New server experiment fixing some design issues

Send response with the request token for matching query/answer.

Add the capability to choose between piggy backend answer or seperate
acking.

Abstract request answering for being able to plug multiple transport
(UDP, TCP, websockets, (D)TLS)

Author: jvermillard

example/newserver/coap_server.go

@@ -0,0 +1,17 @@
+package main
+
+import (
+	"log"
+
+	"github.com/dustin/go-coap"
+)
+
+func main() {
+
+	log.Fatal(coap.UdpListenAndServe("udp", ":5683",
+		coap.FuncRqHandler(func(rq coap.Request) error {
+			log.Printf("Got message path=%q: %#v from %v", rq.Message().Path(), rq.Message(), rq.Addr())
+			rq.Respond(coap.Content, []byte("Yeah!"), nil)
+			return nil
+		})))
+}

serverNew.go

@@ -0,0 +1,145 @@
+package coap
+
+import (
+	"log"
+	"math/rand"
+	"net"
+)
+
+var nextMID uint16 = uint16(rand.Int())
+
+type Request interface {
+	Message() *Message
+	Addr() net.Addr
+	Ack() error
+
+	RespondCode(code COAPCode) error
+
+	Respond(code COAPCode, content []byte, contentType *MediaType) error
+}
+
+type RequestHandler interface {
+	// Handle the message and optionally return a response message.
+	Handle(rq Request) error
+}
+type funcRqHandler func(rq Request) error
+
+func (f funcRqHandler) Handle(rq Request) error {
+	return f(rq)
+}
+
+// FuncRqHandler builds a handler from a function.
+func FuncRqHandler(f func(rq Request) error) RequestHandler {
+	return funcRqHandler(f)
+}
+
+func UdpListenAndServe(n, addr string, rh RequestHandler) error {
+
+	uaddr, err := net.ResolveUDPAddr(n, addr)
+	if err != nil {
+		return err
+	}
+
+	l, err := net.ListenUDP(n, uaddr)
+	if err != nil {
+		return err
+	}
+
+	// init retransmission facilities
+	retrans := NewRetransmitter(l)
+
+	buf := make([]byte, maxPktLen)
+	for {
+		nr, addr, err := l.ReadFromUDP(buf)
+		if err == nil {
+			msg, err := parseMessage(buf[:nr])
+			if err != nil {
+				log.Printf("Error parsing %v", err)
+			}
+			go handleRequest(&msg, addr, l, rh, retrans)
+		}
+	}
+
+	return nil
+}
+
+func handleRequest(msg *Message, addr *net.UDPAddr, s *net.UDPConn, rh RequestHandler, retrans *Retransmitter) {
+	rq := UDPRequest{
+		msg:     msg,
+		addr:    addr,
+		s:       s,
+		acked:   false,
+		retrans: retrans,
+	}
+
+	rh.Handle(&rq)
+}
+
+type UDPRequest struct {
+	msg     *Message
+	addr    *net.UDPAddr
+	s       *net.UDPConn
+	acked   bool
+	retrans *Retransmitter
+}
+
+func (rq *UDPRequest) Message() *Message {
+	return rq.msg
+}
+
+func (rq *UDPRequest) Addr() net.Addr {
+	return rq.addr
+}
+
+func (rq *UDPRequest) Ack() error {
+	// if it's not an ackable message or it was already acked
+	// just do nothing silently
+	if rq.msg.Type != Confirmable || rq.acked {
+		return nil
+	}
+
+	ackMsg := Message{
+		Type:      Acknowledgement,
+		Code:      0,
+		MessageID: rq.msg.MessageID,
+		Payload:   nil,
+	}
+
+	if err := Transmit(rq.s, rq.addr, ackMsg); err != nil {
+		return err
+	}
+	rq.acked = true
+	return nil
+}
+func (rq *UDPRequest) RespondCode(code COAPCode) error {
+	return rq.Respond(code, []byte{}, nil)
+
+}
+
+func (rq *UDPRequest) Respond(code COAPCode, content []byte, contentType *MediaType) error {
+	var msg Message
+
+	if rq.acked {
+		// answer after ack
+		// generate a new MID
+		msg = Message{
+			Type:      NonConfirmable,
+			Code:      code,
+			MessageID: nextMID,
+			Payload:   content,
+			Token:     rq.msg.Token,
+		}
+		nextMID = nextMID + 1
+	} else {
+		// piggybacked answer
+		msg = Message{
+			Type:      Acknowledgement,
+			Code:      code,
+			MessageID: rq.msg.MessageID,
+			Payload:   content,
+			Token:     rq.msg.Token,
+		}
+	}
+
+	return rq.retrans.Record(msg, rq.addr)
+}