Add encoder for stream transports (TCP/TLS). (#23)

* Add encoder for stream transports (TCP/TLS).
Fixes #16.

* Add README text and return null on short buffer.

README.md

@@ -9,7 +9,7 @@ npm install dns-packet
 
 [![build status](https://travis-ci.org/mafintosh/dns-packet.svg?branch=master)](https://travis-ci.org/mafintosh/dns-packet)
 
-## Usage
+## UDP Usage
 
 ``` js
 var packet = require('dns-packet')
@@ -35,6 +35,10 @@ socket.on('message', function (message) {
 socket.send(buf, 0, buf.length, 53, '8.8.8.8')
 ```
 
+## TCP Usage
+
+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 TCP/TLS for privacy reasons.
+
 ## API
 
 #### `var buf = packets.encode(packet, [buf], [offset])`

example_tcp.js

@@ -0,0 +1,30 @@
+'use strict'
+
+const packet = require('./')
+const net = require('net')
+
+const buf = packet.streamEncode({
+  type: 'query',
+  id: 0xdead,
+  flags: packet.RECURSION_DESIRED,
+  questions: [{
+    type: 'A',
+    name: 'google.com'
+  }]
+})
+
+const client = new net.Socket()
+client.connect(53, '8.8.8.8', function () {
+  console.log('Connected')
+  client.write(buf)
+})
+
+client.on('data', function (data) {
+  console.log('Received response')
+  console.log(packet.streamDecode(data))
+  client.destroy() // kill client after server's response
+})
+
+client.on('close', function () {
+  console.log('Connection closed')
+})

index.js

@@ -811,6 +811,29 @@ exports.encodingLength = function (result) {
     encodingLengthList(result.additionals || [], answer)
 }
 
+exports.streamEncode = function (result) {
+  const len = exports.encodingLength(result)
+  const buf = Buffer.allocUnsafe(len + 2)
+  exports.encode(result, buf, 2)
+  buf.writeUInt16BE(len, 0)
+  exports.streamEncode.bytes = len + 2
+  return buf
+}
+
+exports.streamEncode.bytes = 0
+
+exports.streamDecode = function (buf) {
+  const len = buf.readUInt16BE(0)
+  if (buf.length < len + 2) {
+    return null
+  }
+  const result = exports.decode(buf, 2)
+  exports.streamDecode.bytes = exports.decode.bytes + 2
+  return result
+}
+
+exports.streamDecode.bytes = 0
+
 function encodingLengthList (list, enc) {
   let len = 0
   for (let i = 0; i < list.length; i++) len += enc.encodingLength(list[i])

test.js

@@ -289,6 +289,33 @@ tape('name_encoding', function (t) {
   t.end()
 })
 
+tape('stream', function (t) {
+  const val = {
+    type: 'query',
+    id: 45632,
+    flags: 0x8480,
+    answers: [{
+      type: 'A',
+      name: 'test2.example.net',
+      data: '198.51.100.1'
+    }]
+  }
+  const buf = packet.streamEncode(val)
+  const val2 = packet.streamDecode(buf)
+
+  t.same(buf.length, packet.streamEncode.bytes, 'streamEncode.bytes was set correctly')
+  t.same(packet.streamDecode.bytes, packet.streamEncode.bytes, 'streamDecode.bytes was set correctly')
+  t.ok(compare(t, val2.type, val.type), 'streamDecoded type match')
+  t.ok(compare(t, val2.id, val.id), 'streamDecoded id match')
+  t.ok(parseInt(val2.flags) === parseInt(val.flags & 0x7FFF), 'streamDecoded flags match')
+  const answer = val.answers[0]
+  const answer2 = val2.answers[0]
+  t.ok(compare(t, answer.type, answer2.type), 'streamDecoded RR type match')
+  t.ok(compare(t, answer.name, answer2.name), 'streamDecoded RR name match')
+  t.ok(compare(t, answer.data, answer2.data), 'streamDecoded RR rdata match')
+  t.end()
+})
+
 function testEncoder (t, rpacket, val) {
   const buf = rpacket.encode(val)
   const val2 = rpacket.decode(buf)