Using an iframe with a dynamic source breaks the back button in firefox (blazor server)

[Trolldemorted]

Describe the bug

Having an iframe where the src attribute is modified within an InvokeAsync block impairs the "One Page Back"-button experience: If you click the button in firefox (75.0), the iframe appears to reload, but you are not redirected to the previous page.

In Edge and Chrome it works fine. In IE11 my sample throws an ObjectDisposedException, which is most likely a different bug I guess?

To Reproduce

Either clone this repo, or use this snippet:

@page "/i/iframe"
@using System.Diagnostics
@if (Url != null)
{
    <iframe src="@(Url)" style="width:100%; height:100%; border:0; border-style:solid;" />
}
else
{
    <div>Url is null</div>
}

@code {
    [Parameter]
    public string? SomeString { get; set; }
    string? Url = null;

    protected override void OnParametersSet()
    {
        Task.Run(async () =>
        {
            await InvokeAsync(() =>
            {
                Url = "https://demo.codimd.org/CGdlv3HDQwaQe_Y6uWKLhw";
                base.StateHasChanged();
            });
        });
    }
}

Open firefox and the index page, click on "iframe" to navigate to /i/iframe, wait for iframepage and the actual iframe to load, press the back button once, and you will see that your browser does not navigate to the previous page.

Further technical details

• ASP.NET Core version
  3.1.3
• Include the output of dotnet --info

PS C:\Users\Benni\repositories\BlazorServerIframeBug> dotnet --info
.NET Core SDK (gemäß "global.json"):
 Version:   3.1.201
 Commit:    b1768b4ae7

Laufzeitumgebung:
 OS Name:     Windows
 OS Version:  10.0.18363
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   C:\Program Files\dotnet\sdk\3.1.201\

Host (useful for support):
  Version: 3.1.3
  Commit:  4a9f85e9f8

.NET Core SDKs installed:
  2.1.202 [C:\Program Files\dotnet\sdk]
  2.1.508 [C:\Program Files\dotnet\sdk]
  2.1.801 [C:\Program Files\dotnet\sdk]
  2.2.203 [C:\Program Files\dotnet\sdk]
  3.0.100-preview9-014004 [C:\Program Files\dotnet\sdk]
  3.0.100 [C:\Program Files\dotnet\sdk]
  3.1.200 [C:\Program Files\dotnet\sdk]
  3.1.201 [C:\Program Files\dotnet\sdk]

.NET Core runtimes installed:
  Microsoft.AspNetCore.All 2.1.12 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.1.17 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.2.4 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.App 2.1.12 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.1.17 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.2.4 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.0.0-preview9.19424.4 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.0.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.1.3 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 2.0.9 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.12 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.17 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.2.4 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.0.0-preview9-19423-09 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.0.0 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.1.3 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.WindowsDesktop.App 3.0.0-preview9-19423-09 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 3.0.0 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 3.1.3 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

To install additional .NET Core runtimes or SDKs:
  https://aka.ms/dotnet-download

• The IDE (VS / VS Code/ VS4Mac) you're running on, and it's version
  Microsoft Visual Studio Enterprise 2019 Version 16.5.4

[javiercn]

@Trolldemorted thanks for contacting us.

I'm not sure why it is exposing that behavior, but it seems that the app is crashing in some way by what you describe and these lines of code probably need some error handling:

        Task.Run(async () =>
        {
            await InvokeAsync(() =>
            {
                Url = "https://demo.codimd.org/CGdlv3HDQwaQe_Y6uWKLhw";
                base.StateHasChanged();
            });
        });

I would ask what are you trying to achieve to see if we can offer you alternative ways to accomplish the same result.

[Trolldemorted]

In my production use case the src parameter is constructed from a property, which is fetched from a database.

Why do you think the app is crashing? It continues to work just fine - No exceptions in VS debug output, no errors in firefox' console, I can click around, my handlers are being executed correctly, I can navigate between pages, the only problem is the back button, and only in firefox.

Since pressing the back button twice fast enough works (the first button reloads the page, the second press must come before the iframe loads), I assumed that blazor incorrectly pushes a new state to the browser's history when the iframe src is modified in an InvokeAsync block.

[mkArtakMSFT]

@Trolldemorted, it seems that the usage of Task.Run is already a red flag. Try to rework that code to return a task and change the method into static, so the framework is aware when the execution is complete. If you have an issue after that, then share a small repro project with us and we'll see what can be done.

On a side note, do you see the same behavior if Blazor out of picture - if you add same HTML structure in a new html page, will the back button be disabled again?

[Trolldemorted]

I am using Task.Run to have the database access running in a thread without a synchronization context. Are you certain you don't want to fix this bug nevertheless?

The back button is not disabled, it just refers to the same page which pushes a new state as soon as the iframe loads.

Using a normal iframe does not impair firefox' history.