aspnetcore: ASP.NET Core 3.0: NullReferenceException in HttpContext.RequestAborted

We have a middleware that accepts WebSocket requests and receives messages while (!context.RequestAborted.IsCancellationRequested && (socket.State == WebSocketState.Open || socket.State == WebSocketState.Connecting)). After migrating from 2.2 to 3.0 we’re getting the exception below.

System.NullReferenceException: Object reference not set to an instance of an object.
   at Microsoft.AspNetCore.Http.DefaultHttpContext.get_RequestAborted()
   at Pasaj.MessagingMiddleware.Receive(WebSocket socket, HttpContext context, String sessionId, Int32 clientVersion) in C:\Web\Patogh\Patogh\Hubs\MessagingMiddleware.cs:line 103
   at Pasaj.MessagingMiddleware.InvokeAsync(HttpContext context) in C:\Web\Patogh\Patogh\Hubs\MessagingMiddleware.cs:line 96
   at Pasaj.MessagingMiddleware.InvokeAsync(HttpContext context) in C:\Web\Patogh\Patogh\Hubs\MessagingMiddleware.cs:line 96
   at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.Invoke(HttpContext context)
   at Pasaj.HttpExceptionMiddleware.Invoke(HttpContext context) in C:\Web\Patogh\Patogh\Helpers\HttpExceptionMiddleware.cs:line 31
   at CoreProfiler.Web.CoreProfilerMiddleware.Invoke(HttpContext context)
   at AspNetCoreRateLimit.RateLimitMiddleware`1.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Diagnostics.StatusCodePagesMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Diagnostics.StatusCodePagesMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Server.IISIntegration.IISMiddleware.Invoke(HttpContext httpContext)
   at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http.HttpProtocol.ProcessRequests[TContext](IHttpApplication`1 application)

This doesn’t happen every time, maybe 1 in 10,000. But since we’re dealing with hundreds of messages a second, we get this exception every other minute or so.

Further technical details

ASP.NET Core 3.0
IIS on Windows Server 2016

About this issue

Original URL
State: closed
Created 5 years ago
Comments: 16 (10 by maintainers)

Most upvoted comments

Awesome, I’ll close this out.

davidfowl on Jun 6, 2022

@davidfowl Thank you for following up on this issue. But we haven’t had this problem since upgrading to .NET 5.0 and we’re currently using 6.0.

sepehr1014 on Jun 6, 2022

I know it’s not intuitive, but even property getters are not thread safe. RequestAborted has lazy side effects to create the cancellation token. Read the RequestAborted property before the threads fork and don’t even pass HttpContext into those methods so you’re not tempted to use it again.

You don’t need to look at HttpContext.RequestAborted at all but it shouldn’t null ref here, that seems like a bug on our part. I would follow @Tratcher 's advice here and not pass the HttpContext to multiple threads. Get the data you need from the HttpContext before starting the websocket loop.

PS: This code has lots of other bugs and issues that should be fixed. I can help with that but I don’t want to deter from the original issue.

davidfowl on Nov 14, 2019