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, ResolverPermissionError, TcpTimeout, UdpTimeout

Constant Summary collapse

Defaults =

A hash with the default 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",
  log_file: $stdout,
  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('::'),
  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),
}.freeze
C = 
Object.const_get(defined?(RbConfig) ? :RbConfig : :Config)::CONFIG

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.



236
237
238
239
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
 
# File 'lib/net/dns/resolver.rb', line 236

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

  @config = Defaults.merge config
  @raw = false

  # New logger facility
  @logger = Logger.new(@config[:log_file])
  @logger.level = $DEBUG ? Logger::DEBUG : Logger::WARN

  #------------------------------------------------------------
  # 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 == :log_file) || (key == :config_file)

    begin
      eval "self.#{key} = val"
    rescue NoMethodError
      raise ArgumentError, "Option #{key} not valid"
    end
  end
end

Class Method Details

.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) 


141
142
143
 
# File 'lib/net/dns/resolver.rb', line 141

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"



132
133
134
 
# File 'lib/net/dns/resolver.rb', line 132

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.



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

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



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

def defname=(bool)
  case bool
  when TrueClass, FalseClass
    @config[:defname] = bool
    @logger.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) 


604
605
606
 
# File 'lib/net/dns/resolver.rb', line 604

def defname?
  @config[:defname]
end

#dns_search ⇒ Object Also known as: dnsrch

Get the state of the dns_search flag.



632
633
634
 
# File 'lib/net/dns/resolver.rb', line 632

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.



640
641
642
643
644
645
646
647
648
 
# File 'lib/net/dns/resolver.rb', line 640

def dns_search=(bool)
  case bool
  when TrueClass, FalseClass
    @config[:dns_search] = bool
    @logger.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 



685
686
687
688
689
690
691
692
693
 
# File 'lib/net/dns/resolver.rb', line 685

def ignore_truncated=(bool)
  case bool
  when TrueClass, FalseClass
    @config[:ignore_truncated] = bool
    @logger.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) 


680
681
682
 
# File 'lib/net/dns/resolver.rb', line 680

def ignore_truncated?
  @config[:ignore_truncated]
end

#log_file=(log) ⇒ Object

Set a new log file for the logger facility of the resolver class. Could be a file descriptor too:

res.log_file = $stderr

Note that a new logging facility will be create, destroing the old one, which will then be impossibile to recover.



772
773
774
775
776
 
# File 'lib/net/dns/resolver.rb', line 772

def log_file=(log)
  @config[:log_file] = log
  @logger = Logger.new(@config[:log_file])
  @logger.level = $DEBUG ? Logger::DEBUG : Logger::WARN
end

#log_level=(level) ⇒ Object

Set the log level for the built-in logging facility.

The log level can be one of the following:

  • Net::DNS::DEBUG

  • Net::DNS::INFO

  • Net::DNS::WARN

  • Net::DNS::ERROR

  • Net::DNS::FATAL

Note that if the global variable $DEBUG is set (like when the -d switch is used at the command line) the logger level is automatically set at DEGUB.

For further informations, see Logger documentation in the Ruby standard library.



819
820
821
 
# File 'lib/net/dns/resolver.rb', line 819

def log_level=(level)
  @logger.level = level
end

#logger=(logger) ⇒ Object

This one permits to have a personal logger facility to handle resolver messages, instead of new built-in one, which is set up for a $stdout (or $stderr) use.

If you want your own logging facility you can create a new instance of the Logger class:

log = Logger.new("/tmp/resolver.log","weekly",2*1024*1024)
log.level = Logger::DEBUG
log.progname = "ruby_resolver"

and then pass it to the resolver:

res.logger = log

Note that this will destroy the precedent logger.



795
796
797
798
799
800
 
# File 'lib/net/dns/resolver.rb', line 795

def logger=(logger)
  logger.is_a?(Logger) or
      raise(ArgumentError, "Argument must be an instance of Logger class")

  @logger = logger
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")



992
993
994
995
996
997
998
 
# File 'lib/net/dns/resolver.rb', line 992

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(&: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"]



320
321
322
323
324
325
326
327
328
329
330
331
 
# File 'lib/net/dns/resolver.rb', line 320

def nameservers
  @config[:nameservers].map do |entry|
    case entry
    in IPAddr
      entry.to_s
    in [IPAddr]
      [entry[0].to_s]
    in [IPAddr, Integer]
      [entry[0].to_s, entry[1]]
    end
  end
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.

res.nameservers = IPAddr.new("192.168.0.3")

The default is 127.0.0.1 (localhost)



347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
 
# File 'lib/net/dns/resolver.rb', line 347

def nameservers=(arg)
  @config[:nameservers] = Array(arg).flat_map do |entry|
    case entry
    in String
      begin
        IPAddr.new(entry)
      rescue ArgumentError
        nameservers_from_name(entry)
      end
    in IPAddr
      entry
    in [String]
      [[IPAddr.new(entry[0])]]
    in [IPAddr]
      [[entry[0]]]
    in [String, Integer]
      validate_port!(entry[1])
      [[IPAddr.new(entry[0]), entry[1]]]
    in [IPAddr, Integer]
      validate_port!(entry[1])
      [[entry[0], entry[1]]]
    else
      raise ArgumentError, "Wrong argument format, neither String, Array nor IPAddr"
    end
  end
  @logger.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

#port ⇒ Object

Get the port number to which the resolver sends queries.

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



395
396
397
 
# File 'lib/net/dns/resolver.rb', line 395

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.



406
407
408
409
410
411
 
# File 'lib/net/dns/resolver.rb', line 406

def port=(num)
  validate_port!(num)

  @config[:port] = num
  @logger.info "Port number changed to #{num}"
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.



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
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
 
# File 'lib/net/dns/resolver.rb', line 902

def query(argument, type = Net::DNS::A, cls = Net::DNS::IN)
  !@config[:nameservers].empty? or
      raise(Resolver::Error, "No nameservers specified!")

  method = :query_udp
  packet = if argument.is_a? 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?
      @logger.info "Sending #{packet_size} bytes using TCP over RAW socket"
      method = :send_raw_tcp
    else
      @logger.info "Sending #{packet_size} bytes using TCP"
      method = :query_tcp
    end
  else # Packet size is inside the boundaries
    if @raw # Use raw sockets?
      @logger.info "Sending #{packet_size} bytes using UDP over RAW socket"
      method = :send_raw_udp
    elsif use_tcp? # User requested TCP
      @logger.info "Sending #{packet_size} bytes using TCP"
      method = :query_tcp
    else # Finally use UDP
      @logger.info "Sending #{packet_size} bytes using UDP"
    end
  end

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

  ans = send(method, packet, packet_data)

  unless ans
    message = "No response from nameservers list"
    @logger.fatal(message)
    raise NoResponseError, message
  end

  @logger.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? && !ignore_truncated?
    @logger.warn "Packet truncated, retrying using TCP"
    self.use_tcp = true
    begin
      return query(argument, type, cls)
    ensure
      self.use_tcp = false
    end
  end

  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



569
570
571
572
573
574
575
576
577
 
# File 'lib/net/dns/resolver.rb', line 569

def recursive=(bool)
  case bool
  when TrueClass, FalseClass
    @config[:recursive] = bool
    @logger.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) 


558
559
560
 
# File 'lib/net/dns/resolver.rb', line 558

def recursive?
  @config[:recursive]
end

#retry_interval ⇒ Object Also known as: retrans

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



517
518
519
 
# File 'lib/net/dns/resolver.rb', line 517

def retry_interval
  @config[:retry_interval]
end

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

Set the retrasmission interval in seconds. Default 5 seconds.



523
524
525
526
527
528
529
 
# File 'lib/net/dns/resolver.rb', line 523

def retry_interval=(num)
  num.positive? or
      raise(ArgumentError, "Interval must be positive")

  @config[:retry_interval] = num
  @logger.info "Retransmission interval changed to #{num} seconds"
end

#retry_number ⇒ Object

The number of times the resolver will try a query.

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



536
537
538
 
# File 'lib/net/dns/resolver.rb', line 536

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.



542
543
544
545
546
547
548
 
# File 'lib/net/dns/resolver.rb', line 542

def retry_number=(num)
  num.is_a?(Integer) && (num > 0) or
      raise(ArgumentError, "Retry value must be a positive integer")

  @config[:retry_number] = num
  @logger.info "Retrasmissions number changed to #{num}"
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.



848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
 
# File 'lib/net/dns/resolver.rb', line 848

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? "."
    @logger.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 !~ /\.$/ && @config[:dns_search]
    @config[:searchlist].each do |domain|
      newname = name + "." + domain
      @logger.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.
  @logger.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"]



284
285
286
 
# File 'lib/net/dns/resolver.rb', line 284

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.



302
303
304
305
306
307
308
309
310
311
312
313
 
# File 'lib/net/dns/resolver.rb', line 302

def searchlist=(arg)
  case arg
  when String
    @config[:searchlist] = [arg] if valid? arg
    @logger.info "Searchlist changed to value #{@config[:searchlist].inspect}"
  when Array
    @config[:searchlist] = arg if arg.all? { |x| valid? x }
    @logger.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}"



445
446
447
 
# File 'lib/net/dns/resolver.rb', line 445

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 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).



479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
 
# File 'lib/net/dns/resolver.rb', line 479

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

  begin
    port = rand(1024..65_023)
    @logger.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!
      @logger.warn "Port already in use"
      retry
    when 99 # Address is not valid: raw socket
      @raw = true
      @logger.warn "Using raw sockets"
    else
      raise SystemCallError, e
    end
  ensure
    a.close
  end

  case addr
  when String
    @config[:source_address] = IPAddr.new(string)
    @logger.info "Using new source address: #{@config[:source_address]}"
  when IPAddr
    @config[:source_address] = addr
    @logger.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



452
453
454
 
# File 'lib/net/dns/resolver.rb', line 452

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}"



417
418
419
 
# File 'lib/net/dns/resolver.rb', line 417

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 privileges, 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.

Raises:



433
434
435
436
437
438
 
# File 'lib/net/dns/resolver.rb', line 433

def source_port=(num)
  raise(ResolverPermissionError, "Are you root?") unless root?
  validate_port!(num)

  @config[:source_port] = num
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



586
587
588
589
590
591
592
593
594
595
596
597
598
599
 
# File 'lib/net/dns/resolver.rb', line 586

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



711
712
713
 
# File 'lib/net/dns/resolver.rb', line 711

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.



723
724
725
726
 
# File 'lib/net/dns/resolver.rb', line 723

def tcp_timeout=(secs)
  @config[:tcp_timeout] = TcpTimeout.new(secs)
  @logger.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.



745
746
747
 
# File 'lib/net/dns/resolver.rb', line 745

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.



759
760
761
762
 
# File 'lib/net/dns/resolver.rb', line 759

def udp_timeout=(secs)
  @config[:udp_timeout] = UdpTimeout.new(secs)
  @logger.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.



669
670
671
672
673
674
675
676
677
 
# File 'lib/net/dns/resolver.rb', line 669

def use_tcp=(bool)
  case bool
  when TrueClass, FalseClass
    @config[:use_tcp] = bool
    @logger.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) 


653
654
655
 
# File 'lib/net/dns/resolver.rb', line 653

def use_tcp?
  @config[:use_tcp]
end