ttn_decoder.js

function ttn_decoder_fp(bytes) {
  // bytes is of type Buffer

  // IMPORTANT: paste code from src/decoder.js here
    var bytesToInt = function(bytes) {
    var i = 0;
    for (var x = 0; x < bytes.length; x++) {
        i |= +(bytes[x] << (x * 8));
    }
    return i;
    };

    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);
    return ['res4', 'res3', 'res2', 'res1', 'res0', 'runtime_exp', 'data_ok', 'battery_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,
        decode: decode
    };
    }

    // see assignment to 'bitmap' variable for status bit names 
    return decode(
    bytes,
    [bitmap,   temperature,  uint8,       uint16,       uint16      ], // types
    ['status', 'air_temp_c', 'humidity',  'supply_v',   'battery_v' ]  // JSON elements
  );

}


function decodeUplink(input) {
  return {
    data: {
      bytes: ttn_decoder_fp(input.bytes)
    },
    warnings: [],
    errors: []
  };
}