decode.go

package main

import (
	"bufio"
	"encoding/hex"
	"errors"
	"io"
	"log"
	"regexp"
	"strconv"
	"strings"
)

type (
	Decoder struct {
		br *bufio.Reader
	}
	MessageError struct {
		innerErr   error
		Message    []byte
		MessageCRC string
	}
	SmartEnergyMeterData struct {
		ID     string
		Values []ObisData
	}
	ObisData struct {
		OBIS  string
		Value float64
		Unit  string
	}
)

var (
	ErrCRCError   = errors.New("crc error")
	obisDataRegxp *regexp.Regexp
)

func init() {
	obisDataRegxp = regexp.MustCompile(`^(\d{1,3}-\d{1,3}:\d{1,3}\.\d{1,3}\.\d{1,3})\((\d+\.\d{1,3})\*(\w+)\)$`)
}

func NewDecoder(reader io.Reader) *Decoder {
	return &Decoder{
		br: bufio.NewReader(reader),
	}
}

func (d *Decoder) ReadBlock() (*SmartEnergyMeterData, error) {
	var semData SmartEnergyMeterData
	var startOfBlock bool
	var message []byte
	var crc uint16
	for {
		str, err := d.br.ReadString('\n')
		if err != nil {
			return nil, err
		}

		// Remove CR LF from string
		data := strings.Replace(str, "\r", "", 1)
		data = strings.Replace(data, "\n", "", 1)

		if strings.HasPrefix(data, "/") {
			startOfBlock = true
			semData.ID = data[1:]
			crc = 0
		}

		values := obisDataRegxp.FindAllStringSubmatch(data, 1)
		if len(values) == 1 && len(values[0]) == 4 {
			v, err := strconv.ParseFloat(values[0][2], 64)
			if err != nil {
				log.Printf("%v", err)
				continue
			}
			semData.Values = append(semData.Values, ObisData{OBIS: values[0][1], Value: v, Unit: values[0][3]})
		}

		if strings.HasPrefix(data, "!") && startOfBlock {
			crc = crc16(crc, []byte{'!'})
			message = append(message, []byte(str)...)

			crcSum := crc16Sum(crc)
			if data[1:] == crcSum {
				return &semData, nil
			}

			return nil, &MessageError{
				innerErr:   ErrCRCError,
				Message:    message,
				MessageCRC: crcSum,
			}
		}

		if startOfBlock {
			crc = crc16(crc, []byte(str))
			message = append(message, []byte(str)...)
		}
	}
}

func (e *MessageError) Error() string {
	return e.innerErr.Error()
}

func (e *MessageError) Unwrap() error {
	return e.innerErr
}

var crc16Table = [256]uint16{
	0x0000, 0xc0c1, 0xc181, 0x0140, 0xc301, 0x03c0, 0x0280, 0xc241, 0xc601, 0x06c0, 0x0780, 0xc741, 0x0500, 0xc5c1, 0xc481, 0x0440,
	0xcc01, 0x0cc0, 0x0d80, 0xcd41, 0x0f00, 0xcfc1, 0xce81, 0x0e40, 0x0a00, 0xcac1, 0xcb81, 0x0b40, 0xc901, 0x09c0, 0x0880, 0xc841,
	0xd801, 0x18c0, 0x1980, 0xd941, 0x1b00, 0xdbc1, 0xda81, 0x1a40, 0x1e00, 0xdec1, 0xdf81, 0x1f40, 0xdd01, 0x1dc0, 0x1c80, 0xdc41,
	0x1400, 0xd4c1, 0xd581, 0x1540, 0xd701, 0x17c0, 0x1680, 0xd641, 0xd201, 0x12c0, 0x1380, 0xd341, 0x1100, 0xd1c1, 0xd081, 0x1040,
	0xf001, 0x30c0, 0x3180, 0xf141, 0x3300, 0xf3c1, 0xf281, 0x3240, 0x3600, 0xf6c1, 0xf781, 0x3740, 0xf501, 0x35c0, 0x3480, 0xf441,
	0x3c00, 0xfcc1, 0xfd81, 0x3d40, 0xff01, 0x3fc0, 0x3e80, 0xfe41, 0xfa01, 0x3ac0, 0x3b80, 0xfb41, 0x3900, 0xf9c1, 0xf881, 0x3840,
	0x2800, 0xe8c1, 0xe981, 0x2940, 0xeb01, 0x2bc0, 0x2a80, 0xea41, 0xee01, 0x2ec0, 0x2f80, 0xef41, 0x2d00, 0xedc1, 0xec81, 0x2c40,
	0xe401, 0x24c0, 0x2580, 0xe541, 0x2700, 0xe7c1, 0xe681, 0x2640, 0x2200, 0xe2c1, 0xe381, 0x2340, 0xe101, 0x21c0, 0x2080, 0xe041,
	0xa001, 0x60c0, 0x6180, 0xa141, 0x6300, 0xa3c1, 0xa281, 0x6240, 0x6600, 0xa6c1, 0xa781, 0x6740, 0xa501, 0x65c0, 0x6480, 0xa441,
	0x6c00, 0xacc1, 0xad81, 0x6d40, 0xaf01, 0x6fc0, 0x6e80, 0xae41, 0xaa01, 0x6ac0, 0x6b80, 0xab41, 0x6900, 0xa9c1, 0xa881, 0x6840,
	0x7800, 0xb8c1, 0xb981, 0x7940, 0xbb01, 0x7bc0, 0x7a80, 0xba41, 0xbe01, 0x7ec0, 0x7f80, 0xbf41, 0x7d00, 0xbdc1, 0xbc81, 0x7c40,
	0xb401, 0x74c0, 0x7580, 0xb541, 0x7700, 0xb7c1, 0xb681, 0x7640, 0x7200, 0xb2c1, 0xb381, 0x7340, 0xb101, 0x71c0, 0x7080, 0xb041,
	0x5000, 0x90c1, 0x9181, 0x5140, 0x9301, 0x53c0, 0x5280, 0x9241, 0x9601, 0x56c0, 0x5780, 0x9741, 0x5500, 0x95c1, 0x9481, 0x5440,
	0x9c01, 0x5cc0, 0x5d80, 0x9d41, 0x5f00, 0x9fc1, 0x9e81, 0x5e40, 0x5a00, 0x9ac1, 0x9b81, 0x5b40, 0x9901, 0x59c0, 0x5880, 0x9841,
	0x8801, 0x48c0, 0x4980, 0x8941, 0x4b00, 0x8bc1, 0x8a81, 0x4a40, 0x4e00, 0x8ec1, 0x8f81, 0x4f40, 0x8d01, 0x4dc0, 0x4c80, 0x8c41,
	0x4400, 0x84c1, 0x8581, 0x4540, 0x8701, 0x47c0, 0x4680, 0x8641, 0x8201, 0x42c0, 0x4380, 0x8341, 0x4100, 0x81c1, 0x8081, 0x4040,
}

func crc16(crc uint16, data []byte) uint16 {
	for _, b := range data {
		crc = crc16Table[byte(crc)^b] ^ (crc >> 8)
	}

	return crc
}
func crc16Sum(crc uint16) string {
	return strings.ToUpper(hex.EncodeToString([]byte{byte(crc >> 8), byte(crc)}))
}