CoAP server writting payloads to a file

coap-server.go

package main

import (
	"flag"
	"github.com/dustin/go-coap"
	"log"
	"net"
	"os"
	"path/filepath"
)

var (
	addr  = flag.String("addr", ":5683", "Address the server should listen on")
	ntype = flag.String("ntype", "udp", "Network type to use")
)

var cmap map[uint16]bool

type FileServer struct {
	file *os.File
}

func errMsg(m *coap.Message, code coap.COAPCode) *coap.Message {
	var res coap.Message

	res.MessageID = m.MessageID
	if m.IsConfirmable() {
		res.Type = coap.Acknowledgement
		res.Token = m.Token
	}

	res.Code = code
	return &res
}

func (fs FileServer) ServeCOAP(c *net.UDPConn, a *net.UDPAddr, m *coap.Message) *coap.Message {
	log.Printf("Got message in ServeCOAP: path=%q: %#v from %v", m.Path(), m, a)
	if val, ok := cmap[m.MessageID]; ok && val {
		return nil
	}

	if m.Code == coap.POST && m.IsConfirmable() {
		_, err := fs.file.Write(m.Payload)
		if err != nil {
			return errMsg(m, coap.InternalServerError)
		}

		res := &coap.Message{
			Type:      coap.Acknowledgement,
			Code:      coap.Content,
			MessageID: m.MessageID,
			Token:     m.Token,
		}

		cmap[m.MessageID] = true
		return res
	}

	return errMsg(m, coap.BadRequest)
}

func main() {
	flag.Parse()
	args := flag.Args()

	if len(args) < 1 {
		os.Exit(1)
	}

	file, err := os.OpenFile(args[0], os.O_APPEND|os.O_WRONLY, 0644)
	if err != nil {
		panic(err)
	}
	defer file.Close()

	fs := FileServer{file}
	mux := coap.NewServeMux()
	mux.Handle("/"+filepath.Base(args[0]), fs)

	cmap = make(map[uint16]bool)
	log.Fatal(coap.ListenAndServe(*ntype, *addr, mux))
}