TTN payload function for lora-serialization -> openSenseMap.org JSON profile

ttn-decoder-lora-serialization-osem.js

function Decoder (bytes, port) {
  'use strict';

  let boxes = [];

  // maps LoRa ports to openSenseMap configurations
  // should contain
  // [
  //   TEMPSENSOR_ID,
  //   HUMISENSOR_ID
  // ]
  boxes[1] = [
    tempsensor_id,
    humisensor_id,
  ];

  boxes[2] = [
    tempsensor_id,
    humisensor_id,
  ];

  boxes[3] = [
    tempsensor_id,
    humisensor_id,
  ];

  boxes[4] = [
    tempsensor_id,
    humisensor_id,
  ];

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

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

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

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

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

  let bytesToSenseBoxJson = function (bytes) {
    let json;

    try {
      json = decode(bytes,
        [
          uint16,
          humidity
        ],
        boxes[port]
        );

      //temp
      json[boxes[port][0]] = parseFloat(((json[boxes[port][0]] / 771) - 18).toFixed(1));

      //hum
      json[boxes[port][1]] = parseFloat(json[boxes[port][1]].toFixed(1));
    } catch (e) {
      json = { payload: bytes };
    }

    return json;
  };

  return bytesToSenseBoxJson(bytes);
}