messageCodec.go

package coapmq

import (
	"errors"
	"log"
	"strings"

	"github.com/dustin/go-coap"
)

type Cmd struct {
	Type  CMD_TYPE
	Topic string
	Msg   string
}

func GetMsgCmdCode(cmd CMD_TYPE) coap.COAPCode {
	var code coap.COAPCode

	switch cmd {
	case CMD_DISCOVER:
		code = coap.GET
	case CMD_CREATE:
		code = coap.POST
	case CMD_PUBLISH:
		code = coap.PUT
	case CMD_SUBSCRIBE:
		code = coap.GET
	case CMD_UNSUBSCRIBE:
		code = coap.GET
	case CMD_READ:
		code = coap.GET
	case CMD_REMOVE:
		code = coap.DELETE
	case CMD_HEARTBEAT:
		code = coap.Content
	}

	return code
}

//Refer to coapmq RFC:  https://datatracker.ietf.org/doc/draft-koster-core-coap-pubsub
//URI Template:  /{+ps/}{topic}{/topic*}
func EncodeCmdsToPath(cmd CMD_TYPE, topic string) []string {
	var pathURI []string
	// cmd URI: {+ps}/{*topic}
	if cmd == CMD_HEARTBEAT {
		pathURI = append(pathURI, "hb")
	} else {
		pathURI = append(pathURI, "ps")
	}

	pathURI = append(pathURI, topic)

	if cmd == CMD_DISCOVER {
		//TODO add query filter
	}
	return pathURI
}

func EncodeMessage(msgID uint16, cmd CMD_TYPE, msg string, topic string) *coap.Message {
	m := new(coap.Message)
	m.Type = coap.Confirmable
	m.Code = GetMsgCmdCode(cmd)
	m.MessageID = msgID

	m.Payload = []byte(msg)
	m.SetPath(EncodeCmdsToPath(cmd, topic))

	//m.SetOption(coap.ContentFormat, coap.TextPlain)
	m.SetOption(coap.ContentFormat, coap.AppLinkFormat)

	//specific handle for Observe (Refer RFC 7461)
	switch cmd {
	case CMD_SUBSCRIBE:
		m.SetOption(coap.Observe, 0)
	case CMD_UNSUBSCRIBE:
		m.SetOption(coap.Observe, 1)
	}
	return m
}

//Parse receive message to Coapmq.Cmd to get command and topic
func MessageDecode(m *coap.Message) (*Cmd, error) {
	path := m.Path()
	log.Println("msg:", path, " cmd=", path[0])
	if len(path) == 0 {
		//cmd is not valid.
		return nil, errors.New("Invalid parameter")
	}

	c := new(Cmd)
	c.Type = CMD_INVALID
	if len(path) > 1 {
		c.Topic = path[1]
	}

	switch m.Code {
	case coap.GET:
		obseve, found := m.Option(coap.Observe).(uint32)
		if found {
			switch obseve {
			case 0:
				c.Type = CMD_SUBSCRIBE
			case 1:
				c.Type = CMD_UNSUBSCRIBE
			}
		} else {
			if strings.HasPrefix(c.Topic, "?") {
				//it is discover
				c.Type = CMD_DISCOVER
			} else if c.Topic != "" {
				c.Type = CMD_READ
			} else {
				//cmd not valid
			}
		}
	case coap.POST:
		c.Type = CMD_CREATE
	case coap.PUT:
		c.Type = CMD_PUBLISH
	case coap.DELETE:
		c.Type = CMD_REMOVE
	case coap.Content:
		c.Type = CMD_HEARTBEAT
	}

	if c.Type != CMD_INVALID {
		c.Msg = string(m.Payload)
	}
	return c, nil
}