CoAP Server Example

Using CoAP server to provide CoAP resources to remote clients.

Intro

CoAP sessions are considered as request-response pairs. Available handlers for requests are defined as Resources. Each resource can be added to a CoapServer and process certain types of requests.

Creating Resource

All resources must implement the IResource interface. Extending the Resource class is a good start point.

class HelloWorldResource : Resource
{
	// use "helloworld" as the path of this resource
	public HelloWorldResource() : base("helloworld")
	{
		// set a friendly title
		Attributes.Title = "GET a friendly greeting!";
	}
	
	// override this method to handle GET requests
	protected override void DoGet(CoapExchange exchange)
	{
		// now we get a request, respond it
		exchange.Respond("Hello World!");
	}
}

Now this HelloWorldResource will handle GET requests from clients and respond them with a “Hello World!” string.

To handle other types of request, i.e., POST, PUT and DELETE, override related methods.

class HelloWorldResource : Resource
{
	public HelloWorldResource() : base("helloworld")
	{
	}
	
	// override this method to handle GET requests
	protected override void DoGet(CoapExchange exchange)
	{
	}
	
	// override this method to handle POST requests
	protected override void DoPost(CoapExchange exchange)
	{
	}
	
	// override this method to handle PUT requests
	protected override void DoPut(CoapExchange exchange)
	{
	}
	
	// override this method to handle DELETE requests
	protected override void DoDelete(CoapExchange exchange)
	{
	}
}

If not overrided, request will be responded with a 4.05 (Method Not Allowed).

Creating CoAP Server

Prepare a server

// create a new server
var server = new CoapServer();

Or you may specify the port(s) to listen to:

// create a new server on these ports
var server = new CoapServer(5683, 5684);

To override default configurations, create your own ICoapConfig and pass it to the server.

// define custom configurations
ICoapConfig config = new CoapConfig();
// ...

// create a new server with custom config
var server = new CoapServer(config);

Add resources

// add the resource to share
server.Add(new HelloWorldResource());

Remove a resource

server.Remove(...);

Start a server

server.Start();

Stop a server

server.Stop();

Observable Resource

Resources can be enabled as observable simply by setting Observable to true. Call Changed(); whenever a new notification is ready to broadcast. After this call, the DoGet will be called again for each subscriber.

class TimeResource : Resource
{
	Timer _timer;
	DateTime _now;

	// use "time" as the path of this resource
	public TimeResource() : base("time")
	{
		// set a friendly title
		Attributes.Title = "GET the current time";
		
		// mark as observable
		Observable = true;
		
		_timer = new Timer(Timed, null, 0, period);
	}
	
	private void Timed(Object o)
	{
		_now = DateTime.Now;
		
		// notify subscribers
		Changed();
	}
	
	protected override void DoGet(CoapExchange exchange)
	{
		exchange.Respond(_now.ToString());
	}
}

See CoAP Example Server for more.