Introduction
If you're anything like the me, you won’t be content with knowing that browsing to http://MyServer/MyVirtualDir/MyApplication.application downloads, installs and launches MyApplication. You'll want to know how this is achieved. This post goes under the covers of ClickOnce to show you how it's done. Well, at least how some of it is done.
As this post makes quite a lot of references to registry entries, I'll use the standard abbreviations HKCU and HKCR to represent the HKEY_CURRENT_USER and HKEY_CLASSES_ROOT hives respectively.
Retrieving the Deployment Manifest
What happens when you browse to http://MyServer/MyVirtualDir/MyApplication.application?
The first thing to realise is that no 'magic' is happening behind the scenes. When you send an HTTP GET request to a web server (Internet Information Services, IIS, for example) the web server will typically react in one of two ways. It will either establish that your request must be forwarded to a component on the server for processing (a 'handler' in IIS terminology) or will establish that the request represents a static file which should simply have its contents returned.
IIS stores details of handlers, and the requests which are forwarded to each handler, in its metabase. Handlers can be defined in terms of a script map (potentially in combination with a managed handler) or a module mapping. For example:
- Requests matching the pattern *.asp are forwarded, via a script map, to the ISAPI module %windir%\system32\inetsrv\asp.dll.
- Requests matching the pattern *.aspx are forwarded, via a script map, to the ISAPI module %windir%\Microsoft.NET\Framework\v2.0.50727\aspnet_isapi.dll and to the managed handler System.Web.UI.PageHandlerFactory.
- Requests matching the pattern *.shtml are forwarded, via a module mapping, to the pre-registered ServerSideIncludeModule module.
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