The Constrained Application Protocol (CoAP) (https://datatracker.ietf.org/doc/draft-ietf-core-coap/) is a RESTful web transfer protocol for resource-constrained networks and nodes. CoAP.NET is an implementation in C# providing CoAP-based services to .NET applications. Reviews and suggestions would be appreciated.

• [Quick Start] (#quick-start)
• [Build] (#build)
• [License] (#license)
• [Acknowledgements] (#acknowledgements)

CoAP sessions are considered as request-response pair.

Access remote CoAP resources by issuing a [Request] (CoAP.NET/Request.cs) and receive its [Response] (CoAP.NET/Request.cs)(s).

  // new a GET request
  Request request = new Request(Code.GET);
  request.URI = new Uri("coap://[::1]/hello-world");
  request.Execute();
  
  // receive one response
  Response response = request.ReceiveResponse();

There are 4 types of request: GET, POST, PUT, DELETE, defined as Code.GET, Code.POST, Code.PUT, Code.DELETE.

Responses can be received in two ways. By calling request.ReceiveResponse() a response will be received synchronously, which means it will block until timeout or a response is arrived. If more responses are expected, call ReceiveResponse() again.

To receive responses asynchronously, register a event handler to the event request.Responded before executing.

Parsing Link Format

Use RemoteResource.NewRoot() to parse a link-format response. The returned root resource contains all resources stated in the given link-format string.

Request request = new Request(Code.GET); request.URI = new Uri("coap://[::1]/.well-known/core"); request.Execute(); Response response = request.ReceiveResponse(); Resource root = RemoteResource.NewRoot(response.PayloadString);

See [CoAP Example Client] (CoAP.Client) for more.

### CoAP Server

A new CoAP server can be easily built by just inheriting the class
[**LocalEndPoint**] (CoAP.NET/EndPoint/LocalEndPoint.cs)

```csharp
class CoAPServer : LocalEndPoint
{
}

static void Main(String[] args)
{
  CoAPServer server = new CoAPServer();
  Console.WriteLine("CoAP server started on port {0}", server.Communicator.Port);
}

See [CoAP Example Server] (CoAP.Server) for more.

CoAP resources are classes that can be accessed by a URI via CoAP. In CoAP.NET, a resource is defined as a subclass of [LocalResource] (CoAP.NET/EndPoint/LocalResource.cs). By overriding methods DoGet, DoPost, DoPut or DoDelete, one resource accepts GET, POST, PUT or DELETE requests.

The following code gives an example of HelloWorldResource, which can be visited by sending a GET request to "/hello-world", and respones a plain string in code "2.05 Content".

  class HelloWorldResource : LocalResource
  {
      public HelloWorldResource()
          : base("hello-world")
      {
      }

      public override void DoGet(Request request)
      {
          Response response = new Response(Code.Content);
          response.PayloadString = "Hello World from CoAP.NET!";
          request.Respond(response);
      }
  }
  
  class CoAPServer : LocalEndPoint
  {
      public CoAPServer()
      {
          AddResource(new HelloWorldResource());
      }
  }

See [CoAP Example Server] (CoAP.Server) for more.

A few compile symbols are introduced to build for different drafts of CoAP:

• COAPALL -- all supported drafts below
• COAP03 -- [draft-ietf-core-coap-03] (http://tools.ietf.org/html/draft-ietf-core-coap-03)
• COAP08 -- [draft-ietf-core-coap-08] (http://tools.ietf.org/html/draft-ietf-core-coap-08)
• COAP12 -- [draft-ietf-core-coap-12] (http://tools.ietf.org/html/draft-ietf-core-coap-12)
• COAP13 -- [draft-ietf-core-coap-13] (http://tools.ietf.org/html/draft-ietf-core-coap-13)

With COAPALL defined, all supported drafts will be available in class [Spec] (CoAP.NET/Spec.cs):

  public static class Spec
  {
    public static readonly ISpec Draft03;
    public static readonly ISpec Draft08;
    public static readonly ISpec Draft12;
    public static readonly ISpec Draft13;
  }

With one of the other symbols defined (i.e. COAP08), only a specific version of draft will be compiled as the class [Spec] (CoAP.NET/Spec.cs), with constants and static methods instead of various drafts:

  public static class Spec
  {
    public const String Name = "draft-ietf-core-coap-08";
    public const Int32 DefaultPort = 5683;
    public static Byte[] Encode(Message msg);
    public static Message Decode(Byte[] bytes);
  }

See [LICENSE] (LICENSE) for more info.

CoAP.NET is based on [Californium] (https://github.com/mkovatsc/Californium), a CoAP framework in Java by Matthias Kovatsch, Dominique Im Obersteg, and Daniel Pauli, ETH Zurich. See http://people.inf.ethz.ch/mkovatsc/californium.php. Thanks to the authors and their great job.