Microsoft Cloud Authors: Elizabeth White, Yeshim Deniz, Serafima Al, Janakiram MSV, John Katrick

Related Topics: Microsoft Cloud

Microsoft Cloud: Article

How ASP.NET PostBacks and Redirects Work

A question from some of our clients

Last week I got the following two questions from one of our clients

  • “We use ASP.NET PostBacks but can’t find the PurePath for the request triggering the PostBack handler – any hints?”
  • “We see many ThreadAbortExceptions in our ASP.NET Application and we are not sure why they happen – are they expected?”

Time for a little blog that gives some internals on PostBacks as well as Redirects (which are commonly used in PostBack handlers).

What is a PostBack and how does it work?
It’s not my intention to write the 50th blog post about PostBacks – I’d rather recommend checking out the following links for more details on ASP.NET PostBacks and the ASP.NET Page LifeCycle. I am also not necessarily advocating PostBacks here either as there are other ways of implementing web applications (e.g.: ASP.NET MVC) – but – as the question came up I am sure many out there use this feature and may wonder how it works.

The important thing to understand is that a PostBack – as the name implies – POSTs data back to the current url. This allows ASP.NET Developers to implement PostBack code similar to event handlers in rich UI’s where you even get access to before/after values of controls.

In the sample application I use I have a MainForm.aspx page that displays a login control with a username and password field and a login button. When the user clicks the login button the data of the form elements is POSTed back to the server which ultimately calls the Login Button Click event handler. When a user therefore opens a browser and browses to my MainForm.aspx page and then clicks the login button we end up having 2 HTTP Requests to the same MainForm.aspx page. The second request responds with a different page, e.g.: Yes you are logged in or Authentication failed even though it goes to the same URL.

The following illustration shows my login button handler that takes the values POSTed to the MainForm.aspx page and checks whether the username/password combination is correct.

PostBack triggers Login Button Event Handler which does user  authentication and redirects depending on logon success

PostBack triggers Login Button Event Handler which does user authentication and redirects depending on logon success

Also – depending on whether it is the initial page request or a PostBack you may want to execute different code. This can be done by checking the IsPostBack property on the Page objects. Remember our earlier example? The user basically requested the same url – MainForm.aspx – but obviously expects a different result for the 2nd request. The following illustration shows how to implement conditional code depending on PostBack or initial request:

Conditional Code depending on whether this is a PostBack or initial  page request

Conditional Code depending on whether this is a PostBack or initial page request

The answer to the first question I received last week therefore is: Identify the 2 requests on the same initial URL. The following illustration shows how dynaTrace displays the individual URL’s that have been traced so far and how to actually drill to the PurePath for the PostBack request. We see the 2 requests to MainForm.aspx and the two corresponding PurePaths where the second is the one that reflects the PostBack request which ultimately calls our click handler:

Identifying the PostPack PurePath and spotting the click event  handler

Identifying the PostPack PurePath and spotting the click event handler

What’s the difference between Response.Redirect and Server.Transfer?
You probably wonder what really happens after a PostBack. Are we now always staying on the same MainForm.aspx page? Or is there a way to redirect the user to a different url? ASP.NET offers two options (at least I am only aware of these two). There is the option of redirecting the user to a different URL or let the server transfer over to process a different URL.

Let’s go back to my example from above. My user logs in. In case the login is successful I want the user to get to his personalized site. In case the login was not successful I want the user to get back to the login page with an error displayed that the login was not successful. One option to redirect the user to a different url is to use Response.Redirect telling ASP.NET to redirect to a different URL. Technically – Response.Redirect actually sends an HTTP Redirect Response back to the browser causing the browser to request the new URL. This works great – but – it causes an extra roundtrip between browser and server. The following illustration (using the FREE dynaTrace AJAX Edition) shows the Network Requests between browser and server when browsing through the pages of my application. We can spot the redirects that the PostBacks cause by using Response.Redirect:

PostBack's causing an additional roundtrip between browser and  server as it uses HTTP Redirects

PostBack's causing an additional roundtrip between browser and server as it uses HTTP Redirects

My sample application redirects to the same URL but using a different url parameter to indicate which feature of the web site my user should see, e.g.: overview. It is easy to spot what is going on here. First we have the initial request to MainForm.aspx which displays the login dialog (because my user is not yet logged in). The PostBack on MainForm.aspx comes back telling the browser to redirect to MainForm.aspx?action?overview which is then requested by the browser. This behavior goes on for every interaction my user does – basically causing an extra roundtrip that should be avoided. It also causes many exceptions on the server – and that brings me to the second question I received: In order to do the redirect ASP.NET aborts the currently executing thread with a ThreadAbortException. So – whenever you use Response.Redirect – expect to see ThreadAbortExceptions (in case you use something like dynaTrace that actually gives you insight into these internal exceptions).

Fortunately ASP.NET offers a second option to transfer to a different page. Server.Transfer shortcuts the redirect by executing another page request with the new URL in your current ASP.NET thread. When changing my implementation from Response.Redirect to Server.Transfer I get rid of all HTTP Redirects. The following illustration shows what a PurePath that uses Server.Transfer looks like:

Server.Transfer executes transfered URL in same execution thread

Server.Transfer executes transferred URL in same execution thread

Make yourself familiar with internals of ASP.NET. If you use other frameworks such as ASP.NET MVC make sure you do enough research and reading on the options the framework gives you and how things work internally. It is important to save on unnecessary HTTP roundtrips as they can become really expensive for end-user browsing experience. As always, feedback and your thoughts on this topic are welcome.

Related reading:

  1. SharePoint: Performance Problem with LookupField Control The Microsoft.SharePoint.WebControls.LookupField control is used as the default control when editing...
  2. SharePoint: List Performance – How list column indices really work under the hood Have you ever wondered what is really going on under...

More Stories By Andreas Grabner

Andreas Grabner has been helping companies improve their application performance for 15+ years. He is a regular contributor within Web Performance and DevOps communities and a prolific speaker at user groups and conferences around the world. Reach him at @grabnerandi

@ThingsExpo Stories
The IoT Will Grow: In what might be the most obvious prediction of the decade, the IoT will continue to expand next year, with more and more devices coming online every single day. What isn’t so obvious about this prediction: where that growth will occur. The retail, healthcare, and industrial/supply chain industries will likely see the greatest growth. Forrester Research has predicted the IoT will become “the backbone” of customer value as it continues to grow. It is no surprise that retail is ...
Digital Transformation: Preparing Cloud & IoT Security for the Age of Artificial Intelligence. As automation and artificial intelligence (AI) power solution development and delivery, many businesses need to build backend cloud capabilities. Well-poised organizations, marketing smart devices with AI and BlockChain capabilities prepare to refine compliance and regulatory capabilities in 2018. Volumes of health, financial, technical and privacy data, along with tightening compliance requirements by...
Business professionals no longer wonder if they'll migrate to the cloud; it's now a matter of when. The cloud environment has proved to be a major force in transitioning to an agile business model that enables quick decisions and fast implementation that solidify customer relationships. And when the cloud is combined with the power of cognitive computing, it drives innovation and transformation that achieves astounding competitive advantage.
DevOpsSummit New York 2018, colocated with CloudEXPO | DXWorldEXPO New York 2018 will be held November 11-13, 2018, in New York City. Digital Transformation (DX) is a major focus with the introduction of DXWorldEXPO within the program. Successful transformation requires a laser focus on being data-driven and on using all the tools available that enable transformation if they plan to survive over the long term. A total of 88% of Fortune 500 companies from a generation ago are now out of bus...
Dion Hinchcliffe is an internationally recognized digital expert, bestselling book author, frequent keynote speaker, analyst, futurist, and transformation expert based in Washington, DC. He is currently Chief Strategy Officer at the industry-leading digital strategy and online community solutions firm, 7Summits.
DXWordEXPO New York 2018, colocated with CloudEXPO New York 2018 will be held November 11-13, 2018, in New York City and will bring together Cloud Computing, FinTech and Blockchain, Digital Transformation, Big Data, Internet of Things, DevOps, AI, Machine Learning and WebRTC to one location.
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.
Cloud-enabled transformation has evolved from cost saving measure to business innovation strategy -- one that combines the cloud with cognitive capabilities to drive market disruption. Learn how you can achieve the insight and agility you need to gain a competitive advantage. Industry-acclaimed CTO and cloud expert, Shankar Kalyana presents. Only the most exceptional IBMers are appointed with the rare distinction of IBM Fellow, the highest technical honor in the company. Shankar has also receive...
Enterprises have taken advantage of IoT to achieve important revenue and cost advantages. What is less apparent is how incumbent enterprises operating at scale have, following success with IoT, built analytic, operations management and software development capabilities - ranging from autonomous vehicles to manageable robotics installations. They have embraced these capabilities as if they were Silicon Valley startups.
DXWorldEXPO LLC announced today that ICOHOLDER named "Media Sponsor" of Miami Blockchain Event by FinTechEXPO. ICOHOLDER give you detailed information and help the community to invest in the trusty projects. Miami Blockchain Event by FinTechEXPO has opened its Call for Papers. The two-day event will present 20 top Blockchain experts. All speaking inquiries which covers the following information can be submitted by email to [email protected] Miami Blockchain Event by FinTechEXPO also offers s...
Poor data quality and analytics drive down business value. In fact, Gartner estimated that the average financial impact of poor data quality on organizations is $9.7 million per year. But bad data is much more than a cost center. By eroding trust in information, analytics and the business decisions based on these, it is a serious impediment to digital transformation.
Predicting the future has never been more challenging - not because of the lack of data but because of the flood of ungoverned and risk laden information. Microsoft states that 2.5 exabytes of data are created every day. Expectations and reliance on data are being pushed to the limits, as demands around hybrid options continue to grow.
The standardization of container runtimes and images has sparked the creation of an almost overwhelming number of new open source projects that build on and otherwise work with these specifications. Of course, there's Kubernetes, which orchestrates and manages collections of containers. It was one of the first and best-known examples of projects that make containers truly useful for production use. However, more recently, the container ecosystem has truly exploded. A service mesh like Istio addr...
As IoT continues to increase momentum, so does the associated risk. Secure Device Lifecycle Management (DLM) is ranked as one of the most important technology areas of IoT. Driving this trend is the realization that secure support for IoT devices provides companies the ability to deliver high-quality, reliable, secure offerings faster, create new revenue streams, and reduce support costs, all while building a competitive advantage in their markets. In this session, we will use customer use cases...
Cloud Expo | DXWorld Expo have announced the conference tracks for Cloud Expo 2018. Cloud Expo will be held June 5-7, 2018, at the Javits Center in New York City, and November 6-8, 2018, at the Santa Clara Convention Center, Santa Clara, CA. Digital Transformation (DX) is a major focus with the introduction of DX Expo within the program. Successful transformation requires a laser focus on being data-driven and on using all the tools available that enable transformation if they plan to survive ov...
DXWorldEXPO | CloudEXPO are the world's most influential, independent events where Cloud Computing was coined and where technology buyers and vendors meet to experience and discuss the big picture of Digital Transformation and all of the strategies, tactics, and tools they need to realize their goals. Sponsors of DXWorldEXPO | CloudEXPO benefit from unmatched branding, profile building and lead generation opportunities.
Digital Transformation and Disruption, Amazon Style - What You Can Learn. Chris Kocher is a co-founder of Grey Heron, a management and strategic marketing consulting firm. He has 25+ years in both strategic and hands-on operating experience helping executives and investors build revenues and shareholder value. He has consulted with over 130 companies on innovating with new business models, product strategies and monetization. Chris has held management positions at HP and Symantec in addition to ...
With 10 simultaneous tracks, keynotes, general sessions and targeted breakout classes, @CloudEXPO and DXWorldEXPO are two of the most important technology events of the year. Since its launch over eight years ago, @CloudEXPO and DXWorldEXPO have presented a rock star faculty as well as showcased hundreds of sponsors and exhibitors! In this blog post, we provide 7 tips on how, as part of our world-class faculty, you can deliver one of the most popular sessions at our events. But before reading...
The best way to leverage your Cloud Expo presence as a sponsor and exhibitor is to plan your news announcements around our events. The press covering Cloud Expo and @ThingsExpo will have access to these releases and will amplify your news announcements. More than two dozen Cloud companies either set deals at our shows or have announced their mergers and acquisitions at Cloud Expo. Product announcements during our show provide your company with the most reach through our targeted audiences.
Andrew Keys is Co-Founder of ConsenSys Enterprise. He comes to ConsenSys Enterprise with capital markets, technology and entrepreneurial experience. Previously, he worked for UBS investment bank in equities analysis. Later, he was responsible for the creation and distribution of life settlement products to hedge funds and investment banks. After, he co-founded a revenue cycle management company where he learned about Bitcoin and eventually Ethereal. Andrew's role at ConsenSys Enterprise is a mul...