goldilocks.js/lib/mdns.js

'use strict';

var PromiseA = require('bluebird');
var fs = PromiseA.promisifyAll(require('fs'));
var path = require('path');
var idFilename = path.join(__dirname, '..', 'var', 'mdns-id');
var queryName = '_cloud._tcp.local';

var randomId = {
  get: function () {
    return fs.readFileAsync(idFilename)
      .catch(function (err) {
        if (err.code !== 'ENOENT') {
          return PromiseA.reject(err);
        }
        var id = require('crypto').randomBytes(5).toString('hex');
        return randomId.set(id);
      });
  }

, set: function (value) {
    return fs.mkdirAsync(path.dirname(idFilename)).catch(function (err) {
      if (err.code !== 'EEXIST') {
        console.error('failed to mkdir', path.dirname(idFilename), err.toString());
      }
    }).then(function () {
      return fs.writeFileAsync(idFilename, value).then(function () {
        return value;
      });
    });
  }
};

function createResponse(name, ownerIds, packet, ttl, mainPort) {
  var rpacket = {
    header: {
      id: packet.header.id
    , qr: 1
    , opcode: 0
    , aa: 1
    , tc: 0
    , rd: 0
    , ra: 0
    , res1:  0
    , res2:  0
    , res3:  0
    , rcode: 0
  , }
  , question: packet.question
  , answer: []
  , authority: []
  , additional: []
  , edns_options: []
  };

  rpacket.answer.push({
    name: queryName
  , typeName: 'PTR'
  , ttl: ttl
  , className: 'IN'
  , data: name + '.' + queryName
  });

  var ifaces = require('./local-ip').find();
  Object.keys(ifaces).forEach(function (iname) {
    var iface = ifaces[iname];

    iface.ipv4.forEach(function (addr) {
      rpacket.additional.push({
        name: name + '.local'
      , typeName: 'A'
      , ttl: ttl
      , className: 'IN'
      , address: addr.address
      });
    });

    iface.ipv6.forEach(function (addr) {
      rpacket.additional.push({
        name: name + '.local'
      , typeName: 'AAAA'
      , ttl: ttl
      , className: 'IN'
      , address: addr.address
      });
    });
  });

  rpacket.additional.push({
    name: name + '.' + queryName
  , typeName: 'SRV'
  , ttl: ttl
  , className: 'IN'
  , priority: 1
  , weight: 0
  , port: mainPort
  , target: name + ".local"
  });
  rpacket.additional.push({
    name: name + '._device-info.' + queryName
  , typeName: 'TXT'
  , ttl: ttl
  , className: 'IN'
  , data: ["model=CloudHome1,1", "dappsvers=1"]
  });
  ownerIds.forEach(function (id) {
    rpacket.additional.push({
      name: name + '._owner-id.' + queryName
    , typeName: 'TXT'
    , ttl: ttl
    , className: 'IN'
    , data: [id]
    });
  });

  return require('dns-suite').DNSPacket.write(rpacket);
}

module.exports.start = function (deps, config, mainPort) {
  var socket = require('dgram').createSocket({ type: 'udp4', reuseAddr: true });
  var dns = require('dns-suite');
  var nextBroadcast = -1;

  socket.on('message', function (message, rinfo) {
    // console.log('Received %d bytes from %s:%d', message.length, rinfo.address, rinfo.port);

    var packet;
    try {
      packet = dns.DNSPacket.parse(message);
    }
    catch (er) {
      // `dns-suite` actually errors on a lot of the packets floating around in our network,
      // so don't bother logging any errors. (We still use `dns-suite` because unlike `dns-js`
      // it can successfully craft the one packet we want to send.)
      return;
    }

    // Only respond to queries.
    if (packet.header.qr !== 0) {
      return;
    }
    // Only respond if they were asking for cloud devices.
    if (packet.question.length !== 1 || packet.question[0].name !== queryName) {
      return;
    }
    if (packet.question[0].typeName !== 'PTR' || packet.question[0].className !== 'IN' ) {
      return;
    }

    var proms = [
      randomId.get()
    , deps.storage.owners.all().then(function (owners) {
        // The ID is the sha256 hash of the PPID, which shouldn't be reversible and therefore
        // should be safe to expose without needing authentication.
        return owners.map(function (owner) {
          return owner.id;
        });
      })
    ];

    PromiseA.all(proms).then(function (results) {
      var resp = createResponse(results[0], results[1], packet, config.mdns.ttl, mainPort);
      var now = Date.now();
      if (now > nextBroadcast) {
        socket.send(resp, config.mdns.port, config.mdns.broadcast);
        nextBroadcast = now + config.mdns.ttl * 1000;
      } else {
        socket.send(resp, rinfo.port, rinfo.address);
      }
    });
  });

  socket.bind(config.mdns.port, function () {
    var addr = this.address();
    console.log('bound on UDP %s:%d for mDNS', addr.address, addr.port);

    socket.setBroadcast(true);
    socket.addMembership(config.mdns.broadcast);
    // This is supposed to be a local device discovery mechanism, so we shouldn't
    // need to hop through any gateways. This helps with security by making it
    // much more difficult for someone to use us as part of a DDoS attack by
    // spoofing the UDP address a request came from.
    socket.setTTL(1);
  });
};