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# dns-packet
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
```
[](https://travis-ci.org/mafintosh/dns-packet)
## Usage
``` js
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',
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')
```
## API
#### `var buf = packets.encode(packet, [buf], [offset])`
Encodes a DNS packet into a buffer.
#### `var packet = packets.decode(buf, [offset])`
Decode a DNS packet from a buffer
#### `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
name: 'google.com' // which record are you looking for
}
```
And an answers, additional, or authority looks like this
``` js
{
type: 'A', // or SRV, AAAA, etc
name: 'google.com', // which name is this record for
ttl: optionalTimeToLiveInSeconds,
(record specific data, see below)
}
```
Currently the different available records are
#### `A`
``` js
{
data: 'IPv4 address' // fx 127.0.0.1
}
```
#### `AAAA`
``` js
{
data: 'IPv6 address' // fx fe80::1
}
```
#### `TXT`
``` js
{
data: Buffer('some text')
}
```
#### `NS`
``` js
{
data: nameServer
}
```
#### `NULL`
``` js
{
data: Buffer('any binary data')
}
```
#### `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
}
}
```
#### `HINFO`
``` js
{
data: {
cpu: 'cpu info',
os: 'os info'
}
}
```
#### `PTR`
``` js
{
data: 'points.to.another.record'
}
```
#### `CNAME`
``` js
{
data: 'cname.to.another.record'
}
```
#### `DNAME`
``` js
{
data: 'dname.to.another.record'
}
```
#### `CAA`
``` js
{
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