I have a function I wish to be called on every page view, at the earliest possible opportunity. The code gets the users IP address, an increments a counter by 1 in a database.
This code is a basic flood limiter. If more than x requests are made in interval i then it temporarially bans that IP address. This is why the check needs to be as early as possible and on every page.
Calling in MasterPages Page_Init
This seems to work OK, however sometimes the counter increments by more than 1 (I assume if there's a URL re-write or redirect).
Calling in Global.asax on Session_Start
It seems to add ~30 to the counter on each page view.
What's the best way to catch a page view at the earliest possible opportunity, preferably without needing to change every single page on the site?
Inside Global.asax, you can hook to HttpApplication.BeginRequest, which is :
the first event in the HTTP pipeline chain of execution when ASP.NET responds to a request
This will fire for each request (for images, css, javascript, and so on). If you want to filter on pages only, you could write a HttpModule, that only increment your counter according to request extension.