multicast-dns

Low level multicast-dns implementation in pure javascript

npm install multicast-dns

Usage

var mdns = require('multicast-dns')()

mdns.on('response', function(response) {
  console.log('got a response packet:', response)
})

mdns.on('query', function(query) {
  console.log('got a query packet:', query)
})

// lets query for an A record for 'brunhilde.local'
mdns.query({
  questions:[{
    name: 'brunhilde.local',
    type: 'A'
  }]
})

Running the above (change brunhilde.local to your-own-hostname.local) will print an echo of the query packet first

got a query packet: { type: 'query',
  questions: [ { name: 'brunhilde.local', type: 'A', class: 1 } ],
  answers: [],
  authorities: [],
  additionals: [] }

And then a response packet

got a response packet: { type: 'response',
  questions: [],
  answers:
   [ { name: 'brunhilde.local',
       type: 'A',
       class: 1,
       ttl: 120,
       flush: true,
       data: '192.168.1.5' } ],
  authorities: [],
  additionals:
   [ { name: 'brunhilde.local',
       type: 'A',
       class: 1,
       ttl: 120,
       flush: true,
       data: '192.168.1.5' },
     { name: 'brunhilde.local',
       type: 'AAAA',
       class: 1,
       ttl: 120,
       flush: true,
       data: 'fe80::5ef9:38ff:fe8c:ceaa' } ] }

CLI

npm install -g multicast-dns

multicast-dns brunhilde.local
> 192.168.1.1

API

A packet has the following format

{
  questions: [{
    name:'brunhilde.local',
    type:'A'
  }],
  answers: [{
    name:'brunhilde.local',
    type:'A',
    ttl:seconds,
    data:(record type specific data)
  }],
  additionals: [
    (same format as answers)
  ],
  authorities: [
    (same format as answers)
  ]
}

Currently data from SRV, A, PTR, TXT, AAAA and HINFO records is passed

mdns = multicastdns([options])

Creates a new mdns instance. Options can contain the following

{
  multicast: true // use udp multicasting
  interface: '192.168.0.2' // explicitly specify a network interface.
  interfaces: ['192.168.0.2','10.0.0.2'] // explicitly specify a set of network interfaces.
  subnets: ['192.168.0.'], // specify a set of subnet interested, the current value represent 192.168.0.0/24
  port: 5353, // set the udp port
  group_ip: '224.0.0.251', // set the udp multicast group ip
  ttl: 255, // set the multicast ttl
  loopback: true, // receive your own packets
  reuseAddr: true // set the reuseAddr option when creating the socket (requires node >=0.11.13)
  use_group_ip: true // bind the multicasting server socket to the multicast group ip in non-Windows systems
  client_only: true // do not initiate the dns server, use the client component only
}

If neighter interface nor interface is specified, the lib will generate a interface list by first enumerating all network interfaces found on the host. If subnets is a non-empty list, the interfaces used will be obtained by filtering the original list using the values in the subnets. If subnets is not defined or is empty, the original list will be used. If interface is defined, it is used as the sole interface used, regardless of the values of interfaces or subnets. If interface not defined but interfaces is defined, it is used as the list of interfaces used, regardless of the values of subnets.

mdns.on('query', (packet, rinfo))

Emitted when a query packet is received.

mdns.on('query', function(query) {
  if (query.questions[0] && query.questions[0].name === 'brunhilde.local') {
    mdns.respond(someResponse) // see below
  }
})

mdns.on('response', (packet, rinfo))

Emitted when a response packet is received.

The response might not be a response to a query you send as this is the result of someone multicasting a response.

mdns.query(packet, [cb])

Send a dns query. The callback will be called when the packet was sent.

The following shorthands are equivalent

mdns.query('brunhilde.local', 'A')
mdns.query([{name:'brunhilde.local', type:'A'}])
mdns.query({
  questions: [{name:'brunhilde.local', type:'A'}]
})

mdns.respond(packet, [cb])

Send a dns response. The callback will be called when the packet was sent.

// reply with a SRV and a A record as an answer
mdns.respond({
  answers: [{
    name: 'my-service',
    type: 'SRV',
    data: {
      port:9999,
      weigth: 0,
      priority: 10,
      target: 'my-service.example.com'
    }
  }, {
    name: 'brunhilde.local',
    type: 'A',
    ttl: 300,
    data: '192.168.1.5'
  }]
})

The following shorthands are equivalent

mdns.respond([{name:'brunhilde.local', type:'A', data:'192.158.1.5'}])
mdns.respond({
  answers: [{name:'brunhilde.local', type:'A', data:'192.158.1.5'}]
})

mdns.destroy()

Destroy the mdns instance. Closes the udp socket.

Development

To start hacking on this module you can use this example to get started

git clone git://github.com/mafintosh/multicast-dns.git
npm install
node example.js
node cli.js $(hostname).local

License

MIT