dynamic authoritative name server
npm install @cepharum/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.
> This module is a fork of dnsd originally developed for Iris Couch. We've basically improved the code and started adding support for EDNS. Currently, we are using it for dynamic exposure of services in a Docker swarm.
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
const dnsd = require( "dnsd" );
dnsd.createServer( ( req, res ) => {
res.end( "1.2.3.4" );
}, {
// provide custom defaults here
ttl: 3600,
} )
.zone( "example" )
.listen( 5353, "127.0.0.1" )
.once( "listening", () => {
console.log( "Server is 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
const dnsd = require( "dnsd" );
dnsd.createServer(handler)
.zone("example.com", "ns1.example.com", "us@example.com", "now", "2h", "30m", "2w", "10m" )
.listen( 5353, "127.0.0.1" );
function handler(req, res) {
const { remoteAddress, remotePort, type } = req.connection;
console.log( "%s:%s/%s %j", remoteAddress, remotePort, type, req );
const question = res.question[0];
const hostname = question.name;
const length = hostname.length;
const ttl = Math.floor( Math.random() * 3600 );
if ( question.type === "A" ) {
res.answer.push( { name:hostname, type:"A", data:"1.1.1." + length, ttl } );
res.answer.push( { name:hostname, type:"A", data:"2.2.2." + length, 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,"recursionDesired":true,"recursionAvailable":false,"authenticated":false,"checkingDisabled":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,"recursionDesired":true,"recursionAvailable":false,"authenticated":false,"checkingDisabled":false,"question":[{"name":"example.com","type":"A","class":"IN"}]}
This is an example if you need to route your mail server with an MX record.
`javascript`
// Example MX response with dnsd
//
// To test:
// 1. Run this program
// 2. dig @localhost -p 5353 example.com mx
const dnsd = require( "dnsd" );
dnsd.createServer( handler )
.zone( "example.com", "ns1.example.com", "us@example.com", "now", "2h", "30m", "2w", "10m" )
.listen( 5353, "127.0.0.1" );
function handler(req, res) {
const question = res.question && res.question[0]
if ( question.type === "MX" ) {
console.log( "MX lookup for domain: %s", question.name );
res.answer.push( { name:question.name, type:"MX", data:{ weight: 10, name: "mail.example.com" } } );
res.answer.push( { name:question.name, type:"MX", data:{ weight: 20, name: "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
const fs = require("fs")
const dnsd = require("dnsd")
const msg_file = require.resolve( "dnsd/_test_data/registry.npmjs.org-response" );
const msg_data = fs.readFileSync( msg_file );
const message = dnsd.decode( msg_data );
console.dir( message );
`
Output
`javascript`
{
id: 34233,
type: "response",
responseCode: 0,
opcode: "query",
authoritative: false,
truncated: false,
recursionDesired: true,
recursionAvailable: true,
authenticated: false,
checkingDisabled: 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
const dnsd = require("dnsd")
const questions = [ { name: "example.com", class: "IN", type: "TXT" } ];
const message = {
type: "query",
id: 123,
opcode: "query",
recursionDesired: true,
question: questions
};
const msg_data = dnsd.encode( message );
console.log( "Encoded = %j", Array.prototype.slice.apply( msg_data ) );
message = dnsd.decode( 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,
recursionDesired: true,
recursionAvailable: false,
authenticated: false,
checkingDisabled: false,
question: [ { name: 'example.com', type: 'TXT', class: 'IN' } ] }
* 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)
This code is tested with [node-tap][tap].
$ 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