Closing WCF Connections from service - wcf

Question

I have recently started a new job where WCF services are being used. I have used them in the past and am comfortable with them but from what I can recall if the client does not close the connection it has the ability to bring your service down entirely. I am aware of the proper procedure for closing the connections but if the responsibility is on the client, they may not follow the same practices and potentially have the ability to bring the service down. Is there any other way of handling the closing of the connections so that it is not reliant on the client doing the right thing? It seems odd that anyone who has access to your service has the ability to bring it down with such ease...
Thank you very much for any insights!

Answer 1

One option is to use session time out in the server. This actually faults the client channel.
There are only really three ways in which a session can terminated:
1) The client closes the proxy
2) The service's receiveTimeout is exceeded before the client sends another request
3) The service throws a non-fault exception which will fault the channel and so terminate the session
If you don't want the client involved then you only have 2 and 3 neither of which end well for the client - they will get an exception in both situation on the next attempt to talk to the service.
You could use Duplex messaging and get the service to notify the client that its requires session termination - the client then gets an opportunity to close down the proxy gracefully but this is a cooperative strategy
Or you need to use duplex (but still the client will have to call the service).
Here is some important points of the service implementation:
a: Use a static dictionary to keep the Client’s IP and callback channel. Before writing on the share object, lock the object.
b: Gets the IP address of the client using the GetAddressAsString method. You can get the IP of the client from the incoming message. The following statement shows how can we get the IP adddress of the Client in WCF:
RemoteEndpointMessageProperty clientEndpoint = OperationContext.Current.IncomingMessageProperties[RemoteEndpointMessageProperty.Name] as RemoteEndpointMessageProperty;
String ipAddress = clientEndpoint.Address;
If you are using the namepipe binding, you will not get the RemoteEndpointMessageProperty.
c: When the client creates the proxy of the service, it will call StartingService method immediately. Inside the StartingService method, I am keeping the callback channel of the client and current instance into the dictionary.
d: When the user of WCF service wants to disconnect a client, he/she will call the Disconnect method with the IP Address of the client.
e: The Disconnect method uses the IP Address to get the callback channel of the client and associate service instance of the client from the dictionary. Eventually, it notifies the client by using callback channel and close the incoming channel.
Here is the implementation through code:
[ServiceContract(CallbackContract=typeof(INotifyClientCallback),SessionMode=SessionMode.Required)]
public interface IService1
{
[OperationContract]
bool StartingService();
}
public interface INotifyClientCallback
{
[OperationContract(IsOneWay = true)]
void Disconnecting();
}
INotifyClientCallback interface for Callback.
Step 2: Implementation of the Contact:
[ServiceBehavior(InstanceContextMode = InstanceContextMode.PerSession)]
public class Service1 : IService1
{
private static readonly Dictionary subscribers = new Dictionary();
public static event EventHandler onClientAdded;
///
/// Returns the IP Address of the Client
///
///
public string GetAddressAsString()
{
if (!OperationContext.Current.IncomingMessageProperties.ContainsKey(RemoteEndpointMessageProperty.Name))
{
return "127.0.0.1";
}
RemoteEndpointMessageProperty clientEndpoint =
OperationContext.Current.IncomingMessageProperties[RemoteEndpointMessageProperty.Name] as RemoteEndpointMessageProperty;
return clientEndpoint.Address;
}
public bool StartingService()
{
//Get the callback reference
INotifyClientCallback callback = OperationContext.Current.GetCallbackChannel();
string IPAddress = GetAddressAsString();
lock (subscribers)
{
if (!subscribers.ContainsKey(IPAddress))
{
subscribers[IPAddress] = new CommunicationStore()
{ NotifyCallback = callback,
IService = OperationContext.Current.InstanceContext
};
if (onClientAdded != null)
{
onClientAdded(IPAddress, null);
}
}
}
return true;
}
public static void Disconnect(string ipAddress)
{
if (subscribers.ContainsKey(ipAddress))
{
CommunicationStore com = subscribers[ipAddress];
if (((ICommunicationObject)com.NotifyCallback).State == CommunicationState.Opened)
{
try
{
//fires the callback method
com.NotifyCallback.Disconnecting();
com.IService.IncomingChannels.FirstOrDefault().Close();
}
catch (Exception)
{
throw;
}
}
}
}
}
public class CommunicationStore
{
public InstanceContext IService { get; set; }
public INotifyClientCallback NotifyCallback { get; set; }
}