Disable Long Polling Fallback Transport for Blazor Server

[TanayParikh]

Disable Long Polling Fallback Transport for Blazor Server

Long Polling is a fall-back transport utilized when WebSockets aren't available. This can lead to a degraded user experience. Thus, the Long Polling fallback has been removed, and both the client and server now support only WebSockets by default.

Version introduced

.NET 6 rc 1

Old behavior

If WebSockets are unavailable for a circuit (ex. network issues or browser incompatibility), Long Polling is used instead.

New behavior

Client	Server	Message
WS (without browser WS support)	WebSockets	Unable to connect, please ensure you are using an updated browser that supports WebSockets.
WS (with WS connection being rejected)	WebSockets	Unable to connect, please ensure WebSockets are available. A VPN or proxy may be blocking the connection.
WS	LongPolling	An unhandled error has occurred. Console Error: Unable to initiate a SignalR connection to the server. This might be because the server is not configured to support WebSockets. To troubleshoot this, visit https://aka.ms/blazor-server-websockets-error.
LongPolling	WebSockets	An unhandled error has occurred.

Reason for change

Improve overall end-user-experience by enforcing WebSocket use.

Recommended action

Ensure WebSockets are functioning as expected with your application. If you must use Long Polling, the following client and server side changes must be made:

Server Side

In Startup.cs, replace endpoints.MapBlazorHub() with:

endpoints.MapBlazorHub(configureOptions: options => 
{ 
    options.Transports = HttpTransportType.WebSockets | HttpTransportType.LongPolling; 
});

Client Side

In Pages/_Layout.cshtml, update the blazor.server.js script tag to include the autostart="false" attribute:

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

Below the blazor.server.js script tag, add the following snippet. WebSockets (1) and Long Polling (4) are the supported HTTPTransportTypes.

<script>
    (function start() {
        Blazor.start({
            configureSignalR: builder => builder.withUrl('_blazor', 1 | 4) // WebSockets and Long Polling
        });
    })()
</script>

Category

• Binary compatibility (the newer version can be used without recompiling)
• Source compatibility (successfully recompiling against newer version requires source changes)

Affected APIs

Not detectable via API analysis

---

Issue metadata

• Issue type: breaking-change

[mkArtakMSFT]

Closing as we've reverted this change after discovering some unforeseen effects of it.

@gewarren FYI, in case there was any change made in docs in response to this announcement.

[TanayParikh]

Closing as we've reverted this change after discovering some unforeseen effects of it.

@gewarren FYI, in case there was any change made in docs in response to this announcement.

Thanks @mkArtakMSFT.

Regarding the documentation, can we leave as is for now (as it reflects the latest RC1 release) and only revert the doc changes when we release RC2. Would like to minimize confusion for those who may still be upgrading to RC1 for the next month or so.

[mkArtakMSFT]

Yes, of course, @TanayParikh !