Catching System.Net.WebException Exceptions??

[naikvi]

Hi Sir,

I am implementing the Bayeux Protocol via your library in situations where I have a failover implementation on the server side but I have a single virtual IP address I interact with. Therefore, when the server fails over I encounter a TCP reset and after that I need to renegotiate the connection. However, from my client side, I don't receive anything indicating that the TCP reset occurred. When I look at the debug output I see that your library encountered the System.Net.WebException and this would be useful for my client to be notified of. How do I get access to this exception or at least get an error notification in my client when using this protocol to know that I should re-negotiate the handshake and subscription? Is it possible to get access to this exception or get an error reported back to me for it?

Thank you.

[grEvenX]

Hi, it's been a while since I've been deep into the source, but if I remember correctly an exception of this type should make the library automatically reconnect and re-subscribe any subscription.
Have you tested that it doesn't work out of the box?

[naikvi]

You might be right about that because I see the exception reported in the output window of Visual Studio (in debug mode) about 3 to 4 times before it quits. My thinking is that perhaps the re-try is occurring too quickly as my server side takes a while (maybe a good 10 seconds) to bring the virtual IP down on one box and back up on the other (through a failover). I am not sure if this can be verified by the output but I can paste it in here:

A first chance exception of type 'System.Net.WebException' occurred in System.dll
System.Net.WebException: The underlying connection was closed: A connection that was expected to be kept alive was closed by the server.
at System.Net.HttpWebRequest.EndGetResponse(IAsyncResult asyncResult)
at Cometd.Client.Transport.LongPollingTransport.GetResponseCallback(IAsyncResult asynchronousResult) in C:\Users\naikv\Desktop\Oyatel-CometD.NET-0fcf58c\cometd\client\transport\LongPollingTransport.cs:line 240
A first chance exception of type 'System.Net.WebException' occurred in System.dll
System.Net.WebException: The underlying connection was closed: An unexpected error occurred on a send. ---> System.IO.IOException: Unable to write data to the transport connection: An existing connection was forcibly closed by the remote host. ---> System.Net.Sockets.SocketException: An existing connection was forcibly closed by the remote host
at System.Net.Sockets.Socket.BeginSend(Byte[] buffer, Int32 offset, Int32 size, SocketFlags socketFlags, AsyncCallback callback, Object state)
at System.Net.Sockets.NetworkStream.BeginWrite(Byte[] buffer, Int32 offset, Int32 size, AsyncCallback callback, Object state)
--- End of inner exception stack trace ---
at System.Net.Sockets.NetworkStream.BeginWrite(Byte[] buffer, Int32 offset, Int32 size, AsyncCallback callback, Object state)
at System.Net.Security.SslState.StartSendBlob(Byte[] incoming, Int32 count, AsyncProtocolRequest asyncRequest)
at System.Net.Security.SslState.ForceAuthentication(Boolean receiveFirst, Byte[] buffer, AsyncProtocolRequest asyncRequest)
at System.Net.Security.SslState.ProcessAuthentication(LazyAsyncResult lazyResult)
at System.Net.TlsStream.CallProcessAuthentication(Object state)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
at System.Net.TlsStream.ProcessAuthentication(LazyAsyncResult result)
at System.Net.TlsStream.BeginWrite(Byte[] buffer, Int32 offset, Int32 size, AsyncCallback asyncCallback, Object asyncState)
at System.Net.TlsStream.UnsafeBeginWrite(Byte[] buffer, Int32 offset, Int32 size, AsyncCallback asyncCallback, Object asyncState)
at System.Net.PooledStream.UnsafeBeginWrite(Byte[] buffer, Int32 offset, Int32 size, AsyncCallback callback, Object state)
at System.Net.ConnectStream.WriteHeaders(Boolean async)
--- End of inner exception stack trace ---
at System.Net.HttpWebRequest.EndGetResponse(IAsyncResult asyncResult)
at Cometd.Client.Transport.LongPollingTransport.GetResponseCallback(IAsyncResult asynchronousResult) in C:\Users\naikv\Desktop\Oyatel-CometD.NET-0fcf58c\cometd\client\transport\LongPollingTransport.cs:line 240
A first chance exception of type 'System.Net.WebException' occurred in System.dll
System.Net.WebException: The underlying connection was closed: An unexpected error occurred on a send. ---> System.IO.IOException: Unable to write data to the transport connection: An existing connection was forcibly closed by the remote host. ---> System.Net.Sockets.SocketException: An existing connection was forcibly closed by the remote host
at System.Net.Sockets.Socket.BeginSend(Byte[] buffer, Int32 offset, Int32 size, SocketFlags socketFlags, AsyncCallback callback, Object state)
at System.Net.Sockets.NetworkStream.BeginWrite(Byte[] buffer, Int32 offset, Int32 size, AsyncCallback callback, Object state)
--- End of inner exception stack trace ---
at System.Net.Sockets.NetworkStream.BeginWrite(Byte[] buffer, Int32 offset, Int32 size, AsyncCallback callback, Object state)
at System.Net.Security.SslState.StartSendBlob(Byte[] incoming, Int32 count, AsyncProtocolRequest asyncRequest)
at System.Net.Security.SslState.ForceAuthentication(Boolean receiveFirst, Byte[] buffer, AsyncProtocolRequest asyncRequest)
at System.Net.Security.SslState.ProcessAuthentication(LazyAsyncResult lazyResult)
at System.Net.TlsStream.CallProcessAuthentication(Object state)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
at System.Net.TlsStream.ProcessAuthentication(LazyAsyncResult result)
at System.Net.TlsStream.BeginWrite(Byte[] buffer, Int32 offset, Int32 size, AsyncCallback asyncCallback, Object asyncState)
at System.Net.TlsStream.UnsafeBeginWrite(Byte[] buffer, Int32 offset, Int32 size, AsyncCallback asyncCallback, Object asyncState)
at System.Net.PooledStream.UnsafeBeginWrite(Byte[] buffer, Int32 offset, Int32 size, AsyncCallback callback, Object state)
at System.Net.ConnectStream.WriteHeaders(Boolean async)
--- End of inner exception stack trace ---
at System.Net.HttpWebRequest.EndGetResponse(IAsyncResult asyncResult)
at Cometd.Client.Transport.LongPollingTransport.GetResponseCallback(IAsyncResult asynchronousResult) in C:\Users\naikv\Desktop\Oyatel-CometD.NET-0fcf58c\cometd\client\transport\LongPollingTransport.cs:line 240

Can you tell by the output above if you are reattempting the subscription?

Thank you very much for responding back. By the way, I posted an earlier question asking if it works under HTTPS and it definitely does as I was able to get it working and am using it for this example.

[naikvi]

Hi Sir,

I made progress on this when I used the Java cometd library (at http://cometd.org/documentation/cometd-java/client). I decided to have my application monitor to see if client.isConnected() became ever false through a separate thread and if so, I know (or assume) that I lose TCP connection and/or cometd subscription connection and then I simply reissue the connection and I can get events again.

However, in your C# library, when I check for the flag form.client.Connected I find that every so often it becomes false even though I haven't lost connection. This makes me think that this doesn't represent a connection lost but instead represents a general longpoll timeout. Therefore, I am still unable to use this logic efficiently. I still see that a loss of connection does also occur when I get a TCP connection loss BUT what ends up happening is that the library ends up connecting/disconnecting/reconnecting too many times. Is there another flag that can tell me if the connection is lost?

Thank you sir.

[arvydas]

I'm also experiencing the same issue with Rails faye server.