Xamarin.iOS app crashes with NotImplementedException

[alexsorokoletov]

Actual Behavior

1. Run Xamarin.iOS app that sends data to event hub using the SDK, start app on Wi-Fi.
2. Switch off Wi-Fi, leave LTE/4G on.
3. App crashes with exception (see stack trace below).

Expected Behavior

1. App is not crashing and continues to send data.

Versions

• OS platform and version: Xamarin iOS 10/11
• .NET Version: Mono 5.
• NuGet package version or commit ID: 1.0.3/1.10

Xamarin Exception Stack:
System.NotImplementedException: The method or operation is not implemented.
  at System.Net.Sockets.MultipleConnectAsync.InternalConnectCallback (System.Object sender, System.Net.Sockets.SocketAsyncEventArgs args) <0x100a61198 + 0x00270> in <a4d230a362d74681a411a66f6d0be184#144952ab42dcea6e3ed69fcacf2c25f1>:0
  at System.Net.Sockets.SocketAsyncEventArgs.Complete () <0x100a621dc + 0x0002b> in <a4d230a362d74681a411a66f6d0be184#144952ab42dcea6e3ed69fcacf2c25f1>:0
  at System.Net.Sockets.Socket+<>c.<.cctor>b__306_3 (System.IAsyncResult ares) <0x100992db0 + 0x001af> in <a4d230a362d74681a411a66f6d0be184#144952ab42dcea6e3ed69fcacf2c25f1>:0
  at System.Net.Sockets.SocketAsyncResult+<>c.<Complete>b__27_0 (System.Object state) <0x100a628ec + 0x00067> in <a4d230a362d74681a411a66f6d0be184#144952ab42dcea6e3ed69fcacf2c25f1>:0
  at System.Threading.QueueUserWorkItemCallback.System.Threading.IThreadPoolWorkItem.ExecuteWorkItem () <0x1007ed708 + 0x0004f> in <e9a408feb7af4c46b81589c1b3a3e1a6#144952ab42dcea6e3ed69fcacf2c25f1>:0
  at System.Threading.ThreadPoolWorkQueue.Dispatch () <0x100627c20 + 0x001cb> in <e9a408feb7af4c46b81589c1b3a3e1a6#144952ab42dcea6e3ed69fcacf2c25f1>:0
  at ObjCRuntime.Runtime.ThreadPoolDispatcher (System.Func`1[TResult] callback) <0x10090f374 + 0x0003b> in <21d68dce9d574fa1a5570d0bc0bc7703#144952ab42dcea6e3ed69fcacf2c25f1>:0
  at System.Threading._ThreadPoolWaitCallback.PerformWaitCallback () <0x1007ed568 + 0x00067> in <e9a408feb7af4c46b81589c1b3a3e1a6#144952ab42dcea6e3ed69fcacf2c25f1>:0

See similar error in Ably ably/ably-dotnet#161

[serkantkaraca]

Does it work if you start on cellular data?
Have you changed default transport type on the client?

[alexsorokoletov]

@serkantkaraca let me check, default transport is same, Amqp, as in #223.

[alexsorokoletov]

@serkantkaraca this issue is reproduced when switching from Wi-Fi to cellular. No problem if we start with cellular at once.

[alexsorokoletov]

Additional similar stack trace (leads to this line in Mono https://github.com/mono/mono/blob/master/mcs/class/System/System.Net.Sockets/SocketAsyncEventArgs.cs#L257)

System.NotImplementedException: The method or operation is not implemented.   
  at System.Net.Sockets.SocketAsyncEventArgs.FinishOperationAsyncFailure (System.Exception exception, System.Int32 bytesTransferred, System.Net.Sockets.SocketFlags flags) [0x00000] in /Library/Frameworks/Xamarin.iOS.framework/Versions/11.6.1.2/src/mono/mcs/class/System/System.Net.Sockets/SocketAsyncEventArgs.cs:257 
  at System.Net.Sockets.MultipleConnectAsync.AsyncFail (System.Exception e) [0x0001a] in /Library/Frameworks/Xamarin.iOS.framework/Versions/11.6.1.2/src/mono/mcs/class/referencesource/System/net/System/Net/Sockets/_MultipleConnectAsync.cs:305 
  at System.Net.Sockets.MultipleConnectAsync.Fail (System.Boolean sync, System.Exception e) [0x0000c] in /Library/Frameworks/Xamarin.iOS.framework/Versions/11.6.1.2/src/mono/mcs/class/referencesource/System/net/System/Net/Sockets/_MultipleConnectAsync.cs:273 
  at System.Net.Sockets.MultipleConnectAsync.DoDnsCallback (System.IAsyncResult result, System.Boolean sync) [0x000b4] in /Library/Frameworks/Xamarin.iOS.framework/Versions/11.6.1.2/src/mono/mcs/class/referencesource/System/net/System/Net/Sockets/_MultipleConnectAsync.cs:133 
  at System.Net.Sockets.MultipleConnectAsync.DnsCallback (System.IAsyncResult result) [0x00008] in /Library/Frameworks/Xamarin.iOS.framework/Versions/11.6.1.2/src/mono/mcs/class/referencesource/System/net/System/Net/Sockets/_MultipleConnectAsync.cs:78 
  at (wrapper managed-to-native) System.Runtime.Remoting.Messaging.AsyncResult:Invoke (System.Runtime.Remoting.Messaging.AsyncResult)
  at System.Runtime.Remoting.Messaging.AsyncResult.System.Threading.IThreadPoolWorkItem.ExecuteWorkItem () [0x00000] in /Library/Frameworks/Xamarin.iOS.framework/Versions/11.6.1.2/src/mono/mcs/class/corlib/System.Runtime.Remoting.Messaging/AsyncResult.cs:210 
  at System.Threading.ThreadPoolWorkQueue.Dispatch () [0x00074] in /Library/Frameworks/Xamarin.iOS.framework/Versions/11.6.1.2/src/mono/mcs/class/referencesource/mscorlib/system/threading/threadpool.cs:856 
  at ObjCRuntime.Runtime.ThreadPoolDispatcher (System.Func`1[TResult] callback) [0x00006] in /Users/builder/data/lanes/5665/6857dfcc/source/xamarin-macios/src/ObjCRuntime/Runtime.cs:244 
  at System.Threading._ThreadPoolWaitCallback.PerformWaitCallback () [0x00009] in /Library/Frameworks/Xamarin.iOS.framework/Versions/11.6.1.2/src/mono/mcs/class/referencesource/mscorlib/system/threading/threadpool.cs:1208 

There is an easier repro now - run app that constantly sends data to event hub using AMQP (iOS simulator is okay) and then disconnect from Wi-Fi on the host. Simulator app will crash after short time with this error.

Issue filed in Xamarin Bugzilla by another person https://bugzilla.xamarin.com/show_bug.cgi?id=60772

Similar issue in Websocket4Net kerryjiang/WebSocket4Net#108

[alexsorokoletov]

We decided to put to test version where we have TransportType=AmqpWebSockets instead of TransportType=Amqp in our connection string. Will keep you updated about results

[serkantkaraca]

Thanks Alex. I am checking out our code base to find out why we hit NotImplemented on Mono.

[serkantkaraca]

Does it fail the same way if you start the app w/o any available network connection? It seems Mono Socket will crash with NotImplementedException if connection attempt fails.

[serkantkaraca]

The issue seems to be here: https://github.com/mono/mono/blob/0bcbe39b148bb498742fc68416f8293ccd350fb6/mcs/class/referencesource/System/net/System/Net/Sockets/_MultipleConnectAsync.cs#L61

Dns.BeginGetHostAddresses doesn't complete async call and handle the exception from DnsCallback.

Are you observing NotImplementedException as the unhandled exception causing the crash or as first chance?

[alexsorokoletov]

Does it fail the same way if you start the app w/o any available network connection? It seems Mono Socket will crash with NotImplementedException if connection attempt fails.

don't have a sample for that since we need to be online to start the app usually, from what I see it would be exactly same scenario

Are you observing NotImplementedException as the unhandled exception causing the crash or as first chance?

unhandled

[serkantkaraca]

Opened a new issue in Mono repository to track this: mono/mono#6428

[migueldeicaza]

There is now a fix there, but we need this to get backported to test it.

[alexsorokoletov]

Looks like TransportType=AmqpWebSockets has less crashes and handles socket errors better than Amqp.
Thank you Miguel for the changes, glad to see it in master.

[serkantkaraca]

The issue is fixed in Mono