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

UDP 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',
    class: 'IN',
    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')

Also see the UDP example.

TCP, TLS, HTTPS

While DNS has traditionally been used over a datagram transport, it is increasingly being carried over TCP for larger responses commonly including DNSSEC responses and TLS or HTTPS for enhanced security. See below examples on how to use dns-packet to wrap DNS packets in these protocols:

API

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

Encodes a DNS packet into a buffer containing a UDP payload.

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

Decode a DNS packet from a buffer containing a UDP payload.

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

Encodes a DNS packet into a buffer containing a TCP payload.

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

Decode a DNS packet from a buffer containing a TCP payload.

`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
  class: 'IN', // one of IN, CS, CH, HS, ANY. Default: IN
  name: 'google.com' // which record are you looking for
}

And an answers, additional, or authority looks like this

{
  type: 'A', // or SRV, AAAA, etc
  class: 'IN', // one of IN, CS, CH, HS
  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
}

`CAA`

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

`CNAME`

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

`DNAME`

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

`DNSKEY`

{
  flags: 257, // 16 bits
  algorithm: 1, // octet
  key: buffer
}

`DS`

{
  keyTag: 12345,
  algorithm: 8,
  digestType: 1,
  digest: buffer
}

`HINFO`

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

`MX`

{
  preference: 10,
  exchange: 'mail.example.net'
}

`NS`

{
  data: nameServer
}

`NSEC`

{
  nextDomain: 'a.domain',
  rrtypes: ['A', 'TXT', 'RRSIG']
}

`NSEC3`

{
  algorithm: 1,
  flags: 0,
  iterations: 2,
  salt: buffer,
  nextDomain: buffer, // Hashed per RFC5155
  rrtypes: ['A', 'TXT', 'RRSIG']
}

`NULL`

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

`OPT`

{
  type: 'OPT',
  name: '.',
  udpPayloadSize: 4096,
  flags: packet.DNSSEC_OK,
  options: [{
    code: 12,
    data: Buffer.alloc(31)
  }]
}

`PTR`

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

`RRSIG`

{
  typeCovered: 'A',
  algorithm: 8,
  labels: 1,
  originalTTL: 3600,
  expiration: timestamp,
  inception: timestamp,
  keyTag: 12345,
  signersName: 'a.name',
  signature: buffer
}

`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
  }
}

`TXT`

{
  data: 'text' || Buffer || [ Buffer || 'text' ]
}

When encoding, scalar values are converted to an array and strings are converted to UTF-8 encoded Buffers. When decoding, the return value will always be an array of Buffer.

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

License

MIT

Arachnid / dns-packet