.NET Core 3.1 Websocket error: The specified network name is no longer available

Microsoft.AspNetCore.Connections.ConnectionResetException: The client has disconnected
 ---> System.Runtime.InteropServices.COMException (0x80070040): The specified network name is no longer available. (0x80070040)
   --- End of inner exception stack trace ---
   at Microsoft.AspNetCore.Server.IIS.Core.IO.AsyncIOOperation.GetResult(Int16 token)
   at Microsoft.AspNetCore.Server.IIS.Core.IISHttpContext.ReadBody()
   at System.IO.Pipelines.PipeCompletion.ThrowLatchedException()
   at System.IO.Pipelines.Pipe.GetReadResult(ReadResult& result)
   at System.IO.Pipelines.Pipe.ReadAsync(CancellationToken token)
   at System.IO.Pipelines.Pipe.DefaultPipeReader.ReadAsync(CancellationToken cancellationToken)
   at Microsoft.AspNetCore.Server.IIS.Core.IISHttpContext.ReadAsync(Memory`1 memory, CancellationToken cancellationToken)
   at Microsoft.AspNetCore.Server.IIS.Core.HttpRequestStream.ReadAsyncInternal(Memory`1 buffer, CancellationToken cancellationToken)
   at Microsoft.AspNetCore.WebUtilities.FileBufferingReadStream.ReadAsync(Byte[] buffer, Int32 offset, Int32 count, CancellationToken cancellationToken)
   at Microsoft.AspNetCore.WebUtilities.StreamHelperExtensions.DrainAsync(Stream stream, ArrayPool`1 bytePool, Nullable`1 limit, CancellationToken cancellationToken)
   at Microsoft.AspNetCore.Mvc.Formatters.NewtonsoftJsonInputFormatter.ReadRequestBodyAsync(InputFormatterContext context, Encoding encoding)
   at Microsoft.AspNetCore.Mvc.ModelBinding.Binders.BodyModelBinder.BindModelAsync(ModelBindingContext bindingContext)
   at Microsoft.AspNetCore.Mvc.ModelBinding.ParameterBinder.BindModelAsync(ActionContext actionContext, IModelBinder modelBinder, IValueProvider valueProvider, ParameterDescriptor parameter, ModelMetadata metadata, Object value)
   at Microsoft.AspNetCore.Mvc.Controllers.ControllerBinderDelegateProvider.<>c__DisplayClass0_0.<<CreateBinderDelegate>g__Bind|0>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeInnerFilterAsync>g__Awaited|13_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeFilterPipelineAsync>g__Awaited|19_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Awaited|17_0(ResourceInvoker invoker, Task task, IDisposable scope)
   at Microsoft.AspNetCore.Routing.EndpointMiddleware.<Invoke>g__AwaitRequestTask|6_0(Endpoint endpoint, Task requestTask, ILogger logger)
   at MyApp.Utility.Extensions.<>c.<<UseMyAppSocket>b__0_0>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.AspNetCore.Diagnostics.ExceptionHandlerMiddleware.<Invoke>g__Awaited|6_0(ExceptionHandlerMiddleware middleware, HttpContext context, Task task)

I have a few customers complaining of getting disconnected from my webservice using a websocket. They are using a JS Angular client to connect. I have logic client side to reconnect on failure, but the customer reports it never does, or that they can see multiple attempts being made and failing. Does this error indicate the client disconnected was caused on the client side? Any way to find out definitively?

I've pinched this from https://dba.stackexchange.com/questions/149539/the-specified-network-name-is-no-longer-available, as it solved the problem for me, but that article was not easy to find.

The problem turned out to be some long-running queries, which on average took 20s, but sometimes took 70s, which was longer than the default timeout, hence the exception was thrown.

For long running queries

Implement a longer command timeout value for the application connection strings connecting to the SQL Server.

Example

<connectionStrings> 
    <add name="webconfigconnectionString" connectionString="server=SQLServerName;database=dbName;uid=u‌​serName;password=ABC‌​123;Connect Timeout=120" />
</connectionStrings>

This might not be a great solution, but it should at least stop the failures, while you figure out how to improve performance of the query.

For DNS trouble-shooting

Although DNS wasn't my problem, I've copied this over from the dba.stackexchange answer, in case it helps someone else.

As a Band-Aid and trouble-shooting aid add and entry to the hosts file on your app servers (not the SQL Server) at c:\windows\system32\drivers\etc

SQLServerIPAddress SQLServerName

Example:

172.16.0.5 ProductionSQLBox

That way, the SQL Server name will be resolved by the hosts file until you can find the real problem for what's going on with name resolution.

Be sure and test the hosts file by pinging the SQL box from the app server via a command line. Or, alternately create a DSN with the ODBC Administrator within Control Panel and test the connection there.