.NET Core URL Rewrite for migrating from webforms to .NET Core

Really wanted to get better at this myself so had some fun experimenting getting something to work. Sadly I had some troubling using .AddRedirect to also match on the querystring.

So I came up with the following solution, I hope this helps you:

var rewriteOptions = new RewriteOptions()
            .Add(new RuleForU1AndU2())
            .Add(new RuleForU1());

And then having 2 rules:

public class RuleForU1 : IRule
{
    private int StatusCode { get; } = (int)System.Net.HttpStatusCode.MovedPermanently;

    public void ApplyRule(RewriteContext context)
    {
        var request = context.HttpContext.Request;
        var url = request.Path.Value;
        var queryString = request.QueryString.Value;

        if (!url.Equals("/details.aspx", StringComparison.OrdinalIgnoreCase) || queryString.Length == 0)
        {
            context.Result = RuleResult.ContinueRules;
            return;
        }

        var regexMatches = Regex.Matches(queryString, @"^?u1=(.*)");
        if(regexMatches.Count == 0)
        {
            context.Result = RuleResult.ContinueRules;
            return;
        }

        string newUrl = regexMatches[0].Groups[1].Value;

        var response = context.HttpContext.Response;
        response.StatusCode = StatusCode;
        response.Headers[Microsoft.Net.Http.Headers.HeaderNames.Location] = newUrl;
        context.Result = RuleResult.EndResponse;
        return;
    }
}

public class RuleForU1AndU2 : IRule
{
    private int StatusCode { get; } = (int)System.Net.HttpStatusCode.MovedPermanently;

    public void ApplyRule(RewriteContext context)
    {
        var request = context.HttpContext.Request;
        var url = request.Path.Value;
        var queryString = request.QueryString.Value;

        if (!url.Equals("/details.aspx", StringComparison.OrdinalIgnoreCase) || queryString.Length == 0)
        {
            context.Result = RuleResult.ContinueRules;
            return;
        }

        var regexMatches = Regex.Matches(queryString, @"^?u1=(.*)&u2=(.*)");
        if (regexMatches.Count == 0)
        {
            context.Result = RuleResult.ContinueRules;
            return;
        }

        string newUrl = $"{regexMatches[0].Groups[1].Value}/{regexMatches[0].Groups[2]}";

        var response = context.HttpContext.Response;
        response.StatusCode = StatusCode;
        response.Headers[Microsoft.Net.Http.Headers.HeaderNames.Location] = newUrl;
        context.Result = RuleResult.EndResponse;
        return;
    }
}

I didn't really put any effort into code reuse... and you can probably merge the 2 rules into one rule, but I don't know what your full usecase is (like will there also be a u3?) So... I hope this helps you get closer to where you need to go :)