How can ensure that iframe loaded in ASP.Net Core Razor

Question

i have simple project ASP.Net Core with Razor. In this project I have single page that just open iframe. That works fine, but I want to know when iframe not loaded, is it possible?

@page
@using Microsoft.AspNetCore.Http.Extensions
@model IndexModel

<iframe src="@Model.BuildIFrameReference(HttpContext.Request.GetDisplayUrl())"
        frameborder="0"
        style="overflow: hidden;overflow-x: hidden;overflow-y: hidden;height: 100%;width: 100%;position: absolute;top: 0px;left: 0px;right: 0px;bottom: 0px"
        height="100%"
        width="100%"/>

Answer 1

So I choose different way to do this.I add new middleware that ping iframe url. If url for iframe returned not successed status code or have X-Frame-Options: Deny header I make redirect to default page.

public class CheckIframeUrlMiddleware
  {
    private readonly HttpClient _client;
    private readonly RequestDelegate _next;

    public CheckIframeUrlMiddleware(RequestDelegate next)
    {
      _next = next;
      _client = new HttpClient();
    }

    public async Task InvokeAsync(HttpContext context, IframeReferenceBuilder _builder)
    {
      try
      {
        var response = await _client.GetAsync(_builder.BuildIFrameReference(context.Request.GetDisplayUrl()));

        if (!response.IsSuccessStatusCode)
          context.Response.Redirect(_builder.Settings.RedirectDomain);

        if (response.Headers.TryGetValues("X-Frame-Options", out var values) && values.Contains("DENY"))
          context.Response.Redirect(_builder.Settings.RedirectDomain);

        await _next.Invoke(context);
      }
      catch
      {
        context.Response.Redirect(_builder.Settings.RedirectDomain);
      }
    }
  }