Microsoft Cloud Authors: Elizabeth White, Mihai Corbuleac, Pat Romanski, David Bermingham, Steven Mandel

Related Topics: Microsoft Cloud

Microsoft Cloud: Article

Programmatically Posting Data to ASP .NET Web Applications

Create powerful automated utilities

Programmatically posting data to a traditional ASP page is an extremely useful and well-known technique. However, I recently discovered that posting data to an ASP .NET Web application from another program is not well understood and requires several new programming tricks. In this article I'll show you how to use the HttpWebRequest class and the ASP .NET ViewState mechanism to programmatically send form data to an ASP .NET Web application and then capture the response. This will provide you with a powerful new way to write utility programs for your Web applications. (Note: This article assumes you are familiar with creating ASP .NET Web applications, using classes in the .NET Framework, and have intermediate familiarity with the C# language.)

The best way to demonstrate what we will accomplish is with two screenshots. Figure 1 shows a simple ASP .NET Web application. If the user types "red" in the upper textbox control and clicks the submit button, the application displays "roses are red" in the lower textbox as shown. If the user types and sends anything other than "red," "blue," or "green," the application responds with "unknown color."

Suppose we want to post data programmatically and examine the response. In other words, we want a console application or some other type of program to simulate typing a value in the Enter-a-color textbox and clicking the submit button, and then determine what the response is. Figure 2 shows a console application that does just that. You can see the value of TextBox2 is "roses are red."

Even though this example is a console application, the underlying code can be used in any .NET program. In the following sections I'll walk you through the core code that posts data to ASP .NET and explain it in detail, then we'll briefly look at some variations to show you how to deal with server-side controls other than TextBox. I'll conclude with a discussion of some of the ways you can use this technique in a production environment.

The Problem
Listing 1 shows the source code for the simple ASP .NET Web application shown in Figure 1. For simplicity, I used a basic text editor (yes, Notepad) and put the logic code in the same file as the HTML display code. I used the Visual Basic .NET language for the Web application, but I could have used any .NET language.

If we want to send "red" to this application, we have to deal with three problems. How do we assign "red" to the TextBox1 control; how do we tell the ASP .NET server that Button1 has been clicked; and how do we capture the response from the server?

The ViewState Value
Listing 2 shows the complete console application source code that generated the output shown in Figure 2. As you can see I used C# but I could have used Visual Basic .NET or any other .NET language. I'll walk you through this code in the next three sections and explain exactly how it works.

After declaring five namespaces so I wouldn't have to fully qualify each class, I declared and assigned a variable for the URL of the Web application:

string url = "http://localhost/PostToASPdotNET/colors.aspx";

Next comes the trickiest part and the key to the entire programmatic post technique:

string viewstate = InitialViewState(url);

I declare and assign a value for the Web application's ViewState. What is this? Even though HTTP is a stateless protocol - that is, each Request-Response pair is an isolated transaction - ASP .NET works behind the scenes to simulate a stateful environment. One of the ways ASP .NET does this is through the use of an HTML hidden input named __VIEWSTATE. It's a Base64-encoded string value that represents the state of the page when the server last processed it. In this way pages can retain values between successive calls. To correctly post information to an ASP .NET application, we need to send the ViewState value to the server. Where do we get this value from?

The easiest way to get the initial ViewState value for a Web application is to launch Internet Explorer, get the page, and then do a View -> Source from the menu bar (see Figure 3).

As you can see, the initial value of __VIEWSTATE is "dDw0NjgyMT gwODQ7Oz7iZ4VvNPCaZ3SL6rj+ucrH9CSs8Q==", so I could have written:

string viewstate = "dDw0NjgyMTgwODQ7Oz7iZ4VvNPCaZ3SL6rj+ucrH9CSs8Q==";

This manual determination of the ViewState value is awkward because the whole point of our technique is to post data programmatically rather than manually.

I wrote a helper method InitialViewState() that queries the Web application for its initial __VIEWSTATE value and returns it as a string. I'll discuss the InitialViewState() method in the next section; for now, just assume that we can get that value. The raw ViewState value needs processing from the UrlEncode() method:

viewstate = HttpUtility.UrlEncode(viewstate);

UrlEncode() converts characters that the ASP .NET server would misinterpret into escaped sequences. For example, the "/" characters are converted into %2F sequences. After we have the ViewState value, we can construct the full data string that we will post to the Web application, copy the post data to a byte array, and deal with a proxy server if there is one:

string data = "TextBox1=red&TextBox2=empty&Button1=clicked&__VIEWSTATE=" +
byte[] buffer = Encoding.UTF8.GetBytes(data);
string proxy = null;

In this example, there are four name-value pairs. The first pair, TextBox1=red, is exactly what you might expect. It assigns "red" to the control with an ID attribute "TextBox1". The second pair, TextBox2=empty, is probably not expected if you have experience posting data to traditional ASP pages. Because TextBox2 is a server-side control, it contributes to the ViewState value and we must post it to the server to keep the ViewState value valid. The value we assign, "empty," is irrelevant and we could have used anything. I prefer to use values like "empty" that are somewhat self-documenting. The third name-value pair, Button1= clicked, is a little more subtle than it appears. Because Button1 is a server-side control we must post it to keep the ViewState value synchronized. Assigning any value to it has no effect so we could have written Button1= by itself. I like to assign a value like "clicked" as it makes the code more readable. The fourth name-value pair is the __VIEWSTATE pair (note: two underscores) I discussed earlier and the real key to programmatically posting to ASP .NET servers.

After we set up the data string we copy it into a byte array using the GetBytes() method in the System.Text namespace because the method that will post the data later requires the data to be stored as bytes. Then we set up a value for a proxy server. Because I ran my example on a local machine, I just assigned null for its value.

The HttpWebRequest Class
Let's continue walking through the source code by examining the HttpWebRequest class that actually posts our data.

Start by creating an HttpWebRequest object. Notice that, rather unusually, we use an explicit Create() method rather than calling a constructor with the new keyword:

HttpWebRequest req = (HttpWebRequest)WebRequest.Create(url);

After creating the HttpWebRequest, we supply values for five of its properties.

req.Method = "POST";
req.ContentType = "application/x-www-form-urlencoded";
req.ContentLength = buffer.Length;
req.Proxy = new WebProxy(proxy, true); // ignore for local addresses
req.CookieContainer = new CookieContainer(); // enable cookies

We use the POST method because we're sending form data, and we set the ContentType property to "application/x-www-form-urlencoded". This is a MIME (Multipurpose Internet Mail Extension) type that essentially tells the ASP .NET server to expect form data. We set the ContentLength property to the number of bytes of post data that we stored in a byte array buffer earlier.

The Boolean true parameter in the WebProxy constructor means to ignore the proxy for local addresses as I'm doing in this example. Assigning a value to the CookieContainer property is required. Notice that we assign an empty CookieContainer object. This is one of the little details that caused me a lot of trouble when I was figuring out this technique.

Before we can post our request to the ASP .NET application, we have to add the post data to the Request object.

Stream reqst = req.GetRequestStream(); // add form data to request stream
reqst.Write(buffer, 0, buffer.Length);

After we declare a Stream object, we get the RequestStream from the HttpWebRequestObject and then add to it using the Write() method. Write() requires a Byte array instead of a string; that's why we converted the post data from a string into bytes earlier. Another important detail is to remember to call the Flush() method to actually add the post data to the Request stream.

Finally we're ready to post to our application:

Console.WriteLine("\nPosting 'red' to " + url);
HttpWebResponse res = (HttpWebResponse)req.GetResponse(); // send request, get

If you're new to this type of programming, you might have expected something like "req.SendData()" instead of declaring an HttpWebResponse and assigning its value with the GetResponse() method like we actually do. The "send" is implicit. Getting the response from the request follows the usual .NET Framework stream pattern:

Console.WriteLine("\nResponse stream is: \n");
Stream resst = res.GetResponseStream(); // display HTTP response
StreamReader sr = new StreamReader(resst);

To summarize, in order to programmatically post data to an ASP .NET Web application, you must send values for all server-side controls and the __VIEWSTATE input. The methods and properties of the HttpWeb Request class are the primary means we use. You must also be aware of several details that aren't particularly well documented like the necessity of setting the CookieContainer property of your HttpWebRequest object.

The InitialViewState() Helper Method
In the previous sections, we assumed we had a method named InitialViewState() that returns the critical ViewState value. Let's walk through that helper method.

The InitialViewState() accepts as input a string that represents the URL of the Web application of which we are determining the ViewState. The key is to use the WebClient class that is similar to the HttpWebRequest class in that it can send an HTTP request and get the response. However, the WebClient class is much simpler; it can send only a basic HTTP GET request and accept the response stream, but that's all we need to get the initial value of the __VIEWSTATE variable.

First we declare and create a WebClient object using its only default constructor:

WebClient wc = new WebClient();

Next we use that object to create a stream of information to the URL of the Web application:

Stream st = wc.OpenRead(url);
StreamReader sr = new StreamReader(st);

Now we read through the response stream of the initial Web application page line by line, looking for the line that contains the __VIEWSTATE variable so we can parse out its value. Recall that the ViewState is contained in a single line that looks like:

<input type="hidden"
value="dDw0NjgyMTgwODQ7Oz7iZ4VvNPCaZ3SL6rj+ucrH9CSs8Q==" />

We can use the String.Index Of() method to determine if we are at the target line.


if (line.IndexOf("__VIEWSTATE") != -1) // found line
  int startIndex = line.IndexOf("value=") + 7;
  int endIndex = line.IndexOf("\"", startIndex);
  int count = endIndex - startIndex;
  return line.Substring(startIndex, count);

When we have found the line that contains the __VIEWSTATE value, we can extract it using the String.Substring() method, looking for the characters that follow "value=" and are before the next double-quote character.

The example presented and explained in the previous sections accepts user input into a TextBox control and also displays output in a TextBox. What if your application uses other controls? Consider an ASP .NET Web application that has a checkbox, a button, and a label control:


<form method="post" runat="server" >
  <asp:CheckBox id="CheckBox1" runat="server"
  Text="Check Me" /> <br>
  <asp:Button id="Button1" runat="server" Text="Button"
  OnClick="Button1_Click"/> <br>
  <asp:Label id="Label1" runat="server" />

Imagine that the page has some logic that displays a message on the Label control according to whether or not the CheckBox control is checked. To simulate a user checking the CheckBox and clicking the submit Button control, construct a data string like:

data = "CheckBox1=checked&Button1=clicked&Label1=empty&__VIEWSTATE=" & viewstate

To simulate checking the CheckBox control, we put CheckBox1=checked in the data string. Somewhat surprisingly, "checked" is not relevant and as long as we specify any value there, the server will interpret the control as checked. If we want to simulate an unchecked CheckBox, we leave out any value and put CheckBox1= in the string:

data = "CheckBox1=&Button1=clicked&Label1=empty&__VIEWSTATE=" & viewstate

As explained before, we need to supply any value for the Button control, and "clicked" is nicely self-documenting. We must include the Label control too because it contributes to the __VIEWSTATE value, but in this case it doesn't matter whether we supply a value or not (so I used "empty"). Of course we need the initial __VIEWSTATE value.

Depending on which controls you have in your ASP .NET Web application, there are many variations possible, but with a little experimentation you can programmatically post data to any combination of controls.

Now that you can programmatically post data to an ASP .NET Web application, what are some of the ways you can employ this technique in a production environment? I have used this technique in virtually every Web-based product I've worked on. One valuable use is to construct Developer Regression Tests (DRTs) for your Web application. DRTs are a sequence of automated tests that are run after you make changes to your application. They are designed to determine if your new code has broken existing functionality before you check in the code.

For the example application in this article, you could create a simple text file of test cases:

001:red:roses are red
002:blue:the sky is blue
003:green:grass is green

The first line of this file has a test case ID, followed by the input, and then the expected result. Read this file line by line, parse out the three fields, programmatically post the input string, examine the response stream to see if the actual response matches the expected result or not, and then log the pass or fail result. Notice that test case 003 would catch a logic error in our application (see Listing 1).

There are many ways you can modify the code I've presented here. I have left out all error-checking for the sake of clarity and you'll want to add all the usual checks; the .NET try-catch mechanism is powerful and adding it to this code will save you a lot of time in the long run. In particular, the InitialViewState() method is quite brittle.

I have hard-coded most values. To make the code in this article more flexible you can parameterize the code in several ways. For example, a parameterization I often use takes the form:

bool ResponseStringHasTarget(string url, string proxy, string data, string target)

where the method returns true if the response from data sent to the application URL using proxy server proxy contains a string target. It could then be called like:


if (ResponseStringHasTarget(url, proxy, data, target) == true)

There are many other ways you can customize and modify the code in this article to suit your own particular needs.

The ability to programmatically post data to a traditional ASP Web page is extremely useful and fairly well understood. But the techniques required to post data to an ASP .NET Web application are not well documented or generally known. This article has shown you how to programmatically post data to a Web application from any .NET program. The key class that posts the request and gets the response is the HttpWebRequest class. However, the technique that we use to post to traditional ASP pages must be significantly modified by taking into account the application's initial __VIEWSTATE attribute and the state of all server-side controls.

By using the techniques in this article you can create extremely powerful automated tests for any ASP .NET Web application and write a wide range of useful utility tools.

Resources and References

  • Warren, S. "Taking a Bite Out of ASP.NET ViewState." November 27, 2001: Taking a Bite Out of ASP.NET ViewState
  • "Client-Side Functionality in a Server Control." .NET Framework Developer's Guide: Client-Side Functionality in a Server Control
  • "HttpWebRequest Class." .NET Framework Class Library: HttpWebRequest Class
  • "Control.ViewState Property." .NET Framework Class Library: Control.ViewState Property
  • More Stories By James McCaffrey

    Dr. James McCaffrey works for Volt Information Sciences, Inc., where he manages technical training for software engineers working at Microsoft's Redmond, WA campus. He has worked on several Microsoft products, including Internet Explorer and MSN Search. James can be reached at [email protected] or [email protected]

    Comments (1) View Comments

    Share your thoughts on this story.

    Add your comment
    You must be signed in to add a comment. Sign-in | Register

    In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.

    Most Recent Comments
    portsj 08/19/08 07:19:18 PM EDT

    This code does not work for me. I created a new website and a C# console application in VS.NET 2005. HttpWebResponse res = (HttpWebResponse)req.GetResponse(); throws a 500 error. Also, viewstate = HttpUtility.UrlEncode(viewstate); should be
    viewstate = HttpUtility.UrlDecode(viewstate);

    Can you please test your code and provide me with working code and/or advise how to make it work?

    Thanks in advance,

    @ThingsExpo Stories
    SYS-CON Events announced today that DatacenterDynamics has been named “Media Sponsor” of SYS-CON's 18th International Cloud Expo, which will take place on June 7–9, 2016, at the Javits Center in New York City, NY. DatacenterDynamics is a brand of DCD Group, a global B2B media and publishing company that develops products to help senior professionals in the world's most ICT dependent organizations make risk-based infrastructure and capacity decisions.
    SYS-CON Events announced today TMCnet has been named “Media Sponsor” of SYS-CON's 18th International Cloud Expo, which will take place on June 7–9, 2016, at the Javits Center in New York City, NY, and the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Technology Marketing Corporation (TMC) is the world's leading business-to-business and integrated marketing media company, servicing niche markets within the com...
    The IoT has the potential to create a renaissance of manufacturing in the US and elsewhere. In his session at 18th Cloud Expo, Florent Solt, CTO and chief architect of Netvibes, will discuss how the expected exponential increase in the amount of data that will be processed, transported, stored, and accessed means there will be a huge demand for smart technologies to deliver it. Florent Solt is the CTO and chief architect of Netvibes. Prior to joining Netvibes in 2007, he co-founded Rift Technol...
    Join IBM June 8 at 18th Cloud Expo at the Javits Center in New York City, NY, and learn how to innovate like a startup and scale for the enterprise. You need to deliver quality applications faster and cheaper, attract and retain customers with an engaging experience across devices, and seamlessly integrate your enterprise systems. And you can't take 12 months to do it.
    This is not a small hotel event. It is also not a big vendor party where politicians and entertainers are more important than real content. This is Cloud Expo, the world's longest-running conference and exhibition focused on Cloud Computing and all that it entails. If you want serious presentations and valuable insight about Cloud Computing for three straight days, then register now for Cloud Expo.
    IoT device adoption is growing at staggering rates, and with it comes opportunity for developers to meet consumer demand for an ever more connected world. Wireless communication is the key part of the encompassing components of any IoT device. Wireless connectivity enhances the device utility at the expense of ease of use and deployment challenges. Since connectivity is fundamental for IoT device development, engineers must understand how to overcome the hurdles inherent in incorporating multipl...
    Machine Learning helps make complex systems more efficient. By applying advanced Machine Learning techniques such as Cognitive Fingerprinting, wind project operators can utilize these tools to learn from collected data, detect regular patterns, and optimize their own operations. In his session at 18th Cloud Expo, Stuart Gillen, Director of Business Development at SparkCognition, will discuss how research has demonstrated the value of Machine Learning in delivering next generation analytics to im...
    Manufacturers are embracing the Industrial Internet the same way consumers are leveraging Fitbits – to improve overall health and wellness. Both can provide consistent measurement, visibility, and suggest performance improvements customized to help reach goals. Fitbit users can view real-time data and make adjustments to increase their activity. In his session at @ThingsExpo, Mark Bernardo Professional Services Leader, Americas, at GE Digital, will discuss how leveraging the Industrial Interne...
    The paradigm has shifted. A Gartner survey shows that 43% of organizations are using or plan to implement the Internet of Things in 2016. However, not just a handful of companies are still using the old-style ad-hoc trial-and-error ways, unaware of the critical barriers, paint points, traps, and hidden roadblocks. How can you become a winner? In his session at @ThingsExpo, Tony Shan will present a methodical approach to guide the holistic adoption and enablement of IoT implementations. This ov...
    SYS-CON Events announced today that Stratoscale, the software company developing the next generation data center operating system, will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. Stratoscale is revolutionizing the data center with a zero-to-cloud-in-minutes solution. With Stratoscale’s hardware-agnostic, Software Defined Data Center (SDDC) solution to store everything, run anything and scale everywhere...
    Angular 2 is a complete re-write of the popular framework AngularJS. Programming in Angular 2 is greatly simplified – now it's a component-based well-performing framework. This immersive one-day workshop at 18th Cloud Expo, led by Yakov Fain, a Java Champion and a co-founder of the IT consultancy Farata Systems and the product company SuranceBay, will provide you with everything you wanted to know about Angular 2.
    Digital payments using wearable devices such as smart watches, fitness trackers, and payment wristbands are an increasing area of focus for industry participants, and consumer acceptance from early trials and deployments has encouraged some of the biggest names in technology and banking to continue their push to drive growth in this nascent market. Wearable payment systems may utilize near field communication (NFC), radio frequency identification (RFID), or quick response (QR) codes and barcodes...
    SYS-CON Events announced today that Men & Mice, the leading global provider of DNS, DHCP and IP address management overlay solutions, will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. The Men & Mice Suite overlay solution is already known for its powerful application in heterogeneous operating environments, enabling enterprises to scale without fuss. Building on a solid range of diverse platform support,...
    You deployed your app with the Bluemix PaaS and it's gaining some serious traction, so it's time to make some tweaks. Did you design your application in a way that it can scale in the cloud? Were you even thinking about the cloud when you built the app? If not, chances are your app is going to break. Check out this webcast to learn various techniques for designing applications that will scale successfully in Bluemix, for the confidence you need to take your apps to the next level and beyond.
    The increasing popularity of the Internet of Things necessitates that our physical and cognitive relationship with wearable technology will change rapidly in the near future. This advent means logging has become a thing of the past. Before, it was on us to track our own data, but now that data is automatically available. What does this mean for mHealth and the "connected" body? In her session at @ThingsExpo, Lisa Calkins, CEO and co-founder of Amadeus Consulting, will discuss the impact of wea...
    Whether your IoT service is connecting cars, homes, appliances, wearable, cameras or other devices, one question hangs in the balance – how do you actually make money from this service? The ability to turn your IoT service into profit requires the ability to create a monetization strategy that is flexible, scalable and working for you in real-time. It must be a transparent, smoothly implemented strategy that all stakeholders – from customers to the board – will be able to understand and comprehe...
    So, you bought into the current machine learning craze and went on to collect millions/billions of records from this promising new data source. Now, what do you do with them? Too often, the abundance of data quickly turns into an abundance of problems. How do you extract that "magic essence" from your data without falling into the common pitfalls? In her session at @ThingsExpo, Natalia Ponomareva, Software Engineer at Google, will provide tips on how to be successful in large scale machine lear...
    SYS-CON Events announced today that Ericsson has been named “Gold Sponsor” of SYS-CON's @ThingsExpo, which will take place on June 7-9, 2016, at the Javits Center in New York, New York. Ericsson is a world leader in the rapidly changing environment of communications technology – providing equipment, software and services to enable transformation through mobility. Some 40 percent of global mobile traffic runs through networks we have supplied. More than 1 billion subscribers around the world re...
    SYS-CON Events announced today that Fusion, a leading provider of cloud services, will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. Fusion, a leading provider of integrated cloud solutions to small, medium and large businesses, is the industry's single source for the cloud. Fusion's advanced, proprietary cloud service platform enables the integration of leading edge solutions in the cloud, including cloud...
    There is an ever-growing explosion of new devices that are connected to the Internet using “cloud” solutions. This rapid growth is creating a massive new demand for efficient access to data. And it’s not just about connecting to that data anymore. This new demand is bringing new issues and challenges and it is important for companies to scale for the coming growth. And with that scaling comes the need for greater security, gathering and data analysis, storage, connectivity and, of course, the...