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, SvcParam, SvcParams

Constant Summary collapse

Port =

Default DNS Port

53
UDPSize =

Default DNS UDP packet size

512
RequestID =

:nodoc:

{}
RequestIDMutex =

:nodoc:

Thread::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. :raise_timeout_errors can be used to raise timeout errors as exceptions instead of treating the same as an NXDOMAIN response.

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)



326
327
328
329
330
 
# File 'lib/resolv.rb', line 326

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

Class Method Details

.allocate_request_id(host, port) ⇒ Object

:nodoc:



635
636
637
638
639
640
641
642
643
644
645
 
# File 'lib/resolv.rb', line 635

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

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

:nodoc:



659
660
661
662
663
664
665
666
667
668
 
# File 'lib/resolv.rb', line 659

def self.bind_random_port(udpsock, bind_host="0.0.0.0") # :nodoc:
  begin
    port = random(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:



647
648
649
650
651
652
653
654
655
656
657
 
# File 'lib/resolv.rb', line 647

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.



289
290
291
292
293
294
295
296
297
 
# File 'lib/resolv.rb', line 289

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

.random(arg) ⇒ Object

:nodoc:



619
620
621
622
623
624
625
 
# File 'lib/resolv.rb', line 619

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

Instance Method Details

#close ⇒ Object

Closes the DNS resolver.



360
361
362
363
364
365
366
 
# File 'lib/resolv.rb', line 360

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



398
399
400
401
402
403
 
# File 'lib/resolv.rb', line 398

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



452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
 
# File 'lib/resolv.rb', line 452

def each_name(address)
  case address
  when Name
    ptr = address
  when IPv4, IPv6
    ptr = address.to_name
  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.



510
511
512
513
514
 
# File 'lib/resolv.rb', line 510

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:



587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
 
# File 'lib/resolv.rb', line 587

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

#fetch_resource(name, typeclass) ⇒ Object 



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
556
557
558
559
560
561
562
563
564
565
566
567
 
# File 'lib/resolv.rb', line 516

def fetch_resource(name, typeclass)
  lazy_initialize
  truncated = {}
  requesters = {}
  udp_requester = begin
    make_udp_requester
  rescue Errno::EACCES
    # fall back to TCP
  end
  senders = {}

  begin
    @config.resolv(name) do |candidate, tout, nameserver, port|
      msg = Message.new
      msg.rd = 1
      msg.add_question(candidate, typeclass)

      requester = requesters.fetch([nameserver, port]) do
        if !truncated[candidate] && udp_requester
          udp_requester
        else
          requesters[[nameserver, port]] = make_tcp_requester(nameserver, port)
        end
      end

      unless sender = senders[[candidate, requester, nameserver, port]]
        sender = requester.sender(msg, candidate, nameserver, port)
        next if !sender
        senders[[candidate, requester, 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
          # Retry via TCP:
          truncated[candidate] = true
          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
    end
  ensure
    udp_requester&.close
    requesters.each_value { |requester| 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:



374
375
376
377
 
# File 'lib/resolv.rb', line 374

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



385
386
387
388
389
 
# File 'lib/resolv.rb', line 385

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:



428
429
430
431
 
# File 'lib/resolv.rb', line 428

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.



439
440
441
442
443
 
# File 'lib/resolv.rb', line 439

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:



491
492
493
494
 
# File 'lib/resolv.rb', line 491

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.



500
501
502
503
504
 
# File 'lib/resolv.rb', line 500

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

#lazy_initialize ⇒ Object

:nodoc:



347
348
349
350
351
352
353
354
355
 
# File 'lib/resolv.rb', line 347

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

#make_tcp_requester(host, port) ⇒ Object

:nodoc:



578
579
580
581
582
583
584
585
 
# File 'lib/resolv.rb', line 578

def make_tcp_requester(host, port) # :nodoc:
  return Requester::TCP.new(host, port)
rescue Errno::ECONNREFUSED
  # Treat a refused TCP connection attempt to a nameserver like a timeout,
  # as Resolv::DNS::Config#resolv considers ResolvTimeout exceptions as a
  # hint to try the next nameserver:
  raise ResolvTimeout
end

#make_udp_requester ⇒ Object

:nodoc:



569
570
571
572
573
574
575
576
 
# File 'lib/resolv.rb', line 569

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



343
344
345
 
# File 'lib/resolv.rb', line 343

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