dns-packet

An abstract-encoding compliant module for encoding / decoding DNS packets. Lifted out of multicast-dns as a separate module.

npm install dns-packet

Usage

var packet = require('dns-packet')
var dgram = require('dgram')

var socket = dgram.createSocket('udp4')

var buf = packet.encode({
  type: 'query',
  id: 1,
  flags: packet.RECURSION_DESIRED,
  questions: [{
    type: 'A',
    name: 'google.com'
  }]
})

socket.on('message', function (message) {
  console.log(packet.decode(message)) // prints out a response from google dns
})

socket.send(buf, 0, buf.length, 53, '8.8.8.8')

API

var buf = packets.encode(packet, [buf], [offset])

Encodes a DNS packet into a buffer.

var packet = packets.decode(buf, [offset])

Decode a DNS packet from a buffer

var len = packets.encodingLength(packet)

Returns how many bytes are needed to encode the DNS packet

Packets

Packets look like this

{
  type: 'query|response',
  id: optionalIdNumber,
  flags: optionalBitFlags,
  questions: [...],
  answers: [...],
  additionals: [...],
  authorities: [...]
}

The bit flags available are

packet.RECURSION_DESIRED
packet.RECURSION_AVAILABLE
packet.TRUNCATED_RESPONSE
packet.AUTHORITATIVE_ANSWER
packet.AUTHENTIC_DATA
packet.CHECKING_DISABLED

To use more than one flag bitwise-or them together

var flags = packet.RECURSION_DESIRED | packet.RECURSION_AVAILABLE

And to check for a flag use bitwise-and

var isRecursive = message.flags & packet.RECURSION_DESIRED

A question looks like this

{
  type: 'A', // or SRV, AAAA, etc
  name: 'google.com' // which record are you looking for
}

And an answers, additional, or authority looks like this

{
  type: 'A', // or SRV, AAAA, etc
  name: 'google.com', // which name is this record for
  ttl: optionalTimeToLiveInSeconds,
  (record specific data, see below)
}

Currently the different available records are

A

{
  data: 'IPv4 address' // fx 127.0.0.1
}

AAAA

{
  data: 'IPv6 address' // fx fe80::1
}

TXT

{
  data: Buffer('some text')
}

NS

{
  data: nameServer
}

NULL

{
  data: Buffer('any binary data')
}

SOA

{
  data:
    {
      mname: domainName,
      rname: mailbox,
      serial: zoneSerial,
      refresh: refreshInterval,
      retry: retryInterval,
      expire: expireInterval,
      minimum: minimumTTL
    }
}

SRV

{
  data: {
    port: servicePort,
    target: serviceHostName,
    priority: optionalServicePriority,
    weight: optionalServiceWeight
  }
}

HINFO

{
  data: {
    cpu: 'cpu info',
    os: 'os info'
  }
}

PTR

{
  data: 'points.to.another.record'
}

CNAME

{
  data: 'cname.to.another.record'
}

DNAME

{
  data: 'dname.to.another.record'
}

CAA

{
  flags: 128, // octet
  tag: 'issue|issuewild|iodef',
  value: 'ca.example.net'
}

If you need another one, open an issue and we'll try to add it.

License

MIT