Blog Feed Post

A breaking change between versions of ASP.NET AJAX

When working directly with JSON serialized ASMX services, be it via jQuery, pure XmlHttpRequest calls, or anything else other than the ScriptManager, one question inevitably arises. That question is of the inexplicable .d attribute that appeared in ASP.NET 3.5.

What is it? Why is it there?

In this post, I’ll use both a 2.0 and a 3.5 example ASMX web service to illustrate exactly what’s going on. I’ll also show you why it’s a good change.

An example

Following a concrete example always helps to better clarify these things. For that purpose, let’s assume that we want to call a web service and retrieve an instance of the following Person class:

public class Person
  public string FirstName;
  public string LastName;

The ASMX web service to return an instance of that class could be simple as this:

public class PersonService : WebService
  public Person GetPerson()
    Person p = new Person();
    p.FirstName = "Dave";
    p.LastName = "Ward";
    return p;

Because our WebService class is decorated with the [ScriptService] attribute, the ASP.NET AJAX Extensions (System.Web.Extensions) will automatically serialize the return value as JSON if properly requested.

Note: A common anti-pattern that I’ve seen in practice is using a return type of string and returning a manually JSON serialized object. Don’t. It’s unnecessary and results in doubled effort on both the server and in the browser.

Let the framework handle this task unless you have a good reason not to use the built-in functionality. It works just fine in most scenarios.

Calling the service and inspecting its result

Using jQuery to consume an ASMX web service is simple, but does require jumping through a few hoops. We can use this jQuery to consume the Person service we just created:

  type: "POST",
  contentType: "application/json; charset=utf-8",
  url: "PersonService.asmx/GetPerson",
  data: "{}",
  dataType: "json",
  success: function(msg) {
    // Do interesting things here.

Making that call against an ASP.NET 2.0 site with the ASP.NET AJAX Extensions 1.0 installed, this JSON object would be the return value:

2.0 JSON Response in Firebug

I find that it often helps to visualize the JSON in a more human readable format. This is the same JSON object as seen in the Firebug screenshot above:

{"__type"    : "Person",
 "FirstName" : "Dave",
 "LastName"  : "Ward"}

Within the success callback shown above, you may access properties of the Person exactly as you would expect. For example, msg.FirstName will evaluate to “Dave”.

Waiter, there’s a .d in my msg soup!

Eventually, you’ll finally convince management to let you upgrade the site to ASP.NET 3.5. After all, you can use an object initializer to cut the size of the web service in half!

However, your msg.FirstName statement now results in the dreaded undefined.

What happened? Let’s inspect the ASP.NET 3.5 response in Firebug:

3.5 JSON Response in Firebug

The entire Person object is wrapped within a new “d” object now. Alternatively we might visualize it this way:

{"d":{"__type"    : "Person",
      "FirstName" : "Dave",
      "LastName"  : "Ward"}}

As you’ve probably figured out by now, the solution is to reference the property as msg.d.FirstName now. In our example, this will again resolve correctly as “Dave”.

This is the case with all ASMX services JSON serialized through the ASP.NET AJAX Extensions in ASP.NET 3.5. Even if you’re only returning a scalar return value, such as a string, int, or boolean, the result will always be enclosed within the “d”.

Why did it change?

While I wish this unexpected change had been more clearly announced, it’s a good one. Here’s how Dave Reed explained it to me:

{"d": 1 }


Is not a valid JavaScript statement, where as this:






So the wrapping of the "d" parameter prevents direct execution of the string as script. No Object or Array constructor worries.

[] is JavaScript’s array literal notation, allowing you to instantiate an array without explicitly calling a constructor. To expand on Dave’s explanation, simply consider this code:

["Dave", alert("Do Evil"), "Ward"]

That literal array declaration will execute the alert in most browsers. Danger!

Update: For an even better description of why the .d is important, from Dave Reed himself, be sure to see his comment below.


I hope this post has helped clarify any confusion caused by the “d” in ASP.NET 3.5’s JSON serialized ASMX services, and made you aware of why it’s worth the hassle. As sophisticated as XSS exploits have become in recent years, unexpected script execution has the potential for devastating consequences. That extra “d” is well worth the short-term hassle.

Microsoft often catches flak over security related issues, but rarely gets credit when they do things right. I, for one, think the ASP.NET team deserves credit for remaining vigilant and often preempting these exploits for us.

Thanks, guys.


Originally posted at Encosia. If you're reading this elsewhere, come on over and see the original.

A breaking change between versions of ASP.NET AJAX

Read the original blog entry...

More Stories By Dave Ward

Dave Ward wrote his first computer program in 1981, using good ‘ol Microsoft Color BASIC and cassette tapes for data storage. Over the years since then, he has had the opportunity to work on projects ranging from simple DOS applications to global telecommunications networks spanning multiple platforms.

Latest Stories
DX World EXPO, LLC, a Lighthouse Point, Florida-based startup trade show producer and the creator of "DXWorldEXPO® - Digital Transformation Conference & Expo" has announced its executive management team. The team is headed by Levent Selamoglu, who has been named CEO. "Now is the time for a truly global DX event, to bring together the leading minds from the technology world in a conversation about Digital Transformation," he said in making the announcement.
"Space Monkey by Vivent Smart Home is a product that is a distributed cloud-based edge storage network. Vivent Smart Home, our parent company, is a smart home provider that places a lot of hard drives across homes in North America," explained JT Olds, Director of Engineering, and Brandon Crowfeather, Product Manager, at Vivint Smart Home, in this SYS-CON.tv interview at @ThingsExpo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
SYS-CON Events announced today that Conference Guru has been named “Media Sponsor” of the 22nd International Cloud Expo, which will take place on June 5-7, 2018, at the Javits Center in New York, NY. A valuable conference experience generates new contacts, sales leads, potential strategic partners and potential investors; helps gather competitive intelligence and even provides inspiration for new products and services. Conference Guru works with conference organizers to pass great deals to gre...
DevOps is under attack because developers don’t want to mess with infrastructure. They will happily own their code into production, but want to use platforms instead of raw automation. That’s changing the landscape that we understand as DevOps with both architecture concepts (CloudNative) and process redefinition (SRE). Rob Hirschfeld’s recent work in Kubernetes operations has led to the conclusion that containers and related platforms have changed the way we should be thinking about DevOps and...
The Internet of Things will challenge the status quo of how IT and development organizations operate. Or will it? Certainly the fog layer of IoT requires special insights about data ontology, security and transactional integrity. But the developmental challenges are the same: People, Process and Platform. In his session at @ThingsExpo, Craig Sproule, CEO of Metavine, demonstrated how to move beyond today's coding paradigm and shared the must-have mindsets for removing complexity from the develop...
In his Opening Keynote at 21st Cloud Expo, John Considine, General Manager of IBM Cloud Infrastructure, led attendees through the exciting evolution of the cloud. He looked at this major disruption from the perspective of technology, business models, and what this means for enterprises of all sizes. John Considine is General Manager of Cloud Infrastructure Services at IBM. In that role he is responsible for leading IBM’s public cloud infrastructure including strategy, development, and offering m...
The next XaaS is CICDaaS. Why? Because CICD saves developers a huge amount of time. CD is an especially great option for projects that require multiple and frequent contributions to be integrated. But… securing CICD best practices is an emerging, essential, yet little understood practice for DevOps teams and their Cloud Service Providers. The only way to get CICD to work in a highly secure environment takes collaboration, patience and persistence. Building CICD in the cloud requires rigorous ar...
Companies are harnessing data in ways we once associated with science fiction. Analysts have access to a plethora of visualization and reporting tools, but considering the vast amount of data businesses collect and limitations of CPUs, end users are forced to design their structures and systems with limitations. Until now. As the cloud toolkit to analyze data has evolved, GPUs have stepped in to massively parallel SQL, visualization and machine learning.
"Evatronix provides design services to companies that need to integrate the IoT technology in their products but they don't necessarily have the expertise, knowledge and design team to do so," explained Adam Morawiec, VP of Business Development at Evatronix, in this SYS-CON.tv interview at @ThingsExpo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
To get the most out of their data, successful companies are not focusing on queries and data lakes, they are actively integrating analytics into their operations with a data-first application development approach. Real-time adjustments to improve revenues, reduce costs, or mitigate risk rely on applications that minimize latency on a variety of data sources. In his session at @BigDataExpo, Jack Norris, Senior Vice President, Data and Applications at MapR Technologies, reviewed best practices to ...
Widespread fragmentation is stalling the growth of the IIoT and making it difficult for partners to work together. The number of software platforms, apps, hardware and connectivity standards is creating paralysis among businesses that are afraid of being locked into a solution. EdgeX Foundry is unifying the community around a common IoT edge framework and an ecosystem of interoperable components.
"ZeroStack is a startup in Silicon Valley. We're solving a very interesting problem around bringing public cloud convenience with private cloud control for enterprises and mid-size companies," explained Kamesh Pemmaraju, VP of Product Management at ZeroStack, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
Large industrial manufacturing organizations are adopting the agile principles of cloud software companies. The industrial manufacturing development process has not scaled over time. Now that design CAD teams are geographically distributed, centralizing their work is key. With large multi-gigabyte projects, outdated tools have stifled industrial team agility, time-to-market milestones, and impacted P&L stakeholders.
"Akvelon is a software development company and we also provide consultancy services to folks who are looking to scale or accelerate their engineering roadmaps," explained Jeremiah Mothersell, Marketing Manager at Akvelon, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
Enterprises are adopting Kubernetes to accelerate the development and the delivery of cloud-native applications. However, sharing a Kubernetes cluster between members of the same team can be challenging. And, sharing clusters across multiple teams is even harder. Kubernetes offers several constructs to help implement segmentation and isolation. However, these primitives can be complex to understand and apply. As a result, it’s becoming common for enterprises to end up with several clusters. Thi...