Class: Resolv::DNS

Inherits:
Object
  • Object
show all
Defined in:
lib/resolv.rb

Overview

Resolv::DNS is a DNS stub resolver.

Information taken from the following places:

Direct Known Subclasses

MDNS

Defined Under Namespace

Modules: Label, OpCode, RCode Classes: Config, DecodeError, EncodeError, Message, Name, Query, Requester, Resource

Constant Summary collapse

Port =

Default DNS Port

53
UDPSize =

Default DNS UDP packet size

512
RequestID =

:nodoc:

{}
RequestIDMutex =

:nodoc:

Mutex.new

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(config_info = nil) ⇒ DNS

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)

334
335
336
337
338
# File 'lib/resolv.rb', line 334

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

Class Method Details

.allocate_request_id(host, port) ⇒ Object

:nodoc:


628
629
630
631
632
633
634
635
636
637
638
# File 'lib/resolv.rb', line 628

def self.allocate_request_id(host, port) # :nodoc:
  id = nil
  RequestIDMutex.synchronize {
    h = (RequestID[[host, port]] ||= {})
    begin
      id = rangerand(0x0000..0xffff)
    end while h[id]
    h[id] = true
  }
  id
end

.bind_random_port(udpsock, bind_host = "0.0.0.0") ⇒ Object

:nodoc:


652
653
654
655
656
657
658
659
660
661
# File 'lib/resolv.rb', line 652

def self.bind_random_port(udpsock, bind_host="0.0.0.0") # :nodoc:
  begin
    port = rangerand(1024..65535)
    udpsock.bind(bind_host, port)
  rescue Errno::EADDRINUSE, # POSIX
         Errno::EACCES, # SunOS: See PRIV_SYS_NFS in privileges(5)
         Errno::EPERM # FreeBSD: security.mac.portacl.port_high is configurable.  See mac_portacl(4).
    retry
  end
end

.free_request_id(host, port, id) ⇒ Object

:nodoc:


640
641
642
643
644
645
646
647
648
649
650
# File 'lib/resolv.rb', line 640

def self.free_request_id(host, port, id) # :nodoc:
  RequestIDMutex.synchronize {
    key = [host, port]
    if h = RequestID[key]
      h.delete id
      if h.empty?
        RequestID.delete key
      end
    end
  }
end

.open(*args) ⇒ Object

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.


299
300
301
302
303
304
305
306
307
# File 'lib/resolv.rb', line 299

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

.random(arg) ⇒ Object

:nodoc:


602
603
604
605
606
607
608
# File 'lib/resolv.rb', line 602

def self.random(arg) # :nodoc:
  begin
    SecureRandom.random_number(arg)
  rescue NotImplementedError
    rand(arg)
  end
end

.rangerand(range) ⇒ Object

:nodoc:


616
617
618
619
620
621
622
623
# File 'lib/resolv.rb', line 616

def self.rangerand(range) # :nodoc:
  base = range.begin
  len = range.end - range.begin
  if !range.exclude_end?
    len += 1
  end
  base + random(len)
end

Instance Method Details

#closeObject

Closes the DNS resolver.


368
369
370
371
372
373
374
# File 'lib/resolv.rb', line 368

def close
  @mutex.synchronize {
    if @initialized
      @initialized = false
    end
  }
end

#each_address(name) ⇒ Object

Iterates over all IP addresses for name retrieved from the DNS resolver.

name can be a Resolv::DNS::Name or a String. Retrieved addresses will be a Resolv::IPv4 or Resolv::IPv6


406
407
408
409
410
411
# File 'lib/resolv.rb', line 406

def each_address(name)
  each_resource(name, Resource::IN::A) {|resource| yield resource.address}
  if use_ipv6?
    each_resource(name, Resource::IN::AAAA) {|resource| yield resource.address}
  end
end

#each_name(address) ⇒ Object

Iterates over all hostnames for address retrieved from the DNS resolver.

address must be a Resolv::IPv4, Resolv::IPv6 or a String. Retrieved names will be Resolv::DNS::Name instances.


453
454
455
456
457
458
459
460
461
462
463
464
465
# File 'lib/resolv.rb', line 453

def each_name(address)
  case address
  when Name
    ptr = address
  when IPv4::Regex
    ptr = IPv4.create(address).to_name
  when IPv6::Regex
    ptr = IPv6.create(address).to_name
  else
    raise ResolvError.new("cannot interpret as address: #{address}")
  end
  each_resource(ptr, Resource::IN::PTR) {|resource| yield resource.name}
end

#each_resource(name, typeclass, &proc) ⇒ Object

Iterates over all typeclass DNS resources for name. See #getresource for argument details.


509
510
511
512
513
# File 'lib/resolv.rb', line 509

def each_resource(name, typeclass, &proc)
  fetch_resource(name, typeclass) {|reply, reply_name|
    extract_resources(reply, reply_name, typeclass, &proc)
  }
end

#extract_resources(msg, name, typeclass) ⇒ Object

:nodoc:


570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
# File 'lib/resolv.rb', line 570

def extract_resources(msg, name, typeclass) # :nodoc:
  if typeclass < Resource::ANY
    n0 = Name.create(name)
    msg.each_answer {|n, ttl, data|
      yield data if n0 == n
    }
  end
  yielded = false
  n0 = Name.create(name)
  msg.each_answer {|n, ttl, data|
    if n0 == n
      case data
      when typeclass
        yield data
        yielded = true
      when Resource::CNAME
        n0 = data.name
      end
    end
  }
  return if yielded
  msg.each_answer {|n, ttl, data|
    if n0 == n
      case data
      when typeclass
        yield data
      end
    end
  }
end

#fetch_resource(name, typeclass) ⇒ Object


515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
# File 'lib/resolv.rb', line 515

def fetch_resource(name, typeclass)
  lazy_initialize
  requester = make_udp_requester
  senders = {}
  begin
    @config.resolv(name) {|candidate, tout, nameserver, port|
      msg = Message.new
      msg.rd = 1
      msg.add_question(candidate, typeclass)
      unless sender = senders[[candidate, nameserver, port]]
        sender = requester.sender(msg, candidate, nameserver, port)
        next if !sender
        senders[[candidate, nameserver, port]] = sender
      end
      reply, reply_name = requester.request(sender, tout)
      case reply.rcode
      when RCode::NoError
        if reply.tc == 1 and not Requester::TCP === requester
          requester.close
          # Retry via TCP:
          requester = make_tcp_requester(nameserver, port)
          senders = {}
          # This will use TCP for all remaining candidates (assuming the
          # current candidate does not already respond successfully via
          # TCP).  This makes sense because we already know the full
          # response will not fit in an untruncated UDP packet.
          redo
        else
          yield(reply, reply_name)
        end
        return
      when RCode::NXDomain
        raise Config::NXDomain.new(reply_name.to_s)
      else
        raise Config::OtherResolvError.new(reply_name.to_s)
      end
    }
  ensure
    requester.close
  end
end

#getaddress(name) ⇒ Object

Gets the IP address of name from the DNS resolver.

name can be a Resolv::DNS::Name or a String. Retrieved address will be a Resolv::IPv4 or Resolv::IPv6

Raises:


382
383
384
385
# File 'lib/resolv.rb', line 382

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

#getaddresses(name) ⇒ Object

Gets all IP addresses for name from the DNS resolver.

name can be a Resolv::DNS::Name or a String. Retrieved addresses will be a Resolv::IPv4 or Resolv::IPv6


393
394
395
396
397
# File 'lib/resolv.rb', line 393

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

#getname(address) ⇒ Object

Gets the hostname for address from the DNS resolver.

address must be a Resolv::IPv4, Resolv::IPv6 or a String. Retrieved name will be a Resolv::DNS::Name.

Raises:


429
430
431
432
# File 'lib/resolv.rb', line 429

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

#getnames(address) ⇒ Object

Gets all hostnames for address from the DNS resolver.

address must be a Resolv::IPv4, Resolv::IPv6 or a String. Retrieved names will be Resolv::DNS::Name instances.


440
441
442
443
444
# File 'lib/resolv.rb', line 440

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

#getresource(name, typeclass) ⇒ Object

Look up the typeclass DNS resource of name.

name must be a Resolv::DNS::Name or a String.

typeclass should be one of the following:

  • Resolv::DNS::Resource::IN::A

  • Resolv::DNS::Resource::IN::AAAA

  • Resolv::DNS::Resource::IN::ANY

  • Resolv::DNS::Resource::IN::CNAME

  • Resolv::DNS::Resource::IN::HINFO

  • Resolv::DNS::Resource::IN::MINFO

  • Resolv::DNS::Resource::IN::MX

  • Resolv::DNS::Resource::IN::NS

  • Resolv::DNS::Resource::IN::PTR

  • Resolv::DNS::Resource::IN::SOA

  • Resolv::DNS::Resource::IN::TXT

  • Resolv::DNS::Resource::IN::WKS

Returned resource is represented as a Resolv::DNS::Resource instance, i.e. Resolv::DNS::Resource::IN::A.

Raises:


490
491
492
493
# File 'lib/resolv.rb', line 490

def getresource(name, typeclass)
  each_resource(name, typeclass) {|resource| return resource}
  raise ResolvError.new("DNS result has no information for #{name}")
end

#getresources(name, typeclass) ⇒ Object

Looks up all typeclass DNS resources for name. See #getresource for argument details.


499
500
501
502
503
# File 'lib/resolv.rb', line 499

def getresources(name, typeclass)
  ret = []
  each_resource(name, typeclass) {|resource| ret << resource}
  return ret
end

#lazy_initializeObject

:nodoc:


355
356
357
358
359
360
361
362
363
# File 'lib/resolv.rb', line 355

def lazy_initialize # :nodoc:
  @mutex.synchronize {
    unless @initialized
      @config.lazy_initialize
      @initialized = true
    end
  }
  self
end

#make_tcp_requester(host, port) ⇒ Object

:nodoc:


566
567
568
# File 'lib/resolv.rb', line 566

def make_tcp_requester(host, port) # :nodoc:
  return Requester::TCP.new(host, port)
end

#make_udp_requesterObject

:nodoc:


557
558
559
560
561
562
563
564
# File 'lib/resolv.rb', line 557

def make_udp_requester # :nodoc:
  nameserver_port = @config.nameserver_port
  if nameserver_port.length == 1
    Requester::ConnectedUDP.new(*nameserver_port[0])
  else
    Requester::UnconnectedUDP.new(*nameserver_port)
  end
end

#timeouts=(values) ⇒ Object

Sets the resolver timeouts. This may be a single positive number or an array of positive numbers representing timeouts in seconds. If an array is specified, a DNS request will retry and wait for each successive interval in the array until a successful response is received. Specifying nil reverts to the default timeouts:

5, second = 5 * 2 / nameserver_count, 2 * second, 4 * second

Example:

dns.timeouts = 3

351
352
353
# File 'lib/resolv.rb', line 351

def timeouts=(values)
  @config.timeouts = values
end