OWIN WebSockets SendAsync on IIS sometimes returns a task that never completes

[darkl]

This issue was found while investigating this issue.

When running a long running WebSocket server hosted on IIS, sometimes SendAsync returns a task that never completes nor terminates. I would expect the task to fault at some point, but it remains in state WaitingForActivation.

A repro can be found here. First run OwinHangSample and then WebSocketClient. You will see that after some time (a few minutes), the WebSocketClient stops receiving messages. Debugging the sample further (for instance storing the SendAsync task in a static variable), shows that the last SendAsync Task is stuck in WaitingForActivation state.

Elad

[Tratcher]

Katana provides a minimal wrapper for System.Web.WebSockets in this scenario. Can you reproduce this using System.Web directly?
See

AspNetKatana/src/Microsoft.Owin.Host.SystemWeb/WebSockets/OwinWebSocketWrapper.cs

Line 86 in 6fcee95

return WebSocket.SendAsync(buffer, OpCodeToEnum(messageType), endOfMessage, cancel);

[darkl]

Probably it is possible to reproduce this using System.Web directly. What further actions do you suggest (i.e. how should I modify the repro, and where should I move the issue to)?

Thanks
Elad

[Tratcher]

If you can eliminate your Microsoft.Owin dependencies and repro with only System.Web then I can help you track down the right person to investigate.

[darkl]

Created a branch without OWIN dependencies.

Thanks!
Elad

[Tratcher]

@Eilon can you recommend someone for System.Web WebSockets debugging?

[Eilon]

@Tratcher usually I'd recommend you 😄 I can give you a name in person.

[flin-8]

Hi guys,
Do we know where the issue lies yet?

[Tratcher]

Not yet. I've passed this off to the Asp.Net 4 servicing team to investigate.

[flin-8]

Great thanks!

[Jinhuafei]

@flin-zap It looks like the client side causes the issue. If you enable socket tracing, you will see the following log. At the end of the log, the receive operation never completed. I also tried two other websocket clients(System.Net.WebSockets.ClientWebSocket and JavaScript WebSocket), and all worked well.

System.Net.Sockets Verbose: 0 : [7728] Entering Socket#45004109::ReceiveAsync()
System.Net.Sockets Verbose: 0 : [7728] Exiting Socket#45004109::ReceiveAsync() -> Boolean#1
System.Net.Sockets Verbose: 0 : [13504] Entering Socket#45004109::SendAsync()
System.Net.Sockets Verbose: 0 : [13504] Entering Socket#45004109::SendAsync(Boolean#1)
System.Net.Sockets Verbose: 0 : [7728] Data from Socket#45004109::FinishOperation(SendAsync)
System.Net.Sockets Verbose: 0 : [7728] 00000000 : 89 94 4D C8 F0 48 7C E7-C1 70 62 FA C0 79 75 E8 : ..M..H|..pb..yu.
System.Net.Sockets Verbose: 0 : [7728] 00000010 : C2 72 7E FA CA 7D 7B E8-A0 05 : .r~..}{...
System.Net.Sockets Verbose: 0 : [7728] Data from Socket#45004109::FinishOperation(ReceiveAsync)
System.Net.Sockets Verbose: 0 : [7728] 00000000 : 8A 14 : ..
System.Net.Sockets Verbose: 0 : [7728] Entering Socket#45004109::ReceiveAsync()
System.Net.Sockets Verbose: 0 : [7728] Exiting Socket#45004109::ReceiveAsync() -> Boolean#1
System.Net.Sockets Verbose: 0 : [7728] Data from Socket#45004109::FinishOperation(ReceiveAsync)
System.Net.Sockets Verbose: 0 : [7728] 00000000 : 31 2F 31 38 2F 32 30 31-38 20 32 3A 33 32 3A 35 : 1/18/2018 2:32:5
System.Net.Sockets Verbose: 0 : [7728] 00000010 : 36 20 50 4D : 6 PM
System.Net.Sockets Verbose: 0 : [7728] Entering Socket#45004109::ReceiveAsync()
System.Net.Sockets Verbose: 0 : [7728] Exiting Socket#45004109::ReceiveAsync() -> Boolean#1

[darkl]

Dear @Jinhuafei,

Thanks for your help. I understand that this is the client's fault, but what would you suggest to do on the server side? I would expect the Task to fault after some timeout. Should the server developer handle this issue themselves?

Elad

[darkl]

By the way, the original code works fine when using OWIN self-host. Any ideas why?

Elad

[darkl]

I tried to debug the WebSocket4Net codebase. The code is waiting for a reply after calling ReceiveAsync. As I mentioned in my previous comment, this does work fine on OWIN self-host, and on many other WebSockets implementations (for instance vtortola).
I couldn't find anything wrong while debugging the WebSocket4Net code. I feel like this issue is caused by both IIS and WebSocket4Net, but it's hard for me to point exactly how.

Elad

[bigbearzhu]

Narrowed down this a bit more. Fiddler shows that the server doesn't reply with the message sent through. Interestingly it shows that a Ping message was sent to the server from WebSocket4Net almost at the same time of the last message sent. I tried sending a Ping message manually immediately after sending a message. It hangs very quickly (< 5 messages). It seems IIS just don't like Ping and normal message coming together.

A fork to show the issue can be found here

When I set EnableAutoSendPing on the websocket to false, it seems working fine.

[Tratcher]

@pan-wang @anurse does this look like any of the IIS websocket issues you've seen?

[anurse]

Might be aspnet/WebSockets#100 - I believe that was fixed in ANCM, not sure if the fix was in ANCM or the core websocket handling though. It's possible a similar fix is needed elsewhere.

[Tratcher]

This resembles a known IIS bug that was fixed in recent Windows releases (1703 or 1709). What OS version are you testing on? See winver.exe.

[darkl]

[bigbearzhu]

I have tested using the code on latest Windows 10 Version 1709 (OS Build 16299.125) with IIS Express (iisexpress 10.0.14358.1000). It still failed almost immediately. Fortunately, on the same machine, IIS (w3wp 10.0.16299.15) doesn't fail like before, but it can still get stuck for a few seconds and then continued every minute or so. I believe it is much better now!

At the same time, we tested this on another server machine with Windows Server 2016 Version 1607 (OS Build 14393.2007) It does have same issue with both IIS Express and IIS. So I guess it confirmed @Tratcher's reply. @Tratcher do you have reference to the original bug? Thanks

[Tratcher]

aspnet/WebSockets#100 is the only public reference. I'll check if there's a corresponding fix for IIS Express.

[bigbearzhu]

Thanks @Tratcher for your effort! Let's hope this update will be rolled into Azure Web App hosting OS soon. So far I could only disable the auto ping to work around it as the hosting OS is still 10.0.14393.0.

[Tratcher]

It looks like the fix has not been ported to IIS Express yet. There is a plan to update express, but no specific schedule.

[darkl]

Resolved in newer Windows versions