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The Constrained Application Protocol (CoAP) is a specialized web transfer protocol for use with constrained nodes and constrained networks in the Internet of Things. The protocol is designed for machine-to-machine (M2M) applications such as smart energy and building automation.

The go-coap provides servers and clients for DTLS, TCP-TLS, UDP, TCP in golang language.




Server UDP/TCP

	// Server
	// Middleware function, which will be called for each request.
	func loggingMiddleware(next mux.Handler) mux.Handler {
		return mux.HandlerFunc(func(w mux.ResponseWriter, r *mux.Message) {
			log.Printf("ClientAddress %v, %v\n", w.Client().RemoteAddr(), r.String())
			next.ServeCOAP(w, r)
	// See /examples/simple/server/main.go
	func handleA(w mux.ResponseWriter, req *message.Message) {
		err := w.SetResponse(codes.GET, message.TextPlain, bytes.NewReader([]byte("hello world")))
		if err != nil {
			log.Printf("cannot set response: %v", err)

	func main() {
		r := mux.NewRouter()
		r.Handle("/a", mux.HandlerFunc(handleA))
		r.Handle("/b", mux.HandlerFunc(handleB))

		log.Fatal(coap.ListenAndServe("udp", ":5688", r))

		// for tcp
		// log.Fatal(coap.ListenAndServe("tcp", ":5688",  r))

		// for tcp-tls
		// log.Fatal(coap.ListenAndServeTLS("tcp", ":5688", &tls.Config{...}, r))

		// for udp-dtls
		// log.Fatal(coap.ListenAndServeDTLS("udp", ":5688", &dtls.Config{...}, r))


	// Client
	// See /examples/simpler/client/main.go
	func main() {
		co, err := udp.Dial("localhost:5688")
		// for tcp
		// co, err := tcp.Dial("localhost:5688")
		// for tcp-tls
		// co, err := tcp.Dial("localhost:5688", tcp.WithTLS(&tls.Config{...}))

		// for dtls
		// co, err := dtls.Dial("localhost:5688", &dtls.Config{...}))

		if err != nil {
			log.Fatalf("Error dialing: %v", err)
		ctx, cancel := context.WithTimeout(context.Background(), time.Second)
		defer cancel()
		resp, err := co.Get(ctx, "/a")
		if err != nil {
			log.Fatalf("Cannot get response: %v", err)
		log.Printf("Response: %+v", resp)

Observe / Notify

Server example.

Client example.


Server example.

Client example.


In order to run the tests that the CI will run locally, the following two commands can be used to build the Docker image and run the tests. When making changes, these are the tests that the CI will run, so please make sure that the tests work locally before committing.

$ docker build . --network=host -t go-coap:build --target build
$ docker run --mount type=bind,source="$(pwd)",target=/shared,readonly --network=host go-coap:build go test './...'


Apache 2.0

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