require 'socket'
require 'fcntl'
require 'timeout'
require 'thread'

begin
  require 'securerandom'
rescue LoadError
end

# Resolv is a thread-aware DNS resolver library written in Ruby.  Resolv can
# handle multiple DNS requests concurrently without blocking the entire ruby
# interpreter.
#
# See also resolv-replace.rb to replace the libc resolver with Resolv.
#
# Resolv can look up various DNS resources using the DNS module directly.
#
# Examples:
#
#   p Resolv.getaddress "www.ruby-lang.org"
#   p Resolv.getname "210.251.121.214"
#
#   Resolv::DNS.open do |dns|
#     ress = dns.getresources "www.ruby-lang.org", Resolv::DNS::Resource::IN::A
#     p ress.map { |r| r.address }
#     ress = dns.getresources "ruby-lang.org", Resolv::DNS::Resource::IN::MX
#     p ress.map { |r| [r.exchange.to_s, r.preference] }
#   end
#
#
# == Bugs
#
# * NIS is not supported.
# * /etc/nsswitch.conf is not supported.

class Resolv
  
  ##
  # Tests whether we're running on Windows
  
  WINDOWS = /mswin|cygwin|mingw|bccwin/ =~ RUBY_PLATFORM || ::RbConfig::CONFIG['host_os'] =~ /mswin/

  ##
  # Looks up the first IP address for +name+.

  def self.getaddress(name)
    DefaultResolver.getaddress(name)
  end

  ##
  # Looks up all IP address for +name+.

  def self.getaddresses(name)
    DefaultResolver.getaddresses(name)
  end

  ##
  # Iterates over all IP addresses for +name+.

  def self.each_address(name, &block)
    DefaultResolver.each_address(name, &block)
  end

  ##
  # Looks up the hostname of +address+.

  def self.getname(address)
    DefaultResolver.getname(address)
  end

  ##
  # Looks up all hostnames for +address+.

  def self.getnames(address)
    DefaultResolver.getnames(address)
  end

  ##
  # Iterates over all hostnames for +address+.

  def self.each_name(address, &proc)
    DefaultResolver.each_name(address, &proc)
  end

  ##
  # Creates a new Resolv using +resolvers+.

  def initialize(resolvers=[Hosts.new, DNS.new])
    @resolvers = resolvers
  end

  ##
  # Looks up the first IP address for +name+.

  def getaddress(name)
    each_address(name) {|address| return address}
    raise ResolvError.new("no address for #{name}")
  end

  ##
  # Looks up all IP address for +name+.

  def getaddresses(name)
    ret = []
    each_address(name) {|address| ret << address}
    return ret
  end

  ##
  # Iterates over all IP addresses for +name+.

  def each_address(name)
    if AddressRegex =~ name
      yield name
      return
    end
    yielded = false
    @resolvers.each {|r|
      r.each_address(name) {|address|
        yield address.to_s
        yielded = true
      }
      return if yielded
    }
  end

  ##
  # Looks up the hostname of +address+.

  def getname(address)
    each_name(address) {|name| return name}
    raise ResolvError.new("no name for #{address}")
  end

  ##
  # Looks up all hostnames for +address+.

  def getnames(address)
    ret = []
    each_name(address) {|name| ret << name}
    return ret
  end

  ##
  # Iterates over all hostnames for +address+.

  def each_name(address)
    yielded = false
    @resolvers.each {|r|
      r.each_name(address) {|name|
        yield name.to_s
        yielded = true
      }
      return if yielded
    }
  end

  ##
  # Indicates a failure to resolve a name or address.

  class ResolvError < StandardError; end

  ##
  # Indicates a timeout resolving a name or address.

  class ResolvTimeout < TimeoutError; end

  ##
  # Resolv::Hosts is a hostname resolver that uses the system hosts file.

  class Hosts
    if WINDOWS
      require 'win32/resolv'
      DefaultFileName = Win32::Resolv.get_hosts_path
    else
      DefaultFileName = '/etc/hosts'
    end

    ##
    # Creates a new Resolv::Hosts, using +filename+ for its data source.

    def initialize(filename = DefaultFileName)
      @filename = filename
      @mutex = Mutex.new
      @initialized = nil
    end

    def lazy_initialize # :nodoc:
      @mutex.synchronize {
        unless @initialized
          @name2addr = {}
          @addr2name = {}
          open(@filename, 'rb') {|f|
            f.each {|line|
              line.sub!(/#.*/, '')
              addr, hostname, *aliases = line.split(/\s+/)
              next unless addr
              addr.untaint
              hostname.untaint
              @addr2name[addr] = [] unless @addr2name.include? addr
              @addr2name[addr] << hostname
              @addr2name[addr] += aliases
              @name2addr[hostname] = [] unless @name2addr.include? hostname
              @name2addr[hostname] << addr
              aliases.each {|n|
                n.untaint
                @name2addr[n] = [] unless @name2addr.include? n
                @name2addr[n] << addr
              }
            }
          }
          @name2addr.each {|name, arr| arr.reverse!}
          @initialized = true
        end
      }
      self
    end

    ##
    # Gets the IP address of +name+ from the hosts file.

    def getaddress(name)
      each_address(name) {|address| return address}
      raise ResolvError.new("#{@filename} has no name: #{name}")
    end

    ##
    # Gets all IP addresses for +name+ from the hosts file.

    def getaddresses(name)
      ret = []
      each_address(name) {|address| ret << address}
      return ret
    end

    ##
    # Iterates over all IP addresses for +name+ retrieved from the hosts file.

    def each_address(name, &proc)
      lazy_initialize
      if @name2addr.include?(name)
        @name2addr[name].each(&proc)
      end
    end

    ##
    # Gets the hostname of +address+ from the hosts file.

    def getname(address)
      each_name(address) {|name| return name}
      raise ResolvError.new("#{@filename} has no address: #{address}")
    end

    ##
    # Gets all hostnames for +address+ from the hosts file.

    def getnames(address)
      ret = []
      each_name(address) {|name| ret << name}
      return ret
    end

    ##
    # Iterates over all hostnames for +address+ retrieved from the hosts file.

    def each_name(address, &proc)
      lazy_initialize
      if @addr2name.include?(address)
        @addr2name[address].each(&proc)
      end
    end
  end

  ##
  # Resolv::DNS is a DNS stub resolver.
  #
  # Information taken from the following places:
  #
  # * STD0013
  # * RFC 1035
  # * ftp://ftp.isi.edu/in-notes/iana/assignments/dns-parameters
  # * etc.

  class DNS

    ##
    # Default DNS Port

    Port = 53

    ##
    # Default DNS UDP packet size

    UDPSize = 512

    ##
    # Creates a new DNS resolver.  See Resolv::DNS.new for argument details.
    #
    # Yields the created DNS resolver to the block, if given, otherwise
    # returns it.

    def self.open(*args)
      dns = new(*args)
      return dns unless block_given?
      begin
        yield dns
      ensure
        dns.close
      end
    end

    ##
    # Creates a new DNS resolver.
    #
    # +config_info+ can be:
    #
    # nil:: Uses /etc/resolv.conf.
    # String:: Path to a file using /etc/resolv.conf's format.
    # Hash:: Must contain :nameserver, :search and :ndots keys.
    # :nameserver_port can be used to specify port number of nameserver address.
    #
    # The value of :nameserver should be an address string or
    # an array of address strings.
    # - :nameserver => '8.8.8.8'
    # - :nameserver => ['8.8.8.8', '8.8.4.4']
    #
    # The value of :nameserver_port should be an array of
    # pair of nameserver address and port number.
    # - :nameserver_port => [['8.8.8.8', 53], ['8.8.4.4', 53]]
    #
    # Example:
    #
    #   Resolv::DNS.new(:nameserver => ['210.251.121.21'],
    #                   :search => ['ruby-lang.org'],
    #                   :ndots => 1)

    def initialize(config_info=nil)
      @mutex = Mutex.new
      @config = Config.new(config_info)
      @initialized = nil
    end

    def lazy_initialize # :nodoc:
      @mutex.synchronize {