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dns-lint

Fast, lightweight, pure JavaScript (ES5.1) implementation for DNS / mDNS.

Works great in Web Browsers and in node.js!

Detailed error checking makes it great for

capture
packing (JSON to DNS)
parsing (DNS to JSON)
linting (finding errors in packets)
debugging

No external dependencies for modern browsers. Uses DataView, Uint8Array, Uint16Array, and ArrayBuffer

Similar API to dns.js and native-dns-packet.

{ "header": {
    "id": 54231
  , "qr": 0
  , "opcode": 0
  , "aa": 0
  , "tc": 0
  , "rd": 1
  , "ra": 0
  , "res1": 0
  , "res2": 0
  , "res3": 0
  , "rcode": 0
  }
, "question": [
    { "name": "bowie._sftp-ssh._tcp.local"
    , "type": 1
    , "typeName": "A"
    , "class": 1
    , "className": "IN"
    , "byteLength": 32
    }
  ]
, "answer": []
, "authority": []
, "additional": []
, "byteLength": 44
}

Install

npm install git+https://git@git.daplie.com:Daplie/dns-lint

Test:

pushd node_modules/dns-lint

npm test

Usage

CLI

You can work directly from node_modules/dns-lint:

pushd node_modules/dns-lint/

Capture mDNS broadcast packets

# example
# node bin/mdns-capture.js <file-prefix>
node bin/mdns-capture.js mdns-test

# in another terminal
dig @224.0.0.251 -p 5353 -t PTR _services._dns-sd._udp.local

Parsing a saved packet

# example
# node bin/dns-parse.js </path/to/packet.dns.bin>
node bin/dns-parse.js samples/a-0.mdns.bin

You can also parse a saved packet from the native-dns-packet directory. these test packets have the binary for each record type and what it's parsed output should be.

Library

packet = dnsjs.unpack(arrayBuffer)
packet = dnsjs.unpackRdatas(arrayBuffer, packet)
packet.answers[0].data = dnsjs.unpackRdatas(arrayBuffer, packet, packet.answers[0])

node.js:

var nodeBuffer = fs.readFileSync('./samples/a-0.mdns.bin');
var arrayBuffer = nodeBuffer.buffer;

var dnsjs = require('dns-lint');
var packet = dnsjs.unpack(arrayBuffer);

console.log(packet);

Browser:

var arrayBuffer = new Uint8Array.from([ /* bytes */ ]).buffer;

var packet = pdns.unpack(arrayBuffer);

console.log(packet);

Contributing and Development

How to add a new parser

Each RR (aka Resource Record or RData) parser is individual. Examples include:

A (dns.type.a.js)
AAAA (dns.type.aaaa.js)
CNAME (dns.type.cname.js)
TXT (dns.type.txt.js)
SRV (dns.type.srv.js)

Let's say that To create a parser for a type which we don't currently support, just add the appropriate information to dns.types.js and create a file for the name of the type in the format dns.type.<typename>.js.

For example, if CNAME wasn't already supported and I wanted to add support for it I would follow these steps:

Update dns.types.js

  A: 			0x01	//   1
, NS: 		0x02  //   2
, CNAME: 	0x05  //   5    // I would simply add this line
, SOA: 		0x06  //   6

Capture a packet to test/fixtures/<domain>.<tld>.<type>.bin

This will construct and send a DNS query and save the first result that comes back.

In some cases (such as CNAME), the typical (or required) way to illicit the desired response is to make a request of a different type.

If that's the case, manually rename the the file afterwards.

Ideally you should have some idea of what the result file should look like and should place that in test/fixtures/<domain>.<tld>.<type>.json

node bin/capture-query.js --name www.google.com --type CNAME

Create dns.type.cname.js

Copy dns.type.TEMPLATE.js to the type for which you wish to create support (dns.type.cname.js in this example) and fill in the blanks.

var unpackLabels = exports.DNS_UNPACK_LABELS || require('./dns.unpack-labels.js').DNS_UNPACK_LABELS;
exports.DNS_TYPE_CNAME = function (ab, packet, record) {
  // record = { rdstart, rdlength, type, class }
  // example of not parsing and just leaving as binary data
  record.data = new Uint8Array(ab.slice(record.rdstart, record.rdstart + record.rdlength));

  return record;
};

}('undefined' !== typeof window ? window : exports));

Document what you've learned in doc/<type>.txt

You may be right or you might be wrong, but you might be right.

In any case, take a minute to document some of the gritty details of what you learned about this record type - tips, tricks, little-known facts, etc.

This may help (or wildly mislead) others if there's a bug in your parser that they need to track down. At the very least someone can follow a few links you followed and your thought process.

Check that my changes include these files

├── README.md
├── demo.html         (add the appropriate script tag)
├── doc
|   └── cname.txt
├── dns.classes.js    (not necessarily, but potentially)
├── dns.type.cname.js
├── dns.types.js
├── package.json      (bump the minor version)
└── test
    └── fixtures
        ├── www.google.com.cname.bin
        └── www.google.com.cname.js

mDNS Documentation

This document is currently used and update for testing purposes of DNS packets with Daplie applications. Please make note of any errata, as the organization of this document is based on the step by step process of debugging current issues regarding DNS, and not necessarily a demonstration on how to fix those issues. This document is for learning purposes and meant to assist future developers avoid similar bugs.

Objective

Create a robust DNS library that checks all possible combinations of DNS flags and messages in order to debug current DNS state for Daplie system and potentially develope DNS library with built in linting for use of Daplie, inc and community.

How to duplicate DNS crash:

>> cd ~/dns_test
>> node listen.jss

Then in another terminal enter:

>> dig @224.0.0.251 -p 5353 -t PTR _cloud._tcp.local

The listener then crashes with an output of:

START DNS PACKET
/home/daplie/dns_test/node_modules/dns-js/lib/bufferconsumer.js:52
      throw new Error('Buffer overflow')
      ^

Error: Buffer overflow
    at BufferConsumer.slice (/home/daplie/dns_test/node_modules/dns-js/lib/bufferconsumer.js:52:13)
  s  at Function.DNSRecord.parse (/home/daplie/dns_test/node_modules/dns-js/lib/dnsrecord.js:237:46)
    at /home/daplie/dns_test/node_modules/dns-js/lib/dnspacket.js:164:30
    at Array.forEach (native)
    at Function.DNSPacket.parse (/home/daplie/dns_test/node_modules/dns-js/lib/dnspacket.js:159:17)
    at /home/daplie/dns_test/cloud-respond.js:86:31
    at Array.forEach (native)
    at /home/daplie/dns_test/cloud-respond.js:11:21
    at Array.forEach (native)
    at Object.module.exports.respond (/home/daplie/dns_test/cloud-respond.js:10:11)

After commenting out lines 45-53 in dns_test/node_modules/dns-js/lib/bufferconsumer.js and rerunning the previous commands, the result is a new error:

START DNS PACKET
buffer.js:829
    throw new RangeError('Index out of range');
    ^

RangeError: Index out of range
    at checkOffset (buffer.js:829:11)
    at Buffer.readUInt8 (buffer.js:867:5)
    at BufferConsumer.byte (/home/daplie/dns_test/node_modules/dns-js/lib/bufferconsumer.js:67:22)
    at BufferConsumer.name (/home/daplie/dns_test/node_modules/dns-js/lib/bufferconsumer.js:120:14)
    at Function.DNSRecord.parse (/home/daplie/dns_test/node_modules/dns-js/lib/dnsrecord.js:187:14)
    at /home/daplie/dns_test/node_modules/dns-js/lib/dnspacket.js:164:30
    at Array.forEach (native)
    at Function.DNSPacket.parse (/home/daplie/dns_test/node_modules/dns-js/lib/dnspacket.js:159:17)
    at /home/daplie/dns_test/cloud-respond.js:86:31
    at Array.forEach (native)

which is located in the node.js buffer module. The API is here.

However, the error we are working with will most likely be dealt with by parsing through the binary and putting it in a format that is acceptable to a custom buffer, since the current buffer.js does doesn't seem to do the trick.

Using

function pad(str, len, ch) {

  while (str.length < len) {
    str = ch + str;
  }

  return str;
}

the binary output comes out as:

In order to figure out where the dnspacket code is going wrong, We will have to write our own test code to see if the dns code is doing what it's supposed to be doing.

Looking at the code below:

// parses through the flags
// val can be 1 or 0
// (val & 0x8000) >> 15 does the following
// val = 0000 0000 0000 0001
//     & 1001 0000 0000 0000
//    _______________________
//       0000 0000 0000 0000
// same if val were 0
// but if val were 0x8000
// then
// (val & 0x8000) >> 15 does the following
// val = 1001 0000 0000 0001
//     & 1001 0000 0000 0000
//    _______________________
//       1001 0000 0000 0000
// >>15= 0000 0000 0000 0001

function parseFlags(val, packet) {
  packet.header.qr = (val & 0x8000) >> 15;
  packet.header.opcode = (val & 0x7800) >> 11;
  packet.header.aa = (val & 0x400) >> 10;
  packet.header.tc = (val & 0x200) >> 9;
  packet.header.rd = (val & 0x100) >> 8;
  packet.header.ra = (val & 0x80) >> 7;
  packet.header.res1 = (val & 0x40) >> 6;
  packet.header.res2 = (val & 0x20) >> 5;
  packet.header.res3 = (val & 0x10) >> 4;
  packet.header.rcode = (val & 0xF);
}

One effective way to check is to create a dns packet, pass it to a custom packer and parser function and compare the input and output:

'use strict';

// order one http://www.binarytides.com/dns-query-code-in-c-with-linux-sockets/
// order two http://www.zytrax.com/books/dns/ch15/

function parse(i) {
  var header = {
   // first byte appears to be reverse
    qr: (i & 0x8000) >> 15
  , opcode: (i & 0x7800) >> 11
  , aa: (i & 0x400) >> 10
  , tc: (i & 0x200) >> 9
  , rd: (i & 0x100) >> 8

  // second byte appears to be second byte, but also in reverse
  , ra: (i & 0x80) >> 7
  , res1: (i & 0x40) >> 6 // z
  , res2: (i & 0x20) >> 5 // ad
  , res3: (i & 0x10) >> 4 // cd
  , rcode: (i & 0x1F)
  };

  return header;
}

function pack(header) {
  var val = 0;

  val += (header.qr << 15) & 0x8000;
  val += (header.opcode << 11) & 0x7800;
  val += (header.aa << 10) & 0x400;
  val += (header.tc << 9) & 0x200;
  val += (header.rd << 8) & 0x100;
  val += (header.ra << 7) & 0x80;
  val += (header.res1 << 6) & 0x40;
  val += (header.res2 << 5) & 0x20;
  val += (header.res3 << 4) & 0x10;
  val += header.rcode & 0x1F;

  return val;
}

var start = {
  qr: 1
, opcode: 12
, aa: 0
, tc: 0
, rd: 1
, ra: 0
, res1: 0
, res2: 0
, res3: 0
, rcode: 0
};

var i = pack(start);

var obj = parse(i);

console.log(i);
console.log(start);
console.log(obj);
// does a recursive check to see if start and obj are equal
require('assert').deepEqual(start, obj);

How to print out hex values of the DNS message in node.js?

socket.on('message', function (message, rinfo) {
  console.log('Received %d bytes from %s:%d\n',
    message.length, rinfo.address, rinfo.port);
  //console.log(msg.toString('utf8'));

  console.log(message.toString('hex'));

DNS sec: security puts a signature on a DNS packet and imprints a signature so that the sender of the packet is confirmed

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