Dynamic authoritative name server
npm install wk-modern-dnsddnsd is a Node.js package for working with DNS. It converts binary DNS messages to and from convenient JavaScript objects; and it provides a server API, for running a custom name server.
dnsd is available as an npm module.
$ npm install dnsd
This simple DNS server responds with an "A" (address) record of 1.2.3.4 for every request.
``javascript`
var dnsd = require('dnsd')
dnsd.createServer(function(req, res) {
res.end('1.2.3.4')
}).listen(5353, '127.0.0.1')
console.log('Server running at 127.0.0.1:5353')
Now test your server:
$ dig @localhost -p 5353 foo.example A
; <<>> DiG 9.8.1-P1 <<>> @localhost -p 5353 foo.example A
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 27955
;; flags: qr rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; WARNING: recursion requested but not available
;; QUESTION SECTION:
;foo.example. IN A
;; ANSWER SECTION:
foo.example. 3600 IN A 1.2.3.4
;; Query time: 1 msec
;; SERVER: 127.0.0.1#5353(127.0.0.1)
;; WHEN: Wed Aug 8 05:10:40 2012
;; MSG SIZE rcvd: 45
This example logs all requests. For address (A) queries, it returns two records, with a random TTL, and the final octet of the IP address is the length of the hostname queried.
`javascript
var dnsd = require('dnsd')
var server = dnsd.createServer(handler)
server.zone('example.com', 'ns1.example.com', 'us@example.com', 'now', '2h', '30m', '2w', '10m')
.listen(5353, '127.0.0.1')
console.log('Server running at 127.0.0.1:5353')
function handler(req, res) {
console.log('%s:%s/%s %j', req.connection.remoteAddress, req.connection.remotePort, req.connection.type, req)
var question = req.question[0]
, hostname = question.name
, length = hostname.length
, ttl = Math.floor(Math.random() * 3600)
if(question.type == 'A') {
res.answer.push({name:hostname, type:'A', data:"1.1.1."+length, 'ttl':ttl})
res.answer.push({name:hostname, type:'A', data:"2.2.2."+length, 'ttl':ttl})
}
res.end()
}
`
Test the SOA response:
$ dig @localhost -p 5353 example.com soa
; <<>> DiG 9.8.1-P1 <<>> @localhost -p 5353 example.com soa
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 30176
;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; WARNING: recursion requested but not available
;; QUESTION SECTION:
;example.com. IN SOA
;; ANSWER SECTION:
example.com. 600 IN SOA ns1.example.com. us.example.com. 1344403648 7200 1800 1209600 600
;; Query time: 5 msec
;; SERVER: 127.0.0.1#5353(127.0.0.1)
;; WHEN: Wed Aug 8 05:27:32 2012
;; MSG SIZE rcvd: 72
And test the address (A) response:
$ dig @localhost -p 5353 example.com a
; <<>> DiG 9.8.1-P1 <<>> @localhost -p 5353 example.com a
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 19419
;; flags: qr aa rd; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 0
;; WARNING: recursion requested but not available
;; QUESTION SECTION:
;example.com. IN A
;; ANSWER SECTION:
example.com. 1222 IN A 1.1.1.11
example.com. 1222 IN A 2.2.2.11
;; Query time: 1 msec
;; SERVER: 127.0.0.1#5353(127.0.0.1)
;; WHEN: Wed Aug 8 05:27:34 2012
;; MSG SIZE rcvd: 61
Server output for these queries:
Server running at 127.0.0.1:5353
127.0.0.1:34427/udp4 {"id":30176,"type":"request","responseCode":0,"opcode":"query","authoritative":false,"truncated":false,"recursion_desired":true,"recursion_available":false,"authenticated":false,"checking_disabled":false,"question":[{"name":"example.com","type":"SOA","class":"IN"}]}
127.0.0.1:59596/udp4 {"id":19419,"type":"request","responseCode":0,"opcode":"query","authoritative":false,"truncated":false,"recursion_desired":true,"recursion_available":false,"authenticated":false,"checking_disabled":false,"question":[{"name":"example.com","type":"A","class":"IN"}]}
`javascript`
// Example MX response with dnsd
//
// To test:
// 1. Run this program
// 2. dig @localhost -p 5353 example.com mx
var dnsd = require('dnsd')
var server = dnsd.createServer(handler)
server.zone('example.com', 'ns1.example.com', 'us@example.com', 'now', '2h', '30m', '2w', '10m')
server.listen(5353, '127.0.0.1')
console.log('Listening at 127.0.0.1:5353')
function handler(req, res) {
var question = res.question && res.question[0]
if(question.type != 'MX')
return res.end()
console.log('MX lookup for domain: %s', question.name)
res.answer.push({'name':question.name, 'type':'MX', 'data':[10, 'mail.example.com']})
res.answer.push({'name':question.name, 'type':'MX', 'data':[20, 'mail.backupexample.com']})
return res.end()
}
The MX data attribute needs to be an Array to work properly, the first value is the priority, the second is the server.
This server name must be a domain string and not an IP address. Make sure you have an A record or CNAME setup for this.
See http://support.google.com/a/bin/answer.py?hl=en&answer=140034 for more info on MX records and configuration.
`javascript
var fs = require('fs')
var dnsd = require('dnsd')
var msg_file = require.resolve('dnsd/_test_data/registry.npmjs.org-response')
, msg_data = fs.readFileSync(msg_file)
, message = dnsd.parse(msg_data)
console.dir(message)
`
Output
`javascript`
{ id: 34233,
type: 'response',
responseCode: 0,
opcode: 'query',
authoritative: false,
truncated: false,
recursion_desired: true,
recursion_available: true,
authenticated: false,
checking_disabled: false,
question: [ { name: 'registry.npmjs.org', type: 'A', class: 'IN' } ],
answer:
[ { name: 'registry.npmjs.org',
type: 'CNAME',
class: 'IN',
ttl: 85,
data: 'isaacs.iriscouch.net' },
{ name: 'isaacs.iriscouch.net',
type: 'CNAME',
class: 'IN',
ttl: 2821,
data: 'ec2-23-23-147-24.compute-1.amazonaws.com' },
{ name: 'ec2-23-23-147-24.compute-1.amazonaws.com',
type: 'A',
class: 'IN',
ttl: 356336,
data: '23.23.147.24' } ] }
`javascript
var dnsd = require('dnsd')
var questions = [ {name:'example.com', class:'IN', type:'TXT'} ]
, message = {type:'query', id:123, opcode:'query', recursion_desired:true, question:questions}
, msg_data = dnsd.binify(message)
console.log('Encoded = %j', Array.prototype.slice.apply(msg_data))
message = dnsd.parse(msg_data)
console.log('Round trip:')
console.dir(message)
`
Output:
`javascript`
Encoded = [0,123,1,0,0,1,0,0,0,0,0,0,7,101,120,97,109,112,108,101,3,99,111,109,0,0,16,0,1]
Round trip:
{ id: 123,
type: 'request',
responseCode: 0,
opcode: 'query',
authoritative: false,
truncated: false,
recursion_desired: true,
recursion_available: false,
authenticated: false,
checking_disabled: false,
question: [ { name: 'example.com', type: 'TXT', class: 'IN' } ] }
dnsd is [defaultable][def]. The option convenient (true by default) adds convenience code when running a server. Convenience mode adds several features, mostly to build standards-compliant name servers.
`javascript`
var dnsd_easy = require('dnsd')
var dnsd_hard = dnsd_easy.defaults({convenient: false})
First, your handler's response object already has .type = "response" set; then there are many helpers processing your response:
* You can pass a value to res.end(), with special handling depending on type:res.answer
* Array: those values will be added to the section.res
* Object: that object will be sent as a response ( is unused).A
* String: the response will add an anser record with your value as the IP address.SOA
* Automatically respond to queries with the SOA record.A
* Responses to an query with no answers will add the SOA record to the response..zone()
* If the response records are missing a TTL, use the one from the definition (the SOA` record)
Without convenience mode, dnsd will simply send your response verbatim, as you define it (or throw an encoding error for missing or bad data).
Follow uses [node-tap][tap]. If you clone this Git repository, tap is included.
$ tap test
ok test/api.js ........................................ 10/10
ok test/convenience.js ................................ 22/22
ok test/message.js .................................. 176/176
ok test/print.js ...................................... 10/10
ok test/server.js ..................................... 35/35
total ............................................... 253/253
ok
Apache 2.0
See the Apache 2.0 license.
[tap]: https://github.com/isaacs/node-tap
[def]: https://github.com/iriscouch/defaultable