ASP.NET Core URL rewriting with query parameters - asp.net-core

Question

I have a LitElement based SPA with an ASP.NET Core backend which hosts the static files and a REST API for loading data into the SPA.
The user starts with /index.html and the client-side router brings him to, f.e.,
/data-analysis or /dashboard.
When the user now presses the browser refresh button she gets 404 which is to be expected since the server does not know any of these subpaths.
I read elsewhere that I have to take care of this on the server side, so I came up with this middleware in my Startup.cs Configure method:
app.Use(async (c, next) =>
{
//Identify subpaths...
c.Request.Path = "/index.html";
await next();
});
For all subpaths it brings the user back to index.html which is nice. Better yet would be to let the client side know which subpath to restore. For this I added the following lines to the code above:
var url = c.Request.Path.Value;
c.Request.QueryString = c.Request.QueryString.Add("page", $"{url.Substring(1)}");
I expected the client to see a window.location of, f.e.
.../index.html?page=data-analysis
but the query string never arrives, window.location.search is always empty on the client side.
Is this possible at all or am I misunderstanding something here?
Nicolas

Answer 1

Studying Microsofts documentation about the URL rewriting middleware led me to the conclusion that I should redirect and not rewrite! The following code produces the desired result. Note that the 'return' statement is critical, because no further middleware should be called!
app.Use(async (c, next) =>
{
var url = c.Request.Path.Value;
//Identify subpaths...
if(... should redirect ...)
{
c.Response.Redirect($"/index.html?page={url.Substring(1)}");
return;
}
await next();
});