support bit flags

README.md

@@ -20,6 +20,7 @@ var socket = dgram.createSocket('udp4')
 var buf = packet.encode({
   type: 'query',
   id: 1,
+  flags: packet.RECURSION_DESIRED,
   questions: [{
     type: 'A',
     name: 'google.com'
@@ -55,6 +56,7 @@ Packets look like this
 {
   type: 'query|response',
   id: optionalIdNumber,
+  flags: optionalBitFlags,
   questions: [...],
   answers: [...],
   additionals: [...],
@@ -62,6 +64,29 @@ Packets look like this
 }
 ```
 
+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

example.js

@@ -6,6 +6,7 @@ var socket = dgram.createSocket('udp4')
 var buf = packet.encode({
   type: 'query',
   id: 1,
+  flags: packet.RECURSION_DESIRED,
   questions: [{
     type: 'A',
     name: 'google.com'

index.js

@@ -101,8 +101,11 @@ header.encode = function (h, buf, offset) {
   if (!buf) buf = header.encodingLength(h)
   if (!offset) offset = 0
 
+  var flags = (h.flags || 0) & 32767
+  var type = h.type === 'response' ? RESPONSE_FLAG : QUERY_FLAG
+
   buf.writeUInt16BE(h.id || 0, offset)
-  buf.writeUInt16BE(h.type === 'response' ? RESPONSE_FLAG : QUERY_FLAG, offset + 2)
+  buf.writeUInt16BE(flags | type, offset + 2)
   buf.writeUInt16BE(h.questions.length, offset + 4)
   buf.writeUInt16BE(h.answers.length, offset + 6)
   buf.writeUInt16BE(h.authorities.length, offset + 8)
@@ -116,10 +119,12 @@ header.encode.bytes = 12
 header.decode = function (buf, offset) {
   if (!offset) offset = 0
   if (buf.length < 12) throw new Error('Header must be 12 bytes')
+  var flags = buf.readUInt16BE(offset + 2)
 
   return {
     id: buf.readUInt16BE(offset),
-    type: buf.readUInt16BE(offset + 2) & RESPONSE_FLAG ? 'response' : 'query',
+    type: flags & RESPONSE_FLAG ? 'response' : 'query',
+    flags: flags & 32767,
     questions: new Array(buf.readUInt16BE(offset + 4)),
     answers: new Array(buf.readUInt16BE(offset + 6)),
     authorities: new Array(buf.readUInt16BE(offset + 8)),
@@ -503,6 +508,13 @@ question.encodingLength = function (q) {
   return name.encodingLength(q.name) + 4
 }
 
+exports.AUTHORITATIVE_ANSWER = 1 << 10
+exports.TRUNCATED_RESPONSE = 1 << 9
+exports.RECURSION_DESIRED = 1 << 8
+exports.RECURSION_AVAILABLE = 1 << 7
+exports.AUTHENTIC_DATA = 1 << 5
+exports.CHECKING_DISABLED = 1 << 4
+
 exports.encode = function (result, buf, offset) {
   if (!buf) buf = Buffer(exports.encodingLength(result))
   if (!offset) offset = 0

test.js

@@ -97,6 +97,7 @@ tape('query', function (t) {
 tape('response', function (t) {
   testEncoder(t, packet, {
     type: 'response',
+    flags: packet.TRUNCATED_RESPONSE,
     answers: [{
       type: 'A',
       name: 'hello.a.com',
@@ -118,6 +119,7 @@ tape('response', function (t) {
   testEncoder(t, packet, {
     type: 'response',
     id: 100,
+    flags: 0,
     additionals: [{
       type: 'AAAA',
       name: 'hello.a.com',