git ssb

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// Copyright 2012 Iris Couch, all rights reserved.
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//
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// Encode DNS messages
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var util = require('util')
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var constants = require('./constants')
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module.exports = { 'State': State
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                 }
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var SECTIONS = ['question', 'answer', 'authority', 'additional']
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function State () {
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  var self = this
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  self.header = new Buffer(12)
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  self.position = 0
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  self.question   = []
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  self.answer     = []
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  self.authority  = []
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  self.additional = []
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  self.domains = {} // The compression lookup table
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}
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State.prototype.toBinary = function() {
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  var self = this
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  var bufs = [self.header]
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  self.question  .forEach(function(buf) { bufs.push(buf) })
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  self.answer    .forEach(function(buf) { bufs.push(buf) })
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  self.authority .forEach(function(buf) { bufs.push(buf) })
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  self.additional.forEach(function(buf) { bufs.push(buf) })
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  return Buffer.concat(bufs)
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}
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State.prototype.message = function(msg) {
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  var self = this
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  // ID
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  self.header.writeUInt16BE(msg.id, 0)
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  // QR, opcode, AA, TC, RD
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  var byte = 0
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  byte |= msg.type == 'response' ? 0x80 : 0x00
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  byte |= msg.authoritative      ? 0x04 : 0x00
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  byte |= msg.truncated          ? 0x02 : 0x00
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  byte |= msg.recursion_desired  ? 0x01 : 0x00
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  var opcode_names = ['query', 'iquery', 'status', null, 'notify', 'update']
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    , opcode = opcode_names.indexOf(msg.opcode)
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  if(opcode == -1 || typeof msg.opcode != 'string')
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    throw new Error('Unknown opcode: ' + msg.opcode)
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  else
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    byte |= (opcode << 3)
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  self.header.writeUInt8(byte, 2)
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  // RA, Z, AD, CD, Rcode
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  byte = 0
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  byte |= msg.recursion_available ? 0x80 : 0x00
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  byte |= msg.authenticated       ? 0x20 : 0x00
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  byte |= msg.checking_disabled   ? 0x10 : 0x00
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  byte |= (msg.responseCode & 0x0f)
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  self.header.writeUInt8(byte, 3)
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  self.position = 12 // the beginning of the sections
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  SECTIONS.forEach(function(section) {
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    var records = msg[section] || []
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    records.forEach(function(rec) {
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      self.record(section, rec)
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    })
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  })
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  // Write the section counts.
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  self.header.writeUInt16BE(self.question.length    , 4)
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  self.header.writeUInt16BE(self.answer.length      , 6)
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  self.header.writeUInt16BE(self.authority.length   , 8)
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  self.header.writeUInt16BE(self.additional.length  , 10)
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}
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State.prototype.record = function(section_name, record) {
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  var self = this
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  var body = []
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    , buf
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  // Write the record name.
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  buf = self.encode(record.name)
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  body.push(buf)
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  self.position += buf.length
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  var type = constants.type_to_number(record.type)
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    , clas = constants.class_to_number(record.class)
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  // Write the type.
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  buf = new Buffer(2)
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  buf.writeUInt16BE(type, 0)
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  body.push(buf)
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  self.position += 2
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  // Write the class.
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  buf = new Buffer(2)
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  buf.writeUInt16BE(clas, 0)
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  body.push(buf)
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  self.position += 2
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  if(section_name != 'question') {
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    // Write the TTL.
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    buf = new Buffer(4)
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    buf.writeUInt32BE(record.ttl || 0, 0)
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    body.push(buf)
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    self.position += 4
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    // Write the rdata. Update the position now (the rdata length value) in case self.encode() runs.
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    var match, rdata
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    switch (record.class + ' ' + record.type) {
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      case 'IN A':
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        rdata = record.data || ''
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        match = rdata.match(/^(\d+)\.(\d+)\.(\d+)\.(\d+)$/)
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        if(!match)
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          throw new Error('Bad '+record.type+' record data: ' + JSON.stringify(record))
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        rdata = [ +match[1], +match[2], +match[3], +match[4] ]
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        break
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      case 'IN AAAA':
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        rdata = (record.data || '').split(/:/)
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        if(rdata.length != 8)
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          throw new Error('Bad '+record.type+' record data: ' + JSON.stringify(record))
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        rdata = rdata.map(pair_to_buf)
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        break
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      case 'IN MX':
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        var host = record.data[1]
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        rdata = [ buf16(record.data[0])
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                , self.encode(host, 2 + 2) // Adjust for the rdata length + preference values.
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                ]
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        break
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      case 'IN SOA':
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        var mname   = self.encode(record.data.mname, 2) // Adust for rdata length
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          , rname   = self.encode(record.data.rname, 2 + mname.length)
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        rdata = [ mname
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                , rname
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                , buf32(record.data.serial)
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                , buf32(record.data.refresh)
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                , buf32(record.data.retry)
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                , buf32(record.data.expire)
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                , buf32(record.data.ttl)
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                ]
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        break
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      case 'IN NS':
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      case 'IN PTR':
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      case 'IN CNAME':
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        rdata = self.encode(record.data, 2) // Adjust for the rdata length
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        break
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      case 'IN TXT':
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        rdata = record.data.map(function(part) {
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          part = new Buffer(part)
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          return [part.length, part]
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        })
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        break
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      case 'IN SRV':
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        rdata = [ buf16(record.data.priority)
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                , buf16(record.data.weight)
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                , buf16(record.data.port)
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                , self.encode(record.data.target, 2 + 6, 'nocompress') // Offset for rdata length + priority, weight, and port.
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                ]
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        break
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      case 'IN DS':
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        rdata = [ buf16(record.data.key_tag)
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                , new Buffer([record.data.algorithm])
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                , new Buffer([record.data.digest_type])
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                , new Buffer(record.data.digest)
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                ]
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        break
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      case 'IN SSHFP':
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        rdata = [ new Buffer([record.algorithm])
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                , new Buffer([record.fp_type])
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                , new Buffer(record.fingerprint)
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                ]
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        break
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      case 'NONE A':
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        // I think this is no data, from RFC 2136 S. 2.4.3.
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        rdata = []
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        break
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      default:
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        throw new Error('Unsupported record type: ' + JSON.stringify(record))
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    }
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    // Write the rdata length. (The position was already updated.)
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    rdata = flat(rdata)
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    buf = new Buffer(2)
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    buf.writeUInt16BE(rdata.length, 0)
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    body.push(buf)
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    self.position += 2
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    // Write the rdata.
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    self.position += rdata.length
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    if(rdata.length > 0)
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      body.push(new Buffer(rdata))
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  }
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  self[section_name].push(Buffer.concat(body))
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}
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State.prototype.encode = function(full_domain, position_offset, option) {
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  var self = this
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  var domain = full_domain
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  domain = domain.replace(/\.$/, '') // Strip the trailing dot.
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  position = self.position + (position_offset || 0)
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  var body = []
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    , bytes
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  var i = 0
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  var max_iterations = 127 // Theoretical upper limit for number of labels in a DNS name; see https://en.wikipedia.org/wiki/Subdomain#Overview
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  while(++i < max_iterations) {
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    if(domain == '') {
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      // Encode the root domain and be done.
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      body.push(new Buffer([0]))
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      return Buffer.concat(body)
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    }
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    /* FIXME
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    else if(self.domains[domain] && option !== 'nocompress') {
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      // Encode a pointer and be done.
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      body.push(new Buffer([0xc0, self.domains[domain]]))
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      return Buffer.concat(body)
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    }
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    */
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    else {
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      // Encode the next part of the domain, saving its position in the lookup table for later.
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      self.domains[domain] = position
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      var parts = domain.split(/\./)
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        , car = parts[0]
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      domain = parts.slice(1).join('.')
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      // Write the first part of the domain, with a length prefix.
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      //var part = parts[0]
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      var buf = new Buffer(car.length + 1)
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      buf.write(car, 1, car.length, 'ascii')
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      buf.writeUInt8(car.length, 0)
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      body.push(buf)
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      position += buf.length
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      //bytes.unshift(bytes.length)
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    }
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  }
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  throw new Error('Too many iterations encoding domain: ' + full_domain)
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}
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//
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// Utilities
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//
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function buf32(value) {
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  var buf = new Buffer(4)
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  buf.writeUInt32BE(value, 0)
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  return buf
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}
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function buf16(value) {
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  var buf = new Buffer(2)
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  buf.writeUInt16BE(value, 0)
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  return buf
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}
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function flat(data) {
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  return Buffer.isBuffer(data)
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          ? Array.prototype.slice.call(data)
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          : Array.isArray(data)
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            ? data.reduce(flatten, [])
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            : [data]
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}
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function flatten(state, element) {
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  return (Buffer.isBuffer(element) || Array.isArray(element))
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          ? state.concat(flat(element))
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          : state.concat([element])
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}
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function pair_to_buf(pair) {
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  // Convert a string of two hex bytes, e.g. "89ab" to a buffer.
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  if(! pair.match(/^[0-9a-fA-F]{4}$/))
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    throw new Error('Bad '+record.type+' record data: ' + JSON.stringify(record))
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  return new Buffer(pair, 'hex')
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}
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