Asp.Net Core [FromRoute] auto url decode

Question

If we have such controller endpoint in Asp.Net Core:

[HttpGet("/api/resources/{someParam}")]
public async Task<ActionResult> TestEndpoint([FromRoute] string someParam)
{
    string someParamUrlDecoded = HttpUtility.UrlDecode(someParam);
    // do stuff with url decoded param...
}

Is there some way to configure [FromRoute] parsing behavior in such way that it will inject into someParam already url decoded value?

Answer 1

One way to achieve whatever you're trying to do is to create a custom Attribute. Within the attribute you can essentially intercept the incoming parameter and perform whatever you need.

Attribute Definition:

public class DecodeQueryParamAttribute : ActionFilterAttribute
{
    public override void OnActionExecuting(ActionExecutingContext context)
    {
        string param = context.ActionArguments["param"] as string;
        context.ActionArguments["param"] = "Blah"; // this is where your logic is going to sit
        base.OnActionExecuting(context);
    }
}

And within the controller, you'll need to decorate the action method with the attribute as done below. Route can be modified according to your need.

[HttpGet("/{param}")]
[Attributes.DecodeQueryParamAttribute]
public void Process([FromRoute] string param)
{
    // value of param here is 'Blah'
    // Action method
}

As a word of caution, when you are going to have encoded strings being passed as query string parameters, you may want to check about allowing Double Escaping and its implications.