Class: Net::DNS::Resolver

Inherits:
Object
  • Object
show all
Defined in:
lib/net/dns/resolver.rb,
lib/net/dns/resolver/timeouts.rb

Overview

Net::DNS::Resolver - DNS resolver class

The Net::DNS::Resolver class implements a complete DNS resolver written in pure Ruby, without a single C line of code. It has all of the tipical properties of an evoluted resolver, and a bit of OO which comes from having used Ruby.

This project started as a porting of the Net::DNS Perl module, written by Martin Fuhr, but turned out (in the last months) to be an almost complete rewriting. Well, maybe some of the features of the Perl version are still missing, but guys, at least this is readable code!

Environment

The Following Environment variables can also be used to configure the resolver:

  • RES_NAMESERVERS: A space-separated list of nameservers to query.

    # Bourne Shell
$ RES_NAMESERVERS="192.168.1.1 192.168.2.2 192.168.3.3"
$ export RES_NAMESERVERS

# C Shell
% setenv RES_NAMESERVERS "192.168.1.1 192.168.2.2 192.168.3.3"

  • RES_SEARCHLIST: A space-separated list of domains to put in the search list.

    # Bourne Shell
$ RES_SEARCHLIST="example.com sub1.example.com sub2.example.com"
$ export RES_SEARCHLIST

# C Shell
% setenv RES_SEARCHLIST "example.com sub1.example.com sub2.example.com"

  • LOCALDOMAIN: The default domain.

    # Bourne Shell
$ LOCALDOMAIN=example.com
$ export LOCALDOMAIN

# C Shell
% setenv LOCALDOMAIN example.com

  • RES_OPTIONS: A space-separated list of resolver options to set. Options that take values are specified as option:value.

    # Bourne Shell
$ RES_OPTIONS="retrans:3 retry:2 debug"
$ export RES_OPTIONS

# C Shell
% setenv RES_OPTIONS "retrans:3 retry:2 debug"

Defined Under Namespace

Classes: DnsTimeout, Error, NoResponseError, TcpTimeout, UdpTimeout

Constant Summary collapse

Defaults =

An hash with the defaults values of almost all the configuration parameters of a resolver object. See the description for each parameter to have an explanation of its usage.

{
  :config_file => "/etc/resolv.conf",
  :port => 53,
  :searchlist => [],
  :nameservers => [IPAddr.new("127.0.0.1")],
  :domain => "",
  :source_port => 0,
  :source_address => IPAddr.new("0.0.0.0"),
  :source_address_inet6 => IPAddr.new('::'),
  :spoof_mac => false,
  :interface => "eth0",
  :retry_interval => 5,
  :retry_number => 4,
  :recursive => true,
  :defname => true,
  :dns_search => true,
  :use_tcp => false,
  :ignore_truncated => false,
  :packet_size => 512,
  :tcp_timeout => TcpTimeout.new(5),
  :udp_timeout => UdpTimeout.new(5),
}
C = 
Object.const_get(defined?(RbConfig) ? :RbConfig : :Config)::CONFIG
@@logger = 
nil

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(config = {}) ⇒ Resolver

Creates a new resolver object.

Argument config can either be empty or be an hash with some configuration parameters. To know what each parameter do, look at the description of each. Some example:

# Use the sistem defaults
res = Net::DNS::Resolver.new

# Specify a configuration file
res = Net::DNS::Resolver.new(:config_file => '/my/dns.conf')

# Set some option
res = Net::DNS::Resolver.new(:nameservers => "172.16.1.1",
                             :recursive => false,
                             :retry => 10)

Config file

Net::DNS::Resolver uses a config file to read the usual values a resolver needs, such as nameserver list and domain names. On UNIX systems the defaults are read from the following files, in the order indicated:

  • /etc/resolv.conf

  • $HOME/.resolv.conf

  • ./.resolv.conf

The following keywords are recognized in resolver configuration files:

  • domain: the default domain.

  • search: a space-separated list of domains to put in the search list.

  • nameserver: a space-separated list of nameservers to query.

Files except for /etc/resolv.conf must be owned by the effective userid running the program or they won’t be read. In addition, several environment variables can also contain configuration information; see Environment in the main description for Resolver class.

On Windows Systems, an attempt is made to determine the system defaults using the registry. This is still a work in progress; systems with many dynamically configured network interfaces may confuse Net::DNS.

You can include a configuration file of your own when creating a resolver object:

# Use my own configuration file
my $res = Net::DNS::Resolver->new(config_file => '/my/dns.conf');

This is supported on both UNIX and Windows. Values pulled from a custom configuration file override the the system’s defaults, but can still be overridden by the other arguments to Resolver::new.

Explicit arguments to Resolver::new override both the system’s defaults and the values of the custom configuration file, if any.

Parameters

The following arguments to Resolver::new are supported:

  • nameservers: an array reference of nameservers to query.

  • searchlist: an array reference of domains.

  • recurse

  • debug

  • domain

  • port

  • srcaddr

  • srcport

  • tcp_timeout

  • udp_timeout

  • retrans

  • retry

  • usevc

  • stayopen

  • igntc

  • defnames

  • dnsrch

  • persistent_tcp

  • persistent_udp

  • dnssec

For more information on any of these options, please consult the method of the same name.

Disclaimer

Part of the above documentation is taken from the one in the Net::DNS::Resolver Perl module.

Raises:

  • (ArgumentError) 


240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
 
# File 'lib/net/dns/resolver.rb', line 240

def initialize(config = {})
  raise ArgumentError, "Expected `config' to be a Hash" unless config.is_a?(Hash)

  # config.downcase_keys!
  @config = Defaults.merge config
  @raw = false

  #------------------------------------------------------------
  # Resolver configuration will be set in order from:
  # 1) initialize arguments
  # 2) ENV variables
  # 3) config file
  # 4) defaults (and /etc/resolv.conf for config)
  #------------------------------------------------------------



  #------------------------------------------------------------
  # Parsing config file
  #------------------------------------------------------------
  parse_config_file

  #------------------------------------------------------------
  # Parsing ENV variables
  #------------------------------------------------------------
  parse_environment_variables

  #------------------------------------------------------------
  # Parsing arguments
  #------------------------------------------------------------
  config.each do |key,val|
    next if key == :config_file
    begin
      eval "self.#{key.to_s} = val"
    rescue NoMethodError
      raise ArgumentError, "Option #{key} not valid"
    end
  end
end

Instance Attribute Details

#spoof_mac ⇒ Object

Returns the value of attribute spoof_mac.



280
281
282
 
# File 'lib/net/dns/resolver.rb', line 280

def spoof_mac
  @spoof_mac
end

Class Method Details

.logger=(logger) ⇒ Object 



282
283
284
285
286
287
288
 
# File 'lib/net/dns/resolver.rb', line 282

def self.logger= logger
  if logger.respond_to?(:warn) && logger.respond_to?(:debug) && logger.respond_to?(:info)
    @@logger = logger
  else
    raise ArgumentError, "Invalid logger provided to #{self.class}"
  end
end

.platform_windows? ⇒ Boolean

Returns true if running on a Windows platform.

Note. This method doesn’t rely on the RUBY_PLATFORM constant because the comparison will fail when running on JRuby. On JRuby RUBY_PLATFORM == ‘java’.

Returns:

  • (Boolean) 


143
144
145
 
# File 'lib/net/dns/resolver.rb', line 143

def platform_windows?
  !!(C["host_os"] =~ /msdos|mswin|djgpp|mingw/i)
end

.start(*params) ⇒ Object

Quick resolver method. Bypass the configuration using the defaults.

Net::DNS::Resolver.start "www.google.com"



134
135
136
 
# File 'lib/net/dns/resolver.rb', line 134

def start(*params)
  new.search(*params)
end

Instance Method Details

#axfr(name, cls = Net::DNS::IN) ⇒ Object

Performs a zone transfer for the zone passed as a parameter.

It is actually only a wrapper to a send with type set as Net::DNS::AXFR, since it is using the same infrastucture.



961
962
963
964
 
# File 'lib/net/dns/resolver.rb', line 961

def axfr(name, cls = Net::DNS::IN)
  info "Requested AXFR transfer, zone #{name} class #{cls}"
  query(name, Net::DNS::AXFR, cls)
end

#debug(*args) ⇒ Object 



296
297
298
299
300
 
# File 'lib/net/dns/resolver.rb', line 296

def debug *args
  if @@logger
    @debug *args
  end
end

#defname=(bool) ⇒ Object

Set the flag defname in a boolean state. if defname is true, calls to Resolver#query will append the default domain to names that contain no dots. Example:

# Domain example.com
res.defname = true
res.query("machine1")
  #=> This will perform a query for machine1.example.com

Default is true.



651
652
653
654
655
656
657
658
659
 
# File 'lib/net/dns/resolver.rb', line 651

def defname=(bool)
  case bool
  when TrueClass,FalseClass
    @config[:defname] = bool
    info("Defname state changed to #{bool}")
  else
    raise ArgumentError, "Argument must be boolean"
  end
end

#defname? ⇒ Boolean Also known as: defname

Checks whether the defname flag has been activate.

Returns:

  • (Boolean) 


634
635
636
 
# File 'lib/net/dns/resolver.rb', line 634

def defname?
  @config[:defname]
end

#dns_search ⇒ Object Also known as: dnsrch

Get the state of the dns_search flag.



662
663
664
 
# File 'lib/net/dns/resolver.rb', line 662

def dns_search
  @config[:dns_search]
end

#dns_search=(bool) ⇒ Object Also known as: dnsrch=

Set the flag dns_search in a boolean state. If dns_search is true, when using the Resolver#search method will be applied the search list. Default is true.



670
671
672
673
674
675
676
677
678
 
# File 'lib/net/dns/resolver.rb', line 670

def dns_search=(bool)
  case bool
  when TrueClass,FalseClass
    @config[:dns_search] = bool
    info("DNS search state changed to #{bool}")
  else
    raise ArgumentError, "Argument must be boolean"
  end
end

#domain ⇒ Object

Return a string with the default domain.



377
378
379
 
# File 'lib/net/dns/resolver.rb', line 377

def domain
  @config[:domain].inspect
end

#domain=(name) ⇒ Object

Set the domain for the query.



382
383
384
 
# File 'lib/net/dns/resolver.rb', line 382

def domain=(name)
  @config[:domain] = name if valid? name
end

#ignore_truncated=(bool) ⇒ Object 



715
716
717
718
719
720
721
722
723
 
# File 'lib/net/dns/resolver.rb', line 715

def ignore_truncated=(bool)
  case bool
  when TrueClass,FalseClass
    @config[:ignore_truncated] = bool
    info("Ignore truncated flag changed to #{bool}")
  else
    raise ArgumentError, "Argument must be boolean"
  end
end

#ignore_truncated? ⇒ Boolean Also known as: ignore_truncated

Returns:

  • (Boolean) 


710
711
712
 
# File 'lib/net/dns/resolver.rb', line 710

def ignore_truncated?
  @config[:ignore_truncated]
end

#info(*args) ⇒ Object 



302
303
304
305
306
 
# File 'lib/net/dns/resolver.rb', line 302

def info *args
  if @@logger
    @@logger.info *args
  end
end

#interface ⇒ Object 



471
472
473
 
# File 'lib/net/dns/resolver.rb', line 471

def interface
  @config[:interface]
end

#interface=(iface) ⇒ Object 



539
540
541
 
# File 'lib/net/dns/resolver.rb', line 539

def interface=(iface)
  @config[:interface] = iface
end

#mx(name, cls = Net::DNS::IN) ⇒ Object

Performs an MX query for the domain name passed as parameter.

It actually uses the same methods a normal Resolver query would use, but automatically sort the results based on preferences and returns an ordered array.

res = Net::DNS::Resolver.new
res.mx("google.com")



975
976
977
978
979
980
981
 
# File 'lib/net/dns/resolver.rb', line 975

def mx(name, cls = Net::DNS::IN)
  arr = []
  query(name, Net::DNS::MX, cls).answer.each do |entry|
    arr << entry if entry.type == 'MX'
  end
  arr.sort_by { |a| a.preference }
end

#nameservers ⇒ Object Also known as: nameserver

Get the list of resolver nameservers, in a dotted decimal format-

res.nameservers
  #=> ["192.168.0.1","192.168.0.2"]



350
351
352
 
# File 'lib/net/dns/resolver.rb', line 350

def nameservers
  @config[:nameservers].map(&:to_s)
end

#nameservers=(arg) ⇒ Object Also known as: nameserver=

Set the list of resolver nameservers. arg can be a single ip address or an array of addresses.

res.nameservers = "192.168.0.1"
res.nameservers = ["192.168.0.1","192.168.0.2"]

If you want you can specify the addresses as IPAddr instances.

ip = IPAddr.new("192.168.0.3")
res.nameservers << ip
#=> ["192.168.0.1","192.168.0.2","192.168.0.3"]

The default is 127.0.0.1 (localhost)



370
371
372
373
 
# File 'lib/net/dns/resolver.rb', line 370

def nameservers=(arg)
  @config[:nameservers] = convert_nameservers_arg_to_ips(arg)
  info "Nameservers list changed to value #{@config[:nameservers].inspect}"
end

#packet_size ⇒ Object

Return the defined size of the packet.



387
388
389
 
# File 'lib/net/dns/resolver.rb', line 387

def packet_size
  @config[:packet_size]
end

#packet_size=(arg) ⇒ Object 



391
392
393
394
395
396
397
398
 
# File 'lib/net/dns/resolver.rb', line 391

def packet_size=(arg)
  if arg.respond_to? :to_i
    @config[:packet_size] = arg.to_i
    info "Packet size changed to value #{@config[:packet_size].inspect}"
  else
    @logger.error "Packet size not set, #{arg.class} does not respond to to_i"
  end
end

#port ⇒ Object

Get the port number to which the resolver sends queries.

puts "Sending queries to port #{res.port}"



404
405
406
 
# File 'lib/net/dns/resolver.rb', line 404

def port
  @config[:port]
end

#port=(num) ⇒ Object

Set the port number to which the resolver sends queries. This can be useful for testing a nameserver running on a non-standard port.

res.port = 10053

The default is port 53.



415
416
417
418
419
420
421
422
 
# File 'lib/net/dns/resolver.rb', line 415

def port=(num)
  if (0..65535).include? num
    @config[:port] = num
    info "Port number changed to #{num}"
  else
    raise ArgumentError, "Wrong port number #{num}"
  end
end

#query(argument, type = Net::DNS::A, cls = Net::DNS::IN) ⇒ Object

Performs a DNS query for the given name. Neither the searchlist nor the default domain will be appended.

The argument list can be either a Net::DNS::Packet object or a name string plus optional type and class, which if omitted default to A and IN.

Returns a Net::DNS::Packet object.

# Executes the query with a +Packet+ object
send_packet = Net::DNS::Packet.new("host.example.com", Net::DNS::NS, Net::DNS::HS)
packet = res.query(send_packet)

# Executes the query with a host, type and cls
packet = res.query("host.example.com")
packet = res.query("host.example.com", Net::DNS::NS)
packet = res.query("host.example.com", Net::DNS::NS, Net::DNS::HS)

If the name is an IP address (Ipv4 or IPv6), in the form of a string or a IPAddr object, then an appropriate PTR query will be performed:

ip = IPAddr.new("172.16.100.2")
packet = res.query(ip)

packet = res.query("172.16.100.2")

Use packet.header.ancount or packet.answer to find out if there were any records in the answer section.



875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
 
# File 'lib/net/dns/resolver.rb', line 875

def query(argument, type = Net::DNS::A, cls = Net::DNS::IN)
  if @config[:nameservers].size == 0
    raise Resolver::Error, "No nameservers specified!"
  end

  method = :query_udp
  packet = if argument.kind_of? Net::DNS::Packet
    argument
  else
    make_query_packet(argument, type, cls)
  end

  # Store packet_data for performance improvements,
  # so methods don't keep on calling Packet#data
  packet_data = packet.data
  packet_size = packet_data.size

  # Choose whether use TCP, UDP or RAW
  if packet_size > @config[:packet_size] # Must use TCP, either plain or raw
    if @raw # Use raw sockets?
      info "Sending #{packet_size} bytes using TCP over RAW socket"
      method = :send_raw_tcp
    else
      info "Sending #{packet_size} bytes using TCP"
      method = :query_tcp
    end
  else # Packet size is inside the boundaries
    if @raw # Use raw sockets?
      info "Sending #{packet_size} bytes using UDP over RAW socket"
      method = :send_raw_udp
    elsif use_tcp? # User requested TCP
      info "Sending #{packet_size} bytes using TCP"
      method = :query_tcp
    else # Finally use UDP
      info "Sending #{packet_size} bytes using UDP"
      method = :query_udp
    end
  end

  if type == Net::DNS::AXFR
    if @raw
      info "AXFR query, switching to TCP over RAW socket"
      method = :send_raw_tcp
    else
      info "AXFR query, switching to TCP"
      method = :query_tcp
    end
  end

  ans = self.send(method, packet, packet_data)

  # Don't have any responses with the raw,
  # since currently raw is only used when source_address is changed
  if @raw
    return nil
  end

  if not ans
    message = "No response from nameservers list"
    # NoMethodError: undefined method `fatal' for nil:NilClass
    #@logger.fatal(message)
    warn(message)
    raise NoResponseError, message
  end

  info "Received #{ans[0].size} bytes from #{ans[1][2]+":"+ans[1][1].to_s}"
  response = Net::DNS::Packet.parse(ans[0],ans[1])

  if response.header.truncated? and not ignore_truncated?
    info "Packet truncated, retrying using TCP"
    self.use_tcp = true
    begin
      return query(argument,type,cls)
    ensure
      self.use_tcp = false
    end
  end

  return response
end

#recursive=(bool) ⇒ Object Also known as: recurse=

Sets whether or not the resolver should perform recursive queries. Default is true.

res.recursive = false # perform non-recursive query



599
600
601
602
603
604
605
606
607
 
# File 'lib/net/dns/resolver.rb', line 599

def recursive=(bool)
  case bool
  when TrueClass,FalseClass
    @config[:recursive] = bool
    info("Recursive state changed to #{bool}")
  else
    raise ArgumentError, "Argument must be boolean"
  end
end

#recursive? ⇒ Boolean Also known as: recurse, recursive

This method will return true if the resolver is configured to perform recursive queries.

print "The resolver will perform a "
print res.recursive? ? "" : "not "
puts "recursive query"

Returns:

  • (Boolean) 


588
589
590
 
# File 'lib/net/dns/resolver.rb', line 588

def recursive?
  @config[:recursive]
end

#retry_interval ⇒ Object Also known as: retrans

Return the retrasmission interval (in seconds) the resolvers has been set on.



545
546
547
 
# File 'lib/net/dns/resolver.rb', line 545

def retry_interval
  @config[:retry_interval]
end

#retry_interval=(num) ⇒ Object Also known as: retrans=

Set the retrasmission interval in seconds. Default 5 seconds.



551
552
553
554
555
556
557
558
 
# File 'lib/net/dns/resolver.rb', line 551

def retry_interval=(num)
  if num > 0
    @config[:retry_interval] = num
    info "Retransmission interval changed to #{num} seconds"
  else
    raise ArgumentError, "Interval must be positive"
  end
end

#retry_number ⇒ Object

The number of times the resolver will try a query.

puts "Will try a max of #{res.retry_number} queries"



565
566
567
 
# File 'lib/net/dns/resolver.rb', line 565

def retry_number
  @config[:retry_number]
end

#retry_number=(num) ⇒ Object Also known as: retry=

Set the number of times the resolver will try a query. Default 4 times.



571
572
573
574
575
576
577
578
 
# File 'lib/net/dns/resolver.rb', line 571

def retry_number=(num)
  if num.kind_of? Integer and num > 0
    @config[:retry_number] = num
    info "Retrasmissions number changed to #{num}"
  else
    raise ArgumentError, "Retry value must be a positive integer"
  end
end

#search(name, type = Net::DNS::A, cls = Net::DNS::IN) ⇒ Object

Performs a DNS query for the given name, applying the searchlist if appropriate. The search algorithm is as follows:

  1. If the name contains at least one dot, try it as is.

  2. If the name doesn’t end in a dot then append each item in the search list to the name. This is only done if dns_search is true.

  3. If the name doesn’t contain any dots, try it as is.

The record type and class can be omitted; they default to A and IN.

packet = res.search('mailhost')
packet = res.search('mailhost.example.com')
packet = res.search('example.com', Net::DNS::MX)
packet = res.search('user.passwd.example.com', Net::DNS::TXT, Net::DNS::HS)

If the name is an IP address (Ipv4 or IPv6), in the form of a string or a IPAddr object, then an appropriate PTR query will be performed:

ip = IPAddr.new("172.16.100.2")
packet = res.search(ip)
packet = res.search("192.168.10.254")

Returns a Net::DNS::Packet object. If you need to examine the response packet whether it contains any answers or not, use the Resolver#query method instead.



819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
 
# File 'lib/net/dns/resolver.rb', line 819

def search(name,type=Net::DNS::A,cls=Net::DNS::IN)

  return query(name,type,cls) if name.class == IPAddr

  # If the name contains at least one dot then try it as is first.
  if name.include? "."
    debug "Search(#{name},#{Net::DNS::RR::Types.new(type)},#{Net::DNS::RR::Classes.new(cls)})"
    ans = query(name,type,cls)
    return ans if ans.header.anCount > 0
  end

  # If the name doesn't end in a dot then apply the search list.
  if name !~ /\.$/ and @config[:dns_search]
    @config[:searchlist].each do |domain|
      newname = name + "." + domain
      debug "Search(#{newname},#{Net::DNS::RR::Types.new(type)},#{Net::DNS::RR::Classes.new(cls)})"
      ans = query(newname,type,cls)
      return ans if ans.header.anCount > 0
    end
  end

  # Finally, if the name has no dots then try it as is.
  debug "Search(#{name},#{Net::DNS::RR::Types.new(type)},#{Net::DNS::RR::Classes.new(cls)})"
  query(name+".",type,cls)

end

#searchlist ⇒ Object

Get the resolver search list, returned as an array of entries.

res.searchlist
#=> ["example.com","a.example.com","b.example.com"]



314
315
316
 
# File 'lib/net/dns/resolver.rb', line 314

def searchlist
  @config[:searchlist].inspect
end

#searchlist=(arg) ⇒ Object

Set the resolver searchlist. arg can be a single string or an array of strings.

res.searchstring = "example.com"
res.searchstring = ["example.com","a.example.com","b.example.com"]

Note that you can also append a new name to the searchlist.

res.searchlist << "c.example.com"
res.searchlist
#=> ["example.com","a.example.com","b.example.com","c.example.com"]

The default is an empty array.



332
333
334
335
336
337
338
339
340
341
342
343
 
# File 'lib/net/dns/resolver.rb', line 332

def searchlist=(arg)
  case arg
  when String
    @config[:searchlist] = [arg] if valid? arg
    info "Searchlist changed to value #{@config[:searchlist].inspect}"
  when Array
    @config[:searchlist] = arg if arg.all? {|x| valid? x}
    info "Searchlist changed to value #{@config[:searchlist].inspect}"
  else
    raise ArgumentError, "Wrong argument format, neither String nor Array"
  end
end

#source_address ⇒ Object Also known as: srcaddr

Get the local address from which the resolver sends queries

puts "Sending queries using source address #{res.source_address}"



460
461
462
 
# File 'lib/net/dns/resolver.rb', line 460

def source_address
  @config[:source_address].to_s
end

#source_address=(addr) ⇒ Object Also known as: srcaddr=

Set the local source address from which the resolver sends its queries.

res.source_address = "172.16.100.1"
res.source_address = IPAddr.new("172.16.100.1")

You can specify arg as either a string containing the ip address or an instance of IPAddr class.

Normally this can be used to force queries out a specific interface on a multi-homed host. In this case, you should of course need to know the addresses of the interfaces.

Another way to use this option is for some kind of spoofing attacks towards weak nameservers, to probe the security of your network. This includes specifing ranged attacks such as DoS and others. For a paper on DNS security, checks htpt://www.marcoceresa.com/security/

Note that if you want to set a non-binded source address you need root priviledges, as raw sockets will be used to generate packets. The class will then generate an exception if you’re not root.

The default is 0.0.0.0, meaning any local address (chosen on routing needs).



498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
 
# File 'lib/net/dns/resolver.rb', line 498

def source_address=(addr)
  unless addr.respond_to? :to_s
    raise ArgumentError, "Wrong address argument #{addr}"
  end

  begin
    port = rand(64000)+1024
    info "Try to determine state of source address #{addr} with port #{port}"
    a = TCPServer.new(addr.to_s,port)
  rescue SystemCallError => e
    case e.errno
    when 98 # Port already in use!
      info "Port already in use"
      retry
    when 99 # Address is not valid: raw socket
      if Process.uid == 0
        @raw = true
        info "Using raw sockets"
      else
        raise RuntimeError, "Raw sockets requested but not running as root."
      end
    else
      raise SystemCallError, e
    end
  else
    a.close
  end

  case addr
  when String
    @config[:source_address] = IPAddr.new(addr)
    info "Using new source address: #{@config[:source_address]}"
  when IPAddr
    @config[:source_address] = addr
    info "Using new source address: #{@config[:source_address]}"
  else
    raise ArgumentError, "Unknown dest_address format"
  end
end

#source_address_inet6 ⇒ Object

Get the local ipv6 address from which the resolver sends queries



467
468
469
 
# File 'lib/net/dns/resolver.rb', line 467

def source_address_inet6
  @config[:source_address_inet6].to_s
end

#source_port ⇒ Object Also known as: srcport

Get the value of the source port number.

puts "Sending queries using port #{res.source_port}"



428
429
430
 
# File 'lib/net/dns/resolver.rb', line 428

def source_port
  @config[:source_port]
end

#source_port=(num) ⇒ Object Also known as: srcport=

Set the local source port from which the resolver sends its queries.

res.source_port = 40000

Note that if you want to set a port you need root priviledges, as raw sockets will be used to generate packets. The class will then generate the exception ResolverPermissionError if you’re not root.

The default is 0, which means that the port will be chosen by the underlaying layers.



444
445
446
447
448
449
450
451
452
453
 
# File 'lib/net/dns/resolver.rb', line 444

def source_port=(num)
  unless root?
    raise ResolverPermissionError, "Are you root?"
  end
  if (0..65535).include?(num)
    @config[:source_port] = num
  else
    raise ArgumentError, "Wrong port number #{num}"
  end
end

#state ⇒ Object Also known as: print, inspect

Return a string representing the resolver state, suitable for printing on the screen.

puts "Resolver state:"
puts res.state



616
617
618
619
620
621
622
623
624
625
626
627
628
629
 
# File 'lib/net/dns/resolver.rb', line 616

def state
  str = ";; RESOLVER state:\n;; "
  i = 1
  @config.each do |key,val|
    if key == :log_file or key == :config_file
      str << "#{key}: #{val} \t"
    else
      str << "#{key}: #{eval(key.to_s)} \t"
    end
    str << "\n;; " if i % 2 == 0
    i += 1
  end
  str
end

#tcp_timeout ⇒ Object

Return an object representing the value of the stored TCP timeout the resolver will use in is queries. This object is an instance of the class TcpTimeout, and two methods are available for printing informations: TcpTimeout#to_s and TcpTimeout#pretty_to_s.

Here’s some example:

puts "Timeout of #{res.tcp_timeout} seconds" # implicit to_s
  #=> Timeout of 150 seconds

puts "You set a timeout of " + res.tcp_timeout.pretty_to_s
  #=> You set a timeout of 2 minutes and 30 seconds

If the timeout is infinite, a string “infinite” will be returned.



741
742
743
 
# File 'lib/net/dns/resolver.rb', line 741

def tcp_timeout
  @config[:tcp_timeout].to_s
end

#tcp_timeout=(secs) ⇒ Object

Set the value of TCP timeout for resolver queries that will be performed using TCP. A value of 0 means that the timeout will be infinite. The value is stored internally as a TcpTimeout object, see the description for Resolver#tcp_timeout

Default is 5 seconds.



753
754
755
756
 
# File 'lib/net/dns/resolver.rb', line 753

def tcp_timeout=(secs)
  @config[:tcp_timeout] = TcpTimeout.new(secs)
  info("New TCP timeout value: #{@config[:tcp_timeout]} seconds")
end

#udp_timeout ⇒ Object

Return an object representing the value of the stored UDP timeout the resolver will use in is queries. This object is an instance of the class UdpTimeout, and two methods are available for printing information: UdpTimeout#to_s and UdpTimeout#pretty_to_s.

Here’s some example:

puts "Timeout of #{res.udp_timeout} seconds" # implicit to_s
  #=> Timeout of 150 seconds

puts "You set a timeout of " + res.udp_timeout.pretty_to_s
  #=> You set a timeout of 2 minutes and 30 seconds

If the timeout is zero, a string “not defined” will be returned.



775
776
777
 
# File 'lib/net/dns/resolver.rb', line 775

def udp_timeout
  @config[:udp_timeout].to_s
end

#udp_timeout=(secs) ⇒ Object

Set the value of UDP timeout for resolver queries that will be performed using UDP. A value of 0 means that the timeout will not be used, and the resolver will use only retry_number and retry_interval parameters.

Default is 5 seconds.

The value is stored internally as a UdpTimeout object, see the description for Resolver#udp_timeout.



789
790
791
792
 
# File 'lib/net/dns/resolver.rb', line 789

def udp_timeout=(secs)
  @config[:udp_timeout] = UdpTimeout.new(secs)
  info("New UDP timeout value: #{@config[:udp_timeout]} seconds")
end

#use_tcp=(bool) ⇒ Object Also known as: usevc=

If use_tcp is true, the resolver will perform all queries using TCP virtual circuits instead of UDP datagrams, which is the default for the DNS protocol.

res.use_tcp = true
res.query "host.example.com"
  #=> Sending TCP segments...

Default is false.



699
700
701
702
703
704
705
706
707
 
# File 'lib/net/dns/resolver.rb', line 699

def use_tcp=(bool)
  case bool
  when TrueClass,FalseClass
    @config[:use_tcp] = bool
    info("Use tcp flag changed to #{bool}")
  else
    raise ArgumentError, "Argument must be boolean"
  end
end

#use_tcp? ⇒ Boolean Also known as: usevc, use_tcp

Get the state of the use_tcp flag.

Returns:

  • (Boolean) 


683
684
685
 
# File 'lib/net/dns/resolver.rb', line 683

def use_tcp?
  @config[:use_tcp]
end

#warn(*args) ⇒ Object 



290
291
292
293
294
 
# File 'lib/net/dns/resolver.rb', line 290

def warn *args
  if @@logger
    @@logger.warn *args
  end
end