Add basic EDNS(0) OPT RR support

* Add EDNS(0) OPT RR for UDP payload size in query.

* Rework PR #34, fixes #36.  Add support for options in an OPT pseudo-RR.

* Include tweaks from @silverwind

index.js

@@ -77,6 +77,7 @@ name.decode = function (buf, offset) {
 name.decode.bytes = 0
 
 name.encodingLength = function (n) {
+  if (n === '.') return 1
   return Buffer.byteLength(n) + 2
 }
 
@@ -664,6 +665,84 @@ raaaa.encodingLength = function () {
   return 18
 }
 
+const roption = exports.option = {}
+
+roption.encode = function (option, buf, offset) {
+  if (!buf) buf = Buffer.allocUnsafe(roption.encodingLength(option))
+  if (!offset) offset = 0
+  const oldOffset = offset
+
+  buf.writeUInt16BE(option.code, offset)
+  offset += 2
+  buf.writeUInt16BE(option.data.length, offset)
+  offset += 2
+  option.data.copy(buf, offset)
+  offset += option.data.length
+
+  roption.encode.bytes = offset - oldOffset
+  return buf
+}
+
+roption.encode.bytes = 0
+
+roption.decode = function (buf, offset) {
+  if (!offset) offset = 0
+  const option = {}
+
+  option.code = buf.readUInt16BE(offset)
+  const len = buf.readUInt16BE(offset + 2)
+  option.data = buf.slice(offset + 4, offset + 4 + len)
+
+  roption.decode.bytes = len + 4
+  return option
+}
+
+roption.decode.bytes = 0
+
+roption.encodingLength = function (option) {
+  return option.data.length + 4
+}
+
+const ropt = exports.opt = {}
+
+ropt.encode = function (options, buf, offset) {
+  if (!buf) buf = Buffer.allocUnsafe(ropt.encodingLength(options))
+  if (!offset) offset = 0
+  const oldOffset = offset
+
+  const rdlen = encodingLengthList(options, roption)
+  buf.writeUInt16BE(rdlen, offset)
+  offset = encodeList(options, roption, buf, offset + 2)
+
+  ropt.encode.bytes = offset - oldOffset
+  return buf
+}
+
+ropt.encode.bytes = 0
+
+ropt.decode = function (buf, offset) {
+  if (!offset) offset = 0
+  const oldOffset = offset
+
+  const options = []
+  let rdlen = buf.readUInt16BE(offset)
+  offset += 2
+  let o = 0
+  while (rdlen > 0) {
+    options[o++] = roption.decode(buf, offset)
+    offset += roption.decode.bytes
+    rdlen -= roption.decode.bytes
+  }
+  ropt.decode.bytes = offset - oldOffset
+  return options
+}
+
+ropt.decode.bytes = 0
+
+ropt.encodingLength = function (options) {
+  return 2 + encodingLengthList(options || [], roption)
+}
+
 const renc = exports.record = function (type) {
   switch (type.toUpperCase()) {
     case 'A': return ra
@@ -679,6 +758,7 @@ const renc = exports.record = function (type) {
     case 'NS': return rns
     case 'SOA': return rsoa
     case 'MX': return rmx
+    case 'OPT': return ropt
   }
   return runknown
 }
@@ -696,15 +776,29 @@ answer.encode = function (a, buf, offset) {
 
   buf.writeUInt16BE(types.toType(a.type), offset)
 
+  if (a.type.toUpperCase() === 'OPT') {
+    if (a.name !== '.') {
+      throw new Error('OPT name must be root.')
+    }
+    buf.writeUInt16BE(a.updPayloadSize || 4096, offset + 2)
+    buf.writeUInt8(a.extendedRcode || 0, offset + 4)
+    buf.writeUInt8(a.ednsVersion || 0, offset + 5)
+    buf.writeUInt16BE(a.flags || 0, offset + 6)
+
+    offset += 8
+    ropt.encode(a.options || [], buf, offset)
+    offset += ropt.encode.bytes
+  } else {
     let klass = classes.toClass(a.class === undefined ? 'IN' : a.class)
     if (a.flush) klass |= FLUSH_MASK // the 1st bit of the class is the flush bit
     buf.writeUInt16BE(klass, offset + 2)
-
     buf.writeUInt32BE(a.ttl || 0, offset + 4)
 
+    offset += 8
     const enc = renc(a.type)
-  enc.encode(a.data, buf, offset + 8)
+    enc.encode(a.data, buf, offset)
-  offset += 8 + enc.encode.bytes
+    offset += enc.encode.bytes
+  }
 
   answer.encode.bytes = offset - oldOffset
   return buf
@@ -721,6 +815,15 @@ answer.decode = function (buf, offset) {
   a.name = name.decode(buf, offset)
   offset += name.decode.bytes
   a.type = types.toString(buf.readUInt16BE(offset))
+  if (a.type === 'OPT') {
+    a.udpPayloadSize = buf.readUInt16BE(offset + 2)
+    a.extendedRcode = buf.readUInt8(offset + 4)
+    a.ednsVersion = buf.readUInt8(offset + 5)
+    a.flags = buf.readUInt16BE(offset + 6)
+    a.flag_do = ((a.flags >> 15) & 0x1) === 1
+    a.options = ropt.decode(buf, offset + 8)
+    offset += 8 + ropt.decode.bytes
+  } else {
     const klass = buf.readUInt16BE(offset + 2)
     a.ttl = buf.readUInt32BE(offset + 4)
 
@@ -730,6 +833,7 @@ answer.decode = function (buf, offset) {
     const enc = renc(a.type)
     a.data = enc.decode(buf, offset + 8)
     offset += 8 + enc.decode.bytes
+  }
 
   answer.decode.bytes = offset - oldOffset
   return a
@@ -738,7 +842,7 @@ answer.decode = function (buf, offset) {
 answer.decode.bytes = 0
 
 answer.encodingLength = function (a) {
-  return name.encodingLength(a.name) + 8 + renc(a.type).encodingLength(a.data)
+  return name.encodingLength(a.name) + 8 + renc(a.type).encodingLength(a.data || a.options)
 }
 
 const question = exports.question = {}
@@ -798,6 +902,7 @@ exports.RECURSION_DESIRED = 1 << 8
 exports.RECURSION_AVAILABLE = 1 << 7
 exports.AUTHENTIC_DATA = 1 << 5
 exports.CHECKING_DISABLED = 1 << 4
+exports.DNSSEC_OK = 1 << 15
 
 exports.encode = function (result, buf, offset) {
   if (!buf) buf = Buffer.allocUnsafe(exports.encodingLength(result))

test.js

@@ -321,6 +321,44 @@ tape('stream', function (t) {
   t.end()
 })
 
+tape('opt', function (t) {
+  const val = {
+    type: 'query',
+    questions: [{
+      type: 'A',
+      name: 'hello.a.com'
+    }],
+    additionals: [{
+      type: 'OPT',
+      name: '.',
+      udpPayloadSize: 4096
+    }]
+  }
+  testEncoder(t, packet, val)
+  let buf = packet.encode(val)
+  let val2 = packet.decode(buf)
+  const additional1 = val.additionals[0]
+  let additional2 = val2.additionals[0]
+  t.ok(compare(t, additional1.name, additional2.name), 'name matches')
+  t.ok(compare(t, additional1.udpPayloadSize, additional2.udpPayloadSize), 'udp payload size matches')
+  t.ok(compare(t, 0, additional2.flags), 'flags match')
+  additional1.flags = packet.DNSSEC_OK
+  additional1.extendedRcode = 0x80
+  // padding, see RFC 7830
+  additional1.options = [{
+    code: 12,
+    data: Buffer.alloc(31)
+  }]
+  buf = packet.encode(val)
+  val2 = packet.decode(buf)
+  additional2 = val2.additionals[0]
+  t.ok(compare(t, 1 << 15, additional2.flags), 'DO bit set in flags')
+  t.ok(compare(t, true, additional2.flag_do), 'DO bit set')
+  t.ok(compare(t, additional1.extendedRcode, additional2.extendedRcode), 'extended rcode matches')
+  t.ok(compare(t, additional1.options, additional2.options), 'options match')
+  t.end()
+})
+
 tape('unpack', function (t) {
   const buf = Buffer.from([
     0x00, 0x79,