Question

I have an ASP.NET WebApi application that has some controller methods that expect certain strings to be passed in as method parameters (declared as part of the route template).

On all the methods, the strings passed in are base64-encoded — which means each controller method must base64-decode them before doing anything with them. While I can obviously have each method do this easily enough, I was wondering if there was a way to perform the decoding before the string actually gets passed to the controller method. I presume this is something along the lines of an action filter or custom formatter, but I’m not familiar enough with asp.net web api to know where to start on that?

Summary:
I’ve got route templates like : {controller}/{encodedString}/whatever
where {encodedString} is always a base64-encoded string.
and controllers with methods like

GetWhatever(string encodedString)
{
  Base64Decode(encodedString);
  // do other stuff...
}

I would like to use some part of the asp.net webapi pipeline to decode {encodedString} before the controller method is actually called. What path should I start down in order to do this?

Answer 1

You can create a custom model binder and attach it to the parameters using the ModelBinderAttribute. In the model binder you then do the base64 decoding.

For a reference on parameter binding in Web API check:

How WebAPI does Parameter Binding