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# dns-packet
[](https://www.npmjs.org/package/dns-packet) [](https://www.npmjs.org/package/dns-packet) [](https://github.com/github/mafintosh/dns-packet/workflows/ci.yml) [](https://coveralls.io/github/mafintosh/dns-packet?branch=master)
An [abstract-encoding](https://github.com/mafintosh/abstract-encoding) compliant module for encoding / decoding DNS packets. Lifted out of [multicast-dns](https://github.com/mafintosh/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](examples/udp.js).
## 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](examples/tcp.js)
- [DNS over TLS](examples/tls.js)
- [DNS over HTTPS](examples/doh.js)
## 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'
}
```
#### `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](https://tools.ietf.org/html/rfc6891) 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](https://github.com/mafintosh/dns-packet/blob/master/optioncodes.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
}
}
```
#### `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