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Modifying the HTTP Response Using FiltersDecember 2

When a browser requests an ASP.NET page from a web server, the ASP.NET engine takes that request through a number of steps that, together, generate the resulting markup, which is returned to the requesting browser for display. The stages in this process are referred to as the HTTP Pipeline and perform tasks like authentication, authorization, and having the requested page render its content. During one of the later stages in the HTTP Pipeline the rendered markup is handed off to a response filter which, if supplied, has an opportunity to inspect and modify the markup before it is returned to the requesting browser.

With a little bit of code you can create your own response filters and associate them with a particular page, a particular type of page (such as ASP.NET resources that generate HTML), or for all ASP.NET resources. And if you are using IIS 7's integrated mode you can have your filter work with the output of any content type. This article provides an overview of response filters and shows two such filters: a naive filter that strips out whitespace to reduce the size of the markup sent over the wire, and a filter that adds a copyright message to the bottom of all web pages. You can download these two filters, along with a simple demo application, at the end of this article, with examples in both C# and Visual Basic.

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A Google Chart API Custom Server ControlNovember 25

Last week's article, Creating Charts with the Google Chart API, looked at how to use Google's free Chart API to generate line, pie, bar, and other types of charts from an ASP.NET page. The Google Chart API is callable via a URL that contains the chart type, size, data, and other parameters in the querystring and returns the chart as an image. Displaying a chart using this API is as simple as adding an Image Web control to a page and setting its ImageUrl property to the Google Chart API URL with an appropriately formatted querystring.

Last week's article explored the essential querystring parameters and provided an example on how to programmatically construct this querystring to plot data from a database query. In a nutshell, constructing this querystring involved about 50 lines of code to get the data, express the data as percentages relative to one another, and build up the other parameters. Wouldn't it be much easier if we could create a chart by dropping a Google Chart API Web control on the page, set a few properties, and then bind it to a data source control, like a SqlDataSource or ObjectDataSource? That way we could create and display charts using the Google Chart API without having to write a lick of code.

Over the past week I built such a Web control. The Web control does not provide the full suite of Google Chart API features - it only allows for the creation of line, bar, and

Creating Charts with the Google Chart APINovember 18

I've always wondered how the phrase "A picture is worth a thousand words" came about. I like to think that it was coined by some mid-level manager viewing a sales figures report that consisted of metrics from the past 1,000 days. After scanning this long list of numbers, he found, at the bottom of the page, a line chart that summarized the numbers, and uttered that now well-known adage. Charts and graphs provide a succinct synopsis of large amounts of data. With charts a person can quickly spot trends, compare different resultsets, or recognize patterns.

There are many ways to create charts in an ASP.NET web page. You can use the classes in the System.Drawing namespace to programmatically generate charts; you can use the Microsoft Office Web Components (OWC). There are also open-sourcecharting tools and a plethora of third-party components, as well. Microsoft has even entered the game and introduced

Troubleshooting Website Problems by Examining the HTTP TrafficNovember 11

I started my career as a web developer with Microsoft's Active Server Pages (ASP), the predecessor to ASP.NET. ASP was a very simple scripting engine and lacked the tools that ASP.NET developers today take for granted, most notably a debugger. Debugging an ASP script typically involved littering the code with Response.Write statements to output the values of variables at different points in time of the script's life-cycle. Debugging an ASP.NET page is so much easier thanks to the Visual Studio debugger, which allows you to set breakpoints, step through executing code, use Watch windows to keep an eye on variable values as they change, and an Intermediate window to evaluate statements during debug time.

While the Visual Studio debugger has greatly improved the debugging story, there are certain scenarios where a server-side debugger is of little or no help. In certain cases the problem is not in the server-side code but instead in what is being sent from the client to the server (or vice-a-versa). These types of scenarios are quite common when creating AJAX-enabled web applications, as the data exchanged between the client and server during a partial page postback affects the code executed on the server-side and how the page is updated on response. This technique is also quite useful when debugging pages that perform different Response.Redirects based on various parameters, or when trying to ascertain why images, videos, or other external content is not properly lo

Converting Flat, Comma-Delimited Values Into a Normalized Data ModelNovember 4

In my job as an independent software developer I help a lot of small businesses enhance their existing company website or internal web applications to include new features or adopt best practices. Many of these businesses have vital line of business applications that were created many years ago by an employee who was not a professional software developer, but perhaps a member of the IT team or someone who was learning how to program or programmed as a hobby. A common mistake made by people without a solid background in creating data-driven applications is using flat, non-normalized data models.

Consider an application used in a healthcare setting may need to record each doctor's professional and educational degrees. Because there are a fixed number of degrees - PhD, MD, DDS, OB/GYN, RN, etc. - these degrees should be spelled out in a separate database table. And because each doctor can have multiple degrees, there should be a third table that maps what doctors are associated with what degrees. Such a data model would be normalized. A non-normalized data model would instead try to capture each doctor's degrees within the same table that contains the doctor's other information (his name, address, DOB, etc.). This might be implemented as several columns in the table (Degree1, Degree2, Degree3, and so on) or as a single column that contains a comma-delimited list of degrees, like "PhD, MD, OB/GYN".

While there are certain circumstances where non-normalized dat