asp.net - Detect from browser if specific application is installed

Question

We have an advanced webpage (ASP.NET, C#), and a application which needs to be installed on the client computer in order to utilize the webpage to its fullest. The application is a tray app, and has primarily two tasks. Detect when certain events happen on the webserver (for instance invited to a meeting, or notify of an upcoming meeting). The other task the trayapp has is to use a custom protocol (trayapp://) to perform some ajax calls back to the server.

One problem we have is how to determine if the application is installed on the local machine or not. Now the user has to tick a checkbox to inform the website that the application is installed, and that it's safe to call the trayapp:// url calls.

Is there any way, for instance through a JavaScript or similar to detect if our application is installed on the local machine?

The check needs to work for IE, FF and Opera browsers.

Answer 1

When installing your client-side app you could modify the browser configuration to include another request header in HTTP requests and then have the server code look for that header, for example as a supported mime type using the following registry key (for Internet explorer)

HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersion
                                                      Internet SettingsAccepted Documents

I am not sure if Opera and FF use this same key, but they likely have similar configuration options, but this should at least get you on the right track.