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:

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.

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)



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# File 'lib/resolv.rb', line 329

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:



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# File 'lib/resolv.rb', line 620

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:



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# File 'lib/resolv.rb', line 644

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:



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# File 'lib/resolv.rb', line 632

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.



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# File 'lib/resolv.rb', line 294

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

.random(arg) ⇒ Object

:nodoc:



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# File 'lib/resolv.rb', line 604

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.



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# File 'lib/resolv.rb', line 363

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



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# File 'lib/resolv.rb', line 401

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.



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# File 'lib/resolv.rb', line 448

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.



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# File 'lib/resolv.rb', line 506

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:



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# File 'lib/resolv.rb', line 572

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 



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# File 'lib/resolv.rb', line 512

def fetch_resource(name, typeclass)
  lazy_initialize
  begin
    requester = make_udp_requester
  rescue Errno::EACCES
    # fall back to TCP
  end
  senders = {}
  begin
    @config.resolv(name) {|candidate, tout, nameserver, port|
      requester ||= make_tcp_requester(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:



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# File 'lib/resolv.rb', line 377

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



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# File 'lib/resolv.rb', line 388

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:



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# File 'lib/resolv.rb', line 424

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.



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# File 'lib/resolv.rb', line 435

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:



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# File 'lib/resolv.rb', line 487

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.



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# File 'lib/resolv.rb', line 496

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

#lazy_initialize ⇒ Object

:nodoc:



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# File 'lib/resolv.rb', line 350

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

#make_tcp_requester(host, port) ⇒ Object

:nodoc:



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

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

#make_udp_requester ⇒ Object

:nodoc:



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# File 'lib/resolv.rb', line 559

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



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# File 'lib/resolv.rb', line 346

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