C# 4 and .NET 4

1348 ❘ ChaPTer 45 peer-tO-peer netwOrkinG
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Cloud.AllLinkLocal — This static field gets a cloud that contains all the link local clouds available
to the peer.
Cloud.Available — This static field gets a cloud that contains all the clouds that are available to the
peer, which includes link local clouds and (if available) the global cloud.
When created, you can set the Comment and Data properties if you want. Be aware of the limitations of
these properties, though. You will receive a PeerToPeerException if you try to set Comment to a string
greater than 39 Unicode characters or an ArgumentOutOfRangeException if you try to set Data to a
byte[] greater than 4,096 bytes. You can also add endpoints by using the EndPointCollection property.
This property is a System.Net.IPEndPointCollection collection of System.Net.IPEndPoint objects.
If you use the EndPointCollection property you might also want to set the UseAutoEndPointSelection
property to false to prevent automatic generation of endpoints.
When you are ready to register the peer name you can call the PeerNameRegistration.Start() method.
To remove a peer name registration from the PNRP service you use the PeerNameRegistration.Stop()
method.
The following code registers a secured peer name with a comment:
PeerName pn = new PeerName("Peer classifier", PeerNameType.Unsecured);
PeerNameRegistration pnr = new PeerNameRegistration(pn, 8080);
pnr.Comment = "Get pizza here";
pnr.Start();
resolving Peer names
To resolve a peer name you must carry out the following steps:
1. Generate a peer name from a known P2P ID or a P2P ID obtained through a discovery technique.
2. Use a resolver to resolve the peer name and obtain a collection of peer name records. You can limit the
resolver to a particular cloud and/or a maximum number of results to return.
3. For any peer name records that you obtain, obtain peer name, endpoint, comment, and additional data
information as required.
This process starts with a PeerName object similar to a peer name registration. The difference here is that
you use a peer name that is registered by one or more remote peers. The simplest way to get a list of active
peers in your link local cloud is for each peer to register an unsecured peer name with the same classifier
and to use the same peer name in the resolving phase. However, this is not a recommended strategy for
global clouds because unsecured peer names are easily spoofed.
To resolve peer names you use the PeerNameResolver class. When you have an instance of this class you
can choose to resolve peer names synchronously by using the Resolve() method, or asynchronously using
the ResolveAsync() method.
You can call the Resolve() method with a single PeerName parameter, but you can also pass an optional
Cloud instance to resolve in, an int maximum number of peers to return, or both. This method returns
a PeerNameRecordCollection instance, which is a collection of PeerNameRecord objects. For example,
the following code resolves an unsecured peer name in all link local clouds and returns a maximum of
5 results:
PeerName pn = new PeerName("0.Peer classifier");
PeerNameResolver pnres = new PeerNameResolver();
PeerNameRecordCollection pnrc = pnres.Resolve(pn, Cloud.AllLinkLocal, 5);
The ResolveAsync() method uses a standard asynchronous method call pattern. You pass a unique
userState object to the method and listen for ResolveProgressChanged events for peers being found and
the ResolveCompleted event when the method terminates. You can cancel a pending asynchronous request
with the ResolveAsyncCancel() method.
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