git ssb

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// Copyright 2012 Iris Couch, all rights reserved.
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//
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// Parse DNS messages
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var util = require('util')
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var constants = require('./constants')
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module.exports = { 'id': id
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                 , 'qr': qr
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                 , 'aa': aa
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                 , 'tc': tc
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                 , 'rd': rd
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                 , 'ra': ra
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                 , 'ad': ad
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                 , 'cd': cd
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                 , 'rcode': rcode
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                 , 'opcode': opcode
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                 , 'record_count': record_count
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                 , 'record_name' : record_name
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                 , 'record_class': record_class
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                 , 'record_ttl'  : record_ttl
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                 , 'record_type' : record_type
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                 , 'record_data' : record_data
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                 , 'uncompress'  : uncompress
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                 , 'sections'    : sections
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                 , 'mx': mx
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                 , 'srv': srv
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                 , 'soa': soa
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                 , 'txt': txt
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                 , 'sshfp': sshfp
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                 }
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function id(msg) {
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  return msg.readUInt16BE(0)
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}
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function qr(msg) {
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  return msg.readUInt8(2) >> 7
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}
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function opcode(msg) {
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  return (msg.readUInt8(2) >> 3) & 0x0f
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}
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function aa(msg) {
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  return (msg.readUInt8(2) >> 2) & 0x01
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}
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function tc(msg) {
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  return (msg.readUInt8(2) >> 1) & 0x01
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}
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function rd(msg) {
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  return msg.readUInt8(2) & 0x01
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}
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function ra(msg) {
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  return msg.readUInt8(3) >> 7
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}
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function ad(msg) {
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  return msg.readUInt8(3) >> 5 & 0x01
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}
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function cd(msg) {
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  return msg.readUInt8(3) >> 4 & 0x01
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}
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function rcode(msg) {
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  return msg.readUInt8(3) & 0x0f
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}
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function record_count(msg, name) {
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  if(name == 'question')
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    return msg.readUInt16BE(4)
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  else if(name == 'answer')
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    return msg.readUInt16BE(6)
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  else if(name == 'authority')
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    return msg.readUInt16BE(8)
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  else if(name == 'additional')
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    return msg.readUInt16BE(10)
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  else
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    throw new Error('Unknown section name: ' + name)
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}
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function record_name(msg, section_name, offset) {
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  var rec = record(msg, section_name, offset)
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  return rec.name
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}
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function record_class(msg, section_name, offset) {
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  var rec = record(msg, section_name, offset)
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  return rec.class
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}
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function record_type(msg, section_name, offset) {
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  var rec = record(msg, section_name, offset)
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  return rec.type
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}
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function record_ttl(msg, section_name, offset) {
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  var rec = record(msg, section_name, offset)
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  return rec.ttl
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}
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function record_data(msg, section_name, offset) {
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  var rec = record(msg, section_name, offset)
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  return rec.data
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}
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function record_class(msg, section_name, offset) {
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  var rec = record(msg, section_name, offset)
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  return rec.class
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}
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function record(msg, section_name, offset) {
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  if(typeof offset != 'number' || isNaN(offset) || offset < 0)
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    throw new Error('Offset must be a natural number')
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  // Support msg being a previously-parsed sections object.
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  var sects = Buffer.isBuffer(msg)
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                ? sections(msg)
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                : msg
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  var records = sects[section_name]
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  if(!records)
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    throw new Error('No such section: "'+section_name+'"')
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  var rec = records[offset]
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  if(!rec)
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    throw new Error('Bad offset for section "'+section_name+'": ' + offset)
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  return rec
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}
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function sections(msg) {
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  // Count the times this message has been parsed, for debugging and testing purposes.
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  if('__parsed' in msg)
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    msg.__parsed += 1
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  var position = 12 // First byte of the first section
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    , result = {'question':[], 'answer':[], 'authority':[], 'additional':[]}
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    , need = { 'question'  : record_count(msg, 'question')
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             , 'answer'    : record_count(msg, 'answer')
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             , 'authority' : record_count(msg, 'authority')
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             , 'additional': record_count(msg, 'additional')
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             }
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  var states = ['question', 'answer', 'authority', 'additional', 'done']
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    , state = states.shift()
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  while(true) {
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    if(state == 'done')
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      return result
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    else if(result[state].length == need[state])
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      state = states.shift()
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    else if(!state)
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      throw new Error('Unknown parsing state at position '+position+': '+JSON.stringify(state))
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    else
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      add_record()
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  }
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  function add_record() {
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    var record = {}
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    var data = domain_parts(msg, position)
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    record.name = data.parts.join('.')
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    position += data.length
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    record.type  = msg.readUInt16BE(position + 0)
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    record.class = msg.readUInt16BE(position + 2)
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    position += 4
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    if(state != 'question') {
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      record.ttl    = msg.readUInt32BE(position + 0)
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      var rdata_len = msg.readUInt16BE(position + 4)
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      position += 6
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      record.data = msg.slice(position, position + rdata_len)
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      position += rdata_len
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      if(constants.type(record.type) === 'OPT') {
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        // EDNS
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        if(record.name !== '')
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          throw new Error('EDNS record option for non-root domain: ' + record.name)
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        record.udp_size = record.class
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        delete record.class
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        record.extended_rcode = (record.ttl >> 24)
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        record.edns_version   = (record.ttl >> 16) & 0xff
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        record.zero           = (record.ttl >>  8)
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        delete record.ttl
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        record.data = Array.prototype.slice.call(record.data)
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      }
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    }
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    result[state] = result[state] || []
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    result[state].push(record)
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  }
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}
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function mx(msg, data) {
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  return [ data.readUInt16BE(0)
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         , uncompress(msg, data.slice(2))
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         ]
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}
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function srv(msg, data) {
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  return { 'priority': data.readUInt16BE(0)
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         , 'weight'  : data.readUInt16BE(2)
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         , 'port'    : data.readUInt16BE(4)
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         , 'target'  : uncompress(msg, data.slice(6)) // Techncially compression is not allowed in RFC 2782.
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         }
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}
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function soa(msg, data) {
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  var result = domain_parts(msg, data)
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    , offset = result.length
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    , mname = result.parts.join('.')
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  result = domain_parts(msg, data.slice(offset))
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  var rname = result.parts.join('.')
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  offset += result.length
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  return { 'mname'  : mname
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         , 'rname'  : rname //.replace(/\./, '@')
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         , 'serial' : data.readUInt32BE(offset + 0)
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         , 'refresh': data.readUInt32BE(offset + 4)
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         , 'retry'  : data.readUInt32BE(offset + 8)
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         , 'expire' : data.readUInt32BE(offset + 12)
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         , 'ttl'    : data.readUInt32BE(offset + 16)
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         }
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}
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function txt(msg, data) {
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  var parts = []
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  while(data.length) {
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    var len = data.readUInt8(0)
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    parts.push(data.slice(1, 1+len).toString('ascii'))
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    data = data.slice(1+len)
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  }
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  return parts
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}
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function sshfp(msg, data) {
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  return { 'algorithm': data.readUInt8(0)
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         , 'fp_type'  : data.readUInt8(1)
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         , 'fingerprint'  : data.slice(2)
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         }
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}
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function uncompress(msg, offset) {
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  var data = domain_parts(msg, offset)
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  return data.parts.join('.')
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}
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function domain_parts(msg, offset) {
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  if(Buffer.isBuffer(offset)) {
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    var full_message = msg
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    msg = offset
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    offset = 0
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  }
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  if(typeof offset != 'number' || isNaN(offset) || offset < 0 || offset > msg.length)
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    throw new Error('Bad offset: ' + offset)
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  var parts = []
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    , real_length = 0
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    , jumped = false
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  var i = 0
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  while(true) {
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    if(++i >= 100)
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      throw new Error('Too many iterations uncompressing name')
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    var byte = msg.readUInt8(offset)
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      , flags = byte >> 6
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      , len   = byte & 0x3f // 0 - 63
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    offset += 1
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    add_length(1)
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    if(flags === 0x03) {
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      offset = (len << 8) + msg.readUInt8(offset)
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      add_length(1)
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      jumped = true
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      // If processing so far has just been on some given fragment, begin using the full message now.
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      msg = full_message || msg
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    }
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    else if(len == 0)
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      return {'parts':parts, 'length':real_length}
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    else {
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      parts.push(msg.toString('ascii', offset, offset + len))
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      offset += len
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      add_length(len)
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    }
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  }
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  function add_length(amount) {
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    if(! jumped)
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      real_length += amount
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  }
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}
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