go-coap client

client.go

package main

import (
	"context"
	"log"
	"os"
	"time"

	"github.com/plgd-dev/go-coap/v2/udp"
)

func main() {
	co, err := udp.Dial("localhost:5683")
	if err != nil {
		log.Fatalf("Error dialing: %v", err)
	}
	path := "/a"
	if len(os.Args) > 1 {
		path = os.Args[1]
	}

	ctx, cancel := context.WithTimeout(context.Background(), time.Second)
	defer cancel()
	resp, err := co.Get(ctx, path)
	if err != nil {
		log.Fatalf("Error sending request: %v", err)
	}
	log.Printf("Response payload: %v", resp.String())
}

server.go

package main

import (
	"bytes"
	"log"

	coap "github.com/plgd-dev/go-coap/v2"
	"github.com/plgd-dev/go-coap/v2/message"
	"github.com/plgd-dev/go-coap/v2/message/codes"
	"github.com/plgd-dev/go-coap/v2/mux"
)

func handleA(w mux.ResponseWriter, r *mux.Message) {
	err := w.SetResponse(codes.Content, 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))

	log.Fatal(coap.ListenAndServe("udp", ":5683", r))
}