I'm having some problems with my WCF server and client connections.
If I use my service and client normally, meaning my client connects and disconnects thru normal operations (myclient.Close()) everything works fine. But in the instance that I have the server running and I use the visual studio "Stop" button to exit my client application, my server and client communications seems to mess up and the server doesn't clean up the connection correctly and any new connections from my client are very unstable and only certain function calls work until one function will throw an exception of:
System.ServiceModel.CommunicationException: An error occurred while receiving the HTTP response to http://localhost:8080/Design_Time_Addresses/Service_Beta1/Service. This could be due to the service endpoint binding not using the HTTP protocol. This could also be due to an HTTP request context being aborted by the server (possibly due to the service shutting down). See server logs for more details. ---> System.Net.WebException: The underlying connection was closed: An unexpected error occurred on a receive.
And many other exceptions after that, and I'll spare you from reading those.
If I shutdown the server and client and restart both, all my calls work fine until I do the drastic "Stop" in visual studio. How can I force the server to clean up improperly closed connections? I know in production the "Stop" button is gone and in theory there shouldn't be problems, but I don't want to have server connection problems from crashes of clients or bad disconnects. Because inevitably there will be those cases. It's best to fix this now before you have 20+ clients trying to connect and getting exceptions.
Thanks
Sorry for taking such a long time to post a reply. My problem is I was passing back a datatable to the client but wasn't giving the table a name on creation. See below.
Dim dt As New DataTable() 'Passing just a blank un-named table to client gave errors.
Dim dt As New DataTable("Table") 'Naming the table like so passes just fine.
Related
On this previous question: Tell when wcf client lost connection One of the commenters states:
Your service should not care whether a network cable was disconnected.
One feature of TCP is that unless someone is actively sending data, it
can tolerate momentary interruptions in network connectivity.
This is even more true in WCF, where there are layers of extra
framework to help protect you against network unreliability.
I'm having an issue where this is not working correctly. I have WCF client that makes a connection to the server using a DuplexChannelFactory. The connection stays open for 3 minutes. I disconnect the client from the internet and reconnect. The client regains internet connection, however any calls made from the server to that client fail. Once the client reconnects it begins working again.
When I pull the plug on the internet, the client throws several exceptions but the channel is still listed as being in an open state. Once the connection is regained and I made a request from the server to the client, I get errors such as: The communication object, System.ServiceModel.Channels.ServiceChannel, cannot be used for communication because it has been Aborted.
Obviously if the request comes in when the client is offline it won't work, but I'm trying to get it so this channel will recover once the internet comes back without having to set up a new connection.
Should this be working as-is, based on the comment I listed above? Or is there something I need to change to make that actually work?
The issue here is that the channel you're trying to use is in a faulted state, and cannot be used any longer (as the error message indicates).
Your client needs to trap (catch) that exception, and then abort the current channel and create a new one. WCF will not do that for you automatically, you have to code for it yourself.
You could also check the CommunicationState of the channel to see if it is faulted, and recover that way.
A final option would be to use the OnFaulted event handler, and when the channel is faulted, abort the channel and create a new one.
I have a Windows Service running on a client machine which communicates to our server using WCF. The basic process is this:
Every 3 minutes, the client makes a connection to the server using a DuplexChannelFactory (CreateChannel).
While this connection is open, the server sends messages to the client.
The connection must remain open constantly because the server may need to communicate with the client at any time. This is why we are refreshing the connection every few minutes.
For the most part this system works fine. However if the client has a spotty Internet connection, the channel becomes aborted. Here's what happens in this case:
The client opens a connection. This connection stays open for 3 minutes until it is closed and re-opened.
During the first connection, the computer loses Internet connection for a few seconds.
The Windows Service running on the client throws a System.Net.Sockets.SocketException and System.ServiceModel.CommunicationException. The code currently does not catch these exceptions.
The computer regains Internet connection.
The server tries to communicate with the client (still during the first 3 minutes).
Since the first connection is still open, the server cannot communicate and gets the following error: The communication object, System.ServiceModel.Channels.ServiceChannel, cannot be used for communication because it has been Aborted.
I'm trying to figure out how I can catch the errors that happen in step 3 so that I can close the current connection and re-open it. I currently have a function to handle the Faulted event, but this event is not hit when the connection is lost. I've tried looking into global error handling but it seems like most of the tutorials are for the server side, not client. Also, since the connection is just staying open indefinitely, there is nowhere I can put a try/catch block since there is no code that is actually running at the time it happens.
I was able to accomplish catching these exceptions by using the FirstChanceException event handler. I had to use this event because the exceptions were being handled automatically deeper down so I couldn't catch them.
In the Windows Service's OnStart function:
Dim currentDomain As AppDomain = AppDomain.CurrentDomain
AddHandler currentDomain.FirstChanceException, AddressOf HandleException
And the function I wrote checks if the exception is of a certain type I know the connection has failed and I create a new connection.
In our production environment, we have a WCF serivce that is very frequently called.
We noticed that sometimes, calls to this service (only this one) fail on timeout for a period of time, after everything falls into place and the service responds correctly again.
I used Dynatrace to try to understand what's happening, I noticed that for the calls resulting on a timeout, the method of the service is never called ! And at the same time the server throw this error
A blocking operation was interrupted by a call to
WSACancelBlockingCall
and the client throws a Timeout Exception.
I want to understand the cause of this errors. Is the server error caused by the client's TimeoutException (when the client close its connection) ? Otherwise why do the server throw this error ?
Can you attach a screenshot of that PurePath?
The TimeoutException is simply thrown by the caller of a service when the called web services doesnt return within the default timeout - typically something like 60s. And - once the client aborts its network connection it will cause the exception in the server who has accepted that connection.
There can be multiple reasons for this slow behavior, e.g: you are maxing out the number of connections you have in your client - or the server implementation is overloaded and cant handle incoming requests. Definitely look at the number of worker threads/connections configured on both sides
If you want specific help on dynatrace freel free to send over the PurePaths - check out http://bit.ly/sharepurepath
hope this helps
I have a simple client server apps that uses WCF (netTcpBinding) when i'm launching the server and sending messages through the client everythings works fine , but when i'm closing the server manually and open it again (without closing the client app at all) the next time the client tries to send a message to the server i get this exception (on the client side):
The socket connection was aborted. This could be caused by an error processing y
our message or a receive timeout being exceeded by the remote host, or an underl
ying network resource issue. Local socket timeout was '00:00:59.9843903'.
if i use basicHttpBinding the problem doesn't occur.
is any one knows why this problem occurs ???
Thanks,
Liran
This is expected behavior. When you close the server, TCP connection on the server is closed and you can't call it from the client anymore. Starting the server again will not help. You have to catch the exception on the client, Abort current proxy and create and open new one.
With BasicHttpBinding it works because NetTcpBinding uses single channel for whole life of the proxy (the cannel is bound to TCP connection) whereas BasicHttpBinding creates new one for each call (it reuses existing HTTP connection or create new one if connection doesn't exist).
The setup is as follows:
A C++ client connects via OLEDB/SQL Native Client to a SQL Server 2005 database located on another machine. The server is setup with mirroring (automatic failover) with a synchronized server located on yet another server and a witness server on another server.
Occassionally (once every couple of days), our application seizes up in that it appears to attempt to establish a database connection to the database and rather than simply failing and OLEDB throwing a database connection failure it just gets "stuck" (we have a timeout for the connection but it's never timing out). 24 to 36 hours later we'll get an error:
TCP Provider: An existing connection was forcibly closed by the remote host.
And things will continue you on with lots of these errors and our app will eventually need to be restarted. We can't really figure out what condition could be causing this behavior and what we can do about it?
In preliminary research, I've seen some related problems that were solved by setting the Connection Lifetime connection string property to something non-zero.
Does anyone have any thoughts on what might be going on here?