Add EDNS OPT de/encoding

* Add ECS processing.  See #46

* Add support for Padding.  Simplify ECS to not do CIDR parsing.

* Done implementing the EDNS0 options that make sense

* Default to string values from IANA for EDNSO option codes.  Add tests for mappings.

* Add a few more aliases for option codes

* Update README for EDNS0 options

* I think this is what is desired.  Happy to change it more if you want.

* Address code review comments from @silverwind

README.md

@@ -258,8 +258,25 @@ And an answer, additional, or authority looks like this
   udpPayloadSize: 4096,
   flags: packet.DNSSEC_OK,
   options: [{
+    // pass in any code/data for generic EDNS0 options
     code: 12,
     data: Buffer.alloc(31)
+  }, {
+    // Several EDNS0 options have explicit support
+    code: 'padding',
+    length: 31
+  }, {
+    code: 'CLIENT-SUBNET',
+    family: 2, // 1 for IPv4, 2 for IPv6
+    sourcePrefixLength: 64, // used to truncate IP address
+    scopePrefixLength: 0,
+    ip: 'fe80::'
+  }, {
+    code: 'tcp-keepalive',
+    timeout: 150 // increments of 100ms.  This means 15s.
+  }, {
+    code: 'key-tag',
+    tags: [1, 2, 3]
   }]
 }
 ```

index.js

@@ -4,6 +4,7 @@ const types = require('./types')
 const rcodes = require('./rcodes')
 const opcodes = require('./opcodes')
 const classes = require('./classes')
+const optioncodes = require('./optioncodes')
 const ip = require('ip')
 
 const QUERY_FLAG = 0
@@ -671,12 +672,68 @@ roption.encode = function (option, buf, offset) {
   if (!offset) offset = 0
   const oldOffset = offset
 
-  buf.writeUInt16BE(option.code, offset)
+  const code = optioncodes.toCode(option.code)
+  buf.writeUInt16BE(code, offset)
   offset += 2
+  if (option.data) {
     buf.writeUInt16BE(option.data.length, offset)
     offset += 2
     option.data.copy(buf, offset)
     offset += option.data.length
+  } else {
+    switch (code) {
+      // case 3: NSID.  No encode makes sense.
+      // case 5,6,7: Not implementable
+      case 8: // ECS
+        // note: do IP math before calling
+        const spl = option.sourcePrefixLength || 0
+        const fam = option.family || (ip.isV4Format(option.ip) ? 1 : 2)
+        const ipBuf = ip.toBuffer(option.ip)
+        const ipLen = Math.ceil(spl / 8)
+        buf.writeUInt16BE(ipLen + 4, offset)
+        offset += 2
+        buf.writeUInt16BE(fam, offset)
+        offset += 2
+        buf.writeUInt8(spl, offset++)
+        buf.writeUInt8(option.scopePrefixLength || 0, offset++)
+
+        ipBuf.copy(buf, offset, 0, ipLen)
+        offset += ipLen
+        break
+      // case 9: EXPIRE (experimental)
+      // case 10: COOKIE.  No encode makes sense.
+      case 11: // KEEP-ALIVE
+        if (option.timeout) {
+          buf.writeUInt16BE(2, offset)
+          offset += 2
+          buf.writeUInt16BE(option.timeout, offset)
+          offset += 2
+        } else {
+          buf.writeUInt16BE(0, offset)
+          offset += 2
+        }
+        break
+      case 12: // PADDING
+        const len = option.length || 0
+        buf.writeUInt16BE(len, offset)
+        offset += 2
+        buf.fill(0, offset, offset + len)
+        offset += len
+        break
+      // case 13:  CHAIN.  Experimental.
+      case 14: // KEY-TAG
+        const tagsLen = option.tags.length * 2
+        buf.writeUInt16BE(tagsLen, offset)
+        offset += 2
+        for (const tag of option.tags) {
+          buf.writeUInt16BE(tag, offset)
+          offset += 2
+        }
+        break
+      default:
+        throw new Error(`Unknown roption code: ${option.code}`)
+    }
+  }
 
   roption.encode.bytes = offset - oldOffset
   return buf
@@ -687,10 +744,38 @@ 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.type = optioncodes.toString(option.code)
-  option.data = buf.slice(offset + 4, offset + 4 + len)
+  offset += 2
+  const len = buf.readUInt16BE(offset)
+  offset += 2
+  option.data = buf.slice(offset, offset + len)
+  switch (option.code) {
+    // case 3: NSID.  No decode makes sense.
+    case 8: // ECS
+      option.family = buf.readUInt16BE(offset)
+      offset += 2
+      option.sourcePrefixLength = buf.readUInt8(offset++)
+      option.scopePrefixLength = buf.readUInt8(offset++)
+      const padded = Buffer.alloc((option.family === 1) ? 4 : 16)
+      buf.copy(padded, 0, offset, offset + len - 4)
+      option.ip = ip.toString(padded)
+      break
+    // case 12: Padding.  No decode makes sense.
+    case 11: // KEEP-ALIVE
+      if (len > 0) {
+        option.timeout = buf.readUInt16BE(offset)
+        offset += 2
+      }
+      break
+    case 14:
+      option.tags = []
+      for (let i = 0; i < len; i += 2) {
+        option.tags.push(buf.readUInt16BE(offset))
+        offset += 2
+      }
+    // don't worry about default.  caller will use data if desired
+  }
 
   roption.decode.bytes = len + 4
   return option
@@ -699,7 +784,22 @@ roption.decode = function (buf, offset) {
 roption.decode.bytes = 0
 
 roption.encodingLength = function (option) {
+  if (option.data) {
     return option.data.length + 4
+  }
+  const code = optioncodes.toCode(option.code)
+  switch (code) {
+    case 8: // ECS
+      const spl = option.sourcePrefixLength || 0
+      return Math.ceil(spl / 8) + 8
+    case 11: // KEEP-ALIVE
+      return (typeof option.timeout === 'number') ? 6 : 4
+    case 12: // PADDING
+      return option.length + 4
+    case 14: // KEY-TAG
+      return 4 + (option.tags.length * 2)
+  }
+  throw new Error(`Unknown roption code: ${option.code}`)
 }
 
 const ropt = exports.opt = {}

optioncodes.js

@@ -0,0 +1,59 @@
+'use strict'
+
+exports.toString = function (type) {
+  switch (type) {
+    // list at
+    // https://www.iana.org/assignments/dns-parameters/dns-parameters.xhtml#dns-parameters-11
+    case 1: return 'LLQ'
+    case 2: return 'UL'
+    case 3: return 'NSID'
+    case 5: return 'DAU'
+    case 6: return 'DHU'
+    case 7: return 'N3U'
+    case 8: return 'CLIENT_SUBNET'
+    case 9: return 'EXPIRE'
+    case 10: return 'COOKIE'
+    case 11: return 'TCP_KEEPALIVE'
+    case 12: return 'PADDING'
+    case 13: return 'CHAIN'
+    case 14: return 'KEY_TAG'
+    case 26946: return 'DEVICEID'
+  }
+  if (type < 0) {
+    return null
+  }
+  return `OPTION_${type}`
+}
+
+exports.toCode = function (name) {
+  if (typeof name === 'number') {
+    return name
+  }
+  if (!name) {
+    return -1
+  }
+  switch (name.toUpperCase()) {
+    case 'OPTION_0': return 0
+    case 'LLQ': return 1
+    case 'UL': return 2
+    case 'NSID': return 3
+    case 'OPTION_4': return 4
+    case 'DAU': return 5
+    case 'DHU': return 6
+    case 'N3U': return 7
+    case 'CLIENT_SUBNET': return 8
+    case 'EXPIRE': return 9
+    case 'COOKIE': return 10
+    case 'TCP_KEEPALIVE': return 11
+    case 'PADDING': return 12
+    case 'CHAIN': return 13
+    case 'KEY_TAG': return 14
+    case 'DEVICEID': return 26946
+    case 'OPTION_65535': return 65535
+  }
+  const m = name.match(/_(\d+)$/)
+  if (m) {
+    return parseInt(m[1], 10)
+  }
+  return -1
+}

test.js

@@ -4,6 +4,7 @@ const tape = require('tape')
 const packet = require('./')
 const rcodes = require('./rcodes')
 const opcodes = require('./opcodes')
+const optioncodes = require('./optioncodes')
 
 tape('unknown', function (t) {
   testEncoder(t, packet.unknown, Buffer.from('hello world'))
@@ -352,10 +353,26 @@ tape('opt', function (t) {
   t.ok(compare(t, 0, additional2.flags), 'flags match')
   additional1.flags = packet.DNSSEC_OK
   additional1.extendedRcode = 0x80
-  // padding, see RFC 7830
+  additional1.options = [ {
-  additional1.options = [{
+    code: 'CLIENT_SUBNET', // edns-client-subnet, see RFC 7871
-    code: 12,
+    ip: 'fe80::',
-    data: Buffer.alloc(31)
+    sourcePrefixLength: 64
+  }, {
+    code: 8, // still ECS
+    ip: '5.6.0.0',
+    sourcePrefixLength: 16,
+    scopePrefixLength: 16
+  }, {
+    code: 'padding',
+    length: 31
+  }, {
+    code: 'TCP_KEEPALIVE'
+  }, {
+    code: 'tcp_keepalive',
+    timeout: 150
+  }, {
+    code: 'KEY_TAG',
+    tags: [1, 82, 987]
   }]
   buf = packet.encode(val)
   val2 = packet.decode(buf)
@@ -363,7 +380,16 @@ tape('opt', function (t) {
   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.ok(compare(t, 8, additional2.options[0].code))
+  t.ok(compare(t, 'fe80::', additional2.options[0].ip))
+  t.ok(compare(t, 64, additional2.options[0].sourcePrefixLength))
+  t.ok(compare(t, '5.6.0.0', additional2.options[1].ip))
+  t.ok(compare(t, 16, additional2.options[1].sourcePrefixLength))
+  t.ok(compare(t, 16, additional2.options[1].scopePrefixLength))
+  t.ok(compare(t, additional1.options[2].length, additional2.options[2].data.length))
+  t.ok(compare(t, additional1.options[3].timeout, undefined))
+  t.ok(compare(t, additional1.options[4].timeout, additional2.options[4].timeout))
+  t.ok(compare(t, additional1.options[5].tags, additional2.options[5].tags))
   t.end()
 })
 
@@ -509,6 +535,38 @@ tape('unpack', function (t) {
   t.end()
 })
 
+tape('optioncodes', function (t) {
+  const opts = [
+    [0, 'OPTION_0'],
+    [1, 'LLQ'],
+    [2, 'UL'],
+    [3, 'NSID'],
+    [4, 'OPTION_4'],
+    [5, 'DAU'],
+    [6, 'DHU'],
+    [7, 'N3U'],
+    [8, 'CLIENT_SUBNET'],
+    [9, 'EXPIRE'],
+    [10, 'COOKIE'],
+    [11, 'TCP_KEEPALIVE'],
+    [12, 'PADDING'],
+    [13, 'CHAIN'],
+    [14, 'KEY_TAG'],
+    [26946, 'DEVICEID'],
+    [65535, 'OPTION_65535'],
+    [64000, 'OPTION_64000'],
+    [65002, 'OPTION_65002'],
+    [-1, null]
+  ]
+  for (const [code, str] of opts) {
+    const s = optioncodes.toString(code)
+    t.ok(compare(t, s, str), `${code} => ${str}`)
+    t.ok(compare(t, optioncodes.toCode(s), code), `${str} => ${code}`)
+  }
+  t.ok(compare(t, optioncodes.toCode('INVALIDINVALID'), -1))
+  t.end()
+})
+
 function testEncoder (t, rpacket, val) {
   const buf = rpacket.encode(val)
   const val2 = rpacket.decode(buf)