Blazor Server and Azure SignalR File Download Troubleshoot

Raymond Lei 1

We are trying out Azure SignalR with Blazor Server (dotnet 6), we followed the tutorial from this documentation: https://learn.microsoft.com/en-us/aspnet/core/blazor/file-downloads?view=aspnetcore-7.0 Building the file functionality (using the stream method) worked without using Azure SignalR. But when we set up the Azure SignalR(Premium tier), the file download is broken (the rest of the app seems to be working fine though), the browser isn't reporting any error and the WebSocket connection seems to be fine. We are not sure why this is. Thank you!

VenkateshDodda-MSFT 19,226 Reputation points Microsoft Employee

2023-04-10T05:47:45.86+00:00

@Raymond Lei Thank you for reaching out to Microsoft Q&A, apologize for any inconvenience caused on this. I see you have already posted the similar issue in StackOverflow here ,Jason has shared that Blazor server side uses SignalR and it has buffer limitations as well and requested to increase the ApplicationMaxBufferSize and TransportMaxBufferSize in your code. Just want to check have you tried to implement it and are you still facing the issue if yes, please do help us with the error message to check and assist you further.
Also you can use Live trace tool for Azure SignalR service to troubleshoot connectivity and messaging issues.
Raymond Lei 1 Reputation point

2023-04-12T03:16:15.0333333+00:00

Hello, I already tried incrementing the buffer sizes and I am still getting no error messages, the issues still persist...Also, the buffer size adjusting options are not part of AddSiganlR...
VenkateshDodda-MSFT 19,226 Reputation points Microsoft Employee

2023-04-18T07:38:02.82+00:00

@Raymond Lei Apologize for the delay in my response.
I have checked with SignalR engineering team internally on this and sharing the below.

Could you please upgrade the Azure SignalR SDK to the latest version 1.12.2 (Change the version from the project file <PackageReference Include="Microsoft.Azure.SignalR" Version="1.21.2" />) It provides better stability and help us with more logs if something is wrong.

When you use client stream to download large files (say over 200MB), currently their client has high possibility hit the service SlowClient throttling rule and the client will be closed with SlowClient reason by the service. For now, we you can use the download a file via a URL solution if the size is larger than 100MB.
VenkateshDodda-MSFT 19,226 Reputation points Microsoft Employee

2023-04-19T16:08:13.2033333+00:00

Hello @Raymond Lei ,
Following up to see if you have a chance to check my previous response and helped. Do let us know if you have any further questions on this.

Raymond Lei 1

Hello, I am sorry for the late response. I updated the package Azure SiganlR to 1.12.2. The good news is that I am seeing the SlowClient message on Live Trace Tool on Azure SiganlR Service, but the size of the download file is only around 3MB though
I am getting this error on the client side:

blazor.server.js:1  Uncaught (in promise) Error: Cannot send data if the connection is not in the 'Connected' State.
    at bt.send (blazor.server.js:1:52080)
    at kt._sendMessage (blazor.server.js:1:68715)
    at kt._sendWithProtocol (blazor.server.js:1:68756)
    at kt.send (blazor.server.js:1:68864)
    at Object.endInvokeJSFromDotNet (blazor.server.js:1:131918)
    at blazor.server.js:1:3594
send @ blazor.server.js:1
_sendMessage @ blazor.server.js:1
_sendWithProtocol @ blazor.server.js:1
send @ blazor.server.js:1
endInvokeJSFromDotNet @ blazor.server.js:1
(anonymous) @ blazor.server.js:1
Promise.then (async)
beginInvokeJSFromDotNet @ blazor.server.js:1
(anonymous) @ blazor.server.js:1
_invokeClientMethod @ blazor.server.js:1
_processIncomingData @ blazor.server.js:1
connection.onreceive @ blazor.server.js:1
o.onmessage @ blazor.server.js:1

VenkateshDodda-MSFT 19,226 Reputation points Microsoft Employee

2023-05-08T03:53:36.6866667+00:00

@Raymond Lei Thanks for your response. This would need one on one offline support, for deeper investigations and might need to engage product team as well and I will suggest you open a support ticket.

In case if you don't have the support plan then please send an email with your SubscriptionID and link to this thread to AzCommunity@microsoft.com with subject line as "ATTN: Venkatesh" so I can enable one-time free support on your subscription to assist you further.

1 answer

Bruce (SqlWork.com) 57,891 Reputation points

2023-04-12T16:31:11.2866667+00:00

when you switch to Azure SignalR you no longer control buffer size. It would be a better design to allow javascript to upload the file to a webapi, then you would not have file size restrictions and better performance.

if the files are not too large, you could use javascript interop to read the file as a data url and upload in chunks.
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Blazor Server and Azure SignalR File Download Troubleshoot

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