
   if (low_res_data_map_.empty()) {
     return;
   }
   GoogleString inline_script;
   HtmlElement* current_element = element;
   // Check script for changing src to low res data url is inserted once.
   if (!is_script_inserted_) {
     StaticAssetManager* manager =
         driver()->server_context()->static_asset_manager();
     inline_script = StrCat(
         manager->GetAsset(
             StaticAssetEnum::DELAY_IMAGES_INLINE_JS,
             driver()->options()),
         kDelayImagesInlineSuffix,
         manager->GetAsset(
             StaticAssetEnum::DELAY_IMAGES_JS,
             driver()->options()),
         kDelayImagesSuffix);
     HtmlElement* script_element =
         driver()->NewElement(element, HtmlName::kScript);
     driver()->AddAttribute(
         script_element, HtmlName::kDataPagespeedNoDefer, NULL);
     if (insert_after_element) {
       DCHECK(element->keyword() == HtmlName::kImg ||
              element->keyword() == HtmlName::kInput);
       driver()->InsertNodeAfterNode(current_element, script_element);
       current_element = script_element;
     } else {
       DCHECK(element->keyword() == HtmlName::kBody);
       driver()->AppendChild(element, script_element);
     }
     AddJsToElement(inline_script, script_element);
     is_script_inserted_ = true;
   }

   // Generate javascript map for inline data urls where key is url and
   // base64 encoded data url as its value. This map is added to the
   // html at the end of last low res image.
   GoogleString inline_data_script;
   for (StringStringMap::iterator it = low_res_data_map_.begin();
        it != low_res_data_map_.end(); ++it) {
     inline_data_script = StrCat(
         "\npagespeed.delayImagesInline.addLowResImages('",
         it->first, "', '", it->second, "');");
     StrAppend(&inline_data_script,
               "\npagespeed.delayImagesInline.replaceWithLowRes();\n");
     HtmlElement* low_res_element =
         driver()->NewElement(current_element, HtmlName::kScript);
     driver()->AddAttribute(
         low_res_element, HtmlName::kDataPagespeedNoDefer, NULL);
     if (insert_after_element) {
       driver()->InsertNodeAfterNode(current_element, low_res_element);
       current_element = low_res_element;
     } else {
       driver()->AppendChild(element, low_res_element);
     }
     AddJsToElement(inline_data_script, low_res_element);
   }
   low_res_data_map_.clear();
 }

 void DelayImagesFilter::InsertHighResJs(HtmlElement* body_element) {
   if (insert_low_res_images_inplace_ || !is_script_inserted_) {
     return;
   }
   GoogleString js;
   if (lazyload_highres_images_) {
     StrAppend(&js,
               "\npagespeed.delayImages.registerLazyLoadHighRes();\n");
   } else {
     StrAppend(&js,
               "\npagespeed.delayImages.replaceWithHighRes();\n");
   }
   HtmlElement* script = driver()->NewElement(body_element, HtmlName::kScript);
   driver()->AddAttribute(script, HtmlName::kDataPagespeedNoDefer, NULL);
   driver()->AppendChild(body_element, script);
   AddJsToElement(js, script);
 }

 bool DelayImagesFilter::ShouldRewriteInplace() const {
   const RewriteOptions* options = driver()->options();
   return (options->use_blank_image_for_inline_preview() ||
           !(options->enable_aggressive_rewriters_for_mobile() &&
             driver()->request_properties()->IsMobile()));
 }

 void DelayImagesFilter::DetermineEnabled(GoogleString* disabled_reason) {
   AbstractLogRecord* log_record = driver()->log_record();
   if (!driver()->request_properties()->SupportsImageInlining()) {
     log_record->LogRewriterHtmlStatus(
         RewriteOptions::FilterId(RewriteOptions::kDelayImages),
         RewriterHtmlApplication::USER_AGENT_NOT_SUPPORTED);
     set_is_enabled(false);
     return;
   }
   CriticalImagesFinder* finder =
       driver()->server_context()->critical_images_finder();
   if ((finder->Available(driver()) == CriticalImagesFinder::kNoDataYet) &&
       !driver()->options()->Enabled(RewriteOptions::kSplitHtmlHelper)) {
     log_record->LogRewriterHtmlStatus(
         RewriteOptions::FilterId(RewriteOptions::kDelayImages),
         RewriterHtmlApplication::PROPERTY_CACHE_MISS);
     set_is_enabled(false);
     return;
   }
   log_record->LogRewriterHtmlStatus(
       RewriteOptions::FilterId(RewriteOptions::kDelayImages),
       RewriterHtmlApplication::ACTIVE);
   set_is_enabled(true);
 }

 }  // namespace net_instaweb
	/*
	* Copyright 2011 Google Inc.
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	// Author: pulkitg@google.com (Pulkit Goyal)
	//
	// Contains implementation of DelayImagesFilter, which delays all the high
	// quality images whose low quality inlined data url are available within their
	// respective image tag.

	#include "net/instaweb/rewriter/public/delay_images_filter.h"

	#include <map>
	#include <utility>

	#include "base/logging.h"
	#include "net/instaweb/http/public/log_record.h"
	#include "net/instaweb/rewriter/public/critical_images_finder.h"
	#include "net/instaweb/rewriter/public/request_properties.h"
	#include "net/instaweb/rewriter/public/resource_tag_scanner.h"
	#include "net/instaweb/rewriter/public/rewrite_driver.h"
	#include "net/instaweb/rewriter/public/rewrite_options.h"
	#include "net/instaweb/rewriter/public/server_context.h"
	#include "net/instaweb/rewriter/public/static_asset_manager.h"
	#include "pagespeed/kernel/base/string.h"
	#include "pagespeed/kernel/html/html_element.h"
	#include "pagespeed/kernel/html/html_name.h"
	#include "pagespeed/kernel/http/semantic_type.h"
	#include "pagespeed/opt/logging/enums.pb.h"

	namespace net_instaweb {

	const char DelayImagesFilter::kDelayImagesSuffix[] =
	"\npagespeed.delayImagesInit();";

	const char DelayImagesFilter::kDelayImagesInlineSuffix[] =
	"\npagespeed.delayImagesInlineInit();";

	const char DelayImagesFilter::kImageOnloadCode[] =
	"pagespeed.switchToHighResAndMaybeBeacon(this);";

	// Js snippet with the code for image elements to load the high resolution
	// image once onload triggers (for the low resolution data url). This code
	// also adds the checkImageForCriticality logic when the page has been
	// instrumented (i.e. when pagespeed.CriticalImages is defined).
	const char DelayImagesFilter::kImageOnloadJsSnippet[] =
	"window['pagespeed'] = window['pagespeed'] \|\| {};"
	"var pagespeed = window['pagespeed'];"
	"pagespeed.switchToHighResAndMaybeBeacon = function(elem) {"
	"setTimeout(function(){elem.onload = null;"
	// Set srcset before src to avoid potentially loading 2 sizes.
	"var srcset = elem.getAttribute('data-pagespeed-high-res-srcset');"
	"if (srcset) {elem.srcset = srcset;}"
	"elem.src = elem.getAttribute('data-pagespeed-high-res-src');"
	"if (pagespeed.CriticalImages) {elem.onload = "
	"pagespeed.CriticalImages.checkImageForCriticality(elem);}"
	"}, 0);"
	"};";

	DelayImagesFilter::DelayImagesFilter(RewriteDriver* driver)
	: CommonFilter(driver),
	num_low_res_inlined_images_(0),
	insert_low_res_images_inplace_(false),
	lazyload_highres_images_(false),
	is_script_inserted_(false),
	added_image_onload_js_(false) {
	}

	DelayImagesFilter::~DelayImagesFilter() {}

	void DelayImagesFilter::StartDocumentImpl() {
	num_low_res_inlined_images_ = 0;
	// Low res images will be placed inside the respective image tag if the user
	// agent is not a mobile, or if mobile aggressive rewriters are turned off.
	// Otherwise, the low res images are inserted at the end of the flush window.
	insert_low_res_images_inplace_ = ShouldRewriteInplace();
	lazyload_highres_images_ = driver()->options()->lazyload_highres_images() &&
	driver()->request_properties()->IsMobile();
	is_script_inserted_ = false;
	added_image_onload_js_ = false;
	}

	void DelayImagesFilter::MaybeAddImageOnloadJsSnippet(HtmlElement* element) {
	if (added_image_onload_js_) {
	return;
	}
	added_image_onload_js_ = true;
	HtmlElement* script = driver()->NewElement(NULL, HtmlName::kScript);
	driver()->AddAttribute(script, HtmlName::kDataPagespeedNoDefer, NULL);
	// Always add the image-onload js before the current node, because the
	// current node might be an img node that needs the image-onload js for
	// setting its onload handler.
	driver()->InsertNodeBeforeNode(element, script);
	AddJsToElement(kImageOnloadJsSnippet, script);
	}

	void DelayImagesFilter::EndDocument() {
	low_res_data_map_.clear();
	}

	void DelayImagesFilter::EndElementImpl(HtmlElement* element) {
	if (element->keyword() == HtmlName::kBody) {
	InsertLowResImagesAndJs(element, /* insert_after_element */ false);
	InsertHighResJs(element);
	} else if (driver()->IsRewritable(element) &&
	(element->keyword() == HtmlName::kImg \|\|
	element->keyword() == HtmlName::kInput)) {
	// We only handle img and input tag images. Note that delay_images.js and
	// delay_images_inline.js must be modified to handle other possible tags.
	// We should probably specifically not include low res images for link
	// tags of various sorts (favicons, mobile desktop icons, etc.). Use of low
	// res for explicit background images is a more interesting case, but the
	// current DOM walk in the above js files would need to be modified to
	// handle the large number of tags that we can identify in
	// resource_tag_scanner::ScanElement.
	HtmlElement::Attribute* low_res_src =
	element->FindAttribute(HtmlName::kDataPagespeedLowResSrc);
	if (low_res_src == NULL \|\| low_res_src->DecodedValueOrNull() == NULL) {
	return;
	}
	HtmlElement::Attribute* src = element->FindAttribute(HtmlName::kSrc);
	semantic_type::Category category =
	resource_tag_scanner::CategorizeAttribute(
	element, src, driver()->options());
	if (category != semantic_type::kImage \|\|
	src->DecodedValueOrNull() == NULL) {
	return; // Failed to find valid Image-valued src attribute.
	}
	++num_low_res_inlined_images_;
	if (CanAddPagespeedOnloadToImage(*element)) {
	driver()->log_record()->SetRewriterLoggingStatus(
	RewriteOptions::FilterId(RewriteOptions::kDelayImages),
	RewriterApplication::APPLIED_OK);
	// Rename src -> data-pagespeed-high-res-src
	driver()->SetAttributeName(src, HtmlName::kDataPagespeedHighResSrc);
	// Rename srcset -> data-pagespeed-high-res-srcset
	HtmlElement::Attribute* srcset =
	element->FindAttribute(HtmlName::kSrcset);
	if (srcset != NULL) {
	driver()->SetAttributeName(
	srcset, HtmlName::kDataPagespeedHighResSrcset);
	}
	if (insert_low_res_images_inplace_) {
	// Set the src as the low resolution image.
	driver()->AddAttribute(element, HtmlName::kSrc,
	low_res_src->DecodedValueOrNull());
	// Add an onload function to set the high resolution image after
	// deleting any existing onload handler. Since we check
	// CanAddPagespeedOnloadToImage before coming here, the only onload
	// handler that we would delete would be the one added by our very own
	// beaconing code. We re-introduce this beaconing onload logic via
	// kImageOnloadCode.
	element->DeleteAttribute(HtmlName::kOnload);
	driver()->AddAttribute(element, HtmlName::kOnload, kImageOnloadCode);
	// Add onerror handler just in case the low res image doesn't load.
	element->DeleteAttribute(HtmlName::kOnerror);
	// Note: this.onerror=null to avoid infinitely repeating on failure:
	// See: http://stackoverflow.com/questions/3984287
	driver()->AddAttribute(element, HtmlName::kOnerror,
	StrCat("this.onerror=null;", kImageOnloadCode));
	MaybeAddImageOnloadJsSnippet(element);
	} else {
	// Low res image data is collected in low_res_data_map_ map. This
	// low_res_src will be moved just after last low res image in the flush
	// window.
	// It is better to move inlined low resolution data later in the DOM,
	// otherwise they will block further parsing and rendering of the html
	// page.
	// Note that the high resolution images are loaded at end of body.
	const GoogleString& src_content = src->DecodedValueOrNull();
	low_res_data_map_[src_content] = low_res_src->DecodedValueOrNull();
	}
	}
	if (num_low_res_inlined_images_ == driver()->num_inline_preview_images()) {
	if (!insert_low_res_images_inplace_) {
	InsertLowResImagesAndJs(element, /* insert_after_element */ true);
	}
	}
	}
	element->DeleteAttribute(HtmlName::kDataPagespeedLowResSrc);
	}

	void DelayImagesFilter::InsertLowResImagesAndJs(HtmlElement* element,
	bool insert_after_element) {
	if (low_res_data_map_.empty()) {
	return;
	}
	GoogleString inline_script;
	HtmlElement* current_element = element;
	// Check script for changing src to low res data url is inserted once.
	if (!is_script_inserted_) {
	StaticAssetManager* manager =
	driver()->server_context()->static_asset_manager();
	inline_script = StrCat(
	manager->GetAsset(
	StaticAssetEnum::DELAY_IMAGES_INLINE_JS,
	driver()->options()),
	kDelayImagesInlineSuffix,
	manager->GetAsset(
	StaticAssetEnum::DELAY_IMAGES_JS,
	driver()->options()),
	kDelayImagesSuffix);
	HtmlElement* script_element =
	driver()->NewElement(element, HtmlName::kScript);
	driver()->AddAttribute(
	script_element, HtmlName::kDataPagespeedNoDefer, NULL);
	if (insert_after_element) {
	DCHECK(element->keyword() == HtmlName::kImg \|\|
	element->keyword() == HtmlName::kInput);
	driver()->InsertNodeAfterNode(current_element, script_element);
	current_element = script_element;
	} else {
	DCHECK(element->keyword() == HtmlName::kBody);
	driver()->AppendChild(element, script_element);
	}
	AddJsToElement(inline_script, script_element);
	is_script_inserted_ = true;
	}

	// Generate javascript map for inline data urls where key is url and
	// base64 encoded data url as its value. This map is added to the
	// html at the end of last low res image.
	GoogleString inline_data_script;
	for (StringStringMap::iterator it = low_res_data_map_.begin();
	it != low_res_data_map_.end(); ++it) {
	inline_data_script = StrCat(
	"\npagespeed.delayImagesInline.addLowResImages('",
	it->first, "', '", it->second, "');");
	StrAppend(&inline_data_script,
	"\npagespeed.delayImagesInline.replaceWithLowRes();\n");
	HtmlElement* low_res_element =
	driver()->NewElement(current_element, HtmlName::kScript);
	driver()->AddAttribute(
	low_res_element, HtmlName::kDataPagespeedNoDefer, NULL);
	if (insert_after_element) {
	driver()->InsertNodeAfterNode(current_element, low_res_element);
	current_element = low_res_element;
	} else {
	driver()->AppendChild(element, low_res_element);
	}
	AddJsToElement(inline_data_script, low_res_element);
	}
	low_res_data_map_.clear();
	}

	void DelayImagesFilter::InsertHighResJs(HtmlElement* body_element) {
	if (insert_low_res_images_inplace_ \|\| !is_script_inserted_) {
	return;
	}
	GoogleString js;
	if (lazyload_highres_images_) {
	StrAppend(&js,
	"\npagespeed.delayImages.registerLazyLoadHighRes();\n");
	} else {
	StrAppend(&js,
	"\npagespeed.delayImages.replaceWithHighRes();\n");
	}
	HtmlElement* script = driver()->NewElement(body_element, HtmlName::kScript);
	driver()->AddAttribute(script, HtmlName::kDataPagespeedNoDefer, NULL);
	driver()->AppendChild(body_element, script);
	AddJsToElement(js, script);
	}

	bool DelayImagesFilter::ShouldRewriteInplace() const {
	const RewriteOptions* options = driver()->options();
	return (options->use_blank_image_for_inline_preview() \|\|
	!(options->enable_aggressive_rewriters_for_mobile() &&
	driver()->request_properties()->IsMobile()));
	}

	void DelayImagesFilter::DetermineEnabled(GoogleString* disabled_reason) {
	AbstractLogRecord* log_record = driver()->log_record();
	if (!driver()->request_properties()->SupportsImageInlining()) {
	log_record->LogRewriterHtmlStatus(
	RewriteOptions::FilterId(RewriteOptions::kDelayImages),
	RewriterHtmlApplication::USER_AGENT_NOT_SUPPORTED);
	set_is_enabled(false);
	return;
	}
	CriticalImagesFinder* finder =
	driver()->server_context()->critical_images_finder();
	if ((finder->Available(driver()) == CriticalImagesFinder::kNoDataYet) &&
	!driver()->options()->Enabled(RewriteOptions::kSplitHtmlHelper)) {
	log_record->LogRewriterHtmlStatus(
	RewriteOptions::FilterId(RewriteOptions::kDelayImages),
	RewriterHtmlApplication::PROPERTY_CACHE_MISS);
	set_is_enabled(false);
	return;
	}
	log_record->LogRewriterHtmlStatus(
	RewriteOptions::FilterId(RewriteOptions::kDelayImages),
	RewriterHtmlApplication::ACTIVE);
	set_is_enabled(true);
	}

	} // namespace net_instaweb