npm package: @homebridge/dns-packet
Description: An abstract-encoding compliant module for encoding / decoding DNS packets
Author: Mathias Buus
Latest version: 5.4.1
Deprecated: This package is no longer maintained

# dns-packet
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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 @homebridge/dns-packet
```

## Notice

This fork of the original [dns-packet](https://github.com/mafintosh/dns-packet) library was used in the early 
beta builds of the [ciao](https://github.com/homebridge/ciao) library. It was replaced with an encoder/decoder
directly packaged into ciao improving on dns-packet with support for message compression, properly splitting
dns packets according to the MTU and generally improving readability and maintainability (as it is also 
written in TypeScript).  
You may or may not use this fork or derive your work from it. Though keep in mind, that it is no longer maintained.

## UDP Usage

``` js
const dnsPacket = require('@homebridge/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](optioncodes.js) for all supported option codes. If the `data` property is present on an 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'
}
```

#### `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