NullReferenceException in IISHttpContext

[martincostello]

Describe the bug

Since updating a website running in Azure App Service to use ASP.NET Core 2.2.0 with in-process hosting, I've observed a small number of NullReferenceExceptions being thrown via Application Insights.

System.NullReferenceException:
   at Microsoft.AspNetCore.Server.IIS.Core.IISHttpContext.GetOriginalPath (Microsoft.AspNetCore.Server.IIS, Version=2.2.0.0, Culture=neutral, PublicKeyToken=adb9793829ddae60)
   at Microsoft.AspNetCore.Server.IIS.Core.IISHttpContext.InitializeContext (Microsoft.AspNetCore.Server.IIS, Version=2.2.0.0, Culture=neutral, PublicKeyToken=adb9793829ddae60)
   at Microsoft.AspNetCore.Server.IIS.Core.IISHttpContextOfT`1+<ProcessRequestAsync>d__2.MoveNext (Microsoft.AspNetCore.Server.IIS, Version=2.2.0.0, Culture=neutral, PublicKeyToken=adb9793829ddae60)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult (System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at Microsoft.AspNetCore.Server.IIS.Core.IISHttpServer+<HandleRequest>d__27.MoveNext (Microsoft.AspNetCore.Server.IIS, Version=2.2.0.0, Culture=neutral, PublicKeyToken=adb9793829ddae60)

To Reproduce

Application experiencing the issue was built from this commit: martincostello/website@ee2ca4b

Expected behavior

HTTP request is processed successfully.

Screenshots

Additional context

Add any other context about the problem here.
Include the output of dotnet --info

[martincostello]

Looking at the code in master, it would seem that GetRawUrlInBytes() saw NativeRequest->pRawUrl to be null or empty, and returned null, which then isn't handled by GetOriginalPath().

https://github.com/aspnet/AspNetCore/blob/85e2147ff037cc9950249fbb9d095ad47ec4184a/src/Shared/HttpSys/RequestProcessing/NativeRequestContext.cs#L141-L151

https://github.com/aspnet/AspNetCore/blob/3c09d644cccdb21801f7a79e1188a1a1212de5d9/src/Servers/IIS/src/Microsoft.AspNetCore.Server.IIS/Core/IISHttpContext.cs#L185-L186

[pakrym]

Do you know which request URL causes the issue?

[martincostello]

I’ll dig further through AI later today for you to find out.

[martincostello]

AI doesn't appear to have captured any other telemetry events for the specific exceptions (I guess it's happening too early in the request flow for managed code for any route matching to have run), but from looking at request logs, the best I can tell is that it was a request to the root of the website.

[bartdk-be]

Same issue over here. Any workaround available ?
Are we sure this is related to the In/OutOfProcess option ?

[martincostello]

For me this only started once I switched to in-process hosting after the roll out to Azure App Service of the hosting bundle was completed.

[pakrym]

Do you have timestamps of these exceptions? Feels a bit like AppServices warmup request.

[martincostello]

Four timestamps for these exceptions are:

• 20/12/2018, 18:24:13
• 21/12/2018, 00:37:07
• 21/12/2018, 13:45:57
• 25/12/2018, 15:38:01

[pakrym]

@martincostello do you have Always On enabled?

[martincostello]

In case you meant me, yes I do.

[jkotalik]

The frequency of requests there looks like it is coming from the app warmup request after IIS restarts from Always On. To confirm, can you turn off app warmup for a period and see if exceptions are still being thrown? If that’s the case, the null ref is coming from the warmup request. This behavior is “fine” as the request was fake and it is supposed to startup Program.Main. However, we should more gracefully handle this type of request and not throw. Get Outlook for iOS<https://aka.ms/o0ukef>

…

________________________________ From: Martin Costello <notifications@github.com> Sent: Thursday, December 27, 2018 12:27 PM To: aspnet/AspNetCore Cc: Subscribed Subject: Re: [aspnet/AspNetCore] NullReferenceException in IISHttpContext (#6075) In case you meant me, yes I do. — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub<https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Faspnet%2FAspNetCore%2Fissues%2F6075%23issuecomment-450225392&data=02%7C01%7CJustin.Kotalik%40microsoft.com%7Ce47a17cf79c14ed8965508d66c39c6a7%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636815392732641734&sdata=rXZLEMMAusc4ZBH47OXhlM1sQaNAzPMZuUSHa4a7H2w%3D&reserved=0>, or mute the thread<https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fnotifications%2Funsubscribe-auth%2FAH6uFVu8-uWuEVZkvZG2WobO1z3nwajcks5u9S1HgaJpZM4ZdnOe&data=02%7C01%7CJustin.Kotalik%40microsoft.com%7Ce47a17cf79c14ed8965508d66c39c6a7%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636815392732651747&sdata=c%2BBvm7xm2865OIYE3l20Cp3c14zwpX9OMzwm%2BENkVWU%3D&reserved=0>.

[martincostello]

I've disabled Always On and will leave it for a few days to see if it happens again, but it only happened a handful of times in the last 7 days as it is.