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

` js
const dnsPacket = require('dns-packet')
const dgram = require('dgram')

const socket = dgram.createSocket('udp4')

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

socket.on('message', message => {
console.log(dnsPacket.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:

- TCP
- DNS over TLS
- DNS over HTTPS

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

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

The bit flags available are

` js
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

` js
var flags = packet.RECURSION_DESIRED | packet.RECURSION_AVAILABLE
`

And to check for a flag use bitwise-and

` js
var isRecursive = message.flags & packet.RECURSION_DESIRED
`

A question looks like this

` js
{
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 answer, additional, or authority looks like this

` js
{
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)
}
`

Supported record types

#### A

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

#### AAAA

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

#### CAA

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

#### CNAME

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

#### DNAME

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

#### DNSKEY

` js
{
flags: 257, // 16 bits
algorithm: 1, // octet
key: Buffer
}
`

#### DS

` js
{
keyTag: 12345,
algorithm: 8,
digestType: 1,
digest: Buffer
}
`

#### HINFO

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

#### MX

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

#### NAPTR

` js
{
data:
{
order: 100,
preference: 10,
flags: 's',
services: 'SIP+D2U',
regexp: '!^.*$!sip:customer-service@example.com!',
replacement: '_sip._udp.example.com'
}
}
`

#### NS

` js
{
data: nameServer
}
`

#### NSEC

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

#### NSEC3

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

#### NULL

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

#### OPT

EDNS0 options.

` js
{
type: 'OPT',
name: '.',
udpPayloadSize: 4096,
flags: packet.DNSSEC_OK,
options: [{
// pass in any code/data for generic EDNS0 options
code: 12,
data: Buffer.alloc(31)
}, {
// Several EDNS0 options have enhanced support
code: 'PADDING',
length: 31,
}, {
code: 'CLIENT_SUBNET',
family: 2, // 1 for IPv4, 2 for IPv6
sourcePrefixLength: 64, // used to truncate IP address
scopePrefixLength: 0,
ip: 'fe80::',
}, {
code: 'TCP_KEEPALIVE',
timeout: 150 // increments of 100ms. This means 15s.
}, {
code: 'KEY_TAG',
tags: [1, 2, 3],
}]
}
`

The options PADDING, CLIENT_SUBNET, TCP_KEEPALIVE and KEY_TAG support enhanced de/encoding. See optionscodes.js for all supported option codes. If the data property is present on a option, it takes precedence. On decoding, data will always be defined.

#### PTR

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

#### RP

` js
{
mbox: 'admin.example.com',
txt: 'txt.example.com'
}
`

#### SSHFP

` js
{
algorithm: 1,
hash: 1,
fingerprint: 'A108C9F834354D5B37AF988141C9294822F5BC00'
}
``

#### RRSIG

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

#### SOA

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

#### SRV

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

#### TLSA

` js
{
usage: 3,
selector: 1,
matchingType: 1,
certificate: Buffer
}
`

#### TXT

` js
{
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 record type, open an issue and we'll try to add it.

License

MIT