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

#### <tt>mdns = multicastdns([options])</tt>

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. defaults to all
port: 5353, // set the udp port
ip: '224.0.0.251', // set the udp 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)
}

#### ‘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.

#### <tt>mdns.query(packet, [cb])</tt>

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'}]
})

#### <tt>mdns.respond(packet, [cb])</tt>

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'}]
})

#### <tt>mdns.destroy()</tt>

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