WCF Peer to Peer, Are There Nodes Out There?

Question

I am using WCF in .NET 3.5 to implement a peer to peer networking application. To resolve peer nodes I am using PNRP.

IGlobalStoreServiceContract is my contract as shown below,

[ServiceContract(Namespace = "http://GlobalStoreEventDriven.API", CallbackContract = typeof(IGlobalStoreServiceContract))]
internal interface IGlobalStoreServiceContract
{
    [OperationContract(IsOneWay = true)]
    void NotifyGlobalStoreDataInserted(string globalGroup, DateTime maxDateTime);

    [OperationContract(IsOneWay = true)]   
    void RegisterNode();

    [OperationContract(IsOneWay = true)]
    void SynchronizeMemberList(Guid clientId);
}

I am using some code like this to join each node to the peer to peer network.

DuplexChannelFactory<IGlobalStoreChannel> channelFactory = new DuplexChannelFactory<IGlobalStoreChannel>(instance, "GlobalStoreAPIEndPoint");
IGlobalStoreChannel globalStoreChannel = channelFactory.CreateChannel();

globalStoreChannel.Open();

My question is as soon as I have opened the channel how can I best tell if other peer nodes are on the network?

For instance I could call one of the methods in my contract RegisterNode, and each node in the network could use a callback to call SynchronizeMemberList. I would then know whether other nodes were there.

The trouble with that is it is all asynchronous. If I call RegisterNode and no one replies, it doesn't really mean no one is there, it could just mean that I didn't wait long enough.

What do you reckon? Any suggestions?

Answer 1

See Peer-to-Peer Programming with WCF and .NET Framework 3.5: Peer Name by Amit Bahree and Chris Peiris:

The final logical step after creating and publishing a peer is resolving a peer. What good is it to publish something to the cloud if another peer cannot find you? We use the PeerNameResolver class to resolve for a specific peer in a given cloud. The PeerNameResolver can resolve a peer to either a PeerRecord or a cloud, depending on the parameters that are passed. The resolution process finishes either when the maximum number of record entries for the PeerRecordCollection is reached or when it has reached the end of various clouds.

The PeerNameResolver class exposes an overloaded method that is called Resolve and is used to resolve a given peer synchronously.

Listing 17 shows us how to try to resolve for a peer that is called MySecurePeer. The Resolve method returns a collection of type PeerNameRecordCollection through which we iterate. Listing 18 shows the result of this when running on a computer that has three network cards.

PeerName myPeer = new PeerName("MySecurePeer", PeerNameType.Secured);
PeerNameResolver resolver = new PeerNameResolver();

PeerNameRecordCollection results = resolver.Resolve(myPeer);

Console.WriteLine("{0} Peers Found:", results.Count.ToString());
int i = 1;

foreach (PeerNameRecord peer in results)
{
    Console.WriteLine("{0} Peer:{1}", i++, peer.PeerName.ToString());
    foreach (IPEndPoint ip in peer.EndPointCollection)
    {
        Console.WriteLine("\t Endpoint: {0}", ip.ToString());
    }
}

So, I guess you should check out PeerNameResolver.Resolve Method:

This method associates peer names to clouds. Calling the PeerNameResolver method is similar to calling the Resolve method for each peer name record in the PeerNameRecordCollection. Note that using the Resolve method on an individual peer name record does not invalidate resolving multiple peer names.

For every Resolve method, there is an equivalent ResolveAsync method. They are identical in the parameters they are passed, except that the ResolveAsync method includes a system token in its parameter list for asynchronous event handling.

Answer 2

OK, thanks for that. But I am wondering something. I am trying to support a central server approach as well as PNRP.

The central server approach overrides the CustomPeerResolverService class. Does this method of using the PeerNameResolver you have suggested still work with a central server?

I guess what I am asking is whether PeerNameResolver only works with PNRP or not.

Another question I was wondering about is how do I know what the peer name is? You are saying this,

PeerName myPeer = new PeerName("MySecurePeer", PeerNameType.Secured);

So where does the peer name "MySecurePeer" come from? In my code I am specifying a mesh name of 'net.p2p://iC3GlobalStoreEventMesh/EventMesh/' and have endpoints specified like this,

  <endpoint name="GlobalStoreAPIEndPoint"
            binding="netPeerTcpBinding" bindingConfiguration="PeerTcpConfig"
            contract="GlobalStoreEventDrivenAPI.IGlobalStoreServiceContract"
            address="net.p2p://iC3GlobalStoreEventMesh/EventMesh/">
  </endpoint>

Thanks.