Skip to main content

HTML5 XmlHttpRequest 2 v/s Flash\Silverlight approach to cross-origin requests

A few days back I had posted on XmlHttpRequest Level 2, describing how cross-origin requests can be achieved. A few folks on my team asked me how different it is from Flash\Silverlight's approach to achieve cross domain request\response with crossdomain.xml. The approach that these plugins take to send a request and receive a response is completely different from that of XmlHttpRequest's approach.

In case of Flash\Silverlight a policy file crossdomain.xml is created for the site. This file would contain a list of all sites that can make a cross domain request to this site. For example, if http://yoursite.com lists http://friendssite.com in crossdomain.xml file, then http://friendssite.com is allowed to access all the resources of http://yoursite.com. Here the access control mode is set to per site. XHR 2 on the other hand, follows a different approach altogether. It works on the per page access control model. In this case, every page has to respond with a 'Access-Control-Allow-Origin' header to the foreign site. With this approach only a part of a website can be accessed by a foreign site, keeping the rest of the website inaccessible.

Another difference to note is that, in case of Flash\Silverlight the browser fetches the crossdomain.xml defined for the website and analyzes it. If a foreign site is not allowed to make cross domain calls then the browser restricts the call being made. In case of XHR 2, a request is sent first and then a check is performed to see whether the response header contains 'Access-Control-Allow-Origin' header. If this header allows the foreign site then it can read the response, otherwise the response is inaccessible to javascript.
Labels:

Comments

Post a Comment

Popular posts from this blog

De-obfuscating javascript code in Chrome Developer Tools

I had blogged about JavaScript debugging with Chrome Developer Tools  some time back, wherein I have explained how these developer tools can help in debugging javascript code. Today Google Chrome 12 was released and my Chrome browser was updated to this version. As with every release, there have been some improvements made on performance, usability etc,. One feature that stood out for me is the ability to De-obfuscate the javascript code. What is Minification? Minification is the process of removing unnecessary characters such as white spaces, comments, new lines from the source code. These otherwise would be added to make the code more readable. Minifying the source code helps in reducing the file size and thereby reducing the time taken to download the file. This is the reason why most of the popular javascript libraries such as jQuery are minified. A minified jQuery file is of 31 KB in size where as an uncompressed one is about 229 KB. Unfortunately, debugging minified javascript f
7 comments
Read more

Adding beforeRender and afterRender functions to a Backbone View

I was working on a Backbone application that updated the DOM when a response was received from the server. In a Backbone View, the initialize method would perform some operations and then call the render method to update the view. This worked fine, however there was scenario where in I wanted to perform some tasks before and after rendering the view. This can be considered as firing an event before and after the function had completed its execution. I found a very simple way to do this with Underscore's wrap method.
Post a Comment
Read more

On GraphQL and building an application using React Apollo

When I visualize building an application, I would think of using React and Redux on the front-end which talks to a set of RESTful services built with Node and Hapi (or Express). However, over a period of time, I've realized that this approach does not scale well when you add new features to the front-end. For example, consider a page that displays user information along with courses that a user has enrolled in. At a later point, you decide to add a section that displays popular book titles that one can view and purchase. If every entity is considered as a microservice then to get data from three different microservices would require three http  requests to be sent by the front-end app. The performance of the app would degrade with the increase in the number of http requests. I read about GraphQL and knew that it is an ideal way of building an app and I need not look forward to anything else. The GraphQL layer can be viewed as a facade which sits on top of your RESTful services o
Post a Comment
Read more