ASP.NET Core 6 中如何实现基于请求头的路由

想在 ASP.NET Core 6 中基于 X-Forwarded-Host 请求头（request header）路由到对应的 Controller Action，请问如何实现？

回答

DynamicRouteValueTransformer 专治路由疑难杂症，用它解决了

1）继承 DynamicRouteValueTransformer 实现 DemoRouteValueTransformer

public class DemoRouteValueTransformer : DynamicRouteValueTransformer
{
    public override ValueTask<RouteValueDictionary> TransformAsync(HttpContext httpContext, RouteValueDictionary values)
    {
        if (httpContext.Request.Headers.TryGetValue("X-Forwarded-Host", out var forwardedHost)
            && forwardedHost.ToString().Equals("q.cnblogs.com", StringComparison.OrdinalIgnoreCase))
        {
            values = values ?? new RouteValueDictionary();
            values["controller"] = "Home";
            values["action"] = "Demo";
        }

        return ValueTask.FromResult(values);
    }
}

2）注册 DemoRouteValueTransformer 到 DI 容器

services.AddScoped<DemoRouteValueTransformer>();

3）添加动态路由规则

app.UseEndpoints(endpoints =>
{
    endpoints.MapDynamicControllerRoute<DemoRouteValueTransformer>("/");
    endpoints.MapControllerRoute(
        name: "default",
        pattern: "{controller=Home}/{action=Index}/{id?}");
});

注：MapDynamicControllerRoute 要放在 MapControllerRoute 之前，不然会走 MapControllerRoute 默认路由 /Home/Index