multicast-dns

Low level multicast-dns implementation in pure javascript

npm install multicast-dns

Usage

1var mdns = require('multicast-dns')()
2
3mdns.on('response', function(response) {
4  console.log('got a response packet:', response)
5})
6
7mdns.on('query', function(query) {
8  console.log('got a query packet:', query)
9})
10
11// lets query for an A record for 'brunhilde.local'
12mdns.query({
13  questions:[{
14    name: 'brunhilde.local',
15    type: 'A'
16  }]
17})

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

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

And then a response packet

1got a response packet: { type: 'response',
2  questions: [],
3  answers:
4   [ { name: 'brunhilde.local',
5       type: 'A',
6       class: 'IN',
7       ttl: 120,
8       flush: true,
9       data: '192.168.1.5' } ],
10  authorities: [],
11  additionals:
12   [ { name: 'brunhilde.local',
13       type: 'A',
14       class: 'IN',
15       ttl: 120,
16       flush: true,
17       data: '192.168.1.5' },
18     { name: 'brunhilde.local',
19       type: 'AAAA',
20       class: 'IN',
21       ttl: 120,
22       flush: true,
23       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

1{
2  questions: [{
3    name: 'brunhilde.local',
4    type: 'A'
5  }],
6  answers: [{
7    name: 'brunhilde.local',
8    type: 'A',
9    ttl: seconds,
10    data: (record type specific data)
11  }],
12  additionals: [
13    (same format as answers)
14  ],
15  authorities: [
16    (same format as answers)
17  ]
18}

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

1{
2  multicast: true // use udp multicasting
3  interface: '192.168.0.2' // explicitly specify a network interface. defaults to all
4  port: 5353, // set the udp port
5  ip: '224.0.0.251', // set the udp ip
6  ttl: 255, // set the multicast ttl
7  loopback: true, // receive your own packets
8  reuseAddr: true // set the reuseAddr option when creating the socket (requires node >=0.11.13)
9}

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

Emitted when a query packet is received.

1mdns.on('query', function(query) {
2  if (query.questions[0] && query.questions[0].name === 'brunhilde.local') {
3    mdns.respond(someResponse) // see below
4  }
5})

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

1mdns.query('brunhilde.local', 'A')
2mdns.query([{name:'brunhilde.local', type:'A'}])
3mdns.query({
4  questions: [{name:'brunhilde.local', type:'A'}]
5})

mdns.respond(packet, [cb])

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

1// reply with a SRV and a A record as an answer
2mdns.respond({
3  answers: [{
4    name: 'my-service',
5    type: 'SRV',
6    data: {
7      port: 9999,
8      weight: 0,
9      priority: 10,
10      target: 'my-service.example.com'
11    }
12  }, {
13    name: 'brunhilde.local',
14    type: 'A',
15    ttl: 300,
16    data: '192.168.1.5'
17  }]
18})

The following shorthands are equivalent

1mdns.respond([{name:'brunhilde.local', type:'A', data:'192.158.1.5'}])
2mdns.respond({
3  answers: [{name:'brunhilde.local', type:'A', data:'192.158.1.5'}]
4})

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