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#Socket Helpers Plugin for Xamarin and Windows (PCL)

This library aims to provide useful functionality around the base sockets-for-pcl classes, including hub-style communications, custom protocol helpers and support for typed messaging, and error handling/life cycle and reliability options.

There is a NuGet package with here with the latest functionality. This is all alpha so it is possible that new versions will break existing code.

Service Discovery

Alpha code for service discovery is now included in the project. Please see here for an overview of the design and usage.

Creating a basic inline service definition

// responds to all requests with its ip/port as a string
var serviceDef = new FuncyJsonServiceDefinition<string, string>()  
{
    DiscoveryRequestFunc = () => "EHLO",
    ResponseForRequestFunc = _ => String.Format("{0}:{1}", myIP, myPort)
};

Host side - publishing according to the service definition

// set up publisher and start listening
var publisher = serviceDef.CreateServicePublisher();  
publisher.Publish();  

Client side - discovering services according to the service definition

// set up discoverer and response handler
var discoverer = serviceDef.CreateServiceDiscoverer();  
discover.DiscoveredServices.Subscribe(svc => /* handle your responses */);

// start sending discovery requests
discoverer.StartDiscovering(); 

Typed Message Transmission

Alpha code for strongly typed object transmission is included in the project via JsonProtocolMessenger. JsonProtocolMessenger wraps a TcpSocketClient and facilitates sending and receiving strongly typed objects. It exposes an IObservable<TMessage> of messages received, and a Send(TMessage message) method for sending to the other party. Serialisation is handled by JSON.NET.

Connecting

Here, client is a connected TcpSocketClient. TMessage is a type from which all your messages derive, object is fine if you have no overarching base class.

// wrap a connected socket in a JsonProtocolMessenger, start running the send/receive functions
var messenger = new JsonProtocolMessenger<TMessage>(newClient);
messenger.StartExecuting();

Receiving Messages

To handle received messages subscribe to the Messages property directly, or perform Rx operations over it as neccessary. Messages are not replayed or cached, only messages received from the point of a subscription onwards will be fire for that subscription. If you are expecting to receive messages immediately on connect, you should set up those subscriptions before calling StartExecuting.

// e.g. log any messages we receive to the console
messenger.Messages
         .Subscribe(msg=> Debug.WriteLine(msg));
    
// e.g. print the names of people who send us HelloMessages to the console
messenger.Messages
         .OfType<HelloMessage>() // only HelloMessages will pass through here
         .Subscribe(msg => Debug.WriteLine("{0} says hello.", msg.Name));

// e.g. don't proceed until we get a ReadyMessage from the other end
// this kind of subscription has to be made *after* StartExecuting has been called. 
await messenger
         .Messages
         .OfType<ReadyMessage>
         .FirstAsync()
         .ToTask();

Sending Messages

Call Send on JsonProtocolMessenger.

var msg = new Message { Content = "Hi" };
messenger.Send(msg);

Type Resolution

JsonProtocolMessenger includes the object type name as part of the protocol when sending, so that the receiving end knows what it should deserialize to. When a message is received, JsonProtocolMessenger uses Type.GetType(typeName) to resolve the type. This might fail to resolve the type in some obscure situations, notably when running in a LINQPad query and transmitting an object whose class is defined in the query itself. To help JsonProtocolMessenger find your type, you can add assemblies to its AdditionalTypeResolutionAssemblies property. These assemblies will be searched if the initial Type.GetType() call does not return a type. In the LINQPad case specifically, you should also add #DEFINE NONEST to the top of your query to prevent it from nesting types within its UserQuery class.