datacake_decoder.js

function Decoder(bytes, port) {
    // bytes is of type Buffer

    // see https://github.com/4-20ma/ModbusMaster/blob/master/src/ModbusMaster.h
    var modbus_code = {
        0x00: "Success",
        0x01: "IllegalFunction",
        0x02: "IllegalDataAddress",
        0x03: "IllegalDataValue",
        0x04: "SlaveDeviceFailure",
        0xE0: "InvalidSlaveID",
        0xE1: "InvalidFunction",
        0xE2: "ResponseTimedOut",
        0xE3: "InvalidCRC"
    };

    var bytesToInt = function (bytes) {
        var i = 0;
        for (var x = 0; x < bytes.length; x++) {
            i |= +(bytes[x] << (x * 8));
        }
        return i;
    };

    var modbus = function (bytes) {
        if (bytes.length !== modbus.BYTES) {
            throw new Error('Modbus status must have exactly 1 byte');
        }
        return {
            "code": bytes[0],
            "text": modbus_code[bytes[0]]
        };
    };
    modbus.BYTES = 1;

    var unixtime = function (bytes) {
        if (bytes.length !== unixtime.BYTES) {
            throw new Error('Unix time must have exactly 4 bytes');
        }
        return bytesToInt(bytes);
    };
    unixtime.BYTES = 4;

    var uint8 = function (bytes) {
        if (bytes.length !== uint8.BYTES) {
            throw new Error('int must have exactly 1 byte');
        }
        return bytesToInt(bytes);
    };
    uint8.BYTES = 1;

    var uint16 = function (bytes) {
        if (bytes.length !== uint16.BYTES) {
            throw new Error('int must have exactly 2 bytes');
        }
        return bytesToInt(bytes);
    };
    uint16.BYTES = 2;

    var uint16fp1 = function (bytes) {
        if (bytes.length !== uint16.BYTES) {
            throw new Error('int must have exactly 2 bytes');
        }
        var res = bytesToInt(bytes) * 0.1;
        return res.toFixed(1);
    };
    uint16fp1.BYTES = 2;

    var uint32 = function (bytes) {
        if (bytes.length !== uint32.BYTES) {
            throw new Error('int must have exactly 4 bytes');
        }
        return bytesToInt(bytes);
    };
    uint32.BYTES = 4;

    var latLng = function (bytes) {
        if (bytes.length !== latLng.BYTES) {
            throw new Error('Lat/Long must have exactly 8 bytes');
        }

        var lat = bytesToInt(bytes.slice(0, latLng.BYTES / 2));
        var lng = bytesToInt(bytes.slice(latLng.BYTES / 2, latLng.BYTES));

        return [lat / 1e6, lng / 1e6];
    };
    latLng.BYTES = 8;

    var temperature = function (bytes) {
        if (bytes.length !== temperature.BYTES) {
            throw new Error('Temperature must have exactly 2 bytes');
        }
        var isNegative = bytes[0] & 0x80;
        var b = ('00000000' + Number(bytes[0]).toString(2)).slice(-8)
            + ('00000000' + Number(bytes[1]).toString(2)).slice(-8);
        if (isNegative) {
            var arr = b.split('').map(function (x) { return !Number(x); });
            for (var i = arr.length - 1; i > 0; i--) {
                arr[i] = !arr[i];
                if (arr[i]) {
                    break;
                }
            }
            b = arr.map(Number).join('');
        }
        var t = parseInt(b, 2);
        if (isNegative) {
            t = -t;
        }
        t = t / 1e2;
        return t.toFixed(1);
    };
    temperature.BYTES = 2;

    var humidity = function (bytes) {
        if (bytes.length !== humidity.BYTES) {
            throw new Error('Humidity must have exactly 2 bytes');
        }

        var h = bytesToInt(bytes);
        return h / 1e2;
    };
    humidity.BYTES = 2;

    // Based on https://stackoverflow.com/a/37471538 by Ilya Bursov
    // quoted by Arjan here https://www.thethingsnetwork.org/forum/t/decode-float-sent-by-lopy-as-node/8757
    function rawfloat(bytes) {
        if (bytes.length !== rawfloat.BYTES) {
            throw new Error('Float must have exactly 4 bytes');
        }
        // JavaScript bitwise operators yield a 32 bits integer, not a float.
        // Assume LSB (least significant byte first).
        var bits = bytes[3] << 24 | bytes[2] << 16 | bytes[1] << 8 | bytes[0];
        var sign = (bits >>> 31 === 0) ? 1.0 : -1.0;
        var e = bits >>> 23 & 0xff;
        var m = (e === 0) ? (bits & 0x7fffff) << 1 : (bits & 0x7fffff) | 0x800000;
        var f = sign * m * Math.pow(2, e - 150);
        return f.toFixed(1);
    }
    rawfloat.BYTES = 4;

    var bitmap = function (byte) {
        if (byte.length !== bitmap.BYTES) {
            throw new Error('Bitmap must have exactly 1 byte');
        }
        var i = bytesToInt(byte);
        var bm = ('00000000' + Number(i).toString(2)).substr(-8).split('').map(Number).map(Boolean);
        // Only Weather Sensor
        return ['res5', 'res4', 'res3', 'res2', 'res1', 'res0', 'dec_ok', 'batt_ok']
            .reduce(function (obj, pos, index) {
                obj[pos] = bm[index];
                return obj;
            }, {});
    };
    bitmap.BYTES = 1;

    var decode = function (bytes, mask, names) {

        var maskLength = mask.reduce(function (prev, cur) {
            return prev + cur.BYTES;
        }, 0);
        if (bytes.length < maskLength) {
            throw new Error('Mask length is ' + maskLength + ' whereas input is ' + bytes.length);
        }

        names = names || [];
        var offset = 0;
        return mask
            .map(function (decodeFn) {
                var current = bytes.slice(offset, offset += decodeFn.BYTES);
                return decodeFn(current);
            })
            .reduce(function (prev, cur, idx) {
                prev[names[idx] || idx] = cur;
                return prev;
            }, {});
    };

    if (typeof module === 'object' && typeof module.exports !== 'undefined') {
        module.exports = {
            unixtime: unixtime,
            uint8: uint8,
            uint16: uint16,
            uint32: uint32,
            temperature: temperature,
            humidity: humidity,
            latLng: latLng,
            bitmap: bitmap,
            rawfloat: rawfloat,
            uint16fp1: uint16fp1,
            modbus: modbus,
            decode: decode
        };
    }

    if (bytes.length === 1) {
        return { "modbus": modbus(bytes) };
    }


    if (port === 1) {
        return decode(
            bytes,
            [modbus, uint8, uint8, rawfloat, rawfloat, rawfloat,
                rawfloat, rawfloat, rawfloat
            ],
            ['modbus', 'status', 'faultcode', 'energytoday', 'energytotal', 'totalworktime',
                'outputpower', 'gridvoltage', 'gridfrequency'
            ]
        );
    } else {
        return decode(
            bytes,
            [modbus, rawfloat, rawfloat, rawfloat, temperature, temperature,
                rawfloat, rawfloat
            ],
            ['modbus', 'pv1voltage', 'pv1current', 'pv1power', 'tempinverter', 'tempipm',
                'pv1energytoday', 'pv1energytotal'
            ]
        );
    }

}