dns-packet

What is dns-packet?

The dns-packet npm package is a library for encoding/decoding DNS packets. It supports both Node.js and the browser and can handle various DNS record types. It is useful for creating custom DNS servers, clients, or for manipulating DNS packets for analysis or testing.

What are dns-packet's main functionalities?

Encoding DNS packets

This feature allows you to encode a DNS packet into a buffer. The example code shows how to create a DNS query packet for the domain 'example.com'.

const dnsPacket = require('dns-packet');
const encodedPacket = dnsPacket.encode({
  type: 'query',
  id: 1,
  flags: dnsPacket.RECURSION_DESIRED,
  questions: [{
    type: 'A',
    name: 'example.com'
  }]
});

Decoding DNS packets

This feature allows you to decode a DNS packet from a buffer. The example code demonstrates how to decode a buffer into a DNS packet object.

const dnsPacket = require('dns-packet');
const buffer = Buffer.from('...'); // a buffer containing a DNS packet
const decodedPacket = dnsPacket.decode(buffer);

Streaming DNS packet encoding/decoding

This feature allows you to encode and decode DNS packets in a streaming fashion, which is useful for handling DNS packets in a network stream. The example code creates a simple DNS server that responds to all queries with the IP address '127.0.0.1'.

const dnsPacket = require('dns-packet');
const net = require('net');

const server = net.createServer((socket) => {
  socket.pipe(dnsPacket.streamDecode())
    .on('data', (packet) => {
      console.log('received packet:', packet);
      const response = dnsPacket.streamEncode({
        type: 'response',
        id: packet.id,
        questions: packet.questions,
        answers: [{
          type: 'A',
          name: packet.questions[0].name,
          data: '127.0.0.1'
        }]
      });
      socket.write(response);
    });
});

server.listen(53);

Other packages similar to dns-packet

native-dns-packet

This package is similar to dns-packet, offering low-level DNS packet encoding/decoding with a focus on Node.js. It is an alternative that might be used in scenarios where native Node.js Buffer handling is preferred.

dns2

dns2 is a more comprehensive DNS toolkit that includes packet encoding/decoding functionalities similar to dns-packet. It also provides higher-level DNS server and client implementations, making it a more feature-rich option.

node-dns

node-dns is another DNS library that provides similar packet manipulation capabilities. It differs from dns-packet by offering a full DNS resolver and server implementation, potentially making it a better choice for more complex DNS-related tasks.

README

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 Usage

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 TCP/TLS for privacy reasons.

See the TCP example.

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
}

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.

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

Changelog

Version 4.0.0 - 2018-02-04

• Feature: Added streamEncode and streamDecode methods for encoding TCP packets.
• Breaking: Changed the decoded value of TXT records to an array of Buffers. This is to accomodate DNS-SD records which rely on the individual strings record being separated.
• Breaking: Renamed the flag_trunc and flag_auth to flag_tc and flag_aa to match the names of these in the dns standards.