wifi location server (draft). using the find android client here: https://github.com/schollz/find

wifi_location_server.js

'use strict';

const fs = require('fs');
const http = require('http');
const os = require('os');



const HEADERS = {
  'Content-Type': 'application/json',
  'Access-Control-Allow-Origin': '*'
};

const FILE = 'reads.json';

const PORT = 6789;



function time() {
  const d = new Date();
  return d.toTimeString().split(' ')[0];
}



function getMyIPs() {
  const ips = {};
  const ifaces = os.networkInterfaces();

  for (let dev in ifaces) {
    ifaces[dev].forEach((details) => {
      if (details.family === 'IPv4') {
        ips[dev] = details.address;
      }
    });
  }

  return ips;
};

function getMyIP() {
  const o = getMyIPs();
  for (let k in o) {
    const v = o[k];
    if (v !== '127.0.0.1') {
      return v;
    }
  }
}



function load() {
  try {
    return JSON.parse( fs.readFileSync(FILE).toString() );
  } catch (ex) {}
}

function save(o) {
  try {
    fs.writeFileSync(FILE, JSON.stringify(o));
    return true;
  } catch (ex) {}
}

function returnJSON(res, o, isError) {
  res.writeHead(isError ? 500 : 200, HEADERS);
  return res.end(JSON.stringify(o));
}



function clone(o) {
  return JSON.parse( JSON.stringify(o) );
}



function byMac(a, b) {
  a = a.mac;
  b = b.mac;
  if (a < b) { return -1; }
  if (a > b) { return  1; }
  return 0;
}

function arrayOfMacs(o) {
  o = clone(o).sort(byMac);
  return o.map((row) => { return row.mac; })
}

function cmpMacs(a, b) {
  const o = {a:0, b:0, both:0};
  a.forEach((k) => {
    if (b.indexOf(k) !== -1) { ++o.both; }
    else { ++o.a; }
  });
  b.forEach((k) => {
    if (a.indexOf(k) === -1) { ++o.b; }
  });
  return o;
}

function calc(reads, read) {
  const r0 = arrayOfMacs(read);
  let bestH = 0;
  let bestV = '?';
  for (let k in reads) {
    const r = arrayOfMacs(reads[k]);
    const d = cmpMacs(r0, r);
    const h = d.both - d.a/10 - d.b/20;
    if (h > bestH) {
      bestV = k;
      bestH = h;
    }
    console.log('diff against ' + k, d, h);
  }
  console.log('BEST: ' + bestV);
  return {h:bestH, v:bestV};
}



let latestRead = [];
const namedReads = load() || {};
console.log(`named reads loaded: ${Object.keys(namedReads).length}`);



http.createServer((req, res) => {
  if (req.url === '/favicon.ico') {
    res.writeHead(200, {'Content-Type': 'image/x-icon'} );
    return res.end();
  }

	console.log(`${time()} - ${req.method} ${req.url}`);
  
  if (req.url === '/latest') {
    return returnJSON(res, latestRead);
  }
  
  if (req.url === '/reads') {
    return returnJSON(res, namedReads);
  }
  
  const body = [];
	
  req.on('data', function(chunk) {
    body.push(chunk.toString());
  });
  
  req.on('end', function() {
    // if (body.length === 0) { return; }
    try {
      const o = JSON.parse( body.join('') );
      latestRead = o['wifi-fingerprint'];
      
      if (req.url === '/learn') {
        namedReads[o.location] = latestRead;
        save(namedReads);
        console.log('learn', o.location, latestRead);
        return returnJSON(res, 'ok');
      } else { // location === 'tracking'
        let loc = calc(namedReads, latestRead);
        //console.log('track', latestRead, '->', loc);
        console.log('track', loc);
        return returnJSON(res, loc);
      }
    } catch (ex) {
      console.error(ex);
      return returnJSON(res, ex.toString() + ex.stack, true);
    }
  });
}).listen(PORT);

const ip = getMyIP();
console.log(`Running WIFI location server on port http://${ip}:${PORT} ...`);