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decoder.js
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decoder.js
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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('uint8 must have exactly 1 byte');
}
return bytesToInt(bytes);
};
uint8.BYTES = 1;
var uint16 = function(bytes) {
if (bytes.length !== uint16.BYTES) {
throw new Error('uint16 must have exactly 2 bytes');
}
return bytesToInt(bytes);
};
uint16.BYTES = 2;
var uint32 = function(bytes) {
if (bytes.length !== uint32.BYTES) {
throw new Error('uint32 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;
}
return t / 1e2;
};
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;
}
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 ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h']
.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,
decode: decode
};
}