Patent Publication Number: US-11647096-B2

Title: Method and apparatus for automatically optimizing the loading of images in a cloud-based proxy service

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of application Ser. No. 16/357,766, filed Mar. 19, 2019, which is a continuation of application Ser. No. 14/818,277, filed Aug. 4, 2015, now U.S. Pat. No. 10,237,365, which is a continuation of application Ser. No. 13/894,839, filed May 15, 2013, now U.S. Pat. No. 9,098,477, which is hereby incorporated by reference. 
    
    
     FIELD 
     Embodiments of the invention relate to the field of network communication; and more specifically, to automatically optimizing the loading of images in a cloud-based proxy service. 
     BACKGROUND 
     Images can be more than half of the data that makes up a typical website. Although there are tools that may automatically reduce the size of the images on behalf of the website owner, many of the images may not be needed for the page as they may never be seen by the user. For example, some pages are longer than the viewport of the device (a window or other viewable area on the screen) and require the user to scroll to view the entire page. An example of such a page is a blog, which typically is a relatively long page with a series of stories, the most recent of which are on top. When the page is loaded, only the images within the viewport (the visible portion of the client window) can be viewed. However, most client network application such as browsers download all of the images on the page before the page is ready. This may slow down page performance and waste bandwidth for images that may never be seen (e.g., if the user does not scroll down to actually view the images that are not on the viewport). 
     Most client network applications create an image placeholder for each single image that is referenced in a web page. Most images are externally sourced and downloaded by the client network application and are displayed in the location of the corresponding image placeholders. If an image cannot be displayed (e.g., an error occurred when the image was attempted to be downloaded), most client network applications display a broken image or other error display in the location of the corresponding image placeholder. 
     Image loading by itself does not block client-side scripts (e.g., JavaScript) from executing. However, image loading may block the firing of the ‘onload’ event. An ‘onload’ event is typically used within the &lt;body&gt; element of a page and executes a client-side script once a web page has completely loaded all the content including images, script files, style files, etc. One slow image loading can delay the ‘onload’ event long enough to create user-visible lag in web page rendering. 
     One technique for responsive image loading includes ‘capturing’ the Document Object Model (DOM). In this technique, document.write is used in the Head tag of the page to encapsulate all of the subsequent HTML in a Plaintext node. Then the rest of the DOM is parsed as text and feed back to component modules that manipulate it. For example, a component module may convert all image ‘src’ attributes to a desired value based on the detected properties of the client browser. The manipulated DOM is then passed back to document.write and a fresh document is created from it. Although this technique provides website authors much more control over the way a page is parsed, it essentially co-opts parsing of the DOM from the browser and re-implements it in JavaScript. This can result in unexpected (or even negative) behavioral and performance-related side-effects. It also creates additional execution overhead and it occurs on the browser&#39;s user interface (UI) thread. This technique also creates difficulty in examining and debugging because one must consider the implementation of ‘capturing’ the DOM as well as the considering the underlying browser. 
     SUMMARY 
     A method and apparatus for automatically optimizing the loading of images in a cloud-based proxy service is described. In one embodiment, a request is received at a proxy server for a web page, the request originating from a client network application of a client device. The requested web page includes multiple references to multiple images. The proxy server retrieves the requested web page. The proxy server modifies code of the retrieved page such that the client network application will not, for each of the images, initially request those images when parsing the page, and adds code to the retrieved page that, when executed by the client network application, causes at least two of the images to be requested with a single request. The proxy server transmits the modified web page to the client device. The client device receives the modified web page and executes the code that causes a single request for the at least two images to be transmitted. In one embodiment, two or more images are requested by the client in a single request and returned to the client in a degraded form (a form that is a smaller file size than the original file size). The full quality counterparts of the images may be subsequently requested. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may best be understood by referring to the following description and accompanying drawings that are used to illustrate embodiments of the invention. In the drawings: 
         FIG.  1    illustrates an exemplary system for a cloud-based proxy service according to one embodiment; 
         FIG.  2    is a flow diagram that illustrates exemplary operations performed on a proxy server for deferred image loading according to one embodiment; 
         FIG.  3    is a flow diagram that illustrates exemplary operations for modifying a page such that the client network application will not (at least initially) load at least certain images of the page according to one embodiment; 
         FIG.  4    is a flow diagram that illustrates exemplary operations performed by one or more client-side scripts for deferred loading of images according to one embodiment; 
         FIG.  5    is a flow diagram that illustrates exemplary operations that are performed by the set of client-side scripts when causing the client network application to request the image according to one embodiment; 
         FIG.  6 A  illustrate an example of one embodiment of deferred image loading; 
         FIG.  6 B  illustrates the continuation of the example illustrated in  FIG.  6 A ; 
         FIG.  7    is a flow diagram that illustrates exemplary operations performed on a proxy server for auto-resizing of images according to one embodiment; 
         FIG.  8    is a flow diagram that illustrates exemplary operations performed on a client device for causing image(s) referenced in a web page to be requested by the client network application with a set of one or more dimensions according to one embodiment; 
         FIG.  9    is a flow diagram that illustrates exemplary operations performed by a set of one or more client-side scripts for determining the display size of the image according to one embodiment; 
         FIG.  10    is a flow diagram illustrating exemplary operations performed by a proxy server for performing auto-resizing of images according to one embodiment; 
         FIG.  11    is an exemplary interface for the control servers that allows a customer to enable or disable the deferred image loading and/or image auto-resizing functionality described herein, according to one embodiment; and 
         FIG.  12    illustrates an exemplary format for an image tag included in a page prior to the proxy server neutralizing the image tag; 
         FIG.  13    illustrates the neutralized version of the image tag of  FIG.  12    according to one embodiment; 
         FIG.  14    illustrates a single URL that may be created by the image manager for requesting multiple images in a single request according to one embodiment; 
         FIG.  15    illustrates an exemplary format for bulk image responses according to one embodiment; 
         FIG.  16    illustrates an exemplary implementation of image request reduction according to one embodiment; 
         FIG.  17    is a flow diagram that illustrates exemplary operations for optimizing image loading according to one embodiment; and 
         FIG.  18    illustrates an exemplary format of a computer system of devices of the cloud-based proxy service according to one embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     In the following description, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known circuits, structures and techniques have not been shown in detail in order not to obscure the understanding of this description. Those of ordinary skill in the art, with the included descriptions, will be able to implement appropriate functionality without undue experimentation. 
     References in the specification to “one embodiment,” “an embodiment,” “an example embodiment,” etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. In the following description and claims, the terms “coupled” along with its derivatives, may be used. “Coupled” is used to indicate that two or more elements, which may or may not be in direct physical or electrical contact with each other, co-operate or interact with each other. 
     A method and apparatus for automatically optimizing the loading of images is described. In one embodiment, the loading of the images is automatically managed in a cloud-based proxy service that includes one or more proxy servers that are situated between the end users (e.g., users using a browser or other client network application to access network content) and origin server(s) that host the network content. In the cloud-based proxy service, requests for network resources (e.g., web pages such as HTML documents, images, word processing documents, PDF files, movie files, music files, or other computer files) are received at a proxy server of the cloud-based proxy service. The proxy server may modify the requested resource prior to transmitting a response to the requesting client (if the network resource is not stored in a locally available cache, the proxy server may transmit a request to the appropriate origin server for the network resource). As will be described in greater detail later herein, the proxy server may cause the loading of images in a page to be optimized. In one embodiment, the cloud-based proxy service is available as a service over the Internet and does not require customers (e.g., domain owners and/or personnel working on behalf of domain owners) to install additional hardware or software in order to support the service. In one embodiment, the cloud-based proxy service is provisioned through a change in Domain Name System (DNS) records of the customers. 
     The proxy server is configured to automatically cause image loading to be optimized for a client device. Optimized image loading may include one or more of the following: prioritizing the loading of image(s) whose corresponding image placeholder(s) are in the viewport and optionally in close proximity to the viewport over those image(s) whose corresponding image placeholder(s) are not in the viewport and/or not in close proximity to the viewport (sometimes referred herein as deferred image loading), automatically resizing image(s) to a size appropriate for how they are set as being displayed and/or the size of the viewport of the requesting device (sometimes referred herein as image auto-resizing), reducing the number of requests for images of the page (sometimes referred herein has image request reduction), and progressive enhancement image loading where degraded versions of images precede their full quality counterparts (sometimes referred herein as progressive enhancement). In one embodiment, which one or more optimizations that are applied to a page depends on the type of client network application and/or whether the client is connecting over a mobile operator&#39;s network (where bandwidth is typically limited and latency may be high) versus connecting over a wired or WiFi network (where bandwidth and latency are less of a concern). 
     Deferred image loading priorities the loading of images whose corresponding image placeholders are in the viewport (or in some embodiments in close proximity to the viewport) over images whose corresponding image placeholders are not in the viewport and/or not in close proximity to the viewport. The other image(s) whose corresponding placeholder(s) of the page that are not in the viewport may be loaded as they are needed (e.g., when they become in the viewport) or as there are spare network resources available. 
     As an example of image auto-resizing, if an image that is 1000 pixels by 1000 pixels is set to be displayed at 100 pixels by 100 pixels, the image may be automatically resized and delivered to the visitors at the appropriate size (e.g., 100 pixels by 100 pixels). As another example, if the size of the viewport of a device is 960 by 640 pixels (which is a common size for mobile devices), a background image that is 2000 pixels wide will be automatically downsized so that more pixels are not delivered to the visitor than can be displayed. 
     As described above, one image loading optimization is reducing the number of requests for images of the page. In one embodiment, the number of requests is reduced by grouping multiple, different requests for images, into a single request (known herein as a bulk request) (e.g., a single HTTP request). For example, the image manager (executed by the client network application) may create a single canonical URL that represents multiple images of the page that are to be sent back into a response. This single URL may be created by combining the individual URLs for all images into a single string and appending them to the query parameters of the single request (typically in URL-encoding). In some embodiments a single request includes all images for the page. In other embodiments, there may be multiple requests for images of the page each of which itself includes requests for multiple images. 
     In one embodiment, the management of images may be different depending on the connection of the client. For example, the management of images may be different for visitors connecting over a mobile operator&#39;s network (where bandwidth is typically limited and latency may be high) versus visitors connecting over a wired or WiFi network (where bandwidth and latency are less of a concern). By way of example, in one embodiment, if a visitor is connecting over a mobile operator&#39;s network (e.g., 2G, 3G, 4G), only the images that are in the viewport will be delivered to the visitors; whereas if a visitor is connecting over a wired or WiFi network, the images in the viewport will be prioritized and the other images will be loaded in the background (which may be prioritized based on where they appear in the page). 
     In one embodiment, the image loading optimizations described herein (deferred image loading, auto-resizing, image request reduction, and/or progressive enhancement) are provided through the cloud-based proxy service that is available on the Internet as a service and does not require customers to install additional hardware or software in order for the image optimizations to be performed. In addition, the image loading optimizations can be performed automatically without requiring the user to change any of their HTML. 
       FIG.  1    illustrates an exemplary system for a cloud-based proxy service according to one embodiment. The cloud-based proxy service illustrated in  FIG.  1    includes a set of proxy server(s)  120  that are situated between the client computing devices  110 A-I and the origin servers  130 A-N. In one embodiment, the proxy server(s)  120  are reverse proxy servers. Certain network traffic is received and processed through the set of proxy server(s)  120 . For example, web traffic (e.g., HTTP requests/responses, HTTPS requests/responses, etc.) for domains of the origin servers  130 A-N may be received and processed at the proxy server(s)  120 . In one embodiment, the domain owners  135 A-L are customers of the cloud-based proxy service and certain network traffic for their websites are received at processed at the proxy server(s)  120 . 
     The client devices  110 A-I are computing devices (e.g., laptops, workstations, smartphones, palm tops, mobile phones, tablets, gaming systems, set top boxes, etc.) that are capable of transmitting and receiving network traffic. Each of the client devices  110 A-I executes a client network application that is capable of transmitting network traffic and loading network traffic. For example, the client network application may be a web browser or other application that can access network resources (e.g., web pages, images, word processing documents, PDF files, movie files, music files, or other computer files). 
     The origin servers  130 A-N are computing devices that serve network resources (e.g., web pages, images, word processing documents, PDF files movie files, music files, or other computer files). Although not illustrated in  FIG.  1   , it should be understood that the network resources of the origin servers  130 A-N may be stored separately from the device that responds to the requests. 
     The cloud-based proxy service may provide different services for customers (e.g., the domain owners  135 A-L). By way of example, the cloud-based proxy service may provide services including protecting against Internet-based threats (e.g., proactively stopping botnets, cleaning viruses, trojans, and worms, etc.), providing performance services for customers (e.g., acting as a node in a content delivery network (CDN) and dynamically caching customer&#39;s files closer to visitors, page acceleration, content optimization services, etc.), and/or other services. In one embodiment and as described in greater detail later herein, the cloud-based proxy service also provides image loading optimization (e.g., deferred image loading, auto-resizing, image request reduction, and/or progressive enhancement) for the domain owners  135 A-L. 
     Generally speaking, the proxy server(s)  120  receive certain network traffic from the client devices  110 A-I that are destined for one of the origin servers  130 A-N. For example, a proxy server  120  may receive requests for an action to be performed on an identified resource of an origin server (e.g., an HTTP GET request, an HTTP POST request, other HTTP request methods, or other requests to be applied to an identified resource on an origin server) from the client devices  110 A-I. As illustrated in  FIG.  1   , the incoming traffic  154  is received at one of the proxy server(s)  120 . 
     The proxy server(s)  120  analyze the incoming traffic  154  and take one or more actions on the incoming traffic. In some embodiments, the incoming traffic  154  is received at a particular proxy server  120  as a result of a DNS request  150  for a domain of one of the domain owners  135 A-L resolving  152  to an IP address of the proxy server  120 . By way of example, DNS record(s) for the domain “example.com” may resolve to an IP address of a proxy server  120 . In some embodiments, multiple domains that may be owned by different domain owners may resolve to the same proxy server  120  (e.g., the same IP address or a different IP address of the proxy server  120 ). 
     By way of a specific example, the incoming traffic  154  may be a request for a web page which includes a set of one or more images. A proxy server  120  that receives a request for a page determines whether deferred image loading, auto-resizing, image request reduction, and/or progressive enhancement is enabled for that web page. The proxy server  120  may retrieve the requested page from its cache if available and it has not expired. Alternatively, the proxy server  120  may issue a request to the appropriate origin server  130  for the page (part of the outgoing traffic  156 ). The proxy server  120  receives incoming traffic  158  from the origin server (e.g., an HTTP response with the requested content). 
     After retrieving the requested page and after determining that image loading optimization (e.g., deferred image loading, auto-resizing, image request reduction, and/or progressive enhancement) is enabled for that page, the proxy server  120  modifies the retrieved page to cause the loading of the images to be deferred, cause the size of the images that are loaded to be optimized for the page and device, cause the number of requests for the images to be reduced, and/or cause degraded versions of images to precede their full quality counterparts. The proxy server(s)  120  transmit responses to the client devices  110 A-I in the outgoing traffic  159 . 
     The DNS system  140  is used to refer to the DNS system as a whole and includes multiple DNS servers to resolve DNS requests. As illustrated, the DNS system  140  includes the authoritative name server  142 , which may be an authoritative name server for the cloud-based proxy service and the domains hosted at the origin servers  130 A-N. It should be understood that the DNS system  140  may include more DNS servers (e.g., preferred domain servers, top-level domain name servers, or other domain servers) than illustrated. It should also be understood that there may be multiple authoritative web servers for the service and they may be geographically distributed. In one embodiment, the authoritative name servers for each the domains have been changed to the authoritative name server  142 , which is associated with the service. It should be understood that the backup authoritative name servers serving the domains may also be changed. In one embodiment, the zone file records  144  for the domains of the domain owners  135 A-L are changed such that DNS resolution requests for those domains resolve to the proxy server(s)  120 . 
     Although not illustrated in  FIG.  1   , in one embodiment the cloud-based proxy service includes multiple nodes (referred herein as “proxy service nodes”). Each proxy service node may include any of one or more proxy servers, one or more control servers, one or more DNS servers (e.g., one or more authoritative name servers), and one or more other pieces of networking equipment (e.g., one or more routers, switches, hubs, etc.). The proxy service node may be part of the same physical device or multiple physical devices. For example, the proxy server(s), control server(s), and DNS server(s) may be virtual instances running on the same physical device or may be separate physical devices. Each proxy service node may be part of a data center or a collocation site. 
     The cloud-based proxy service also includes the control server(s)  125  which are operated by the service. In one embodiment, the control server(s)  125  provide a set of tools and interfaces for the domain owners  135 A-L and is accessible over the Internet. For example, the control server(s)  125 , among other things, allow the customers  135 A-L to register for the cloud-based proxy service and configure  182  the image loading settings. In some embodiments, the domain owners  135 A-L register for the cloud-based proxy service including changing their authoritative name server(s) to authoritative name server(s) of the service (the service may specify to the domain owners the name server(s) to use). Although not illustrated, the control server(s)  125  may provide an interface (e.g., a website) for the domain owners  135 A-L to register for the cloud-based proxy service and possibly change their authoritative name server(s) and DNS record(s). In addition, the IP address(es) that resolve to their origin server(s), which host content of their domain, are changed to point to a proxy server  120 , which are typically chosen by the service. In other embodiments, individual DNS records are changed to point to a proxy server  120  (or point to other domain(s) that point to a proxy server of the service). For example, a DNS record of a domain owner can be changed to point to a CNAME that corresponds with a proxy server  120 . The control server(s)  125  may transmit a DNS update  185  to the DNS system  140  to change the DNS record(s) of a domain owner. Regardless of the embodiment, traffic from visitors that are directed to a customer&#39;s domain is received at one of the proxy server(s)  120 . 
     Upon configuring image loading for their domain (e.g., deferred image loading and/or image automatic resizing), the control server  125  transmits the appropriate setting  183  to the proxy server(s)  120 . This setting may be stored in the proxy server(s)  120  and accessed when receiving a request for a page of their domain. 
     After a page is retrieved, the proxy server  120  modifies the page for automatically optimizing image loading. In a specific example, the proxy server  120  parses the retrieved page and analyzes its image tags, and modifies the image tags such that the image will not be displayed and the client network application will not request the image. This is sometimes referred herein as neutralizing the image tag. In one embodiment, the image objects remain in the Document Object Model (DOM) (that is, they are not removed from the DOM). For example, the proxy server  120  changes the src attribute (which specifies the location of the image—often a URL) such that the client network application will not issue a request for the image, while maintaining the information specifying the location of the image. For example, the proxy server  120  may modify the name of the src attribute to a value that is unrecognized by the client network application. By way of example, the proxy server  120  may prepend “data-cf” to the “src” attribute in the HTML (e.g., modify “src” to “data-cfsrc”) of the retrieved page. This causes the client network application to not make a request for that image as it does not recognize “data-cfsrc”. Of course this is just an example and there are other ways to prevent the client network application from making the request for the image. 
     If the image tag has a style attribute, then the proxy server  120  changes the style attribute such that the client network application will not apply the style while still maintaining the information of the style (e.g., that style will be reapplied when the image is ready to be loaded). For example, the proxy server  120  may modify the name of the style attribute to a value that is unrecognized by the client network application. For example, the proxy server  120  may prepend “data-cf” to the “style” attribute in the HTML (e.g., modify “style” to “data-cfstyle”). This causes the client network application to not apply the style. Of course this is just an example and there may be other ways to prevent the client network application from applying the style. 
     The proxy server  120  also causes the image and/or the image placeholder to not be displayed while maintaining an image object in the DOM. In one embodiment, the proxy server  120  adds a style attribute to the image tag that causes the client network application to not display the image placeholder. For example, the proxy server  120  may add a style with the following value: style=“display:none;”. As another example, the proxy server  120  may add a style with the following value: style=“visibility:hidden;”. As another example, the proxy server  120  may add a style with the following value: style=“display:none;visibility:hidden;”. For purposes of explanation, the added style attribute is sometimes referred herein as the “null style attribute.” In another embodiment, the proxy server  120  may cause a different image to be initially loaded by the client network application. This different image may not be visible to the user (e.g., the image may be a transparent image that the client network application renders in the background color where the image is to be placed). The different image may be of a small size (e.g., 1 by 1 pixels), which may be stretched according to the height and/or width of the original image. By way of example, the proxy server  120  may add a source attribute to the image tag that specifies the location of the different image, and may further have the width and/or height set the same as the original image. The proxy server  120  may alternatively add a source attribute to the image tag that embeds the image data inline into the html (e.g., add the image as a data Uniform Resource Identifier (URI) object), and may further set the width and/or height to be the same as the original image. 
     In some embodiments, the proxy server  120  inserts a set of one or more client-side scripts (e.g., JavaScript) and/or reference(s) to a set of one or more client-side scripts that, when executed by the client network application, restore the source attribute (and style attribute if one was originally included) for the image, when the corresponding image placeholder is located in the viewport or with a defined distance to the viewport. Since some client network applications may not be capable of executing client-side scripts or have disabled client-side scripts, the proxy server  120  may wrap the original image tag in a noscript tag. In this way, if the client network application does not support client-side scripts or has disabled execution of client-side scripts, the images will be loaded as they would normally. 
       FIG.  12    illustrates an exemplary format for an image tag included in a page prior to the proxy server  120  neutralizing the image tag.  FIG.  13    illustrates the neutralized version of the image tag of  FIG.  12    according to one embodiment. As illustrated in  FIG.  13   , the “src” attribute has been modified to “data-cfsrc”, the “style” attribute has been modified to “data-cfstyle”; a new style has been added with the value: style=“display:none;visibility:hidden;”, and the original image tag is wrapped in a noscript tag. 
     In one embodiment, the proxy server  120  causes the optimized image loading to be performed on only those images that belong to the same domain as the requested page. For example, if the page is example.com; in this embodiment the proxy server  120  causes the loading of images to be optimized only on images of example.com (e.g., example.com/image.gif); not other domains (e.g., images of the domain example2.com). In another embodiment, the proxy server  120  causes the optimized image loading to be performed only on those images that are located on domains that are customers of the cloud-based proxy service. For example, if the image source is a third party source that is not on a domain that is a customer of the cloud-based proxy service, then in one embodiment the proxy server  120  does not neutralize that image tag for image loading optimization. In other embodiments, all images are subject to image loading optimization. 
     In one embodiment, the proxy server  120  adds code to the web page that, when executed by the client network application, selects the appropriate image loading optimization(s), initiates those selected image loading optimization(s), and participates in the execution of those selected image loading optimization(s). For example, the added code may be one or more client-side scripts and/or a reference to one or more client-side scripts that. This code (these client-side script(s)) will sometimes be referred herein as the image manager 
     Deferred Loading of Images 
     In one embodiment, if deferred image loading is enabled for the requested network resource (or enabled for the domain of the requested network resource), the proxy server  120  modifies the page such that the loading of the image(s) whose corresponding image placeholder(s) are in the viewport and optionally in close proximity to the viewport will be prioritized over those image(s) whose corresponding image placeholder(s) are not in the viewport and/or not in close proximity to the viewport. The proxy server  120  may also modify the page such that the other image(s) of the page whose corresponding image placeholder(s) that are not in the viewport may be loaded as they are needed (e.g., when they are scrolled into the viewport) or as there are spare network resources available. 
     As previously described, in one embodiment, the proxy server  120  adds one or more client-side scripts and/or a reference to one or more client-side scripts that, when executed by the client network application, prioritizes the loading of the image(s) whose corresponding image placeholder(s) are in the viewport of the client network application or within a defined distance of the viewport over the image(s) whose corresponding image placeholder(s) are not in the viewport (if any). In one embodiment, the client-side script(s) attempts to determine the size of the viewport, the type of client device (this may help determine the size of the screen of the device), the type of network connection (e.g., over a mobile operator&#39;s network (where bandwidth is typically limited and latency may be high), over a wired or WiFi network (where bandwidth and latency are typically less of a concern)), and/or the location in the page where the images would be displayed with respect to the viewport. 
     In one embodiment, when the client side script determines that the location where the image is to be displayed is in the viewport or is within a threshold distance amount from the viewport (e.g., is less than X number of pixels from the viewport), the client-side script performs a number of actions to cause the client network application to request and display the image. For example, the client-side script rewrites the source attribute to cause the client network application to make a request for the image (e.g., by removing “data-cf” from “data-cfsrc”). If a style attribute for the image was originally included in the HTML (and modified by the proxy server  120 ), the client-side script rewrites the style attribute according to the original style attribute (e.g., by removing “data-cf” from “data-cfstyle”). The client-side script also removes the null style attribute, which causes the image (if retrieved) to be displayed. 
     In one embodiment, if the client is connecting through a mobile connection (through a mobile operator&#39;s network where bandwidth is typically limited and latency may be high), the client-side script causes only the image(s) whose corresponding image placeholder(s) are in the viewport or that are within a certain distance from the viewport to be loaded; whereas if the client is not connecting through a mobile connection (e.g., a wired network, WiFi, etc.), the image(s) whose corresponding image placeholder(s) are in the viewport and/or within a certain distance from the viewport are prioritized and the other images are loaded in the background (which may be prioritized based on where they appear in the page). 
       FIG.  2    is a flow diagram that illustrates exemplary operations performed on a proxy server for deferred image loading according to one embodiment. The operations of this and other flow diagrams will be described with reference to the exemplary embodiments of  FIG.  1   . However, it should be understood that the operations of the flow diagrams can be performed by embodiments of the invention other than those discussed with reference to  FIG.  1   , and the embodiments of the invention discussed with reference to  FIG.  1    can perform operations different than those discussed with reference to the flow diagrams. 
     At operation  210 , a proxy server  120  receives a request for a page (e.g., an HTML page) that originates from a client network application of a client device. The request may be received as a result of a DNS request for the domain of the page resolving to an IP address of the proxy server  120 . Next, at operation  215 , the proxy server  120  determines that deferred image loading is enabled for the requested page. In one embodiment, the proxy server  120  accesses a set of one or more page rules for the domain of the requested page to determine whether deferred image loading has been enabled. Enabling deferred image loading will be described in greater detail later herein. In some embodiments the operation of  215  is optional (e.g., the deferred image loading is applied to every page). Flow then moves to operation  220 . 
     At operation  220 , the proxy server  120  retrieves the requested page. If the requested page is available in the proxy server&#39;s cache and it has not expired, the proxy server  120  may retrieve the requested page from its cache. The proxy server  120  may also retrieve the requested page from the origin server (e.g., transmit a request to the origin server for the page and receive a response from the origin server that includes the page). Flow then moves to operation  225 . 
     At operation  225 , the proxy server  120  modifies the page to prioritize the loading of the images of the page whose corresponding image placeholders are in the viewport or within a defined distance to the viewport. The defined distance to the viewport is a value that is small enough such that the visitor may scroll the viewport to view that image. For example, the defined distance may be within 100 pixels of the viewport. The defined distance may be predefined in one embodiment (e.g., hard coded in the code of the page) or determined based on the size of the viewport of the client network application. 
     As an example of modifying the page, the proxy server  120  may modify the image tags such that they will not (at least initially) be requested by the client network application. In addition, the proxy server  120  may also add one or more client-side scripts (e.g., JavaScript) and/or references to one or more client-side scripts that, when executed by the client network application, cause the images to be loaded when the corresponding image placeholders are located within the viewport of the client network application or within a defined threshold distance from the viewport (e.g., within 100 pixels from the viewport). 
     Flow then moves to operation  230  where the proxy server  120  transmits the modified page to the requesting client device. The proxy server  120  may also store the modified page in its cache such that upon receiving a subsequent request for the page (from the same client device or from a different client device), the proxy server  120  may transmit the modified page to the requesting client device without having to modify the page again. 
       FIG.  3    is a flow diagram that illustrates exemplary operations for modifying a page such that the client network application will not (at least initially) load at least certain images of the page according to one embodiment. At operation  310 , the proxy server  120  begins to parse the page in an attempt to locate the image tags in the page (e.g., “&lt;img . . . /&gt;”). If an image tag is detected at operation  315 , then flow moves to operation  320 , otherwise flow moves to operation  350  where the operations of  FIG.  3    end. 
     At operation  320 , if the parser detects that there is a style attribute within the image tag, then flow moves to operation  325 ; otherwise flow moves to operation  330 . At operation  325 , the style attribute is modified to cause the client network application (e.g., the browser) to not apply the style, while maintaining the value of the style. The value of the style is maintained so that it can be reapplied when/if the image is to be loaded. For example, the proxy server  120  may prepend “data-cf” to the “style” attribute in the HTML (e.g., modify “style” to “data-cfstyle”), which causes the client network application to not apply the style. Flow moves from operation  325  to operation  330 . 
     At operation  330 , a style attribute is added to the image tag to cause the client network application not to display the image placeholder. For example, “style=“display:none;visibility:hidden;” may be added to the image tag to cause the client network application not to display the image placeholder. As another example, the proxy server  120  may add a style with the following value: style=“display:none;”. As another example, the proxy server  120  may add a style with the following value: style=“visibility:hidden;”. Flow moves from operation  330  to operation  335 . 
     In another embodiment, instead of adding a style attribute to the image tag to cause to cause it not to be displayed, the proxy server  120  may cause a different image to be initially loaded by the client network application and displayed in the original image&#39;s placeholder. This different image may not be visible to the user (e.g., the image may be a transparent image that the client network application renders in the background color where the image is to be placed). The different image may be of a small size (e.g.,  1  by 1 pixels), which may be stretched according to the height and/or width of the original image. By way of example, the proxy server  120  may add a source attribute to the image tag that specifies the location of the different image, and may further have the width and/or height set the same as the original image. The proxy server  120  may alternatively add a source attribute to the image tag that embeds the image data inline into the html (e.g., add the image as a data Uniform Resource Identifier (URI) object), and may further set the width and/or height to be the same as the original image. 
     At operation  335 , the source attribute of the image tag is modified to cause the client network application to not issue a request to the source of the image, while maintaining the information that specifies the location of the image. For example, the proxy server  120  may modify the name of the src attribute to a value that is unrecognized by the client network application. By way of example, the proxy server  120  may prepend “data-cf” to the “src” attribute in the HTML (e.g., modify “src” to “data-cfsrc”), which causes the client network application to not make the request since it does not recognize “data-cfsrc”. Flow moves from operation  335  back to operation  310  where the page continues to be parsed. 
     Although not illustrated in  FIG.  340   , in some embodiments the proxy server also maintains the original image tag but wraps it within a noscript tag. In this way, if a client network application does not support client-side scripts or has them disabled, the images will be displayed as they would normally. In such an embodiment, the proxy server may copy the content of the original image tag and operate on the copied image tag when making the above modifications. Also, in such an embodiment, the image tag that has been modified for deferred image loading may be placed in the HTML directly before or directly after the original image tag that has been wrapped in a noscript tag. 
     In one embodiment, the proxy server defers the loading of only those images that have a source on the same domain as the requested page. In such an embodiment, after detecting an image tag, the proxy server determines whether the source of the image tag is of the same domain as the requested page. If they are the same, then the operations described with respect to operations  320  to  335  are performed. If they are not the same, then those operations would not be performed. 
     In another embodiment, the proxy server defers the loading of only those images that have a source with a domain that resolves to a proxy server of the cloud-based proxy service, even if that domain is different than the domain as the requested page. In such an embodiment, after detecting an image tag, the proxy server determines whether the source of the image tag is of a domain that resolves to a proxy server of the cloud-based proxy service. For example, the proxy server may have a list of the domains that resolve to a proxy server of the cloud-based proxy service. If the domain resolves to a proxy server of the cloud-based proxy service, then the operations described with respect to operations  320  to  335  are performed. If the domain does not resolve to a proxy server of the cloud-based proxy service, then those operations would not be performed. 
     In another embodiment, the proxy server defers the loading of each of the images, regardless of the source of the image. 
     In addition to modifying the image tags such that they will not (at least initially) be requested by the client network application, the proxy server also adds one or more client-side scripts (e.g., JavaScript) and/or references to one or more client-side scripts that, when executed by the client network application, causes the images to be loaded when the corresponding image placeholders are located in the viewport or within a defined distance to the viewport. For example, the client-side script(s), when executed by the client network application, detects the location of the image placeholders (at least for those images whose loading has been deferred) with respect to the viewport. When an image placeholder is located within the viewport or, in some embodiments within a certain distance from the viewport (e.g., within 100 pixels of the viewport), the client-side script(s) perform a number of actions to cause the client network application to request and display the corresponding image. For example, the client-side script(s) rewrite the source attribute to cause the client network application to make a request for the image (e.g., by removing “data-cf” from “data-cfsrc”). If a style attribute for the image was originally included in the HTML (and modified by the proxy server  120 ), the client-side script(s) rewrite the style attribute according to the original style attribute (e.g., by removing “data-cf” from “data-cfstyle”). The client-side script(s) also remove the null style attribute, which causes the image (if retrieved) to be displayed. 
     In some embodiments, the client-side script(s) only cause the images whose corresponding image placeholders are located in the viewport and optionally those that are within a certain distance from the viewport to be loaded (e.g., if the requesting client device is connecting over a mobile operator&#39;s network such as 3G or 4G). Thus, in these embodiments, only when an image placeholder scrolls into the viewport or within a certain distance from the viewport, the client-side script(s) will cause the client network application to request and download the corresponding image. In other embodiments, for example if the requesting client device is not connecting over a mobile operator&#39;s network (e.g., a WiFi connection, a wired connection, etc.), the client-side script(s) prioritize the loading of the images whose corresponding image placeholders are currently located in the viewport and optionally those that are within a certain distance from the viewport; and causes other image(s) (if any) to be loaded in the background when bandwidth is available. 
       FIG.  4    is a flow diagram that illustrates exemplary operations performed by one or more client-side scripts for deferred loading of images according to one embodiment. The operations described with reference to  FIG.  4    are performed by the set of one or more deferred loading client-side scripts that are either included in the modified page that is transmitted to the requesting client device and/or referenced in the modified page. 
     At operation  410 , the set of client-side scripts determine whether an image placeholder is in the viewport or in some embodiments if it is within a defined distance from the viewport. In order to determine this, the current size of the viewport of the client device is determined. In some embodiments the set of client-side scripts perform a series of checks to determine the size of the viewport (the viewport width and height variables). These checks may include determining whether there is an innerWidth variable defined in the window. If there is, the innerWidth and innerHeight may be used for the viewport width and height variables. If there is not, the client-side script(s) may determine whether the clientWidth (or clientHeight) variable is defined for the document. If there is, the clientWidth and clientHeight variables are used for the viewport width and height variables. If there is not, the client-side script(s) may read the body element and read the clientWidth and clientHeight variables and use those for the viewport width and height variables. 
     In addition to determining the size of the viewport, the set of client-side scripts also determine the location of the image placeholders with respect to the viewport. For example, the position of the scrollbar is determined and from that value, the width of the top border of the image placeholder is subtracted. That value is then added to the height of the viewport (e.g., as determined by the viewport height variable). The resulting value is subtracted from the top of the bounding rectangle of the image placeholder. The resulting value is a pixel distance from the top of the image placeholder to the viewport. 
     If the image placeholder is not in the viewport or within a certain distance from the viewport, then flow moves to operation  420  (which is optionally performed in some embodiments). If the image placeholder is in the viewport or within a certain distance from the viewport, then flow moves to operation  415  where the client-side scripts cause the client network application to request the corresponding image. For example, the set of client-side scripts rewrite the source attribute to cause the client network application to make a request for the image (e.g., by removing “data-cf” from “data-cfsrc”). If a style attribute for the image was originally included in the HTML (and modified by the proxy server  120 ), the set of client-side scripts rewrite the style attribute according to the original style attribute (e.g., by removing “data-cf” from “data-cfstyle”). The set of client-side scripts also remove the null style attribute, which causes the image (if retrieved) to be displayed. Flow moves from operation  415  back to operation  410 . 
       FIG.  5    is a flow diagram that illustrates exemplary operations that are performed by the set of client-side scripts when causing the client network application to request the image according to one embodiment. For example, the operations described with reference to  FIG.  5    may be performed as part of the operation  415  of  FIG.  4   . At operation  510 , the set of client-side scripts determine whether the style attribute of the image that is to be requested was modified to cause the client network application to not apply the style. By way of example and not limitation, if the proxy server  120  modified the style attribute to cause the client network application to not apply the style while maintaining the value of the style by prepending “data-cf” to the “style” attribute (e.g., “style” was changed to “data-cfstyle”), the set of client-side scripts analyzes the image tag to determine whether that specific attribute name (data-cfstyle) is included in the image tag. If the original style attribute of the image was modified, then flow moves to operation  515 , otherwise flow moves to operation  520 . 
     At operation  515 , the set of client-side scripts restore the modified style attribute of the image to its original value. For example, the set of client-side scripts may restore the name of the style attribute to “style” (e.g., remove “data-cf” from “data-cfstyle”). Next, flow moves to operation  520  where the set of client-side scripts remove the style attribute that was added to the image tag to cause the image placeholder to not be displayed (the null style attribute). Next, flow moves to operation  525  where the set of client-side scripts restore the source attribute of the image tag to its original value. By way of example, if the proxy server  120  modified the name of the source attribute (e.g., by prepending “data-cf” to “src”), the set of client-side scripts restore the original name of the source attribute (e.g., by removing “data-cf” from “data-cfsrc”). 
     As will be described in greater detail later herein, the set of client-side scripts may also request the image to have a particular size based on how the image is used on the page and the size of the viewport. For example, the set of client-side scripts may determine that an image is 1000 pixels by 1000 pixels, but is set to be displayed at 100 pixels by 100 pixels. The set of client-side scripts may cause the client network application to request the image have a smaller size (e.g., 100 pixels by 100 pixels). In response to this request, the proxy server or other device in the service may automatically resize the image accordingly and deliver the resized image, or retrieve a smaller sized version of the image (e.g., from cache) and deliver the resized image to the client device. As another example, if the set of client-side scripts determine that the size of the viewport of a device is 960 by 640 pixels (which is a common size for mobile devices), but a background image is 2000 pixels wide, the set of client-side scripts may cause the client network application to request the background image to be of a size no larger than can be displayed by the device. 
     In some embodiments, even if the image placeholder is not in the viewport or within a defined distance from the viewport, the set of client-side scripts cause the client network application to request the image when there is available bandwidth. In one embodiment, available bandwidth depends on whether the client is connecting through a mobile operator&#39;s network or through a different type of network (e.g., wired, WiFi, etc.). 
     At operation  420 , the set of client-side scripts determine whether the client device is connecting through a mobile connection (e.g., 2G, 3G, 4G, etc.). The set of client-side scripts may determine the connection of the requesting′ client device by examining the navigator property, which some mobile browsers use to reveal information relating to the connection the browser is using (e.g., WiFi, 2G, 3G, 4G, etc.). If the client is connecting through a mobile connection, then flow moves back to operation  410 . If the client is not connecting through a mobile connection (e.g., the client is connecting via WiFi, a wired network, etc.), then flow moves to operation  415  where the set of client-side scripts cause the client network application to request the image. Thus, in this embodiment, if the client is connecting through a mobile connection, then the client-side script(s) only cause the client network application to request images when they are in the viewport or optionally within a certain distance from the viewport (at least for those images whose loading has been deferred). 
       FIGS.  6 A and  6 B  illustrate one embodiment of deferred image loading.  FIGS.  6 A and  6 B  represents a client device rendering a page  605  (e.g., an HTML page), which the client device has received from a proxy server such as the proxy server  120 . The page  605  includes the image placeholders  610 ,  615 ,  620 , and  625 . The page may also include other elements such as text, etc. The page  605  has been modified by the proxy server such that the images of the page  605  will be loaded only when they are in the viewport. For example, the page  605  includes or references the deferred image loading script(s)  630 . It should be understood that the deferred image loading script(s)  630  are not displayed. It should also be understood that the deferred image loading example illustrated in  FIGS.  6 A and  6 B  is exemplary and other embodiments may load images when they are within a defined distance from the viewport and/or if there is available bandwidth. 
     The image placeholders  610  and  615  are currently within the viewport  630 . Accordingly, the deferred image loading script(s)  630  cause the client network application to request and display the images that correspond to the image placeholders  610  and  615 . The image placeholders  620  and  625  are not within the viewport  630 . As a result, those corresponding images will not be requested. The image placeholders  620  and  625  are represented with dashed lines to indicate that the corresponding images have not been requested and downloaded. 
     In  FIG.  6 B , the user has scrolled down the page  605  such that the image placeholder  620  is now within the viewport  630 . Accordingly, the deferred image loading script(s)  630  cause the client network application to request and display the image corresponding to the image placeholder  620 . Since the image placeholder  625  is still not within the viewport  630 , it will not be requested and displayed. 
     Auto-Resizing of Images 
     As previously described, in some embodiments, images are automatically optimized to the size and resolution specific for the page and the requesting device (referred herein as auto-resizing). Auto-resizing of images may be performed independently of the deferred image loading process described herein or in conjunction with the deferred image loading process described herein. 
     In one embodiment, a set of one or more client-side scripts (these client-side script(s) may share at least some of the functionality of the client-side script(s) for deferred image loading) that are included in the page and/or referenced in the page that includes the reference to the image, cause the client-network application to request a size of that image according to the presented dimensions of the image and/or the size of the viewport of the client device. As an example, these set of client-side scripts are included and/or referenced in the page example.com and cause an image located at example.com/image.gif to be requested with a size based on the presented dimensions of that image and/or the current size of the viewport of the client device. 
       FIG.  7    is a flow diagram that illustrates exemplary operations performed on a proxy server for auto-resizing of images according to one embodiment. At operation  710 , a proxy server  120  receives a request for a page (e.g., an HTML page) from a client device. The request may be received as a result of a DNS request for the domain of the page resolving to an IP address of the proxy server  120 . Next, at operation  715 , the proxy server  120  determines that image auto-resizing is enabled for the requested page. In one embodiment, the proxy server  120  accesses a set of one or more page rules for the domain of the requested page to determine whether image auto-resizing has been enabled. Enabling image auto-resizing will be described in greater detail later herein. In some embodiments the operation of  715  is optional (e.g., the automatic image resizing is applied to every page). Flow then moves to operation  720 . 
     At operation  720 , the proxy server  120  retrieves the requested page. If the requested page is available in the proxy server&#39;s cache and it has not expired, the proxy server  120  may retrieve the requested page from its cache. The proxy server  120  may also retrieve the requested page from the origin server (e.g., transmit a request to the origin server for the page and receive a response from the origin server that includes the page). Flow then moves to operation  725 . 
     At operation  725 , the proxy server  120  modifies the page such that at least some images will be automatically resized based on how those images are used on the page and/or the size of the viewport. For example, the proxy server  120  may modify the code of the page such that when the client network application issues a request for the image, that request will include an indication of a set of one or more requested dimensions for the image. The proxy server  120  may modify the image tags such that they will not (at least initially) be requested by the client network application. In one embodiment, the proxy server  120  may modify the source attribute of the image tags in a similar way as described with respect to  FIG.  3   . In addition, the proxy server  120  also adds one or more client-side scripts (e.g., JavaScript) and/or references to one or more client-side scripts that, when executed by the client network application, cause the client network application to request the images with dimensions based on how the image is set to be displayed and/or the size of the viewport. 
     In one embodiment, only those images that are located on the same domain as the requested page may be automatically resized. In another embodiment, only those images that are located on the same domain as the requested page and other domains of customers of the service may be automatically resized. In yet another embodiment, any image, regardless of whether that image is located on a domain of a customer of the service, may be automatically resized. 
     Flow then moves to operation  730  where the proxy server  120  transmits the modified page to the requesting client device. The proxy server  120  may also store the modified page in its cache such that upon receiving a subsequent request for the page (from the same client device or from a different client device), the proxy server  120  may transmit the modified page to the requesting client device without having to modify the page again. 
       FIG.  8    is a flow diagram that illustrates exemplary operations performed on a client device for causing image(s) referenced in a web page to be requested by the client network application with a set of one or more dimensions according to one embodiment. In one embodiment, the operations described with reference to  FIG.  8    are performed at least in part by a set of one or more client-side scripts that are included in the page being rendered by the client network application and/or referenced in the page being rendered by the client network application. 
     In one embodiment, the operations described with reference to  FIG.  8    are performed only for those images that belong to the same domain as the page. For example, if the requested page is example.com, in some embodiments the operations of  FIG.  8    are performed only for images of example.com (e.g., example.com/image.gif). 
     At operation  805 , a client network application receives a web page with a reference to an image. For example, the client network application of a client device  110  may receive the web page from a proxy server  120 . Next, at operation  810 , an image is determined to be ready to be requested. For example, the client network application is ready to make a request for the image. In one embodiment, this request may have been deferred as previously described herein (e.g., the image may be in the viewport or within a defined distance from the viewport). 
     Next, at operation  815 , the set of client-side scripts determine the display size of the image. The display size of the image refers to the displayed dimensions of the image. The set of client-side scripts may determine the display size of the image based on the presented dimensions of the image (how the code of the page is configured to display the image) and/or the size of the viewport of the client network application. 
     Next, at operation  820 , the set of client-side scripts cause the client network application to request the image, where the request includes an indication of one or more requested dimensions for the image that are equal or substantially equal to the determined display size of the image. For example, the set of client-side scripts cause the original URL of the image to be rewritten to include a query string that indicates the requested width and/or height of the image. By way of a specific example, if the determined display size of the image located at www.example.com/image.gif is 960 by 640, the client-side scripts may cause the client network application to request the image at www.example.com/image.gif?_cfgetx=img.rx:960;img.rx:640. This request, which is received by the proxy server, notifies the proxy server of the size of the image that should be returned to the client. 
     To cause the client network application to request the image, the set of client-side scripts may also rewrite the source attribute to cause the client network application to make a request for the image (e.g., by removing “data-cf” from “data-cfsrc”). If a style attribute for the image was originally included in the HTML (and modified by the proxy server  120 ), the client-side script rewrites the style attribute according to the original style attribute (e.g., by removing “data-cf” from “data-cfstyle”). The client-side script also removes the null style attribute, which causes the image (if retrieved) to be displayed. 
     Next, at operation  825 , the client network application receives the image, which has a size that is equal or substantially equal to the requested dimensions. For example, the proxy server, upon receiving a request for an image that includes an indication of requested dimensions (e.g., a query string that indicates the width and/or height of the image that is being requested), returns the image with those dimensions or an image that is within a certain range of those dimensions. For example, in one embodiment, the proxy server stores within its cache (e.g., when acting as a CDN), multiple versions of the image, each of which having a different dimension. If there is an image that has the requested dimensions or is within a range of the requested dimensions (e.g., is within X number of pixels of the width and/or Y number of pixels of the height), the proxy server returns that version of the image to the requesting client device. If the proxy server does not have a copy of the image with the requested dimensions or within a range of the requested dimensions, then it will resize the image according to the requested dimensions. It should be understood that the proxy server may issue a request to the origin server for the image if it does not have an image of a suitable size. Next, at operation  830 , the client network application displays the image in its corresponding image placeholder. 
       FIG.  9    is a flow diagram that illustrates exemplary operations performed by a set of one or more client-side scripts for determining the display size of the image according to one embodiment. For example, the operations described with reference to  FIG.  9    may be performed during operation  815  described with reference to  FIG.  8   . 
     Next, at operation  915 , the set of client-side scripts attempt to determine the presented dimensions for the image. The set of client-side scripts may determine the presented dimensions for the image by performing a set of one or more actions. For example, the set of client-side scripts may analyze the image tag to determine whether it has the width and/or height set. As another example, the set of client-side scripts may examine the Cascaded Style Sheets (CSS) style(s) (if one exists) to determine how it is governing the size of the image. Flow then moves to operation  920 . 
     At operation  920 , a determination is made whether the presented dimensions for the image were determined. The presented dimensions for the image may not be able to be determined if the width and/or height attributes are not set in the image tag or CSS. If the presented dimensions were not determined, then flow moves to operation  925  where the set of client-side scripts cause the client network application to request the image. If the presented dimensions were determined, then flow moves to operation  930 . 
     At operation  930 , the set of client-side scripts determine whether the presented dimensions of the image is larger than the current size of the viewport. In one embodiment, the set of client-side scripts perform a series of checks to determine the size of the viewport (the viewport width and height variables) as previously described herein. If the presented dimensions of the image are larger than the current viewport size, then flow moves to operation  935 . If the presented dimensions of the image are smaller or equal to the current viewport size, then flow moves to operation  940 . At operation  940 , the set of client-side scripts set the display size of the image as the size of the presented dimensions. 
     At operation  935 , the set of client-side scripts set the display size of the image as less than or equal to the size of the viewport. For example, if the size of the viewport of the device is 960 by 640 pixels, but the background image is 2000 pixels wide, the set of client-side scripts may set the display size of the image as having dimensions no greater than 960 by 640. 
     The proxy server, upon receiving a request for an image that includes a query string that indicates the width and/or height of the image that is being requested, returns the image with those dimensions or an image that is within a certain range of those dimensions. For example, in one embodiment, the proxy server stores within its cache (e.g., when acting as a CDN), multiple versions of the image, each of which having a different dimension. By way of a specific example, the proxy server may store a different version of the image for different known client devices (e.g., a different version for a mobile phone with known display dimensions as compared to a different version for a tablet with known display dimensions). If there is an image that has the requested dimensions or is within a range of the requested dimensions (e.g., is within X number of pixels of the width and/or Y number of pixels of the height), the proxy server returns that version of the image to the requesting client device. If the proxy server does not have a copy of the image with the requested dimensions or within a range of the requested dimensions, then it will resize the image according to the requested dimensions. It should be understood that the proxy server may issue a request to the origin server for the image if it does not have an image of a suitable size. 
       FIG.  10    is a flow diagram illustrating exemplary operations performed by a proxy server for performing auto-resizing of images according to one embodiment. At operation  1010 , the proxy server  120  receives a request for an image, the request indicating a particular width and/or height of the image. For example, the proxy server may receive a request for an image at the following URL example.com/image.gif may be requested with the following URL example.com/image.gif?_cfgetx=img.rx=100;img.ry=100; which requests that the image image.gif should be approximately 100 by 100 pixels. Flow then moves to operation  1015 . 
     At operation  1015 , the proxy server determines whether it has a cached version of the requested image with the requested dimensions or optionally within a predefined range (e.g., within X number of pixels of the width (e.g., 50 pixels) and/or within Y number of pixels of the height (e.g., 50 pixels)). If it does, then flow moves to operation  1020  where the proxy server transmits a response to the requesting client device with the retrieved image. If the proxy server does not have a cached version of the requested image with the requested dimensions or optionally within a predefined range, then flow moves to operation  1025  where the proxy server retrieves the image. The proxy server may retrieve the image from the origin server (e.g., by issuing a request to the origin server for the image) if it does not have the image in its cache (if in its cache, the proxy server may retrieve the image from the cache). Flow then moves to operation  1025 . 
     At operation  1025 , the proxy server resizes the image according to the requested dimensions. Using the example above, if the original size of the image located at example.com/image.gif is 1000 by 1000 pixels, the proxy server may resize the image to 100 by 100 pixels. Resizing the image typically includes compressing the image while maintaining the aspect ratio of the image. Flow then moves to operation  1030  where the proxy server transmits a response to the requesting client device with the resized image. Flow then moves to operation  1035 , where the proxy server stores the resized image in its cache. 
     Thus, based on how the image is set to be displayed and the size of the viewport, an appropriately sized image will be received and displayed. This saves bandwidth in downloading files that are larger than what will be displayed and reduces the page loading time. This also helps with visitors with limited data plans not saturate their data plan caps (e.g., mobile users). In addition, this may be done without the customer having to change a single line of their HTML code. 
     Although  FIG.  10    illustrates a particular order of operations, it should be understood that such order is exemplary (e.g., alternative embodiments may perform the operations in a different order, combine certain operations, overlap certain operations, etc.). By way of a specific example,  FIG.  10    may be augmented by the following. After receiving a request for the image and there is not a version of the image in cache with the requested dimensions or within a predefined range of the requested dimensions, the image may be transmitted to the requesting client device without it being resized. The resizing of the image and storing of the resized image occur as a separate process in the background. This alternative embodiment has the benefit of returning the image quickly to the first visitor (at least the first visitor requesting those specific dimensions of the image) and resizing the image for future visitors that request the image have similar dimensions. 
     Configuring Deferred Image Loading and/or Image Resizing 
     In one embodiment, customers of the service (e.g., domain owners and/or personnel working on behalf of domain owners) configure their domain or portion of their domain (e.g., particular page(s) of their domain) for deferred image loading and/or image resizing, without modifying a single line of HTML code. For example, the control servers  125  may provide an interface for the customers to configure the image loading settings for their site (whether deferred image loading and/or image resizing are enabled). 
       FIG.  11    is an exemplary interface  1110  for the control servers  125  that allows a customer to enable or disable the deferred image loading and/or image auto-resizing functionality described herein, according to one embodiment. In one embodiment, the interface  1110  is available over the Internet as a website. However, in other embodiments, the functionality of the interface  1110  may be provided through a mobile application interface. The toggle button  1115  allows the customer to enable or disable auto-resizing of images. The toggle button  1120  allows the customer to enable or disable deferred loading of images. Upon making a change to the image loading settings, the control servers  125  update the proxy servers  120  with the updated image loading settings. For example, upon enabling the deferred image loading, the proxy server(s)  120  that receive requests for the customer&#39;s pages will insert the set of client-side script(s) and/or references to the set of client-side script(s) that provide the functionality of the deferred image loading. Upon enabling the image auto-resizing, the proxy server(s)  120  that receive requests for the customer&#39;s pages will insert the set of client-side script(s) and/or references to the set of client-side script(s) that provide the functionality of the image auto-resizing. 
     Minimizing the Number of Requests for Images 
     In one embodiment, if the image request reduction loading optimization is enabled for the requested network resource (or enabled for the domain of the requested network resource), the proxy server  120  modifies the page such that the number of requests for images of the page is reduced. In one embodiment, the number of requests is reduced by grouping multiple, different requests for images, into a single request (known herein as a bulk request) (e.g., a single HTTP request). For example, the image manager (a set of one or more client-side scripts executed by the client network application) may create a single canonical URL that represents multiple images of the page that are to be sent back in a response. This single URL may be created by combining the individual URLs for all images into a single string and appending them to the query parameters of the single request (typically in URL-encoding).  FIG.  14    illustrates a single URL that may be created by the image manager for requesting multiple images in a single request. As illustrated in  FIG.  14   , the single URL includes multiple images of the page (example.com/1.png, example.com/2.png, and example.com/3.png) and is formatted using URL-encoding. Although  FIG.  14    illustrates the single URL including images from the same domain (example.com), in some embodiments the single URL may include images from multiple domains. 
     The bulk request may be transmitted to the proxy server  120 , which receives and decodes the bulk request and attempts to retrieve the images indicated in the bulk request. The proxy server  120  may retrieve the images from its cache if available and not expired or alternatively may issue requests for the images to the appropriate origin servers. 
     After retrieving the images requested in the bulk request, in one embodiment the proxy server  120  transmits a bulk response to the requesting client device that includes the images requested in the bulk request (at least those images in which the proxy server  120  was successful in retrieving). In one embodiment, the proxy server  120  ensures that the encoding of each image is in the same format, which may require re-encoding an image into that common format if it is not already in that format. By way of example, the proxy server  120  may ensure that each image is in the Portable Network Graphics (PNG) format.  FIG.  15    illustrates an exemplary format for bulk image responses according to one embodiment. 
     In another embodiment, after retrieving the images requested in the bulk request, the proxy server  120  transmits the responses to the requesting device one image at a time (not though a bulk response). 
       FIG.  16    illustrates an exemplary implementation of image request reduction according to one embodiment. The client device  110 A transmits a request  1610  for example1.com/index.html, which is received by the proxy server  120 . The request  1610  may be received as a result of a DNS request for example1.com resolving to an IP address of the proxy server  120 . The proxy server  120  retrieves the requested resource. In one embodiment, if the requested resource is in cache and has not expired, the proxy server  120  retrieves the requested resource from its cache. However, if the requested resource is not in cache or has expired, the proxy server  120  issues a request  1615  to the origin server  130 A, which serves the requested resource. The proxy server  120  receives the response  1620  from the origin server  130 A which includes the requested resource. The requested resource includes multiple images, some of which are sourced at the domain example1.com and some which are sourced at the domain example 2.com. For example, the image tags  1622  and  1624  are for images sourced at the domain example1.com (e.g., example1.com/1.png and example1.com/2.png) and the image tag  1626  is for an image sourced at the domain example 2.com (e.g., example 2.com/1.png). 
     The proxy server  120  modifies the HTML for image loading optimization at operation  1625 . As described above, in one embodiment the proxy server  120  neutralizes the images included in the requested resource. For example, the image tags  1622 ,  1624 , and  1626  are neutralized into the neutralized image tags  1640 ,  1642 , and  1644  respectively, such that the client device  110 A will not request the corresponding images (at least initially). The proxy server  120  also adds the image manager  1635 , which is a set of one or more client-side scripts and/or a set of one or more references to client-side scripts that, when executed by the client network application of the client device  110 A, will, among other actions, cause the number of requests for images included in the response to be reduced. By way of a specific example, the image manager  1635 , when executed, will cause the client network application of the client device  110 A to create a bulk request for the images included in the requested resource. The proxy server  120  transmits the modified page to the requesting client device  110 A in the response  1630 . 
     The client device  110 A loads the image manager at operation  1650 . The image manager  1650  scans the DOM for all image tags that have been neutralized and registers them for eventual loading. When appropriate, the image manager interfaces with localStorage to retrieve stored degraded versions of images (if available), which will be described with greater detail later herein. LocalStorage (sometimes referred to as HTML5 Storage), is storage that is locally available on the client device, persistent, and can be accessed by code executing by the client network application in certain circumstances. 
     The image manager  1635  causes the bulk image request  1655  to be transmitted to the proxy server  120 . The bulk image request  1655  is a single request that indicates multiple requests for multiple images (namely example1.com/1.png, example1.com/2.png, and example2.com/1.png). In one embodiment, the bulk image request  1655  is communicated to the proxy server  120  through a single URL that represents multiple images of the page that are to be sent back into the response. 
     The proxy server  120  receives and decodes the bulk image request  1655  to determine the individual images being requested and their location. The proxy server  120  then retrieves the images indicated in the bulk image request  1655 . The proxy server  120  may receive the images from its cache if available and not expired. Alternatively the proxy server  120  may issue requests for the images to the appropriate origin servers. As illustrated in  FIG.  16   , the proxy server  120  issues requests for the images and receives responses with the images from the origin servers  130 A-B. In particular, there is a request/response pair  1660  between the proxy server  120  and the origin server  130 A to retrieve the image located at example1.com/1.png, a request/response pair  1665  between the proxy server  120  and the origin server  130 A to retrieve the image located at example1.com/2.png, and there is a request/response pair  1670  between the proxy server  120  and the origin server  130 B to retrieve the image located at example 2.com/1.png. 
     After receiving the images, the proxy server  120  returns them to the client device  110 A in one or more responses. The proxy server  120  may also cache the images so that it may locally retrieve them for subsequent request. In one embodiment, the proxy server  120  returns the images to the client device  110 A in a bulk response. In another embodiment, the proxy server  120  returns the images to the client device  110  in multiple responses (e.g., a different response for each different image being returned). As illustrated in  FIG.  16   , the proxy server  120  creates and transmits the bulk image response  1675  to the client device  110 A, which includes the requested images. 
     In one embodiment, the proxy server  120  does not wait until each image is retrieved prior to transmitting them in the bulk image response  1675 . The images may begin to stream back to the client device  110 A as they are retrieved, which may or may not be in the order in which they are requested. For example, the images may be transferred to the client device  110 A as binary data and parsed by the client using client-side scripting (e.g., JavaScript) typed containers (this functionality is also known as Typed Arrays). Not all client network applications currently support Typed Arrays. In one embodiment, the image manager  1635  when executed by the client network application of client device  110 A, determines whether the client network application supports Typed Arrays. For example, the image manager  1635  may execute the following function to determine whether the client network application supports Typed Arrays: 
     function supportsTypedArrays( ) {return typeof window.ArrayBuffer !==‘undefined’;} The image manager  1635  may cause an indication to be transmitted to the proxy server  120  of whether the client network application of the client device  110 A supports Typed Arrays. 
     In one embodiment, a DOM Blob API is used to convert the binary representation of an image into a displayable object in the DOM. A Blob object represents a file-like object of immutable raw data. A Blob is created using the binary representation of each image, which is then converted into a displayable object using URL.createObjectURL. In one embodiment, the image manager  1635 , when executed by the client network application of client device  110 A, determines whether the client network application supports DOM Blobs. For example, the image manager  1635  may execute the following function to determine whether the client network application supports DOM Blobs: 
     
       
         
           
               
               
               
               
             
               
                   
                   
               
             
            
               
                   
                   
                 function supportsDOMBlobs( ) { 
                   
               
               
                   
                   
                  return typeof window.Blob !== ‘undefined’ || 
                   
               
               
                   
                   
                   typeof window.BlobBuilder !== ‘undefined’; } 
               
               
                   
                   
               
            
           
         
       
     
     Although  FIG.  16    illustrates the same type of image being requested and returned (PNG images), it should be understood that there can be many different types of images being requested and embodiments are not limited to a specific type of image. In some embodiments, the proxy server  120  ensures that each image is in the same format, which may involve re-encoding an image into that format if it is not already in that format. 
     Progressive Enhancement 
     In one embodiment, if the progressive enhancement image loading optimization is enabled for the requested network resource (or enabled for the domain of the requested network resource), the proxy server  120  modifies the page such that degraded versions of images may precede their full quality counterparts. By way of example, with reference to  FIG.  16   , the proxy server  120  may transmit degraded versions of the requested images in the bulk image response  1675 . Since images are critical to the final layout and display of most web pages, progressive enhancement allows degraded versions of images to precede their full-quality counterparts for the benefit of faster rending while maintaining a consistent layout. The degraded images (e.g., a compressed version of the full-quality counterparts) will be of a smaller file size which will be able to be quickly returned and displayed by the requesting client device. A number of techniques may be used to reduce the image file size including removing color information, lowering quality level, and/or pixel-level filtering. 
     In one embodiment and if the client network application supports localStorage (typically HTML5 compliant client network applications support localStorage), the degraded images are cached in the localStorage to further minimize outbound requests. The degraded image data can be referenced by the image manager and the applied to the neutralized images in order to create a degraded presentation to the end user (potentially avoiding network requests when presenting the degraded images to the end user). In one embodiment, the size of the images are reduced such that they will fit within the limited capacity of the localStorage of the client network application (the original size of the image is also transmitted to the client network application so that the client can scale each image appropriately). 
     In addition to or in lieu of storing the degraded images on the client (e.g., in localStorage), a manifest can be kept of the images (the non-degraded versions) that are likely to be available in cache. This manifest (referred to as the cache manifest), can be stored on the client (e.g., in localStorage) and used to decide to not preload images in a degraded form that are likely to be in cache for subsequent page views. In one embodiment, the manifest is in JavaScript Object Notation (JSON) format. 
     In one embodiment, the image manager, when executed by the client network application, determines whether the client network application supports WebWorkers, which is a JavaScript API for concurrent execution. If WebWorkers is not supported by the client network application, a polyfill may be used instead. In one embodiment, the image manager may execute the following function to determine whether the client network application supports WebWorkers: 
     function supportsWebWorkers( ) {return typeof window.Worker !==‘undefined’;} 
     After receiving the degraded image data and knowing the size of the image in its raw format (full quality counterpart), the client network application can render that image at the appropriate scale. For example, if supported by the client network application, it may use the HTML5 Canvas 2D API and assign the resulting image data to the previously neutralized image. The image manager may determine whether the HTML5 Canvas 2D API is supported by the client network application. In one embodiment, the image manager may execute the following function to determine whether the client network application supports HTML5 Canvas 2D API: 
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                   
                 function supportsCanvas2D( ) { 
               
               
                   
                   
                  var canvas = document.createElement(‘canvas’); 
               
               
                   
                   
                  if (typeof canvas.getContext === ‘undefined’) { 
               
               
                   
                   
                    return false; } 
               
               
                   
                   
                  try { 
               
               
                   
                   
                    var context = canvas.getContext(‘2d’); 
               
               
                   
                   
                   } catch(e) { 
               
               
                   
                   
                    return false; 
               
               
                   
                   
                   } 
               
               
                   
                   
                   return !!context; 
               
               
                   
                   
                  } 
               
               
                   
                   
               
            
           
         
       
     
     In one embodiment, Data URLs are used as the final format when representing degraded images since the Canvas 2D API can export its contents as a Data URL. Data URLs can also be used as a fallback in the case that the client network application does not support Typed Arrays, WebWorkers, Dom Blobs, or the Canvas 2D API since the Data URLs can be created on the proxy server and streamed directly to the requesting client device. 
     After degraded images are displayed to the user and loading is complete (e.g., the ‘onload’ event has fired), their full quality counterparts may be requested and displayed asynchronously. In one embodiment, their full quality counterparts are only requested if their corresponding image placeholders are in the viewport (or in some embodiments in close proximity to the viewport), or as there are spare network resources available. 
       FIG.  17    is a flow diagram that illustrates exemplary operations for optimizing image loading according to one embodiment. Although not illustrated in  FIG.  17   , prior to the operations of  FIG.  17    the client device has requested a resource and received a response that has been modified for optimized image loading. For example, the image tags of the response have been neutralized and the response includes an image manager as previously described herein. 
     At operation  1710 , a determination is made whether the client network application is on a mobile device. For example, the image manager may use jQuery or other techniques to determine the type of client network application (e.g., whether the client network application is a browser typically seen on mobile devices or a browser typically employed on desktop devices). If the client network application is not on the mobile device (e.g., a desktop device received the response), then flow moves to operation  1715  and deferred image loading of the images on the page is performed as previously described herein. If the client network application is on a mobile device, then flow moves to operation  1720 . 
     At operation  1720 , a determination is made whether the mobile device is connecting through a mobile operator network (e.g., 2G, 3G). Bandwidth is typically limited on mobile operator networks and latency may be high (as opposed to wired or WiFi networks where bandwidth and latency are usually less of a concern). In one embodiment, the image manger determines the connection of the requesting client device by examining the navigator property, which some mobile browsers use to reveal information relating to the connection. If the connection is determined to be over a mobile operator network, then flow moves to operation  1730 . If the connection is not determined to be over a mobile operator network or it cannot be determined whether the connection is over the mobile operator network (e.g., the navigator property is not used or it is otherwise not possible to detect the connection on the device), then flow moves to operation  1725 . 
     At operation  1725 , a determination is made whether one or more benchmarks suggest that latency is high. In one embodiment, the image manager executes a set of one or more tests to determine the latency. For example, the image manager may approximate a measurement of overhead by timing and analyzing a request for a single resource of known size that is guaranteed not to be in the cache of the client network application (e.g., a random file name or wildcard domain may be used). This resource is typically a small file that is not visible to the user. The time taken to load the image can be used an approximation for connection latency. If the benchmark(s) suggest that the latency is high, then flow moves to operation  1730 , otherwise flow moves to operation  1715 . 
     At operation  1730 , a determination is made for each of the images included in the page whether that image is likely to be available in cache (the non-degraded version of the image). For example, the image manager may access the cache manifest (e.g., stored in localStorage) to determine whether each image is represented on the cache manifest and thus likely to be available in cache. If an image is likely to be available in cache, then flow moves to operation  1740  where that image is removed from the list of images to be preloaded in a degraded form and flow then moves to operation  1735 . If the image is not likely to be available in cache, then flow moves to operation  1735 . 
     At operation  1735 , a determination is made for each of the images that are not likely to be available in cache whether there is a degraded version of that image in localStorage. For those images that do not have a degraded version stored in localStorage, flow moves to operation  1745  and those images are requested in bulk form, and then operation moves to operation  1750 . For example, the image manager creates a single request that represents each image on the page that is not likely to be in cache or does not have a degraded version stored in localStorage. For example, a single canonical URL may be created combining the individual URLs for each of these images. By way of example, the request may be transmitted to the proxy server described herein. If each image is likely to be in cache or there is a degraded version of each image stored in localStorage, then flow moves to operation  1750 . 
     After transmitting the bulk request for images in operation  1745 , the client device will typically begin to receive the requested images in a degraded form. For example, the images may be received at the client device as binary data and parsed by the client using client-side scripting (e.g., JavaScript) typed containers if supported. 
     At operation  1750 , a determination is made whether the ‘onload’ event has fired yet. If the ‘onload’ event has not fired, then flow moves to operation  1755  and the image manager assigns the degraded image data to the neutralized image tags. As previously described, the image manager may use a number of techniques including use of WebWorkers, DOM Blobs, Canvas 2D, and/or Data URLs to cause the degraded image data to be displayed, depending on the capabilities of the client network application. Flow moves from operation  1755  back to operation  1750  to wait for the ‘onload’ event to fire. After the ‘onload’ event has fired, then flow moves to operation  1715 . 
     As illustrated in  FIG.  18   , the computer system  1800 , which is a form of a data processing system, includes the bus(es)  1850  which is coupled with the processing system  1820 , power supply  1825 , memory  1830 , and the nonvolatile memory  1840  (e.g., a hard drive, flash memory, Phase-Change Memory (PCM), etc.). The bus(es)  1850  may be connected to each other through various bridges, controllers, and/or adapters as is well known in the art. The processing system  1820  may retrieve instruction(s) from the memory  1830  and/or the nonvolatile memory  1840 , and execute the instructions to perform operations described herein. The bus  1850  interconnects the above components together and also interconnects those components to the display controller &amp; display device  1870 , Input/Output devices  1880  (e.g., NIC (Network Interface Card), a cursor control (e.g., mouse, touchscreen, touchpad, etc.), a keyboard, etc.), and the optional wireless transceiver(s)  1890  (e.g., Bluetooth, WiFi, Infrared, etc.). In one embodiment, the client devices  110 A-I, the control server(s)  125 , the proxy server(s)  120 , and/or the origin servers  130 A-N can take the form of the computer system  1800 . 
     The techniques shown in the figures can be implemented using code and data stored and executed on one or more computing devices (e.g., client devices, servers, etc.). Such computing devices store and communicate (internally and/or with other computing devices over a network) code and data using machine-readable media, such as machine-readable storage media (e.g., magnetic disks; optical disks; random access memory; read only memory; flash memory devices; phase-change memory) and machine-readable communication media (e.g., electrical, optical, acoustical or other form of propagated signals—such as carrier waves, infrared signals, digital signals, etc.). In addition, such computing devices typically include a set of one or more processors coupled to one or more other components, such as one or more storage devices, user input/output devices (e.g., a keyboard, a touchscreen, and/or a display), and network connections. The coupling of the set of processors and other components is typically through one or more busses and bridges (also termed as bus controllers). The storage device and signals carrying the network traffic respectively represent one or more machine-readable storage media and machine-readable communication media. Thus, the storage device of a given computing device typically stores code and/or data for execution on the set of one or more processors of that computing device. Of course, one or more parts of an embodiment of the invention may be implemented using different combinations of software, firmware, and/or hardware. 
     While the flow diagrams in the figures show a particular order of operations performed by certain embodiments of the invention, it should be understood that such order is exemplary (e.g., alternative embodiments may perform the operations in a different order, combine certain operations, overlap certain operations, etc.). 
     While the invention has been described in terms of several embodiments, those skilled in the art will recognize that the invention is not limited to the embodiments described, can be practiced with modification and alteration within the spirit and scope of the appended claims. The description is thus to be regarded as illustrative instead of limiting.