Configurable Reconnection Behavior

[myrup]

Describe the bug

After upgrading from asp.net core 3.1 to 6.0 Blazor is still working, but the browser can no longer locate Blazor.defaultReconnectionHandler._reconnectCallback .

We use this to implement browser refresh on reconnections.

Exceptions (if any)

TypeError: undefined is not an object (evaluating 'Blazor.defaultReconnectionHandler._reconnectCallback)

Further technical details

• ASP.NET Core version: 6.0

dotnet --info Output

.NET SDK (reflecting any global.json):
 Version:   6.0.100
 Commit:    9e8b04bbff

Runtime Environment:
 OS Name:     Mac OS X
 OS Version:  12.0
 OS Platform: Darwin
 RID:         osx-arm64
 Base Path:   /usr/local/share/dotnet/sdk/6.0.100/

Host (useful for support):
  Version: 6.0.0
  Commit:  4822e3c3aa

.NET SDKs installed:
  6.0.100 [/usr/local/share/dotnet/sdk]

.NET runtimes installed:
  Microsoft.AspNetCore.App 6.0.0 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 6.0.0 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]

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

[TanayParikh]

Hello @myrup, thanks for contacting us.

Blazor.defaultReconnectionHandler._reconnectCallback is an undocumented internal API, and we do not recommend using it directly within your application code as its subject to change without notice.

In this specific case, the reconnection logic was refactored as a part of https://github.com/dotnet/aspnetcore/pull/36126/files.

[myrup]

@TanayParikh What's the recommended way of making the browser reload on a reconnect then? When googling the problem the following pattern seems fairly reoccurring (now broken):

Blazor.defaultReconnectionHandler._reconnectCallback = function (d) {
    document.location.reload();
}

We need something like this while waiting for #27576

[TanayParikh]

When googling the problem the following pattern seems fairly reoccurring (now broken):

Thanks for pointing that out. I see the following resource that recommend that approach:

• https://www.syncfusion.com/faq/how-do-i-reconnect-blazor-server-side-automatically#:~:text=To%20reconnect%20the%20Blazor%20server%20automatically%20you%20need,%3D%20function%20%28d%29%20%7B%20document.location.reload%20%28%29%3B%20%7D%20%3C%2Fscript%3E

I don't believe we have an official way to automatically reload the page on reconnect (someone can correct me if I'm wrong). If you absolutely need a workaround, you could try listening for when the #components-reconnect-modal display changes from none to block. Note this is entirely unsupported / undocumented, and may or may not work, or may stop working abruptly.

As you mentioned #27576 would optimally resolve this.

[ghost]

We've moved this issue to the Backlog milestone. This means that it is not going to be worked on for the coming release. We will reassess the backlog following the current release and consider this item at that time. To learn more about our issue management process and to have better expectation regarding different types of issues you can read our Triage Process.

[BrennanConroy]

Wouldn't https://docs.microsoft.com/aspnet/core/blazor/fundamentals/signalr?view=aspnetcore-6.0#modify-the-reconnection-handler-blazor-server let you do this?

[TanayParikh]

Wouldn't https://docs.microsoft.com/aspnet/core/blazor/fundamentals/signalr?view=aspnetcore-6.0#modify-the-reconnection-handler-blazor-server let you do this?

Yep you're right, I believe that'd work as well. Nice catch!

[myrup]

@BrennanConroy Yeah, I also considered using that, but I gave up on it because I find the documentation lacking on how to create a reconnectionHandler without breaking normal reconnection behaviour.

Blazor stops automatically reconnecting (reconnectionOptions are ignored) when I specify a reconnectionHandler. I don't know the wirings of a default onConnectionDown and onConnectionUp , so I don't know how to overload them without breaking things. I simply wish to hook into reconnections while using default reconnection logic.

[myrup]

To whom it may concern I managed to hack this together with:

Blazor.start().then(() => {
    Blazor.defaultReconnectionHandler._reconnectionDisplay = {
        show: () => {},
        update: (d) => {},
        rejected: (d) => document.location.reload()
    };
});

But I'm still using the internal api because it's undocumented how to overload reconnectionHandler (@BrennanConroy) without breaking things.

My concerns echo the unresolved #29991 , so maybe it should be reopened?

[TanayParikh]

I don't know the wirings of a default onConnectionDown and onConnectionUp , so I don't know how to overload them without breaking things.

The default wirings are here:

aspnetcore/src/Components/Web.JS/src/Platform/Circuits/DefaultReconnectionHandler.ts

Lines 23 to 40 in f186d9c

	onConnectionDown(options: ReconnectionOptions, _error?: Error): void {
	if (!this._reconnectionDisplay) {
	const modal = document.getElementById(options.dialogId);
	this._reconnectionDisplay = modal
	? new UserSpecifiedDisplay(modal, options.maxRetries, document)
	: new DefaultReconnectDisplay(options.dialogId, options.maxRetries, document, this._logger);
	}
	if (!this._currentReconnectionProcess) {
	this._currentReconnectionProcess = new ReconnectionProcess(options, this._logger, this._reconnectCallback, this._reconnectionDisplay);
	}
	}
	onConnectionUp(): void {
	if (this._currentReconnectionProcess) {
	this._currentReconnectionProcess.dispose();
	this._currentReconnectionProcess = null;
	}

And it's set here:

aspnetcore/src/Components/Web.JS/src/Boot.Server.ts

Lines 49 to 51 in f186d9c

	Blazor.defaultReconnectionHandler = new DefaultReconnectionHandler(logger);
	options.reconnectionHandler = options.reconnectionHandler || Blazor.defaultReconnectionHandler;

[pcarnella]

To whom it may concern I managed to hack this together with:

Blazor.start().then(() => {
    Blazor.defaultReconnectionHandler._reconnectionDisplay = {
        show: () => {},
        update: (d) => {},
        rejected: (d) => document.location.reload()
    };
});

This isn't working for me, F12 error: Blazor has already started. I put the code in _layout:
...

<script src="_framework/blazor.server.js"></script>

<script>
    Blazor.start().then(() => {
        Blazor.defaultReconnectionHandler._reconnectionDisplay = {
            show: () => {},
            update: (d) => {},
            rejected: (d) => document.location.reload()
        };
    });
</script>

...

Any other ideas for forcing reload after publish/app pool recycle?

EDIT: Got it to work by adding autostart="false" to: <script src="_framework/blazor.server.js" autostart="false"></script>. Thanks @myrup !

[TanayParikh]

For:

<script src="_framework/blazor.server.js"></script>

Add an autostart="false" attribute and value to the <script> tag for the Blazor script.

Please see https://docs.microsoft.com/aspnet/core/blazor/fundamentals/startup?view=aspnetcore-6.0 for more details.

[kostya9]

The fix with setting a custom _reconnectionDisplay removes the nice overlay informing the user about the reconnect. I hacked together a wrapper that leaves the overlay intact and reloads the page if the server was rebooted and we can't recover:

Blazor.start().then(() => {
        Object.defineProperty(Blazor.defaultReconnectionHandler, '_reconnectionDisplay', {
            get() {
                return this.__reconnectionDisplay;
            },
            set(value) {
                this.__reconnectionDisplay = {
                    show: () => value.show(),
                    update: (d) => value.update(d),
                    rejected: (d) => document.location.reload()
                }
            }
        });
    });

[aryehsilver]

I get an error when using any of these options:
Uncaught TypeError: Cannot set properties of undefined (setting '_reconnectionDisplay')

[TanayParikh]

I'll just reiterate @BrennanConroy's point above about the official recommended approach to achieve this behavior is documented here: https://docs.microsoft.com/aspnet/core/blazor/fundamentals/signalr?view=aspnetcore-6.0#modify-the-reconnection-handler-blazor-server

_reconnectionDisplay is a framework internal undocumented API subject to change without notice, and we do not recommend taking that approach.

[aryehsilver]

@TanayParikh But I don't want to reconstruct the whole reconnection display! Why can't there be an official way to customise it without reconstructing it?
It is a very sought after feature so why can't you give an official way to reload the page when it can't connect to the server?
This should even be the default in every application. Why would an end user want anything else? If it can't connect the app is useless so what else would you want to do besides reload?

[myrup]

@aryehsilver @TanayParikh @BrennanConroy I agree the official way is borderline useless because of its complexity to implement. I suggest making something like _reconnectionDisplay officially supported.

[aryehsilver]

I suggest making something like _reconnectionDisplay officially supported.

@myrup That will never happen, it would be too useful!

[TanayParikh]

Re-opening to consider adding additional doc details on the reconnection behavior or provide alternate reconnection configurability.

Thread summary is there are concerns with the existing documented approach as it overrides the existing reconnection behavior.

[ghost]

We've moved this issue to the Backlog milestone. This means that it is not going to be worked on for the coming release. We will reassess the backlog following the current release and consider this item at that time. To learn more about our issue management process and to have better expectation regarding different types of issues you can read our Triage Process.

[TanayParikh]

Thanks all for the discussion, I'm closing this issue out as a duplicate, and tracking progress here: #9256